I have a Clarke 150 ltr compressor and the original pressure switch broke so I replaced it with another one. When I start it, it builds pressure fine upto 150 psi (is this right) and then cuts out. Then though, instead of being quiet, air rushes out somewhere on the switch until it drops down to 110 and then kicks in again. This takes about 30 seconds. Have I done something wrong?

This is an easy fix.. you need an new safety valve or a new switch.

If the safety valve releases pressure before the max pressure replace it.
the switch has a cut in pressure of 120 psi (this means compressor will start when pressure falls to 120 psi.
The cut off pressure is 150 psi. This means the unit will shut off at 150 psi.
You need to watch supply pressure to see if it exceeds 150 psi. If it does replace switch.


Safety Valve Part Number:AB-9415379
Pressure Switch Part Number:AB-9415626

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To increase the life of your compressor you will need to lower the pressure setting of your pressure switch, or replace it with new one that will cut-out at 120. Most compressors have the pressure switch set to cut-out at about 125 psi. Lately, I have seen compessors being sold with factory set pressure from 150 to 200psi. Most single stage compressors can easily handle 120 to 125, however higher pressures are pushing the motor/pump to the limits. This is like driving your car at full speed everywhere you drive. Your car lasts many years because for the most part, you are only uning 20 to 40 % of capacity. Problem is that pressure switch is not really designed to be adjusted (factory set) but not impossible. Look for model number of the pressure switch itself and google for more info. If in fact it cannot be adjusted replace it with generic switch at lower setting. The lower the pressure cut-out , longer life of motor pump. Tiny hole in head is an unloader of sorts and helps the motor to overcome head pressure (yes, this method is less efficient than using pressure switch with unloader valve, however cheaper to build).

There is a differential between the shut-off and start pressures of about 20 psi and these pressures are adjustable on some switches. What the switch must do as well is relieve the pressure on the compressor head so that the motor does not try start against a load. You shoud hear the pressure relieving when the compressor shuts off, if not you need to rectify this problem, otherwise check the pressure that the motor cuts in at and set it or replace the switch.

Have a look to see if the pressure relief valve is not opening before the pressure switch is supposed to shut off the compressor?

most likely the regulator is shoot. But also try checking for leaks with dish soap and water in a spray bottle.

Hi

Can you hear any leakage, if not then I would suspect a valve is jammed open.

Gently tap valve housing with a soft hammer, may dislodge the valve.

well their is safety air pressure valve make sure it good which 99% they are good is pressure too high check the regulator is it set to high. that is. extra air and lots of regulators do dump air any ways so that's no big deal, it is normal

No, there is a problem with the check valve . the check valve is allowing the unit to start with a load on it . replace the check valve it will fix the problem

Your pressue builds up and stays trapped in head which causes the motor to lock up. Your pressure switch is probably bad.