Dust collection systems are often overlooked when it comes to plant improvements due to the often high capital costs involved. We here at Baghouse.com have prepared this small list of improvements that can be made to your dust collection system with minimal investment. 

October 26th 2011 | Baghouse.com – Corporate executives are looking for any conceivable way to lower operating costs in our struggling economy, plant operators are being pushed by the corporate brass to find someway of doing more with less, and maintenance managers are trying to make sure all of these cutbacks do not compromise process operation. One area that many industrial plants can easily increase efficiency, and therefore lower operating costs is to look to their pulse jet baghouse dust collection systems.

Here are three small tweaks for your pulse jet dust collection system to increase operating efficiency without a major overhaul or great expense.

1. Ensure Filter Bags Are Installed Correctly
2. Install a Clean-On-Demand System
3. Integrate All System Controls (Clean-on-Demand, timer boards, manometers, etc.)

1. Correctly Install Filter Bags

Filter Bags are the heart and soul of a baghouse. If they are not installed correctly the entire system will suffer, efficiency will go down, filters will fail prematurely, system downtime will ensue and affect the entire process. Check that filters with flanges and cuff are folded over and smooth and not wrinkled around the cage to prevent leakage, and premature failure due to bag abrasion. Bottom-loading filters should be installed with seams 180° from the cage collar gap.

Snapband for dust collection systems

An example of how a snapband filter bag should be installed to maximize your dust collection system efficiency.

Additionally, there are several specific issues to watch out for depending on the exact design of filter bags being used. For snapband construction, check that the seams are set properly in the tubesheet. This can be done running your fingers along the edge of each bag during installation/maintenance checking that each one is smooth, with no wrinkles, gaps, or binds in the snapband. For designs with gaskets or rubber o-rings make sure these are not pinched by the clamps in a way that will allow leaks, or cause accelerated wear.

Additionally, with all bag types, all seams should be at a 45° angle from the aisle to minimize fraying due to increased can velocity, all clamps should be set 90° from the seams, and all filters need to be set properly in the cage groves.*

*Additional Tip: Have everything as uniform (clamps, seams, etc. all set in the same direction) as possible to make it easier to diagnose and remedy problems.

2. Clean-On-Demand System

Manually having a technician initiate the cleaning cycle for your dust collection systems can consume a large amount of time, and lead to less than desirable results such as over/under cleaning, operating at higher differential pressure (raising system resistance, and fan load), and lower collection efficiency. Simplify the process and remove the need to be a industrial filtration expert out of the equation by installing a clean-on-demand system.

Dust Collection Systems Timer Boards

Using a clean-on-demand timer board for your baghouse will simplify the cleaning process, and result in more effective cleaning of your dust collection system.

These systems are comprised of a differential pressure gauge, and a control board. The DP gauge monitors the difference in pressure between the clean-air and dirty-air sections of the baghouse (thus giving you the pressure drop over the filters at any given time). DP gauge is connected to the control board, which has a high and low pressure setting which serve as the start and stop markers for the system. When the DP in the baghouse rises past your high setting (indicating the bags need to be cleaned), the controller starts the pulse-jet cleaning cycle, once the pressure reaches the preset low, the pulse-jet system is disengaged.

For a relatively small capital investment clean-on-demand systems can dramatically improve your system efficiency by ensuring the minimum amount of cleaning cycles necessary are initiated, which in turn leads to lower compressed air usage, lower operating differential pressures, and less filter wear. These benefits will lower system operating maintenance costs, while seeing improvement in collection efficiency, and extended filter bag life.

3. Integrate Dust Collection System Controls

Maintaining the correct amount of dustcake on your filters is essential to achieve the maximum collection potential of your filter bags. In fact it is the dustcake itself that does the filtering in a baghouse, not the filter bags! * When the pulse-jet cleaning system engages, it removes the excess dust from the filter surface. Essentially what this does is rearrange the dustcake on the filters, removing a portion of it, and leaving behind the minimum amount needed to reform the dustcake for optimum efficiency. When cleaning cycles are carried out, if each row is pulsed one after another in sequential order, high internal air velocities between the filters (can velocity) can cause the recently dislodged dust to be redeposited on the recently cleaned bags in the previous rows. Since the dust is carried at higher than normal velocities, it can penetrate the fabric (instead of settling on top and forming part of the dustcake) and embed itself therein. This will eventually lead to filter blinding, and a reduction of filter service life.

Installing a sequential controller can help you avoid this problem. This device controls the order in which the bags are cleaned, staggering the cleaning pulse pattern between non-adjacent rows. For example, in a baghouse with 10 rows of bags, you can set the cleaning pattern to first clean rows 1,4,7,10 then 2,5,8, and finally, 3,6,9. You can also set the controller to only fire when the pressure in the compressed air header is at full, providing a consistent pulse force that will properly clean the bags every time. Additionally, to further promote longer filter life, see that each pulse duration is set as short as possible, generally around 0.1 sec.

If you do not currently have a DP clean-on-demand system, an alternative is to use a timer control to regulate system cleaning. When using a timer board setup, it is vital to set the intervals to match your system parameters, ensuring that the filters are neither over, or under cleaned. Maintaining a sufficient level of dustcake is vital to achieving a high system efficiency.

Finally, it is possible to integrate all of these different systems into one unified control panel for operator convenience. You can have all of your controllers relayed to a central LED controller, which then is connected to an external PLC controller or computer for remote monitoring, and recording of all system activity. From here it is then possible to configure all control parameters e.g. timer settings, clean-on-demand DP points, pulse-jet firing order, etc. Additionally, having all operating data in one convenient location will allow for quickly pinpointing problems before they become major issues.

*This does not apply to filter bags with membrane such as ePTFE. In that case, the membrane itself acts as a sort of permeant filter cake while surface dust provides no additional filtering.

Save Money By Increasing Dust Collection System Efficiency

These three tips are just a few of the many ways to increase the operating efficiency of your baghouse dust collection systems with only limited investment of time, material, and capital. Without a doubt, these improvements will pay for themselves many times over throughout the life of the system. At a time when new environmental regulations are requiring pollution control equipment to function at higher and higher efficiencies, not only will turing your attention to improving your dust collection systems lower your operating expenses, but it will also ensure that facilities stay in compliance and avoid costly fines and forced closures.


About the Author

| Dominick DalSanto is an Author & Environmental Technologies Expert, specializing in Dust Collection Systems. With nearly a decade of hands-on working experience in the industry, Dominick’s knowledge of the industry goes beyond a mere classroom education. He is currently serving as Online Marketing Director & Content Manager at Baghouse.com. His articles have been published not only on Baghouse.com , but also on other industry related blogs and sites. In his spare time, Dominick writes about travel and life abroad for various travel sites and blogs.

Filter Bags

Leak testing being performed in a Baghouse

By Dominick DalSanto
Environmental Technologies Expert & Author

Why Periodic Leak Testing of Filter Bags is Vital

Operating a dust collection system with leaking filter bags defeats its sole intended purpose. A few leaking filter bags or even one within a collector/system can result in a substantial emissions increase. Leak testing of your Baghouse filter bags needs to be a regular part of any maintenance program to ensure system efficiency, and maintain compliance with emissions/safety regulations and avoid the fines and/or safety hazards that come with it.

All filter bags will eventually wear all out and need to be replaced. Baghouse maintenance programs should include periodic leak testing to ensure a few or even one faulty bag does not reduce the operating efficiency of the entire system. On occasion, a defective filter will fail early and need to be replaced. In other instances there may be a temporary or unanticipated event that can cause of premature failure of Baghouse filter bags. Once identified these should be investigated to ensure the incident does not occur again, and determine the extent of the damage done to the system. Examples may include: abrasion, thermal durability, and chemical attack.

  • Abrasion from several different sources often leads to excessive wear (and therefore premature failure) of the filter bags. The most obvious is caused by excessive particulate loads in the gas stream. This may have been caused by the unexpected failure, or shutdown/maintenance of a pre-filter (such as a cyclone, or air scrubber for NOx and SOx). Poor design may also lead to particulate laden air striking the filters in certain spots more than others such as near the cuff, or dirty-air inlet. Other sources of abrasion damage include: improperly installed filters that rub against each other, and excessive cleaning cycles.
  • Degradation of the filter bags’ Thermal Durability may also be a potential cause of early failure. When operating temperatures that rise above the designed limits of the fabric, whether for short or long term, filters will begin to degrade and eventually fail. Changes in the plant process, fuel source, maintenance shutdowns of other systems, etc…may result in temperature spikes that will irreparably damage Baghouse filters.
  • Chemical attacks can also result in bag failure. These can occur when gas stream characteristics are not taken into consideration when selecting the filter fabric and/or treatments/finishes. Other times unexpected changes occur in the gas stream that cause changes in the composition of the gas. Operating temperatures may also fluctuate,  dropping below the dew point allowing condensation of the chemicals on the fabric.

Filter Bag Leak Testing – How it is Done

To perform a standard leak test several things need to be done before the actual test can take place. First, since testing requires temporary isolation from the facility process, and shutdown, you must determine the best time for each unit and/or compartment to be tested. Second, safety measures for plant personnel must be taken into account when estimating total down time. Units must be given sufficient time for cooling, atmospheric testing to check for harmful gases, and personnel assigned to perform both the test and fulfill any and all safety regulations regarding confined space entry (both OSHA, and In-house). Once the preliminary steps have been taken, the actual testing can begin.

Filter Bags - Leak Testing

A vital part of any Baghouse system maintenance plan is regular leak testing of the filter bags.

First, florescent leak detection powder is added upstream of the unit such as at a maintenance access in the ductwork. Then after sufficient time has past for the powder to work its way through the system, the unit is shutdown. Once it is possible, a technician will enter into the unit with a UV light source i.e. a black light to examine the filter bags for leaks. The powder fluoresces under the UV light, thereby making it easy for the technician to see even the smallest of holes. The technician makes note of any faulty filters, which can then be replaced.

Regular Maintenance is Key to Getting the Highest Efficiency from Your Baghouse

Baghouse systems are the most efficient, and cost effective solution for particulate matter control in industrial settings – but only if they are maintained properly. A vital part of any Baghouse system maintenance program is regular leak testing of the filter bags. By conducting this and other maintenance tasks, your Baghouse system will operate smoothly, and provide the best of results.

Looking for Leak Testing Services?

Baghouse.com has the expertize to locate and remedy leaks in not only your filters, but also duct work, collector housing, and more. To learn more about Baghouse.com leak testing services and leak testing supplies or receive a free quote on Baghouse leak testing please contact us for a free quote.



Often our customers find it difficult to determine exactly what kind of Filter Media they require for their specific Dust collection system. Other times they know the particular type of filter media they need, but are unable to determine the exact size they need for their Baghouse.

To assist our customers, we at Baghouse.com have prepared this article to help you select the right filter media to match your specific needs.

If you would like to speak directly with one of our dust collection experts for additional help in selecting your Filter Media, or if you would like to receive a free Baghouse Filters quote, please call us at  800 351 6200 or Contact Us using our online form.


Step 1 – Filter Media Selection

Choose the media from which your filter bags will be constructed of based on the type of application they will be used for. Take the following things into consideration prior to selecting your filter media:

•    Temperature – Do your bags need to withstand extreme temperatures?
•    Material – What is the filter being used for?
•    Chemistry – Can your filter withstand the chemical makeup of the dust particles
•    Resistance- Is the filter media able to resist the abrasion of the dust particles

Choosing the correct filter media is an important and sometimes difficult process. To assist you in the identification of the right media for your bags, keep the following in mind: Filter bag performance is directly related to how well it can tolerate the environment in which it is being used. How efficiently it can remove the dust particles from its fabric and its ability to be cleaned by the dust collector is also important. You must first learn to identify the type of filter media currently used in your application. Below you will find a list of typical construction methods:

•    Woven felts
•    Non-woven felts
•    Natural fibers
•    Synthetics (Thermoset or Thermoplastics such as Polypropylene “PPRO” – Polyphenylene sulfide “PPS” – Polyester “PE”)

For additional information on media types please examine our Filter Fabrics Chart below. A simple test to determine if a material is a thermoplastic is to take a small swatch and put a flame to it. A thermoplastic material will begin to melt when exposed to direct heat. The selection criterion eliminates materials based on temperature and chemical characteristics. The first cut is usually made based on temperature. Then the chemical characteristics of the gas stream are considered to further refine the search. Next, the efficiency of the material further dictates the construction of the material such as the weight, oz/sq. ft., fiber and surface treatments/membranes. Last but not least, if there are still two or more candidates it comes down to a price versus performance trade off.

Dust Collector Filter Fabrics


Popular Materials


Polyester FeltPolyester Felt - Baghouse Filter Fabric

Recommended continuous operation temperature: 275°F
Maximum (short time) operation temperature: 300°F
Supports combustion: Yes
Biological resistance (bacteria, mildew): No Effect
Resistance to alkalis: Fair
Resistance to mineral acids: Fair+
Resistance to organic acids: Fair
Resistance to oxidizing agents: Good
Resistance to organic solvents: Good
Available weights: 10 oz. – 22 oz.

Polypropylene Felt - Dust Collector Filter Fabric

Polypropylene Felt

Polypropylene Felt

Recommended continuous operation temperature: 190°F
Maximum (short time) operation temperature: 210°F
Supports combustion: Yes
Biological resistance (bacteria, mildew): Excellent
Resistance to alkalis: Excellent
Resistance to mineral acids: Excellent
Resistance to organic acids: Excellent
Resistance to oxidizing agents: Good
Resistance to organic solvents: Excellent
Available weights: 12 oz. – 18 oz


High Temperature Materials


Conex® / Nomex® Felt (Aramid) - Dust Collector Filter Fabric

Conex® / Nomex® Felt (Aramid)

Conex® / Nomex® Felt (Aramid)

Recommended continuous operation temperature: 400°F
Maximum (short time) operation temperature: 425°F
Supports combustion: No
Biological resistance (bacteria, mildew): No Effect
Resistance to alkalis: Good
Resistance to mineral acids: Fair
Resistance to organic acids: Fair+
Resistance to oxidizing agents: Poor
Resistance to organic solvents: Good
Available weights: 10 oz. – 22 oz.

P84® Felt Polyimide - Dust Collector Filter Fabric

P84® Felt Polyimide

P84® Felt Polyimide

Recommended continuous operation temperature: 475°F
Maximum (short time) operation temperature:500°F
Supports combustion: No
Biological resistance (bacteria, mildew): No Effect
Resistance to alkalis: Fair
Resistance to mineral acids: Good+
Resistance to organic acids: Good+
Resistance to oxidizing agents: Good+
Resistance to organic solvents: Excellent
Available weights: 14 oz. – 18 oz.

Ryton® Felt / PPS - Dust Collector Filter Fabric

Ryton® Felt / PPS

Ryton® Felt / PPS

Recommended continuous operation temperature: 375°F
Maximum (short time) operation temperature: 400°F
Supports combustion: No
Biological resistance (bacteria, mildew): No Effect
Resistance to alkalis: Excellent
Resistance to mineral acids: Excellent
Resistance to organic acids: Excellent
Resistance to oxidizing agents: Fair
Resistance to organic solvents: Excellent
Available weights: 16 oz. – 18 oz.

Dust Collector Filter Specialty Materials


Homopolymer Acrylic Felt - Dust Collector Filter Fabric

Homopolymer Acrylic Felt

Homopolymer Acrylic Felt

Recommended continuous operation temperature: 250°F
Maximum (short time) operation temperature: 275°F
Supports combustion: Yes
Biological resistance (bacteria, mildew): Good+
Resistance to alkalis: Fair
Resistance to mineral acids: Good+
Resistance to organic acids: Excellent
Resistance to oxidizing agents: Good
Resistance to organic solvents: Good+
Available weights: 15 oz. – 18 oz.

Epitropic Felt Antistatic - Dust Collector Filter Fabric

Epitropic Felt Antistatic

Epitropic Felt Antistatic

Recommended continuous operation temperature: 275°F
Maximum (short time) operation temperature: 300°F
Supports combustion: Yes
Biological resistance (bacteria, mildew): No Effect
Resistance to alkalis: Fair
Resistance to mineral acids: Fair+
Resistance to organic acids: Fair
Resistance to oxidizing agents: Good
Resistance to organic solvents: Good
Available weights: 14 oz. – 16 oz.

Step 2 – Dust Collector Filter Measurements

Accurate measurements lead to the best fit. It’s likely that your dust collector has been modified over the years due to permitting issues or changes in your process which called for a reconfiguration of the Baghouse. In this case OEM configurations will not fit and you will need to obtain accurate measurements for your filters before ordering replacement filter bags. If you currently have filter bags installed that are functioning properly, you can remove one of these bags to get the proper measurements for your replacement order. A spare bag that has not been used yet can also be measured if available. However, be sure to verify the bag measured is the same as the bags currently being used in the dust collector. If you are removing a used bag to measure, please be sure to use all necessary precautionary measures set in place prior to removal i.e. gloves, protective garments and respiratory equipment if needed. It is best not to rely only on the numbers off the unit of OEM filter specifications because of possible changes to the configurations. Of course the best solution is to mail the manufacturer a new or used bag that can be used a guide sample.

Flat Width: Place the filter on a flat surface such as a large table or cement floor. With the filter stretched out, press down on the side. Using a measuring tape, very accurately record the width. Be sure to hold the filter down firmly on an even surface when taking this measurement.

Diameter: When measuring the tube sheet hole of a pulse jet style dust collector, first make sure the hole has not been damaged or warped in any way. Clean the surface thoroughly with a wire brush then using a micrometer, measure the hole in both directions. If the measurements are at all different locate another hold and repeat this process.

Length: Remove the filter from the unit. Preferably with the assistance of another person, stretch the filter out. While maintaining tension on the filter record the length from the longest point at each end using a measuring tape. Do not include and straps, metal caps or other hanging hardware in the measurement, just the length of the filter itself.

Step 3 – Top & Bottom Construction

The top and bottom construction of a filter bag involves a variety of possible configurations. Identifying the type of cleaning process used by your dust collector will help to determine which configuration is needed. The most common types of dust collectors are “Pulse-Jet” “Shaker” “Reverse Air”. The chart below can help you identify which type of dust collector filter you are using.

Filter Configuration Chart

Pulse-Jet Dust Collectors (Reverse jet) – Found in almost every industrial environment. They are the most popular design and are seen in nearly all industry segments. Pulse-Jet Units can be divided into two major groups Top load or bottom load units sometime called top entry (walk-in plenum) or bottom entry (common in bin vents) because of the point of entry used to change out the filters.

Typical filter configuration for a top load unit:
Snap Band Top (double-beaded ring)
Disk Bottom (w/o wear strip)

Typical filter configuration for a bottom load unit:
Raw End Top
Disk Bottom (w/o wear strip)

Shaker Dust Collectors (Mechanical Cleaning) – Usually found in older applications where unscheduled down time is not a major concern.

Typical filter Top Configurations
Loop Top
Grommet Top
Strap or Tail Top
Metal Hanger or Cap

Typical Filter Bottom Configurations
Corded Cuff with Clamp
Snap Band
(Double-Beaded Ring)

Reverse-Air Dust Collectors – Usually found in very large air handling environments such as power generation and cement plants although they do have uses in a variety of industries. Sometimes called a structural bag, these filters usually have a series of support rings spaced every few feet throughout the length of the bag.

