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Steven Irving sez: > As for the quality of O2. I beg to differ with Ronnie. All O2 > cylinders have a vacuum pulled when returned to the store. If > purchased from Air Products anyway. It's the number of vacuums > pulled, that differs between the various bottles. This may be true if you buy from one of The Big Boys (like Air), but it's certainly not true if you are buying from your local Joe's Welding, Inc. However, I think that we are ignoring another area of concern by only focusing on O2: what about He for trimix? He is frequently ganged with argon and krypton in gas panels for GTAW and/or MIG welding. Though good practice has checkvalves on the tanks, etc, good practice is not always followed, and given the cost and non-critical nature of these gasses, the tanks are certainly not pumped down prior to refil. (Even delicate welding of Al or Ti can withstand substantial argon or He contamination in the shield gas before weld quality becomes an issue.) There is no "life support" grade of He available to my knowledge. How much argon or krypton can you tollerate in "trimix" before there are substantial decompression issues? Note that this issue may actually be more serious than the O2 issue, as 1) O2 is usually only used in conjunctiuon with acetylene, and 2) if any quantity of acetylene were left in an O2 tank, there would be substantial fireworks at refil time (acetylene will spontaneously combust at just over 2 ATA's). -frank -- fhd@in*.ne* | [M]athematics is not the study of intangible Platonic 1 212 559 5534 | worlds, but of tangible formal systems which have arisen 1 917 992 2248 | from real human activities. 1 718 746 7061 | -- Saunders MacLane
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