Vintage valve o-rings

[Ron]

I have recently become certified to visual tanks and rebuild valves (officially instead of unofficially). PSI/PCI is a really smart group of guys, and they really advocate 90 durometer o-rings. In the past, I have used 70-75 durometer o-rings in rebuilding my vintage valves, but I recently ordered the 90 durometer ones as they are pretty cheap and I need more anyway. I am swapping these o-rings out this week as according to my literature they are more resistant to extrusion. I was wondering what everyone's experience was regarding this. Has anyone ever witnessed the lower duro rings extrude on a tank valve or neck? Are there any down sides to using the stiffer o-rings?

[luis]

At least in theory, the softer O-ring may conform a bit better if there is a minor scratch, but the 90 durometer will definitely resist extrusion better. That being said, the tank neck O-ring (and hose 3/8” ports) are very captive and if properly seated, there is metal to metal contact leaving basically no gap for the O-ring to extrude.

One place were the higher durometer can make a difference is in the regulator to valve interface (yoke or DIN). This type of face seal have been known to extrude if they are not seated properly (in both yoke and DIN… yes, contrary to what tech divers will tell you, I have seen DIN O-ring blow out inside the fitting).

I tend to prefer the 70 durometer O-rings for most applications, but have had good luck with both.

One other draw back of the higher durometer is that they tend to take a set a bit easier in the long run when they are compressed. If you service your valves and regulators every… lets say at east five to ten years, I don’t think either O-ring would be a big difference.

I have witnessed several yoke O-rings extrude and as far as I recall one tank neck O-ring extrude. In the case of the tank neck O-ring, the valve was obviously not properly seated.

The yoke and DIN O-ring blow outs were mostly operator error, but a couple of times the yoke or yoke screw was also deformed/ defective. A 90 durometer O-ring could have been less susceptible to operator error of minute defects in the connection.

[Ron]

Thanks Luis, that is good to know.

[NEDiver51]

Is the tank a Worthington? I know they had a problem with that on some of their tanks but it had nothing to do with the o-ring. Even with the o-ring removed the valve would not seat against the tank. With the valve seated you should not be able to see the o-ring between the valve and the tank, if you can it will not hold no matter what o-ring you use. This was only a small number of tanks that had this problem but some may still be out there.

[Greg Barlow]

For most dynamic applications I use 70-75 durometer O-rings, and 90 durometer for static. I also use a light coating of Christolube on just about every O-ring that I install. Typically, it is such a small amount that it just makes the surface appear a bit shiny. I use a bit more on the one found inside of the HP balance chamber of a diaphragm reg.

Greg

[usddude]

Hey Greg, what do you mean....dynamic or static applications?

usd

[Ron]

Steve, as in moving or non-moving. Greg is a science type so I will translate for you

An o-ring in a tank valve neck is a static application.

Your spring block o-ring in your conshelf is a dynamic application.

Hope that helps man.

[Herman]

Steve, as in moving or non-moving. Greg is a science type so I will translate for you

An o-ring in a tank valve neck is a static application.

Your spring block o-ring in your conshelf is a dynamic application.

Hope that helps man.

Oh goody I get to kick this can of worms again.

Not exactly Ron, while most consider O-rings in a service such as the tank neck seal as static, it's not. To be truly static it also has to not have any relative motion between the sealing parts during installation as well as while in service, the O-ring between the reg and the tank valve is an example of a true static O-ring. The rub...if you will forgive the pun...is that when most o-rings used in scuba are installed, like tank neck o-ring, there is motion between the sealed parts and the o-ring, making it dynamic at that point in time and once it is dynamic it stays that way regardless of how little it moves. Granted I am being picky but truly static o-rings needs no lubrication as opposed to dynamic ones that need to be lubed to prevent distortion when it slides past the mating surfaces. When assembling a tank valve there are mating surfaces sliding past the O-ring, therefore it needs to be lubed and is dynamic at that point in time. Yea, I'm being a picky SOB but if I can't mess you, who can I mess with.

.......oh crap, I was going to see if you had a certain o-ring, not the best time to mess with you.

[usddude]

Thanks Ron, I understand now. Static=stationary and Dynamic=movement. Herman you are digging in a bit deeper but with some thought I know what you are saying. I believe there is movement of every part of the regulator upon assembly. So what about constant movement during operation. Does that narrow down static and dynamic? Is there really absolutely no static oring's in a regulator......what about valves in this regard.

