Why is my compressor always full of water?

[Fritz Maurer]

I have a single stage Quincy, 12 CFM, that my dad bought new in 1952. The oil in the crankcase always looks like the day the factory put it in. I sometimes wonder if changing the oil is of any explainable value. My problem is with a home-built unit with a 2-stage DeVilbliss , 18 CFM. The crankcase oil is white in 4 to 6 months time. Cannot understand why this is occurring. The Quincy has fins on the discharge tube where my home-built does not; but the home-build has fins on the interstage tubing between the cylinders, although I dont know if this even has anything to do with the problem. Another thing I noticed was that the Quincy puts a noticeably larger amount of water in the tank than does the DeVilbliss. Thanks, Fritz

 

[BAnNC]

Moisture in the air gets trapped in the tank when you use it a lot, or use it and don't drain the water out.
Water getting into the oil says there is something causing the moist air to get in contact with the lube in the pump, maybe going past the rings?

 

[Stephen Newell]

If the compressor is too small for your needs it will run more generating heat which condenses more water than it would normally. A certain amount of water condenses in all compressors is why they put a drain plug on the tank. In damp weather the tank will need to be drained much more often than if the weather was dry. I usually set the drain cock to drain slightly all the time when the weather is especially humid.

What kind of oil are you using? If you are using detergent oil it can give the appearance of water in the oil because it will foam.

 

[Fritz Maurer]

Oil? ATF, 15-40, UTF, AW46... whatever is handy at the time. Have to drain it too often to keep dedicated oil around til the cause of this problem is determined.

 

[kencombs]

Are you sure the white is water and not air from foaming? I've seen compressors with too much oil in them foam up from the rod dipping too deep into the oil. Maybe drain some into a glass container and see if water separates after setting for a few days.

 

[Steve in VA]

For what its worth, every compressor I've seen specifies non-detergent 30w oil. It might be that whatever is handy is causing the problem. Perhaps drain and refill once with 30w non-d just to see.

 

[Destroked 450]

(quoted from post at 07:41:33 06/11/23) Oil? ATF, 15-40, UTF, AW46... whatever is handy at the time. Have to drain it too often to keep dedicated oil around til the cause of this problem is determined.

30w non detergent is the recommended oil for most piston air compressors
That what my Quincy calls for and what we ran in the Gardner Denver and Curtis compressors at work
Run that oil in my small Speedair compressor as well, never noticed foaming or moisture in any of them

 

[Fritz Maurer]

Dont have to put it in a glass. If the unit sits idle for a few days, water is the first thing out the drain plug. Have a 5 gallon pail under it, with several drainings in it, that is still white 2 years later. I keep it around because I was always curious if the water could be boiled out of it.

 

[Stephen Newell]

It may be using the wrong oil is why the rings are allowing water to pass into the oil. Under normal circumstances you should be able to go years on air compressor oil before changing it. It's not like a car engine where you have dirt from combustion and heat the oil just lubricates. The compressor should have 30 w non-detergent oil.

 

[dhermesc]

If you are running nondetergent oil it will look good - it doesn't carry dirt. All the dirt is settled to the bottom of the crankcase making a nice thick layer of sludge.


I remember my dad changing the oil in my grandpa's (his FIL) M Farmall. It had sat for months and dad just pulled the plug and let it drain. A little water came out then the oil came outlooking like it had just been poured in - dad was a little taken aback because he knew there were some hours on the oil as he had borrowed the tractor several times while he was farming grandpa's land. He also knew the oil had to years old. He dropped the pan and about an 1/2 inch of sludge covered the bottom of the pan - how the oil came out looking clean with that on the bottom .... Scraped the sludge out and rinsed the pan with gas and reinstalled it with RTV since he didn't have a gasket (and it looked like that was all that it had in the first place). Never forget the contrast in the clean oil and the filthy sludgy oil pan.

 

[Fritz Maurer]

Well Ill try it, Im open to anything... but AW is non-detergent, I thought that would have covered it.

 

[Steve in VA]

AW46 is 20 weight so unless your in colder conditions, its pretty light. That in addition to residual of what ever you've used previously is likely the root cause. IMHO.

 

[john in la]

I would consider a few things.

Proper 30w non detergent air compressor oil. It allows the water to settle to the bottom and not mix with the oil.

Proper oil level to prevent foaming.

How often is compressor used. Is it building up excessive water from condensation from non use.

Is the compressor over sized not allowing it to run long enough to get hot and burn of condensation.

 

[Stephen Newell]

There is always the possibility the damage is already been done using too thin of an oil. If the compressor oil doesn't do it you may need a new compressor pump.