Originally published: February 26, 2014
Last updated: August 27, 2026
Before replacing filters, adjusting a cleaning controller, or troubleshooting airflow because of an unusual differential-pressure reading, make sure the reading itself is accurate.
Plugged pressure taps, contaminated sensing lines, moisture, incorrect tubing connections, and faulty gauges or transmitters can all produce misleading DP readings. A false reading can send a maintenance team troubleshooting a problem that doesn’t actually exist.
This second article in our series on baghouse differential pressure will answer that question.
Why Do Dust Collectors Get False DP Readings?
A differential-pressure connection samples the dirty-air side of the collector, and another samples the clean-air side. Tubing carries those pressure signals to a gauge, switch, controller, or transmitter, which calculates the difference between them.
That means the measurement depends on an entire chain: Pressure tap → sensing line → instrument → display/control signal
A problem anywhere in that chain can produce a bad reading. This is especially important because modern DP controllers may do more than display a number. They can use that measurement to start and stop filter cleaning or activate alarms.
First Ask: Does the Reading Make Sense?
One of the easiest ways to spot a measurement problem is to compare the DP reading with what the collector is actually doing.
Suppose your DP suddenly reads extremely high, but: The pickup airflow hasn’t noticeably changed. The cleaning system is working normally and the process hasn’t changed. The filters were recently inspected, and there is no other indication of increased resistance. That doesn’t prove the DP reading is wrong, but it gives you a reason to verify it before making expensive changes.
The opposite applies as well. An unusually low reading shouldn’t automatically be interpreted as exceptionally clean filters.
As Dominick Dal Santo explains: “We’ve been at several plants where Plant Managers were making maintenance decisions around a differential-pressure number that wasn’t accurate. Before you start replacing filters or changing settings, verify that the gauge and sensing lines are actually telling you the truth.”
Check the Pressure Taps and Sensing Lines
Plugged sensing lines are one of the first things we check when a DP reading seems questionable. The dirty-side tap is particularly vulnerable because it is exposed to dust. Moisture can also enter the tubing and interfere with the pressure signal.
Inspect for:
- ⦿ Dust buildup or blockage
- ⦿ Moisture or condensation
- ⦿ Cracked, pinched, disconnected, or deteriorated tubing
- ⦿ Loose fittings
- ⦿ Damaged pressure taps
Also verify that the lines are connected to the correct high (+) and low (-) ports. Reversed connections can produce incorrect or negative readings depending on the instrument.
New automatic gauge-line cleaning devices can help prevent dust, moisture, and debris from clogging differential-pressure sensing lines and causing inaccurate readings. These systems periodically purge the pressure lines, helping keep DP measurements reliable while reducing the need for manual cleaning and troubleshooting. If plugged gauge lines are a recurring problem at your facility, contact us to discuss options for adding an automatic line-cleaning system to your existing dust collectors.
How Can You Verify the Gauge or Transmitter?
If the taps and tubing appear clear, compare the installed instrument with a known-good reference differential-pressure gauge or manometer. If both instruments see the same high- and low-side pressures but give significantly different readings, the installed gauge or transmitter may require calibration, repair, or replacement.
For an electronic transmitter, troubleshooting may also include checking:
- ⦿ Power supply
- ⦿ Wiring and terminal connections
- ⦿ Zero calibration
- ⦿ Pressure range configuration
- ⦿ Analog output, such as a 4–20 mA signal
- ⦿ PLC/BMS scaling where applicable
This is an important addition for modern plants. Sometimes the transmitter itself is measuring correctly while the control system is displaying the wrong value because the signal has been incorrectly scaled or configured.
Could the DP Reading Be Correct After All?
If you verify the instrument and pressure lines and the unusual DP remains, start looking at the collector.
- ⦿ For high DP, investigate filter loading, cleaning-system operation, compressed-air supply, moisture, process changes, airflow, and hopper conditions.
- ⦿ For unexpectedly low DP, inspect for filter damage, missing filters, tubesheet leakage, housing leaks, or reduced airflow.
Use Trends to Catch Bad Readings Earlier
This is one area where electronic monitoring provides a significant advantage. A technician looking at a gauge once per week might see 4.2 in. w.g. and assume everything is normal. A historical trend might reveal that DP instantly jumped from 3.1 to 4.2 at 2:13 Tuesday afternoon and has remained perfectly flat ever since. That behavior deserves investigation.
Modern controllers and remote IoT sensors can track differential pressure continuously and provide alarms when pressure exceeds defined limits or when cleaning fails to bring DP back down. Connected systems can extend that capability with historical trend data, AI analysis and remote visibility.
Don't Troubleshoot the Collector Until You Trust the Measurement
Keep sensing lines and pressure taps part of your preventive maintenance program. Periodically verify instruments, particularly when readings begin behaving differently from the established baseline. For electronic systems, don’t forget the wiring, signal scaling, alarms, and controller configuration.
And when an unexpected reading appears, verify the measurement before making major maintenance decisions. Sometimes a strange differential-pressure reading means you have a filter problem. Sometimes it means you have a $20 piece of tubing telling you that you have a filter problem.
Director of Operations | Dust Collection Specialist | Industrial Filtration Consultant
Dominick DalSanto is an author and environmental technologies expert specializing in dust collection systems. He has nearly a decade of hands-on working experience in the industry. Dominick is the sales director and sales technical advisor for an industrial dust collection equipment manufacturer. Personally took the lead on key projects each year from sales engineer to field advisor to project manager to business relations. Born in San Bernardino County, California, and raised in Chicago, he currently resides in Buenos Aires, Argentina.