Typical Top Configurations
Compression band w/Metal Cap & Hook

Typical Bottom Configurations
Compression band
Snap Band
Cord w/Metal Clamp

Snap Band - Dust Collector Filter Configuration

Snap Band

Raw Edge - Dust Collector Filter Configuration

Raw Edge

Cord - Dust Collector Filter Configuration


Hanger - Dust Collector Filter Configuration


Grommet - Dust Collector Filter Configuration


Loop - Dust Collector Filter Configuration


Strap - Dust Collector Filter Configuration


Support Ring - Dust Collector Filter Configuration

Support Ring

Rubber O-Ring - Dust Collector Filter Configuration

Rubber O-Ring

Disk - Dust Collector Filter Configuration


Disk With Wear Strip - Dust Collector Filter Configuration

Disk With Wear Strip

Flange - Dust Collector Filter Configuration


Hem - Dust Collector Filter Configuration


Sewn Flat - Dust Collector Filter Configuration

Sewn Flat

Envelope - Dust Collector Filter Configuration


Step 4 – Additional Options

Ground Wires – Use to comply with Factory Mutual requirements for static dissipation. Ground wire can be made from stainless steel or copper however this technique only works on a localized area of the filter. For optimal static dissipation look at conductive fiber filter made with Epitropic or Stainless Steel fibers.

Wear Cuffs – Used to combat abrasion at the bottom of the bag either from a sandblasting effect or from bag-to-bag abrasion due to turbulence in the bag house. Usually 2 to 4 inches in length and made of a material similar to that of the body of the filter bag.

Special Finishes – There are many finish options that can be added to the filter media at the time it is manufactured. Please refer to the materials selection area for further details. If you want to order a specific brand or special type of finish please add that request into the additional comments section when ordering.


About the Author

| Dominick DalSanto is an Author & Environmental Technologies Expert, specializing in Dust Collection Systems. With nearly a decade of hands-on working experience in the industry, Dominick’s knowledge of the industry goes beyond a mere classroom education. He is currently serving as Online Marketing Director & Content Manager at Baghouse.com. His articles have been published not only on Baghouse.com , but also on other industry related blogs and sites. In his spare time, Dominick writes about travel and life abroad for various travel sites and blogs.

This article has been designed to educate customers by giving a brief overview of all the Dust Collection Systems available today. A detailed explanation of the benefits and drawbacks of each type of system can be found in further articles on Baghouse.com

What is a Dust Collector?

After the contaminated air is captured by a Dry Dust Collection system, either by means of a Central Collection System, or in a unit Collector. The dust filled air then needs to be treated and the contaminates removed, before the air can be recirculated back into the facility or dispersed into the atmosphere. The Dust Collector separates the particles from the airstream and sends it on to its final destination.

Why are Dust Collectors Needed?

There are many reasons why having a proper Dust Collection System installed in your facility is needed, a few important reasons are:

•    To protect employees and society from exposure to pollution,
•    To recover valuable products from the dust filled air
•    To facilitate compliance with health and air emission standards.

Types of Dust Collectors

The five principal types of industrial dust collectors that will be discussed in this article are:

•    Cyclone Collectors (Inertial separators)
•    Baghouses (Fabric collectors)
•    Wet scrubbers
•    Electrostatic precipitators
•    Unit collectors

Cyclone Collectors (Inertial Separators)

Inertial separators
work by making use of one or more of the following forces centrifugal, gravitational, and inertial in order to separate dust from the airstream. Once separated, the dust is removed to a hopper by gravity for temporary storage. While this type of collect can be used in applications where particle sizes are large and only a “rough” air filtration is desired, the main usage for this type of collector is as a precleaner, to remove larger particles and debris and avoid overloading and damaging more efficient dust collectors.

The three types of Inertial Separators are:

•    Settling Chambers
•    Baffle Chambers
•    Centrifugal Collectors

A Settling Camber is a large box installed into the ductwork.  The sudden larger area for the airstream to pass through causes the air stream to slow down, which in turns causes the larger particles to settle to the bottom of the chamber. This type of collector is rarely used as the primary dust collector due to it’s large space requirements, and low efficiency. However, the fact that it can be fashioned from almost any material and its simple design, which requires little maintenance, leads it to being a wise choice as a precleaner for a more efficient Dust Collector.

A Baffle Chamber has a fixed baffle plate that causes the airflow to rapidly change its direction, first turning downward, and then making a 180 degree turn back up. In the process, the larger particles fall to the bottom of the chamber and can be collected from there. As with Settling Chambers this type of collector is best used as a precleaner for another more efficient collector further in the collection system. Also like a Settling Chamber its relatively simple design and low maintenance needs make it an excellent choice for the beginning of any large scale collection system.

Centrifugal Collectors create a vortex in the airstream within an enclosure, similar to water going down a drain. Normally this is done by having the airstream enter the collect at an angle, which causes it to spin. As the airstream is spun around the collector, the particles strike the wall and fall into the hopper below.

Within this category there are two main types of systems in use:

•    Single Cyclone systems
•    Multiple Cyclone systems

A Single Cyclone Collector creates a dual vortex, a main downward vortex to disperse the coarser matter, and a secondary upward vortex to remove the finer particles on the return to the outlet to the duct system.

A Multiple Cyclone Collector works in the same manner as the Single Cyclone variety albeit with several small dynamiter cyclones instead of just one. The multiple cyclones work in parallel and share the same air input and output.

Between the two, the Multiple Cyclone Collector will operate more efficiently because of being longer in length and smaller in dynamiter. The smaller dynamiter cause the centrifugal force generated to be greater, and the longer length allows for more contact with the surface of the collector by the particles thereby causing more particles to be removed from the airstream. However, a greater loss of pressure is found in Multiple Cyclone Collectors than in Single Cyclone Collectors.

Again as with the other kinds of Inertial Separators, this systems main advantage is the lack of moving parts thus requiring less maintenance and repair. While it can be designed to remove a specific size range of particles, it still remains best used as a precleaner to eliminate coarse particles and ease the load on more efficient Dust Collectors further along in the system.

Advantages & Disadvantages – Centrifugal Collectors

Types Advantages Disadvantages
Cyclones Have no moving parts Have low collection efficiency for respirable particulates
Can be used as precleaners to remove coarser particulates and reduce load on more efficient dust collectors Suffer decreased efficiency if gas viscosity or gas density increases
Can be designed to remove a specific size range of particles Are susceptible to erosion
Have drastically reduced efficiency due to reduction in airflow rate
Cannot process sticky dust
Multiple Cyclones Have no moving parts Have low collection efficiency for respirable particulates
Are more efficient than single-cyclone separators Are prone to plugging due to smaller diameter tubes
Have low pressure drop when used as a precleaner Improper gas distribution may result in dirty gas bypassing several tubes
Cannot process sticky dust
For a given gas volume, occupy more space than single-cyclone separators

Common Operating Problems & Solutions – Cyclone Collectors

Symptom Cause Solution
Erosion High concentrations of heavy, hard, sharp-edged particles Install large-diameter “roughing” cyclone upstream of high-efficiency, small-diameter cyclone.
Line high-efficiency cyclone with refractor or erosion-resistant material.
Corrosion Moisture and condensation in cyclone Keep gas stream temperature above dewpoint.
Insulate cyclone.
Use corrosion-resistant material such as stainless steel or nickel alloy.
Dust Buildup Gas stream below dewpoint Maintain gas temperature above dewpoint.
Very sticky material Install vibrator to dislodge material.
Reduced Efficiency or Dirty Discharge
Leakage in ductwork of cyclone Clean cyclone routinely.
Check for pluggage and leakage and unplug or seal the ductwork.
Close all inspection ports and openings.
Reduced gas velocity in cyclone Check the direction of fan rotation; if rotation is wrong, reverse two of the tree leads on motor.

Common Operating Problems and Solutions – Multiclones

Symptom Cause Solution
Erosion High concentrations of heavy, hard, sharp-edged particles Install cast iron tubes.
Install a wear shield to protect tubes
Overloaded tubes Uneven gas flow and dust distribution Install turning vanes in elbow, if elbow precedes inlet vane.
Loss of volume in tubes
Uneven pressure drop across tubes
Plugging in inlet vanes, clean gas outlet tubes, and discharge hopper Low gas velocity Install turning vanes in elbow inlet
Uneven flow distribution Insulate multiclone
Moisture condensation Install bin-level indicator in collection hopper.
Overfilling in discharge hopper Empty hopper more frequently.
Reduced efficiency or dirty gas stack Leakage in ductwork Seal all sections of ductwork and multiclone to prevent leaks
Leakage in multiclone

Startup/Shutdown Procedures – Centrifugal Collectors

Type Startup Shutdown
Cyclones 1. Check fan rotation. 1. Allow exhaust fan to operate for a few minutes after process shutdown until cyclone is empty.
2. Close inspection doors, connections, and cyclone discharge. 2. If combustion process is used, allow hot, dry air to pass through cyclone for a few minutes after process shutdown to avoid condensation.
3. Turn on fan. 3. Turn off exhaust fan.
4. Check fan motor current. 4. Clean discharge hopper.
5. Check pressure drop across cyclone.
Multiclones 1. Conduct same startup procedures as cyclones. 1. Conduct same shutdown procedures as cyclones.
2. At least once a month, measure airflow by conducting a pitot traverse across inlet to determine quantity and distribution of airflow.
3. Record pressure drop across multiclone.
4. If flow is significantly less than desired, block off rows of cyclone to maintain the necessary flow per cyclone.

Preventative Maintenance Procedures – Centrifugal Collectors

Type Frequency Procedure
Cyclones Daily Record cyclone pressure drops.
Check stack (if cyclone is only collector).
Record fan motor amperage.
Inspect dust discharge hopper to assure dust is removed.
Weekly Check fan bearings.
Check gaskets, valves, and other openings for leakage.
Monthly Check cyclone interior for erosion, wear, corrosion, and other visible signs of deterioration.
Multiclones Daily Same as cyclones.
Weekly Same as cyclones.
Monthly Check multiclone interior for erosion, wear, corrosion, and improper gas and dust distribution.
Inspect individual cyclones and ducts for cracks caused by thermal expansion or normal wear.

Fabric Dust Collectors

Fabric Collectors (commonly known as a Baghouse) are among the most widely used dust collection systems. They benefit from having the potential to be one of the most efficient (up to 99% of very fine particles) and cost effective dust collection systems you can choose.

The way they work

The Gas stream enters into the Baghouse via the location’s duct system. Once inside the dust filled gases come into contact with the filter bags within. As the gases pass through the filters the dust particles are trapped on the filter media. Over time a layer of cake dust is built up on the surface of the filter bags. This is the secret to this filter medium’s high efficiency potential. Once the cake dust has formed, it further impedes the passage of dust through the filters in four different ways:

•    Inertial Collection: The incoming Gas stream strikes the filter media, which is located perpendicular to the Gas flow before changing direction causing the dust particles to remain on the filter.
•    Interception: Particles that do not cross the fluid streamlines come in contact with fibers because of the fiber size.
•    Brownian movement: By means of diffusion, there is an increased chance of contact between the filter and the dust particles due to their molecular motion.
•    Electrostatic Forces: An increased attraction can occur between the dust particles and the filter media when an electrostatic charge is found on the dust particles.

Air to Cloth Ratio

An understanding of the term Air to Cloth Ratio is vital to understand the mechanics of any Baghouse system regardless of the exact type used. This ratio is defined as the amount of air or process gas entering the Baghouse divided by the sq. ft of cloth in the Baghouse. An example of an Air to Cloth Ratio is provided below courtesy of http://www.usairfiltration.com

(Bag diameter in inches x pi x bag length in inches)
Total Cloth area = 144 x total number of bags
A standard 6” bag has a 5-7/8” diameter
This bag is 12’ long
There are a total of 132 bags in the Baghouse
= (5-7/8” x 3.1416 x 144”) ÷ 144 x 132
= (5.875” x 3.1416 x 144”) ÷ 144 x 132
= (2657.79) ÷ 144 x 132
= 18.46 SF of cloth per bag x 132 bags
Total cloth area = 2,436 sq. ft.
Assume the Baghouse is handling 13,000 ACFM of air
Air to cloth ratio = ACFM ÷ total cloth area
= 13,000 ÷ 2,436
= 5.34 : 1

Different Baghouse designs

There are three main types of Baghouse systems currently in use today. The same basic mechanics are present in all of them, the main difference being how filter bags are cleaned.

•    Mechanical Shaker
•    Reverse Air
•    Reverse Jet (Or Pulse Jet)

A Mechanical Shaker is a design where the filter bags are suspended from the top of the Baghouse by horizontal beams and fastened to a cell plate on the bottom. When the Gas stream enters at the bottom of the Baghouse it is then forced up through the inside of the tubular filter bags, thereafter passing unto the airflow outlet at the top. The cleaning of this type of Baghouse is done by a shaking of the top horizontal bar that the filter bags are attached to.  This is caused by a motor driven shaft and cam system that sends waves down the surface of the filter bags causing the dust to fall off the interior of them into the hopper below.  This Baghouse has a relatively low Air to Cloth Ratio requiring large amounts of space. Despite this draw back, the simple design remains a noted advantage, leading to this system being widely used in the mineral processing industry.

In a Reverse Air Baghouse, filter bags are connected to a cell plate on the bottom of the Baghouse and are suspended from an adjustable hanger frame on top. The Gas stream, as in the Mechanical Shaker design enters into the Baghouse and passes through the filter bags from the bottom leading to the dust collecting again on the interior of the filter bags, thereafter leaving through the outlet port at the top.  Again the main difference in this style of Baghouse system when compared to others is the cleaning mechanism. In this system, a cleaning cycle starts with injecting clean air into the Collector in the reverse direction of the normal flow. This causes the compartment to become pressurized. The pressure causes the bags to collapse slightly releasing the cake dust to crack and fall off to be collected by the hopper below.  Since it is necessary to shut down normal airflow to the Baghouse during the cleaning cycle, this type of Baghouse is normally compartmentalized so as to allow for only a partial shutdown of the system.

With a Reverse Jet or Pulse Jet Baghouse, the same basic design is found as in the other types of Baghouse design, however, with a few very important differences. In a Pulse Jet Baghouse, the baghouse filter bags are individually overlaid on a metal cage, which is then attached to a cell plate at the top of the compartment. The Gas stream enters the Baghouse at the bottom and is forced through the outside to the inside of the filter bags after which the Gas stream exits the compartment from the outlet port at the top. The main advantage of this Baghouse is that it does not require a shutdown of any kind to run a cleaning cycle. A digital sequential timer is attached to the one of the filter bags inside the Baghouse. This timer signals a solenoid valve to start the cleaning cycle when it detects a certain amount of build up on the bag. It consists of a small burst of compressed air being fired down through the filter bags. Which cause the excess cake dust to fall off into hopper at the bottom of the Baghouse where it can be collected. The cleaning cycle of the Pulse Jet collectors provides a more complete cleaning and reconditioning of the filter bags than in the Shaker, and Reverse Air designs. Also the short nature of the cleaning cycle also leads to a reduction in the recirculation and redeposit of dust. Finally, enabled by the continuous cleaning feature of the design, this kind of collection system has a higher Air to Cloth Ratio so the space requirements are much lower than in other systems.

Cartridge Collectors

Unlike Baghouse collectors which feature the use of woven or felt filter bags, Cartridge Collectors use perforated metal cartridges that are cylindrical shaped and open on one or both ends lined with a pleated nonwoven filtering media. Once installed, one end of the cartridge is sealed off and the open end is used for the clean exhaust. Similar to a Baghouse, the Gas stream is forced through the outside of the cartridge to the inside where it then exits back into the system. Cartridge Collectors are also compatible with Reverse or Pulse Jet cleaning. Large numbers of these Collectors can be installed and used for continuous filtration for a location’s dust collection system.

Advantages and Disadvantages – Baghouses

Types Advantages Disadvantages
Shaker Baghouses Have high collection efficiency for respirable dust Have low air-to-cloth ratio (1.5 to 2 ft/min)
Can use strong woven bags, which can withstand intensified cleaning cycle to reduce residual dust buildup Cannot be used in high temperatures
Simple to operate Require large amounts of space
Have low pressure drop for equivalent collection efficiencies Need large numbers of filter bags
Consist of many moving parts and require frequent maintenance
Personnel must enter Baghouse to replace bags, creating potential for exposure to toxic dust
Can result in reduced cleaning efficiency if even a slight positive pressure exists inside bags
Reverse Air Baghouses Have high collection efficiency for respirable dust Have low air-to-cloth ratio (1 to 2ft/min)
Are preferred for high temperatures due to gentle cleaning action Require frequent cleaning because of gentle cleaning action
Have low pressure drop for equivalent collection efficiencies Have no effective way to remove residual dust buildup
Cleaning air must be filtered
Require personnel to enter baghouse to replace bags, which creates potential for toxic dust exposure
Pulse Jet (Reverse Jet) Baghouses Have a high collection efficiency for respirable dust Require use of dry compresses air
Can have high air-to-cloth ratio (6 to 10ft/min) May not be used readily in high temperatures unless special fabrics are used
Have increased efficiency and minimal residual dust buildup due to aggressive cleaning action Cannot be used if high moisture content or humidity levels are present in the exhaust gases
Can clean continuously
Can use strong woven bags
Have lower bag wear
Have small size and fewer bags because of high air-to-cloth ratio
Some designs allow bag changing without entering Baghouse
Have low pressure drop for equivalent collection efficiencies

Common Operating Problems and Solutions – Baghouses*

Symptom Cause Solution
High Baghouse pressure drop Baghouse undersized consult vendor
Install double bags
Add more compartments or modules
Bag cleaning mechanism not properly adjusted Increase cleaning frequency
Clean for longer duration
Clean more vigorously
Shaking not strong enough (S) Increase shaker speed
Compartment isolation damper valves not operating properly (S, RA) Check linkage
Check valve seals
Check air supply of pneumatic operators
Compressed air pressure too low (PJ) Increase pressure
Decrease duration and frequency
Check compressed-air dryer and clean it if necessary
Check for obstructions in piping
Repressurizing pressure too low (RA) Speed up repressurizing fan.
Check for leaks
Check damper valve seals
Pulsing valves failed (PJ) Check diaphragm
Check pilot valves
Bag tension too tight (RA) Loosen bag tension
Bag tension too loose (S) Tighten bags
Cleaning timer failure Check to see if timer is indexing to all contacts
Check output on all terminals
Not capable of removing dust from bags Check for condensation on bags
Send dust sample and bags to manufacturer for analysis
Dryclean or replace bags
Reduce airflow
Excessive reentrainment of dust Empty hopper continuously
Clean rows of bags randomly instead of sequentially (PJ)
Incorrect pressure-drop reading Clean out pressure taps
Check hoses for leaks
Check for proper fluid level in manometer
Check diaphragm in gauge
Dirty Discharge at stack Bags leaking Replace bags
Isolate leaking compartment or module
Tie off leaking bags and replace them later
Bag clamps not sealing Smooth out cloth under clamp and re-clamp
Check and tighten clamps
Failure of seals in joints at clean/dirty air connection Caulk or weld seams
Insufficient filter cake Allow more dust buildup on bags by cleaning less frequently.
Use precoating on bags (S, RA).
Bags too porous Send bag in for permeability test and review with manufacturer
High compressed-air consumption (PJ) Cleaning cycle too frequent Reduce cleaning cycle, if possible
Pulse too long Reduce pulsing duration
Pressure too high Reduce supply pressure, if possible
Diaphragm valve failure Check diaphragm and springs
Check pilot valve
Reduced compressed-air pressure (PJ) Compressed-air consumption too high See previous solutions
Restrictions in compressed-air piping Check compressed-air piping
Compressed-air dryer plugged Replace dessicant in the dryer
Bypass dryer temporarily, if possible
Replace dryer
Compressed-air supply line too small Consult design
Compressor worn out Replace rings
Check for worn components
Rebuild compressor or consult manufacturer
Pulsing valves not working Check pilot valves, springs, and diaphragms
Timer failed Check terminal outputs
Moisture in Baghouse Insufficient preheating Run the system with hot air only before process gas flow is introduced
System not purged after shutdown Keep fan running for 5 to 10 min after process is shut down
Wall temperature below dewpoint Raise gas temperature
Insulate unit
Lower dewpoint by keeping moisture out of system
Cold spots through insulation Eliminate direct metal line through insulation
Water/moisture in compressed air (PJ) Check automatic drains
Install aftercooler
Install dryer
Repressurizing air causing condensation (PJ) Preheat repressurizing air
Use process gas as source of repressurizing air
Material bridging in hopper Moisture in Baghouse See previous solutions
Dust stored in hoppers Remove dust continuously
Hopper slope insufficient Rework or replace hoppers
Screw conveyor opening too small Use a wide, flare trough
High rate of bag failure, bags wearing out Baffle plate worn out Replace baffle plate
Too much dust Install primary collector
Cleaning cycle too frequent Slow down cleaning
Inlet air not properly baffled from bags Consult vendor
Shaking too violent (S) Slow down shaking mechanism
Repressurizing pressure too high (RA) Reduce pressure
Pulsing pressure too high (PJ) Reduce pressure

* S =  Shaker
RA = Reverse Air
PJ  = Pulse Jet

Startup/Shutdown Procedures – Baghouses

Startup Shutdown
1. For processes generating hot, moist gases, preheat Baghouse to prevent moisture condensation, even if Baghouse is insulated. (Ensure that all compartments of shaker or reverse-air Baghouses are open.) 1. Continue operation of dust-removal conveyor and cleaning of bags for 10 to 20 minutes to ensure good removal of collected dust.
2. Activate Baghouse fan and dust-removal conveyor.
3. Measure Baghouse temperature and check that it is high enough to prevent moisture condensation.

