Should my intake valve be blowing air out ?

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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.

Air Compressor Blowing Air Out Intake? visit our guide!


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Hi all i am having the same issue air coming out the intake filter and the overload switch i have replaced the copper shim gasket all reeds are good so i am at a loss of what else it could be it builds up pressure then stops as it should but when it stops that’s when the air comes out.?? any idea’s. Cheers chris

Depends a bit on what model you have, but this is most likely a bad/dirty/sticky check valve.
You may be able to clean it out and fix it…

I have a ingersol rand rotary screw compressor 7.5 hp and when it stops air is coming out of the intake but stops when starts back up. It’s coming from one of the hard plastic air lines with the quick disconnect. Is that just a stuck check valve?
Also when i open up where oil is poored in it has a build up of air pressure. Is this normal for a rotary screw or is it worn out?

Thanks for any help

Yes, check valve is likely.
Not knowing what model, do you mean on the separator tank? If properly shut down, that pressure should be blown off. Is the gauge showing pressure?

Note to Bill – I don’t think this belongs here, although it kinda does…should be separated fro Chris post, at least, if you can.

Yes, gauge shows approximately 125psi before it shuts down. Up6-7.5tas-125 w/d is the model number. I don’t believe this is a separator tank,(but what do i know) this is the cast iron portion that houses the rotary screw, theres a sight eye for oil level and then beside it a fill screw for oil. Thats what i opened up after compressor shut down and pressurized air came out.
Sorry for not knowing where to post but thank you for responding and helping me out

Ok maybe a update or possibly more confusion. The hard plastic tube with quick disconnects on either end, the one that’s bleeding air back into air filter box when compressor reaches 125psi. I traced it back to a check valve coming off this aluminum radiator cooler that sits on top of compressor. Took valve off pulled plunger out examined seals slid it back forth did find put it back together and on machine. Still does same thing Again while the system is shut off at 125psi bleeding air through filter housing I take off what i call crank case fill… Read more »

I’ll look it up (if it’s out there) and see…
“Hope this is clear to understand, i only know enough to get myself in trouble”
I know what you mean – Can you get pix to clarify what all you’re looking at? Close, but not too close so there’s some “landmarks” as to where whatever is on the machine. Use a second post if you need more than 5 pix.

Do you have the manual? If not here: