UST Power System Model 1110c will not build pressure beyond 50psi

by Brian
(Essex, ct)

UST Power System Compressor (Photo:

UST Power System Compressor (Photo:


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

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.
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 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 gasketing material.

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



Comments for UST Power System Model 1110c will not build pressure beyond 50psi

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Sep 01, 2016
1110c Pressure
by: Dave

I found that the air filter housing had melted at the mounting threads (all plastic) and was constricting the air going into the piston. I have not tried to run without the filter housing yet, but suspect that this may have something to do with the pressure issue. If you have any thoughts, please pass them on.

(Dave, this appears to be a bit off topic, yet will be of interest. Please start a new thread in the UST forum. Thanks. - Moderator)

Dec 07, 2015
1110 C manifold
by: Bill

This page might help:

You may have to build a new manifold using brass fittings from a hardware store.

Dec 05, 2015
Same model 1110C
by: Anonymous

Where can i get the T that connects the tank, compressor and shutoff/regulator. This looks like a 4 way with 1 plugged. Going into tank looks 3/4in, going to shutoff/regulator looks 1/4in, coming from compressor looks 1/2in

Dec 05, 2015
Reeds for 1125c ust air compressure
by: Rod

Broken reed, will not build pressure

Nov 19, 2015
ust air compressor model 1125c
by: Adamsco

Have the 25 gal upright model 1125c seems to be blowing by the head, took the head off expecting to see a blown head gasket but no gasket, only 2 rectangle shaped reeds, just strips that looked ok, am I missing something??,,, thanks, Doug

Jun 09, 2013
Same compressor : max pressure cut doesn't work and motor eventually stalls at 65-70 psi...
by: Alan

I'd be happy to reset the max pressure switch as all I need this for is pumping tires....
As the same new units are on sale from sears/craftsman don't know that putting all the work into rebuilding is worth it- I got it for free...

Bill, what do you think?

Tough call as I don't know your budget. If you can rebuild it cheaper than new, and you typically don't count your time in the equation, then that's the route. If your time is important and has value, probably buying new is a better bet.

There are folks that just love to tear air compressors down and then rebuild them. If this is you, go for it. The fun outweighs the actual and labor cost then.


Jun 05, 2013
Same compressor - can't find parts
by: Tina

We have this same air compressor - the manifold (I think it's called) is broken and I can not find parts or a breakdown anywhere.

Any help would be very much appreciated.

We will be sure to recommend our clients do not buy their air compressors from places that do not provide any manufacturer support or parts.

A typical manifold containing the pipe from the compressor, a regulator, and a discharge coupling can be assembled from brass fittings commonly found in a decent plumbing shop. Get the pipe, nipples, tees, male and female adapters of the same size and thread as the existing manifold.


Feb 11, 2013
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.


Feb 06, 2013
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 conjuction 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 comming 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.

Good luck.


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