Homemade air tank

Scott D Orbaker · Jun 26, 2020

I have a homemade air tank my late Father-In-Law, a retired Stationary Engineer/HVAC guy, made from an old freon tank. I'm wondering how high I can pressurize it safely.

Thanks

Scott

The Famous Grouse · Jun 26, 2020

(quoted from post at 11:34:44 06/26/20) I have a homemade air tank my late Father-In-Law, a retired Stationary Engineer/HVAC guy, made from an old freon tank. I'm wondering how high I can pressurize it safely.

Thanks

Scott

I don't think there's a standard answer to this. It all depends on the internal condition of the tank. This tank is going to have been filled with wet air from another compressor for its whole life. How much corrosion does it have inside?

Grouse

Tracy Brown · Jun 26, 2020

bout 30 lbs. Dispose of it and get a better tank. You have a ticking time bomb.

teddy52food · Jun 26, 2020

Put a gauge on it & fill with water. Have a grease fitting so you can pump pressure to it. When it holds 300 # it should be safe at 200.

Mike M · Jun 26, 2020

They used to sell a fitting with gauge that fit right onto those for that purpose.

ss55 · Jun 26, 2020

Is there an ASME pressure rating label attached or stamped into the tank? If not, use a liquid propane tank instead.

tomNE · Jun 26, 2020

personally; i gave up on air tanks and went with a ryobi 18volt compressor ( they make 2 and i'm talking about the better one) set the air pressure needed and let it work!

JWA · Jun 26, 2020

I have one I built from a freon tank about 20 years ago. I regularly pressurize it to 100PSI with no problems.

matthies · Jun 26, 2020

Had mine for at least 30 years, 120 psi is what the compressor kicks out at. I have T's made and fill them as I get other stuff ready.

hanovertom · Jun 26, 2020

I made one about 15 yrs ago. Have not had any issues @ 120 psi

M-MAN · Jun 26, 2020

When new it had to withstand several hundred pounds pressure.

Steve@Advance · Jun 26, 2020

I've used them for years, never a problem.

But...

Even though they are designed to safely hold the pressure, they are a "one time" use container. There is no provision for years of rust eating away at the thin metal.

What concerns me is how thin they are. "What if" it were dropped on something sharp, or something fell on it? Very real possibility of it ripping open explosively!

David G · Jun 26, 2020

I have one of the old thick steel type, really not a good idea to reuse one of the lightweight ones.

Pete in Holland MI · Jun 26, 2020

Called a hydro test, the standard test to check the integrity of a boiler or pressure vessel is to completely fill it with water and using a small pump, force more water into the thing. Most states require 1.5X the operating pressure of a boiler. Air tanks are generally higher. Once the air is out of a compressor tank, forcing a few ounces of water into the tank will raise the pressure quickly.

The benefit of a hydro test is that if there is a failure, a few ounces of water squirt out and you're back to zero pressure. Testing it with elevated air pressure, if there is a failure, it will be catestrophic.

This is the only way to truely test a tank. Anything else will just be a guess.

Russ from MN · Jun 26, 2020

I have one I made years ago, still works for me, but I never pressurize it to over 100 psi. If your worried about it hydro-test it like suggested.

Scott D Orbaker · Jun 26, 2020

Thank you to everyone. I knew this was the place to get some answers. Definitely won't be putting more than 100psi into it. Just gonna have it for occasional use.

Stephen Newell · Jun 27, 2020

It's like anything else the pressure limit would vary depending on manufacturer however the pressure of compressed air is much lower than freon.

MarkB_MI · Jun 27, 2020

By "freon" I assume you mean R-12. At 70F, R12 is about 70 psi; at 100F it's 117 psi and at 130F it's up to 181. (R-134a has slightly higher pressures; at 130F it's about 200 psi.) So I'll bet that tank was designed for a working pressure of no more than 150 psi. And that was when it was new.

