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In a message dated 6/25/00 1:34:24 AM Eastern Daylight Time,
ajmarve@ba*.ne* writes:
> THe "point" i was referring to was what exactly does the h/y valve do
> for you? whats the most likely failure, free flow or no gas? sure you can
> isolate
> one first stage, but how do you save your
> gas while your doing it?
Al,
The most likely failure in my experience would be a free flowing
regulator. If such a failure occurs the diver does not experience an
immediate, catastrophic air loss. It takes some time to bleed a tank dry.
The time it takes to shut down the free-flowing reg should be counted in
seconds, not minutes. In other words, you should not lose a significant
quantity of gas in this scenario. It takes no more time, and results in no
more gas loss to shut down the failed valve than it would to isolate a set of
doubles. You've protected your air supply, allowing for a self extraction
rather gas sharing, which is always the preferrable option.
Another potential failure for which the h-valve provides good redundancy
for would be an o-ring extraction at the regulator/valve connection. Same
would hold true if the regulator were dislodged from a bump on the ceiling.
(Obviously much less likely a scenario for a diver using DIN regs than one
using Yoke/A-frame regs). Again, the gas loss would not be instantaneous.
There would be plenty of time to shut down the side with a problem and save a
substantial portion of one's gas.
An h-valve will provide no redundancy for a total loss of gas. However,
the most common reason for running a tank totally empty is diver error.
Monitor you SPG from time to time and it's virtually a non-existant problem.
If a catastrophic air loss were to occur you should have a dive partner near
by to share with anyway.
>Another thing, if the h/y is about redundancy for moderate
>deep or overhead dives on a single, what kind of gas management are you
>doing? I can dive for a while on a single tnk, but id need a 160 to do 40
min bt
>at 120+ and stay w/in thirds.< put the calculators down my water is cold at
120.>
Ok, could you manage 25 or 30 minutes at 120 fsw on 100 cubic feet of
gas, and leave the bottom with 1/3 in reserve? If so you'd still could have
a decompression obligation to meet depending on what you were diving. Albeit
likely it's all at a 10 foot stop. Your total runtime for that dive would
likely be around 40 to 45 minutes. I can typically do that dive on a single
95, filled to 2800 psi, do the deco on back gas and step on the boat with
900+ psi in the tank.... i.e. 1/3 in reserve. Obviously by carrying a small
sling bottle the bottom time and decompression obligation could be streched
even further without violating thirds. (In all fairness we're talking about
a warm water location. Cold water and the use of a drysuit with heavy undies
definately takes a toll on gas consumption).
>The other thing that mystifies me with this whole thread is, exactly how
>paranoid about the tables are you guys? if you are so deathly afraid of
>bending on a "no deco" dive, what kind of faith can you possibly have in
>the numbers for planned deco?
I'm not particularly worried about bending on a no-stop or stage deco
dive. But I suppose some folks are.
< metaphorical you, not Bob Decker personally>
I understand that.
Perhaps Trey, JJ or others will voice an opinion on this topic in the not
too distant future. I'd be interested in hearing it.
Regards,
Bob Decker
www.SportDiverHQ.com
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