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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