I thought that a gasket is static and an oring is dynamic...hence the need for an oring....
Gasket for static applications
Oring for dynamic applications

Exceptions? Yeah there are plenty.

I am sure that the oring seal for the lens on the Darrell-Allan 400 bug light is static. A good example of a static oring(exception to the rule)

usd

[Ron]

Herman, you are a wonderfully complex individual, and I say that as a guy who builds networks for a living. I have plenty of o-rings and you are welcome to them

[luis]

I have talked to some very experienced technicians (who I respect their point of view) that will tell you that under no circumstance should you ever lubricate a tank neck O-ring. I personally do not agree, but I can’t argue with the fact that many tanks have been successfully assembled with no lubricant on the O-ring.

Their argument is that any lubricant in the tank neck O-ring will assist it to slide and extrude. My argument is that in a properly seated tank neck there is metal to metal contact and absolutely no gap to allow any O-ring to extrude.

Does the neck O-ring really needs lubricant… well (a very small amount) I think does help and it shouldn’t hurt if properly seated.


The only O-rings that never experience any sliding during assembly are face seals (as Herman mentioned). In the case of Scuba gear, the only face seal I can think of right away is the regulator to tank seal (for both yoke and DIN, they are the same).

Most O-ring in regulators are gland seals or corner crushed seals. Corner crushed seals are like the tank neck O-ring or the 3/8” LP hose port O-rings.

Gland seals are radial sealing O-ring that seal between a male and a female cylindrical shapes. Some gland seals are always dynamic in function, for example piston O-rings, balancing chamber in a RAM, second stage swivel hose, etc. Gland seals that are static during operation are like the Phoenix RAM volcano orifice O-ring, volcano orifice on many second stages, etc.

All gland seals need at least a minimum amount of lubrication for assembly since they often have to compress and slide a fair amount during assembly. And of course if their function requires constant sliding they need to be well lubricated.

Corner crushed seals tend to slide a very minimal amount and the compression of the O-ring only increases towards the end of the screwing of the fitting. Therefore the need of lubricant may not be as critical, but I personally think it helps.

The argument that lubricating an O-ring will help it extrude is IMHO an indication that there is an inappropriate gap allowing the O-ring to extrude. Friction should not be what holds an O-ring in place (that is not to say that sometimes we take whatever we can get when we are trying to seal some of this old gear).


Sorry about the long post… I hope it helps.

[Herman]

Semanics mainly, an o-ring is an o-ring reguardless of how it's used. The same o-ring can be used as a gasket -a true static o-ring- or as a seal- a dynamic o-ring. Off hand, the only true static o-rings I can think of that are used in scuba are the tank valve to reg interface (yoke type) and I have seen one or 2 used as gaskets for BC inflator and dump valves. Every other application has some movement involved, either as part of normal operation or during assembly. Most people consider an o-ring to be static if it is not subject to movement during normal operation but the fact remains, there is movement between the mating surfaces and the o-ring during assembly, making it dynamic at that point in time. Most of the time you can get away with treating it as static because the movement is usually only for a short span and not likely to cause problems. Still, I treat them as dynamic and lube them.

[Herman]

Herman, you are a wonderfully complex individual, and I say that as a guy who builds networks for a living. I have plenty of o-rings and you are welcome to them

I am going to have to remember that one....my wife just thinks I am a pain in the ass.

[Ron]

Herman, you are a wonderfully complex individual, and I say that as a guy who builds networks for a living. I have plenty of o-rings and you are welcome to them

I am going to have to remember that one....my wife just thinks I am a pain in the ass.

Funny, that's another thing we have in common my friend...Anna says the same thing about me

[Robohips77]

One tank neck o-ring extrusion but I lived through the accident.! One DIn to Valve o-ring extrusion and as Luis said it was operator error. Like Greg I use Christo Lube and not the Dow Corning 111 silicone for lubing o-rings. Over an extended period of time I have noticed that the tank/ air fills with O rings lubed with silicone seem to pick up a "smell" of what I would call a "carbon" smell for lack of a better word or scientific explanation. I did however send this air in to Trace Analytics for a quarterly test and it passed with flying colors on there qualifications for Grade E air, but because of my "sniffer" test and request they failed it in the final outcome. So with that said I think I sufficiently high jacked this thread!