U S Air model MK 783 compressor won't build pressure

by Bruce Johnston
(Tamarack Mn)

I have a very old U S Air model MK 783 compressor in my shop. The intake suction seems OK but the output pressure is very weak.

I thought that a new set of rings would boost the output so I replaced them but that didn't help.

Now I'm thinking that it possibly could be the valves. It has four brass valves (two intake and two output) that I can't tell if they are working properly.

I tried cleaning them in a parts washer but that didn't seem to help much. Also, I was wondering if cylinders in compressors can glaze like car engine cylinders and not put out adequate pressure.

I don't know if I should keep trying to fix it or give up. I already have over $100.00 invested in the rings and don't know if its worth continuing to try to fix.

It's a great compressor when its working properly. Any help would be appreciated.
Here is a link to a diagram. It isn't exactly the same though.

www.collinsequip.com/Air%20Compressor/mk%20parts%20dia.pdf

Thanks.

__________________
Bill says....

Bruce, I am not at all familiar with the compressor. Therefore, I don't know if it a piston type, or some other type of air compressor.

Certainly, the intake valve, and compression valve is a potential source for your compressors inability to build pressure.

So, too, could a gasket between high pressure and low pressure inside the pump.

You fixed the piston seals, so it isn't that.

Does a cylinder glaze? I would expect so, but the heat in a compressor is nothing like that in an internal combustion engine, so I wouldn't be concerned about that if it were mine.

Only you can decide if you have spent enough, can't help you there. :-)

Anyway, perhaps another visitor has a comment or two for you on this problem, too?

Cheers,

Bill