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Old 12-22-2011, 05:13 AM   #1
StaggeringGoat
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Default Water heater for air tank?

I happen to have a compressor with no tank. I've been offered a free electric water heater that is only a few years old, doesn't work. What do you guys think about using a water heater tank for a compressed air system? The front of the tank says "test pressure 300 PSI, working pressure 150 PSI max".

I've seen people doing this before but always thought it was similar to PVC air lines - a bad idea. But really, if it's pressure rated, why not? An equivalent sized air tank would cost several hundred if I can find a good used one.
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Old 12-22-2011, 07:44 AM   #2
blue2golf
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Default Re: Water heater for air tank?

I'm no expert, but my instincts tell me no.
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Old 12-22-2011, 07:54 AM   #3
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Default Re: Water heater for air tank?

Chances are it's has a bunch of scale in the bottom. Additionally there is no good way to drain the tank, although it is designed to hold water your tolls weren't designed to run on it. Does anyone know at what pressure the Temperature and Pressure release valves let off at?
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Old 12-22-2011, 08:29 AM   #4
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Default Re: Water heater for air tank?

NO! Pressure ratings for hydraulic use (i.e. filled with water) are typically an order of magnitude higher than pressure ratings for compressed air use.
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Old 12-22-2011, 08:41 AM   #5
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Default Re: Water heater for air tank?

Get your health, life and homeowner's insurance paid up.

Compressed gas tanks are designed to be used for compressed gas, and water heater tanks are designed to hold hot water. I am a firm believer in using things for hat they are intended for, especially in this case. 150psi of air is a totally different thing than 150 psi of water. Totally different design, construction, and purpose. If you have ever seen the Mythbusters episode where they blew a water heater up, it blew the entire thing out of the bottom and it went up through the floors, ceiling, and roof of a mock up house.

Stuff like this is why there are ambulances.
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Old 12-22-2011, 09:57 AM   #6
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Default Re: Water heater for air tank?

NO! Please DO NOT USE a water heater tank for air. The tank is thin metal that is most likley rusted out. Keep your eyes out for a used air tank.
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Old 12-22-2011, 05:16 PM   #7
Jim in Wis
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Default Re: Water heater for air tank?

Well, I suppose everyone is right and it's not a good idea...but... that's exactly what I did about 30 years ago. I built a compressor using an old (1940's) refrigeration compressor and a electric hot water tank for the resevoir. It has a pipe plug near the bottom and I use that to drain the sludge out once in a while. It's still running and hasn't ever exploded, not even once. Not even when I got the air hose tangled up in the tractor and drove out. Knocked the tank over, pulled the wires out of the box, etc. I wouldn't recommend anyone using a hot water tank, but I can tell you for sure it can be done.
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Old 12-22-2011, 06:12 PM   #8
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Default Re: Water heater for air tank?

Well.....actually....as long as the PRV is functional.....it will work. But....good chance it's rated for 150 PSI max....a bit too close to typical air pressure for my liking....
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Old 12-22-2011, 07:25 PM   #9
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Default Re: Water heater for air tank?

Do you have a wife? Do you have kids? Do you love them? Do you want to be able to provide for them for years to come? If so, why in heavens name would you take a chance by using a pressure vessel for an unintended purpose??

You don't say what size this tank is, but most electric water heaters are 60 gal. tanks. Do you have any idea how much devastation would be caused by the catastrophic failure of a 60 gal. tank bursting at 100 - 120 psig air pressure?

And, you can bet your insurance company won't give you a dime ... and then they'll cancel your policy.
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Old 12-22-2011, 07:29 PM   #10
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Default Re: Water heater for air tank?

Tank has to be ASME rated as a pressure vessel. Water heaters are not.
You can buy a cheapo 60 gallon compressor for less than a new water heater.
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Old 12-22-2011, 07:30 PM   #11
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Default Re: Water heater for air tank?

My dad had an air tank made out of a water heater tank. It was an old water heater, 3/16" thick walls.
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Old 12-22-2011, 07:43 PM   #12
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Default Re: Water heater for air tank?

Quote:
Originally Posted by Steves32 View Post
Tank has to be ASME rated as a pressure vessel. Water heaters are not.
You can buy a cheapo 60 gallon compressor for less than a new water heater.
Says who? Nothing Harbor Freight sells is ASME rated.
Show me just one 60 gallon compressor for less than a broken water heater and I'll take three.


