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Compressor creating too much load

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Jim

02-13-2002 10:13:01




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I have a 3 hp compressor (Sandborn?) with cast iron pump. It took out my motor last week (burned up the windings) so I put a new motor on. It seems to labor too hard below 30 lbs. The motor winds up to speed but can't maintain the needed rpms and clicks then starts over. At around 40 lbs the motor is not able to get to the "run" rpms and at 45 lbs makes the lights in the garage go dim and evenutally pops the circuit breaker! Plenty of oil in compressor. What would cause the compressor assembly to create an undo load at the motor?

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Jake

02-15-2002 21:16:12




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 Re: Compressor creating too much load - help - in reply to Jim, 02-13-2002 10:13:01  
Has youre new motor have both start and run capacitors, The lights dimming indicat that the motor is not turning fast enough to disengage the starting winding switch and a sure way to burn up another motor. Also are the pulleys correct, small on motor and large on the compressor. Start and run caps are important on a compressor due to the starting loads.



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Jim

02-15-2002 19:31:25




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 Re: Compressor creating too much load - help - in reply to Jim, 02-13-2002 10:13:01  
Interesting progress made: I took the check valve off at the tank side of the system (little plastic ball with a spring behind it) and inspected, no problems that I could see. I then tried "warming up" they system as suggested by running with the pipe off for a minute until the pump felt a little warm. I then put the pipe on and started it up from 0 psi. It ran great... for aobut 30 seconds. Then at about 45 psi, the motor almost stopped (I turned it off) in about 5 seconds.

It acts as if one of the valves us getting stuck at some pressure. I have not checked out the pump yet but might get a chance to take it apart this weekend.

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Dave M

02-14-2002 07:18:48




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 Re: Compressor creating too much load - help - in reply to Jim, 02-13-2002 10:13:01  
I once rented an oil-filled compressor that was full of 30 wt motor oil. That worked fine when the compressor was warm, but at 20 degrees F the motor would blow the breaker every time. There was a lighter oil spec'ed for use at cold temps.
I warmed up the compressor in the garage, put a long extension cord on it and kept it running while I wheeled it to the job. As long as I kept it warm by running it was OK.

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Kevin

02-14-2002 14:04:47




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 Re: Re: Compressor creating too much load - help - in reply to Dave M, 02-14-2002 07:18:48  
Yep, I agree with this one. Cold oil will never let you spool up! When my 2 hp is cold, I hold onto the pressure relief valve for a few minutes never letting the pressure get above 20 lbs. Once oil warms up, I'm good for the rest of the day.



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Jim

02-14-2002 06:53:14




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 Re: Compressor creating too much load - help - in reply to Jim, 02-13-2002 10:13:01  
Thanks for all the help. 1. Oil is OK 2. No new loads on this dedicated circuit, voltage fine 3. I do hear a pisssss s sound when I turn off the motor for about 3 seconds or so 4. Motor says its a 3600 rmp unit, only a 110 volt unit (other spades are not present for 220 connection) 5. runs nice and fast when I disconnect the big tube (aothough a bit of oil came out at one time!) and motor does not cycle (I assume its basically running like this because of no load)

Question: Where are the valves located in the system (I assume in the compressor head and maybe one at the base of the tank?) and where do I get parts. This tool board is great! T

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Roger

02-14-2002 17:13:47




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 Re: Re: Compressor creating too much load - help - in reply to Jim, 02-14-2002 06:53:14  
Check the RPM rating of your old motor. Make sure it is the same. Remove the check valve in your tank and see if the little puck is seized shut or carbon fouled. It is the valve that the discharge line screws into before entering the tank. Check your intake and make sure it is not plugged with a collapsed filter.



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T_Bone

02-14-2002 12:33:43




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 Re: Re: Compressor creating too much load - help - in reply to Jim, 02-14-2002 06:53:14  
Hi Jim,

When replacing a compressor motor you need to pay close attention to the motor RPM as well as the AMP rating of the motor your replacing along with the pulley diameter. The HP rating has little to do with the new motor.

You have some addtional SERIOUS problems with your electrical feed to the compressor. It's telling you that if you don't correct the problems your shop may burn down.

This is not the place to learn how to install or trouble shoot the problems you describe and is beyond your capabilitys from reading your posts.

I say this not to be demeaning but to you, but insure your and your familys life well being.

T_Bone

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Roger

02-13-2002 16:29:07




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 Re: Compressor creating too much load - help - in reply to Jim, 02-13-2002 10:13:01  
Did you replace a 1700 RPM motor with a 3500 RPM motor by any chance? Is you compressor unloading after shutdown (that brief hiss of air for the first few seconds after shutdown)? If your valves are bad you should have a relief valve popping on the compressor pump (if it is a two stage and it is fitted with an interstage relief valve). Try running the pump with the discharge line removed and check the airflow. In-tank check valves are commonly carbon-fouled, escpecially if the compressor is running on motor oil. It may be seized shut, or there may be the remains of a valve spring in there. Discharge lines have also been known to choke off with carbon on old pumps running motor oil.

Good luck.

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chris mf35

02-13-2002 16:08:50




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 Re: Compressor creating too much load - help - in reply to Jim, 02-13-2002 10:13:01  
one of two things: first make sure the motor is connectect for the correct volatage (if it's a dual voltage motor) second (most likly) the valve or check valve that prevents the air in the tank from returning into the cyclinder is bad. rebuilding the head (new valves) is a common maitance on compressors, not expencive or hard.
good luck chris mf35



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old bones

02-13-2002 15:44:09




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 Re: Compressor creating too much load - help - in reply to Jim, 02-13-2002 10:13:01  
check a few things. first, is the wiring heavy enough for the amp draw and distance from the breaker box? have you added anything else to that circuit that would be drawing add'l amperage? are your connections throughout the circuit tight? is the pressure in line let-off valve on the compressor working right? are the valves in the head(s) working right? have you checked the voltage at the outlet to make sure you aren't low-volting the motor? if your lights are pulling down dim, it sounds like you may have at least some kind of circuit trouble ( i.e. too big of breaker for the wire, too small circuit for the load, etc). depending on where you are, most (but not always) lights are hooked to a 15 amp circuit with 14-2 wire. if that's the case, 14-2 wire is not heavy enough. should be at least 12-2 wire, which will handle a 20 amp breaker. i have a smaller compressor like yours that was tripping the breaker on me (60 feet from the breaker box), so i put in a dedicated 20 amp circuit with 10-2 (because of the distance) wire just for the compressor and ended my trouble. maybe there is a real electrician out there with a better idea, but this worked for me after checking out the things i mentioned above.

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olddog

02-14-2002 01:44:53




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 Re: Re: Compressor creating too much load - help - in reply to old bones, 02-13-2002 15:44:09  
What burnt out the first motor? Chances are probably not electrical but mechanical. Check the things on the comp itself. See previous posts.
Any oil in it? Oil gone to goo? Something freezing?



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