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In a message dated 6/26/00 7:42:41 PM Eastern Daylight Time,
DiverIan@pa*.ne* writes:
> An H-valve doesn't really provides good redundancy for these (behind the
> head) failures since you can't see what's gone wrong and the 1st stages are
> only a few inches apart. If gas starts spewing out behind your head is it
> the primary 1st-stage's O-ring that has failed, or that of the secondary,
or
> the tank neck O-ring? Which knob do you reach back and turn off? With
> doubles if you're not sure then you can close off the isolator to ensure
> saving half your gas supply, but not with an H-valve.
Ian,
While you certainly have a point the fact remains it should take less
than 30 seconds to run through the shut off routine, probably much less than
30 seconds. Shut down the valve for the back-up, if the leak continues, open
it back up, switch second stages and shut-down the primary valve. With a
single outlet valve there is no recourse that may solve the problem.
Does an H-valve provide a level of redundancy similar to double tanks
with an isolation manifold? Of course not. Does it provide a higher level
of redundancy than a single outlet valve? Obviously. Is the H-valve a better
choice for the single tank diver than a pony bottle? I think so - Failures
are very rare; it weighs less out of the water; it creates less swimming
resistance in the water; it provides a higher level of redundancy than a
single valve; the temptation to stretch the dive a bit by using the extra air
source is removed; it costs less.
> If you have an
>attentive buddy then he can see what's gone wrong and close the relevant
>valve, but relying on that defeats the aim of self sufficiency.
There are many on this list that believe a good team effort is one of the
keys to correct, safe diving. Self sufficiency is about reducing the overall
risk of a situation, not eliminating the dive partner. It's simpler to make
an unassisted egress from an overhead environment than to have to share gas.
It's easier to make an unassited ascent than to share gas.
Decompression/safety stops are less complicated if there's no need to share
gas. And, unfortunately, there's alway the outside chance a dive partner
could become incapacitated or that a seperation could occur.
>In the case of a behind the head failure you're probably better off getting
the hell out
>of there straight away rather than wasting time guessing which knob to turn
off.
It should be an automatic response taking 15 to 30 seconds at best. Just
as there is an order one learns, and hopefully practices from time to time,
for valve shut-downs using doubles, there should be one for using a H-valve.
Lost time should be virtually insignificant. Guesswork should not even be an
issue.
>I recently converted my single tanks to H-valves, but I see it as a way of
>always diving the same regulator configuration rather than as an appreciable
>amount of additional safety.
Undoubtedly the opportunity to maintain the same configuration is one of
the most attractive features of using H-valves.
>If I'm solo diving I won't rely on the H-valves as my only air-supply
redundancy - I >either use the doubles or carry a 20 cu ft pony slung
stage-bottle style and filled >with air.
I was trying to look at this more from a "DIR" point of view, which
obviously would eliminate solo diving as an option. Regardless, there are
many, many divers in this world that do solo dive and do so using single
valve tanks with no pony. As such the question becomes, would they be better
off with an H-valve than nothing at all? I think the answer would be yes.
Frankly, I think we've about ran this topic into the ground, with the
possible exception of hearing what the correct "DIR" position might be from
Mr. Irvine or Mr. Jablonski.
Regards,
Bob Decker,
www.SportDiverHQ.com
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