halocline
Contributor
Couv, you really know your o-rings!
O-Rings
- Thread starter olkev
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Glad to help. I have learned so much from this site, it feels good to have something to contribute.
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Personally, I have had good results with basic Nitrile (Buna-N) O-rings.
I will use 90 durometer for any application where the O-ring can be extruded…like a gland seal (like piston seals). For face seals (valve to regulator interface, yoke or DIN, they are the same) or corner crush seals (tank neck or hose to 1st stage) either 70 or 90 durometer can be used, but I prefer 90 durometer for that rare chance that the fitting is not seated perfectly and there is a chance of extrusion.
A “properly mated” face seal or corner crushed seal should have very close to zero clearance for the O-ring to be extruded. Therefore, the 90 durometer is not as important and 70 durometer would have the advantage of better conforming to any irregularities (like surface scratches).
Just as a note: gland seals can be static (some of the barrels in second stages, etc.) or dynamic (any moving part, piston, swivels, etc.). Dynamic O-ring seals, other than gland seals, are very rare even in industrial applications.
The max O2 I dive is <40% and even with any high % of O2 (including 100%) a regulator would rarely be exposed to more a few hours a week to any high partial pressure of O2. So, I have not seen a need to change to Viton, but I am open to suggestions. O-rings in a tank valve will have long exposure to O2, but a regulator (for a non-commercial diver) would normally have very limited exposure (sadly, but true).
The way I feel about it, a regulator O-ring is working in a very benign environment as compared to an industrial O-ring. It is exposed to salt water, salt crystals, and some times sand, etc., but the temperature range is relatively small… chemical, oils, industrial dirt are also much harsher that any regulator will experience. Heck many industrial O-rings work 24 hours a day in environments to harsh for the human body.
There is also the issue with shelf live. All the Mil-spec O-ring packages I have seen have a date and they were supposed to be discarded after some time. Well, I have regulators with O-rings that are over 35 years old and they work fine. Again, I am very open to suggestions, but I haven’t yet seen a need to replace them.
I guess that I am a believer on the “if it isn’t broke don’t fix it”.
Let me add that IMO a small O-ring air leak is a major annoyance, but it is rarely of any concern. That being said I have very little tolerance for malfunctioning equipment…I don’t like leaks.
I am far from being an O-ring expert (nor did I stay on a Holiday Inn), but I did worked with a true O-ring expert close to 20 years ago (some people actually make a living from being an O-ring expert). I was going to look up information from the Parker O-ring book and other sources, but decided to just offer some opinions based on some experience instead…
I will use 90 durometer for any application where the O-ring can be extruded…like a gland seal (like piston seals). For face seals (valve to regulator interface, yoke or DIN, they are the same) or corner crush seals (tank neck or hose to 1st stage) either 70 or 90 durometer can be used, but I prefer 90 durometer for that rare chance that the fitting is not seated perfectly and there is a chance of extrusion.
A “properly mated” face seal or corner crushed seal should have very close to zero clearance for the O-ring to be extruded. Therefore, the 90 durometer is not as important and 70 durometer would have the advantage of better conforming to any irregularities (like surface scratches).
Just as a note: gland seals can be static (some of the barrels in second stages, etc.) or dynamic (any moving part, piston, swivels, etc.). Dynamic O-ring seals, other than gland seals, are very rare even in industrial applications.
The max O2 I dive is <40% and even with any high % of O2 (including 100%) a regulator would rarely be exposed to more a few hours a week to any high partial pressure of O2. So, I have not seen a need to change to Viton, but I am open to suggestions. O-rings in a tank valve will have long exposure to O2, but a regulator (for a non-commercial diver) would normally have very limited exposure (sadly, but true).
The way I feel about it, a regulator O-ring is working in a very benign environment as compared to an industrial O-ring. It is exposed to salt water, salt crystals, and some times sand, etc., but the temperature range is relatively small… chemical, oils, industrial dirt are also much harsher that any regulator will experience. Heck many industrial O-rings work 24 hours a day in environments to harsh for the human body.
There is also the issue with shelf live. All the Mil-spec O-ring packages I have seen have a date and they were supposed to be discarded after some time. Well, I have regulators with O-rings that are over 35 years old and they work fine. Again, I am very open to suggestions, but I haven’t yet seen a need to replace them.
I guess that I am a believer on the “if it isn’t broke don’t fix it”.
Let me add that IMO a small O-ring air leak is a major annoyance, but it is rarely of any concern. That being said I have very little tolerance for malfunctioning equipment…I don’t like leaks.
