Compressor problem

[Rosbif]

Hi and thanks for letting me join.
I have an old and trusty Clarke air compressor bought in 1991. It was used and abused for 20yrs and now used rarely. A while back it blew a piece of the gasket out from the head which I replaced and its worked fine since.
Recently when it reached max air and cut off it continuosly blew air out via the on off switch. Replaced the on off switch and no change. A quick google and it advised changing the safety valve which I did. It made no difference.
When the air drops the motor kicks in but it just hums and doesnt turn. If I drain the air completely it fires up no problem but the whole series starts again.
Any help would be appreciated as I hate throwing things away.
I will try to attach pictures of replaced parts and a video of humming motor.
Sorry for the long first post
Regards
John

 

[indykid]

Welcome along, John.

If it has air pressure in the unloader line to continuously blow out, it sounds like the check valve on the receiver isn't sealing. The unloader line should depressurise just the pump and the pipework up to the tank to give the motor a bit of breathing room to get up to speed before it sees any load from the pressure in the pump/receiver. They can get contaminated with various stuff, especially if the head has been off, but the check valve can be disassembled and cleaned which might help in troubleshooting but if the seal or seat are damaged, it might need to be replaced.

The humming motor sounds like the run capacitor (in the box on top of the motor) has failed or is failing. If the capacitance is low, you won't be getting enough phase shift in the start winding of the motor to generate enough torque to get going. It might be enough when there's no load (fully empty receiver) but not when there is some load with the part full receiver.

 

[julianf]

It's the valve.

It's jamming open, and so the pressure switch carries on dumping.

It's also (probably) the reason it's not starting again - as it's not actually managing to dump the cylinders, so it's trying to start under compression.

Look for a "lump" in the pipework, and investigate. You may be able to take it apart and clean it of the accumulated junk.

 

[Red'n'Black]

Sounds exactly like mine. Got any pics?

Mine had a knackered non-return valve and exactly the same symptoms, a new one from Machine Mart fixed it. The bloke was very helpful, the new valve had the flow going through a right angle so some elbow couplers and thread adapters needed which he gave me out of his box-o-bits behind the counter.