On Mon, 1 Mar 2021 12:37:18 +0000, SH wrote:

I have a Stanley air compressor with a 25 litre storage vessel.

when I start it, it pumps up to 120 psi and then the motor cuts out.

Over typically 5 minutes, the air pressure will decay slowly to 80 psi
whereby the compressor motor restarts.

This happens when I am not using any air tools.

I have used a can of gas leak detector and tested all unions and joints
and I can confirm there are no leaks.

This then leaves the compressor pump bit itself... are they actually gas
tight or do they have a normal amount of leakage back to the air inlet port?

I have noticed 'leaks' from a couple of places in the past. One being
the water drain screw underneath and the other the pressure release
valve in the starter solenoid or the non return valve.

If you put the end of the outlet hose in a jar of water you should see
if it's leaking 'from' the system or leaking 'past' any non-return /
start back-pressure release valves etc (the one that goes 'Psssthhh!'
when the compressor shuts off when at full pressure).

Cheers, T i m