When is LP HP?

[ucfdiver]

My tanks seem to be LP in Orlando, and HP in cave country. They magically switch back and forth.

 

[pescador775]

In 1994, I machined three yoke valves to fit my 3500 psi tanks. These tanks have 7/8 necks and standard valves would not fit unless modified. The unusual neck thread on these HP tanks was installed by PST due to European standards and practice, and some CGA or DOT opinion floating around which suggested the safe pressure levels for yoke clamps were about 3000 psi. In publishing this information they had to take into account all mods of these clamps, some going back to the early 1950's, and since some of the valves which these clamps would fit were equally old in terms of service life and design parameters, the rules opted for nixing the yoke at a conservative max pressure. The specific number varies a bit and, recently, some have interpreted this to be the European number of approx 3300 psi corrected for different STP criteria used in the USA which comes out to 3442 psi. Neither the 3000, 3300 or later, the 3442 number applied to me since I was using all new equipment, new type yoke valves and new, high pressure regulators with heavy duty clamps. I have never had a problem or even a hint of a problem with my setup.

As you may now surmise, the tank factories were becoming similarly frustrated having finally recognized that modern yoke connections were pretty competent and that the special neck and DIN valve could be a hindrance to sales inasmuch as yokes were a common international connection. Divers were using klutzy adapters on their regulators to hookup the various valves and that the DIN requirement for pressures at 3500 or above was technically unsupportable even if it was "law". To resolve the issue they designed a new series of tanks which could be legally sold with standard thread installed and which would accept yoke or DIN convertible attachments. For all intents and purposes these are high pressure tanks but slip under the regs governing valve connections and interchangability for HP tanks.

Here are some suggested definitions applicable to SCUBA in the USA:
Low pressure; 1800 psi - 2600 psi
Medium pressure; 3000 psi - 3442 psi
High pressure; 3500 psi
Very high pressure - 4400 psi

 

[hlsooner]

I use nothing but yoke valves on my HP steel tanks, routinely use them on 3800 psi filled tanks, never even a hint of a leak or other problem.