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From: "Dr. S.G. Millard" <ec96@li*.ac*.uk*> wrote on Mon 10 Oct 1994 19:09:47 +0100 (BST) (Subject: Sherwood 'Genesis' manifold..UK use):- > A more general question to other 'Genesis' users...How easy is it in practise to shut off a free-flowing regulator and open up the cross-over valve ? I am not a contortionist and with a drysuit + all the other 'paraphanalia' of cold water deep diving I imagine it might be pretty well impossible to reach over the back of my neck to turn the two valves off/on. I also imagine a fair amount of mental effort (at depth) would go into working out which way to turn each valve. Is this a real problem..or trivial with practise? Trying to turn your own air on or off by reaching over the back of your neck!? Forget it! I could about manage it in the 1960's, with a thin `Submarine Products' cylinder strapped directly to my back without a backpack frame; but with a backpack or a thicker cylinder, or a lot of shoulder muscle - no way. That is why many industrial sets and some aqualungs have the cylinder(s) the other way up with the on/off valves at the bottom end. Some such sets have a long high-pressure tube going up to a normally-placed regulator connection. Some people put cylinders into modern stab-jackets with the valves at the bottom, and have very long regulator hoses to reach the valves as thus placed; but likely those very long hoses would catch on things and cause hydrodynamic drag in swimming. In the usual type of modern aqualung, the diver's cylinder on/off valves are a very vulnerable point, whether to an attacker or (as I have heard of cases of) to them gradually turning themselves off as he pushes through thick kelp.
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