Are viton o-rings really necessary?

[akdeepdiver]

Another religious discussion. My instructors (PSI and NAUI) who dealt with this daily both indicated that BUNA was OK under normal use as long as you replaced them annually. Personally I only use BUNA on my air tanks. On my nitrox tanks and I use EPDM for all static O-rings (tank/valve-face) and Viton for the internal one on the valve stem. Viton holds up better in dynamic applications but if it ever does smoke it emits phosgene (sp?) gas. Not a good thing to be breathing. EPDM is much more O2-friendly but doesn't like to get slid/bent/folded/spindled/mutilated. And don't forget to use an O2-friendly lubricant. The least expensive thing you can buy for your air supply is O-rings. Is your life worth an extra buck?

Good point, but here is where I apply the common sense test. If I am 100 feet under, and something all of a sudden heats the two compressed gas cylinders on my back enough to cause the O-rings to smoke, I think I have a little more to worry about then the minimal exposure to phosgene.

 

[halocline]

Viton holds up better in dynamic applications but if it ever does smoke it emits phosgene (sp?) gas. Not a good thing to be breathing. EPDM is much more O2-friendly but doesn't like to get slid/bent/folded/spindled/mutilated.

You have it backwards; EPDM has better abrasion qualities and viton has better resistance to O2. That's why they use them in high O2 situations.

There are no dynamic o-rings in tank valves, unless you want to count the stem o-ring which is only subjected to a pressure gradient when the valve is open, and is only "dynamic" when you're closing and opening the valve.

Back to the OP, if you're talking about tank neck viton o-rings, it might be worth it to use them if you are planning on nitrox being stored in the tank, or any partial pressure blending. If you're talking about yoke o-rings I would not bother.

BTW, don't use any lube, O2 safe or otherwise, on either of those o-rings.

 

[DanRite]

I only use Viton O-rings. I left the original o-ring on my Hollis DC1/DIN and the internal o-ring shread to pieces after only about 20 dives using EAN 32. I since upgraded it to Viton, and no problems to date. Since then, all my 1st and 2nd stages and valves was upgraded to Viton O-rings. I don't want an O-ring failure while I'm in a cave, that should be the least of my worries.

 

[Puffer Fish]

Another religious discussion. My instructors (PSI and NAUI) who dealt with this daily both indicated that BUNA was OK under normal use as long as you replaced them annually. Personally I only use BUNA on my air tanks. On my nitrox tanks and I use EPDM for all static O-rings (tank/valve-face) and Viton for the internal one on the valve stem. Viton holds up better in dynamic applications but if it ever does smoke it emits phosgene (sp?) gas. Not a good thing to be breathing. EPDM is much more O2-friendly but doesn't like to get slid/bent/folded/spindled/mutilated. And don't forget to use an O2-friendly lubricant. The least expensive thing you can buy for your air supply is O-rings. Is your life worth an extra buck?

You need to ask them if they are chemists before placing any value on their comments.

Not sure where the phosgene story comes from. If you light one on fire (which takes a bit of heat, by the way), you will get a fair number of fairly toxic compounds. There might be a phosgene molecule in there (might not), but there will be lots of other even more toxic stuff coming out.

Light an EPDM (which takes less energy, by the way), inhale the fumes in any concentration and you will not live thru that toxic experience either.

Fumes in any major amount from any o-ring materiial would be toxic.

However, if you have managed to light your Viton o-rings on fire, your problem will not be gasses coming off the viton.

I've seen Buta -N orings turned to paste in less then 6 months, if they are in a place that allows exposure. Not seen an issue with locations like tank o-rings, but the exposure is very different.

 

[halocline]

I only use Viton O-rings. I left the original o-ring on my Hollis DC1/DIN and the internal o-ring shread to pieces after only about 20 dives using EAN 32. I since upgraded it to Viton, and no problems to date. Since then, all my 1st and 2nd stages and valves was upgraded to Viton O-rings. I don't want an O-ring failure while I'm in a cave, that should be the least of my worries.

I highly doubt your problem had anything to do with O2 degradation. Aviation has been using nitrile o-rings for 100% O2 for years. But, if using viton gives you peace of mind, nothing wrong with that.

 

[redacted]

I highly doubt your problem had anything to do with O2 degradation. Aviation has been using nitrile o-rings for 100% O2 for years. But, if using viton gives you peace of mind, nothing wrong with that.

Actually, there may be something wrong with that if the peace of mind is not well reasoned. I think I would still be concerned about the cause of the original o-ring failure if I were planning to venture into caves with that regulator. I would not believe that the problem was the chemistry of the original o-ring and that changing to viton was the cure.

 

[DanRite]

Actually, there may be something wrong with that if the peace of mind is not well reasoned. I think I would still be concerned about the cause of the original o-ring failure if I were planning to venture into caves with that regulator. I would not believe that the problem was the chemistry of the original o-ring and that changing to viton was the cure.

Good point, it was brand new when I puchased it and it works fine, but maybe I should get it looked at. Thanks,

 

[Puffer Fish]

I highly doubt your problem had anything to do with O2 degradation. Aviation has been using nitrile o-rings for 100% O2 for years. But, if using viton gives you peace of mind, nothing wrong with that.

Nitrile O-rings will work reasonably well in captive locations (say a tank valve O-ring), but nitrile when exposed to O2 turns into a sort of nasty paste, so for safety, avoiding nitrile is a very good idea.

Here are the general rules for using materials in pressuried 02 environments:

http://www.documentation.emersonprocess.com/groups/public/documents/bulletins/d100071x012.pdf

This has nothing to do with scuba diving....notice where nitrile fits for use in O2 service? Notice their recommendations.

If you don't believe that, then do this... get a small cylinder, put a variety of o-rings inside it.. then fill with at least 2,000 psi O2... wait 3 months and check them out.

 

[Mr Carcharodon]

Is there even REALLY a difference between viton o-rings and the generic, your gear will blow up if them come in contact with 02 o-rings? Or is that just yet another way for them to overcharge you for something that's not really necessary?

Looking at them side by side I can't even see a difference. If I was to dump all my BAD

Except for the exception of tank o-rings that see high pressure gas for long periods of time I doubt if viton v. nitrile v. EPDM makes much difference. But then this is not like some immutable unknowable subject. Take some o-rings out after a while and look at them and decide if there is much difference. I do not see much.

 

[redacted]

Nitrile O-rings will work reasonably well in captive locations (say a tank valve O-ring), but nitrile when exposed to O2 turns into a sort of nasty paste, so for safety, avoiding nitrile is a very good idea.

Here are the general rules for using materials in pressuried 02 environments:

http://www.documentation.emersonprocess.com/groups/public/documents/bulletins/d100071x012.pdf

This has nothing to do with scuba diving....notice where nitrile fits for use in O2 service? Notice their recommendations.

If you don't believe that, then do this... get a small cylinder, put a variety of o-rings inside it.. then fill with at least 2,000 psi O2... wait 3 months and check them out.

Except for the tank neck o-ring. your suggestion is more than a lifetime of diving for almost all divers. 2 to 4 days should get the equivalent of a year's worth of exposure.

And, while nitrile is on the bottom of the list (for combustion temp) that temperature is still hotter than anything you would boil an egg in.