Hi, all -

I recently bought a new 20 lb. propane tank for my barbeque. The original tank had the old-style fitting which you can't refill (legally), and it was less hassle to just buy a new tank.

Now I'm wondering whether I can use the old tank for portable compressed air. It's in good shape. Can anyone see a problem with using it this way? What sort of fittings would make sense for this?

Thanks...

 

I used to have an old Freon tank that I used for compressed air, and it worked fine. But, I never put more than 80 lbs. of pressure in it. I feel a lot safer pressurizing my store-bought air tank than any other tank. As cheap as the store-bought ones are, the peace of mind they give is priceless.

 

Anyone know the the PSI of LPG? I too have a few old style propane bottles kicking around that I've thought about useing for air. Use to have a freon btl conversion, but retired it when I was told that they were designed for only one pressureasation cycle. Seems water from condensation (and therefor rust) and pressure exceeding the designated use (LPG), would be my main concerns.

 

OK i'm gona sound like someone else on the forum board when i say this. DO NOT use old freon tanks for air tanks. they are made from very thin steel and not designed to last very long and they rust out very fast. that's all i will say on that.

as for the old grill tank i had 2 old style ones, one even had the valve handle broke off, used a wrench to turn it on. i took them to Menards Lumber, they do tank exchanges there and they just took them. Most places that take tanks for exchange will take the old style tanks.

 

Just my 2 cents. To the best of my knowledge, propane tanks use a POL (pressure or iquid) valve that incorporates a a safety valve that will release if the tank exceeds recomended pressure. I think it's 150 lbs.sq/in -- it may even be more. At any rate you should stay well below this limit. The valve is there because pressure will increase when propane warms, which is why you should never keep them in an enclosed area that will heat up, like a van or car trunk. If you do choose to do this, I would just get an old male grilll fitting (remove the regulator) and adapt it to pipe fittings that provide an air hose and schrader valve to fill it with air. That way you retain the original safety valve features of POL tank valve. A good hardware store will have pressure testing devices that are used to test new gas and water lines. They are connected to the pipe and have schrader valve to pressurize the pipe. They also have a guage to measure air pressure to verify the system doesn't leak. This might be just the ticket with a little modification. The guage on these only reads up to 50 lb if i recall, so it would need to be removed or relaced with one with a higher range.

 

I have 2 OLD freon tanks that we use regularly for AIR.... They are both over 20 years old and we have never had a problem.. As long as you keep them painted, and keep the water out of your compressor you're fine.. We pressurize ours to 125psi..

 

I've been using a 20lb tank as a portable source for comp air for years with no problems. I charge mine to 125psi. I did start with a new tank though, so I'd be sure to do a thorough purge if you want to use one that's been filled with propane.

 

I have 2 older 30 pound propane tanks hooked up to my compressor when I need larger amounts of volumne. when the tank was empty I drilled a hole at the end of my main tank and welded a fitting in. Now I just use my quick connect fittings to plug in 1 or 2 extra tanks when I need it. Been using it for about 9 years now. I should say that my original compressor only has a 5 gallon tank, and I did upgrade the motor turning the lung about 7 yrs ago, since then no problems.My 2 cents.

 

Propane tanks are not coated on the inside, so it won't come off and foul gas valves. No coating equals rust from the moisture in the tank. The tanks have no drain valve. Rust equals a weakened tank.

 

I bought a little tank from menards thats just for air, directions say it takes 90 psi. I just ran out and compared the two and the propane tank seems a little heavyer gage.

 

I'm shooting from the hip here but I believe that the propane tank holds mainly liquid propane - the only gas vapor would be on top and that is what is used to cook on the grill. Turn the tank upside down and open the valve and you get the liquid propane. The gas vapor on top is at fairly low pressure - not sure what that is.

Anyway, my point is that these tanks are not really intended to hold compressed air. I'm sure they have a significant factor of safety but I wouldn't defeat that by eliminating the relief valve.

I have seen many of them used successfully as compressed air tanks - usually the ones over 12 years old that can't be refilled legally without pressure testing.

 

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Common temperatures/pressures of HC 290 (Propane):

-43.73F 0 psig
-19.46F 11 psig*
0 F 22.5 psig
32F 54 psig
70F 111 psig
100F 175 psig
163F 380 psig ++

*Anything at or below this, there will be problems with burning equipment.
++ I believe Propane becomes unstable above this temperature/pressure.

 

You can buy conversion kits to turn old propane tanks into portable air tanks; it comes with a fitting that screws into the tank with a tire valve type inlet to fill it and a pressure gauge, and a chunk of air hose with a tire chuck on the end.

 

I picked up a conversion kit for a propane tank on ebay for under $10. The propane tank is considerably heavier than my portable 8 gallon air tank.