Compressor blowing oil out of sump breather

by Ingo
(B.C., Canada)

I had bought a brand new Central Pneumatic Twin Tank , 3 HP. air compressor.I have only run this unit a couple of very short times as it blows the oil out of the sump and out of the sump breather. I have had the head off a few times to try to figure out the problem.The piston rings look OK and have honed out the cylinder again.

I think that my problem is that one - way valve between the tank and the cylinder head .

One time the compressor was vibrating very bad --- I think from the cylinder piston being backpressured from the air pressure leaking back through the one - way valve. I have taken that valve apart. It has a very soft plastic material spring loaded plunger in it which had a couple of small gouges in it which I sanded and filed smooth.

Put that compressor back together and after a few minutes of running it is blowing the oil out of the breather again.

What is your opinion on this ? Am I right about that one - way valve sticking open and pressurizing the oil sump by forcing the air back past the piston rings ?

I am looking to find a new not made in China one way valve, but where I live no one seems to have a clue where to get one. My valve has 3 ports -- one outlet to tank ,one inlet port from piston head and one smaller female outlet to the shutoff switch assembly.


Would certainly appreciate your opinion and advice.

Ingo Grundmann
B.C. , Canada

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Bill says...

Hello Ingo. Thanks for visiting my website and for taking the time to write in.

My, but you've had some issues with your compressor, haven't you?

Usually when the check valve into the tank fails, it's because it doesn't shut tight, and then air bleeds back out of the tank and out of the Unloader Valve when the compressor stops.

While it's possible that it somehow jammed and prevents air from getting into the tank when the compressor is running, unless it was installed backwards, I think that's pretty remote.

When you got the compressor you presumably had to add the lubricating oil. Did you overfill it? That could be one cause.

The breather you speak of is, of course, the intake breather into the compressor head...right?

While oil coming out the breather is not normal, run the compressor for a while anyway and see if enough leaks out to drop the oil level in your sump. Or, drain some out to make sure it's not too high a level.

You seem to be a fairly handy person, so I suspect, if you can't find a check valve to suit, you can make one using components from the plumbing shop.

Good luck.

Bill