Posted by Jack Smith on July 27, 1999 at 16:00:12:
I knew when I posted below about using a cast off freon tank that the freon police would get me! LOL! So, I decided that a few experiments were in order. I know this has always been a concern. If you're familiar with those discount auto store kits that permit one to convert a freon tank to a portable air tank, it would seem to indicate that the practice is safe. I decided to find out, and share the results with the forum. First, let me address the statement that the temperature of the freon affects the steel somehow. Freon compressed in a tank is like any other liquid or gas. Just because it is used as a refrigerant doesn't mean that it is cold in the tank. My measurements verified that the contents of the tank are at ambient temperature. Like water or oil, freon assumes the temperature of its surroundings. When it is released into open air suddenly, or perhaps into a bigger tank or refrigeration unit, the sudden expansion causes the refrigeration effect, just as your sand blaster's siphon hose cools down and sweats inside because it is now colder than its surroundings. So, the brittle steel theory seems invalid. Next, I decided to burst a tank and see what happened. In the end, I did two of them, and here's what I found:
The first tank was connected to a cat pump from a large pressure washer, filled with cold water, and placed in a covered concrete pit for safety. At 310 psi water pressure, the tank spit out the threaded fill stem, and no apparent deformation of the tank itself was noted. The second tank was connected to a large industrial air suppply line, at 500 psi, and placed in the same pit. At 300 psi, there was a loud report, and inspection showed that the fill stem once again was the failure point. I did not dye check the tank itself to find hidden cracks or damage, and I assume that such an incident would cause anyone to stop using the tank, so I went no further. WHile my efforts were not controlled science by any means, they DID show that the threat of bursting while in casual home use is probably overstated. Most home shop compressors are capable of perhaps 125 psi, and it seems that at that pressure, little damage could result.
All of that said, let me ammend my original recocmmendation to suggest the use of a portable air tank, made for such use. These are cheap, fitted with a safety valve, and have not been exposed to freon.(!!) Although in actual day to day practice among hvac mechanics these freon tanks are repeatedly refilled over and over again, it IS not recommended. Though I see little difference between a freon tank, an air tank, a brake bleeder, ect...all of which can fail, and burst, I have never witnessed an accident with one. I admit the potential is there, so I withdraw my suggestion for the use of one. Use an air tank, and be safe. Comments?