halocline
Contributor
Some dive shop owners sure do love to use that line, (would you trust your life to cheap etc....) they must teach it in dive shop ownership school. Anyhow, I'm sure you realize that: a) the o-ring is much more likely to blow when the tank is getting filled or when the reg is first pressurized pre-dive than during a dive, and b) safe diving ALWAYS means having some alternate way of getting air should your gear fail. That includes a buddy or the surface, BTW. Since presumably this heroic dive shop owner learned how to scuba dive at some point, he should understand that.
"Banked 21%" was what you getting filled? How is that different from air, or is it a typo? You didn't pay extra for it, did you?
If you are blowing multiple o-rings on the same tank within a year's use, there is likely something wrong with the valve. If it's a convertible valve, which o-ring is blowing? Try (if you can) a DIN reg in the valve without the insert, or try using a different insert. Any reasonable quality o-ring, nitrile, viton, EPDM, etc... of 70 or 90 duro should do better than what you are describing. 90 duro polyurethane o-rings seem to be very durable, but they're expensive and I've had some dry out and get brittle. But, if the valve and insert are in good condition, no little dings to allow an o-ring to extrude or get nicked, and the insert threads are good so the thing fits well, and the o-rings are the correct size, either duro hardness will work. If you're buying them, 90 duro (although usually you see viton in 85, not 90, I think) is a better bet. But don't get too hung up on o-ring material or a specific duro. They just have to fit correctly.
"Banked 21%" was what you getting filled? How is that different from air, or is it a typo? You didn't pay extra for it, did you?
If you are blowing multiple o-rings on the same tank within a year's use, there is likely something wrong with the valve. If it's a convertible valve, which o-ring is blowing? Try (if you can) a DIN reg in the valve without the insert, or try using a different insert. Any reasonable quality o-ring, nitrile, viton, EPDM, etc... of 70 or 90 duro should do better than what you are describing. 90 duro polyurethane o-rings seem to be very durable, but they're expensive and I've had some dry out and get brittle. But, if the valve and insert are in good condition, no little dings to allow an o-ring to extrude or get nicked, and the insert threads are good so the thing fits well, and the o-rings are the correct size, either duro hardness will work. If you're buying them, 90 duro (although usually you see viton in 85, not 90, I think) is a better bet. But don't get too hung up on o-ring material or a specific duro. They just have to fit correctly.
