919.175260 only gets to 40psi then I have to shut it down

by Jay C.
(San Jose, CA., USA)

919.175260 only gets to 40psi before I have to shut it down


Hi Bill,

I have an older Craftsman air compressor model no. 919.175260 (5hp single stage 60 gal. upright) and when I turn it on it seems to run fine until it reaches 35psi then it slows down, starts to chug and the belt starts to squeal so I shut it down.

If I let it continue with the belt squealing it trips the house circuit breaker.

If I run the compressor with the bottom drain valve open it will run until I shut it down (no problems).

I shut the drain valve, start it up and the same thing happens.

I cleaned the check so it now looks new. I re-installed the check valve and again at 35psi the belt starts to squeal so I shut it down.

I motor is brand new, a WEG 5hp so I don't think that's the problem. Do you have any suggestions?

Many thanks,
Jay

Comments for 919.175260 only gets to 40psi then I have to shut it down

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Mar 18, 2015
Low pressure
by: Doug in s.d.ca

Belt tension:

The belt should move about 1/2 inch with finger pressure at the center of the belt between the pulleys.

Valves:

If a finger valve is broken (or maybe a bad gasket), then compressed air from one cylinder can leak into the other - meaning that the other cylinder now has compressed air in it already when it starts its compression cycle.

Perhaps you can tell by manually rotating the pump sheave while noting what happens at the output tube - you ought to have a similar amount of air coming out twice per revolution, once from each cylinder.

Mar 17, 2015
Responding to Doug Comments
by: Jay

Hi Doug,

The motor was replaced because the main shaft bearing had seized up and would get real hot with no load just running on a bench. It had a few other issues; a bent and worn out copper arm that simulates the brushes and a cracked die cast end plate (see had a good life).

The belt tension I believe was correct. I used a piece of wood that had a "V" cut into each end and was just the right length. I then lightly tapped the piece of wood in between the two pulleys so the belt would remain tight while I secured the motor.

My compressor is in a small outdoor closet and so it is really hard to know which pulley the squeal was coming from.

Yes, I'm using the original pump and it has two cylinders. You said I may have bad valves? Do you mean the flapper valves? I replaced the check valve with no change. Also I would like to replace my existing two piston single stage pump with a two stage type pump, do you think this is a good thing to do? And if so where could I get one and for how much?

Thanks again,
Jay

Mar 17, 2015
Belt squeal 919.175260
by: Bill

Actually, it was Doug that talked about the belt squeal.

If you Google parts for 919.175260 you will find some sources. I would opt for the sears parts direct source and after you drill down, if the parts you want aren't there, there is a number for you to call.

I suspect that some of the parts may be obsolete, though it looks like valve plates are still available. Piston rings.. not sure, ask them.

Don't forget to ask about any gaskets as you will likely have to change them too once you tear down the pump.

Cheers,

Bill

Mar 17, 2015
Responding to Bill's comment.
by: Jay

Hi Bill,

I think you're right about the pump creating too much back pressure and that causes the belt to squeal. I did replace the check valve today and no change. Whenever I test the pump or motor I open the petcock on the bottom of the tank to release the air and what comes out is a combination of air and a light green water liquid. I'm used to the water, but not the oil, so I'm guessing the rings are not catching all of the oil.

Can you suggest the best place for me to get the pump rebuild data I will need? Also a place where I can buy a good rebuild kit?

Once again many thanks,
Jay

Mar 16, 2015
Binds = stall?
by: Doug in s.d.ca

I wonder, why was the motor replaced?

Is your belt tension correct, and is it the correct belt?

Is the squeal from the the drive (motor) pulley or the driven one?

If you're using the original pump, does it have one or two cylinders? If two, you may have bad valves (including checks) in it.


Mar 16, 2015
919.175260 only gets to 40psi
by: Bill

Jay, you've done all the right things.

It sounds as though the back pressure from the tank is creating such a load on the pump and through that to the motor that the pump can no longer turn creating the issues you've outlined.

My first thought when I start reading your post was that is was the check valve. You already fixed that.

Your new motor suggests that it shouldn't be a run capacitor on the motor.

That leaves the pump, and my next thought would be you've got a damaged valve, on the pressure side I would think, that isn't operating properly once the back pressure reaches the 35 PSI.

This were my compressor I'd be pulling the pump apart to have a look.

Bill

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