How a baghouse works
A plain guide for engineers, plant managers and buyers. What happens inside a pulse-jet baghouse, and what decides whether it works well.
The short version
A baghouse is a steel housing full of fabric filter bags. Dusty air goes in, passes through the fabric, and leaves clean. The dust collects on the outside of the bags and is knocked off from time to time into a hopper below.
1. The air comes in
Air from the extraction system enters the collector, usually at the hopper or low on the side. The sudden drop in speed lets the heaviest particles fall straight out. A baffle at the inlet spreads the air and stops it blasting directly onto the bags.
2. The bags filter it
Each bag hangs from a steel plate called the tube sheet and is held open by a wire cage. Air passes through the fabric from outside to inside. Dust is caught on the surface and soon forms a thin layer, the dust cake, which does much of the fine filtering itself.
3. Clean air leaves
Clean air rises up inside each bag, through the tube sheet into the clean-air plenum, and on to the fan and stack.
4. A pulse cleans the bags
Over time the cake gets thicker and the resistance rises. A sequencer then fires a diaphragm valve for a fraction of a second. Compressed air shoots down a blowpipe into one row of bags. The shock wave flexes the fabric and the cake breaks off and falls into the hopper. Rows are cleaned one after another, so the baghouse keeps working throughout.
5. The dust is removed
Dust in the hopper leaves through a rotary valve, screw conveyor or straight into a bin or bulk bag, while keeping air from leaking in.
Terms you will hear
| Air-to-cloth ratio | Air volume per square metre of filter, per minute. The main sizing figure. |
| Differential pressure | The pressure drop across the bags. Shows whether cleaning is working. |
| Tube sheet | The plate the bags hang from. It separates dirty and clean air. |
| Can velocity | Upward air speed between the bags. Too high and dust cannot fall. |
| Blinding | Dust packed into the fabric that pulsing cannot remove. |
What decides how well it works
- Enough filter area. The air-to-cloth ratio must suit the dust. Fine, light dust needs more area.
- The right media. Chosen for temperature, moisture and how sticky the dust is.
- Dry, clean compressed air. Wet air makes dust cake stick and blinds bags.
- Good inlet design. Stops abrasion of the bag bottoms and lets dust fall to the hopper.
- Staying above the dew point. Condensation turns dust to mud on the bags.
Baghouse or something else?
Baghouses suit most industrial dust. For fume and fine dry dust in a tight space, a cartridge collector may be better. For coarse dust, a cyclone may be all you need, or a useful first stage. Wet, sticky or explosive processes sometimes call for a wet scrubber. Compare the options.
FAQ
Why is it called a baghouse?
Because it is a house, a steel housing, full of filter bags. Large industrial units can contain hundreds or thousands of bags.
What is pulse-jet cleaning?
A short burst of compressed air fired down into a row of bags to knock off the dust cake. It cleans the bags while the collector keeps running.
What is a good differential pressure for a baghouse?
It depends on the design. What matters most is that it stays steady. A rising trend points to blinding or a cleaning fault, and a sudden drop to a burst bag.
Send us your dust problem
Tell us what you are extracting, roughly how much air, and where the unit will stand. We will come back with a sizing and a quote. A site visit is free in Gauteng.