Preventive Maintenance Procedures – Baghouses

Frequency    Procedure


•    Check pressure drop.
•    Observe stack (visually or with opacity meter).
•    Walk through system, listening for proper operation.
•    Check for unusual occurrences in process.
•    Observe control panel indicators.
•    Check compressed-air pressure.
•    Assure that dust is being removed from system.


•    Inspect screw-conveyor bearings for lubrication.
•    Check packing glands.
•    Operate damper valves.
•    Check compressed-air lines, including line filters and dryers.
•    Check that valves are opening and closing properly in bag-cleaning sequence.
•    Spot-check bag tension.
•    Verify accuracy of temperature-indicating equipment.
•    Check pressure-drop-indicating equipment for plugged lines.


•    Check all moving parts in shaker mechanism.
•    Inspect fans for corrosion and material buildup.
•    Check drive belts for wear and tension.
•    Inspect and lubricate appropriate items.
•    Spot check for bag leaks.
•    Check hoses and clamps.
•    Check accuracy of indicating equipment.
•    Inspect housing for corrosion.


•    Inspect baffle plate for wear.
•    Inspect bags thoroughly.
•    Check duct for dust buildup.
•    Observe damper valves for proper seating.
•    Check gaskets on doors.
•    Inspect paint, insulation, etc.
•    Check screw conveyor for wear or abrasion.


•    Check fan belts.
•    Check welds.
•    Inspect hopper for wear

Wet Scrubbers

Another effective method of dust collection is the use of Wet Scrubbers (Air Washers). These systems use a scrubbing liquid (usually water) to filter out finer dust particles.  After being filtered the Gas Stream is then sent through a mist eliminator (demister pads) to remove the excess moisture from the Gas stream. Afterward the Gas stream exits the collector through the outlet port and returns back into the system. Wet Scrubbers are ideal:

•    For the collection of explosive material
•    Where “slurry” produced could be reused (either in other parts of process or sold)
•    Where chemical reactions could be generated with other collection methods
•    To absorb excess air

Wet scrubbers have the advantage of low start up costs and low space requirements. They are well suited for treating high temperature and high humidity Gas streams. They also are able to process both air and “sticky” particulates.  The main disadvantages are that they are costly to operate, require a precleaner for any heavy dust loads, cause water pollution that then needs to be addressed, and can erode with high air velocities.

There are a vast variety of different designs and applications of this type of filtration system but all of them have three basic operations they perform:

•    Gas-humidification: The gas-humidification process conditions fine particles to increase their size so they can be collected more easily.
•    Gas-liquid contact: This is the entire basis for the operation of this type of system. The method of contact between the liquid is done in four main ways:

•    Inertial impaction takes place when the Gas stream is forced to flow around the droplets in its path. The stream separates and flows around the droplet. However the larger particles continue to be carried by inertial force in a straight path coming in direct contact with the liquid.
•    Interception: Finer particles while not directly coming in contact with the droplets, do however brush up against the side of them causing them to be absorbed into the liquid.
•    Diffusion occurs when a fine mist is created from the liquid being used. As the particles pass through the mist they make contact with the surfaces of the droplets by means of the Brownian effect, or diffusion.
•    Condensation nucleation is the effect of a gas being cooled below its dew point while within a moisture rich environment, causing the vapor to condense of the surface of the particles thereby encapsulating them.

•    Liquid separation: After going through the cleaning phase the remaining liquid and contaminates must be removed before the Gas stream can be sent back into the system. This is accomplished by means of a Mist Eliminator (Demister Pads). Which remove the liquid and dust mixture from the Gas stream and send it to a collector. Once in the collector, the solid waste settles to the bottom where it is removed by means of a drag chain system to be deposited in a dumpster or another collection area.
Wet Scrubbers are further categorized by pressure drop (in inches water gauge) as follows:

•    Low-energy scrubbers (0.5 to 2.5)
•    Low- to medium-energy scrubbers (2.5 to 6)
•    Medium- to high-energy scrubbers (6 to 15)
•    High-energy scrubbers (greater than 15)
The large amount of different Wet Scrubbers in use makes it impossible to comment on every single design in this article. However a brief overview of the most common types will enable you to understand the basic operational procedures present in all of them.

Low Energy Scrubbers:

•    The most basic design is that of a Gravity Spray Tower Scrubber. In this system the contaminated air enters at the bottom of the cylindrically shaped scrubber and rises through a mist of water sprayed from nozzles at the top. The dirty water collects at the bottom of the tank and the clean air (mist) exits from the top of the collector. This collector has a relatively low efficiency compared to other kinds of Wet Scrubbers. However it’s main advantage is it can handle very heavy dust loads without getting backed up.

•    Dynamic wet precipitators also called Wet Fan Scrubbers are a popular design used for medium energy scrubbing applications. In this system the Gas stream passes through a larger fan that is constantly kept wet with the cleaning liquid. The particles are trapped in the liquid and are then by means of centrifugal force thrown off the spinning fan blades unto the sides of the collector where they eventually settle at the bottom enabling them to be collected.

•    Orifice Scrubbers work in a very similar way to inertial separators but with one important difference, Orifice Scrubbers use a water surface to capture the dust particles. When the Gas stream enters the collector it is rapidly redirected when it comes in contact with the water surface. Causing the dust particles to be removed from the Gas stream. A greater efficiency can be obtained by the addition of liquid spray nozzles to further separate the contaminates from the Gas stream. While these are an effective filtration system one should note that they tend to be ineffective against fine particles as these tend to be redirected off of the water surface by the high surface tension.

Low to Medium Energy Scrubbers:

•    Wet Cyclone Scrubbers are nearly identical to their normal cyclone collector counterparts. In a Wet Cyclone Scrubber the Gas stream enters the collector and is then forced into a cyclone movement by the strategic placement of stationary scrubbing vanes. Liquid is introduced at the top of the collector allowing the dust particles to stick to the wet walls of the collector when they are thrown off by the vortex. As with dry Cyclone Collectors, this type of system has the benefit of few to no moving parts and it is efficient for particles up to 5um and above.

Medium to High Energy Scrubbers:

•    Packed Bed Scrubbers consist of a bed of packing media, which is then sprayed with water. The packing media allows for a very wide distribution of the water, which in turn allows the Gas stream to have the maximum contact with the water during its passage though the collector. Air enters at the bottom of the collector where it first makes contact with the water in the recirculation tank. Then it is forced up through the various layers of the filtering media, and after being sent through a Mist Eliminator is sent back into the system via the exit port at the top.

Within the category of Packed Bed Scrubbers there are three different variations on the implementation of this filtering mechanism they are:

•    Cross-flow scrubbers are designed to minimize height for low-profile applications. In this design the packed media is laid as sheets perpendicular to the Gas stream. The Gas stream enters in one side of the Scrubber and flows horizontally through it passing though the packing media and then exiting out the opposite side
•    Co-current flow scrubbers
•    Counter-current flow scrubbers

High energy Scrubbers:

•    Venturi Scrubbers make use of the Venturi effect to accelerate the Gas stream to speeds of 12,000 to 36,000 ft/min. The Gas stream enters into the Scrubber through a Venturi shaped inlet where it is sprayed with water. The water hitting the extremely high speed air causes it to instantly atomize. The very fine water droplets attach to the dust particles and form a slurry, which then falls to the bottom of the collector. After passing through a Mist eliminator the Gas stream is sent back into the system.

Advantages and Disadvantages – Wet Scrubbers

Advantages Disadvantages
Have low capital costs and small space requirements Have high operating and maintenance costs
Have low capital costs and small space requirements Require corrosion-resistant materials if used with acidic gases
Are able to collect gases as well as particulates (especially “sticky” particulates) Require a precleaner for heavy dust loadings
Have no secondary dust sources Cause water pollution; require further water treatment
Are susceptible to erosion at high velocities
Collect wet products
Require freeze protection

Common Operating Problems and Solutions – Wet Scrubbers

Problem Solution
Wet/dry buildup Keep all areas dry or all areas flooded.
Use inclined ducts to a liquid drain vessel.
Ensure that scrubber is installed vertically.
Maintain liquid seal.
Dust buildup in fan Install clean water spray at fan inlet.
Excessive fan vibration Clean fan housing and blades regularly.
Liquid pump failure Divert some of the recycle slurry to a thickener, settling pond, or waste disposal area and supply clean water as makeup.
Increase the water bleed rate.
Worn valves Use wear-resistant orifice plates to reduce erosion on valve components.
Jammed valves Provide continuous purge between valves and operating manifold to prevent material buildup.
Erosion of slurry piping Maintain pumping velocity of 4 to 6 ft/s to minimize abrasion and prevent sedimentation and settling.
Plugged nozzles Replace nozzles or rebuild heads.
Change source of scrubbing liquid.
Supply filtered scrubbing liquid.
Buildup on mist eliminators For vane-type demisters, spray the center and periphery intermittently to clean components.
For chevron-type demisters, spray the water from above to clean the buildup.

Startup/Shutdown Procedures – Wet Scrubbers

Prestart Checklist Shutdown
1. Start fans and pumps to check their rotation. 1. Shut down fan and fan spray. Insulate scrubber from operation.
2. Disconnect pump suction piping and flush it with water from an external source. 2. Allow liquid system to operate as long as possible to cool and reduce liquid slurry concentrations.
3. Install temporary strainers in pump suction line and begin liquid recycle. 3. Shut off makeup water and allow to bleed normally.
4. With recycle flow on, set valves to determine operating conditions for desired flow rates. Record the valve positions as a future baseline. 4. When pump cavitation noise is heard, turn off pump and pump gland water.
5. Record all system pressure drops under clean conditions. 5. Open system manholes, bleeds, and other drains.
6. Perform all recommended lubrications.
7. Shut down fan, drain the system, and remove temporary strainers.
1. Allow vessels to fill with liquid through normal level controls. Fill large-volume basins from external sources.
2. Start liquid flow to all pump glands and fan sprays.
3. Start recycle pumps with liquid bleed closed.
4. Check insulation dampers and place scrubber in series with primary operation.
5. Start fan and fan inlet spray. Leave inlet control damper closed for 2 min to allow fan to reach speed.
6. Check gas saturation, liquid flows, liquid levels, fan pressure drop, duct pressure drops, and scrubber pressure drop.
7. Open bleed to pond, thickener, or other drain systems so slurry concentration can build slowly. Check final concentration as cross-check on bleed rate.

Preventative Maintenance Procedures – Wet Scrubbers

Frequency Procedure


•    Check recycle flow.
•    Check bleed flow.
•    Measure temperature rise across motor.
•    Check fan and pump bearings every 8 hours for oil level, oil color, oil temperature, and vibration.
•    Check scrubber pressure drop.
•    Check pump discharge pressure.
•    Check fan inlet and outlet pressure.
•    Check slurry bleed concentration.
•    Check vibration of fan for buildup or bleeds.
•    Record inlet and saturation temperature of gas stream.
•    Use motor current readings to detect flow decreases. Use fan current to indicate gas flow.
•    Check pressure drop across mesh and baffle mist eliminators. Clean by high-pressure spraying, if necessary.

•    Check wet/dry line areas for material buildup. Clean, if necessary.
•    Check liquid spray quantity and manifold pressure on mist eliminator automatic washdown.
•    Inspect fans on dirty applications for corrosion, abrasion, and particulate buildup.
•    Check bearings, drive mechanisms, temperature rise, sprocket alignment, sprocket wear, chain tension, oil level, and clarifier rakes.
•    Check ductwork for leakage and excessive flexing, Line or replace as necessary.
•    Clean and dry pneumatic lines associated with monitoring instrumentation.

•    Verify accuracy of instruments and calibrate.
•    Inspect orifice plates.
•    Clean electrical equipment, including contacts, transformer insulation, and cooling fans.
•    Check and repair wear zones in scrubbers, valves, piping, and ductwork.
•    Lubricate damper drive mechanisms and bearings. Verify proper operation of dampers and inspect for leakage.

Electrostatic Precipitators

Electrostatic Precipitators use electrostatic forces to collect dust from the Gas stream. Several high power Direct Current Discharge Electrodes are places inside the collector. The incoming Gases pass by the first set of Discharging Electrodes (ionizing section) that give the particles a negative charge (ionization). The now ionized particles travel pass the next set of electrodes (the collection section) that carry a positive charge. The positively charged plates attract the negatively charged particles causing them to collect on the plates. Cleaning is accomplished by vibrating the electrodes either continuously, or at a timed interval, causing the captured dust to fall off into a hopper below. All of this can be done while the system is operating normally.

Electrostatic Precipitators are best used in an ambient capture type system with low particle loads. Without an automated self-cleaning feature, this type of collector can very easily reach its maximum particle retention limit, which will result in a system failure. Further, for a high dust load system a great amount of dust storage is needed. Media Filtration (Baghouse) or Pleated Filtering Media (Cartridge Collectors) provide a much great surface area for dust storage than Electrostatic Precipitator systems do.  However the advantages of this system are great for their intended applications. They have the ability to be extremely efficient (in excess of 99.9% in some cases), can function within vary large temperature ranges (between 700 °F and -1300°F), and can have large flow rates with minimal pressure and temperature changes. They are also very well suited for the collection of fine dust particles as well as materials like acids and tars which other system may have difficulty with.

All electrostatic Precipitators have four main components:

•    A Power supply to provide the system with electricity
•    An Ionizing section to negatively charge the incoming particles
•    A cleaning system designed to remove collected particles from the Electrode collection plates
•    A housing to enclose the Precipitator section

Within the category of Electrostatic Precipitator Collectors, there are two main types of systems:

•    High Voltage Single State Precipitators (Cottrell type)
•    Low Voltage Dual State Precipitators (Penny type)
High Voltage Single State Precipitators are further divided between two main designs:

Plate Precipitators are made up of several flat parallel plate collectors that are usually between 8 and 12in apart. Placed directly in the middle of each set of directly adjacent plates are a series of high voltage (40,000-70,000 volts) DC Discharge Electrodes. As the Gas stream passes through the plates it is ionized by the Discharge Electrodes and then immediately deposited unto the collection plates. The plates are then cleaned by vibrating the plates causing the debris to fall into a hopper or collection bin below. The majority of Single State Precipitators in use today are of the plate variety.

Tubular Precipitators operate in the same manner as Plate Precipitators however in a different configuration. This design uses a tubular shaped collection device with the Discharge Electrodes placed in the middle of the tube. As the Gas stream flows through the tube it is first ionized by the Discharge Electrode in the center, and then the charged particles are attracted to the inside of the positively charged tube. The cleaning mechanism can be one nearly identical to that of Plate Precipitators or it can be used as part of a Wet Static Precipitator system, wherein the sides of the Precipitator are flushed with water thereby cleaning them.
Tubular Precipitators are widely used in the mineral processing industry. They are highly valuable for use in high temperature Gas streams (boiler exhaust gas on power plants) because of their ability to adjust to the expansion and contraction of metal parts in the system. In addition this type of collector is also able to handle vapor collection, containing adhesive, “sticky”, radioactive, and extremely toxic compounds.

Low Voltage Dual Stage Precipitators contain several grounded plates about one inch from each other with another intermediate plate that also contains a charge. This system uses a much lower voltage than the High Voltage type (a 13,000-15,000 volt DC supply with intermediate supply of 7,500 compared to 40,000 to 70,000). This type of system is widely used to collect fumes and particles generated by welding, grinding or burning operations. They are also used in hooded and ducted welding machines and welding booths.
Low Voltage Dual Stage Precipitators have the advantages of being highly efficient, the possibility of a self contained washing system, and a longer service life since cleaning is only required on a monthly basis. However because maintenance requires removing the Precipitator Frames and the manual cleaning of the cleaning assemblies which are quite delicate, this type of Precipitator requires a great amount more care and caution to be used when performing maintenance.

Advantages and Disadvantages – Electrostatic Precipitators

Advantages Disadvantages
Have collection efficiencies in excess of 99% for all particulates, including sub-micron-sized particles Have high initial investment costs
Usually collect dust by dry methods Do not respond well to process changes such as changes in gas temperature, gas pressure, gas flow rate, gaseous or chemical composition, dust loading, particulate size distribution, or electrical conductivity of the dust
Have lower pressure drop and therefore lower operating costs Have a risk of explosion when gas stream contains combustibles
Can operate at high temperatures (up to 1200º F) and in colder climates Product ozone during gas ionization
Can remove acids and tars (sticky dust) as well as corrosive materials Require large space for high efficiency, and even larger space for dust with low or high resistivity characteristics
Allow increase in collection efficiency by increasing precipitator size Require special precautions to protect personnel from exposure to high-voltage
Require little power Require highly skilled maintenance personnel

Unit Collectors

For certain applications, Unit Collectors are a better choice for a facilities needs than a conventional Central Collection System. These collectors control contamination at their source. They benefit from low initial cost, direct return of captured material to the main material flow, and very low space requirements. These collectors are best used when the dust source is isolated, portable or changes position often. Some examples of instances where this type of collector might be useful are dust-producing operations, such as bins and silos or remote belt-conveyor transfer points.