I am far from being an O-ring expert (nor did I stay on a Holiday Inn), but I did worked with a true O-ring expert close to 20 years ago (some people actually make a living from being an O-ring expert). I was going to look up information from the Parker O-ring book and other sources, but decided to just offer some opinions based on some experience instead…
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halocline
Contributor
I have found that my MK10 with a polyurethene hp piston o-ring has less of an IP drop from 3000-500PSI supply pressure than my MK10 with a hp o-ring from a new kit, which I assume to be EDPM. The only reason I can think of for MK10 IP drop over supply pressure is a slight extrusion of the hp o-ring which causes some friction on the piston shaft. I think I'm getting enough Christolube in there; I lube the o-ring, bullet, and piston shaft.
So, I'm going to order some polyurethene 010 90 duro o-rings and start using them. Actually I was thinking of polyurethene o-rings for the piston head as well, and EDPM or nitrile for everything else. I would not bother with viton for nitrox blends; a crucial one would be the hp piston o-ring and that's the one subject to extrusion, and apparently viton has poor resistance to extrusion and abrasion.
I guess that means I'd think twice about a MK10 for 100% O2 use. My MK2 would be perfect for that, with no dynamic o-rings subject to high pressure.
So, I'm going to order some polyurethene 010 90 duro o-rings and start using them. Actually I was thinking of polyurethene o-rings for the piston head as well, and EDPM or nitrile for everything else. I would not bother with viton for nitrox blends; a crucial one would be the hp piston o-ring and that's the one subject to extrusion, and apparently viton has poor resistance to extrusion and abrasion.
I guess that means I'd think twice about a MK10 for 100% O2 use. My MK2 would be perfect for that, with no dynamic o-rings subject to high pressure.
pescador775
Contributor
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Mattboy and Luis and a couple others are on top of the situation. Let me summarize.
Viton is crap. It has terrible mechanical properties. However, it can be used for some static applications. The best, cost effective material is Buna N. For regulator pistons use urethane in the correct durometer. For everything else except the valve face, use 70 duro Nitrile. For the valve face use 90 duro nitrile. For a tank to be charged with high pressure oxygen, the large valve O ring should be EPDM or Viton, 70 duro. (If made of a funny color the annual tank inspection will possibly go smoother).
Waterskier, this is not rocket science but there are a few general rules as said above. Use a practical method, ala Hoosier, to size the required O rings. Don't overthink it.
Viton is crap. It has terrible mechanical properties. However, it can be used for some static applications. The best, cost effective material is Buna N. For regulator pistons use urethane in the correct durometer. For everything else except the valve face, use 70 duro Nitrile. For the valve face use 90 duro nitrile. For a tank to be charged with high pressure oxygen, the large valve O ring should be EPDM or Viton, 70 duro. (If made of a funny color the annual tank inspection will possibly go smoother).
Waterskier, this is not rocket science but there are a few general rules as said above. Use a practical method, ala Hoosier, to size the required O rings. Don't overthink it.
Exactly,
A few years ago (quite a few actually) I was working on a high pressure pneumatic system on an old fighter aircraft. One of the original seals was made from leather. That seal was not leaking, I just had to open that part of the system up to perform other maintenance.
couv
By large valve oring, I assume you mean the oring in the valve seat, that the regulator seals on. This oring needs to be harder (Shore A-90) durometer. 70 durometer orings typically extrude out & fail at 3000 psi.
Mike D
Retired Instructor
O2 technician
Gas Blender
Mike D
Retired Instructor
O2 technician
Gas Blender
Im kind of confused now too. I thought by large O-ring Pesky meant the tank to Valve O-ring which is larger than the valve to reg O-ring. But, Im pretty sure that has to be 90 duro. I just got my pony bottle back, and Im not sure what they put on for that O-Ring after the VIP, but it extruded last weekend, and Ive lost much of the air. Im guessing it extruded because it was too soft. I know it wasnt Viton, because the one that was on there when I took it in was, and the tech asked me if I was using the pony for O2, and I told him only air, with the possibility of going to 36% Nitrox, continuously blended (not partial pressure). So he put on whatever the O-ring is, based upon that.
Im thinking that both the tank to valve and the valve to regulator O-Rings need to be 90 duro, no matter what the material?
Agreed Waterskier1.
Both 0rings see 3000 psi drop. Standard 70 durometer are typically rated to max 1500 psi.
Mike D
Both 0rings see 3000 psi drop. Standard 70 durometer are typically rated to max 1500 psi.
Mike D
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