Hi,

On diesel compressors, pressure is regulating in two ways:

1. Inlet valve on compressor (open/close)
2. Engine speed

But the engine should never completely stop - they should always continue running, just run at idle when no air is used.

It's hard to say from here, it could be many things.

Does it sound like the engine is struggling and then bogs down, or does it simply stop?

If it bogs down, it can't handle the load at higher pressure - the problem is most probably a dirty air filter or dirty fuel filter.

If ti just stops, it could be that the speed control valve isn't adjusted correctly and pulls the engine speed too low, so it stops.

Or it could be that a safety stop (temperature sensor) trips at higher pressure, which makes the engine stop.

Please let me know if you found the problem and feel free the give some more info/feedback and I'll try to help more.

Thanks!

Cas

ps: if you want to learn more about these wonderful machines, I have a book about diesel compressors.

Hi Cas

Thanks for your reply.

I have overhauled the engine, new piston rings, ground the valves in and fitted new valve stem seals.

The compressor has a manual pressure relief valve to assist starting the engine, with this valve held open the engine runs fine and will run forever. it was probably made in the 1970's and doesnt have any fancy technology like a temperature cut out, when I close the manual valve and let the comperssor produce air it does that fine up until about 60 psi when the engine slows and cuts out(this is not from the speed regulator).

I have removed the outlet valve with the big spring in it, cleaned it and replaced it. No improvement. The control valve that controls the speed of the engine appears fine when taken apart but is not being operated by the compressor/oil pressure(I think compressor oil/pressurised oil should go up a pipe to operate it). I can control the speed of the engine manually ( high revs) and it still stops at 60 psi.

The engine and compressor have clean air filters and a new fuel filter. That only seems to leave the inlet valve.Could the inlet valve cause my compressor to stop?

Thanks John

Hi John,

Thanks for the update.

Let's assume the engine is OK for now, since you overhauled it.

That leaves us with the compressor side of the machine.

At first I thought it could be because of the speed regulator not opening, which makes the engine run outside of it's optimal speed to produce the power needed for higher pressures - but then, it should be able to run at idle at full pressure without any problem - and you mentioned that that you adjusted the speed manually and it still stops.

The only thing I can think of is that your outlet pressure gauge shows 60 psi, but the internal pressure is much higher, because of a blockage or a stuck valve.

How about when you start/run it with outlet valves open - that should have the same effect as using the manual pressure relief valve - please try.

The very last thing I can think of (and have seen before) is that the exhaust system could be full with carbon deposits.

I've fixed this once by running the compressor at the point just before it bogs down (it's struggling but doesn't stall) - this puts extra pressure inside the exhaust system, until it finally cleared with an outburst of black smoke and suit.

Can try and see what happens?

Good luck, please let me know.

All the best,

Cas