To Din or not to Din?

[Jaydubya]

@Jaydubya: FWIW, in my experience, divers will only replace yoke tank o-rings when they fail at the dive site where little attention is paid to carefully cleaning the o-ring and the o-ring groove. When they do replace them, they use one of those pre-packaged save-a-dive kits which comes with crappy Buna-N duro 70 o-rings. There's no telling how old those o-rings are or what kind of conditions in which they have been stored.

Good point regarding the failure of yoke o-rings on rental tanks. I agree that, from the frame of reference of the diver renting yoke-configured tanks, those o-rings seem to extrude more often than the o-ring installed on a DIN reg.

To be fair, though, just because an o-ring is stressed twice as often does not necessarily guarantee a 200% failure rate.
I'm not an expert on o-ring manufacturing, but I'd like to think that a scuba o-ring in a static application can withstand several hundred (thousands?) relaxation-compression cycles.

I'm not an expert on o-rings either but I do have some related experience. I wasn't really thinking of the relaxation/compression cycles since my intuition is that both types of o-rings ought to be able to withstand many load cycles. I was thinking more of the possibility of them getting damaged by a bur or a piece of debris as the regulator or whip is attached to the tank.

I think your idea of regs being cared for better than tanks also has some merit. Being stored in a dirty environment could be a source of debris. Being stored in a higher ozone environment for instance could also accelerate material breakdown. Most elastomers that I am aware of breakdown faster in an ozone rich environment.

 

[Bubbletrubble]

I'm not an expert on o-rings either but I do have some related experience. I wasn't really thinking of the relaxation/compression cycles since my intuition is that both types of o-rings ought to be able to withstand many load cycles. I was thinking more of the possibility of them getting damaged by a bur or a piece of debris as the regulator or whip is attached to the tank.

That's a good point although I would hope that the dive shop would keep the fill whip attachment in proper working order.
I've been on dive boats before where controlling the fill whip end can be an issue with wave motion and divers causing congestion on the deck. I could see how such a situation might lead to an incident which causes damage to the attachment end of the fill whip.

 

[300bar]

Now days I think DIN is a pain to use, also if you are familiar with 1st stage regs you will
know that there are two o-rings, one exposed on a din and one on the opposite side! I have had this o-ring blow
twice on me, back in the older days when yoke couldn't handle this pressure it made sense.
But I would suggest to stick with the yoke unless for some reason you must use din...

You've lost me here, 99% of all yoke regs have that same O-ring.
The weak point with yoke is always the O-ring in the valve.
Blowing the inside one is possible but only when the fit is not secure.
And that goes for Din and Yoke.

 

[300bar]

To be fair, though, just because an o-ring is stressed twice as often does not necessarily guarantee a 200% failure rate.
I'm not an expert on o-ring manufacturing, but I'd like to think that a scuba o-ring in a static application can withstand several hundred (thousands?) relaxation-compression cycles.

I don't fully agree here, just take any bussy divesite/boat and take a look at how many divers twist and turn their 1st stage when they hear some kind of a (slight) hisssssss
That makes the O-ring dynamic instat of static. This just isn't possible with a Din reg.
And that might just be the reason of failiure.