Why Does My Dust Extractor Lose Suction?

Where does lost suction actually come from?

Nine times out of ten, weak suction traces back to one of four places. Working from the tool back to the fan, here is what tends to go wrong:

• The hood or pick-up point. If the capture hood has been moved, damaged, or is simply too far from the work, the air it draws in is diluted with room air before it ever reaches the dust. HSE guidance HSG258, "Controlling airborne contaminants at work", talks about capture velocity for exactly this reason - the air has to move fast enough at the source to overcome how the dust is thrown off.
• The ductwork. Fine dust settles inside the ducts and slowly narrows the bore. For dusts you generally need around 20 metres per second of transport velocity to keep particles airborne, compared with roughly 5 metres per second for a non-settling gas. Drop below that and dust starts dropping out, building up, and choking the run further - a problem that feeds itself.
• The filter. A loaded or blinded filter is the single most common cause of a gradual fade. As the cake of dust thickens, resistance climbs and airflow falls.
• The fan. Worn impeller blades, a slipping or stretched drive belt, a motor running the wrong way after a rewire, or leaks on the negative-pressure side all rob you of pull.

Air leaks deserve a special mention. A split flexible hose, an unclamped joint, or a blast gate left open on an unused branch will bleed away suction from everywhere else on the system. Because the fan is still working hard, people assume the machine is fine - but the air it moves is coming from the wrong place.

Could a blockage or a tired filter be choking your airflow?

Almost always, yes - and the good news is that these two causes are the cheapest to put right. The trick is telling them apart from genuine mechanical wear before you spend money.

The tell-tale signs of a restriction

A blockage or a blinded filter usually announces itself through a change in sound and a change in behaviour:

• The note of the fan rises to a higher, harder-working pitch - a starved fan spins faster because it is moving less air.
• Suction is poor at the tool but the motor feels hot and strained.
• Clearing an obvious clog restores pull instantly, then it fades again over days or weeks as the filter reloads.

By contrast, a mechanical fault - a worn impeller, a slack belt, a reversed motor - tends to give steady, unchanging poor performance regardless of how clean the filter is. If a fresh or freshly shaken filter makes no difference at all, the problem is very likely downstream in the fan or upstream in a duct blockage rather than the filter itself.

A sensible order to check things

1. Isolate the machine and inspect and clean or replace the filter first - it is the most likely culprit and the easiest to rule in or out.
2. Open up and inspect flexible hoses and accessible duct runs for settled dust, kinks or splits.
3. Check every blast gate and damper is set correctly for the branch you are actually using.
4. Look and listen at the fan for belt slip, vibration or a reversed rotation direction.
5. Feel around joints and access panels for air being drawn in where it should not be.

Wood dust is a case where none of this is optional housekeeping. Hardwood dust carries a workplace exposure limit of 3 mg/m³ as an 8-hour time-weighted average, and softwood dust 5 mg/m³; where the two are mixed, the tighter hardwood figure of 3 mg/m³ applies to the whole mixture. A fading extractor is the difference between staying under those limits and quietly drifting over them. It is easy to underestimate how quickly that happens - we cover the wider risk in our note on wood dust, the workshop hazard that is easy to underestimate.