The way I look at it is that one of the most important advantages of a 
set of manifolded doubles is that you have a total picture of your bottom 
gas at all times, and have access to all your gas at all times. Surely 
even a non-deco diver could see the logic in this.

If you are worried about redundancy a Y or H valve would give you that. 
You are then narrowed down to failure of the neck Oring, something I have 
never seen or heard of happening before until Wetlands post. And the 
jury's still out on that one. With a Y valve you have your 2 regs, one of 
which can be shut off in the event of reg or hose failure.

But of course if you have sloppy air mgmt. then we are right back to the 
pony, aren't we?

 Jim

Sender: Art Greenberg  Date: 1/15/99 3:15 PM

>At 01:51 PM 1/15/99 EST, Scaleworks@ao*.co* wrote:
>>To suggest that a single with a y valve is a better setup is absurd. Where is
>>the redundant air source?
>
>Why is the single w/pony better than a single w/Y valve? (Let's say
>the diver owns his/her cylinders so employing a Y valve is an option).
>
>The only failure point advantage of the pony would be the burst disk
>and neck o-ring. Neither has a high failure rate. The failure mode
>for the o-ring, when it does fail, is usually a slow leak that in no
>way would require a bail-out. We all know how to make the risk of burst
>disk failure zero.
>
>If you're willing to discount these advantages of the pony because of
>the low likelihood of failure (the sort of calculated risk we take all
>the time), then all you're left with is more gas. Then I think gas
>management and dive planning are the proper tools, not the pony bottle.
>
>
>Art Greenberg


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