Two Types of Differential Pressure

This post includes 3 sections:

1. One pressure gauge reading is high but the baghouse works fine
2. One pressure gauge reading is high and indicates baghouse problem
3. Explanation about 2 types of differential pressures

One pressure gauge reading is high but the baghouse works fine

When we were doing an onsite project, the customer mentioned that one of their baghouses had a higher differential pressure, which was around 10” H2O. It seemed too high for a baghouse, but apparently it worked fine.

He led us to the baghouse gauge (as shown in Figure 1). At first, we thought that the differential pressure reading was between the clean-air plenum and dirty-air plenum, so we told him it is an indication to replace the bags, since they might all be dirty and clogged. However, after we accidently checked the hose connection points, we found that the differential pressure reading is actually between the baghouse’s inlet and outlet,  and it is a Flange-To-Flange differential pressure, for which a 10” reading is normal. We explained this to him.

This baghouse was manufactured by Dustex.

Figure 1: Differential Pressure of 10" H2O between Baghouse Inlet and Outlet

One pressure gauge reading is high and indicates baghouse problem

Figure 2: Differential Pressure of 10.5" between Clean Air Plenum and Dirty Air Plenum 

The customer wanted us to check the other baghouses’ gauge readings, and we did see a baghouse with a high reading, which was a little bit higher than 10” H2O, as shown in Figure 2.

This time we checked the hose connection points carefully, and the differential pressure reading above was between the clean-air plenum and dirty-air plenum, so this baghouse did need its bags replaced if the gauge still worked and the hoses were not jammed. We also suggested him to check the clean plenum before replacing bags too.

It took us only a couple of minutes to clear the customer’s confusion about differential pressures, and we offered remedies to the problematic baghouses. He was thankful for our advice.

Explanation about 2 types of differential pressures

Normally, all baghouses are equipped with a differential pressure gauge, but what they measure is different.

A baghouse’s differential pressure is a key parameter indicating how well your baghouse is operating.

Differential pressure is measured between,

1.     Clean plenum and dirty plenum (mainly including pressure drop caused by bag itself, bag outlet with or without a venturi), and

2.     Baghouse inlet and outlet, flange to flange (mainly including pressure drop caused by baghouse inlet, bag itself, bag outlet, baghouse outlet) ,

as illustrated in Figure 3.

The Flange-To-Flange differential pressure is always bigger than that between Clean Plenum and Dirty Plenum.

 Figure 3: Illustration of two types of Differential Pressure