My Sangborn 2 stage pump with 6.5 hp GE motor pumps up to 175 psi and holds. When I bleed air off, motor starts at around 120 psi but shuts down. I replaced both capacitors, the 30 amp circuit breaker and then went from a 30 amp to a 40 amp and it continues. I've taken the motor to a repair shop and he repaired a part of switch and said it was fine. I've took it back when it continued and he put it on a load and said it was still fine. I've removed the pump head and found of the 10 reed valves, 6 of them can be moved from side to side slightly but I don't know if it is causing a leak and ultimately an added load on the motor when starting. They are dirty at the edges but don't know if it's preventing them from closing completely. I don't think it's dirty enough for that. I did find 4 valves with cracks from about 1/4 " to 3/8" wide but they don't go completely through the plate. I'm at my end of things to test. On a final point, the motor draws 23.3 amps when pumping up. When the it shuts off and then attempts to re start the motor draws around 107.3 amps for around 4 seconds and then shuts off. The people from Regal Beloit who made the motor for GE say this is normal but after the short 4 seconds it should go to 20 plus amps and continue to run until it satisfies the pressure switch. Now it trips the thermal switch on the motor and shuts off. Is it time to replace the pump or repair it? I've got 2 vehicles to paint and lots of parts to blast and I'm getting tired of messing with this. Got any ideas?
Thanks, Ed

Of everyone who read my post you're the only one to reply so thanks. The pump is a model B5900 by Sangborn and the compressor was mfg by Air Hawk sold by a Big Box store in Ohio in 1993. The tank has been empied several times and I don't allow water to accumulate in it. I'm good about draining it. I pumped up the tank with another compressor to 140 PSI and with the tube from pump head to tank removed was able to spray soap water all over and nothing was leaking. I've orderred another valve just in case I'm not seeing something or if the leak is super slow. I must admit I don't think this is it. I've removed the air cleaner for some of my testing. The original was a foam and oil from the pump moving backwards attached the filter elament so I've made another filter assy that uses a large lawn mower air cleaner. As for the head, today I'll spray it with brake cleaner and make sure nothing is on it to cause a valve to stay open. Cranksase breather puts out a puff of air from the holes on a rythematic cycle when the pump is running so it's open. I'll admit I don't think th ebelt has been tight enough and when I get it together I'll look at that again. When it failed the first time the belt was tight but at that time a part in the motor had failed and has been since repaired. Both pullys are allighed perfectly. I use a square to set it up each time I remove the motor. By now I'm pretty good at it. The pump moves very freely. With the head off I can push the pistons down. Power is direct from the fuse panel in my shop. Yesterday I ordered a check valve and gasket set from Compressor Air Solution in St Louis. A good guy with lots of knowledge of this unit and not a wise guy who knows everything. Although He is plenty smart with this compressor. I've looked at another pump from China from Harbor Ft and one from Home Depot but the one at Home Depot is not available and don't know when it will be. Said to run 35 % cooler with 3rd cylinder and only a single stage. They also claim to use less energy and with so many stars and positive reports no one wonder it's out of stock. I'll post what I find out.
Once again, Thanks for your comments. No wounder you guys are so popular with high marks. You help people like me do something I'm not an expert at. That's how companies get a positive reputation an stay ahead of competation.

Well, I'm ready to pull every bit of my hair out. I've tried everything I can think of as well as the things you suggested. The motor repair man is really knowledgeable and I trust him. However, the added testing he did was to connect a 10 KW belt driven generator to the motor and run it. I can see how this is a load. But to duplicate the entire situation as best as possible, the motor must be hot since it's just pumped up the 80 gal tank to 175 PSI. Then it has to re start even though there is no pressure on the pump, that's sort of momentary because when it gets up to speed, it has to compress air to put into the tank and that is a different load on the motor than when it was starting the generator over and over. I think it's a different load because it's pushing against the tank pressure. In short, I'm convinced the problem is the motor. Unfortunately, my wife feels if the motor repair shop says the motor is OK than it's OK. Of course she knows about as much about this compressor or anything else mechanical as I do about brain surgery.
I feel now my only way out of this is to buy a new motor of good quality. Then if it with no problems, things are OK. If it does the same thing, only the pump is left as a possible problem and I'm pretty sure (not positive at this point) nothing could go wrong with the tank.
Bewildered, Ed