Why does air come out of the oil stick?

by Don
(Jax Fl)

There are two small holes in the top of the oil stick and when the compressor is on, air leaks out from them. It won't build up any more than 40 psi. Central pneumatic 2hp twin tanks, 5gal.

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Hello Don...

What separates the compressed air from the oil sump is the piston rings or piston seals.

As the compressor reciprocates, the piston moves up and down. The oil splashes from the sump up under the piston, lubricating the walls of the cylinder as the piston cycles.

What keeps the oil in the sump and out of the air stream (mostly) are the piston seals.

If air is entering the oil sump while the compressor is pumping compressed air, that tells me that the piston seals are badly worn or nearly worn out, and air is bypassing them into the sump.

The sump vents out the oil fill plug, and voila, you have air coming out the oil fill cap.

Usually that seal bypass isn't enough to stop the air buildup in the tank completely. That your air compressor fills to 40 PSI and continues to run and not fill past that point suggests to me that you have potential valve leakage or perhaps a gasket leak in the pump as well.

Sorry,

Bill

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Nov 22, 2012
LP335SK (040-0387) Pump
by: Troy

I have oil blowing out of the oil breather on the pump. It is blowing out while the pump is running. Can you tell me what my problem is?

Thanks,
Troy
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Troy, if what you mean by breather is the air intake port (maybe with a filter on it) and oil is coming out there, I suspect two problems.

One is that the intake valve is failing, allowing compressed air and oil to blow back out as the compressor cycles. The other is that the piston rings / seals are worn, and you are getting oil blowby into the air pressure chamber as the compressor runs.

Time for some repairs, I fear.

B.

Oct 19, 2012
What are holes for?
by: Don

Thanks Bill. Are the holes in the oil stick cap there for a reason? They are on opposite sides at the top of the stick.
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The vent holes in the oil fill cap are there to let air in and out.

As the compressor works, small amounts of oil are wicked up into the compression chamber, and sent into the tank with the air. When these cylinder seals are worn, there is more oil moving up out of the sump and into the tank.

By the same token, some compressed air will wick past the cylinder seals and into the sump. The vent lets that air out.

It is when you have lots of air blowing out the vent cap you have an indication of significant wear on the piston seals.

B.

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Oil sprays out when I start it, did I overfill it?

by mike
(kapuskasing canada)

oil sprays out when I start it, did I overfill it?
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Hard to tell Mike, since I don't know anything about your air compressor or where the oil is spraying from.

I suspect it's coming from the oil fill tube vent?

If so, and the compressor is fairly knew, it's possible you overfilled it and vibration is kicking the oil out or... you've overfilled it enough that for the first time you are seeing what happens when the piston seal(s) a worn to the point that compressed air is pressurizing the sump, and the oil fill is high enough to block the air from getting out the vent easily.

Bill

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Nov 12, 2013
Oil Seal blows out
by: Bryon

I have the Craftsman vertical single stage air compressor (Model No. 919.184190).
Once the compressor runs for a short period of time and approaches 140-150 psi the oil seal blows out the back of the pump assembly.
Are my piston seals bad? What are my options?
Thanks for your help.

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air comes out oil fill tube

by Linda
(Lancaster Ohio)

The pump is filling with air and air comes out oil fill tube
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When you say the pump is filling with air Linda, I read that to mean that the sump is filling with air?

Typically this compressor problem relates to the piston seals failing, and rather than pushing air down into the tank the air takes an easier path, past the piston seals, and down into the tank.

Since the smaller compressors are typically splash lubed, meaning oil is splashing all around in the sump when the compressor is running, the air that is flowing down into the sump travels up the oil fill tube and out to atmosphere, taking some of the oil with it.

Not knowing the make or model means that others that have a similar problem with their compressors cannot offer suggestions.

If your compressor is well used, depending on the cost invovled, it's probably ready for a tear down and rebuild or replacement.

Cheers,

Bill

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where is the fill tube on HICO Ventpak-He compressor

by gary
(ontario, canada)

I have a 10 horsepower HICO Ventpak-He air compressor. Model # HKH32. I cannot find the fill tube to replace oil.It has a sight glass but I cannot see oil level. Please help if you can.
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Good day, Gary.

I can find no information on your compressor model, though it is suggested elsewhere that the compressor is manufactured by Campbell Hausfeld compressors. I checked their site and could not locate your model or make.

I am hoping that another visitor to this site can comment with the information you need.

Cheers,

Bill

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