The motor current on my dry pump keeps creeping up — what is happening inside?

Powder is building up in the stages and closing the clearances. Rising power draw at the same duty point is the earliest signal a dry pump gives, and it appears long before the noise changes or the pump trips. Treat it as a scheduled-maintenance trigger, not as something to watch.

Dry pumps — screw, claw, multi-stage Roots or combined — run on clearances of a few hundredths of a millimetre with no oil in the gas path. That is what makes them clean, and it is also what makes them intolerant of deposits. Condensable process by-products come out of the vapour phase inside the pump, combine with any solid carryover, and the rotors have progressively less room to turn in. The motor has to work harder for the same gas.

Two counter-measures are built into the machine and both need checking before you blame the pump. Nitrogen purge at the shaft seals and between the stages dilutes and sweeps the by-products; if the purge flow has been reduced or valved off to save nitrogen, deposition accelerates immediately. Body heating keeps by-products in the vapour phase so they leave with the exhaust instead of condensing; a heater or a controller that has failed silently produces exactly this symptom.

Check the exhaust side at the same time. A restricted exhaust line or a loaded exhaust filter raises the pressure the pump discharges against, which raises the pump temperature, which lets the rotors grow thermally into the clearance. The current rises for a reason that has nothing to do with deposits, and replacing the pump would not fix it.

If the pump also trips on over-temperature, the margin is already gone. Continued running from that point risks a rub, and a rubbed rotor loses its clearance permanently — that is a rebuild, not a service. The economics change sharply at this line, which is why the current trend matters more than the trip.

Send the pump model, the full part number from the nameplate, the process, and the current draw now versus when it was new. Say whether it is the standard, harsh or HV variant — the same model number covers builds with very different purge and heating arrangements, and the right answer depends on which one you have.