My dad recently gave me his old air compressor from back when he was doing a lot of home autobody work and painting. It hasn't been used in about 20 years and is really old. Plate on the side of the tank says 1945... Talk about a tank, took 3 of us just to muscle the bare tank in to my truck and two to lift the huge motor. He did have the pump rebuilt back shortly before he quit using it. I think it's about an 80 gal tank. I put new oil in the pump, ran a 220v line in my garage yesterday and fired it up.
The motor doesn't have anything indicating amperage draw and I have no idea what psi the unit is supposed to handle. It has a 300 psi dial gauge and a safety valve that's working but I don't know when it is set to release. I ran it up to about 180 and turned it off. The pressure switch is leaking and it gets worse as the pressure increases.
Here's my problem: 1) Where do I get a new pressure switch for it and
2)how do I determine what pressure it can handle before I have it shutdown?

I haven't pulled the switch off yet to take it apart and see if the leak can be fixed. I know nothing about compressors aside from what I have learned fooling with this one the past couple days. It only took about an hour to leak down from 150 to 100psi and took close to 24 hours to leak the remainder of the air.
Thanks for any help.
Mark

 

I would check Grainger for the pressure switch. You were able to run it up to 180 psi, the commpressor is probally 2 stage, I would have the pressure switch cut out at 175 psi.

 

If there is only one piston then it is a single stage compressor and should not be set higher than 125 PSIG. If there are two or more pistons and they are different sizes then it is a two stage compressor and you can run it up to 200 PSIG if necessary although I wouldn't considering the age of the tank. Be careful there. You should be able to find a pressure switch at either Graingers, Mc Master Carr or look in the yellow pager under " Compressors, Air or gas " and call them. By the way what is the brand name on the compressor itself?

 

My old single stage 60 gal. Magna Force compresser had 2 pistons of the same size & my 80 gal. M.F. 2 stage has one big piston and one small piston. I had to put a new switch on mine & it was already set at 175 from the factory, I didn't have to mess with it.

 

I'm having a hard time telling if it is a single or two stage. It looks like one large piston and one about 1/4 the size of the big one. It's cast as one big unit instead of what the newer ones look like that to me obviously have 2 pistons.
I unfortunately can't read what the safety release valve says on it to see where it is set to release. There is a plate on the platform holding the motor and pump that looks like it had a lot of information but I can't make any of it out anymore.
The big plate on the tank has part and model numbers, etc. Also says:
MASS STD SCAIFE
TANK NE Oakmont, PA
W.P. 200LBS
TEM. 250 F

What does the W.P> stand for?

Thanks all for the info so far. I have a Graingers not far from here and will be paying them a visit.
Mark

 

Mark, the " WP " stands for Working Pressure. Thats the maximum allowable pressure pressure in the tank. Your safty valve should be set somewhat lower than this figure. Can be set at this level but never above.
The info you provided is the receiver info and does not tell us what kind of compressor is mounted on it. If there is a safty valve on the head of the compressor, it (this safty valve ) should be set no higher than 75 PSIG.
It sounds like you have a monoblock compressor where both cylinders are cast into one block of iron. Looking carefully at the block you should be able to determine the rough sizes of the cylinders. from what your last post said it sounds as if you have a two stage compressor. Thats cool!
A 5 HP compressor would have a bore size of something like 4" & 2.5" and a stroke probably 3.5". A picture would go a long way toward identifying this guy.

 

Mark, I forgot to advise you on the pressure switch. Get a grainger # 2F23 switch. It's manufactured by Square D Co and their number is 9013- GHG2 -Form X. The form X gets you a bleeder valve on the side to unload the compressor when it shuts off.

 

W.P. is the rated working pressure of the tank.
the saftey valve for the tank should be the same.
be sure to replace the pressure control with the same type if it is of the unloading type. there will be a small air line that goes to the pressure control that comes from between the outlet of the compressor and the check valve of the tank. You will want to chek the check valve on top the tank to see if it is leaking. Another way to tell if it is a two stage compressor is the air inlet will only feed one of the two cylinders.
Also chek the bottom of the tank for rust/ pinhole leaking.

 

That is what I had honed in on with when I went to Grainger at lunch today. Held off on buying it because I wasn't sure and the bleeder valve was facing up instead of down like on my existing switch... They had another unit in the store with the valve facing down but it was not adjustable and cut off at 125. They had one he could have orderd that was non-adjustable and cut off at 150. Didn't know whether to order the lower rated one or spend twice as much for the higher rating and an adjustable diff. based on what you said I'll go with the 40-200 adjustable and re-plumb the line that goes to the bleeder valve. I guess that's just regular steel tubing?

Thanks for the info in the previous post. It doesn't appear to have a safety valve on the pump itself but there is one right below the pressure switch. I'll try to get some pics and post tonight. Thanks a lot!
Mark

 

The check/bleeder valve was leaking slightly but it's really blowing out around the diaphragm in the pressure switch. Doesn't appear to be any other leaks.
Thanks a lot for the response.
Mark

 

Looks like the tube running to the bleeder valve goes in from the topside so should be easy to use the style switch I saw at Grainger. I talked to my dad he said it's a Kellogg American compressor and was originally set for a 175psi shut-off. Said he may be able to dig up some of the original documentation.

Here's links to a few pics.
Compressor 1
Compressor 2
Compressor 3
Compressor 4
Compressor 5

I forgot to ask my dad but pretty sure it's a 2 stage based on the plumbing I see. Does that look correct based on the pic of the pump?

Thanks a lot to everyone for the help. I'm excited to finally have a big compressor in the garage.
Mark

 

yeap, that would be a 2 stage all right, 175 would probably be the max cut out. what is the nameplate hp & rpm on the motor?

 

You have a Kellogg American two stage 3 HP compressor. Probably a model 331. Good for 200 PSIG although like I said I wouldn't run it up that high. If it were mine I would set it to cut out @ 150 PSIG and cut in @ 125 or so, Whatever the differential is set on your pressure switch. By the way dont try to adjust the differential, very frustrating. If you are using the Square D switch just back out the small spring adjuster all the way, this will give you the min. differential, about 30PSIG.

 

The only plate I see on the motor has a schematic for hooking it up as 110 or 220. No other info. Thanks for the help.

 

Thanks again for the information. Very helpful.
Mark