Repairing air compressor tank - possible?

[grohl]

So about 2 years ago I got a really nice buy on a OLD 80 gallon upright tank with a 5hp/19 CFM compressor for $340. I changed the oil and airfilter, switched the pressure switch from 175 to 125psi, built an air line, and have been enjoying it ever since. I do metal work and the compressor is used for multiple air tools and a plasma cutter.

I have a manual release set up on the bottom drain valve. I keep the tank pressurized and manually switch off the valve to the airline when I am not using it. Through some very minor tank leakage that used to mean the tank would switch on and repressurize every 4-5 days.

Well, yesterday I was working in the garage and the compressor fired up - the second time I had heard it that afternoon. It's kept in a storage closet with the hot water heaters behind a closed door. After the motor cut off, I hear a loud hissing sound at the bottom of the tank. Hmm, I thought, I must have left the bottom release valve open. Nope, it was closed. I reached back behind the valve and felt air coming out - from the tank! I put a mirror back there and saw a 2mm size hole! There is no exterior rust.

I dread the answer that I think I might get - that the bottom must be rusted out and that I will have to replace the tank. Any way to at least attempt to patch this? what about drilling out the hole and exploring the damage? As you can imagine, the unit is 500+ pounds and mounted in the concrete floor on blocks. It's gonna be a pain to do anything with. I appreciate your thoughts....

 

[brblx]

tank rusted out from the inside from lack of maintence. pitch it.

you'd likely have to replace entire bottom of the tank, not just patch a hole.

edit- i've never had to work on large compressors, but i've worked in small shops where we had a couple smaller units setup.

drained them every day...prolly a friggin quart of water.

 

[lxskllr]

Don't really know anything about it, but couldn't it be brazed?

 

[brblx]

Don't really know anything about it, but couldn't it be brazed?

you would weld, not braze. but 99% chance he'd be patching bad metal.

 

[deadlyapp]

you would weld, not braze. but 99% chance he'd be patching bad metal.

Not to mention welding a high pressure air tank is stupid if you're not an experienced welder. There is a reason high pressure tanks have to reach very strict ASME codes.

I would find a competent welder in the area that might be able to ultrasound the tank and see what sort of shape the interior metal is in. As mentioned above I'm sure that the tank has rusted from the inside out if it was not properly taken care of.

 

[IronWing]

You're probably better off replacing it. It likely wouldn't pass a pressure test once patched.

Edit: deadyapp covered it.

 

[Rubycon]

Please post pics if you can!

I :wub: open drive (belt) compressors and yours sounds like a two stage unit if the pressure switch was at 175 psig. It's better to run higher and use a regulator to step down for tools (90+ psi) or painting, etc.

If the compressor itself is still good you should just remove everything from the platform on top of the tank and get it inspected. If it's a "code" tank it should have an inspection plug that can be backed out. Even on smaller vessels the inspection port is large enough for a common borescope to get in there to take a look.

NEVER weld on a pressure vessel unless trained/certified to do so. A botched repair has the potential to cause injury or even death under certain circumstances. Not worth the risk!

 

[Twista]

A pinhole leak in the bottom of an air tank is the first sign that indicates the tank's life has ended.
If you have air coming out of a small hole you can be sure that the material around the leak has thinned to the point where it will be unsafe to use.

time to replace her =[
http://www.doityourself.com/forum/t.../172030-air-compressor-tank-rusty-danger.html

 

[deadlyapp]

Please post pics if you can!

I :wub: open drive (belt) compressors and yours sounds like a two stage unit if the pressure switch was at 175 psig. It's better to run higher and use a regulator to step down for tools (90+ psi) or painting, etc.

If the compressor itself is still good you should just remove everything from the platform on top of the tank and get it inspected. If it's a "code" tank it should have an inspection plug that can be backed out. Even on smaller vessels the inspection port is large enough for a common borescope to get in there to take a look.

NEVER weld on a pressure vessel unless trained/certified to do so. A botched repair has the potential to cause injury or even death under certain circumstances. Not worth the risk!

how much do you :wub: them?

 

[Rubycon]

how much do you :wub: them?

