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Air compressor problem |
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target 
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Joined: Jan/20/2010 Status: Offline Points: 1353 |
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 Topic: Air compressor problemPosted: Oct/13/2011 at 11:42am |
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5hp, 60 gallon twin cylinder single stage. Pump went bad. Bought a new pump also rated at 5hp. Does pump more air than the previous pump. Electric motor on the compressor has a 4.5" pulley. Problem is that when it comes on it will pump to capacity and shut off. Then will not restart because the motor got too hot and tripped the reset. Will not restart until it cools, then does the same thing.
Question is that the new pump is rated for either a 4.5" pulley or a 2.75" pulley. I know that if I change the pulley it will slow down the pump and will deliver less cfm. Will the smaller pulley put less load on the motor and possibly correct the problem? Any ideas? It is 220 volt. |
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tyrodtom
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Joined: Sep/14/2007 Location: Virginia Status: Offline Points: 6214 |
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Posted: Oct/13/2011 at 12:21pm |
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Is your new compressor rated at the same hp and scfm as the old compressor ?
Most light to medium duty comprssors are rated at their starting hp, not their constant running HP. When you look at their amp. rating most of what are called 5 hp compressors are actually 2 1/2 to 3 hp. The electric motor can only substain a 5 hp output for a short time without overheating. If your compressor pump requires a 5hp motor for full pressure you probaly need a more powerful motor, or you can put a bigger pulley on the compressor pump and not run it at it's rated rpm, which your current electric motor might be able to cope with. Most compressors i've seen has quite a bit bigger pulley on the pump, than the motor. Like 2-3 times bigger.
Edited by tyrodtom - Oct/13/2011 at 12:25pm |
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66 American SW, 66 American 2dr, 82 J10, 70 Hornet, Pound, Va.
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billd
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Posted: Oct/13/2011 at 12:38pm |
There may be your answer - to get more output, you need more "input" - more load on the motor to get more air out. Tom is probably on the right path. |
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mstrcrftr
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Joined: Jul/12/2010 Location: houston Status: Offline Points: 2066 |
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Posted: Oct/13/2011 at 4:32pm |
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i had this exact same issue with my compressor a couple of years ago. replaced the compressor head with a real 5hp then the motor burned up.. turns out the motors are not really 5hp they are like 2 1/2 with a capacitor start. i ended up getting a real 5hp motor, believe it or not, cheaper than the original motor. it now runs nonstop and never gets warm
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FuzzFace2
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Joined: Jul/05/2007 Location: Angier, N.C. Status: Offline Points: 10356 |
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Posted: Oct/14/2011 at 11:32am |
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Not a motor or pump replacement but had my small Craftsman compressor not want to re-start after it pumped up and shut down kept tripping the motor over load. What I found was the motor was starting under a load! There is a check valve between pump & tank so when the unit re-starts it is not pumping against the tank PSI. This valve went bad on mine, replaced and all is good. How did I find this you ask? The garage was 40*f and after running the motor was not that hot to touch to trip the over load and when it tried to start motor would hardly turn the pump. I tried to turn the pump by hand and had a hard time. Drain tank so no PSI and I could turn pump. Saw something between out put line & tank so I pulled it apart and the check valve came out in pieces. Big compressors have un-loaders so the pumps do not start under pressor. Just something to look into also Dave ---- |
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tyrodtom
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Posted: Oct/14/2011 at 11:38am |
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When your pump gets up to pressure and shuts off, you'll hear a loud hiss. That's the unloader check valve working. If you don't hear that hiss, it's jambed. I've never seen a compressor without one.
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66 American SW, 66 American 2dr, 82 J10, 70 Hornet, Pound, Va.
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gd5052
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Joined: Jun/16/2011 Location: Illinois Status: Offline Points: 108 |
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Posted: Nov/02/2011 at 8:21am |
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Had the same situation a few years back, Replaced original pump with a 2- stage and after running a few minutes would kick out motor, had to reset switch, Replaced pulley on motor with a smaller one and haven't had a problem since.
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4.0 Rambler
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Posted: Nov/24/2011 at 1:46pm |
If the Pressure is not relieved between the pump and the tank you will have the problem you are experiencing. There is typically a check valve between the pump and the tank. Some units have a in tank check valve. |
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target wrote: