Compressor help

[Tim2203]

I have a mako (older) with 725 hours ,500 hour service was done and I have had no problems until suddenly not making pressure on the 4th stage, stage 1,2,3, pressures all normal . It will very slowly build to 3000 psi but it takes @6 minutes to just fill the 2 whips and it's a 10 cfm machine.Belt looks and feels fine,no leaks that i can find.Could it be a valve in the 4 th stage or maybe carbon holding valve open .Anything else I should check. Thanks .

 

[Wookie]

I'd certainly start with valves, unless you have reason to suspect that there is something wrong with the piston. More likely is an auto drain valve leaking. Take the cover plate off of the auto drain (should be 8 cap screws) and pull the auto drain valves out. inspect the o-rings on the valves, and inspect the drain valve block for pitting or worn out anodizing.

 

[Tim2203]

Thanks , I did find a small leak on the auto drain, replaced gasket on block but did not inspect o-rings on the valves. i'll try that next.

 

[Tim2203]

Thanks Wookie,you were spot on with the auto drain new pistons on the way. The seats on the pistons are bad and the air was passing out the auto drain into the muffler making it hard to hear and find .A much easier fix then the valves.