Comperssor dying? Help diagnose...

[Sam Shank]

I have a craftsman 25gal "5hp" that is about 10 years old. It's direct drive oil-less, and I'm pretty sure it's made by devilbiss or CH. Can't recall right now.

When I turn it on, in the for the first time of the day, it works fine.

When it needs to cycle on when in heavy use, the motor get a few cranks out of the compressor pump, and then stalls out. The motor makes a humming noise and I immediately switch it off so it doesn't burn out.

Does it sounds like tha cap starters are going or is it the whole motor, or do you think it could be the compressor pump?

Any and all suggestions appreciated.

Thanks, Sam

[tod evans]

check your unloaders....02 tod

[Steve Clardy]

Yep. Unloader, check valve in tank isn't holding the tank pressure back from the compressor.

[Matt Meiser]

Could be the check valve between the tank and the pump too. That's what was wrong with the compressor my dad gave me. The check valve keeps the pressure from getting from the tank to the pump after the pump shuts off. The unloader drains the pressure trapped between the pump and the check valve.

[Sam Shank]

Thanks for the info.

How do I find out if it's the check valve or the unloader. I can't seem to think of a way to test.

[Steve Clardy]

Un hook elec.
Remove copper line from compressor head to tank. Check valve is between that line and tank.
If its leaking air there, check valve is bad.
Unloader valve should have a manual pull ring on it to release pressure. See if it releases air when you pull the ring.

[Sam Shank]

I thought the pressure release ring was on the emergency release valve.

Makes sense that it would leak backwards the line is unscrewed after the check valve.

[Steve Clardy]

Oops. Had to go look. Unloader valve [no ring] is next to emergency valve with ring. Sorry about that.