Dual stage, intercooler, full pressure lubrication, recip - that's what I'm talking about. Love the sound. Sure everyone wants a screw at around 25hp and above and that makes sense for 24/7 use where 100s of CFM are needed continuously...


Screws are too darn loud though. Especially the Worthington's. I've been next to some 500hp recips and they are a bit much - the pounding can knock the wind out of you but then again I don't spend much time in engine rooms.

 

[grohl]

The more I think about it the more it looks like it needs to be replaced. I'm pretty bummed about it. My thoughts on replacing the pressure switch were to extend the life of the whole system. I down regulate one arm of the airline to 90 psi for the air tools. The other part feeds right into the plasma cutter since it will accept 125 psi. I am considering finding a certified 80 gal tank to install the motor/pump on top of since it works just fine. I figure a brand new replacement of a compressor this solid would run $1500+

 

[deadlyapp]

Dual stage, intercooler, full pressure lubrication, recip - that's what I'm talking about. Love the sound. Sure everyone wants a screw at around 25hp and above and that makes sense for 24/7 use where 100s of CFM are needed continuously...


Screws are too darn loud though. Especially the Worthington's. I've been next to some 500hp recips and they are a bit much - the pounding can knock the wind out of you but then again I don't spend much time in engine rooms.

I loved the sound of those ones when they kicked on. You could be up 3 floors and feel the structure vibrate as they ran. We had a pair of smaller 300psi systems that weren't nearly as loud, but IIRC they only had 20-25HP motors rather than the 60hp motors that were on these ones.

I never did get to hear both of the 60horse ones run at the same time, we never had a need for that much air at once.

 

[brblx]

can you not just buy a replacement tank? steel tanks, even rated ones, are a lot cheaper than large industrial compressors...

 

[PottedMeat]

can you turn the tank into a smoker?

 

[skyking]

can you not just buy a replacement tank? steel tanks, even rated ones, are a lot cheaper than large industrial compressors...

can you turn the tank into a smoker?

Both are excellent suggestions. Fixing it, not so much.
The place I used to work for has an upright 80 gallon commercial tank in the scrap heap, nothing at all wrong with it. Too bad you are across the country.

 

[Rubycon]

I loved the sound of those ones when they kicked on. You could be up 3 floors and feel the structure vibrate as they ran. We had a pair of smaller 300psi systems that weren't nearly as loud, but IIRC they only had 20-25HP motors rather than the 60hp motors that were on these ones.

I never did get to hear both of the 60horse ones run at the same time, we never had a need for that much air at once.

We run Quincy QR-25s that are rated 250psig continuous, 500psig intermittent. They probably laugh at the 140psig we run them at. They are rock solid and can be abused forever. Good spring bases and couplers will keep vibration down but noise is always going to be an issue close by the unit. At least the unloaders have mufflers.

 

[JulesMaximus]

New tanks aren't cheap either. This 80 gallon tank is almost $1000.

http://www.grainger.com/Grainger/SPEEDAIRE-Air-Tank-1YAC4?Pid=search

 

[DrPizza]

I make rockets in physics class. I think it's funny to put a 2-liter bottle on my rocket launcher and, using compressed air only, launch it under a lab bench. Why it's funny is because even if I warn the kids, they jump. The kids in the neighboring room jump sometimes. Under the lab bench is a storage bay for books. The bottom of it is plywood.

At 100psi, I fired an "empty" (just air in it) 2-liter bottle THROUGH the plywood. In another classroom, I launched a 100psi pressured 2-liter bottle under a regular desk (with a few layers of cardboard under it to avoid damage. It lifted the desk nearly a foot off the ground (and, because it wasn't balanced perfectly on the point of impact, also spun the desk which crashed to the ground.)

2-liters of 100psi air. Shot a cheap plastic 2-liter bottle through a piece of plywood.

I think that should answer any questions about considerations of welding an 80 gallon tank that's going to be put at 125psi. *I* wouldn't go anywhere near such a tank if I knew someone had attempted such a repair. You're welcome to if you want. Before you do, search for stories about people being killed by exploding air compressors. I did a quick search, and saw images that I really didn't care to see; no links. Do your own search.

