Organised by what you can observe, because that is how the problem presents. Each symptom lists the likely causes in the order we would check them — cheapest and most common first.
Differential Pressure Climbing and Not Recovering
The most common call we get, and the one most often misdiagnosed as worn-out bags.
Check compressed air pressure and volume at the header, not at the compressor. Long runs, undersized piping and a shared receiver all starve pulse cleaning. A pulse that sounds right can still be delivering too little volume to shear the cake.
Check the diaphragm valves. A ruptured diaphragm dumps air continuously and drops header pressure for every other valve on the manifold. Listen for a constant hiss with the cleaning system idle.
Check the timer sequence and the solenoids. A failed solenoid leaves a row uncleaned; that row blinds and the rest carry the flow.
Check for condensation. If the process has run below dew point, even once, the cake may be permanently bound to the media. Cleaning will not recover it.
Check the air-to-cloth ratio against the actual airflow, not the design figure. Fans get replaced, dampers get opened, processes get expanded. A collector at 4.5:1 when it was designed for 3.5:1 will never stabilise.
Only then consider the media. If the dust has migrated into the felt rather than sitting on it, the media is wrong for the material — not defective.
Differential Pressure Too Low
Counterintuitively, this is worse news than high pressure. Low differential usually means gas is bypassing the media.
- Bag failure — a hole, a split seam, or a cuff that has come off the tube sheet
- Tube sheet leak — corrosion or a cracked weld around a thimble
- Door or access panel seal failed
- Over-cleaning — pulsing so frequently that no cake ever establishes, which also shortens bag life
Visible emissions with low differential pressure is a bag failure until proven otherwise. Find it before it takes its neighbours with it.
Visible Emissions From the Stack
Isolate which compartment first, then which row. Powder deposits on the clean-air side of the tube sheet point directly at the failed bags — a torch and a mirror find them faster than any instrument.
Common causes in order: bag failure at the cuff, cage wear cutting the bag from inside, abrasion where inlet velocity impinges directly on the bags, and thermal damage from an excursion the media was not specified for.
Bags Failing Prematurely — by Failure Mode
The pattern of failure tells you the cause. Look at where on the bag it failed, not just that it failed.
- Wear at the bottom, outer surface — inlet velocity impinging directly. Needs baffling, not new bags.
- Wear in vertical lines — cage contact. Cage is bent, has too few wires, or the bag is loose on it.
- Failure at the cuff — installation. Snap band not seated, or the tube sheet hole is out of round.
- Media stiff, brittle, discoloured — thermal. Specified for continuous temperature, met an excursion.
- Media weak but visually intact — hydrolysis. Wrong media for a hot, moist process. Classic on aramid.
- Chemical attack, thinning or holes without abrasion — acid dew point, or a media incompatible with the chemistry.
- Blinded, heavy, will not release — ratio too high, or media wrong for a sticky or hygroscopic dust.
Hopper Bridging or Accumulation
A hopper is not storage, and treating it as such is the root of most of these. Material should leave as fast as it arrives.
- Rotary airlock undersized, worn, or rotating too slowly
- Hopper valley angle too shallow for the material’s angle of repose
- Condensation on hopper walls — insulation or trace heating needed
- Level control failed, so the hopper is running full and re-entraining dust
- Discharge running only intermittently when the process is continuous
Cleaning System Not Firing Correctly
Check in this order: control power, timer output, solenoid coil, air supply to the solenoid, diaphragm condition, blow pipe alignment. Misaligned blow pipes are common after a bag change and produce exactly the pattern of one clean row and one dirty row.
A kiln baghouse being treated as a bag quality problem. Characterisation showed the air-to-cloth ratio was wrong, not the media. Correcting the ratio and specifying membrane raised bag life 55% and halved maintenance hours — without replacing the housing.
Read the case study →When to Stop Diagnosing and Measure
If you have changed bags more than once in a year and the same symptom returns, the problem is not the bags. It is the specification — ratio, media, capture, or discharge — and further changeouts are paying for the same mistake repeatedly.
That is the point at which a measured assessment costs less than another set of bags.
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General guidance only goes so far. Send us the material and the process and we will tell you what we would specify.