Engine shuts off when unloader valve closes.

by Brian
(Eau Claire, WI)

I recently got a used Coleman wheelbarrow type compressor, its gas powered. It starts and runs fine, it will build pressure and then idle around 140 psi.

When it gets down to about 100 psi, the unloader valve closes and the engine just shuts off.

If I manually open the unloader valve after it is already opened, then use a tool and the tank gets down below 100 psi, then manually close the valve the engine goes back up in RPMS and will build pressure.

I was wondering if replacing the valve would do the trick, or if it has something more to do with the throttle linkage or something.

I'm fairly familiar with small engines, but am new to compressors. Any information would be helpful, thanks for your time.

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Bill says...

Brian, I envy you your familiarity with small engines, as I have very little.

I do not use a gas powered air compressor myself, though the principle of their operation is pretty straightforward.

Your diagnosis suggests that manually operating the unloader allows the compressor to work, letting it operate automatically doesn't. My first response if it were my air compressor is to change out the valve.

However, you have small engine experience, and the cut in pressure level of the pressure switch is supposed to throttle up the motor, so first, why not check out and see if the signal is getting from the pressure switch to the unloader first.

Cheers,

Bill