Air compressor won't go over 40 psi?

if shuts down at 20 psi regulator is set wrong
it runs but only builds 20 psi, compressor is probably worn out

When it gets to 40 psi turn it off and see if you hear air leaking down from somewhere....if so listen and feel around the edges of the compressor head. If you hear or feel air leaking there you may need to replace a head gasket.

May be a stuck pressure switch or a bad motor. The connecter for the motor to compressor may also be bad.

Try emptying the tanks completely. There should be a bleeder valve for each tank. Sometimes after sitting for a while with pressure, the compressor won't have enough power to start. If you get the same response with empty tanks, there is a problem with the pump pistons.

Dan

Yes,but if the max is 125 you don't want to increase it above 110 and set off the pressure relief valve.

If your pump is shutting off before it reaches it's max psi. then you need to adjust you switch. Under the black case there are two adjustment screws. One is the high\low adjustment, the other is high pressure cut off.
The first will change when the pump turns on and off for your low psi setting and the high setting simultaneously.
The second will allow you to raise or lower just the high setting. There should be a diagram under the black cap to show which is which. Adjust the high side only and just a 1\4 turn then run the compressor and see if that takes care of the high setting.

The pressure switch controls the cut-in and cut-out points for the motor. Some switches have a differential adjustment besides the pressure adjustment. The differential controls the spread between cut-in & cut-out, (say in at 80 PSI, out at100 PSI)

Try looking for these if you didn't get a manual.

Good luck

My air compressor builds up to 40 psi and just keeps running, i have a craftsman 5 GAL, 1HP, 125 PSI and pressure goes up to 40 psi and dose not go any higher and on the other hand engine keeps running and dose not stop. Please advise?
Thanks.
Kia

may need to check the adjustment on presure relief valve on tank or check pop off valve on the top of the pump head.there may be some debree stuck in valve.