1st stage question

[Richard Atyeo]

I bought a al 45 with a us diver titan diaphram 1st stage. When i took the 1st stage in to have it serviced and o2 cleaned i was told you cant use it as an o2 reg. Has anyone else ran into this problem.


Richard

[DA Aquamaster]

It would not be my first choice as the diaphragm is essentially a great big piece of fuel, and I greatly prefer fairly simple "flow through" or even simpler "flow by" piston designs for use as O2 regs.

But with proper cleaning and use of O2 compatible materials to the extent possible in the seat and o-rings, it will *probably* work fine provided you use good technique. But that's a much lower bar than getting a regulator manufacturer or dealer to give it approval for use with 100% O2.

[graepaep]

I had to think about it, it's been a little while since I looked at these. I agree with DA about the diaphram but it is only subject to IP pressure (~140 psi). The HP seat however used to be made out of a rubber material. If it still is then I would definitely not use it since the HP seat is subject to the fill pressure of the tank.

[huxley]

Not 100 percent sure what exact stage it is but think I can narrow it down. Us divers are aqualung stages, and I know that the conshelf is very similar to the newer titan stages from aqualung. They use the same service kit if I;m correct. I would need to look up the exact difference but remember it was one part that is now replaceable while the old design had it as part of the body.
Anyhow I have some conshelfs and other aqualung regs that I service myself after having several bad experiences bringing it to service and redo it myself. Leaks and wrong side o rings as well as bad knowledge of those regs must have contributed to that, since they are not to common.
Those regs are prooven and no need to modify other than a new exterior design or some weight reduction. If you take one apart you will see, simplicity makes those reliable regs. Getting the right service kit is not always easy since aqualung tries to sell these to dealers only.

Anyhow back to your question, diaphragm is not the issue here. Those regs perform well with 100% o2, I obmit they are a little overkill for this purpose since you mod is quite shallow and all you need is a simple unregulated piston reg unless you spend hours on deck and like the comfort. The simpler the better and more reliable.
The conshelf itself is not supposed to be used with high o2 because of a design issue within the body. I believe it was some sharp turns or narrow restriction or something similar. Excessive organic build up, pressure and the heat from friction at this area was considered to be a risk so they declared this as a not o2 regulator.
Whatever you do with it is up to you, I've seen people using it without a problem, not sure if there was ever a recorded problem maybe just sales technique to sell the next better product.
I for myself use it as decko reg, o2 cleaned for up to 50% on my 80. For o2 I have a simple oms workhorse piston unbalanced, those things have 3 parts or so inside and you can almost service them under water.

Hope I could help, send me a pic and I check if that is the one I think it is. If you need manuals let me know, I should have service kits as well or at least a source.

[Sludge]

Anyhow back to your question, diaphragm is not the issue here.

There is a 1 1/2" disk of butyl rubber that comes in direct contact with the oxygen.

[JahJahwarrior]

I've seen them used with o2 before, but the giant rubber disk is a good fuel source for an o2 fire.


OMS workhorse and similar designs are dirt cheap. They have much less fuel source.

[a64pilot]

just curious, but isn't the O ring that seals to the tank valve on all first stage regs in direct contact with O2 at tank pressure? Is it the material it's made form, or is it what it may become contaminated with that is the issue?

[DA Aquamaster]

On a reg intended for O2 service the DIN fitting O-ring will be either Viton or EPDM, which both have higher ignition temps than butyl rubber. EVERYTHNG will burn in a 100% O2 environment if the ignition temperature is high enough so what you are gaining with O2 compatible materials is a slightly higher ignition temperature and greater safety margin when using the regulator.

"O2 clean is also a relative term as even if you did it in a NASA clean room, it starts becoming less clean almost immediately. O2 compatible gases have lower amounts of hydrocarbons to help keep O2 and high percentage O2 nitrox regs cleaner, but contaminants can still build up. That's important as those contaminants may have much lower ignition temps in a high O2 environment. So if you have an adequate ignition temp, you could start a fire, and if you have enough contaminants in the reg to create enough heat to start lighting up the O-rings, etc you'll get more than just a flash fire. A large rubber diaphragm pretty much ensures life will get interesting if it ever catches fire.

I have serviced regs that have had O2 fires, and in most cases it gets brought in as it started leaking during the dive. Once you open it up, you'll see the evidence of the fire in the form of charred o-rings. It's pretty rare to have a reg fail and throw pieces of itself around, but it has happened, and you hear about the occasional rebreather fire that may have similar origins.

Butyl rubber is used in aircraft O2 systems and welding equipment all the time and it's not a problem as the valves are designed to be slow opening with no sharp bends or sharp edges, and they avoid any ignition sources that could be created by adiabatic compression, or by the flow of gas across a sharp edge. Scuba regulators and scuba valves do not have the same design goals and can create those types of ignition sources.

Consequently, divers using O2 for deco should open the tank valve slowly, and ideally depress the second stage slightly, to bring the reg up to pressure slowly with minimal adiabatic heating. In the real world, divers are concerned with all the other aspects of a gas switch and pretty much ignore this (and I'm as guilty as anyone else) so it's a good idea to make the reg as idiot proof as possible. Thus I try to avoid diaphragm regs on my O2 bottle.

[Art Greenberg]

There is a 1 1/2" disk of butyl rubber that comes in direct contact with the oxygen.

Yes. At intermediate pressure. Same as the neoprene hose going to the second stage. So its not really an issue so long as the regulator is working correctly.

[DA Aquamaster]

Yes. At intermediate pressure. Same as the neoprene hose going to the second stage. So its not really an issue so long as the regulator is working correctly.

It's not quite the same issue.

The rubber in the low pressure hose is well downstream of where the adiabatic compression is happening and is fairly far removed from where any ignition will occur. So even if you have a flash fire in the reg, things will be cooled significantly before any thing reaches the hose. However, the diaphragm is right there just downstream of the orifice, and it's far more likely to light up than the hose.

Also, most diaphragms are still pretty thick as the convention in Europe is to use them until they are in actual need of replacement - which is probably every 10 years. However companies are moving toward thinner diaphragms to gain better response time and greater working range in the valve and those thinner diaphragm will tolerate less pressure and less heat and charring in the event of a flash fire, than the older, thicker diaphragms, increasing the risk of a serious gas loss failure rather than leakage past charred o-rings.