That's right, Mark.Â* The bottle we rented at the medical supply place
had a CGA-540 valve.

On 11/10/2019 4:05 PM, wrote:
For welding, just fill is ok.
For medical and PBO, evacuate first is required.

If the previous user left the tank open for a while, there is a small chance of moisture but probably nothing else harmful.
The above protocol is true at the supplier, but not necessarily in the field. The reason for evacuation of the cylinders for medical and PBO (or ABO) is that the O2 refill has a lot number that is recorded by the supplier.

I doubt that many pilots run their tanks to zero pressure before refilling, and then it is unlikely that the valve is left open and the regulator exposed to ambient atmosphere (and thus possible moisture contamination.)

Also, just in case you haven't noticed, medical cylinders generally use the CGA-870 post-type filling port as opposed to the CGA-540 outlet found on welding and Aviator's Breathing Oxygen cylinders. A special adapter will be required to transfill the medical cylinder from a typical CGA-540 fitting.

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Dan, 5J