Depending on the particular desired application is there are a number of different designs available to choose from with a capacity of 200 to 2,000 ft3/min. The two main types are:

•    Fabric Collectors
•    Cyclone Collectors

Unit Fabric Collectors are very similar to their bigger relatives used in a Central Collection System. They usually employ either a Mechanical Shaker, or a Pulse Jet system for cleaning. This type is well suited for the collection of fine particles such as in the mineral processing industry.
Unit Cyclone Collectors also operate on the same principles are the kind used in Central Collection Systems. Dust is collected and deposited into a hopper, which then can be removed later for cleaning. This type of collector is best used in the collection of coarse of larger particles.

Central Collection System

Every Dust Collection System must have a Central Collection System in place in order to send the contaminated air to the filtration system. A Central Collection System consists of a series of collection inlets, and the necessary duct work to transport the dust laden Gas stream to the collector and afterward on to be either recirculated back into the facility or dispersed into the atmosphere. The pressure in this duct system is supplied by the Fan and Motor System.

Fan and Motor

Choosing the right Fan and Motor System requires a number of different factors to be taken into consideration including but not limited to:

•    Volume required
•    Fan static pressure
•    Type of material to be handled through the fan (For example, a Radial Blade Fan should be used with fibrous material or heavy dust loads, and a nonsparking construction must be used with explosive or flammable materials.)
•    Limitations in space
•    Acceptable levels of noise caused by the fan
•    Required operational temperature (For example, sleeve bearings are suitable to 250º F; ball bearings to 550º F.)
•    Adequate size to handle pressure and volume requirements with minimum horsepower usage
•    Whether any corrosive materials are going to be handled and what protective coatings may be needed
•    Ability of fan to accommodate small changes in total pressure while maintaining the necessary air volume
•    Need for an outlet damper to control airflow during cold starts (If necessary, the damper may be interlocked with the fan for a gradual start until steady-state conditions are reached.)

Also to be considered is what type of drive system for the fan you plan to use. A Direct Drive fan is run directly off of a drive shaft from the motor, this provides for lower space needs, but places the fan at a constant unchangeable speed. While Belt Driven fan, which uses a belt to flywheel configuration needs more space, it can allow for the fan speed to be easily changed which is vital for some applications.

There are two main types of fan designs that are used in industrial applications:

•    Centrifugal fans
•    Axial-flow fans

A Centrifugal Fan (also called a Squirrel-cage fan for its resemblance rodent exercise devices) is a fan build with blades (or ribs) surrounding a central hub.  The air enters into the side of the fan and then turns 90° and is accelerated and thrown out of the fan by means of centrifugal force.  The diverging shape of the scroll also converts a portion of the velocity pressure into static pressure. The fan is driven by means of a drive shaft that extends out from the center hub of the fan.

There are three main types of Centrifugal fan blades that can be used:

•    Forward Curved Blades
•    Backward Curved Blades
•    Straight Radial Blades

Forward Curved Bladed Fans have blades that are curved in the direction of the rotation of the fan. These fans are highly sensitive to particulate buildup and are used for high airflow, low pressure applications.

Backward Curved Bladed Fans contain blades that are positioned away from the fans rotation direction. These fans will provide an efficient operation, and can be used in Gas streams with light to medium particle concentration. While they can be fitted with wear protection, this type of blade can still become backed up if the particle load gets to be too heavy. This fan type is most often employed in medium speed, high pressure, and medium airflow applications.

Straight Radial Bladed Fans provide the best choice for heavy particle loads. This design features a series of blades that extend straight out from the center hub. This design is used for high pressure, high speed and low volume applications.

Fan dampeners

Fan dampeners are metal plates that can be adjusted to reduce the energy usage of the fan. Placed on the Outlet port of a fan, they are used to impose a flow resistance to control the Gas stream. They also can be placed on the Inlet port, which can perform the same function, as well as redirect how the Gas stream enters into the fan.

Axial Flow Fans

Axial Flow Fans have blades that are mounted unto a center drive shaft. They induce the air to move parallel to the shaft the blades are mounted on by the screw-like action of the propellers. The air is blown across the axis of the fan hence the name Axial Flow Fans. This type of fan is commonly used in systems with low resistance levels.

The three main different designs of Axial Flow Fans are:

•    Propeller
•    Tube Axial
•    Vane Axial

Propeller Fans is the most simple fan design. It is used to move large an amount of air against very low static pressure from the rest of the system. General and Dilution ventilation are two common uses for this type of axial fan.

The Tube Axial design is very similar to a normal propeller type fan, except that the propeller is enclosed in an open ended cylinder. This design is more efficient than simple propeller types and is often used in moving Gas streams filled with condensable fumes or pigments.

Vane Axial Fans are nearly identical to Tube Axial Fans. But these contain specially attached vanes that are designed to straighten the Gas stream as is passes through the fan. These can produce high static pressures relative to this type of fan. However these fans are in most applications used only for clean air.

Fan Rating Table

Once all of the preceding material has been examined, the final step in the selection of the proper fan for your system is to consult a Fan Rating Table. This is used to list all of the specifications for the various fans produced by a certain manufacturer. When reviewing a Fan Rating Table one must keep these few points in mind:

•    The rating tables show all of the possible pressures and speeds that can be achieved within the limits of the fan’s normal operation range.
•    A fan that operates at a single or fixed speed and has a fixed blade setting will only have one possible rating. The only way to gain multiple ratings is by varying the speed and the blade setting.
•    It may be possible to obtain the same fan in different construction classes
•    Increasing the exhaust volume will in turn increase the static and total pressure in the system

Fan installation

Once a system has been installed in the field, inevitably certain differences between design and field installation will require a field test to be done to find the exact measurements of static pressure and volume. This step is crucial in order for a proper fan system to be selected. A few brief points are good to keep in mind during the installation process that can cause your real world values to change from the original design specifications:

•    Elbows and bends near the fan’s discharge will increase the systems resistance thereby lowering your fan’s performance
•    Make sure to install the impeller in the proper direction desired.
•    Certain types of fittings such as elbows, mitered elbows and square ducts, can cause a nonuniform airflow which in turn will again lower performance
•    Build up of debris in the inlets, blades, passages as well as obstructions should be checked and remedied
•    In a belt driven system one must check the motor sheave and fan sheave are properly aligned and that proper belt tension is present

Electric Motors

An Electric Motor is what supplies the power necessary to operate the fan (Blower) in the Dust Collection System.  Electric Motors are usually grouped as either Induction, or Synchronous designs. Induction designs are the only ones that are used in Dust Collection Systems today.
Induction Motors normally operate on three phase AC current. The two most common types used in Dust Collection Systems are:

•    Squirrel Cage Motors are generally used where a constant speed is desired
•    Slip Ring Motors by contrast are general purpose or continuous rated motors that are used in applications where there is a need for an adjustable speed in the motor.

Another important design consideration is whether the Motor is one of these two enclosure designs:

•    Drip Proof and Splash Proof Motor are types of Open Enclosed Motors, which use a kind of electric motor enclosure that has vents to allow airflow but to prevent liquids and solids from entering the motor. This design is not suitable for application where particles that can damage the interior of a motor are found in the ambient atmosphere around the motor.
•    Totally Enclosed Motors have an exterior fan mounted unto the backside of the motor drive end. The fan blows air over the motor enclosure to provide additional cooling for the motor. Since the actual motor is totally enclosed this design provides the best protection against dust and other contaminates that might damage the motor if allowed inside.
Both Types can also be constructed in explosion and dust ignition proof models to protect against accidental ignition of dust particles.
The following factors need to be considered when choosing which motor meets your needs:

•    Horsepower and RPMs
•    Power supply needs such as voltage, single or three phase AC and frequency
•    The environment in which the motor will have to operate (humidity, temperature, open flames or corrosive elements
•    What kind of load is going to be placed on the motor (fan and other drive mechanisms) and power company restrictions on cold starts.
•    Sufficient power supply for cold starts
•    Overload protection needed for the particular motor

Fan & Motor Troubleshooting Chart

Symtom Probable Cause Solution
Insufficient airflow, low ft3/min Fan
Forward curved impeller installed backwards Reinstall impeller
Fan running backwards Change fan rotation by reversing two of the three leads on the motor
Impeller not centered with inlet collar(s) Make impeller and inlet collar(s) concentric
Fan speed too low Increase fan speed by installing smaller diameter pulley
Elbows or other obstructions restricting airflow Redesign ductwork
Install turning vanes in elbow
Remove obstruction in ductwork
No straight duct at fan inlet Install straight length of ductwork, at least 4 to 6 duct diameters long, where possible
Increase fan speed to overcome this pressure loss
Obstruction near fan outlet Remove obstruction or redesign ductwork near fan outlet
Sharp elbows near fan outlet Install a long radius elbow, if possible
Install turning vanes in elbow
Improperly designed turning vanes Redesign turning vanes
Projections, dampers, or other obstructions near fan outlet Remove all obstructions
Duct System
Actual system more restrictive (more resistant to flow) than expected Decrease system’s resistance by redesigning ductwork
Dampers closed Open or adjust all dampers according to the design
Leaks in supply ducts Repair all leaks in supply duct
Too much airflow, high ft3/min Fan
Backward inclined impeller installed backwards (high horsepower) Install impeller as recommended by manufacturer
Fan speed too fast Reduce fan speed
Install larger diameter pulley on fan
Duct System
Oversized ductwork; less resistance Redesign ductwork or add restrictions to increase resistance
Access door open Close all access and inspection doors
Low static pressure, high ft3/min Fan
Backward inclined impeller installed backwards (high horsepower) Install impeller as recommended by manufacturer
Fan speed too high Reduce fan speed
Install larger diameter pulley on fan
Duct System
System has less resistance to flow than expected Reduce fan speed to obtain desired flow rate
Gas Density
Gas Density lower than anticipated (due to high temperature gases or high altitudes) Calculate gas flow rate at desired operating conditions by applying appropriate correction factors for high temperature or altitude conditions
Low static pressure, low ft3/min Duct System
Fan inlet and/or outlet conditions not same as tested Increase fan speed
Install smaller diameter pulley on fan
Redesign ductwork
High static pressure, low ft3/min Duct System
Obstructions in system Remove obstructions
Duct system too restricted Redesign ductwork
Install larger diameter ducts
High horsepower Fan
Backward inclined impeller installed backwards Install impeller as recommended by manufacturer
Fan speed too high Reduce fan speed
Install larger diameter pulley on fan
Duct System
Oversized ductwork Redesign ductwork
Access door open Close all access/inspection doors
Gas Density
Calculated horsepower requirements based on light gas (e.g., high temperature or high altitude) but actual gas is heavy (eg.,cold startup) Replace motor
Install outlet damper, which will open gradually until fan comes to its operating speed
Fan Selection
Fan not operating at efficient point of rating Redesign system
Change fan
Change motor
Fan does not operate Electrical
Blown Fuses Replace Fuses
Electricity turned off Turn on Electricity
Wrong voltage Check for proper voltage on fan
Motor too small and overload protector has broken circuit Change motor to a larger size
Broken belts Replace belts
Loose pulleys Tighten or reinstall pulleys
Impeller touching scroll Reinstall impeller properly

Dust Disposal

After the Airstream has been cleaned, the dust that has been collected must be disposed of in a proper way to ensure that recontamination is avoided.  In many cases where the collected material is of value, it can be returned to the product stream and reused. However this is not practical in all applications. Minimizing secondary dust problems is also a key component in an effective dust disposal system. Operations such as loading and unloading of the collected material, or the transportation of wet slurry can present further contamination problems that need to be addressed.
All Disposal Systems have to accomplish these four objectives without further contaminating the environment, in order to be effective in their role in the Dust Collection System:

•    Collected material from the hopper must be removed
•    Transportation to storage
•    Storage of the collected material
•    Treatment necessary before final disposal

Removal Of Dust From The Hopper

The hopper must be emptied of the collected dust on a regular basis to prevent overfilling. Often this process is done while the collector is still operating. If this is the case, rotary air locks, or tipping valves need to be used in order to maintain a positive air seal and thus avoid massive pressure loss that would be detrimental to the normal operation of the system. Some materials display what is called a bridging tendency, which is a tendency to stick together and form long strands that can over time build up into bridge like formations that can impede the normal operations within a hopper. If material of this kind is present in the system, special equipment such as bin vibrators, rappers, or air jets should be used to ensure that the material that has a bridging tendency does not interfere with normal operation of the hopper.

Dust Transportation

Once the dust has been removed from the collector, it must be transported to a storage area where is can be given any final treatments needed before it is disposed of.  There are four main systems that can be used to transport the collected material to holding there are:

•    Screw conveyers
•    Air conveyers
•    Air Slides
•    Pressurized piping system for wet material (Slurry)

Screw conveyers use rotating shaft to move material to the desired location. These systems are very effective methods of dust transportation.  However several areas of concern in this type of system are that they tend to have a noted lack of easy access for maintenance purposes, the castings and bearings can wear out easily when used with abrasive materials with air leaks being the end result.

Air Conveyers are used mainly for dry dust applications. Making use of a high velocity low air volume principle, these collectors are a great choice because of their few moving parts and their ability to move dust both vertically and horizontally. The main concerns with this system are that the piping can over time suffer from excessive wear from abrasive compounds. They also require large initial investments of capital and have higher operating costs.

Air Slides are widely used for light dust loads with nonabrasive materials. Air fluidization of the dust is the main operating principle behind this system. This system while able to transport great amounts of material has the downside of only being able to do so in a horizontal direction. Areas of concern are the need to maintain a constant down pitch in the ductwork, and greater maintenance costs.

Pressurized piping systems are needed when transporting the slurry made from using a Wet Scrubber design. This system is used to send the slurry to a settling pond for further treatment. Great care must be taken by the operators of this system to ensure that no leakage occurs which would result in an environmental hazard caused by water pollution.

Dust Storage

Storage tanks and Silos are the most common storage locations for dry dust compounds after their collection.  These sites are then fitted to allow loading of the material into enclosed trucks or rail cars below.
When using a wet collection system often times a settling pond is needed.  In a settling pond the captured particles are separated by means of the process of decantation.  The slurry from the Wet Scrubbers is left to sit in a large pond or basin, allowing the captured particles to over time slowly settle to the bottom of the pond; afterwards the clean water is discharged. Again certain factors to consider in the use of a settling pond are that the water holding area can only be decanted in the warmer, dryer part of the year, and in most instances two settling ponds are needed to operate efficiently.

Final Disposal

When deciding on a final disposal method, one must remember that great care needs to exercised in order to avoid recirculation of the dust by the wind. Sometimes in because of this concern, and for easier transportation, the captured material is processed into pellets before final disposal.  Generally four different options are available for the final disposal of the collected material:
•    Placement in a landfill
•    Recycling
•    Byproduct utilization
•    Collected material may be suitable for backfilling land fills and quarries

Selection of a Dust Collector

The differences in design, operation, efficiency, space requirement, construction, and maintenance needs, as well as the initial start up, operating, and maintenance costs differ greatly between various products and systems. However in choosing which system will meet your needs the best, the following point should be considered:

Dust concentration and Particle size – Within any kind application the specific sizes and dust concentrations can vary enormously. Therefore, knowing the exact range of particle size and concentration levels that will be present will be vital in your choosing the proper Collection System.

Degree of collection required – How intensive of a filtration action is needed is determined by several factors. The exact dangers and hazards of the contaminates to be captured, its potential as a public health risk or nuisance, site location, the allowable emission rate by the regulatory body for the given substance, characteristics of the dust, and any recyclable value.

Characteristics of the Gas stream – Differences in Gas stream temperatures and humidity levels can great affect certain types of collectors. For example Gas temperatures above 180° F (82°C) will destroy many types of filter media (Filter Bags) used in Fabric Collectors (Baghouses). Water vapor or steam can blind certain types of Filter Media. Corrosive and other chemicals can erode certain metals and other materials used in the construction of many Collectors.

Types of Dust – Certain types of Collectors have a great deal of physical contact between the particles and the Collector itself. A number of different materials such as silica or metal ore are quite abrasive and can cause erosion through prolonged contact with the Collector. Other “sticky” compounds can attach themselves to the interior surfaces of the collector and cause blockages. The size and distinct shape of some types of dust render certain collection methods useless. When certain types of materials are fluidized into the air they become highly combustible. Under these circumstances Electrostatic Precipitators are instantly ruled out, along with most Inertial Separators.

Disposal Methods – Differences in disposal methods betweens different locations. Collectors can be arranged to unload their collected matter either in a continuous mode or at a predetermined time interval. Removal of collected matter from dry systems can also result in secondary causes of dust pollution and contamination. While using a Wet Scrubber System will eliminate this concern, proper handling of slurry created during the cleaning cycle will involve an entirely different set of problems, such as precautions against water pollution, and proper care and maintenance of the retention ponds.


About the Author

| Dominick DalSanto is an Author & Environmental Technologies Expert, specializing in Dust Collection Systems. With nearly a decade of hands-on working experience in the industry, Dominick’s knowledge of the industry goes beyond a mere classroom education. He is currently serving as Online Marketing Director & Content Manager at Baghouse.com. His articles have been published not only on Baghouse.com , but also on other industry related blogs and sites. In his spare time, Dominick writes about travel and life abroad for various travel sites and blogs.

At least 281 combustible dust fires and explosions occurred in general industry between 1980 and 2005 in the United States, which caused at least 119 fatalities and 718 injuries; including seven catastrophic dust explosions in the past decade, involving multiple fatalities and significant community economic impact; and occurred in a wide range of industries and involved many types of combustible dusts.

According to a report by the US Chemical Safety Board (CSB) a major factor that lead to the high amount of incidents was the overall lack of education regarding the danger of Dust Explosions. Without this information, plant operators are not able to implement proper safety precautions, and adequately train their personal about the precautions they need to take to minimize the chance of a Dust Explosion occurring in their facility.  This article has been prepared to help bring awareness to the dangers of Dust Explosions, and what precautions can be taken to avoid them.

What Is A Dust Explosion?

A factory that has been destroyed by a Dust Explosion

A Dust Explosion that begins in the Dust Collection System can lead to the destruction of an entire facility.

Most solid organic materials, in addition to many metals and inorganic nonmetallic materials, when reduced to a finely divided size, and sufficiently dispersed into the atmosphere will explode under the right conditions. Many combustible dusts are intentionally manufactured for a wide range of applications such as Metallic Powder Coatings, or certain foodstuffs such as Corn Starch, Flour, and Granulated Sugar. Others are produced during the manufacture and transport of materials such as wood processing, and stone quarrying. Additionally, during the manufacturing process for many materials, actions such as milling, polishing, and transportation may create substantial amounts of dust that can later accumulate on a wide range of surfaces.

Any industry that produces materials of a fine particle size that are combustible, and many that simply though their day-to-day operation create large amounts of secondary dust are at risk for Dust Explosions. Industries such as Metal, Food, Plastic, and Wood Processing are just a few that are at risk for this kind of industrial accident.

The Anatomy of a Dust Explosion

The Beginnings

The basics of combustion deal with the so called “Fire Triangle” that illustrates the importance of the three main factors that need to be present for combustion to take place. These three are Fire, Heat (Ignition Source) and Oxygen. With regards to Dust Explosions, we need to add another two ingredients to create what has been termed the “Dust Explosion Pentagon” Dispersion and Confinement. When all five of these factors are present in the right balance, a dust explosion will occur. The more of these factors that can be controlled or be kept below the combustion threshold, the less likely there will be an incident.

