Purchasing and maintenance people commonly call Baghouse.com requesting assistance to figure out what kind of filter bags they need for their top load baghouse. Often, they do not know which measurements they need to identify the filter size and configuration required to quote replacement filters for their baghouse.
This short article will explain the key features of the most common baghouse filter style: the top load, snap band style baghouse filter.
Description of a Top Load Baghouse
Top load baghouses are known for their efficiency, reliability and ease of maintenance, making them a popular choice for many industrial applications.
A top load baghouse has a housing with the filter bags arranged so that they hang vertically. The dirty air ductwork usually connects to the baghouse hopper, allowing the dirty air to enter from the bottom of the filters.
The dust particles are captured on the outer surface of the filter bags (falling to the hopper), while the clean air passes through the filters and then travels up through the bag and out the top of the housing.
In top load pulse jet baghouses, the filters are installed into the tubesheet from above. The tubesheet is a metal plate in the baghouse where the filters are installed, separating the clean air from the dirty air. On a pulse jet baghouse, the tubesheet is near the top ¼ of the baghouse and it is a smooth steel sheet with uniform holes into which each filter is installed.
To allow access to the filters, smaller units will generally have removable doors or hatches on the top of the unit surrounded by railings while larger units will have a walk-in clean air plenum which allows entry to the baghouse through a door in the side.
Snap Band Filters for Top Load Baghouses
Cut view of the ring (snap band) and the layer of sown fabric around it that allows for a tight fit against the tube sheet
The snap band is a metal ring sewn into the top of the bag and covered with fabric. The snap band is used to secure and seal the filter bags to the tube sheet.
The pressure from the band pushing against the sides of the hole (when aligned correctly) forms an airtight seal.
To install a snap band bag, the bag is inserted into the round tube sheet hole. The snap band is deformable, allowing the user to manipulate its shape and insert the band into the tubesheet hole. When released, the snap band “snaps” into place, tightly locking the filter into the hole.
Once installed, a metal wire cage is inserted into the cage to hold it open during operation. Then the blowpipes are installed above the filters.
Why Are Snap Band Filters So Popular?
Snap bands ensure a tight fit at the connection points between the filter bag and the tubesheet, preventing air or dust from bypassing the filter bag. Additionally, they are easy to install and more reliable than older methods that require the use of hold down hardware or clamps to secure the bags into the tubesheet.
Snap Band Filter Bag & Cage Terminology
The relationship between snap band size, bag diameter, and cage diameter has to be carefully calculated, since each component plays a crucial role in ensuring the effective installation, sealing, and performance of filter bags.
Here is a brief explanation of each one of these dimensions:
● Tubesheet Hole size/Snap Band Size
An accurate measurement of the tubesheet hole will ensure that the snap band of the filter will have a tight fit
The tube sheet hole size refers to the diameter of the opening in the tubesheet where the filter bag’s snap band is inserted. This size must match the snap band diameter to ensure a tight fit and prevent leakage or bypass of dust-laden air. Snap bands are sized down to 1/32” so this measurement should be taken with calipers if possible. Always measure across the center of the hole in a straight line from one edge to the opposite edge.
● Bag Diameter
The bag diameter refers to the width of the filter bag when laying flat
The bag diameter refers to the width of the filter bag body (NOT the snap band at the top of the bag, which is considered a separate piece). Since we cannot accurately measure the true diameter of the bag outside of a proper jig in the factory, we usually ask customers to measure the flat width instead, which is the width of the bag when laid flat. The bag diameter is almost always slightly smaller than the snap band/tubesheet hole size.
● Cage Diameter
The cage diameter is the outside diameter (OD) of the cage body measured at the center of the cage
The cage diameter is the outside diameter (OD) of the cage body that goes inside the filter bag. The cage diameter will always be slightly smaller than the bag diameter, usually ¼” smaller. If the bags fit too tightly to the cage, the cages will be very difficult to install and remove, and the bags will not flex properly when pulsed and the cleaning power will be reduced, thus contributing to poor operation of the system.
So, when looking to get replacement filters and/or cages for your pulse jet baghouse, you need to gather the following information: (1) tubesheet hole diameter, (2) the bag flat width and length and (3) the cage body outside diameter (OD) and length.
If you are unable to shut the unit down to take the hole measurement, we can still quote you the bags with only the bag flat width and length. Then, once you place an order, we can confirm the exact tube sheet hole size by having you send us a used bag to test fit at our facility. Alternatively, we can send you a pre production sample bag to test fit before we release your order to production.
Instructions to Measure Snap Band Filter Bag & Cage Size Step by Step
Common Sizes of Top Load Bags and Cages
With so many different baghouse manufacturers, there is no “standard” size for top load bags. However, there are some common sizes/configurations that are used by multiple OEMs. Common size combinations include:
Small diameter bags: 4” and 5”
● 5” tubesheet hole, 4.5” bag diameter, 4.25” cage diameter
● 5” tubesheet hole, 4.625” bag diameter, 4.5” cage diameter
● 5” tubesheet hole, 4.875” bag diameter, 4.5” cage diameter
Large diameter bags: 6”
● 6” tubesheet hole, 5.875” bag diameter, 5.5” cage diameter
● 6” tubesheet hole, 5.875” bag diameter, 5.625” cage diameter
● 6.2” tubesheet hole, 5.875” bag diameter, 5.5” cage diameter
● 6.25” tubesheet hole, 5.875” bag diameter, 5.5” cage diameter (Most common)
● 6.25” tubesheet hole, 6” bag diameter, 5.875” cage diameter
Measuring Pleated Filters For Top Load Baghouses
Pleated filters can be used in top load baghouses, often as retrofits for units originally designed to take traditional bags and cages. Some units are designed from the factory to use pleated filters. This is most common with small bin vent style units. Would you like to know if pleated filters would be a good option for your baghouse? Contact us to review your application.
Similar to bags and cages, when looking for replacement pleated filters, we will need to know the tube sheet hole size along with the filter diameter and length.
The Dangers of Size Drift
Size drift in top load baghouses can be quite risky to the efficiency of your dust collector. This happens when measurements are taken inaccurately, and over time, the bags end up being a bit too big or too small for the system.
This can lead to various issues, like:
- ● Reduced filtration efficiency
- ● Compromised dust capture
- ● Increased emissions
- ● Potential damage to equipment components
To prevent these problems, it’s important to measure accurately and keep an eye on things to catch any drift early.
Additional Tips When Changing the Filters
Any cages that are bent, rusty, or have shape edges should be discarded and replaced. Filters that are installed onto damaged cages will suffer early filter failure.
- ● Before removing the filters, the blow pipes must be removed to allow access to the tube sheet.
- ● If reusing cages, these must be carefully removed and set aside so as not to damage them before putting new filters on them and inserting them back into the tube sheet.
- ● When reusing existing cages it’s usually best to remove only a section of filters at once, since there is only limited space to stack the cages at the top of the baghouse.
- ● Any cages that are bent, rusty, or have shape edges should be discarded and replaced. Filters that are installed onto damaged cages will suffer early filter failure.
Understanding the dimensions and components of a top load baghouse will help us order the exact replacement pieces, proper installation, sealing, and long filter life.
