2 stage air compressor

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Old 01-13-12, 11:24 PM
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Unhappy 2 stage air compressor

My 2 stage air comp. Has ran fine until last week the electric motor just hums i can push on the pulley & it will run slugish up & down in rpm . I took the belts off and moved the comp. Pulley by hand it has air pressure givn me alot of resistance,then i will get past it then it will turn a little easier and so on . I hooked up a new motor and it will run but it pulls 80 amps when the nameplate is 20 amps .it also pulls my voltage down because of this load.i am an electrician its not the motor nor the start and run caps. Does anyone have any pointers ??
 
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Old 01-14-12, 04:23 AM
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Thumbs up Welcome to our forums!

You don't say if the motor appears to run fine when the belt is removed.
The first thing I would try is to make sure the tank is drained of air and then disconnect the air line from the compressor to the receiver tank and run it to see what happens.
If it runs ok then the check valve could be plugged or bad.

It would also be helpful if we had more info like the make and model and how old it is.
A picture of it uploaded to a free host like Photo Bucket with a link could also be useful.
 
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Old 01-14-12, 12:13 PM
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This air compressor is a champion rv15a . The motor is brand new & it does run fine . When i run the air comp. Rite now it pulls the motor down then i hafta shut it down because i am afraid of burning up the new motor. It does run but it wont run long when there is so much of a load on it. My amp probe reads 87 amps when the nameplate current is 20 amps @230 volts.when i turn the compressor pulley by hand it will turn approx. 1-turn then it builds air pressure & gets hard for a little bit then gets easier again, its almost like the air pressure is giving me this hard resistance. Thanks, fatbuoy
 
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Old 01-14-12, 12:28 PM
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Re-read my previous post and let us know how it goes.
 
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Old 01-14-12, 12:53 PM
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Several possibilities including stuck discharge valves. Disconnect the discharge piping to the tank AND the intercooler piping between the high and low pressure cylinders and see if it then turns over easily by hand. If not, it is a mechanical problem, either broken rings or seized bearings or worse.
 
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Old 01-14-12, 04:52 PM
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Furd i will try what you have recommended. I dont think it is a serious problem,do you know if these units have problems out of the reed valves ? My comp. Has purred like a kitten for years. I have taken very good care of this unit,making sure to keep a clean air filter & oil .whenever you have a good functioning 2-stage air comp. Should the load put to the motor be of a constant resistance ? In other words if i were to take the belt off and turn the comp. Pulley by hand should the resistance i get on pushing the pulley be constant or will it be variable ??
 
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Old 01-14-12, 07:27 PM
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I don't have a lot of experience with small compressors, and by small I mean under 250 horsepower. I will say that turning a piston-type compressor by hand the resistance should slowly increase as the low pressure piston approaches dead center and then release somewhat and repeat with the high pressure piston approaching dead center and then all over again, sort of a push easy then hard cycle. This will be more apparent with your thumb held over the discharge port. With all the tubing disconnected it should turn quite easily.

If it does turn hard with all the tubing disconnected then the next step is to remove the cylinder heads and try turning. If still hard then it is broken ring(s) or bearings.
 
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Old 01-17-12, 07:39 AM
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Could be the belt(s) are too tight or motor pulley misaligned with pump flywheel. Or maybe you're spinning it to fast? Strange that you can rotate it by hand but not with the motor, you sure 20 amps is enough to move it?
 
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Old 01-17-12, 07:32 PM
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Mark, that was the problem i didnt think that aligning driver & driven was so crutial but it is . At first i just alighned em by site but i took a good straight edge & alighned them good & made sure my force-deflection on my belts was rite. It made all the difference. I would not have thought that having the belts to tight would matter that much but it does. It came from the factory with a 5 hp 1-phase 230 volt motor. When u dont have everything lined up just rite it makes a big difference. My motor was drawing 87 amps with every thing done wrong , with driver & driven pulleys alighned properly & proper tension on my v-belts it is pulling 21 amps which is within the correct ampacity for my motor.
 
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Old 01-18-12, 06:44 AM
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That was cheap enough to fix Glad it worked out for you.
 
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Old 01-18-12, 06:35 PM
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I am new to this web-site & realy dont know how every thing works yet. Once i have got alot of replies and fixed my problem what do i do ? Do i delete this forum ? If so how ? I appreciate all the input guys !!! I hope i can b of help to people that i can by this website . I think this site is awesome !! I have a master electrician license in the city of knoxville & the state of tn. If i can help anyone i will b glad to do so. Thanks again guys !! Fatbuoy
 
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Old 01-19-12, 07:24 AM
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