Gang,

I had some time to waste yesterday, waiting for a phone call that never
materialized, so I did a little research into the o-ring information
available on the net. The best resource I found was from Parker Hannifin
http://www.parker.com/o-ring/Products/orings.htm

And a good place to purchase o-rings is: http://allorings.com/

Now, following the application tree we find that several different
compounds
(like hundreds) are available that would be suitable for SCUBA, but we
narrow it down to basically two.

Floating Pneumatic Piston Seal:

Contained Chemical Recommended Compound
O2, hot V1164-75
O2, cold C0873-70
Helium B0612-70
Nitrogen B0612-70
Argon B0612-70
Trimix 16/50/34 B0612-70

http://www.parker.com/o-ring/Products/allcomps.htm will get you to the
page where compounds are listed.

Hot O2 gets Viton o-rings, where cold O2 gets neoprene. There are other
different compounds recommended for tube boss fittings (where your hoses
attach to the regulator, and tank valves), face seals (DIN fitting to
valve), but Butyl Rubber will work well for 99.9% of uses, especially
if you change them out yearly.

Seems like good old Butyl Rubber, AKA B0612-70, 70 durometer will be the
most applicable and economical. And, they are all black.

Scott


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