motor over heats

by david
(holly ridge,n.c. usa)

speedaire--mod #3JR76 as the press goes up the comp. becomes harder to turn. at zero press the comp. turns freely @ 30 pounds of press, I can barly turn the pully by hand. at 50 I cannot turn the pully by hand. what can you advice of this problem? thanks.

Bill says...

As air is being compressed into your tank, the pressure in the tank builds, and this causes back-pressure. The compressor pump, and the electric motor, have to work harder to pump air into the tank.

That's normal, and the system is designed to accommodate that increasing load.... unless!

That you can't turn the pump sheave by hand as the pressure in the tank increases doesn't surprise me, unless you are closely related to the incredible Hulk, that is.

As your motor works harder in response to the increasing load, the motor will get warmer. That, too, is normal... unless!

Unless you have a load issue, that is increasing that load beyond the capability of the motor. The motor then will get really hot, and may go off on thermal overload. If it goes off on thermal overload, don't just keep resetting it, but find out what's causing the higher load.

It could be....

-motor wearing out
-check valve seized
-pump mechanical issue

or even other things.

I can't begin to diagnose your compressor problem more than that from the information you have provided.



Comments for motor over heats

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Sep 09, 2010
Compressor Hard to Turn Over
by: Terry - East Texas

Looking at this post, there are a couple of things that stick out to me as possible problems.

As Bill said previously, there are several variables in play here.

My take is that these two are where you need to look:

1. You will need to check for blockage or a stuck check valve at the tank inlet. Most probably has accumulated rust and debris, and frozen in place. This is a simple one way valve that lets air freely flow into the tank from the compressor pump, but not back out of the tank.

Even though the tank is showing an increase in pressure, obviously rising from zero to 30 psi and then to 50 psi, it becomes so difficult to pump that the electric motor overheats. The check valve is most probably stuck in a near closed position, but open just enough to let some compressed air get through. And obviously open enough to let air escape back to the compressor pump, pressurizing the piston, making it hard to turn over by hand. The more pressure, the harder it is to turn over by hand.

2. I suspect that your unloader valve may not be working too, especially because you can't turn it by hand. Most unloaders will unload the pressure from the pistons after the compressor shuts off, either electrically, or mechanically, to allow for easier restart of the pump. If it was working properly, and the pump had stopped with the unloader valve open to release the pressure, then you should hear air escaping from the possible faulty check valve from above. And it would continue until tank was drained. Since you did not mention hearing any air escaping, it leads me to believe that the unloader is inoperative. In this case if the unloader is not operating at all, then pressure leaking back through the faulty check valve to the compressor pump is constant and thus hard to turn over by hand.

Even though there is a one way valve at the piston discharge port, it will be overloaded with pressure in this case.

Search this site for Bill's postings on unloader valves.

Check valves at the tank can many times be cleaned and reused. Or if rusting and pitting is too severe it may have to be replaced.

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Takes A long Tpme To Build Up Air

by Jerry
(Tuscaloosa Al.)

It's A Fork Shaped Piece On Top Of The Head Broke It's On A 3Z181 Can U Help

Bill says...

I think you are talking about the intake valve, Jerry, but from your description, I can't be sure.

Visit the Troubleshooting page, click on the link to won't build pressure, and there is a tips page linked from there that gives many of the reasons why a compressor won't build air pressure properly.



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