Air Compressor won't reach shut off pressure

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Old 06-05-10, 02:21 PM
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Air Compressor won't reach shut off pressure

I have a IR SS5L5 air compressor (single stage 5hp). I drained the air down to ~10 - 20 psi to drian the condensate out and now when I turn it back on, it won't hit the shut off pressure (135psi) it just runs and runs. I checked the intake and feel suction and removed the output line to tank and feel pressure there (so I know the motor is at least working, whether it is making enough pressure, I don't know).

I checked both pressure relief valves and they seem to be working correctly and the check valve I believe is working correctly due to the pressure in the tank remains constant.

When the compressor is running I hear a hissing sound from the pressure switch. I think this is coming from the unloader valve which is part of the pressure switch. I neve paid attention to this in the past so it may have always done this but I am not sure.

When the compressor is not running, I do not hear any air leaking.
 
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Old 06-06-10, 03:40 AM
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leaky unloader

This may or may not be why the compressor won't shut off at the rated pressure. But it is a problem. Check the compression fitting at the pressure switch side of the unloader line to see if it's loose and maybe tighten it. If that does not work, change the pressure switch, hopefully that'll take care of it.
 
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Old 06-06-10, 02:44 PM
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Unloader Valve Fixed

I believe I have fixed the unloader valve. Their is plunger in it that was not being allowed to seal off due to the pressure switch. The switch is working now allowing the plate that strikes the plunger to swing out of the way while the compressor is running. So it is now sealing off the unloader valve and then when I shut off the compressor (manually) the plate strikes the plunger and releases the air between the motor and the check valve.

I also took some soapy water and checked the fittings and did not see any major leaks.

The compressor still will just run and not hit the shut off pressure of 135psi. It will only get to around 75psi. Any ideas for next steps? Should I still replace the switch?
 
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Old 06-06-10, 07:15 PM
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Make sure the belt isn't slipping at the higher pressure. Next would be to check the valves.
 
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Old 06-07-10, 07:01 AM
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Ditto on furd's suggestion about the valve. Pop the head off and take a look at the valves. Look for any that are not tight against the valve plate. They may be bent or cruddy. Or the plate may be out of flat. A little piece of carbon stuck between an intake valve and its seat will throw everything off. So clean well and replace or fix any damaged parts (and the head gasket). Good luck.
 
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Old 06-07-10, 08:17 PM
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Gaskets

I talked with a service rep. today on my compressor as it seems it is barely in warranty. They are going to send me the head and valve gasket that goes between the valve asm and cylinder. The rep. said that most of the time with that compressor the lower gasket doesn't seal between the cylinders. So when I have the head off I'll look at the valves as well. I'll let you know what I find.
 
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Old 06-12-10, 03:08 PM
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Up and Running

I received my gaskets and took it apart this morning. I disassembled the valves and cleaned them up and replaced the gaskets. Everything seems to be working fine now. As the IR rep. stated, the lower gasket was leaking between the valves (between the intake and exhaust). They recommend checking the head bolts every so often and re-tighten if necessary.
 
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