Speed variance as PSI builds

by Steve Orin
(St. Cloud, FL)

2 year old 31/2 horse upright Husky, 60 gal. tank. Running speed varies once above 90psi, from a near stall to normal speeds.

No power fluntuations & unit connected directly to dedicated hardwire.

Oil & air filter good - serviced regularly. Unit's in clean environment.

Could Check valve be cause or would speed slow steadily as pump tries to overcome tank PSI? This is second compressor with like problem in 4 years.

Bill says...

Steve, sure, it could be the check valve, and it's always a good idea to pull it and clean it to be sure. Make sure you dump all the air first, of course.

The compressor motor will see increasing load as the air pressure in the tank increases. In most cases, any change in speed is hard to notice, as the compressor is built to handle those load increases.

Your compressor speed fluctuation bothers me. If there were a consistent problem, the motor would lug, and then lug worse, as the load increases.

Another possible issue could be the run capacitor reacting somehow.

It seems clear that the compressor is reacting to changing load conditions, it is just that it should react the same way every time.

The wiring may be hard to the compressor, but what, if anything, is also pulling power from that same circuit that the air compressor is on?



Comments for Speed variance as PSI builds

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Feb 07, 2012
by: Steve

Well, it was not the check valve. After replacing the unit ran once, fine. Second time the pump froze & I barely saved the motor by switching off. After a lot of reading I believe the problem is system wide, across all brands of compressors of this type. Due to poor manufacturing standards units in this price range are considered throw away items, not expect to last more than a year or two. Now I have to consider fixing or replacing. Perhaps I just need to buy a new compressor every other year!

Dec 17, 2011
Me again
by: Steve

Bill, I agree about the inconsistent variance. Runs about 3/4 speed when the switch triggers & begins to vary around 90lbs. Often changes speed up & down till it gets above 100 with some slight squealing from the belt as the motor heaves. Oddly, as the PSI gets higher speed often levels out at nearly acceptable speeds! The hard part seems to be in the mid-range. I can smell overheating from the motor as soon as the switch triggers on.
As I said, the circuit is a dedicated line with the breaker about 5' away. Hardwired, not multi-strand. I wonder if there's a meter I could put inline to tell me if power varies as the motor runs & speed changes?


Steve, yes, an amp meter (multi-meter) will tell you the amperage draw as the motor is running. Still it is odd that the load increase seems to be both caused by, and varied by, the pressure build. I'm writing this as an invitation to anyone else to chime in here if they have any ideas for Steve.


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Husky 60 gallon slow building pressure

My husky 60 gallon is having a hard time building pressure! Takes along time to build 90-135 psi! They want $280 for a new pump I'm just not sure that's the problem... Filters alittle dirty but even with it removed it acts like its getting too much air. There is no funny noises, doesn't use oil. Where can I look to find anything else wrong besides buying a universal pump.. 2.5 years old and only 2 yr warranty!!! Go figure.

Bill says...

A bunch of things to consider.

Make sure the power supply hasn't changed, the belt is at the right tension, you have checked the intake filter, but is there air puffing back out of the intake valve?

Feel under the unloader valve to make sure no air is bleeding out there while the compressor is running.

Pop over to the Troubleshooting section on the site map page, and follow the links to more info about why air compressors run but don't build pressure.



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