Yoke valves on a PST HP120?

[Luis H]

In 1999, a dealer lost one of my tanks and replaced it with a new HP 100. I mulled over what to do with this tank with the unusual neck thread and funny valve. I decided to start using the new tank but I needed two more to match. Since I normally carry three matching tanks on a weekend trip and since I had an existing investment in equipment with yoke clamps including tanks, regulators, compressors, etc, I decided to stay with the yoke format while trading up to the new type tanks; and that meant I needed to swap out tanks and get yoke valves for the new ones. I traded some cylinders, bought two more HP's and then had a buddy machine three Sherwood yoke valves to the 7/8 thread. The mods were described on the net which seemed to surprise some people and there was some "stroke" talk about weak yokes, etc. However, I have not had any problems with this arrangement. Since then, I have tried to explain to the SB people about the actual potential of the yoke clamp and the valves and O rings which characterize the modern yoke valve but I doubt that it has stuck. Some yoke clamps are functional up to 4000 psi with a safe margin. I know this from "stretch" tests which I performed. There is no black magic about the actual mod. The valve has to be stripped and shimmed into a lathe, then turned. Clean the modified valve in O2 safe solvent, reassemble including the correct disk, and install the O ring, then insert in tank to about 30-40 lb-ft torque.

Yeap…I agree with you. I don’t know if you have seen some of my several write ups about yoke versus DIN connections.

They both have advantages and disadvantages.

I started using DIN fitting back in the early 70’s before they were available in any US manufactured regulator. I actually found a letter I wrote to Scubapro back in 1977 to see if they had a DIN connection for the MK-5. At the time it wasn’t even called a DIN it was just a threaded connection.

In any case I have gone back to using all yokes due to the convenience and long term durability.

And yes a modern yoke can easily handle 5000 psi with plenty of safety factor. Cousteau used vintage yokes with 5000 psi many years ago.

 

[oxyhacker]

Though not necessarily with just any O-ring.

And yes a modern yoke can easily handle 5000 psi with plenty of safety factor. Cousteau used vintage yokes with 5000 psi many years ago.

 

[pescador775]

About the O ring; I understand that the duplex valve (DIN/yoke) which is becoming popular on the newer HP tanks uses the old style, 112 O ring for the yoke connection. I don't think highly of this arrangement but I guess it works. I mean, where are the complaints about blow outs, etc? Back in the day, before the new type, thin, 90 duro (014) O ring came into use, the fat, soft, 70 duro rings would occasionally pinch or extrude under high pressure. Still, that was probably more commonly related to poor maintenance than anything. I think that rental tank users have had problems even with the newer valve/O ring combinations. We used to hear their stories on SB from time to time.

The fat O ring was being used in similar way to a washer, eg they were compressed between the regulator and the valve; the tighter the yoke, the more the ring was compressed. The modern yoke valve does not allow this. In 1977, the valve face was redesigned by Sherwood specifically to accomodate high pressures. The amount of O ring compression is limited by the design of the valve face. I call this design "semi-captured". It is actually good to torque down a yoke on the modern valve. That is the reason that US Divers original, 4000 psi, yoke clamp design which appeared in the 1970's had that huge, thick yoke and knob. In any case, we're back to the fat washer setup on those combination valves. I guess that the manufacturer is using a harder rubber, as is done with the thin O ring, since that may increase reliability.

 

[Under Pressure]

While yokes used to be used for higher pressures, all standards have now changed so that the maximum pressure for a yoke valve is 230 Bar. Nowhere in the world is a yoke used above that pressure anymore.

 

[Hoosier]

Modern Sherwood Yoke valves are even rated at 5000 psi. Based on my limited experience, if you put more than 3400 psi, you need to get duro 90 O-ring, otherwise, you have to replace an O-ring more frequently. As you may know, duro represents the hardness, not CS (fat or thin).


The following picture shows an O-ring rapture with a frequent overfill:

 

[oxyhacker]

Are you sure about that? If you are referring to the big "5000" on the lablel, my impression is that that's just the model number, and has nothing to do with pressure.

Modern Sherwood Yoke valves are even rated at 5000 psi.

 

[Hoosier]

A pair of Sherwood Yoke valves came with 5000 psi rating (and sticker 5000 psi) and burst disk. I have already sold it after replacing with DIN, but I might still keep the pictures somewhere in my archives.

 

[oxyhacker]

Collectors items! Should have held on to them, just to bang skeptics like me over the head with.

I would love to see the pictures, if you ever find them.

A pair of Sherwood Yoke valves came with 5000 psi rating (and sticker 5000 psi) and burst disk. I have already sold it after replacing with DIN, but I might still keep the pictures somewhere in my archives.

 

[WD8CDH]

I had a Sherwood 5000 valve that had a 8333psi burst disk in it. The Sherwood 5000 SCUBA valve uses the same rebuild kit as some of the Sherwood 6000psi industrial valves.

 

[Hoosier]

Collectors items! Should have held on to them, just to bang skeptics like me over the head with.

I would love to see the pictures, if you ever find them.

Really..... ? I gave away these valves (pair) to a local college kid when I replaced my all valves with DIN. I thought it was the pointless to use 5000psi valve on 3000 psi tanks...

Sorry. I can't find the picture. I used to take some picture for sale, but I might not take any pictures because I just gave it away.

I will ask some pictures when I can meet the kid.