Viton vs Nitrile O-rings...
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Viton is a trade name for a family of compounds, in addition to different durometer (hardness).
Viton® grades; A fluoroelastomers, vinylidene fluoride, hexafluoropropylene
Viton A, with a slightly higher durometer is a great o-ring material
Viton® grades; A fluoroelastomers, vinylidene fluoride, hexafluoropropylene
Viton A, with a slightly higher durometer is a great o-ring material
fppf
Contributor
LOL, no that is not light reading by any means. If you have trouble sleeping and your not of the engineering type, read before bed.
Even though there is a lot of information that most people could care less about, there is some interesting things to learn about orings that most don't know. The section on failure analysis is time well spent. Most people don't know that many types of oring materials can get "bent" per say. Under pressure they can on gas, just like divers, and then blister when the pressure is released.
Viton is the tradmark name from DuPont.
Even though there is a lot of information that most people could care less about, there is some interesting things to learn about orings that most don't know. The section on failure analysis is time well spent. Most people don't know that many types of oring materials can get "bent" per say. Under pressure they can on gas, just like divers, and then blister when the pressure is released.
Viton is the tradmark name from DuPont.
Sorry to dig up an old thread. I was considering using EPDM instead of Viton-90 for my static applications, but I can only find EPDM in 70 durometer. I assume I'm just looking at more frequent replacement, or is this actually a problem?
Zung
Contributor
EPDM 70 is fine for IP areas. I even have some on SPG hoses & plugs without any dire consequences. EPDM 90 is nearly impossible to source, but given the low price of Viton 90's nowadays, it's no big deal.
Durometer differences will not make the EPDM last any longer, it would help if you are concened about extrusion issues.
My experiece is that it depends on two factors:
1. The pressure the o-ring is under
2. What level of nitrox is being used.
Two years ago, I got a pressure gauge that had EPDM installed on the connection tube by mistake (new unit) and they managed to last less than 6 months. I typically use 36%, and those O-rings are only sort of static and very exposed. It turned the O-rings into a sort of paste. After taking it apart and seeing the effect, I am only surprised how fast it destroyed them.
So is there any reason to use EPDM over Viton other than cost? Phosphene?
boydski
Contributor
A couple of years ago we had a bad batch of EPDM O-rings that were sold to us as 90 durometer tank neck o-rings. We had a large number of failures (primarily extrusions of size 214 and 116). We tested the o-rings and found them to be very soft (less than 70), so have switched back to Viton O-rings and have not experienced an extrusion since.
With the viton o-rings readily available and nearly the same price as EPDM, we'll stick with viton for piece of mind.
YMMV,
With the viton o-rings readily available and nearly the same price as EPDM, we'll stick with viton for piece of mind.
YMMV,
....here we go again. I'll leave it to Puffer Fish to explain the advantages and disadvantages of FKM, EPDM, etc in the different applications mentioned here as he is indeed a true expert. But time and time again I see the statement, "for oxygen systems the aviation industry uses Nitrile/NBR/Buna N, etc." I've never worked in General Aviation so I cannot say for sure what puddle jumpers use, but on the military and commercial aircraft I've worked on I can say that most GOX (gaseous oxygen) system connections are metal on metal. The flexible seals I have come across in O2 systems have been Teflon or MS9385 (Mil Spec) which is Silicone! Military O-Ring MS9385 Mil Spec O-Rings
I cannot post proprietary info, but here is a PDF file I found online for a Boeing 737 O2 system just downstream of the bottle.
http://www.aerosup.com/Document/35/B737-300-400-500-ATA-CHAPTER-35-PART-2.pdf
Scroll down to page 57 item 55
I also don't know where this business of phosgene (or was it phosphine) gas came into these discussions. If FKM o-rings produce a toxic gas, it would have to be at a temperature high enough for me to believe one would have bigger problems.
Cheers,
Couv
I cannot post proprietary info, but here is a PDF file I found online for a Boeing 737 O2 system just downstream of the bottle.
http://www.aerosup.com/Document/35/B737-300-400-500-ATA-CHAPTER-35-PART-2.pdf
Scroll down to page 57 item 55
I also don't know where this business of phosgene (or was it phosphine) gas came into these discussions. If FKM o-rings produce a toxic gas, it would have to be at a temperature high enough for me to believe one would have bigger problems.
Cheers,
Couv
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Haha yeah, sorry to bring it up again. I've seen a lot of discussion on nitrile vs "ox compatible", but I was less satisfied by the EPDM/FKM discussion. McMaster-Carr has a nice table explaining the properties of various rubbers, but it's in terms of good/fair/poor. I'd really like more of a technical applications explanation, just for my own interest. I'm not running anything above 32% in the near future, nor do I do partial pressure, and in terms of O2 I'm sort of content to blindly follow industry standards.
Although I (clearly) don't know either way, phosgene does sound like a more reasonable byproduct than phosphine.
Although I (clearly) don't know either way, phosgene does sound like a more reasonable byproduct than phosphine.
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