The United States Air Compressor Co.'' brand, model MK 6611 - do i need 2 unloader valves?

by James

First off i have never torn into an air compressor before this one. But now in saying that this a ''The United States Air Compressor Co.'' brand, model MK 6611 with a serial no. of 35634 MK. And on the pump itself says NO.44927 MK.


Picked this up at an auction with no info on if. I quickly realize the motor was bad so replaced it with a modern one of the same specks. But before firing it up i wanted to see if there was any noticeable damage.

Pulled the covers off the sides of the housing and there was a part that looked like a counter weight and then a spring with maybe a bronze end on it.

Took the cover off the end opposite of the flywheel and that's where i found the remaining parts to a totally destroyed piece that looks to be an auto mechanism to press and release an unloader valve once compressor has shut off or at least dropped below a certain r.p.m.

At a running r.p.m. the 4 weights each have an ear on them and as they spin outwards the ears will press the bronze piece back in and therefor shuts the unloader valve back off.

I would like to replace the part with an original if that even possible but i doubt it is purchase-able so there for i would like to know if there is a way to safely bypass that unloader valve because i believe that this unit has two unloader valves.

Any help or info is appreciated as i wasn't able to find much on this old girl.

Other than that one part, everything seems to be in good shape especially for its age. I'm sorry but it wont let me send any pictures through this.

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Comments for The United States Air Compressor Co.'' brand, model MK 6611 - do i need 2 unloader valves?

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Oct 29, 2018
MK 6611
by: Doug in s.d.ca.

Probably not.

Please go ahead and post your pix as described by Bill, and we'll see...

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