All those saying the world is going to end, do you have any specific reasons why? Why would 120 pounds of air be worse than 150 pounds of water pressure? The tank is rated to 300 PSI/150 PSI working pressure. It's funny we were just having a discussion about PEX and everyone says that gas pressure and water pressure are the same thing.....

Please, if you're just going to sceam about safety don't bother responding. If you have a good reaosn why it's unsafe I'd love to hear it.

And yes, I saw what mythbusters did to a water heater, do you realize how much heat, pressure, and steam it took to do that?
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Old 12-22-2011, 07:47 PM   #13
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Default Re: Water heater for air tank?

Quote:
Originally Posted by StaggeringGoat View Post
Says who? Nothing Harbor Freight sells is ASME rated.
Show me just one 60 gallon compressor for less than a broken water heater and I'll take three.


All those saying the world is going to end, do you have any specific reasons why? Why would 120 pounds of air be worse than 150 pounds of water pressure? The tank is rated to 300 PSI/150 PSI working pressure. It's funny we were just having a discussion about PEX and everyone says that gas pressure and water pressure are the same thing.....

Please, if you're just going to sceam about safety don't bother responding. If you have a good reaosn why it's unsafe I'd love to hear it.

And yes, I saw what mythbusters did to a water heater, do you realize how much heat, pressure, and steam it took to do that?
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Old 12-22-2011, 07:59 PM   #14
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Default Re: Water heater for air tank?

I would use it.






Lot of kitty cats in this thread that don't know what they are talking about.
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Old 12-22-2011, 08:12 PM   #15
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Default Re: Water heater for air tank?

Quote:
Originally Posted by keller_S10 View Post
I would use it.
Lot of kitty cats in this thread that don't know what they are talking about.
Usually statements of that sort are followed by credentials.

Water tanks live with water and they fail because of it. I'm thinking a new water tank may be just fine. But who takes apart a new water heater to obtain the tank?
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Old 12-22-2011, 08:17 PM   #16
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Default Re: Water heater for air tank?

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Originally Posted by Zeke View Post
Water tanks live with water and they fail because of it. I'm thinking a new water tank may be just fine. But who takes apart a new water heater to obtain the tank?
I tend to agree with you on that but the tank I want to use is only a couple years old. The owner is getting rid of it because the element failed and he's going with gas. Most of the glass lining should still be intact. I would not use a very old one. Even air tanks get plenty of water in them.
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Old 12-22-2011, 08:36 PM   #17
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Default Re: Water heater for air tank?

Quote:
Originally Posted by StaggeringGoat View Post
Says who? Nothing Harbor Freight sells is ASME rated.
You should read a little before you shoot your mouth off like that.
It took me but 5 seconds on google to find an ASME rated tank at HF:
http://www.harborfreight.com/5-hp-60...sor-93274.html
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Old 12-22-2011, 08:38 PM   #18
StaggeringGoat
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Default Re: Water heater for air tank?

Quote:
Originally Posted by rlitman View Post
You should read a little before you shoot your mouth off like that.
It took me but 5 seconds on google to find an ASME rated tank at HF:
http://www.harborfreight.com/5-hp-60...sor-93274.html
Excuse me, one of the 29 different compressors they sell actually is rated. The rest aren't. I own several.
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Old 12-22-2011, 09:00 PM   #19
Chris Adams
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Default Re: Water heater for air tank?

Not taking sides in the hot water heater tank debate, however, I have seen it done years ago and is still working. Wouldn't do it my self, usable tanks just too darn cheap around here.

On the ASME HF tank, yes and no. I have a dead one in the back yard right now.
Low hours.
Was not drained enough.
Tank leaks out the weld at the bottom, making it a very heavy paperweight.

Looks like the ones in the pictures, but is an earlier model with two air outlets at the top.

HF must have been pretty unhappy with this tank (USA built, ASME certified) because they swapped to a newer tank on all their two stage units, and had to re-plump the discharge hose radically.

Different maker and different configuration, but with the same motor and compressor.

Point being, ASME can and do fail, at low hours.
Some older home made last about forever.
Do it right, I'm sure it would work, but I would keep the D-switch set down around 120. I would pressure check it (look up on line to see how to do it yourself) and be safe.

Again, though, myself, I would just snag a 50-150 buck used tank.
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Old 12-23-2011, 07:24 AM   #20
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Default Re: Water heater for air tank?

Obviously others have done it with success but I tend to shy away from the idea due to fatigue, even in a fairly new tank.

FWIW, if you look around you can usually find a used air tank that the compressor is gone on and pick it up cheap. Might even want to check the local metal yards.
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