Compressor fault

[Greeves250]

I made an earlier post on this compressor but haven't fixed the problem. To recap - it was suggested that I drain the compressor and flush it. Short of running it with parafin for a while (which I'm loathed to do) I've replaced the old oil and run it up but the problem persists. When it gets to 50psi the belt slips (just like it did before with the old oil). With 50psi in the reciever the pulley seems hard to turn by hand like turning over a big 2-stroke motorcycle engine and feeling the compression (conversely with no pressure in the reciever it feels easy to turn by hand). Could it be that air is backing up into the compressor?. Is this possible?. Could it be a faulty NRV (non return valve) or something to do with the cylinder head?.

 

[rtbcomp]

The pressure in the pump will always be greater than that in the tank otherwise it wouldn't fill the tank, so backpressure shouldn't be a problem whilst running. It will cause starting problems though.

Is the belt too slack, is it the correct profile (ie not running in the bottom of the pullley groove), is the motor the correct size and speed (should most likely be 1440 rpm).

If the NRV jams shut at 50 psi that would cause a problem, though it's unlikely. For what they cost you could try a new one or even dismantle and clean the old one.

If someone's fitted a stronger spring that might cause a problem.

 

[Greeves250]

Starts no problem at all. The Belt tension is fine - about 1/2" play and there are two belts, by the way. The NRV has a very old looking rubber seal behind the plunger that looks like it was once rubber but has now hardened to something resembling Bakalite. Could that be the problem?. I can't hear any leaking air though.

 

[the snooper]

take it out and test it without one just to give you an idea

 

[rtbcomp]

Starts no problem at all. The Belt tension is fine - about 1/2" play and there are two belts, by the way. The NRV has a very old looking rubber seal behind the plunger that looks like it was once rubber but has now hardened to something resembling Bakalite. Could that be the problem?. I can't hear any leaking air though.

How strong is the spring? It should be quite weak, just enough to close the valve. If the rubber has hardened maybe someone has put a stronger spring in to try a fix?

 

[the snooper]

got to be some serious pressure build up to make the belts slip if the belts are not at fault

 

[Greeves250]

Spring pressure is quite weak. It's a brass plunger with a replaceable rubber pastile retained with a nut and washer. It's certainly not got any sealing properties any more as the rubber has hardened with. I'll replace it and get back to you with the results.