So I have built the compressor and it is working well.

The problem is the unloader valve in the pressure switch.

It is a 'square-D' pressure switch and it seems the unloader valve is sticking open.

I replaced the unloader valve (had a spare), and now the second one is sticking. Do the unloader valves have a working PSI range? This one seems to be open below 100PSI, but closes up as the pressure builds.

Currently the unloader valve is horizontal. Is it supposed to be in a different orientation?

Pics to follow.

The unloader valve is doing its job (releasing the pressure off the head). Your real problem is your check valve, its located where the large line off the head enters the tank. The check valve is leaking back into the line causing the unloader to continuously drain. Replace the check valve and your unloader valve will stop leaking.

Nope.

The check valve is brand new.

The air is coming from the unloader valve, and once it unloads, there is no more air. Tanks holds full pressure for at least 24 hours.

If I manually turn off the compressor, and let it drain down to the pressure switch engagement point, the unloader will let air by once the compressor starts running, but (it appears) only until a specific PSI (unknown at the moment). As it pumps up and I am messing with it, it slowly reduces the leakage amount until it shuts off.

So, does the unloader valve have a 'pressure range'?

TIA,

I don't know what brand your unloader valve is, but I went through two Load Genies from Grainger that would stick open and constantly leak air through the little orifice in the unloader. I'd always have to go by and tap on it with something to get it to spring shut.

The first one I thought was just from crud in the lines, I wasn't as careful with the pipe dope as I should have been and there was moisture corrosion in the copper lines.

So I bought a brand new one and had the exact same problem develop within 3 or 4 days of replacing it. I used Teflon tape this time, and all of the lines were brand new. I pulled then new valve out and started examining it and the old one. There was a drag and "catchy" spot on both of them, I'd guess from the machining process when they were built.

So I sanded down the "shaft" till it was lapped smooth and shiny, this was still a little snug for my taste so I dug through my drill bits until I found one just ever so slightly larger (a little less than 1/32") than the hole that the shaft slides up and down in. I centered the contraption up in the drill press, and zipped the bit through the hole.

Problem solved, it never stuck open again, and actually worked like it should have from the start..

- Lee

Unloader valves, well check valves are rated by CFM, but the Load Genie I mentioned, and what I think you are talking about are an all in one Unloader/Check Valve.

If you've got one rated higher than what your compressor puts out, it'll probably still work just not as efficiently. If the valve is rated higher than the compressors out put the valve will cause the compressor head and lines before the it to build up pressure until it's enough to force the spring valve open, then it will spring closed again until the compressor builds up enough pressure again. It's not that big of a deal, it just makes a lot of racket sounds a bit like a machine gun, with it rapidly opening and closing.

I guess it could wear the valve out quicker, and maybe put more wear on the compressor rapidly building up and releasing pressure.

If the check valve is matched to the compressors cfm then it should open when the compressor is turning and remain open until it stops.

- Lee