60 gal air compressor bogs down


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Old 09-24-21, 11:03 AM
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60 gal air compressor bogs down

Hi Everyone!

I have a 2005, 60 gal., single stage, 7ph (peak), belt drive, Sanborn air compressor which is wired directly to the breaker box by a short piece of romex wire. It has performed well for 16 years until recently, receiving regular but modest use. All parts are original. Model LA7006056.

In recent months it performed fine at start up but then the motor slows down and has a lower, labored sound when the pressure is roughly 60psi, although the compressor did still go to its usual maximum (120psi or so) but perhaps more slowly than when the compressor was newer. Then last Saturday, it began sounding labored when the pressure built up to 30psi or so, and did not go beyond about 70 psi, although it continued to run while sounding labored.

If I open the tank’s petcock at the bottom of the tank, it runs fine and continues pumping air into the tank (which then leaks out the open petcock).

Help please.
 
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Old 09-24-21, 11:47 AM
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Have you inspected the compressor? Does it have oil? Is it seizing up?
 
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Old 09-24-21, 11:54 AM
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Thank you for your reply, Pilot! At all times, there as been full-synthetic oil up to the proper place in the sight glass. The motor and pump do not seem to be seizing up, since they seem to run fine with the petcock open.
 
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Old 09-24-21, 11:59 AM
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Could be the unloader valve stuck open... but if the motor is changing pitch, might be more serious problems.
 
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Old 09-24-21, 12:03 PM
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Hmmm. Thank you, XSleeper! One further input I can add is that it does not leak air, if that is a consequence of an unloader valve stuck open. So, for example, if I turn on the compressor and fill it with 30 psi and then turn it off, the air does not leak out. Does that clue help? Thank you again!
 
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Old 09-24-21, 12:14 PM
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Check voltage at motor terminals (assume 240 vac). If voltage ok, need to check that all air connections are tight. If all connections tight, need to check if belt tension is correct. If belt tension is correct, need to check the seals on the compressor piston.
 
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Old 09-24-21, 12:18 PM
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Ok, b-bob. Thanks. The 240AC is confirmed. The connections are tight. I will have to check the belt. No seals are leaking audibly, although I am not sure if that is the same thing.
 
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Old 09-24-21, 07:16 PM
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Sanborn or Coleman powermate ?

A clog/obstruction in the air feed line between the compressor and tank or a restrictive check valve could cause that problem but both are pretty rare.

You are describing a tired motor. I might be tempted to replace the run capacitor.
Leaks won't cause the motor to slow down.
 
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Old 09-30-21, 01:30 PM
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Thanks for your help, PJ! In the absence of another idea, I will replace the run capacitor.
 
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Old 10-01-21, 08:34 AM
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If it was the capacitor it would have trouble starting up, it does nothing once it's running.
My guess would be a leaking check valve that's mounted to the tank, or the valve plate assembly.
If one of those is leaking it allows pressure to build up on the back side of the reed valve.
Part # 11
https://www.ereplacementparts.com/po...47_117233.html
 
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Old 10-01-21, 08:50 AM
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Hmmm. Thank you for your input, Joe. One thing I should mention, though, is that it has a start capacitor and also a run capacitor. Does that change your thought, Joe? In other words, PJ was suggesting replacing the run capacitor, not the start capacitor. Is that right, PJ?

Thank you for your further thoughts, Guys!
 
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Old 10-01-21, 03:37 PM
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PJ is correct. The start capacitor is removed from the motor auxiliary winding at around 75 percent rated RPM if centrifugal switch is working properly. The run capacitor remains connected to the motor auxiliary winding to maintain running torque.
 
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Old 10-11-21, 08:30 AM
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Thanks, Beezlebob! I will report back after changing the run capacitor.
 
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Old 10-19-21, 07:28 AM
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Update

Hi Everyone!

Update: I replaced both the run capacitor and the start capacitor and it did not help. Any ideas guys?

Original post below:

I have a 2005, 60 gal., single stage, 7ph (peak), belt drive, Sanborn air compressor which is wired directly to the breaker box by a short piece of romex wire. It has performed well for 16 years until recently, receiving regular but modest use. All parts are original. Model LA7006056.

In recent months it performed fine at start up but then the motor slows down and has a lower, labored sound when the pressure is roughly 60psi, although the compressor did still go to its usual maximum (120psi or so) but perhaps more slowly than when the compressor was newer. Then last Saturday, it began sounding labored when the pressure built up to 30psi or so, and did not go beyond about 70 psi, although it continued to run while sounding labored.

If I open the tank’s petcock at the bottom of the tank, it runs fine and continues pumping air into the tank (which then leaks out the open petcock).

Help please.
 
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Old 10-19-21, 09:46 AM
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would probably pull the compressor top valve plate and look at them they may be worn out.
 
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Old 10-19-21, 09:58 AM
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Thank you for your reply, Alan! What are you recommending? That I open the compressor at the place labeled #15?



 
 

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