 

[grohl]

OK, ok! Currently searching for a replacement tank. First shop I called here in town wanted $715 for a 80gal with a top plate. Ouch.

Found a new 120 gal on CL, guy wants $150. Score. Problem - no top plate. I was thinking of cutting off the top plate/pump/motor and welding it onto the new tank...OR...leaving them separate. Would welding TO a new tank compromise it? Notice I am NOT talking about welding and repairing the old one.

 

[arkcom]

OK, ok! Currently searching for a replacement tank. First shop I called here in town wanted $715 for a 80gal with a top plate. Ouch.

Found a new 120 gal on CL, guy wants $150. Score. Problem - no top plate. I was thinking of cutting off the top plate/pump/motor and welding it onto the new tank...OR...leaving them separate. Would welding TO a new tank compromise it? Notice I am NOT talking about welding and repairing the old one.

I'd leave them separate. Mount the motor/pump on the wall or something.

 

[Jeff7]

Not to mention welding a high pressure air tank is stupid if you're not an experienced welder. There is a reason high pressure tanks have to reach very strict ASME codes.

I would find a competent welder in the area that might be able to ultrasound the tank and see what sort of shape the interior metal is in. As mentioned above I'm sure that the tank has rusted from the inside out if it was not properly taken care of.

Yes, the difference between a pressure vessel and a bomb is that a bomb is designed to release all of its potential energy in a very short period of time.
If a pressurized pressure vessel fails abruptly, you're going to have some serious problems - even worse if you're anywhere near it.
Don't modify them unless you know exactly what you are doing. (And even then, don't do it.)

 

[Rubycon]

I'd leave them separate. Mount the motor/pump on the wall or something.

Fabricate a mount for the motor/pump/pressure switch, put the motor controller on the wall. The mount can be made from steel "u" stock stick welded together, etc. Use drilled angle stock and decent springs to support the weight and shoot 5/8" Hilti drop ins into the concrete, for example. Don't forget an expansion coupling on the pump discharge connecting to the tank. Depending on how your unloader/switch setup is will determine how this is connected to the piping leading to the tank. The tank can be anywhere you wish, out of site, out of mind. You can even put it up in an attic if you use an automatic (timed) solenoid based drain system, etc.

 

[Eli]

As has been said, NO.

 

[Rubycon]

I make rockets in physics class. I think it's funny to put a 2-liter bottle on my rocket launcher and, using compressed air only, launch it under a lab bench. Why it's funny is because even if I warn the kids, they jump. The kids in the neighboring room jump sometimes. Under the lab bench is a storage bay for books. The bottom of it is plywood.

At 100psi, I fired an "empty" (just air in it) 2-liter bottle THROUGH the plywood. In another classroom, I launched a 100psi pressured 2-liter bottle under a regular desk (with a few layers of cardboard under it to avoid damage. It lifted the desk nearly a foot off the ground (and, because it wasn't balanced perfectly on the point of impact, also spun the desk which crashed to the ground.)

2-liters of 100psi air. Shot a cheap plastic 2-liter bottle through a piece of plywood.

I think that should answer any questions about considerations of welding an 80 gallon tank that's going to be put at 125psi. *I* wouldn't go anywhere near such a tank if I knew someone had attempted such a repair. You're welcome to if you want. Before you do, search for stories about people being killed by exploding air compressors. I did a quick search, and saw images that I really didn't care to see; no links. Do your own search.

Not to dismiss danger here but if one knocked off an inspection port on a 80 gallon receiver at 125 psi it's not going anywhere - especially since they are supposed to be bolted to the floor!

Coke bottle rockets are impressive because they have a low mass and achieve good velocity despite their poor aerodynamic abilities. Plenty of youtube videos of fools shooting other fools with 'em. Even with a few strokes of a bicycle pump a launch packs a punch similar to getting kicked by a jackass. (donkey)

 

[Possessed Freak]

Dual stage, intercooler, full pressure lubrication, recip - that's what I'm talking about

Got it beat, I have one of these in my garage. Works great for filling up paintball tanks. Since I know the fourth stage gets above 4000 PSI, I now want to rig it to use a different regulator so I can fill to 4k instead of 3200 which is what my internal regulator maxes at.