It's been a long time since I've seen one of those tank conversion kits, so I'll bet your tank is over 30 years old. And as Steve said, these were intended to be disposable containers. Have you ever tried to drain the water out of it? If it has any water in it (and it probably does), I'd be real suspicious of it. I certainly wouldn't put more than 100 psi in it, but it would probably be best to toss it.

rrlund · Jun 27, 2020

I've got a store bought tank and it still scares me to pump it up. Dad knew a guy who had the bright idea to put a tubeless valve stem in a hand held sprayer so he wouldn't have to pump it up by hand. It split half his head off when it exploded. NEVER underestimate the power of compressed air. I knew a guy who broke both arms when a plow tire exploded when he was inflating it.

Janicholson · Jun 27, 2020

No offense intended, but pressure of any fluid or gas is a result of pumping a specific amount into the container, or heat/cold applied to it when closed. Air can be any pressure (High pressure SCUBA air tanks operate at 3500 psi). My intent here is to provide information that keeps the idea of safety as a result of the strength and condition of the container, not what is in it. Jim

JMOR · Jun 27, 2020

I used Freon tanks on a home built air compressor. Maybe a few years before it rusted thru. Very thin metal. Freon was moisture free, whereas air is loaded with water. Just about 3 months ago I cleaned out my garage and threw away 10-15 freon tanks. I call using them as air tanks, asking for trouble. How much is your life worth?

T in NE · Jun 27, 2020

I bought a dead air compressor at a consignment sale and a couple fittings and an air hose later, I've got a 25 gallon, 150psi, wheeled air bubble

MARK ROBKE · Jun 27, 2020

I was taught that putting air in a R 12 freon tank was very unsafe, because the residual freon would react with the moisture in the air, and create hydrochloric acid, which would rust out the tank and cause it to rupture and explode. I've read a few stories about air tanks exploding, and causing very bad damage. It does not take a lot of pressure to cause a huge explosion. No way would should you use it! Mark.

Stephen Newell · Jun 28, 2020

The pressure of a liquid is equal to what ever air space there might be in a container. Yes that pressure can vary depending on the temperature but isn't that much. I believe a freon tank the pressure of the gas is in the 500-600 lb range. The container is certainly strong enough for even 175lbs compressed air. Most of us use only pressure in the range of 120 psi anyway.

Traditional Farmer · Jun 28, 2020

As cheap as air tanks are to buy why would you want to chance using a dangerous one?

dr sportster · Jun 28, 2020

Slice it right in half welding some angle add some mesh you have a nice grill for small cook outs. Go to H-F and buy an air tank.

MarkB_MI · Jun 28, 2020

> The pressure of a liquid is equal to what ever air space there might be in a container. Yes that pressure can vary depending on the temperature but isn't that much. I believe a freon tank the pressure of the gas is in the 500-600 lb range. The container is certainly strong enough for even 175lbs compressed air. Most of us use only pressure in the range of 120 psi anyway.

Actually, no. Most of the freon in a tank is liquid. Its vapor pressure is a function of its temperature, and we can easily look up the vapor pressure using charts like <a href="https://www.hudsontech.com/refrigerants/our-products/pressure-temperature-charts/r-12/">this one</a>. That chart tops out at 150F (234 psi), but I think it's a reasonable assumption that an R12 tank should never see anything close to 500 psi. I suspect disposable freon tanks are designed to fail in a controlled fashion if their maximum working pressure is exceeded, but I wouldn't bet my money or my life on it.

Charging a 30 year old disposable tank up to 175 psi is a crap shoot. One with fatal consequences if you crap out.

Stephen Newell · Jun 28, 2020

The point I was trying to make is a freon tank is designed for 500-600lbs pressure sort of like a water pipe may be rated for 400 pounds. Not that anyone expects a pressure that amount will be used but stronger than needed for safety reasons. Now a freon tank, even an old one shouldn't deteriorate on the inside because there isn't any water in freon. The only issue might be to use one for a very long time for compressed air because air does have moisture and could corrode the tank on the inside since the freon tank is probably not coated on the inside like a compressor tank should be.

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