Quincy compressor - the Pressure Switch "Chatters" just before cut-out and carbons the contacts!

by Don
(Virginia Beach, VA)

Quincy two cylinder driven by 3 phase 5 horsepower motor works well.


I have replaced the pressure switch, the hydraulic unloader, the associated cylinder unloader, and the unit still chatters just before cut-off.

The chattering of the contacts can last up to 5 seconds and it has cost me two pressure switches 140/175 Square 'D' and new contacts in the controller!

Is it possible that a bad cylinder valve is causing this pulsing condition?

I have other air compressors in this same configuration that work fine but, I can't figure out what the problem is! I'm about to start removing the cylinder valves to see if that is where the problem is!!!

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Jun 25, 2013
Chatter at setpoint
by: Anonymous

Check where your pressure switch sensing line is located. If it is coming off a discharge line and not the receiver tank you will be subject to pulsation which can cause chatter. The comp pressure switch needs a more static source to sense from. Sometimes the pressure switch can be sensitive to the setpoint and may need adjustment to find it's sweet spot, especially if it is a mechanical switch.

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Quincy QR-25 Model 350 - head safety valve going off

Quincy QR-25 Model 350 - safety valve on head is going off when pressure builds up.

What can cause this?

Thank you,
John
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John, yours is a two cylinder, two stage compressor. If the PRV you are referring to is in the line between the two cylinders, it is likely that the intake valve on the second cylinder is not working properly. Instead of allowing air to flow into the cylinder, and / or stopping it from flowing back out, air pressure builds in the line to the point where the PRV lets go.

Cheers,

Bill

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Nov 10, 2016
valve inspection
by: dave

I am experiencing a similar problem. Are any specialized tools required to remove and inspect the valves, or can it be accomplished with typical hand tools?

Thank you

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qt5 compressor slows down after three minutes

I have a QT5 upright on an 80 gal tank. My motor burnt the main windings.

I bought a new motor, hooked it up , turned it on, the compressor ran fine for about three minutes then started to slow down.

I turned the power off and looked at the guage it had 50 psi on the tank. What would cause the compressor to slow down ?
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The motor slows because it is having trouble running against an increasing load.

The increasing load is because the back pressure from the tank increases as the pressure builds, and the motor has to work harder to overcome that. That should not, normally, be a problem.

Same motor size? Same power supply? Any change in the sound of the compressor? Intake filter clean?

These are some of the questions that need answering to help diagnose the problem.

Cheers,

bill

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qt15qcb1 compressor slows down at 80 psi tank pressure

i have a quincy compressor model number qt15qcb1. it has a baldor 10 hp 3 phase motor. this morning i changed out a leaking unloader check valve. turn comp back on and build up 120 psi with no problems. i drained some air to verify everthing was working correctly. again 120psi no problem. after that i thought i would blow the dust off the compressor. the next time it kicked on it was turning very slow. i drained the tank, removed check valve it double check it, and cleaned the air intake filters. check valve was clean and free moving. turned it back on and it runs and sounds perfect untill the tank reaches about 60 psi and it starts to slow down and cunitues to get slower as pressur increases. i removed the electric motor and had a electric motor shop inspect it, they found nothing wrong. any ideas?

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Jul 03, 2012
Compressor slowing down under load
by: Buster

Try turning the compressor by hand after is slows down and see if it is in a bind or turns freely. I would check the voltage going to the motor, a three phase motor will run with one phase dead, but will not run long and slows and tends to overheat. Check that you have all three phases of power and there isn't a fuse blown or breaker tripped or bad, and check that the contactor is good on all three phases, and the connections in the motor connection box are good.
I assume this is a belt drive compressor and you have checked the tension on the belts and they are not slipping under load, just checking, lol.
Let me know if any of this helps.
Buster

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Quincy QSI 750

by Nathan
(Beaumont, Tx)

the compressor should be running at 115 psi, but is only at 80psi and showing that its at 20%, whats wrong?
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Not a lot to go on here, Nathan.

I have obtained a copy of the manual for the Quincy QSI air compressors, and will upload it to the Quincy page on this website shortly.

Check there for the manual, and see if it helps.

Cheers,

Bill

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I have a Quincy 30 hp screw compressor should it cycle on off or stay running?

by Silvino
(Hillsboro)

Can it regulate down to "0" cfm on the inlet while running or does it need to shut down when it reaches the setpoint and I'm not spraying. I got a good deal on it but use little air right now compared to what it can produce. Its not running yet and I'm wondering if I can use it for a single spray gun operation

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Won't build pressure...

by Audie Vickers
(Burlington, NC)

I have a Quincy QM15A scroll compressor. The main contactor needed replacing. In the process of wiring it back up I reversed two of the three-phase leads causing the compressor to run backwards (approx. 5 sec). Got it running the correct direction but now it won't build any pressure. I suspect the air inlet valve is stuck. Suggestions? The repair people are swamped right now and can't be out 'till next week sometime.
Thanks.

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