Air coming out of the compressor oil vent

by Larry
(Frankfort, Ky, US)

When the compressor is pumping oil spits out of the vent. This happens while it is pumping and it also spits oil out after it stops. It slowing leaks out air through the vent over time. Is this an issue with my pump or is the vent filter not working correctly?

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Bill says...

The oil sump vent is to allow outside air into the sump of the compressor, to prevent the system pulling a vacuum inside as oil is, in the normal operation of the air compressor, consumed.

The first thing I think of after reading your post is that you have overfilled the oil sump, and since your compressor is likely a splash lube kind, that's what's happening. Oil is splashing out of the sump, up the filler tube, and out the vent hole.

The continual bleeding of air suggests an air leak from the tank to the sump, or air bypassing the piston seals and slightly pressurizing the sump, bleeding air and oil out the vent.

I don't think you have an oil vent cover problem. I do think you may have a problem with your pump piston seals and perhaps even the check valve.

Cheers,

Bill