One Last Pneumatics Question at the 11th Hour

[anthonygraff24]

I sincerely hope this will be my last pneumatics question this year. Our pressure switch is not working. Our compressor starts and runs and never stops. In the past it would stop at 115-120psi, when the pressure switch flipped. Now it is not stopping. We have no leaks in our system and, for testing purposes, we took the relief valve off of the compressor. Is this a busted pressure switch? The only reason I'm asking is because when we used a broken switch in the past the compressor just wouldn't start in the first place. Now it just runs indefinitely. Any help and you would be the bomb. :D :ahh:

[jdaming]

What code platform are you using?

I would try and see if the digital signal is coming out of the pressure switch.

Your likely problems are:
Pressure switch bad
Pressure switch wired incorrectly
PWM cable bad
PWM cable plugged into DSC the wrong way
DSC slot bad

I would first see if the control system is reading the digital input and back up from there.

[Jon Stratis]

The switch could break in either a closed or open position. When pressurizing the system, use a multimeter on the pressure switch to measure the resistance. If you see it flip by the time you get to 120 PSI, you'll know the issue is in your code or the wiring somewhere, and not in the switch.

Also, last year I came across a team whose pressure switch seemed to not be working. We swapped in a new one and it still didn't seem to be working. We later found out the pressure gauge they had was busted - it was reading 120 PSI, but the pressure was actually significantly lower. Once the gauge was swapped out, we could see the switch was actually operating correctly.

[bachster]

for testing purposes, we took the relief valve off of the compressor.

This statement has me a bit worried. The relief valve is there for your safety and to protect the rest of the system from being over-pressurized, ESPECIALLY if your switch is failing to turn off the compressor. If your relief valve was venting at a lower pressure, preventing you from being able to tell if the switch was working, you need to calibrate the relief valve to vent at 120 psi. Please put it back on, calibrate it, then continue your trouble shooting.

You don't say whether your system is reaching 120 psi with the compressor running. I assume it is, but if not, this could indicate your regulator is attached backwards. There is an arrow on the regulator indicating the direction of pressure drop (ie, high pressure goes in the back of the arrow, low pressure comes out).

Jon's suggestion to check the gauge is also a good one. We've had some gauges (even brand new ones) that needed a "tap" to get the needle unstuck.