settle disagreement on din/yoke valve and max pressure

[MEL-DC Diver]

first the dot will not authorize yokes for that high.. 3446 is the most thats why those tanks are rated that way.. The big issue is, can the yoke you are using handle the pressure.. alot of the older yokes are not made to support pressures that high (some of the really old yoke really weren;t meant for even 3000 psi!!!)... the newer yokes are beefier... Also the higher the pressure goes the greater your chance for o-ring extrusion..

Funny, I was going to raise a question along these lines today. Now, I am the first to admit that when it comes to tanks and valves that I am a relative novice. Basically, I dive 80 Cu. Ft. steel tanks that I rent from the shop set up for yoke. My reg is a yoke Zeagle ZX/50D that I have about 15 dives on. I have never had any problems until yesterday when I set up my rig.

I hooked my first stage up to the tank and made the LP connection to my inflator hose, turned on my gas, and purged my reg and BAM! - air bursting from my tank/first stage connection. I reconnected a couple of times more, each time with the same result - o-ring extrustion. Anyway, I replaced the o-ring w/ a new one and re-connected and had no problems on my first dive. On my second dive, I was on the boat and gearing up when it happened again. I re-seated the o-ring and did a few purge tests and it seemed to be fine after that. This whole thing was odd and more than a little disconcerting. Visual inspection of my first stage revealed no problems w/ it. I have never had any problems like this before and am not anxious to have them again, so can anybody shed a little light on what this problem might be? I was at 3200 and 3100 psi, respectively - could it be an 'old' yoke on the tank?

 

[gjmmotors]

Yeah that is what I thought about the older tanks, I had never seen a yoke valve on a HP tank until the new PST's came around.
- g mount

The older HP tanks were 3500 psi and came with 300 bar valve and there were no yoke regs, or valves, made that would fit a HP tank. The LP tanks came with a 232 bar DIN valve that had an incert that could be screwed in to accept a yoke reg just like the E series tanks do now. This incert could be screwed into a 300 bar valve but still would not work with a yoke reg, even if it would fit, as it would screw in to far to seal the o-ring to the reg first stage.

Yoke regs I've owned over the years were stamped with 3000 PSI right on the yoke which leads me to believe that they were not designed to handle the increased pressure of HP tanks. Now many of us pump our LP tanks to 3000 psi even though they're stamped with a working pressure of 2640 psi at 10% overfill and they work just fine with high pressure burst disks installed. I'm sure the reg would probably work just as well at the higher pressure but would you really want a first stage with a 3000 psi yoke attached to a 3500 psi tank right behind you're head?

If you're interested in going with a DIN valve go with the high pressure, 300 bar, valve and be done with it.

 

[Rick Inman]

Some further explanation on how this question came up.

I was given a PST E series Steel 100 . Of course it came with the 3500 din valve, and like padipro said, the inserts that came with my LP Faber 95's screw in too far for a yoke reg to seal onto.

Since I already have the two 95's that you can remove the inserts from and turn into din, and now I have the din steel 100, and because din is superior anyway, I'm going to order the din conversion kit for my Atomic M1. So the question is mostly theoretical. Here's how it came up.

A friend I was diving with has an LP95 that has a yoke valve with a 5000psi working pressure. I have an extra yoke 3000psi valve and he offered to trade me so I could put the 5000psi yoke valve into the hp100 to use until I get the conversion kit.

That's how the question came up.

BTW, the Atomic M1 yoke is rated to 300 bar, so the 3500psi is no problem.

 

[DA Aquamaster]

Recently I had a customer call ScubaPro about his 1 year old reg and he was told that the yoke could not handle the 3442psi on his new PST. Yet most of the people that I see diving the PST tanks use them with a yoke connection, becasue this is what they already have and are familar with them. It's all very dodgy.

Scubapro lists the maximum working pressure for both the international (yoke) and 200 bar DIN connection as 232 bar/3365 psi. So technically 3442 to 3500 psi tanks are over this limit. But on the other hand, 77 to 135 psi is not a great deal of pressure over the limit and would most likely fall within the design's fudge factor.

So SP is not going to approve it as it exceeds the design specifications. But it would probably work without any serious issues - in most cases, most of the time. Whether you use it then or not is a question of whether you are personally ok with your life support equipment working most of the time.

