25+year old Craftsman 3hp air compressor, won't start after tank pressurized

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Old 08-06-14, 01:59 PM
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25+year old Craftsman 3hp air compressor, won't start after tank pressurized

I bought a brand new Craftsman compressor back in 1987. It is a 20 gallon 3hp compressor. It is not oilless. It does have a single piston with a separate 3hp electric motor and a belt.

It has worked well for many many years even after the one time I forgot to check its oil and the pump seized. LOL I put new oil in it and spun the pump by hand and it started working great again, that was in 1996 when that happened.

As of the last couple of years, it is gotten to the point where the compressor would start up perfectly when empty but when the pressure dropped to 85psi and it would cycle back on, it would stall and trip the breaker. I have it set to pump up to 110 and start up at 85psi.

The cylinder has a larger line going directly from the top of the cylinder to the tank and a small line going from the top of the cylinder to the electrical switch box (unsure of the names).

I have researched my stalling problem and it appears that it might be a problem with the pressure check valve but my old compressor doesn't seem to have a check valve like modern compressors.

The circuit it was on worked flawlessly for the first 6 years it was hooked up to. It was only in the last couple of years that it got worse and worse. Its at the point where I have to turn it off once its pressurized and then turn it back on when the pressure gets below 30psi or just grab the large pump pulley and give it a spin when its trying to start.

I would really rather not have to replace the pump motor so I am hoping its the check valve or something like that. How can I check it and what should I be looking for?

I am attaching a couple of pictures so you can see what I have.
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Old 08-06-14, 02:08 PM
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Welcome to the forums Bo!

I have a little bit older but similar compressor [basically that one's little brother] I'm not sure how you check it but I suspect the motor is getting tired which would explain it now tripping the breaker. There are some members that are real good at diagnosing and repairing compressors so stay tuned as they'll hopefully have time to chime in later.
 
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Old 08-06-14, 02:23 PM
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At the tank connection of the larger line from compressor there is a check/bleed-off valve. It checks and holds air in tank and bleeds off pressure to compressor for next start. Check with Sears with your model# and get a new valve. If they don't have it Grainger will. There are several sizes of them, so you need exact measurements if going through Grainger.
I have replaced several of them.
While you are doing things, replace the start capacitor. Both items should be less than $20.

Good luck!

RR
 
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Old 08-06-14, 05:40 PM
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I went ahead and took the check valve off. You are correct, it was at the compressor tank. I also then took the starting capacitor off and had my next door neighbor test it. He is a professional electronics technician and has a actual capacitor tester and he said that the cap tests out perfectly well. So tomorrow I shall take the check valve to Grainger (there is one less than a mile from my house) and hopefully that should resolve the problem. Can the check valves be cleaned? It seems like it is a very simple item. A spring with a plunger on it.
 
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Old 08-06-14, 05:59 PM
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You can spend time and energy cleaning, but it moves with every pump stroke so eventually wears out. It is brass and that is fairly soft. Their expense is minor compared to other items. Bought one this year for my 1979 compressor as the old one was worn enough it was sticking and draining 60 gal tank in a couple hours. I think that is the third one for it.

RR
 
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Old 08-07-14, 12:06 AM
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I will go ahead and get a new one. I'm going to bring the old one with me but is there any info that Grainger will need to get the right one or will having it be enough?
 
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Old 08-07-14, 05:31 AM
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Having it should be enough, there's not much to it, usually just the pipe and compression threaded on opposite ends. They'll have to match those and since yours is an older compressor, it was probably made here and chances are a standard check valve will do ya. But still.. be ready to do a little modification just in case. You may have to cut the exhaust pipe a little if the valve is too tall, as an example. No big thing.
 
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Old 08-08-14, 04:33 PM
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Well brought it with me. The guy at Grainger ended up finding one that would work if we got a 3/8ths to 1/2" adapter. It was a little bit more money that I was hoping to spend though, the valve was 23 dollars and the adapter was like 3 dollars. I decided to wait til next week get it.

Came home and cleaned up the existing valve as best as i could and put it back together just to see what happens.

The compressor is working like it did when it was new. When the tank gets filled and the motor stops, I hear the quick hiss of the air in the line bleeding off and no more leaks. The tank stays pressurized. I then let the air out of the compressor so it dropped to 80psi and it started up perfectly. I then filled up the car tires and the compressor cycled at least 5 times and it fired up each time it got to 80psi. So I guess the valve was the problem.

I'm going to go ahead and buy the new check valve next week but at least I know that the old valve is the problem.
 
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