HP Steel tanks with Yoke valves

[ChrisA]

Notice that the working pressure of those new steel tanks is 3442. They picked that odd-ball number for a good reason. Technically it is ust "under the wire" for when a DIN connection would be requied. DIN is required for 3500 PSI tanks but not for 3442PSI.

You can buy a $50 adaptor to ues your DIN reg on a yoke tank or you can have the reg converted for about the same price.

 

[pescador775]

I use 3500 psi tanks made by Pressed Steel Tank. In 1999, to maintain compatibility of all my gear, I machined several Sherwood standard yoke valves to 7/8 machine thread, the type used on the small necks of the HP tanks. I have never had a problem with this arrangement. However, the valve face O rings employed are the white, urethane type know as "10000 psi" O rings. Although I have also tried the soft, black O rings without problem I feel more confident in the white O ring. I measured the yoke stretch on a Scubapro MK 20 first stage when clamped to a 3500 psi head. It amounted to 0.003 inch. Just for kicks, I hooked up a 50 year old reg to the same head. The yoke stretch was about 0.008 if memory serves. There is no doubt in my mind that a modern yoke is good for 3500 psi and possibly more. The same yoke as currently used on some USD regs used to be marked "4000 psi" until international standards orgs got into the act. Those yokes have 0.004 stretch at 3500. Now, I can't speak to the different style valves, especially those with inserts. Those things could be iffy, eg I can't state positively that an O ring is secure in an arrangement like that. I've not used them or tested them.

 

[Curly]

I know this is an old thread, but here's a related issue:

I have an X7-100 HP tank, and an Aqualung Couteau first stage (yoke). When I was considering whether to look for the yoke-to-DIN conversion kit (which seems to be out of stock everywhere now), I noticed that they reg's yoke was stamped "3000 psi" on one side, and "232 bar" on the other.

232 bar does not = 3000 psi, but more like 3365 psi.

Any idea about this discrepancy?

Also -- in speaking with a technician, I heard that most modern yoke regs can handle the 3300-3442 "HP" (actually "mid") pressure. The problem, as stated above, is typically with o-ring extrusion, and the "soft" parts of the first stage (including seats).

I've used the yoke with fills over 3300 with the Worthington without incident. One was a "hot" fill that quickly dipped to the 3100 range when submerged in cold northeast water. I do have one of the nice fat white o-rings on the convertible valve.

Still looking for the DIN conversion kit.

 

[pescador775]

"3000/232". The people who drone on about the "official" ratings of the yoke system should realize that these numbers mean nothing wrt the actual capabilities of modern A clamps including the O rings. The "3000" number is a carry over from when the manufacturers' lawyers dropped the rating from the realistic figure of 4000 psi. They did this to draw a distinction between the 3000 psi aluminum tank and the DIN equipped 3500 psi tank. Later, someone at USD decided to double stamp your reg with a new, European standard, again without reflection on what the yoke clamp can do but just to do something "official" and liability proof, supposedly. In fact, to them both were "official" so, both were correct. It probably escaped their attention that the numbers were actually very different. Look, these criteria are decided by committees who operate on concensus and to be "safe" they have to take into account the existence of older, weaker yokes that were manufactured in a day when tank pressures were 2250 psi and when the yokes were known to be safe up to 3000 psi. The newer yokes are twice as strong. Nevertheless, since these criteria exist and are "official", they are stamped on newer, stronger yokes as well. Sometimes, more than one standard is stamped on the yoke simply because the older, American reference was 3000 and the newer, Euro ref is 232, and get this, the new, newer, US number is 237 bar. (I can explain why but please don't ask). Well, alright, it involves a trick to extract the highest number possible for the yoke because PST knows what the yoke can actually do and even that number is a serious low ball. It means nothing as regards the actual strength of the system regardless which pressure is marked. Modern yokes such as the Scubapro and US Divers can easily withstand 4000 psi, and that includes the O ring if it is a quality product designed for high pressures. This debate is understandable but misguided, but not as misguided as the idiots who bow to officialdom, the written standards and mark their products accordingly.

 

[pescador775]

I get a little frustrated by all this as one could surmise. One more thing, I cannot understand these reports of O ring "extrusion". I can only guess. There are three reasons why this could happen. One, a damage ring, regulator or valve. Two, a soft, "hardware store" O ring. Three, the yoke is not tightened. The modern yoke must be tightened. This will not hurt the O ring or yoke. If a person is too weak to tighten the clamp then use should be restricted to 3000 psi or less, or get a DIN system.