Thin yolks vs tank pressure.

[Eric Sedletzky]

I'm just wondering what the rating is on the thin yolks on older regulators.
I know they were fine for LP tanks of the past but has anybody ever seen one break and blast away from too high a tank pressure such as over 3000 PSI?

 

[Nemrod]

No, but, I do see some stretch. N

 

[redacted]

The Captain has said he uses them with no problem. I have not tried the light yoke (3/8ths screw) but do use the older "3000" yokes with the 7/16th inch yoke screw. I believe the expected failure mode is the yoke will slowly stretch and gets to the point where it will not made a good seal on the tank. My old style Mk3 has the 7/16th screw.

 

[Luis H]

I have also seen some of the thin yokes flex, but don’t expect a catastrophic failure.
The most likely failure mode is for the yoke to flex enough to allow the O-ring to extrude and blow the O-ring.

 

[Eric Sedletzky]

OK, I won't worry about it then. I just didn't want to get popped in the back of the head by a projectile first stage.

Thanks

 

[captain]

The US Navy was using the early thin yokes on 3000 psi cylinders since the mid 1950's

 

[Nemrod]

I would not worry about it too much unless I was going past 3,000 psi. Of course thsi is one of the things the factory heavy yokes or phoenix bring to the party is the bullet proof yokes. Unfortunately the standard factory heavy yoke opening is not enough in most cases to accept a banjo with modern valves. I wish vdh would make a long-heavy yoke (hint, hint) for those who want to use a banjo rather than a Phoenix.

N

 

[Zung]

Watch, wait and you will find.
I've been able to buy current SP yoke parts on eBay for cheap from the TEC (and other) guys who favor DIN. I think I paid less than $10 a piece on the average.

 

[Akimbo]

I still have a clamp-on pressure gauge from the early 1960s with a 3000 PSI gauge on it. I used it hundreds of times on Aluminum 80s. I can put a caliper on the yoke so you can compare the cross sections… but I believe you have nothing to be concerned over.

 

[John C. Ratliff]

I went through the US Navy Underwater Swimmers School in 1967, and we were using this "thin" yolk all the time on 3000 psi systems (the Navy AL twin 90s). I have used them on my 3000 psi twin 50s with no problem (Aquamaster).

I understand that USD says that a Mistral can be used on 3000 psi systems (one of their manuals said to test for leaks at 3000 psi), and that Cousteau used them at even higher pressures (La Spiro Mistral). But I had one bad experience, not with the yolk (which did just fine), but with the seat being damaged on one Mistral at 3000 psi. It could have been a very old seat too, but I wanted to pass that along.

SeaRat