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Help troubleshooting a Quincy 350 L air compressor

Tom75

Plastic
Joined
Jun 23, 2023
Hi everyone,
I’m wondering if anyone can help me trouble shoot my Quincy 350 L compressor with a 10 hp electric motor. I have done an overhaul kit on it ( gaskets, rings, valves etc. ). I also rebuilt the unloaded valve assembly that is located on the crankcase and installed a check valve ( oneway valve ) on the tank.
My question or trouble is when the compressor has built up air and shuts off ( @ 175 psi ) there is a small air leak in the crank case. I’m thinking it has something to do from the unloader valve assembly on the crank case…….How can I test or trouble shoot it to find where the leak is coming from?
 
Most probably you have a worn discharge valve. On one or both of your high pressure cylinders, the exhaust valve is probably leaking. Connected to the HP exhaust valve is the copper tube that goes down to the tank. This tube generally remains pressurized, so if the valve leaks the air goes back through the valve and on down into the crankcase. And that air is wet, so you will see water in your oil.

It isn't a complicated fix. They are easy to work on. Take them apart and lap the plate flat again and put them back together and that should fix the leak. Or, you can buy valve assemblies if you don't want to do all that lapping.

metalmagpie
 
Hi,
Thank you for replying!
I had lapped the valves but I’m saying that they probably could have used a little more lapping. I was using 400 grit and 1000 grit paper.
Could I trouble shoot it to find the exhaust valve that leaks by undoing the copper line on the top of the unloader tower(s) and seeing if air escapes from it or if the air stops leaking from the crank case, to identify which or both are the leakers? ( I know they copper line is pressurized so air will leak from there when disconnected ).
 
Well I take that back, I don’t think that would work now that I’m thinking about it. The unloader tower has a gasket so unless the gasket is punctured no air can enter in that way.
 
Check your hydraulic unloader valve down on the crankcase. That can leak air back into the crankcase when not running. Usually the ball is not seating properly due to dirt or worn seat. If the ball itself is good, a firm tap with a brass punch [with the ball on it's seat] will often solve the problem. This can even be done with the assembly in place as long as you have good access to the valve.
 
Check your hydraulic unloader valve down on the crankcase. That can leak air back into the crankcase when not running. Usually the ball is not seating properly due to dirt or worn seat. If the ball itself is good, a firm tap with a brass punch [with the ball on it's seat] will often solve the problem. This can even be done with the assembly in place as long as you have good access to the valve.
Hi, Thank you for replying! I will check the valve out and re seat the ball like you said with a brass punch tomorrow. I’ll let you know if that solved the problem.
Thanks you!
 
Don't take it apart until you are sure. With pressure in the tank, shut off/disconnect the air supply to the unloader. If the leak continues, it is not the valve.
 
Don't take it apart until you are sure. With pressure in the tank, shut off/disconnect the air supply to the unloader. If the leak continues, it is not the valve.
Okay will do, I’ll be checking it out tomorrow and let you know
Thank you 😃
 
Okay will do, I’ll be checking it out tomorrow and let you know
Thank you 😃
Hi, it solved the air leak! Thank you for your advice. I did as you mentioned by firmly giving a couple taps to the ball and that seated it properly and leak is stopped.
Thank you 🙏
 








 
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