When a material is finely divided into a dust or power form it in most cases it becomes much more likely to combust than it would in a solid state. The reason for this is because when a material is smaller in size, and is dispersed into the air, it creates a much larger surface area to ignite. For example, a 1 kg sphere of a material with a density of 1g/cm3 would be about 27 cm across and have a surface area of 0.3 m3. However, if it was broken up into spherical dust particles 50µm in diameter (about the size of flour particles) it would have a surface area of 60 m² This greatly increased surface area allows the material to burn much faster, and the extremely small mass of each particle allows it to catch on fire with much less energy than the bulk material, as there is no heat loss to conduction within the material.

The source of ignition in a Dust Explosion is often times very difficult if not impossible to determine with absolute certainty. This is because in an industrial setting there is such a larger amount of possible ignition sources that after an incident, it cannot always be pinpointed with absolute certainty.  Some possible sources include, Open Flames, Electrostatic Discharge, Friction, Chemical Reactions, Arcing (From machinery or other equipment) and Hot Surfaces.

Primary and Secondary Explosions

Primary Dust Explosions, in an industrial setting, usually involve a dust cloud (Dispersed Dust) that is ignited by an ignition source. This explosion while possibly involving a substantial amount of dust is often not the most devastating. That is because this initial explosion can cause a pressure wave that can dislodge settled dust from other areas within a facility (Such as on the top of structural elements like beams and columns, high shelving, and machinery, or other areas that dust and debris may collect) causing it to disperse and then cause a much larger explosion that is termed a Secondary Dust Explosion. The majority of fatalities, and damage caused by dust explosion incidents, are actually caused by Secondary Dust Explosions.

Conditions That Lead To A Dust Explosion

The same CSB report cited earlier, after having discussed several different Industrial Dust Explosion Incidents, concluded that while all had many different factors that contributed to the respective incidents, all had the following circumstances in common:

* Facility management failed to conform to NFPA (National Fire Protection Agency) standards that would have prevented or reduced the effects of the explosions.
* Company personnel, government standards enforcement officials, insurance underwriters, and health and safety professionals inspecting the facilities failed to identify dust explosion hazards or recommend protective measures.
* The facilities contained unsafe accumulations of combustible dust and housekeeping to remove such accumulations was inadequate.
* Workers and managers were often unaware of dust explosion hazards.
* Procedures and training to eliminate or control combustible dust hazards were inadequate.
* Previous fires and other warning events were accepted as normal, and their causes were not identified and resolved.
* Dust collectors were inadequately designed or maintained to minimize explosions.
* Process changes were made without adequately reviewing them for potential hazards.

Listed here are a few of the summery reports published by the CSB. As you will see the above-mentioned factors all played a role in the eventual incidents.

Organic Dust Fire and Explosion: Massachusetts (3 killed, 9 injured)

In February 1999, a deadly fire and explosion occurred in a foundry in Massachusetts. The Occupational Safety Health Administration (OSHA) and state and local officials conducted a joint investigation of this incident. The joint investigation report1 indicated that a fire initiated in a shell molding machine from an unknown source and then extended into the ventilation system ducts by feeding on heavy deposits of phenol formaldehyde resin dust. A small primary deflagration occurred within the ductwork, dislodging dust that had settled on the exterior of the ducts. The ensuing dust cloud provided fuel for a secondary explosion, which was powerful enough to lift the roof and cause wall failures. Causal factors listed in the joint investigation report included inadequacies in the following areas:

* Housekeeping to control dust accumulations;
* Ventilation system design;
* Maintenance of ovens; and,
* Equipment safety devices.

Organic Dust Fire and Explosion: North Carolina (6 killed, 38 injured)

In January 2003, devastating fires and explosions destroyed a North Carolina pharmaceutical plant that manufactured rubber drug-delivery components. Six employees were killed and 38 people, including two firefighters, were injured. The U.S. Chemical Safety and Hazard Investigation Board (CSB), an independent Federal agency charged with investigating chemical incidents, issued a final report2 concluding that an accumulation of a combustible polyethylene dust above the suspended ceilings fueled the explosion. The CSB was unable to determine what ignited the initial fire or how the dust was dispersed to create the explosive cloud in the hidden ceiling space. The explosion severely damaged the plant and caused minor damage to nearby businesses, a home, and a school. The causes of the incident cited by CSB included inadequacies in:

* Hazard assessment;
* Hazard communication; and
* Engineering management.

The CSB recommended the application of provisions in National Fire Protection Association standard NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids, as well as the formal adoption of this standard by the State of North Carolina.

Organic Dust Fire and Explosion: Kentucky (7 killed, 37 injured)

In February 2003, a Kentucky acoustics insulation manufacturing plant was the site of another fatal dust explosion. The CSB also investigated this incident. Their report3 cited the likely ignition scenario as a small fire extending from an unattended oven, which ignited a dust cloud created by nearby line cleaning. This was followed by a deadly cascade of dust explosions throughout the plant. The CSB identified several causes of ineffective dust control and explosion prevention/mitigation involving inadequacies in:

* Hazard assessment;
* Hazard communication;
* Maintenance procedures;
* Building design; and,
* Investigation of previous fires.

Metal Dust Fire and Explosion: Indiana (1 killed, 1 injured)

Finely dispersed airborne metallic dust can also be explosive when confined in a vessel or building. In October 2003, an Indiana plant where auto wheels were machined experienced an incident, which was also investigated by the CSB. A report has not yet been issued, however, a CSB news release told a story similar to the previously discussed organic dust incidents: aluminum dust was involved in a primary explosion near a chip melting furnace, followed by a secondary blast in dust collection equipment.

Prevention, Safety and Mitigation

Now that we have discussed many of the contributing factors that can lead to a Dust Explosion, we are going to highlight several areas that if given the proper attention, will lead to a safer working environment, and lessen the potential for property damage bodily harm.

Hazard Analysis

We have discussed the great danger that Dust Explosions can pose to life and property. Now we have listed several areas that if given the proper attention will greatly reduce the probability of a dust explosion occurring, and should one occur, lessen the severity of said explosion, possibly saving lives and lessening the damage to the facility in the process.

Facility Dust Hazard Assessment

Being aware that the possibility of a Dust Explosion exists is the first step to avoiding one. As mentioned previously, most dusts or powders will burn and if dispersed in the air in the right proportions and may explode. The same CSB study quoted earlier found that despite the long history of Dust Explosions in industry, in many cases the hazards involved with explosive dusts were largely ignored by plant operators, as well as by outside insurance auditors and government inspectors. Therefore, recognizing the great potential for this kind of accident during the initial design of the facility and while doing regular hazard analysis, are crucial

Here are some of the items to look for when conducting a facility hazard analysis with regard to the potential for Dust Explosions.

Dust Combustibility

Above all else, it must be determined whether or not that various types of dust produced in the facility are indeed combustible. As stated before, most materials in dust or powder form will burn when dispersed into the air in the right proportions. However, those proportions vary with each material. Therefore, it is vital for those responsible to gather as much data as possible about the particular materials present in the facility. One potential source of said data is the particular material’s MSDS or Material Safety Data Sheet. In some cases, additional information such as combustibility test results will be available from chemical manufacturers. However as noted before, many times a manufacturer MSDS may be lacking sufficient data regarding the combustibility of the material in dust or powder form. Therefore additional testing may be necessary to determine this information.

Electrical Considerations

Areas that require a special electrical equipment classification due to the presence (or potential presence) of dubitable dust need to be identified during a facility hazard analysis. There are several published sources of guidelines and/or regulations regarding special electrical equipment classification. These include: The OSHA Electrical standard (29 CFR Part 1910
Subpart S), NFPA 70, the National Electrical Code®, and NFPA 499, Recommended Practice for the Classification of Combustible Dusts and of Hazardous (classified) Locations for Electrical Installations in Chemical Process Areas.

Several of these guidelines identify three different groups of combustible dusts, (Metal, Carbonaceous and Other) and the different safety considerations that are needed for each. For example Metal dusts are considered electrically conductive; therefore special care needs to be taken to ensure that no electrical current can pass through layers of the dusts causing short circuits and arcs, which could then lead to an ignition. Additionally, in certain industrial settings, other high-energy ignition sources such as welding arcs may be present and need to be accounted for.

Potential For Dust Accumulation

The exact amount of dust accumulation necessary for an explosion to occur can vary greatly. As discussed earlier variables such as particle size, methods of dispersion, ventilation system models, air currents, physical barriers and volume of the area where the airborne dust exists can all vary in each different type of dust. With the site-specific data at hand, potential areas of concern can be identified. And the hazard analysis can then be tailored to the specific circumstances in each area and the full range of variables affecting the hazard.

Even seemingly small amounts of accumulated dust can cause catastrophic damage. The CSB estimated, for example, that the explosion that devastated a pharmaceutical plant in 2003 and killed six employees was caused by dust accumulations mainly under 0.25 inches deep. The NFPA warns that more than 1/32 of an inch of dust over 5 percent of a room’s surface area presents a significant explosion hazard.

Many different locations throughout a facility can be a potential starting point for a conflagration. An area where dust is concentrated is an obvious place to start. In Dust Collectors for example, a combustible mixture of diffused dust and air can be found whenever the Collector is operating. Additionally, locations where dust can settle whether occupied, or concealed spaces (such as in ceiling rafters, the tops of shelving, etc). When conducting the Hazard Analysis, careful consideration needs to be given to all possible scenarios in which any previously identified settle dust can be dispersed into the air, either though normal operations, or potential failure modes.

Precautionary Measures

After hazards have been assessed and hazardous locations are identified, one or more of the following prevention, protection and/or mitigation methods may be applied.

Dust Control

Controlling the amount of dust generated, where it is generated, and the dispersion of it throughout the facility, is key to reducing the likelihood of an explosion from occurring. The following steps should be taken in this regard:

* Minimize the amount of dust that escapes from processing equipment and ventilation systems.
* Install a Dust Collection System and monitor it closely to ensure it is operating properly.
* Where possible, install materials (Surfaces) that collect dust poorly and facilitate easy cleaning.
* Inspect and note all hidden or concealed spaces where dust accumulation might occur.
* Maintain a set schedule for cleaning all dust prone areas, and follow it closely.
* Use cleaning methods that do not themselves generate dust clouds when ignition sources are present.
* Locate Relief Valves away from dust hazard zones.
* Maintain a comprehensive dust control program, with hazard dust inspections, testing, housekeeping, and control initiatives.

In several of the cases highlighted earlier, the initial explosion spread by means of ductwork that connected various equipment (usually the Dust Collection System, and/or different parts of the ventilation system) throughout the plant. It is therefore vital that these ductwork systems be fitted with isolation values and inspected regularly to remove excess sitting dust accumulations.

Additionally, certain dust generating operations (such as the use of abrasives, blasting, grinding, or buffing) fall under OSHA  (or similar governmental agencies) ventilation requirements.

Ignition Control

Along with Dust Control, controlling all possible ignition sources also plays a major role in any comprehensive Dust Control Program. Along with Electrical Considerations, there are many other areas that merit attention with regard to ignition potential. Here are several key recommendations for controlling possible Dust Ignition sources.

* Proper Installation, Classification, Operation, and Maintenance of all Electrical Equipment and Wiring (Class II wiring methods and equipment such as “dust ignition-proof” and “dust-tight” should be employed)
* Employ adequate Static Electricity control methods such as Grounding Wires/Rods, etc.
* Limit Smoking, Open Flames, and Sparks in work area.
* Limit or isolate sources of mechanical sparks and friction
* Separate foreign materials that may ignite combustibles from process materials.
* Limit contact between heated surfaces and heating system from combustible dusts.
* Install spark arrestors/spark traps in all dust collector ductwork.

Further resources including US regulation, guidelines, and recommendations can be found in the following sources:

* NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids
* OSHA’s Powered Industrial Trucks standard (29 CFR 1910.178).

Damage Control

Despite the best efforts of all parties involved, incidents may still occur. It is therefore, the wise course of action is to prepare for the worst, and implement a strategy that will reduce the severity of such an incident should it occur. The following is a list of recommended steps to take to minimize the impact of a Dust Explosion:

* Separate, and Segregate the Hazard to the extent possible. Place distance between the hazard and the work area, and isolate the hazard with barriers where possible.
* Install deflagration venting.
* Install pressure relief valves on applicable equipment.
* Employ Spark/Ember detection systems, and extinguishing equipment.
* To the extent possible, install explosion protection system, including sprinkler systems, and other assorted specialized suppression techniques.

Proper Employee & Management Training

Even with all of the aforementioned precautions, without a workforce, both employees and management, that have been properly educated about the dangers of Dust Explosions, and safety procedures to reduce the likelihood of their occurrence, and control, and limit the damage should they occur, there still remains high degree of probability for a Dust Explosion occurring.


Workers that are trained in preventing, and proper incident response techniques are integral to the safe operation of any facility. They are the people closest to the hazard, if these ones are trained to recognize and prevent these types of occurrences from taking place, they can accomplish much in this regard. These ones should also be encouraged to feel free to report unsafe working conditions, or areas where there could be an improvement in safety standards. Therefore all employees, whether they are working directly in hazard areas or not, should be adequately trained in safe work practices applicable to their job tasks, as well as on the overall plant programs for dust control and ignition source control. Periodic refresher courses should also be arranged to keep these safety issues fresh in their minds, and up to date with any possible changes to the hazard conditions themselves.


A qualified team of managers should be responsible for conducting a facility analysis (or for having one done by qualified outside persons) prior to the introduction of a hazard and for developing a prevention and protection scheme tailored to their operation. Supervisors and managers should be aware of and support the plant dust and ignition control programs. Their training should include identifying how they can encourage the reporting of unsafe practices and facilitate abatement actions.


The dangers of Dust Explosion are quite real; they have caused great amounts of damage to property, and have cost many lives. The importance of implementing a comprehensive dust control program, including hazard analysis, implementation of proven dust control and ignition control techniques, damage mitigation, and employee and management training cannot be overstated.

View this video report by the CSB

About the Author

| Dominick DalSanto is an Author & Environmental Technologies Expert, specializing in Dust Collection Systems. With nearly a decade of hands-on working experience in the industry, Dominick’s knowledge of the industry goes beyond a mere classroom education. He is currently serving as Online Marketing Director & Content Manager at Baghouse.com. His articles have been published not only on Baghouse.com , but also on other industry related blogs and sites. In his spare time, Dominick writes about travel and life abroad for various travel sites and blogs.


ABRASION, FLEX: Fabric wear in a creased area caused by excessive bending, usually associated with cage contact used in baghouse filtration.

ABRASION RESISTANCE: Ability of a fiber or fabric to withstand surface wear.

ABSOLUTE: A degree of filtration that guarantees 100% removal of suspended solids over a specified size found in the filtrate.

ABSOLUTE PRESSURE: The pressure above an absolute vacuum. One atmosphere (14.7 psi) greater than gauge pressure. Symbolized as psia when the pressure is in psi units.

ABSORPTION: The taking in, incorporation or reception of gases, liquids, light or heat. Penetration of one substance into the inner structure of another, using filling the void of the matrix. The process of movement of a drug from the site of application into extracellular compartment of the body.

ACTIVATED CARBON: Charcoal activated by heating to 1472-1652ºF a material of high adsorptive gases, vapors, organics, etc. Has a large internal surface area. Removes dissolved color, odor and taste from liquids or gases. Commonly used in the pharmaceutical industry to remove organic contaminants.

ACTIVATED SLUDGE: Biologically active floc from aeration and settling sewage and/or organic matter.

ADSORPTION: The adhesion of a substance to the surface of a solid or liquid. Adsorption is often used to extract pollutants by causing them to be attached to such adsorbents as activated carbon or silica gel.

AEROBIC BACTERIA: Organisms requiring oxygen to live.

AEROSOL: A dispersion of small liquid or solid particles suspended in air, gas or vapor.

AIR FLOW: Measure of the amount of air that flows through a filter, a variable of the degree of contamination, differential pressure, total porosity and filter area. Commonly expressed in either cubic feet/minute/square foot or liters/minute/square centimeter at a given pressure.

AIR STANDARD: Dry air at 70 degrees F and 29.92” mercury pressure.

AIR-TO-CLOTH (A/C) RATIO: The ratio of gas volume (acfm) to effective cloth area (sq. ft.). In SI units A/C = m3/m2.

AMBIENT: Refers to common environmental conditions in which experiment is conducted.

AFFLUENT: Fluid entering the filter or filter system. Commonly described as influent, it is the opposite of effluent.

AGGLOMERATION, PARTICLE Multiple particles joining or clustering together by surface tension to form large particles, usually held by moisture, static charge or particle architecture.

ALKALINITY: The capacity of water to neutralize acids, a property imparted by the water’s content of carbonates, bicarbonates, hydroxides and occasionally borates, silicates and phosphates. It is expressed in milligrams per liter of equivalent calcium carbonate.

ANAEROBIC: Organism capable of growing without the presence of oxygen.

ANGSTROM: A unit of length 1010 meter used to express wave lengths. Used in measurements of RO filtration in the ionic range.

ANTISTATIC: A condition inherent in or applied to a material usually fabric or plastic, which results in a significant reduction in or the absence of electrical charges. (an electrical resistivity of ~10-10ohm/square or higher.

AQUEOUS: Similar to or resembling water. Referring to solution made in water.

ARIZONA ROAD DUST: Standardized test dusts for both liquid and air classified from natural Arizona dust generally referred to an A.C. Fine and A.C. Course Dust. Both dust materials also carry an ISO designation and have a standardized size distribution of particles.

ASHRAE: American Society of Heating, Refrigerating, and Air Conditioning Engineers.

ASYMMETRIC MEMBRANE: A membrane in which the pore size and structure are not the same from one side of the membrane to the other. These membranes are usually considered directional because of difference in flow characteristics depending on which side of the membrane faces the feed stream.

ASME: American Society of Mechanical Engineers. Published code, which governs the design of pressure housings.

ASSAY: Analytical procedure to determine purity or concentration of a specific substance in a mixture.

AUGMENTATION: In fabric air filtration, the imposition of an electrical field to the collecting surface and.or subjecting the incoming particulate matter to a charging process.

AUTOCLAVE: A chamber for sterilizing with saturated steam filters or equipment by using constant high temperature and pressure.


BACKPRESSURE: A backward surge of pressure from downstream to upstream of the filter. Can be the result of closing a valve or air entrapped in a liquid system.

BACKWASH: Reversal of a fluid flow through the filtration media to remove solids from the filter. To clean or regenerate a filter.

BACTERIA: Free living simple celled, microscopic organisms having a cell wall, lacking a defined nucleus, shape and round, rod-like, spiral or filamentous.

BACTERIAL CHALLENGE: Testing the bacterial retention of a filter.

BAGHOUSE: An air filtration structure utilizing fabric filter bags for the purpose of removing solid particulate from the gas stream.

BAG LIFE: Time a bag filter performs effectively.

BAR: Unit of pressure. 1 bar = 14.5 psi.

BARREN LIQUOR: Liquor for cake washing, which contains little to no valuable liquor; as barren cyanide solution in gold cake slimes washing.

