Oxygen regulators, medical type

Thanks for the advice, Mark. I'd love an EDS system. But here in the East we rarely go high enough to need oxygen, it seems that spending $1000 on a system is overkill for use once a year or so. Also, we have very few convenient places around here to refill, other than at "wave camp".

Do those medical regulators not have a diaphragm? You'd think that's necessary, in order to shut off (at least mostly) the flow coming from the high pressure cylinder? I was guessing they have a diaphragm-based pressure reduction followed by an orifice to set the flow rate, but I may be wrong. And perhaps even the diaphragm system would have some leakage through the high pressure side valve even when it's supposedly shut because the diaphragm senses that the output pressure is high. Then again, these regulators have an "off" position, on the same knob as the non-zero flow rates. If that is simply a zero-size orifice, wouldn't the pressure then build up dangerously in the low-pressure side of that device?