I changed all the gaskets even change the oil and still no pressure.

The air is blowing out the intake valve and also the oil fill cap. Did I do something WRONG ?

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Air blowing out intake
by: Bill

Not knowing the make and model makes responding a bit difficult, friend.

I would surmise from your post that when you reassembled the compressor pump you may have installed the valve plate reversed from what it is supposed to be.

So, when the piston is cycling, air is being pulled in from the tank (not much of which can happen due to a check valve on the tank) and is being blown out the intake.

A selection of valve plates for various compressors
A selection of valve plates for various compressors

As to air coming out of the oil fill cap, if you can feel that happening, that is an indication of extreme wear on the piston seal(s) and enough air is bypassing the piston as it cycles to blow out the vent.

Note that the oil cap is vented to allow any air bypassing the piston seals not to pressurize the oil sump area, yet it sounds as though you have an extreme case.

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Air blowing out of intake
by: Rob (original poster)

Do you think that the problem could be due to oil excessively sticky?

The compressor has always worked alright but it has not been used for quite a longtime.

I decided to drain the oil and found it quite sticky. Now I do not know if it is a characteristic of the oil or which kind of oil should be used (I guess 15W50 could be one) but strange enough it stopped making the usual sound and sounds like stuck, humming. And it blew from the inlet.
Thanks Rob

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Compressor has sticky oil
by: Bill

There should not be a lot of oil in the compressor valve area, Rob. If there is, that suggests that the piston seals aren’t up to snuff.

Too sticky oil? Hmmm, as long as you are using compressor lubricating oil, so named and sold as such almost everywhere that sells compressors, you should be OK.

Air should not be coming out of the intake. I still think you have a valve problem on this compressor.


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