BASKET: Element of a basket strainer. Normally uses a screen as a medium for removal of course bulk solids.

BELT FILTER PRESS: Akin to a rotary drum and belt filter is an automatic pressure filter, where sludge is compressed on an endless rotating belt, dewatering and providing for very dry cake for discharge.

BETA RATIO: Measurement of filter retention efficiency. Ratio of particles exposed to a filter, as a feed stream to the particles down stream (filtrate).

BIAXIALLY STRETCHED MEMBRANE: A microporous membrane from either polypropylene or PTFE that has been stretched in both the MD and CD direction in a manner to form pores of a controlled size and possessing a narrow pore size distribution.

BIOBURDEN: The load or level of microorganisms in a substance to be filtered.

BIOHAZARD: Biological refuse, possibly pathogenic in nature.

BIOSAFETY: Biological safety or non-toxicity of a substance to a living organism. For filters used in health care applications.

BIPOLAR: Have two (opposing) poles, (+) and (-) as applied to ionic charges or particles.

BROWNIAN MOTION: The continuous zigzag motion of suspended minuscule particles. The motion is caused by impact of the molecules in the fluid upon the particles.

BLINDING: Blockage by dust, fume or liquid not being discharged by the cleaning mechanism, results in a reduced gas or liquid flow of increased pressure drop across the filter media.

BLOWDOWN: The use of pressure to remove liquids and/or solids from a vessel.

BREAKTHROUGH: Used to describe the passing of solids through the cake build up of a filter medium. Also called breakpoint.

BRIDGING: Material or particulate blockage across an opening, often of a pore or filter medium.

BUBBLE POINT PRESSURE: A test to determine the maximum pore size openings of a filter. The differential gas pressure in which a wetting liquid (e.g. water) is pushed out of the largest pores and a steady stream of gas bubbles are emitted from a wetted filter under specific test conditions. A filter integrity test with specified, validated pressure values for specific pore-size and type filters.

BURST PRESSURE: The pressure causing rupture. The inside-out differential pressure that causes outward pressure on the structural of a filter medium, filter or housing.


CAKE (FILTER): Solids deposited on the filter media. In many cases the cake may serve as its own filter medium.

CAKE RELEASE: Ability of a medium to allow clean separation of the cake from the medium.

CALENDERING: A manufacturing process where woven and/or nonwoven fabrics are pressed between heavy rollers compressing the fibers. The process reduces the filter medium void volume, pore size rating, flow-rate and dirt-hold capacity of the medium.

CANDLE FILTER: A reusable filter consisting of a tube made from ceramics or metal. Flow is from the outside-in with particulate accumulating on the outside of the candle. The candle can be cleaned by various means, including back-pulsing, heat, chemicals etc.

CAPACITY: Volume of product which a housing will accommodate expressed in gallons or similar units. Also, amount which will filter at a given efficiency and flow rate, expressed in gallons per minute or similar units.

CAPSULES: Disposable devices which have an integrated filter and housing, including inlet and outlet.

CARTRIDGE: Filter devise and medium used in a housing to perform the function of coalescing, filtration or separating. Also referred to as an element.

CATHODE: Negative pole or electrode of an electrolytic system.

CAUSTIC: A class or name given to a class or group of chemicals, usually soda or sodium hydroxide.

CD: Refers to the “cross-machine” manufacturing direction of filtration roll stock.

CELLULOSE: (1) fibers used to manufacturer wetlaid paper (2) used as a filter aid in highly refined alpha cellulose form or as the slightly more unbleached form.

CENTER CORE or TUBE: Material formed into a cylinder shape for structural purposes to permit a cartridge to retain its original physical form.

CENTER PIPE or ROD: Component of a housing which is used as a mount for cartridges, typically through the center core.

CENTRIFUGATION: Separating two substances of differing densities by high speed spinning to create centrifugal force. Generally used to separate suspended particles from liquid.

CHROMATOGRAPHY: Separation of substances in a mixture based on their affinity for certain solvents and solid surfaces.

CLARIFICATION: Clearing a liquid by filtration, by the addition of agents to precipitate solids, or by other means.

CLARIFIER: An apparatus for the removal of settleable solids from a fluid by gravity.

CHARGE POLARITY: A particle, fiber or other material carrying an electrostatic charge.

CLARIFIER: A processing unit using flocculation processes to separate solids from liquid often in a non-turbulent zone where heavy solids settle out of solution. Often used for wastewater.

CLARITY: Amount of contaminate left in a filtered liquid.

CLASS 100 ENVIRONMENT: A room environment maintained by air conditioning and filtration so that fewer than 100 particles of size 1 μm or larger are found in a cubic foot of air.

CLASSIFICATION: Condition in which larger particle settle out below the finer ones. Also referred to as stratification. May also be referred to as the action to sort out particles by various groups or to other established criteria.

CLEANABILITY: The ability of a filter element to withstand repeated cleanings, while maintaining adequate dirt capacity.

CLEAN PRESSURE DROP: Differential pressure (drop) across measured in pounds per square inch at rated flow on new elements with clean product.

COAGULATION: In water and wastewater treatment, the destabilization and initial aggregation of colloidal and finely divided suspended matter by the addition of a floc-forming chemical or by biological processes.

COALESCER: Mechanical device which unites discrete droplets of one phase prior to being separated from a second phase. Can only be accomplished when both phases are immiscible.

COALESCING: Action of uniting small droplets of one liquid preparatory to its being separated from another liquid.

COATING: Immersion of filter media in a solution to provide the fibers with a coating that will lubricate and thereby reduce self-abrasion.

COLD STERILIZATION: Removal of all bacteria by filtration through a sterilizing grade 0.2μm absolute filter.

COLLAPSE PRESSURE: The outside-in differential pressure that causes the structure of a filter medium failure of a filter element.

COLLECTION EFFICIENCY: Percentage of contaminate collected.

COLLOID: Very small, insoluble non-diffusible solid or liquid gelatinous particles that remain suspension in a surrounding liquid. Solids usually on the order of 0.2 μm or less.

COMPATIBILITY: Relation to the non-reactivity of filter materials with a substance to be filtered.

COMPRESSABILITY: Degree of physical change in filter cake particles when subjected to normal pressures.

COMPRESSION BAND: Stainless steel band sewn into the end of a bag to provide a surface to clamp against in the baghouse.

CONCENTRATOR: Removes some of the water from a sample to concentrate substances dissolved or suspended in it; usually used to concentrate solutions of biological macromolecules, (proteins & nucleic acids).

CONTAMINATE: Unwanted foreign matter in a fluid which is accumulated from various sources such as systems dirt, residue from moving parts, atmospheric solids.

CONTINUOUS PHASE: Basic product flowing through a filter or filter separator, which continues on through the system after being subjected to solids and/or other liquid separation.

CORE: Commonly refers to a perforated tube, which serves as the center of a filter cartridge (element).

CORE YARN: Used in filtration with fiberglass or synthetic yarn. Spun or texturized yarns are twisted around a filament (core) yarn, adding yarn strength and stability.

CRITICAL OPERATING PRESSURE: Pressure above which filtration or separation equipment may produce reduced efficiency or fails to function properly.

CROSSFLOW (TANGENTIAL FLOW) FILTRATION: A filtration system in which the feed stream flows across the filter media and exits as a retentate stream. The retentate stream is recycled to merge into the feed stream, while a portion of it passes through the filter media, resulting in concentration of the feed stream.

CYCLONE: A conical-shaped vessel for separating mixed sized particulates from the gas stream. The vessel has a tangential entry at the largest diameter allowing the larger particles to drop out and be removed from the bottom of the cone while smaller particulate exits overhead with the majority of the gas stream.


DE: Diatomaceous earth. A filter aid from diatomite’s.

DALTON: Measure of molecular mass.

DI WATER: De-ionized water; water processed through an ion exchange process by passing through a mixed resin bed to remove positive and negative ions. The purity of water is measured by its electric resistance.

DEAD END FILTRATION: Feed stream flows in one direction only, perpendicular to and through the filter medium to emerge as product or filtrate.

DEHYDRATION: Removal of water or hydrocarbon in vapor from an air or gas; also water fro0m another immiscible liquid. Differs from entrainment removal in that the dew point of a gas stream will be lowered by vapor removal. A form of purification.

DENIER: The weight in grams of 9,000 meters of a fiber.

DENSITY: Mass/unit volume, usually expressed in g/cc, lb./cu. ft or lb./gal.

DEPTH FILTRATION: A process that entraps contaminants both within the matrix and on the surface of the filter media.

DESALINATION: Production of fresh (potable) water from sea water, salt or brackish water by one of several processes, e.g. distillation, flash distillation, electrodialysis or reverse osmosis if salt content is not too huge.

DEWATERING: A physical process that removes sufficient water from sludge so that its physical form is changed from essentially that of a fluid to that of a slurry or damp solid.

DESICCANT: Drying agent or medium used in dehydration of air or gas or liquids. Examples: silica gel, activated alumina, molecular sieve etc.

DIALYSIS: The diffusion of solute molecules through a semi-permeable membrane.

DIATOMACEOUS EARTH FILTRATION (D.E.): A filtration method that uses a medium consisting of microscopic shells of single celled plants known as diatoms.

DIATOMITE: Skeletal remains of tiny aquatic plants that lived in the ocean and inland seas millions of years ago.

DIFFERENTIAL PRESSURE – Delta (Δ) P: The change in pressure or the pressure drop across a component or device located within the air stream; the difference between static pressure measured at the inlet and outlet of a component device.

DIFFUSION: In liquid cake washing, removing the original liquor around the individual particles by mixing with the wash liquor. In air, the particle at a size within one or two orders of magnitude of the gas-flow molecules, moves in Brownian motion and collides with a fiber or other filter media material during its random path of travel.

DIFFUSION TEST: A test to determine the integrity of a filter. The test is based upon the transition from diffusional flow to bulk flow of a gas, though a wetted filter.

DIFFUSIONAL INTERCEPTION: In gas filtration, at low gas flow velocities, tiny particles are subject to Brownian motion, enabling them to move out of the gas streamlines and become intercepted by the filter.

DIFFUSIONAL FLOW TEST: To determine the integrity of a filter. The test is based on the measurement of the diffusional flow of a gas through a wetted filter. Either the gas or the downstream liquid, displaced by the gas, may be measured. The transition from diffusional flow to bulk flow (bubble point) can be determined.

DIGESTED SLUDGE: Sludge or thickened mixture of water with sewage solids in which the organic matter has been decomposed by anaerobic bacteria.

DIRECT INTERCEPTION: Gas filtration: particles larger than the pores are removed by direct contact with the filter surface. Some particles smaller than pores can be removed as well depending on the proportion to their size hitting the surface.

DIRT (HOLDING) CAPACITY: Amount of dirt or debris retained by a filter in grams per unit area of the filter medium.

DISCONTINUOUS PHASE: Separated phase or product from the continuous phase. Example: water maybe the discontinuous phase when separated from hydrocarbon, air or gas.

DISPERSION: Operation which results in solid or liquid particles entering into suspension in a fluid. Also applies to a two phase system in which one phase, known as the disperse phase, is distributed throughout the other, known as the continuous phase.

DISPOSABLE FILTERS: Those filters not cleaned or reused. Referred to as one-time or single-use filters.

DISOLVED SOLIDS: Any solid material that will dissolve in a liquid that such as sugar in water.

DISTILLATION: Process of vaporizing a liquid and collecting the vapor, which is then usually condensed into a liquid.

DMF: Drug Master File. A written document that explains the formulation of an active ingredient, referenced in an Investigational New Drug (IND), New Drug Application (NDA), or Amendment to New Drug Application (ANDA) from a company.

DOP: Dioctyl phthalate, a plasticizer that can be aerosolized to particles of extremely uniform size. Retention of DOP aerosol is used as standard procedure for pore size rating of air filters. Typically, 99.97% DOP retention indicates HEPA efficiency.

DOWNSTREAM SIDE OF FILTER: The filtrate or product stream side of the filter. Fluid and/or solids that have passed through the filter.

DRY HEAT STERILIZATION: Sterilization at or above 356ºF using a convection or forced air oven without moisture; may concurrently de-pyrogenate if adequate time and elevated temperature are employed.

DRY SCRUBBER: A chemical reaction chamber that neutralizes acids in a gas stream. Two system types: the spray dryer system injects a slurry, whereas dry sorbent injection systems use a dry powder.

DUPLEX FILTER: Assembly of two filters with a valve for selection of either or both filters.

DUROMTER (SHORE): Measure of hardness. Must be defined as being either A or D scale.

DUST COLLECTION: A term usually associated with an assembly of large pleated elements that collect air-borne particles where large volumes of air flow is found e.g. granaries, cement factories, abrasive production and other manufacturing facilities.

DYNE: The amount of force that cause a mass of one gram to alter its speed by one centimeter per second for each second during which the force acts.


E. coli: Escherichia coli is the most prevalent bacteria in the gastrointestinal tract of humans and animals. It occurs in solids and water as a result of fecal contamination.

END CAP: The end of many types of filter cartridges.

ETO STERILIZATION: Chemical sterilization using ethylene oxide at an elevated temperature of 1500 º F and high relative humidity to facilitate permeation of the ethylene oxide into the material being sterilized.

EFFECTIVE FILTRATION AREA: The portion of filter that fluid flows through during the filtration process.

EFFICIENCY: Degree to which a filter device will perform in removing solids and/or liquids.

EFFLUENT: The fluid which has passed through a filter (filtrate or product stream); outflow from other treatment such as wastewater treatment plants.

ELECTRETS: A dielectric body in which a state of electric polarization is established. An imposed electric field on heated polyolefin following the drawing stage to form a charged fiber or yarn with electrostatic like properties. These properties may decay or by contamination by solvents and materials.

ELECTROCHEMICAL: A process by which electricity is used to effect chemical reaction. The inter-conversion of chemical and electrical energy.

ELECRODIALYSIS: Dialysis (small molecules separated from larger molecules in the same solution/mixture) accelerated by an electromotive force applied to electrodes adjacent to the separating membranes.

ELECTROLYTE: Substances which will conduct an electrical current, either in molten state or in a solution e.g. NaCl in water.

ELECTROPHORESIS: The separation of charged molecules (such as proteins) based on their mobility in an electrical field.

ELECTROSTATICS: Electrical charges on particles and/or fibers in a filter medium create attractive and/or repulsive forces between particles and the fiber/medium. As a direct result, for many types of particles, strong attractive forces produce the intimacy needed to agglomerate even the fines.

ELECTROSTATIC PRECIPITATOR: A type of particulate filtration control that attracts charged particles to oppositely charged surfaces to collect airborne particulates. The particles are charged by ionizing the air with an electric field. The charged particles are then collected by a strong electric field generated between oppositely-charged electrodes.

ELEMENT: Typically a filter, such as a cartridge, pleated or non-pleated.

END CAPS: Components adhered to a filter element with adhesive or other means to contain the filter medium in a form designed for the element.

END POINT: Final objective or, in petroleum distillation, temperature at which the distillation ceases.

ENDOTOXIN: A toxic substance produced by bacteria, but which is released into the surrounding medium only upon the death or disintegration of the bacteria.

ENTRAINED WATER: Discrete water droplets carried by a continuous liquid or gas phase when water is immiscible with the liquid.

EPA: Environment Protection Agency regulates environmental monitoring. Establishes and enforces guidelines.

EXTRACTABLES: Chemicals leached from a filter during a filtration process; usually tested for by soaking in water under controlled conditions; may be removed by pre-flushing with suitable liquid.


FERMENTATION: Enzymatically controlled breakdown of an energy rich compound as a sugar to produce ethyl alcohol, carbon dioxide, and energy, by the action of yeasts which carry the necessary enzymes. Bacterial fermentations also occur.

FEED: Materials to be filtered. Also referred to as concentrate, influent, intake, liquor, mud, prefilt, pulp, slime or sludge.

FIBER: Any particle with length greater than or equal to 0.5 micron and at least five times greater than its diameter, leaving substantially parallel sides.

FIBER METAL FELT: A nonwoven media consisting of extremely fine metal fibers (2-20 micron in diameter) which are compressed and sintered. Used to filter molten polymers in the manufacture of fibers and films and hydraulic fluids for use in aerospace filters.

FIBER MIGRATION: Downstream migration of fibers from a filter medium.

FILL: Yarns that run in the filling or cross-machine direction of a woven fabric.

FILTER: (Noun) A specialized piece of equipment for carrying out filtration, consisting of the filter medium and suitable holder for constraining and supporting the filter in the fluid path.

FILTER: (Verb) Passing a fluid containing particles through a filter medium wherein particles are removed the fluid.

FILTER AID: Small size particle substance of low specific gravity which remains in suspension when mixed with a liquid to be filtered. Increases filtration efficiency of a feed when deposited on a septum by forming a porous cake.

FILTER CAKE: The accumulation of particulate or solids on a surface. Can also mean a pre-coat for filtering.

FILTER EFFICIENCY: A measurement of how well a filter retains particles. The percentage retention of particles of a specific size by a filter.

FILTER LIFE: Measure of a filter’s useful service life based on the amount of standard contaminate required to cause differential pressure to increase to an unacceptable level, typically 2-4 times it initial differential pressure or 50-80% drop in initial flow or the downstream measure of unacceptable particulate.

FILTER MEDIA MIGRATION: Problem caused by a filter medium constructed of a non-continuous or fibrous matrix. Portions of the filter change structure causing fibers to migrate downstream.

FILTER MEDIUM: Permeable material that removes particles from fluid being filtered.

FILTER PAPER: A permeable web of randomly oriented fibers, generally cellulose or glass fiber formed from water draining from a suspension fed in a paper making process. Also, a presentation at a filtration conference.

FILTER PAPER: A permeable web of randomly oriented fibers, generally cellulose or glass fiber formed from water draining from a suspension fed in a paper making process. Also, a presentation at a filtration conference.

FILTER PRESS: Mechanical process where wet solids are compressed between two or multiple surfaces in the same equipment forcing water out of the solids, simultaneously compacting and drying the cake.

FILTRATE: The end product of the filtration process. The liquid exiting the filtrate outlet.

FILTRATION: Removal of particles from a fluid by passing the fluid through a permeable material.

FILTRATION RATE: The volume of liquid that passes through a given area of filter in a specific time.

FINES: Portion of a powder like material composed of particles smaller then the size specified.

FLOW DECAY: Decrease in flow rate caused by filter plugging or clogging.

FLOCCULATION: Growing together of minute size particles to form larger ones, called floc’s.

FLOW DECAY TEST: Determines flow rate and throughput of a filter type or combination of filters on a specific liquid, usually by using small area filters, to determine the sizing of a filter system.

FLOW FATIGUE RESISTANCE: The ability of a filter element to resist structural failure of the filter medium due to flexing caused by cyclic differential pressure.

FLOW RATE: The speed at which a liquid flows and is measured in gallons or liters per minute. Flow rate of a liquid can be affected by the liquids’ viscosity, differential pressure, temperature and type of filter used. Measuring air diffusion.

FLOW RESISTANCE: Resistance offered by a filter medium to fluid flow.

FLUE GAS DESULFERIZATION: The operation of removing sulfur oxides from exhaust gas streams of a boiler or industrial process. Usually a wet scrubber operation.

FLUID: Includes liquids, air or gas as a general term.

