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On Wed, 20 Jul 1994, Callum wrote:

> It occurs to me, reading these threads, that a first stage could be simply
> modified to give a fixed interstage pressure (8-10bar).  Covering up the
> drain holes in the first stage should prevent ambient pressure water from
> acting on the front of the piston, thus maintaining a constant ISP.

I wouldn't do this. Here is my reasoning why: If I experienced a 
regulator malfunction on one of my stage bottles (I usually carry 
travel-mix in one bottle and deco-mix in the other), I can switch the 
regulator from one stage bottle to the other to complete that part of the 
dive/deco.

Yeah, yeah, yeah, I know that both regulators should be oxygen cleaned, 
blah, blah, blah. (BTW: they are oxygen cleaned). 

When I was teaching Mixed Gas Diving classes, I incorporated this 
underwater regulator swap as one of our initial training drills. This was 
at the first water session(air in all tanks), after that we now *had* to 
clean the regs, so we brought them to oxygen service at that time.

dan@sh*.ne*							mig@shadow.net
		"Jimmy Carter is no longer our worst president."

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