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UST Power System Plus Air Compressor Won’t Reach Cut-Out Pressure

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Is your UST power system plus air compressor struggling to reach cut-out pressure? And you’re unsure how to diagnose and fix the problem? Well, fear no more! This article will provide you with all the relevant information on why your UST power system plus compressor can’t reach cut-out pressure, including troubleshooting steps to follow!

Table of Contents

Why Won’t My UST Power System Plus Air Compressor Reach Cut-Out Pressure?

The most likely reason why your UST power system plus air compressor is not reaching cut-off pressure is due to the following failing or compromised parts:

Head Gasket

It is very possible that your UST power system plus compressor appears to be building pressure fine, but at some point during cycling, the pressure stalls and the air is unable to flow into the tank due to a failed head gasket.

Intake Valve

It could also be a failing air intake valve, causing the air to blow right back out of the intake valve instead of being properly drawn into the compressor.

Piston Seal

If the piston ring seals are not working as they should, the pumps will lose significant pressure and efficiency, resulting in a lack of pressure being built in the compressor.

Pump Pressure Valve

The pump pressure valve could be faulty, allowing air that flows into the tank through it to be drawn right back out of the tank.

Other possibilities include leaks in various parts of the system. So, if your UST power system plus air compressor won’t reach cut-out pressure, you should be able to diagnose and fix the problem by following these troubleshooting steps:

  1. Conduct a pump-up test
  2. Inspect system for leaks
  3. Clean filters
  4. Inspect system valves
  5. Evaluate belt condition
  6. Inspect pump rings
  7. Inspect air/oil separator

For more detailed information on each of these UST power system plus air compressor troubleshooting steps visit our Air Compressor Won’t Reach Cut-Out Pressure Troubleshooting guide!

Reader Questions & Responses

UST Power System Plus Air Compressor Won’t Reach Cut-Out Pressure – UST Power System Plus Air Compressor Troubleshooting



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

Ust Power System Compressor
UST Power System Compressor

I disassembled the cylinder head and cleaned the flapper valves and checked they were seated 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


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 the cap is vented.

I rather 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?



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 polishing of the cylinder wall. The rings appeared basically still new, as this unit has maybe a total of 3 or 4 hours of run time. Got it back in 2011. Double checked the flappers, they were still clean from before and appeared to be eating 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”, which gave me a couple of 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 airflow 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.



The main problem I found was, as it turns out, 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 to 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.

The 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 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.

If you have any questions regarding why your UST air compressor won’t reach cut-out pressure, please leave a comment below, with a photo if applicable, so that someone can help you!

By Aidan Weeks

A passionate Mechanical Engineer with endless enthusiasm for fluid power - building off the back of over 18 years of high quality contribution and discussion stimulated by Bill Wade here at About Air Compressors. With both practical and theoretical experience in pneumatics and hydraulics, I'm putting my knowledge to work - and working my grey-matter through my research, assistance and publishing work here at About Air Compressors. Feel free to reach out any time! P.S. A HUGE shout out to Doug who really offers such great value to all visitors to About Air Compressors - once again, feeling like I'm standing on the shoulders of GIANTS by getting to work alongside such a great community

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