Differential pressure measurements provide a reliable metric of baghouse performance. When the differential pressure readings fall too high or too low, it’s a clear indication that it’s time to make adjustments. This article explains how a baghouse works, why monitoring and logging differential pressure is important, and what problems the differential pressure readings can be used to diagnose.

The Way a Baghouse Works

Baghouse filter bags work similarly to window screens, which stop insects from entering a house. Incoming baghouse air passes through the filter media, which captures dust particles on the outside surface of the filter bag. A seasoned bag refers to a surface of accumulated dust (dust cake). The dust cake helps to capture more dust because incoming dust clings to the dust cake. In fact, air filtration through the combination of the dust cake and the filter media provides the highest filtration efficiency. However, there’s a practical limit: a baghouse can’t run efficiently when the dust cake is too heavy. A routine cleaning process is needed to remove the excessive dust cake from the filter bags. This routine cleaning process differs based on the baghouse types.

What is Differential Pressure

Differential pressure (dP) is defined as the pressure drop measured across the tubesheet (the metal plate from which the bags are suspended), from the dirty side of the filter bags to the clean air plenum. For example, with a clean-air side fan or negative pressure baghouse system, the air flow entering the baghouse has a weaker vacuum than the air exiting the baghouse. If the clean-air side fan pulls 10″ w.g. of vacuum pressure, and the dirty air comes into the baghouse at 3.5″ w.g. of vacuum, then the pressure drop across the baghouse is 6.5″ w.g..

Figures below are the typical differential pressure readings while the filter bags are at their different life cycle stages:

• New Filter Bags: 0” to 2″ w.g.
• Seasoned Filter Bags: 2” to 5″ w.g.
• May be Nearing End of Life: > 6″ w.g.

Why Measuring Differential Pressure is Important

Within a baghouse, a number of factors must be monitored to ensure the efficient operation of the dust collection system at all times. Of these, the most important variable is the system differential pressure. This measurement is the key indicator of how the baghouse is operating and the most important factor to consider when diagnosing and troubleshooting issues with the baghouse system. It can be as simple as indicating when it’s time to trigger the routine filter bag cleaning or more extensive service, such as filter bag offline cleaning & reconditioning, or change-out. Continuously monitoring pressure drop can reveal problems early, when they are faster, easier, and cheaper to fix, and helps extend filter bag life. Rapid changes in differential pressure can indicate filtration efficiency problems with the baghouse:

• A sudden drop in differential pressure can indicate that a filter bag leak or rupture has occurred. It can also indicate that structural problems with the baghouse system, such as airlock and conveying system condition, and door seals condition, among other things;
• A sudden increase in differential pressure can indicate that the cleaning system has stopped functioning or a material discharge device has stopped working correctly. It can also indicate that dust particles have been entrained in the filter media’s fibers and are unable to be removed by the dust cleaning cycle (filter media has become blinded).

For More Information

Regular monitoring and logging of baghouse differential pressures is the best way to monitor the performance of a dust collection system. It allows you to take corrective actions sooner and at less expense. If you need help in bringing your baghouse back to health, AoKai Environtec Inc. is always ready to serve. With our Baghouse Inspection & Maintenance service, Aokai can help you ensure that your baghouse is running at maximum efficiency. Contact Aokai for more information about measuring and logging differential pressure to maintain and protect your baghouse’s performance.