Emergency Valve Help

Hello, I’ve been the electronics and pneumatic mentor for a number of years now. I know the system fairly well but I’ve recently come across something that I’m stumped with. Basically the compressor is not shutting off and is releasing air out the emergency valve. It’s really stumping me because I’ve checked for copper strands on the connection points to ensure there isn’t a short but everything is connected well… we had this issue last year at 1 point but it just went away and was fine… now it’s back and I have no clue what it could be. I confirmed the pcm jumper is on the 24v as well and it is. Any suggestions would be appreciated

Have you taken a multimeter to the pressure sensor to confirm an actual signal? Is the connection solid on the PCM side?

This shouldn’t have any effect on the compressor.

+1 to using a DMM in continuity mode

Check your gauges to ensure the system is getting high enough to trigger the switch, it should go somewhere between 105 and 115 PSI (Yes, really, they’re almost never 120). You may need to build a slightly unsafe system with no relief valve to test this.

It is possible that your pressure relief valve is adjusted too low, and venting before the switch can trigger (assuming you are using the standard issue adjustable valve).

On that note, pick yourself up one of these bad boys and never think about it again.


Are you using the Norgren relief valve? If so, it needs to be properly calibrated. It sounds like it’s venting before your pressure switch is signaling the PCM to turn the compressor off.


I’m going to second this recommendation. (Even if it turns out your Norgren valve is OK)
This is a better valve, and cannot be “mis-calibrated” by novice users unscrewing the wrong thing.

Plus, it has a great “PSSSHHHHT!” That will make your robot inspector jump a little if they are not ready for it.


Everyone thank you for your advise. I found the issue. It’s very funny. The valve is suppose to come preset however it must have been worn out. It was triggering before reaching 120psi. This prevented the switch from activating and shutting off the compressor.

We’ve also had a few valves change setpoint due to (what we suspect is) temperature and altitude variation. Fine at one regional, then a good 5psi under one state over a few weeks later.

Something like this is also helpful.

I have even seen a case where the dial gauge was wrong and a team could not figure out why things were never shutting off when the gauge said well above 120. It may have been the units for the gauge were wrong, but I can’t remember – it may just have been way off.

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That’s pretty cool. The main problem is that we use the tiny gauges so it was only like 3 psi short but hard to tell on the tiny gauge

I bought a couple of these for my team a little while ago, but they all seemed to be somewhat far off from 120 psi. I don’t know why it happened that way, but it was a bit frustrating.

We’ve had a few of the 125 PSI ones going closer to 120 PSI, but never enough to dip into the range of a good pressure switch. Some teams have experienced issues apparently, but it seems that no more than one in a handful are bad. Paying for 3-4 is still better than that giant lever arm coming off the brittle compressor casting imo, and inspectors are aware they’re explicitly legal.

Thanks for the tip, we will be giving these a try.

@NShep98 The blue box under R77B states part number 48435K714 which is a 125 PSI model, so if you ordered the 120 PSI model it would makes sense that your results were too low.


I double checked my notes and this is the part number that we ordered. It will certainly be a while before we are able to test them again, I just found it strange that all 3 we bought seemed to not be quite right.

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