Viton Orings bad for 02?

[DA Aquamaster]

I agree. I used to use viton in high O2 reg applications before EPDM o-rings were readily available. They do not hold up well in dynamic applications (where parts move against the o-ring). They are also very prone to damage in static applications during installation if they are not properly lubed.

Personally, I like the Scubapro Mk 2, 3 and 200 regs for deco applications due to their O2 freindly design traits. Hoiwever EPDM o-rings are again not always readily available for all of them so I have consequently used buna o-rings in my Mk 3's and Mk 200's for several years in high O2 applications without incident.

Buna o-rings may degrade faster than EPDM in a high O2 environment, bat as pointed out above, the difference is meaningless given their use in aviation applications and even less so in scuba diving where the hours of exposure to high O2 is very limited.

Buna o-rings do begin to burn at a slightly lower temp than viton and EPDM but again if you ensure their is no ignition source, there will not be a problem. Conversely, given a sufficient ignition source, EPDM and viton will also burn, so at best the issue is one of of redundantcy where EPDM and viton provide a slightly larger margin of error.

 

[Rings890]

Wow! thanks for all the input guys/gals. I understand what the Apeks rep was talking about now during the course. As for my blending whip and cylinders I will be sticking with viton (since I have several). Regs look like a different story. I beleive the Apeks O2 servise kits all come with EPDM Orings now so I guess I will just keep doing what I have been doing.
Thanks again.

 

[oxyhacker]

EPDM looked like the perfect compromise when it started becoming widely and economically available. Several regulator manufacturers picked up on it, and a few of them even hinted that with EPDM and O2-safe lube the regs were good for 100% right out of the box.
Unfortunately, time has shown that this is not necessarily so. There have been a few instances of combustion and vaporization in regulators with EPDM O-rings, and just about all the reg manufacturers have backed off of claiming the regs were OK for 100%.
So there is no clear answer which to use. It's the choice of a compound that has good mechanical properties, doesn't put off really horrible gas should it combust, and may ignite, but not easily, or one that has second rate mechanical properties, puts off really terrible fumes if it ignites, but isn't very likely to to.
Part of the problem with EPDM is that there are many different grades, and they vary quite a bit in how good they are. Some have O2 indexes almost as high a viton, and other OIs little better than nitrile. This is no problem for a manufacturer who is buying in large enough quantities that they can spec exactly what they want, but it can be one for the diver or technician who has to take what he or she can get and can rarely get full specs on the O-rings they are buying.

I think a reg or valve with EPDM O-rings can be used with high FO2s with a reasonable level of safety, however, I now tend to think that any reg intended specifically for 100% probably ought to have viton, at least on the HP side. Ditto valves which will be used at full tank pressure with 100% (as opposed to occasionally seeing 500 or so psi of 100% during PP mixing).

All this is a good reminder that tech diving and the use of high FO2s is still a relatively new, and evolving, field, in which there are often no clear limits or guidelines, and we must learn as we blunder along.

 

[iain/hsm]

When buying 0-rings there are two things the diver knows about and four things he doesn’t.

Size and colour, gets you close but compound, batch, cure date, and tolerance gets you closer.

Incidentally this EPDM nonsense you can blame on the French. When Air Liquid took over US Divers, and subsequently APEX the then general manager of Air Liquid for some reason was quite vociferous about EPDM in oxygen, memos were sent to all sub contractors suppliers etc, yet even after the oxygen fires started to show up I guess no one at the company wanted to upset him, or knew any better. I guess they do now, and those that still don’t, continue to follow.