I can't locate the check valve on my LeRoi Dresser air compressor.

by Tim
(Duncannon PA USA)

LeRoi Dresser air compressor

LeRoi Dresser air compressor

LeRoi Dresser air compressor
LeRoi Dresser air compressor pump
LeRoi Dresser air compressor pressure switch
LeRoi Dresser air compressor plumbing

Hi, I have an older LeRoi 80 gallon air compressor with a Dresser 500 2 stage compressor. It is leaking air through the bottom port of the unloader valve when the pump shuts off. The unloader doesn't seem to be unloading either. It is locate on the front of the compressor pump.

Reading through the posts on your site it would seem that the best place to start is by examining the check valve. The problem is that I can't find anything that looks like a check valve between the pump and the tank or between the pressure switch and tank.

There is a copper line between the high pressure cylinder and the tank. On either end of the line is what appears to be a 90 degree gas line compression fitting.

The pressure switch is plumbed into a standard looking pipe "T" which is plumbed to a pipe nipple going to the tank. There is a plastic line plumbed into the pipe "T" below the pressure switch that runs to the unloader valve.

There are 2 small copper lines that run from each of the cylinders to a "T" and then to the unloader valve. Nothing looks like any pics I have seen of a check valve.

Any thoughts would be appreciated. I can send pics as well. Thanks, Tim.

Comments for I can't locate the check valve on my LeRoi Dresser air compressor.

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May 25, 2016
Compressor Gone
by: Tim in Duncannon

Larry, thanks for the input. I sold the compressor a while ago but it is useful info for others that may be experiencing the same problem. When I found out I would have to drop close to $400 on the special tools to remove the valves I opted to sell it and buy something I could actually work on. I rebuilt a Kellogg 335 with basic hand tools and a cylinder hone.

May 25, 2016
No Check Valve
by: LarryK

It was normal for Leroi to manufacture their reciprocating air compressors without a discharge tank check valve. They relied on the pump HP discharge valve to function as a check valve. If the discharge valve leaked it would result in air blowing from the unloader on shutdown therefore indicating a need for valve maintenance. Leroi felt that having a check valve in the discharge line would mask/hide a valve problem. You need to repair the HP discharge valve and probably check the other three valves.

Mar 30, 2016
special tools for compressor repair
by: Tim in Duncannon

The ability to repair/rebuild without the need for special (expensive) tools was a major factor in my decision to buy the Kellogg. I was also interested in an Ingersoll Rand T30 variant for the same reason but I couldn't find one locally that wasn't beat for a reasonable price.

Mar 29, 2016
by: Doug in s.d.ca

Good point about being fixable without special tools.


Mar 28, 2016
Already sold it
by: Tim in Duncannon

Good to know! Thanks. I sold the compressor a while back because I didn't want to spend $300 on the special tools to take the valves out. I made my own but it broke when i put a 4 ft cheater bar on it and did push-ups (i weigh 225). The valve didn't budge. I bought a Kellogg 325 mostly because it can be completely taken apart with common hand tools. I rebuilt it and it works for my needs. If I had run the Leroi Dresser every day it wouldn't have been a problem but I only ran it when I ran my sandblaster every couple months.

Mar 23, 2016
I can't locate the check valve on my LeRoi Dresser
by: Anonymous

Your compressor does not have or need a tank mounted check valve. The second stage discharge valve/s serves as the check valve. It sounds like the second stage discharge valve/s is leaking. I would inspect it, it may just need a cleaning but might need to be replaced.

May 11, 2015
unloader check valve
by: Doug in s.d.ca

I don't know. However, I expect that once you get into the unloader, the check will become evident.

I'm hoping someone has a good drawing of the pump, as I'm not finding a one.

May 10, 2015
servicing the check valve
by: Tim

So how would I service the check valve? Is it in the high pressure head assembly? I don't think the unloader valve is working properly because I tried to turn the compressor by hand after the pressure switch shut it of and it was very difficult to turn. 15 minutes later is was much easier to turn.

May 09, 2015
check valve
by: Doug in s.d.ca

I'm fairly sure the function is built into the pump, so there won't be a separate check valve.

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