Compressor not kicking off; calibration difficulties

Yesterday I posted a thread about our compressor reaching face-melting temperatures because it’s near-constantly running. That is, it reaches the set PSI, air leaks out and it kicks back up again within seconds.

I did what bjtheone said to do to in the other thread. I simplified the circuit on a test bench (we had to take the system off the robot today anyway), and recorded the results of a series of steps which I’ll list below.
First the simplified circuit:

Dig deep and fight the urge to critique the cable management on this hastily-assembled test bench, please.

bjtheone says to:

  • power up the system, gauges read 0 PSI, compressor comes on

This happens.

  • pressure gauge up stream of the regulator (between it and the compressor) should start to rise

This happens.

  • pressure should climb to whatever you have the pressure switch set to (typically 120 psi)

The pressure climbs to 115

  • compressor will turn off, pressure should hold steady

Compressor kicks off, but does not hold steady

  • pressure gauge on the regulator will read something. Adjust the regulator, via rotating the ribbed knob (usually have to pull the knob up, or push it in). Pressure should change as you rotate the knob. Set the pressure to whatever working pressure you want. Typically 60 PSI.

That worked great, it was easy to set that one to 60 PSI.

  • at that point you should have the high pressure gauge reading 120 PSI, and the low pressure gauge reading 60 (or whatever you chose).

High pressure reads to 115 and the compressor kicks off

  • system should stay like that, without the compressor running, until you use some air, by using your pneumatics

The pressure drops within seconds, unprovoked by actuating the cylinder.

  • once the pressure drops, the compressor should run to bring the pressure back up

It does that, but for no good reason.

On to the calibration of the emergency release valve. I’m following it to the letter (as far as I can tell), but I cannot get it to stop hissing as I turn it.

What do y’all think?

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You have a leak. Happens. The question is, where?

Found it, or one of them. Turn it the other way. When the hissing stops, let the compressor run. IMPORTANT: if the pressure goes over 125 PSI, open the manual vent immediately.

Can I see the bottom of the regulator as well, please?


When the compressor kicks off and pressure drops immediately, is the emergency release valve actively leaking air? If so, it needs to be calibrated until it stops doing that.

If not, you have a leak elsewhere in your system - you can use a small amount of soapy water to check every fitting and connection until you find it. Ensure there’s teflon tape on everything threaded, and that all tubing is cut perfectly flat, and fully inserted.

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I just left for the day. I can send you a pic tomorrow?

Say it did go over 125 PSI. Is the compressor completely hosed and I need to replace it?

Sure, that’s fine.

No, the compressor is fine. The 125 is a safety thing–stuff isn’t rated for more than 120 so the valve should be set to 125.

That’s the thing, I turn the cap on the emergency release valve and while it will hiss more in some places and less in others, the hiss never stops.

Might need a new PRV.

Or could be something else causing the issue–that’s why I was asking about the primary regulator.

If the compressor kicks off at 115, that means that your pressure switch is doing it. If the pressure failed to get above 115 because of the release valve, the release valve would be hissing and the compressor would keep running.

Well, found your leak!

The compressor is just a dumb pump. It goes when the pressure switch actuates, and stops when the pressure switch shuts off. So the compressor is fine. If it goes over 125 that’s a problem with the pressure switch, not the compressor.

I’d recommend reducing your air circuit even more- just the compressor/relief valve, then pressure switch and gauge, then the purge valve (which I think the manual calls a plug valve). Make it the simplest possible. It sounds like you have a leak at the pressure relief valve (what you’re calling the emergency release valve, which is a fine and correct name too). Once that is fixed, start adding components 1 at a time and verify that the system continues to hold pressure without excessive cycling. How much is excessive? A few psi per minute pressure drop max, I think.

Excellent! Should I remove it all, retape and reattach?

I tried two different ones today, neither were able to completely stop hissing while I turned the cap.

Really everything I’m suggesting removing can be done with push-to-connects. Take the tube coming out of the compressor and put it into the pressure switch. Done. Trying to keep it as simple/easy as possible!

I can’t get it to stop hissing no matter which direction I turn it. The hissing lowers but never stops.

With the pressure switch, OK. The release valve has to be connected to the compressor by hard fittings. (R84)

I don’t understand. What I was saying is that the hiss from your release valve is [at least one of] your leak[s]. If the hiss is coming from the base of the valve, then yes, retape that*. If it’s coming from the top, that’s an internal issue to the valve.

* be sure to remove all the tape before adding more!

Wait. Dumb question: WHAT on the PRV are you turning?

There are 3 different hexes and only 1 will affect the hiss…

$10+shipping will remove the pressure relief valve calibration problem


The hiss is coming from the top hole of the emergency release valve. When calibrating it never stops completely, the hiss may lower in intensity but never stops.

Then back up to @EricH’s “dumb question” post.

I just screw that sucker in where the brass KOP pressure relief valve was?

My suggestion could have been phrased better. I’m using ‘compressor’ as shorthand for ‘compressor/relief valve hard-piped assembly’. I was hoping my statement that it could all be done with push-to-connect fittings would make that clear, but it’s best to be exact in this case to avoid confusion.