Posted: 10/20/2014 12:51:09 PM EDT
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I have a 110V 20 gallon air compressor I inherited from my wife's grandfather, and I am having trouble getting it to run. It has a 2 hp electric motor with both a run capacitor and a start capacitor.
If the tank is empty, it starts up just fine, and will fill the entire tank until the cycle is over (~140 psi) If the tank has anything over 20 psi in it, the motor really bogs down (lights dim and RPMs are not that high) and the circuit trips (it is on a 20 amp circuit already). I tried turning the compressor wheel by hand, and if there is pressure in the tank already, it is REALLY hard to rotate. If the tank is empty, it is easy to rotate. So obviously (correct me if I am wrong), the reason the motor is bogged down, is that the pressure from the tank is making the pump too difficult for the motor to turn, causing it to draw too many amps, and tripping the breaker. My initial thought was that it might be a run or start capacitor problem, but because the motor doesn't seem to have any issues as long as it is under load, I am thinking it might be something different. But, maybe I am wrong. Perhaps the start capacitor is shot, meaning that the motor does not spin fast enough to trip the centrifugal switch that activates the run capacitor. Is it a capacitor problem? Is it a check-valve problem? Is it a pressure/switch problem? |
| No expert, but I'm willing to wager on a check valve: http://www.air-compressor-guide.com/learn/air-compressor-parts/air-compressor-check-valve/ |
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check and see if it has an unloader on it. if not suspect a exhaust checkvalve is bad and its holding tank pressure on the piston in the compressor. the unloader does the same thing, something is allowing tank pressure inside the compressor head...... What is an unloader, what does it look like, and where is it located? |
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What is an unloader, what does it look like, and where is it located? Quoted:
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check and see if it has an unloader on it. if not suspect a exhaust checkvalve is bad and its holding tank pressure on the piston in the compressor. the unloader does the same thing, something is allowing tank pressure inside the compressor head...... What is an unloader, what does it look like, and where is it located? heres an article which should get you up to speed..on electric compressors they are normally part of the electric pressure control switch.. http://www.about-air-compressors.com/unloadervalve.html |
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No expert, but I'm willing to wager on a check valve: http://www.air-compressor-guide.com/learn/air-compressor-parts/air-compressor-check-valve/ I'm going with this. |
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I'm going with this. Quoted:
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No expert, but I'm willing to wager on a check valve: http://www.air-compressor-guide.com/learn/air-compressor-parts/air-compressor-check-valve/ I'm going with this. I disconnected the compressor pump off of the check valve, and it turns freely, and no air is flowing from the tank to the pump, so the 1-way valve appears to be still working correctly. The unloader valve can be heard hissing momentarily (as it should) when the pumping cycle is over. But I am not going to discount that just yet. Taken from an link posted above: Compressed air that is trapped over the piston when the compressor shuts off will be evacuated to atmosphere through the unloader valve, to prevent that compressed air pressure from adding load to the start up of the compressor motor, when the pressure switch again calls for air. For example, the last time you did a sit-up, you may have folded your arms over your chest, or if you are particularly masochistic : - ) , even held a weight to your chest. What you were doing is increasing the load against which your muscles have to work to effect the sit up. Compressed air, captured in the cylinder after the compressor shuts off, would increase the load against which the electric motor would have to work. It may increase the load too much, and the motor may fail to start, or it may pull too many amps and fry a fuse or pop a breaker in the panel. When the compressor shuts off, the unloader valve operates, it unloads the trapped air to atmosphere, and that problem is solved Is there a way for the unloader valve to still function properly as the cut-off switch for the power supply, but still not function properly during start-up (i.e. traps too much pressure at the beginning, hindering motor movement)? I disconnected the unloader valve, and the motor and compressor both turn on and start perfectly without any negative side effects. |
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I found some other people with the same problems, but no answers:
http://www.about-air-compressors.com/blows-breaker-only-when-starting-with-partia-pressure-in-tank.html |
| Most likely it has a exhaust check valve seeping back into the chamber..unloader unloads after it shuts off, then over a small amount of time the chamber refills with pressure due to a leaking valve...let compressor build some pressure, let it sit till it won't start on its own, then cycle the unloader and see if it has pressure on it..... |