FLUX: Measure of the amount of fluid that flows through a filter, a variable of time, the degree of contamination, differential pressure, total porosity, viscosity and filter area.

FLY ASH: The air borne combustion residue from burning coal or other fuels.

FORWARD FLOW TEST: An integrity test measuring air diffusion at a low pressure (approximately 5 psi). Similar to a pressure hold test.

FRAZIER PERMEOMETER: Porosity testing device. The normal measurement is air flow in CFM passed through one square foot of fabric at 0.5 inch differential water pressure.

FULLERS EARTH: Medium used in some elements, usually a blend of attapulgus and montmorillonite clay. A finely divided hydrous aluminum silicate. Often a filter aid.


GAUGE PRESSURE: Pressure measured by a pressure gauge. Pressure above ambient pressure when the pressure is used in psi units.

GELATINOUS: Used to describe suspended solids that are slimy and deformable, causing rapid filter plugging.

GMP’s: Good Manufacturing Practices. Food and Drug Administration regulations governing the manufacture of drugs. Sometimes referred to as CGMP’s.

GRADIENT DENSITY: A stratified cross-section. Used to describe a filter medium where larger pores are at the upstream side of the medium with finer pores downstream. The configuration increases dirt-holding capacity and improved filter life. The medium may be inverted when a surface filter effect is desired resulting in lower differential pressure across the medium than if the medium has a single density throughout..

GRAVITY FILTER: Filter in which the driving force for filtration is provided solely by the head of liquor above the filter medium.

GRAVITY SEPARATION: Separation of immiscible phases resulting from a difference in specific gravity by coalescing.

GURLEY TEST: Measure of time required to expel 100 cc’s of air though a filter medium placed within an apparatus that can be fitted with a selection of office sizes and weights. Historically used for paper products and more recently for microporous membranes. (ASTM: D-726).


HVAC FILTERS: Air filters used in heating and air conditioning locales.

HEAVY METAL: Metallic elements having a high density (> 5g/cm5 ), toxic for the most part.

HEPA: An air filter or medium, which captures 99.97% when challenged with DOP 0.3 micron particles under certain laboratory controlled conditions.

HIMA: Health Industry Manufacturer’s Association defines and sets standards governing the validation of filters for sterilizing liquids. . . a trade association, whose membership includes pharmaceutical manufacturers and filter manufacturers.

HOLDING CAPACITY: See Dirt Holding Capacity above.

HOUSING: A metal or plastic tank or tube with an inlet and outlet containing a filter (s), allowing for the flow of a fluid and contaminate through the filter, while containing the process.

HYDROPHILIC: Water accepting or wetting.

HYDROPHOBIC: A membrane or other material which repels and cannot be wetted by aqueous and other high surface tension fluids. When pre-wetted with low surface tension fluid, such as alcohol, the filter will then wet with water.

HYDROMETER: An instrument used to measure the density of a liquid.


IMMISCIBLE: Incapable of being mixed; insoluble.

INERTIAL IMPACTION: Gas filtration: Retention mechanism. Inertial Collection. As the gas stream lines bed in the vicinity of the filter, the carried particles continue in a straight line due to their inertia and impact the filter. Effective primarily for particles about 0.3μm and larger, at high gas velocities and low filter porosity.

IMPERMEABLE: Material that does not permit fluids to pass through.

IMPINGEMENT: Process of removing liquid or solid contaminate from a stream of compressed air or gas by causing the flow to impinge on a baffle plate at high velocity.

INFLUENT: Fluid entering the filter.

IN-LINE FILTER: A filter assembly in which the inlet, outlet & filter element are in line.

INERT: Chemical inactivity; unable to move; totally un-reactive.

INTERIAL IMPACTION: The particle, due to its inertia and usually in stream-line flow, deviates out off the air/gas stream striking a fiber or other material of a filter medium.

INLET PRESSURE: Pressure entering the inlet side of the filter. Also called upstream pressure or line pressure.

INORGANIC MATTER: Chemical substances of mineral origin, not containing carbon to carbon bonding. Generally structured through ionic bonding.

IN-SITU Sterilization or integrity testing of a filter in the system rather than as an ancillary operation such as in autoclave or bubble point stand.

INTEGRITY TEST: Used to predict the functional performance of a filter. The valid use of this test requires that it be correlated to standardized bacterial or particle retention test. Examples: Bubble Point Test, Diffusion Test, Forward Flow Test, Pressure Hold Test.

INTERFACIAL TENSION: Measure of miscibility or solubility of the continuous and discontinuous phases. Increases as miscibility or solubility decreases.

INTERSTICES: Spaces or openings in a filtration medium. Also referred to as pores or voids.

INTERSTITAL: Pertaining to the openings in a filtration medium.

IN-VITRO: In isolation from living organisms in an experimental artificial environment e.g. cells in tissue culture; experiments carried out in test tubes.

IN-VIVO: Within the living organism.

ION(S): An atom or group of atoms that carries a positive or negative electrical charge as a result of having lost or gained one or more of the electrons.

ION EXCHANGE COLUMNS: Vessels filled with ion exchange resin (anion, cation, or mixed) for producing conditioned or DI Water. Also, type of column used for Ion Exchange Chromatography.

ISOTROPIC (SYMMETRIC) MEMBRANE: Membrane in which the pore openings are the same diameter throughout the thickness and on both sides of the membrane. Non-directional, their flow characteristics are independent of which side faces the feed stream.


K or k, the symbol for kilo (1,000).

Kilogram (kg = 1,000g). Kilometer (km = 1,000m). In computers, 1K = 1024 bits of information. 64K memory = 65,536 bits.

KNIFE EDGE SEAL: Narrow, pointed ridge on the sealing surface of an end cap, center seal or cartridges adaptor which provides a seal by biting into the cartridge gasket.


L-TYPE FILTER: Cartridge filter in which the inlet and outlet port axis are at right angles and the filter elements axis is parallel to either port axis.

LAMINAR FLOW: Term synonymous with streamline flow and viscous flow. A flow regime which the flow characteristics are governed mainly by the viscosity of the fluid.

LEAF: Any flat filter element that has or supports the filter septum.

LEAF FILTER: A filter housing and device consisting of a plurality of leaves, often place in a vertical position.

LINE PRESSURE: Inlet pressure, upstream pressure. The pressure in the supply line.

LIQUOR: Material to be filtered. Also referred to as concentrate, feed influent, intake mud, prefilt, slime or sludge.

LIVE STEAM STERILIZATION: Sterilization by flowing saturated steam through a vented vessel or system, usually at 257ºF and 20 psi (Can be performed up to 284ºF and 35 psi.).

LOADED: A filter element that has collected a sufficient quantity of insoluble contaminates such that it can no longer pass rated flow without excessive differential pressure.

LOCK UP: Device that will lock either a column, elements or the body of a housing in place.

LOG REDUCTION VALUE: The logarithm to the base of 10 of the ratio of organisms in the feed to the organisms in the filtrate. Example: Log 1o [10 9/101.7] = 7.3. Also used as a ratio of in/out bioburden in other sterilization methods such as autoclaving.

LOW INTERFACIAL TENSION: Where the interfacial tension of one liquid over the other liquid would be less than 25 dynes/cm at 70 degrees F.

LOX CLEANING: Process of cleaning for liquid oxygen service.

LVM: Low volatile material.


MANOMETER: A U-shaped tube filled with a specific liquid. The difference in height between the liquid in each leg of the tube gives directly the difference in pressure on each leg of the tube. Used to monitor differential pressure.

MARTIN’S DIAMETER: Statistical diameter used in particle size analysis; the mean length of the line, parallel to the microscope traverse, diving each particle into two equal diameters.

MASS DISTRIBUTION: Relative frequency distribution of mass within a particle size distribution. Sometimes presented as cumulative percentage undersize.

MASS TRANSFER RATE: Measurement of the movement of matter as a function of atoms etc.

MD: Refers to the “machine-direction” when manufacturing filtration roll stock.

MEAN EFFICIENCY RATING: The measurement of the average efficiency of a filter medium using the Multi-Pass Test where the average filtration (BETA) ration equals 2.0.

MEAN FLOW PORE MEASUREMENT: It is calculated as the diameter of the pore of a membrane partially voided of liquid such that air flow of the partially wetted membrane is equal to 1/2 the dry air flow. (Theoretical diameter of the mean pore).

MEDIA: Material through which fluid passes in the process of filtration and retains particles. Also, nutrients containing solutions in which cells or microorganisms are grown.

MEDIA MIGRATION: Migration of materials making up the filter medium may cause contamination of the filtrate.

MEDIUM: Principle component of a filter element. Material of controlled or uncontrolled pore size or mass through which a fluid stream is passed to remove foreign particles held in suspension or to repel droplets in the case of coalesced water.

MELTBLOWN: A nonwoven manufacturing process for filtration media, where a molten polymer is extruded out of an orifice with high-velocity air to create fine fibers. The fibers can create roll stock or be spray-spun onto porous tubes to create a finished filter.

MEMBRANE: Media through which a liquid is passed; usually associated with an extremely fine or tight type of filtration. Highly engineered thin polymeric film containing a narrow distribution of pores. Used as the separation mechanism in R/O, Electrodialysis (ED), Ultrafiltration (UF), Nanofiltration (NF) & Microfiltration (MF).

MEMBRANE FILTER: Continuous matrix with fine pores of defined size or a film allowing for the diffusion of a fluid through its structure; sometimes referred to as a dense film in the case where no pores are present.

MERV (Minimum Efficiency Reporting Values) Rating: A system for rating air filters according to their average particle size efficiency on a scale from 1-16 with 16 being the highest capture efficiency for average particles in the 0.3 to 1.0 micron range. The rating is derived from a test method developed by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE).

MESH: A term referring to a woven filtration medium, typically wire cloth or monofilament woven fabric.

MESH COUNT: Number of openings or fractions of openings in a lineal inch of wire cloth or monofilament woven fabric.

MICRON (μm): The common unit of measurement in the filtration industry is the micron or micrometer. One micron equals forty millionths of an inch (0.00004) or expressed differently 25.4 microns equals 0.001 inch.

MICRON RATING: The smallest size of particles a filter can remove.

MICROFILTRATION (MF): Used for clarification, sterilization, to detect or analyze bacteria and other organisms and particulate matter. Separation of particles ranging from 0.1μm to 10μm.

MICROMETER (m): Micron, 1/1,000,000 of a meter. 60gm is approximately the diameter of a human hair.

MICROPOROUS MEMBRANE: Thin polymeric films (e.g. 0.001 to 0.005” thick) often with millions or pores per square inch, aligned as a torturous path, allowing for the passage of a fluid to remove solids. Often used for sterilizing filtration and other fine filtration purposes. Considered a surface filter medium.

MIGRATION: Contaminate released downstream of a filter.

MIL: One thousandth of an inch.

MINIMUM BUBBLE POINT PRESSURE: It is a diffusional flow pressure just before the onset of bulk flow. Minimum critical bubble point pressure: a filter specification derived from diffusional flow, bubble point curves for many filters.

MISCIBLE: Capable of being dissolved. Opposite of immiscible.

MIXED CELLULOSE ESTERS: Synthetic materials derived from naturally occurring cellulose. Materials used in the manufacture of membrane filters. Mixed cellulose esters membranes are used in a wide variety of applications, such as bacteria concentration in water analysis and air sampling.

MOLARITY: The term used to indicate the concentration of dissolved substance in a given solution. The measurement is in moles of dissolved substance per liter of solution.

MOLECULAR WEIGHT: Sum of the atomic weights of all atoms in a molecule. Also, Mole or Mol weight.

MOLECULAR SIEVE: Zeolite, natural or synthetic or similar materials where atoms are arranged in a crystal lattice in such as way that there are a large number of small cavities interconnected by smaller openings or pores of precise uniform size. Used as a drying agent or for absorptive applications.

MONOFILAMENT: Single, large continuous filament of a synthetic yarn. Similar to fishing line in cross-section.

MONOFILAMENT WOVEN FABRIC: Woven fabric from monofilament yarns used as a screen or surface filter. Often used in sifting, belting, medical filters etc. Most common yarns are from polyester, polypropylene and nylon.

MUD: Material to be filtered.

MULLENS BURST TEST: A formal measurement where test specimen (filtration medium) sees a force, which cause it to burst.

MULTIFILAMENT: A number of unbroken continuous fiber stands that run parallel to form a yarn. Typically used to manufacture a woven or knit fabric.

MULTI-PASS: A test system designed to be representative of a typical hydraulic or lubricating circuit. Fresh contaminate is introduced in slurry form into a test reservoir, mixed with the fluid in the reservoir and pumped through the test filter; contaminate not captured by the filter is returned to the reservoir for another pass (or more) though the filter.


NEEDLEFELT: A nonwoven fabric where staple fibers are entangled together through a manufacturing process using barbed needles, providing for a heavy weight filter fabric, which can filter air-borne particles for use in baghouses and suspended particles in liquids from lighter weight needlefelt fabrics for use liquid bag filtration.

NFR: Non-fiber releasing. A filter or medium, which will not release fibers into the filtrate.

NIOSH: Develops basic methodology for analytical test procedures. National Institute of Occupational Safety and Health.

NOMIMAL: An arbitrary term used to describe the degree of filtration and generally not comparable or interchangeable between products or manufacturers. A user should always ask for a copy the test procedure used and results from the manufacturer’s lab notebook to understand each rating.

NOMINAL FILTRATION RATING: An arbitrary micrometer value indicated by the filter manufacturer. The same ratings from two manufacturers are often different and rarely can be compared.

NONPOLAR: Compound or element that’s electron capacity is satisfied. A neutral condition that will remain un-reactive. Not polar. See Polar.

NONWOVEN: A filter fabric that is formed of natural or synthetic fibers that are randomly oriented in filtration media. Typically, held together with a binder or fibers are entangled.

NYLON: When used as a membrane it is hydrophilic. A thermoplastic, polymeric material that has high mechanical strength & compatibility with different chemicals.


OPEN AREA: Pore area of a filter medium, often expressed as a percentage of the total area.

OSMOSIS: Diffusion of a liquid through a semi-permeable membrane from a dilute solution into a more concentrated solution, thus tending to equalize the concentration of each side of the membrane.

OUTLET PRESSURE: Downstream pressure. Pressure exiting the outlet side of the filter.


PACKED BED: Discrete particles such as sand, gravel, anthracite, fabricated rings or saddles, assembled in a confined space as a filtration medium for liquids and gases.

PAPER: Filter medium used on filter elements. A general term applied to resin bonded cellulose.

PARALLEL FILTRATION: Branching a filtration setup. Two assemblies of the same pore size are in parallel, to increase flow rate or simplify filter changes.

PARTICLE: Unit of material structure; a mass having observable length, width, thickness, size and shape.

PARTICLE COUNT: Practice of counting particles of solid matter in groups based on relative size contained in a certain area.

PARTICLE SIZE DISTRIBUTION: The size range and quantity of particles which are measurable in a dry or liquid sample. Used to determine the appropriate filter media for a specific process.

PARTICULATE: Any solid or liquid material in the atmosphere.

PARTICULATE UNLOADING: The process whereby a filter, particularly, a depth filter, can become blocked with particulate matter and subsequently release part of this matter downstream.

PERISTALTIC PUMP: A pump functioning by alternate pinching and release of tubing which drives the fluid forward in a pulsing action. The pump is noninvasive. Only the inner wall of the tubing contacts the fluid.

PERLITE: Material similar to volcanic glass with a concentrated shell structure. Used as a filter aid.

PERMEABILITY: A measure of fabric porosity or openness, expressed in cubic feet of air per minute per square foot of fabric at a 0.5” water column pressure differential in air or by specified conditions for liquid.

PERMEABLE: Material that has openings through which a liquid or gas will pass in filtering.

PERMEATE: The fluid which passes through a membrane, a term usually used with ultrafiltration or R/O.

pH: Measure of a substance’s acidity or alkalinity from 1-14 with 7 being neutral. Measure of hydrogen ion concentration.

PHASE: May be continuous, as the basic product flowing through a housing or discontinuous as the material to be removed from the basic product. Both are distinct and separate.

PHENOLIC RESIN: Synthetic thermosetting resins obtained by the concentration of phenol and substituted phenols with aldehydes. Used as a binder in cellulose and glass fibers for form filter media.

PLASTISOL: Suspension of a thermosetting plastic which can be molded into a desired shape. Used as a combination end cap and gasket on an element.

PLEAT SUPPORT/SPACERS: Used to prevent the collapse of pleats in a pleated paper or membrane cartridge when under the action of differential pressure.

PLEATER: Automated equipment that folds a filter medium roll stock vertically for subsequent incorporation into a filter element. Provides for greater media surface area in a limited space. There are many types of pleaters, including pusher bar, rotary etc.

PLUGGING: Filtered out particles filling the openings (pores) in a medium to the extent of shutting down the flow of a fluid. Also referred to as blinding or blocking.

POINT-OF-USE FILTERS: Filters located immediately prior to where a clean effluent is required in a process.

POLAR: Compound or element capable of receiving or giving electrons. See Non-Polar.

POLYELECTROLYTE: Synthetic, water-soluble, linear polymers characterized by the presence of ionizing groups distributed along a molecular length. Used to promote flocculation.

POLYPROPYLENE: A thermoplastic polymeric material, resistant to a broad range of chemicals. When used as a membrane, polypropylene is hydrophobic.

POLYSULFONE: Has excellent flow rates, high mechanical strength, resistant to a broad range of temperatures, can be sterilized and is hydrophilic. Commonly used membrane material, but is not resistant to many organic solvents.

PORE: Opening in a medium. Also referred to as interstices. Size and shape of the openings are controlled by the manufacturer of the filter medium.

PORE SIZE: Diameter of pore in a filter medium.

PORE SIZE-ABSOLUTE RATING: The rated pore size of a filter. Particles equal or larger than the rated pore size are retained with 100% efficiency.

PORE SIZE-NOMINAL RATING: The pore size at which a particle of defined size will be retained with efficiency below 100% (typically 90-98%). Rating methods vary widely between manufacturers.

PORE SIZE DISTRIBUTION: Exclusive to permeable medium: describes the number of pores in various groups of sizes in a way similar to that discussed under particle size distribution.

POROSITY: The percent of open areas per unit volume of a medium whether it be a filter cake or roll stock, such as a paper, membrane, woven textile or nonwoven fabric.

POROUS METAL: Finely ground chards of sintered metal, which serve as a filter medium. Often used in high-pressure and/or temperature applications.

POROUS PLASTIC: Filter media made from finely ground plastic powder. When filled into a mold and heated, the points of powder contact to fuse, while allowing the spaces between the particles to remain open for fluid flow.

POTABLE: Drinkable (water).

PPM: Parts per million. A unit of concentration.

PRECOAT: A deposit of material (usually inert), such as a filter aid on a septum prior to beginning filtration.

PREFILT: Material to be filtered. Also referred to as concentrate, feed, influent, intake, liquor, mud, pulp slime or sludge.

PREFILTER: Filter for removing gross size contaminate before the product stream enters a finer rated filter.

PRESSURE, ABSOLUTE: Gauge pressure plus 14.7 psi.

PRESSURE, PROOF: A test pressure above normal operating pressure to assure that the part will withstand the norm without damage or leakage.

PRESSURE DIFFERENTIAL: Difference in pressure between two points.

PRESSURE DROP (ΔP): Difference in pressure between two points.

