I picked up an old Bell & Gossett 1/2hp oil-less air compressor,nice and quiet, perfect size for the workshop, blowing off parts, dirt out of actions etc.

Only problem is it won't get up past 55psi. It doesn't shut down, the cutoff switch is ON @ 90, OFF @ 125psi.

It just keeps running. There aren't any leaks, when I shut it down and let it stand it will hold pressure.

I assume there must be some gaskets or reed valves that need replacement but B&G stopped making compressors back in the mid 1960's so they're no help.

Once again I call upon the members of this BBS for expertise. What needs to be done and where can I get parts? I know I can buy a new one for a couple of huderd bucks but i'd like to get this running if possible.



Thanks, Rob

Rob,
I'm no compressor expert, but if it's oil-less I suspect it is a diaphram type. Very similar to a mechanical fuel pump. It's quite possible that there is a hole or tear in the diaphram. It could be quite small. The diaphrams I've seen look like the same material used in inner tubes with a layer or two of fabric inbedded. If that turns out to be the case and you can't find a replacement you might try an inner tube patch. Of course this is all just a guess. You'll have to pull the head off to check it.
If it's Around forty years old, it may be dry rotted and you'll have to source or make a replacement.
I have no clue on a parts source, but if that's what it turns out to be (diaphram) you can make one yourself.

Not really a diaphragm. There are two "heads" on either side of the motor with an air intake. Inside these heads there seem to be pistons with what looks like graphite rings. There is a bit of corrosion in the cylinders. maybe that's the problem or it could be a check valve somewhere. All guesswork on my part.

Just a guess on my part, but if there is corrosion no cylinder is going to do it's job. Ditto for taper too. Keep running it with a contaminated bore and soon the rings will be worthless too, if not already.

The reason it holds pressure is because the check valve(s) (probably in-line somewhere) is/are in good shape, however I doubt the ring/cylinder contact is good enough to make the pressure required to switch the motor off.

I once aquired a 3/4hp Gast compressor that sounds a lot like the one you have. It was one the company I worked for used to maintain pressure on a "dry pipe" fire suppression sprinkler system. Well a fork truck damaged one of the intake filters and it subsequently sucked contaminants into the reed valves. They opted to just chuck it out in the trash and replace it. It would still pump air, but not well. I invested $15 in a new set of reed valves and intake filters and it works good as new. In fact, though rated for only 55psi in the application they had it in, it will go to 110 psi. I keep it set at about 95 though since it starts to struggle a bit at 100.
You might see if Gast parts will interchange as they are a pretty common brand of basic compressor.

Thanks, will check out Gast.

Recoil:
Had the same thing happen exactly. Then some smart guy asked me if I had drained the water out of the tank. Opened the petcock and drained about a tea cup out--closed it back up and I had pressure and the darn thing cycled properly once again.

The tank was the first thing I checked, bone dry.

I'm thinking it's the cylinder wall have some corrosion. I'm going to try a brake hone and if that doesn't work it's the recycling center. I found out no parts available.

thanks anyway guys.