Compressor motor doesn't restart when pressure drops

by Paul
(Pittsburgh)

The unit is a Campbell Hausfeld air compressor with 220V 5hp motor and two cylinder compressor.

When I acquired this 25 year old unit, the previous owner indicated that the pressure regulator valve might need clean(ing).

I dismantled it, but couldn't reassemble it. I went to Grainger and bought a Square D valve with built in unloader, cut off set at 125 psi.

I believe that it should cut back in when pressure drops to 105 psi or 95 psi. The motor stops at 125 psi, but pressure drops down to zero without the motor kicking back in.

Thinking that the valve was defective, I returned to Grainger and exchanged it for another, same specs.

The second valve acted the same way.

After reading some others' questions on this website. I wondered if the unloader valve was working properly. I can see no evidence that it is working.

I re-plumbed the line to the cylinder head. No change in performance.

Considering that cylinder head pressure was causing the unit not to restart, I listened, but could not hear any indication that the motor was attempting to restart.

When it doesn't restart, I toggle the circuit breaker off/on and the motor starts immediately and runs until 125psi is reached.

I'd appreciate you thoughts or suggestions.