UST Power System Air Compressor Will Not Build Pressure Above 50psi – Solutions & Causes

Published Categorized as Air Compressor Not Building Pressure, UST Power System 9 Comments on UST Power System Air Compressor Will Not Build Pressure Above 50psi – Solutions & Causes

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My UST Power System Model 1110c. Was working a couple weeks ago and built up pressure to 100psi. Today, it would only go to 40psi.

UST Power Systems model 1110c will not build pressure beyond 50 PSI
Ust Power System Compressor

I disassembled the cylinder head and cleaned the flapper valves and checked they were seating correctly.

Slight increase in pressure to 50psi, but no more.

My suspicions are now leading to the piston rings. If I can find parts for this, the rings would be the next thing I would do.

But trying to find any online support eludes me at this point.

by Brian
(Essex, ct)
Brian, I have uploaded a photo of a UST Power System compressor, though I cannot find an image of your specific model.

If yours is similar to this, then it has an oil fill tube and a vent. If your piston seals are leaking sufficiently that your compressor will not build pressure past 40 PSI, then you should be able to feel quite a flow of air out of the oil fill tube, as that the cap is vented.

I rather more suspect that you have a gasket that lets go at 40 PSI. That you disassembled and reassembled the pump made a change. Maybe you torqued the bolts down tighter, but you managed to hold off the leaking of the gasket, if that is what it is, for another 10 PSI.

Try a high heat gasket sealer and see if that makes a difference, or make a new gasket from high heat gasket material.

Also, empty the tank, remove, clean and replace the tank check valve.

Did it help?


Reply to Bill
by: Brian


Thanks for your quick comments. Yes, that is the exact model (You must have visited my garage today to get that picture)

Late last night I pulled the entire head to check the cylinder surface and rings. I did a minor honing and polish of the cylinder wall. The rings appeared basically still new, as this unit has maybe a total of 3 or 4 hours run time. Got it back in 2011. Double checked the flappers, they were still clean from before and appeared to be seating well. While there I also polished both sides of the flapper plate.

Just a note that the tank is holding pressure, which leaves out the check valve. Though it does take a long time to just build 50psi at this point, about 5 minutes. Where before it would take 2 or three minutes to build to 100psi.

After reading the section “Compressor Won’t build Pressure”, that gave me a couple ideas in conjunction with your comments.

“Quick Check” Yes, there is some air coming out of the intake opening.

I will try your idea of sealing the gaskets tonight to see if that causes any changes.

Also, there is air flow coming out of the oil fill tube. Come to think of it, you can hear it and it seems to be more than I can remember.

Thanks again,

Brian Kerrigan
You are welcome, Brian. Air out of the intake – that’s an intake valve problem.

Lots of air out of the oil fill cap vent, that’s a piston ring or seal problem.


by: Brian


The main problem I found was, as it turns out, was the gasket on the bottom of the flapper plate. While it was running, before it warmed up, I used the old soapy water method. Sure enough it appeared air was coming from the gasket.

Replaced both upper and lower plate gaskets, in addition of the honing of the piston cylinder and polishing the plate, it now fully gets up to full pressure in about 2 minutes. Faster than it did before.

Only issue now is the check valve has a crack. I think the check valve from a Powermate compressor may be the fit.

Thanks Bill
Brian, so very glad I was able to help with your compressor problem.

I think it another good rule of thumb is if you disassemble the pump to get at the valves, then you want to replace the gaskets with new ones when you reassemble to ensure that they aren’t part of the original problem.

Have a good one.

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I also have a ust model 1110c air compressor that has a cracked cylinder head or “cover”. I called ust and they no longer carry air compressor or parts. Does any one know where I can find parts for it? Or is it time to scrap it and buy a new one?

I know what I would do, Steve. You can get a comparably sized replacement of another model for under $100 new.

The parts issue with the UST will never get better, only worse, so maybe it’s time to cut your losses?

I have a model 1110c compressor by cst. it pumps up pressure to about 90PSI then cuts off and air continue to escape from the bottom of valve.

Have ust power air compressor model 1110c and need replacement tank drain valve. Where can I get one?

Thank you

If you are referring to the tank drain, it’s likely a standard unit, may be metric in threads though. Remove the existing one, Google compressor tank drain valves, and you’ll find lots. No need to try and find a UST one.

the air is coming from the bottom of the pressure switch, bought a new one and still the same thing

I suspect the issue is not the pressure switch, but your tank check valve. For clarification see the page on this site that refers to it, what it is, and what it does if you need additional info.

Empty the tank with the compressor off, remove, clean or replace the check valve and I expect you’ll be back in business.

I need the small hose connecting tank to pressure settings for a pro source model# 1110C up right type on wheels.

Take it (the hose) to your local big box or maybe auto parts store. Shouldn’t be too hard to find something usable.