PRESSURE DROP, CLEAN: Differential pressure (drop) across a housing measured in psi at rated flow on new elements with clean product.

PRETREATMENT: Changing the properties of a liquid-solid mixture by physical or chemical means to improve its filterability.

PRIMARY SLUDGE: That portion of the raw wastewater solids contained in the raw plant influent, which is directly captured and removed in the primary sedimentation process.

PRODUCT: Continuous phase, either liquid or gas, which is being process through filtration or separation equipment.

PROTEIN BINDING: Adsorption of a protein to a surface such as a cellulose nitrate or nylon membrane due to various types of interactions between protein molecules and the surface.

PSEUDOMONAS DIMINUTA: Bacteria used in sterility testing. One of the smallest bacteria, 0.3μm in diameter, used to challenge a sterilizing grade filter during validation testing.

PSI: Pounds per square inch.

PSIA: Pounds per square inch absolute.

PSID: Pounds per square inch differential.

PSIG: Pounds per square inch Gauge.

PULSING BACKFLOW: Intermittent, on-off blowing with or without cake discharge.

PTFE: Highly durable and resistant to range of temperatures and chemicals. PTFE is hydrophobic. Polytetrafluoroethylene is better known as Teflon.

PULSE-JET BAGHOUSE: A baghouse using short intermittent bursts of compressed air to clean dust/particulate from filter bags that are supported by cages.

PYROGEN: Any substance that produces a fever. Pyrogens are lipoplysaccharides which are a by-product of the metabolism of certain bacteria.


QUISCENT: State of rest of a body. In entrainment separation, the body would be a liquid. Also used to describe a sump containing evacuated liquids or solids.


RATED FLOW: Normal operating flow rate at which a product is passed through a housing; flow rate which a housing and medium are designed to accommodate.

RAW SLUDGE: Untreated sewage sludge.

REAGENT: Solution or substance used in analytical testing purposes or procedures.

RECOVERY: Ability of a filter to recover bacteria (or other defined particles) from a solution.

REENTRAINMENT: Process of rendering particles airborne again after they have been once deposited from an air stream.

RED MUD: Filter cake in sodium aluminate filtration.

RETENTION: Ability of a filter to retain particles suspended in a gas or liquid. A percentage of particles originally present.

REGENRATED CELLULOSE: Those rayon’s in which the cellulose raw material is changed physically, but not chemically. Viscose, cuprammonium and nitrocellulose rayon’s are of this type.

REPACK: Cylindrical element used in a single-stage filter separator for removal of one liquid and course solids from another liquid. May be used as a single element, a combination of wafers, or a cluster type. Medium may be excelsior, glass fiber or steel wool; or a combination of glass fibers and metal mesh.

RESIDUE: Solids deposited upon the filter medium during filtration in sufficient thickness to be removed in sizeable pieces. Sometimes referred to as a cake or discharge solids.

RESIDUAL DIRT CAPACITY: The dirt capacity remaining in a service loaded filter element after use, but before cleaning, measured under the same conditions as the dirt capacity of a new filter element.

RETENTION: Ability of a filter medium to retain particles of a given size.

REUSABLE FILTERS: Filters that are washed or cleaned of contaminate, either in-situ or off-line, for additional uses.

REVERSE OSMOSIS (RO): A water treatment method whereby water is forced through a semi-permeable membrane which filters out impurities, such as salt (NaCl) from seawater.

REYNOLDS NUMBER: Any of several dimensionless quantities, of form LVp/N in theory of fluid motion.

ROTARY DRUM: Continuous liquid filter equipment consisting of a large rotating drum covered with a filter cloth and cake, which collects incoming particulate from a contaminated bath or flow. A washing and/or discharge device (scrapper) ultimately cleans the contaminate from the cake as the drum rotates.


SAND FILTER: Filter composed of layers of sand, graded in particle size, so that the courser particles face the unfiltered flow.

SAYBOLT SECONDS UNIVERSAL: Units of viscosity as measured by observing the time in seconds required for 60 ml. of a fluid to drain through a tubular orifice 0.483 inches long by 0.0695 inches in diameter at stated conditions of temperature and pressure.

SCAVENGER: A filter or element in the bottom of a filter that recovers the liquid heel that remains in a filter tank at the end of a cycle.

SCREEN: Often a flat filter from wire cloth mesh or monofilament fabric filter used to classify particles of a certain size to “to screen out particles”. Can also cover an element for protection; also used as a basic material for a separator element of basket in a basket strainer.

SCREW BASE: Element base which is threaded to mount by screwing the cartridge onto the cartridge adaptor.

SCRIM: An open weave textile or nonwoven fabric used as a strengthening member incorporated within the matrix of a filtration medium to provide increased tensile or tear properties.

SCRUBBER: Any device in which a contaminant, solid or gaseous, is removed from a gas stream by impacting it with liquid droplets.

SEDIMENTATION: Action of settling of suspended solids.

SEEDING: The application of a relatively course dust, dry dust to an air filter bag before filtration startup to provide an initial filter cake for immediate high efficiency and to protect the bag from blinding.

SELF-CLEANING: Filtering device designed to clean itself by the use of a blowdown or backwash action.

SEPARATION: Action of separating solids or liquids from themselves (e.g. by size, viscosity, density, charge etc,) or liquids or gases from fluids.

SEPTUM: Any permeable material that physically supports the filter media, usually for filter aids.

SERIAL FILTRATION: Filtration through two or more filters of decreasing pore size, one after the other, to increase throughput, filtration efficiency, or to protect the final filter.

SERVICE LIFE: Length of time an element operates before reaching an unacceptable benchmark e.g. maximum allowable pressure drop.

SHAKER BAGHOUSE: A baghouse using flexible bags applying a cleaning action accomplished by shaking the bags from the top.

SHELL: Outer wall of a housing. Also referred to as the body of a housing.

SIEVE: A screen filter with straight-though capillary pores and identical dimension.

SHIFTING: A separation process which separates solid particles by size, through rapid movement of a screen medium, such as a vibrating action. Used in flour, wheat, abrasive, sugar and aggregate sizing.

SILICIAGEL: regenerated adsorbent, consisting of amorphous silica. Used as a drying agent or dehumidifying agent for gases, liquids or oils.

SILTING INDEX: Measurement of the tendency of a fluid to cause silting in close tolerance devices as a result of fine particles and gelatinous materials being suspended in the fluid; measured by a silting index apparatus.

SINGLE-PASS: This test system is designed to be representative of a typical filter circuit. Fresh contaminates are introduced in a slurry form into the test reservoir, mixed with the fluid and pumped through the test filter. The test is run in such a manner to produce one pass of all fluid and contaminate.

SINTERING: A process of heating materials (e.g. metal or ceramic) to elevated temperature causing mating surfaces to fuse as one.

SIZE DISTRIBUTION: Proportion of particles of each size (by mass, number or volume) in a powder or suspension.

SLIMES: Slurry of fine particles; materials to be filtered. Also referred to as concentrate, feed influent, intake, liquor, mud, prefilt, pulp or sludge.

SLUDGE: A thickened slurry. Municipal sewage is often dewatered to produce a concentrate for disposal. Also, residues and deposits occasionally formed by oils, after extended use.

SLURRY: Thin, watery suspension; a material to be filtered or dewatered.

SOLIDS: Mass or matter contained in a stream, considered an undesirable discontinuous phase and should be removed.

SOLUTE: Liquid which has passed through a filter. Also referred to as discharge liquor, effluent, filtrate, mother liquor or strong liquor.

SOLUTION: Single phase combination of liquid and non-liquid substances of two or more liquids.

SOP: A written document that explains how to complete a specific production-orient-ed task. Standard Operating Procedure.

SPARGING: Steam, compressed air, or gas is forced into a liquid through perforations or nozzles in a pipe as part of fermentation.

SPECIFIC GRAVITY: Ratio of weight of a volume of a substance to the weight of an equal volume of another substance typically compared to water with a specific gravity (Sp.G.) of 1.0.

SPECTROPHOTOMETER: Laboratory instrument which measures the wave length and intensity of a light emitted by most chemical agents. When a sample is atomized and burned, the presence of most elements may be determined by their spectra (wave length) emission down to the parts per million range.

SPIN-ON-FILTER: Cartridge filter in which the filter body and the filter element have been constructed and an integral disposable item. Filter change is rapid by spinning off the used unit from a fixed filter head and rapidly adding on the replacement unit.

SPUNBOND: A nonwoven fabric formed by producing, laying and self-bonding a web of filament material in one continuous set of processing steps. Usually made of polyester or polyolefin’s.

SS: Abbreviation for stainless steel.

SPUN YARN: A continuous yarn for weaving of textiles consisting of staple fibers.

STACKED DISC FILTER: A filter housing and device consisting of a plurality of leaves place in a horizontal position. Used widely in food and beverage filtration.

STAPLE FIBER: A short length of natural or synthetic fiber typically from 1-4 inches in length, used to manufacture yarns for weaving and various types of nonwoven fabrics, such as needlefelt, airlaid and hydroentangled for use in filtration media.

STERILIZING FILTER: A non-fiber releasing filter which produces an effluent in which no microorganisms are present. Typically microporous membranes at or below 0.2 micron pore size rating have this capability.

STOKE’S DIAMETER: Diameter of a sphere having the same density and the same free falling speed as a particle when moving in a homogeneous fluid of the same density and viscosity, under conditions of laminar flow.

STOKE’S LAW: A physical law, which approximates the viscosity of a particle falling under the action of gravity through a fluid. Friction drag controls the rate of fall at a constant velocity known as the terminal or free-setting velocity.

STRATIFICATION: Condition in which the larger particles settle out below the finer ones. Also referred to as classification.

STREAM: Term sometimes used and synonymous with the words product, liquid, air, gas, fluid etc. in speaking of any matter processed by filtration or separation equipment.

STRING WOUND: An inexpensive filter consisting of textile roving (yarn) wrapped around a center core to form a filter medium and filter cartridge (element).

STRONG LIQUOR: Liquid which has passed though the filter. Also referred to as discharge liquid, effluent, filtrate, mother liquor or solute.

SUBSTRATE: Substance or basic material as a filter media or to which a deposit is added.

SULPA (Super ULPA): An air filter or medium, which captures 99.9999% when challenged with DOP 0.3 micron particles under certain laboratory control conditions.

SUMP: Collecting area of a housing located downstream typically from a coalescer element, in which coalesced droplets of the dispersed phase are deposited; also called water leg. May also be used to collect solids in applications where gross solids are present in a stream; also called mud sump.

SUPERNATANT: Liquid above settled solids.

SURFACE ENERGY: Molecular reaction; the breaking away of ion particles from a mass.

SURFACE FILTER: Filter medium that retains particles wholly on the surface and not in the depth of the cross-section of a filter medium e.g. plain weave wire cloth and monofilament woven fabrics or membrane.

SURFACE FILTRATION: A process that traps contaminants larger than the pore size on the top surface of the filter, usually a membrane, wire cloth or monofilament fabric. Contaminants smaller than the specified pore size may pass through the medium or may be captured within the medium by some other mechanism, such as surface affinity, triboelectric potential or other means, which prevents particle penetration.

SURFACE TENSION: Tendency of the surface of a liquid to contract to the smallest area possible under existing circumstances.

SURFACTANT: A soluble compound that reduces the surface tension of a liquid, or reduces interfacial tension between two liquids or between a liquid and a solid.

SURGE: Peak system pressure measured as a function of restricting or blocking fluid flow.

SUSPENDED SOLIDS: Solids that do not dissolve in liquid; those that remain suspended and can be removed by filtration.

SUSPENSION: Any liquid containing un-dissolved solids.

SWING BOLT: Type of housing head closure which reduces service time. Opposite of thru-blot flange where studs are used, such as with ASA type flanges.


TANGENTIAL (CROSSFLOW) FILTRATION: See Crossflow (Tangential) Filtration.

TARE: A deduction of weight, allowing for the weight of a container or medium; the initial weight of a filter.

TENSILE STRENGTH: Resistance to breaking. The amount of force required to break a membrane by stretching.

TENSIOMETER: Device used to read the surface tension of a liquid or to reading the interfacial tension between two immiscible liquids.

TERMINAL PRESSURE: Pressure drop across the unit at the time system is shut down or when the maximum allowable pressure drop is reached.

TERMINAL VELOCITY: Steady velocity achieved by a falling particle when gravitational forces are balanced by viscous forces.

THREE-STAGE FILTER SEPARATORS: Liquid prefilter coalescer separators containing three kinds or types of replaceable elements.

THROUGHPUT: The amount of solution which will pass through a filter prior to plugging.

TIPPING PAN FILTER: Process industry equipment which collects particulate from a liquid stream on a screen over a vacuum forming a dewatered cake and discharging the accumulation by tipping the collection screens.

TORTUOUS PATH: Crooked, twisting or winding path which tends to trap or stop solid particles, commonly referenced in relationship to the flow pattern and makeup of a filter medium.

TRAMP OIL: Free oil contained in emulsion type machine tool coolants. May be from machine leakage and from breakdown of the emulsifying agents in the cutting oil.

TRIBOELECTRIC SERIES (POTENTIAL/CHARGE): An inherent natural or induced positive or negative polarity charge that many materials possess. Fibers or a filtration medium with a triboelectric potential will capture charged and potentially neutral particles, assuming both positive and negative properties on the surface of the material. Triboelectric properties only work in air filtration assuming relative humidity below 90 %.

TRIBOELECTRICITY: The charge of electricity that is generated by friction such as rubbing.

THROUGHPUT: The amount of solution which will pass through a filter before clogging.

TOTAL DISSOLVED SOLIDS: Is the portion of the total solids in the sample that passes through the filter and is indicated by the increase in weight in the vessel after the filtrate has been dried at 356ºF.

TOTAL SOLIDS / SUSPENDED SOLIDS: The material residue left in the vessel after evaporation of a sample and its drying in an oven at 217-221ºF. The increase in weight over that of the empty vessel represents the total solids. Used in analyzing drinking water.

TORTUOUSITY: An continuous path that can be traced from a point on the upstream side of a filter to a point on the downstream side through a twisting pore pathway, traveled by the liquid or gas during filtration.

TRUE DENSITY: Mass of a particle divided by its volume, pores etc. being excluded from the volume calculation.

TURBIDIMETER: An instrument for measurement of turbidity, in which a standard suspension usually is used for reference.

TURBIDITY: Any insoluble particle that imparts opacity to a liquid. A reference point to the total amount of solids contained in a liquid.

TRUBULANT FLOW: Flow regime in which the flow characteristics are governed mainly by the inertia of the fluid. Turbulent flow in ducts is associated with high Reynolds Number (Re). It also gives rise to high drag.


U.S.P.: United States Pharmacopeia/National Formulary: The “Bible” of pharmaceutical manufacturer and test protocol for filtration media using Edition/Title XXI as a basis for evaluation.

ULPA: An air filter or medium, which captures 99.999% when challenged with DOP 0.3 micron particles under certain laboratory controlled conditions.

ULTRAFILTRATION (UF): A separation method operating at 50-200 psi in crossflow filtration mode. Efficiency is approximately 90%. Used to separate large molecules according to their molecular weight.

UNIFORMITY COEFFICIENT: Separation factor applied to the sizing of the sand used in water filtration plants.

UNIFORMITY OF FEED: Uniformity of the mixture of the solids in the feed liquid.

UNLOADING: The release of contaminate downstream that was initially captured by the filter medium.

UPSTREAM SIDE: The feed side of the filter. Fluid that has not yet entered the filter.

USEFUL LIFE: Determined when contamination causes a filter or system to have an adverse (lower) flow rate, low efficiency or high differential pressure, providing for an inefficient operation.


VACUUM: Depression of pressure below atmospheric pressure.

VALIDATION: Demonstration that a process or product does what it is supposed to do by challenging the system and providing complete documentation.

VAN DER WALS FORCES: The relatively weak attractive forces that are operative between neutral atoms and molecules that arise because of the electric polarization induced in each of the particles by the presence of other particles.

VELOCITY: Time rate of motion in a given direction.

VELOCITY HEAD: Velocity pressure or kinetic pressure.

VENT FILTERS: Filters that allow the passage of air while restricting the flow of fluid; typically containing low micron rated microporous membrane media. Common in medical devices and pharmaceutical tanks.

VESSEL: A container, usually used as alternatively to the word housing e.g. filter vessel.

VIBRATORY SIFTER: Process equipment that separates solids by size on a metal screen through a vibrating action. Larger particles remain on the screen as fines fall through, sometimes to one or more higher mesh count screens for further separation of particle size.

VISCOSITY: Degree of fluidity. Resistance to flow as a function of force, or gradual yielding of force. For a given filter and differential pressure, flow rate will decrease as viscosity increases.

VISCOSITY INDEX: Numerical value assigned to a fluid which indicates to what degree the fluid changes in viscosity with change in temperature.

VOID VOLUME: The amount of open or empty area across the full spectrum of a material or substance. A term often used to describe the amount of porosity in a filter medium.

VOLUMETRIC FLOW RATE: Fluid flow expressed as a volume flowing per unit of time (cc.3/sec., ft3/min., etc.)


WARP: The yarns that run lengthwise or in the machine direction in woven goods.

WASTE: Material removed, rejected or otherwise lost in various manufacturing processes.

WASTEWATER: Effluent water carried downstream from a filtration or separation process.

WATER BREAKTHROUGH TEST (WBT): An integrity test for hydrophobic filters or filter medium in which the resistance to water flow is overcome by a specific pressure such that water will flow through a specific pore size of the filter or filter medium. Also called Water Intrusion Test.

WATER FLOW/FLUX: Measure of the amount of water that flows through a filter, a variable of time, the degree of contamination, differential pressure, total porosity and filter area.

WATERHEAD: The height of water in a column. Provides a defined amount of pressure on a surface.

WATER INTRUSION TEST: See Water Breakthrough Test above.

WATER LEG: Area of housing for collection of water.

WEIGHT OF SOLIDS: Measure of solid particulate matter contained in a fluid sample.

WEIR: (1) A diversion dam (2) A device that has a crest and some side containment of know geometric shape, such as a V, trapezoid or rectangle and is used to measure flow of a liquid.

WET CAST MEMBRANE: A process to manufacture microporous membranes, typically from thermoplastic materials, solvents and non-solvents in the formation of a microporous membrane. 75 to 80% of all microporous membranes manufactured use this process.

WET STRENGTH: Strength of a medium when saturated with water.

WETTING AGENT: A surfactant added to a filter medium to insure complete intrusion (wetting) by a high surface tension fluid such as water.

WIRE CLOTH: Woven fabric from metal wire used as a screen, surface filter or media support. Often used in sifting, belting, hydraulic filtration etc. Most common wire used is stainless steel.

WOUND TUBES: Also referred to as string wound filters.


YOKE: End cap used to hold a cartridge in place.


ZETA POTENTIAL: The potential across the diffuse layer of ions surrounding a charged colloidal particle.

About the Author

| Dominick DalSanto is an Author & Environmental Technologies Expert, specializing in Dust Collection Systems. With nearly a decade of hands-on working experience in the industry, Dominick’s knowledge of the industry goes beyond a mere classroom education. He is currently serving as Online Marketing Director & Content Manager at Baghouse.com. His articles have been published not only on Baghouse.com , but also on other industry related blogs and sites. In his spare time, Dominick writes about travel and life abroad for various travel sites and blogs.