Air compressor diagnosis

Thank you to everyone who responded to my last post. I got a moment to do some testing this AM. It's not building oil pressure. It is full of oil. I runs nice and quiet so perhaps it's still in decent shape? In diagnosing this I noted the oil pressure gauge doesn't move--I don't have a spare so I removed the gauge and turned it on and got no oil in the line to the gauge. Next I removed the air line from the tank to the square box thingie that controls the flow of air to the unloaders. I turned the compressor on and put my finger over the line from the tank (why waste air) and it continued past 20psi up to 50 and was still pumping. I disassembled the square box thingie and everything inside looks great--diaphram etc.

So how to fix it not building oil pressure--ideas? I can't justify pulling down the whole pump but I can for instance flush through it with gas/diesel/carb-cleaner via the tube to the oil pressure gauge. I would then drain and replace the oil.

More advise would be appreciated. Again, it was built in 1968 from the plate on the tank (60 gallon to answer someone's question). It'd be nice if I could clean or adjust something and it start working but if it requires ordering parts it's probably not worth fixing--IMHO.
 
I'm not a mechanic but I did stay at a Holiday Inn Express last night. :)

This should be the oil pump. Off hand looks good--but obviously isn't working. Hummmmm. Still want ideas but my flush it out plan looks better now that I'm deeper in.
36981.jpg
 
From looking at the picture, the line from the bottom of the crankcase appears to be the suction line for the oil pump. Make sure it is clear. There may be a strainer inside, can you see it through the oil filler hole?

Looks pretty simple, it should pump if it's getting oil. Might try priming it before connecting the output line.

Did you check the rotation direction?
 
I agree with Steve@advance, make sure motor rotation is correct.
Are all four vanes extending?
Is the inside of the pump cylinder smooth, no groves?
The compressor is worth fixing. Once it is fixed it will out last
any comp. of equal size that you find at the box stores.

Steve A W
 
Pack the oil pump with Vaseline, put the cover back on, leave the suction and discharge lines off. Start the pump, put your finger over the suction port and see if it's sucking. You might want to kind of sneak up on the finger over the port; it might be really sucking and you don't want it to rip your finger prints off. You could probably put some cardboard over the suction port as well. A vacuum gauge would be the best.

If you have suction, then it's something in the sump and plumbing is out of whack. So you get to explore in there.
 
That is a vane pump. Take a pair of needle nose and pull each of those little vane plates out and clean with some carb cleaner and a pipe cleaner. Bet they are stuck. Very typical of a milk pump that has set for a long time.
 

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