 

[pescador775]

Alright, forget what you think you know. The original yoke valves were similar to "medical" valves, which they imitated. All styles of valves in the 1950's whether J, K or R styles, used the yoke clamp connection. However, early on USD began employing O rings while Healthways, Dacor and others used teflon washers for the air tight connection. Although these were vastly superior to the oxygen (medical) valve it became apparent that the O ring was the way to go. The original O ring designs fitted into a rather large annulus (groove) and the regulator sealed to the valve by crushing the O ring. Although an O ring was used, the arrangement was still very similar to the old washer set up. The maximum safe pressure was 3000 psi. During the 60's and 70's there was some experimentation with valve design resulting in several new types which gained market acceptance. However, it was not until 1977, when Sherwood abandoned the old crush washer/O ring concept, that a yoke valve was manufactured which could handle pressures up to 4000 psi. Indeed, in response, beefed up yoke style regulators of the 70's period were stamped "4000wp". This was later changed to 3000wp for liability reasons connected to European standards and advice from lawyers. However, this did not change the fact that the improved Sherwood valve design would soon become universally adopted. The change involved reducing the size of the annulus outer perimeter so that the regulator no longer crushed the O ring but rested on metal (metal to metal) and compressed the valve O ring only enough to form a seal. This arrangement is similar to the "captured" O ring of the DIN. However, since the inner perimeter of the annulus does not capture the O ring it cannot be rightly called captured even if the effect is much the same. This is because the inner radius is not subject to explosive forces from the tank pressure which vector outwards. Pressure trys to force the O ring outwards, but cannot succeed in the new valve because the O ring is locked in place by the metal to metal interface of the regulator and valve. This new design could only be accomplished by making the annulus smaller in diameter and that is the reason that O rings for modern valves are somewhat skinnier than those use in very old valves. If a good valve is fitted with a new, silicone (white) O ring, then 3500 psi is no problem at all for the yoke connection.

 

[Leadking]

While the manufactures can stamp various ratings on their yokes the CGA and ISO actually set the standards. DOT says to use the CGA standard or any other "RECOGNIZED STANDARDS" for outlet configurations. CGA does not recognize the Yoke configuration above 3000 psi, ISO recognizes it to 230 bar @15C/which has been temperature corrected to 3442 psi@70F for the US.

 

[liberato]

Scubapro lists the maximum working pressure for both the international (yoke) and 200 bar DIN connection as 232 bar/3365 psi...

...ISO recognizes it to 230 bar @15C/which has been temperature corrected to 3442 psi@70F for the US.

So, is it just the temperature correction that has 232 bar equaling 3365 psi on the one hand and 230 bar equaling 3442 psi on the other?

 

[pescador775]

About the CGA. I would like to point out that SCUBA valves do not have a CGA designation. Neither do SCUBA regulator connectors. They exist in a world of their own where the manufacturers do what is needed to provide safe equipment above and beyond any CGA influence. The CGA has little competence in this area in any case.

The only safety issue with the yoke connection is long term integrety of the valve and regulator. It happens that rental tanks are abused either by the customers, or by the shops whose employees might bang the tanks around or attempt to change O rings with an ice pick. However, a GOOD valve with a MODERN yoke design can easily abide pressures in the 3500 psi range. Again with the O ring. The white O ring seems to be made of a harder material than the black. This is recommended but not mandatory for a safe hookup at high pressure, not only for the high durometer but also for the fact that the white O rings will outlast the neoprene by a factor of three.

 

[liberato]

I have never seen these white silicone O-rings you mention. Is this something new in SCUBA? In any case, I wouldn't want silicone if I wanted an oxygen clean tank, right?

From Dive Rite Express:

Acrylonitrile-Butadine Copolymers (NBR or Nitrile)
Most O-rings used in SCUBA are made from Nitrile, a hydrocarbon based synthetic rubber. Nitrile offers excellent resistance to many oils and acids and has good physical properties. However, Nitrile is not a very oxygen resistant material and is not considered oxygen compatible. Nitrile is also often referred to as Buna-N.

Fluorocarbon Elastomers(FKM)
O-rings made of FKM have been the preferred choice for oxygen and nitrox compatibility in SCUBA diving applications. FKM is an elastomer with excellent oil and oxygen resistance at high and low temperatures, very good chemical resistance. Even for use with ordinary air, most experts agree that FKM O-rings outperform common Nitrile O-rings. Viton is DuPont Dow's brand name for FKM.

Polyurethane(PUR)
The milky white O-ring occasionally seen in the face of K-valves, sometimes called a 10,000 psi O-ring, is made of Polyurethane. Polyurethane is very abrasion-resistant, but it is sensitive to UV light (sunlight).

Ethylene Propylene Diene Monomer (EPDM)
EPDM O-rings are becoming more common in SCUBA because some people feel it's a better oxygen-compatible material for use in breathing air systems. EPDM is a high performance elastomer with excellent weatherability, heat resistance, dielectric qualities and odor-free characteristics. However, EPDM is less resilient and is not recommended for use with petroleum derivatives.​

 

[pescador775]

Liberato, thanks for that, interesting. Back in the day somebody told me that the white O rings were made of "silicone". polyurethane makes more sense. Anyway, I identified them as "white" and they were once carried by dive shops. Whatever they are made of, they eventually turn yellow or brownish like silicone. They are NOT sensitive to UV as stated above except for the color change. I stocked up on whites some time ago and I swear by them.

About NITROX: there are a lot of misconceptions. Viton, etc are only necessary when pure oxygen is used, and that is only when the exposure occurs over extended time such as would occur with the tank neck ring. I prefer Viton for this particular ring used in emergency O2 tanks. Nitrox has no effect on conventional O ring materials including the white rings.