by Michael Brown
(Solvang, Ca.)

I have a Central pneumatic Compressor that will start up fine but will shut off before pressure is reached.

I have checked the Pressure Switch and it is fine . ie if tank is holding 60 psi and I start it with pressure switch set a 70 psi it will run to 70 turn off and if I bleed air off it will restart by itself as expected.

Central Pneumatic 67847 air compressor

Central Pneumatic 67847 air compressor

If I start from 0 psi it will shut off before it gets to shut off pressure. If I wait a bit reset button clicks and I can reset it and it starts again. Can It be a running capacitor/ starting capacitor or is it more likely just getting too hot from motor getting to the end of its days. Any easy way to check?? These are cheap compressors so obviously don’t want to “waste too much”.

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You’ve checked the pressure switch Michael, and you say it’s fine.

When the compressor shuts off prematurely, is it the pressure switch that is shutting it off, or is the motor going off on reset?

If the pressure switch is toggling off power to the motor before its set point, then my money is on a bum switch.

If the motor is going off on thermal overload, then your guess about the run capacitor may be right on the money.

Can you check and let us know?


 Central Pneumatic only builds to 50 psi?

Steve

i have a 3hp 21gallon central pneumatic compressor.

i bought it at an auction and noticed that half of the air filter assembly was missing. i plugged it in to try and it pumps up to 50 psi good but no further.

Central Pneumatic 21 gallon tank air compressor

Central Pneumatic 21 gallon tank air compressor

i have took the head off and reed valve looked good piston looked good as well.

i did notice when its running it vents a lot of air out oil filler cap. i have not disassembled flap inside of head. what do you think is wrong?

p.s. i have also messed with pressure switch that’s not it either

thanx
steve
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Steve, good that you checked the valves.

A key clue for me though is the air bleeding out the oil fill cap. Where do you think that air is coming from?

Typically, that is a sign of worn compressor cylinder seals. The more wear, the more air that bypasses them into the sump instead of going into the compressor tank, and the more air that bleeds out the oil fill cap.

The seals in your compressor may hold until the tank pressure gets near the 50 PSI level, and then, the increasing back pressure forces the piston seal(s) to leak. Air will always follow the path of least resistance, so, it seems that it is easier to blow the cylinder seals open than it is to exit through the pressure valve and into the tank past the tank check valve.

A pressure at 50 PSI (or any pressure level) with the compressor running is also an indication of a gasket leak inside the pump. My rule of thumb is if you are going to tear down the pump to check things out, have a gasket kit on hand to replace them, and ensure that they are not the problem.