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chemman 05-07-2012 08:40 PM

air compressor rehab questions
Bought a used Sears Best air compressor circa 1978: 30 gal. cast iron tank, dual piston single stage compressor and 2hp motor. The tank check valve was stuck initially, but after a little bit of WD40 and lots of exercise with a screwdriver, it only leaks about a psi a minute now.:( So it's going to need to come out, either for more cleaning or replacement. Along with that are two 2in pipe plugs on one side that I'd like to remove to inspect the tank. Of course all these fittings are stuck, really stuck. Would it be possible to use a propane torch (a small hand held torch, no acetylene monster) to heat (only as much as necessary) the tank to make removing the fittings easier without weakening the tank? I've been applying penetrating oil and I'm guessing there is some kind of thread sealant or thread locker (and some rust) on the threads. To go along with that I can hear some rust rattling around in the tank when I roll it around. Beyond dumping the particulate out, is there anything I should do to the inside of the tank. Or should I just put a filter in the line and try and keep the moisture in the tank to a minimum? There is no low point drain.


joecaption 05-07-2012 10:17 PM

Not sure why you would want to ever remove those plugs, just what is it your expecting to see?
I've never once seen a pressure tank without a drain someplace on the bottom and I used to be a service man for a company that sold compressors.
Some are just tiny petcock valves. A rare few have a pipe plug.
Not much you can do about getting water in the tank. The air is getting hot from being compressed and being pump into a tank that acts like a big condencer, hot inside, colder outside.
If you google the model and ser# there's a company that Sears parts and has parts break downs on line.

chemman 05-08-2012 03:06 PM


Not sure why you would want to ever remove those plugs, just what is it your expecting to see?
If I see severe rust and pitting 1/2 to 3/4 the thickness of the tank, I'm sure as hell not going to use the tank. I don't want to be laying on the ground next to a time bomb that bursts and fills me full of cast iron shrapnel. I tried putting heat on the tank and even with a 2ft breaker bar I couldn't get the check valve to budge. I'll take the tank to a garage and let them beat on it with an impact gun until it comes out. The tank does have a low drain, I must have missed it when I glanced underneath the tank. I think I'll replace it with something easier to get to though. I really need to get a set of flare nut wrenches.:mad:

joecaption 05-08-2012 03:14 PM

Just checking by eye will tell you nothing. If you really want it tested it will need to be static tested. It's lowered into a tank of water and pressureized to at least twice the pressure it's rated for.
Better to just buy a new compressor or at least a new tank that's pressure rated.

Ravenworks 05-08-2012 03:49 PM

I agree with Joes first post,with that if you look at the bottom of the tank it is funnelled to the center so water can drain to it.
The very first thing I did when I got my comp was install a ball valve on the drain,if I am running it hard I will crack it enabling the water to drain and to help keep it out of my system.

Thurman 05-08-2012 06:23 PM

I've worked on many compressors and have never seen one with a cast iron tank. I'm willing to say yours is a steel tank, a cylinder with end caps welded on each end. Those pipe plugs have probably been in there long enough to have a good coating of rust within the threads and will be very hard to remove. As stated, just looking into the tank is not an appropriate test, at static test is the only way to check these tanks. Some, but not all, check valves can be removed and disassembled for a proper cleaning and inspection. You will be better off to replace the check valve if it is leaking at all. Air should only flow one way through a check valve, if it is leaking this allows the air to flow both ways and will lead to the compressor running hot. Underneath the tank there should be a condensate drain. IF you can remove this you should have a hole large enough to get most of the internal loose rust to come out with some shaking/rotating. As stated: When you compress ambient air you are also compressing any moisture within the air. This moisture gets pushed into the tank where it will condense. That is why it is important to keep a tank drained of water. I always use a FRL in my system, that is a Filter, Regulator, and Lubricator put into the line coming out of the compressor.

Missouri Bound 05-08-2012 08:48 PM

I can't tell you about the condition of your tank but I can tell you a story about a tank exploding. One of the fork lift repair companies that I used had a tank mounted in the back of the service van, with an auto start and hooked directly into the gas line so it was basically self-sufficient. The tech went into the van to get a part and opened the side door. He got the part and walked about 3 foot from the tank when it exploded. I heard the blast 200' away and ran to the van immediately. He fortunately was not hit by anything but he was in shock and could not speak. He wandered around glazed eyes muttering and making no sense. Parts of the compressor went through the back window of the van and other imbedded in the roof. Some of the parts flew past him and imbedded in the building next to the van. I called his boss to pick him up since he was basically incoherent and couldn't function. He was literally 2 seconds away from a fatal injury. Anyway, tanks are relatively cheap.....just find a way to replace that 35 year old one.:yes:

joecaption 05-08-2012 09:30 PM

The first thing they showed us when i went to compressor school was pictures of buildings leveled from tanks blowing up.

One big factory i went to had the compressor inside the building right next to where people were working and the complant was, the motor started and stoped all the time and it was leaking water.
I reach for the power shut of and there is none in sight. It was in a completly differant part of the warehouse several hundred ft. away behind a locked cage with pallet loads of stuff in front of the panel.
I shut it down and find the tanks 1/2 full of water and there's pin hole leaks in the tank.
I report back to the owner to tell him what I found and he tells me to just patch it.
I went back to the truck and called OSHA, the boiler inspector, the buiding inspector. Then I pulled the breaker out of the panel and took the pump off the tank and sat there and waited for them to show up.
The owner was pissed at me because he thought i should have just welded a plate to the tank to keep it from leaking. OH well, anyone that stupid deserves what they get.
I may not have sold another compressor or made a friend that day but I may have saved some lives.

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