Oil in air – not improving with new separator

Questions & AnswersOil in air – not improving with new separator
Cas Staff asked 4 years ago

I own number of tow behind compressors and recently I bought an Ingersoll-Rand two cylinder compressor. The engine runs fine, and pressure is good. The problem is there is a lot of oil coming out of the valves typical, of air separator failure.

I replaced the separator with a genuine Ingersoll-Rand one, changed the oil filter, changed the oil (Castrol 68) but there was no improvement. I swapped the tank with one from a similar machine but not change.

I put back the original pressure tank and swapped the compressor element with one from a similar unit, no change.

Its an odd problem I have never experienced in the many years I owned and used many different compressors. I have checked the radiator and pipes to and from it and the scavenger pipe for blockage, they are all clear.


Thank you

1 Answers
Cas Staff answered 4 years ago

Hello Taku,

Thanks for your questions. I see you already tried and replaced most parts.. good!

How did you check the scavenge line? You should be able to blow through it by mouth. You will hear bubbles coming from the screw element.

Also, check the scavenge pipe (inside the separator tank). Is it just above the bottom of the separator? Sometimes it is too long (or the new separator is too short), and the scavenge pipe touches the bottom of the separator. It then sucks closed by the vacuum.

Sometimes there is a check valve between the scavenge pipe and the scavenge line (check valve is on top of the tank top usually). Is it OK?

If this is a machine with a minimum pressure valve. Check that also (of not yet replaced by one from another machine).

If the minimum pressure valve opens too soon (at a low pressure), the oil separator will not function correctly.

Here is a blog post about the scavenge line I did not so long ago.

And here is more info about the minimum pressure valve.

As a test, run it for some longer time and see if the problem disappears. Sometimes ‘oil in air’ problems happen when the compressor stops or starts up. Then the first few minutes there is a lot of oil in the air, but it becomes less afterwards. It will give a clue about where to investigate further.

That’s all I can think of right now!

Hope this was of any help. And I love to hear from you when you managed to fix this problem!

Good luck!


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