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Bruce,
With all due respect allow me provide a little different perspective to your
views, item by item.
> The Iso valve is there for what its describes "Isolation", theres no
> point in having it fully open as it acheives nothing.
- Scuba valves employ ball-gate valves which are designed to operate properly
when fully opened.
- A partially closed valve is more susceptable to being bumped off should one
inadvertantly rub it agaisnt an overhead object.
- By leaving the valve either all the way on or all the way off there can
never be any confussion or hesitation concerning which direction to turn the
valve to achieve the opposite position.
>If you need to
> isolate a cylinder and are losing gas then the quicker the better.
- Closing a fully open valve takes very little time if the diver is actually
willing to practice potentially life saving skills. The amount of gas that
might be lost in the time difference between closing a partially vs. a fully
open valve is inconsequential.
(Take a set of doubles, place the Iso valve in the position you would
normally operate it, purge a regulator while shutting of the valve. Note the
amount of pressure drop that occured. Do the same with a fully open valve.
Did a measurable difference of gas escape during one vs. the other?)
> Remember when this happens every ounce counts. It can be confusing
> only because the loss of gas is still happening from the failed system
> half.
- This confusion could easily lead to a diver opening a partially open valve,
rather than closing, resulting in even more lost time/gas. A fully opened
valve will only turn one way.
>The failed side should still be breathed till exhausted if one can.
- Totally dependent upon the nature of the failure. If the failure is a
freeflowing regulator you're better off to switch regs and shut-down the
failed side. If the leak is in the mainfold/tank it self, being behind your
head you may not know which side is the failed side. In that case breathe
the reg in your mouth, isolate, then start hunting for the failure.
> Then hop onto what should be 50% of what you had when the failure
> occured.
- Again, dependent upon the regulator you may have much more than 50% of your
gas available. The most common failures being a dislodged seal / o-ring
extrusion at the first-stage to tank interface, or a free flowing reglator.
Neither of these results in a catstrophic loss of gas nor a need to isolate
the two sides of the gas supply. Simply shut-down the valve on the offending
side, re-open the iso and have access to all your gas.
>The iso should be just cracked open to allow equalisation and shut
> with the minimum of effort, come on think about this and get your head out
> of the rubbish the agencies print.
- I could care less what the agencies put in print, a valve is either open or
shut. No in-between BS. It is fairly easy to realize that partially
open/shut valves have accounted for more incidents in this sport than fully
openining the valves ever will. I've yet to ever hear anyone tell of single
incident where a fully open valve played a role. Yet I've heard many stories
concerning how partially open/closed valves created problems. There is no
room for "ifs, ands, buts or maybes" in diving. The valve is either on or
off, no compromises.
Half-assed, short cut approaches to solving non-problems such as only partly
opening the iso valve are simply the result of those that are too lazy to
practice important skills to the point of perfection. Lazy
divers/instructors perpetuate the myth that this is an important safety
protocol and others, knowning no better, follow that myth. Then, when faced
with the truth, they cling to their ways defiantely.
A complete valve shut-down drill can be completed in 10 seconds or less if
the diver practices and hones their ability. The quanity of gas lost in 10
seconds is so miniscule that your fate is sealed anyway should that be too
much of a loss.
Valve and manifold failures are so rare as to be worthy of being rated as
non-problems. Take reasonable care of your equipment and you'll never
experience a catstrophic failure of a valve/manifold. At worse you may get a
slow leak, creating a small steady stream of bubbles. That will not result in
any meaningful compromise of your gas supply in the first place. If you have
a small o-ring/seal failure resulting in a slow leak, turn the dive and head
home. It's not that big of deal.
Again, the most common failures associated with the breathing gas system are:
- Failure at the 1st stage/valve interface (dislodging or o-ring
extrusion/failure)
- Free flowing regulator
- Hose rupture
- Burst disk failure
None of these failures needs be particularly life threatening, nor will they
result in a catstropic loss of gas. Simply shut-down the compromised side
and head for home. Among these the most serious, and also easiest to prevent,
is likely the burst disk failure. The U.S. cave diving community solved that
issue many, many years ago. For European divers it is not even an issue.
>It is not common sense to have the iso valve fully open. Common sense is
being >familiar with the on/off directions of all valves and your buddies
valves as well.
Common sense dictates that equipment be used in the manner that is was
designed to be used. Scuba cylinder valves are designed to be used either
fully open or fully shut.
Common sense dictates that the diver conduct risk analysis of their gear,
recognizing those features that are highly subject to life-threatening
failures and backing those up, while also identifying those potential
failures that are very unlikely and also not likely to be life-threatening in
nature.
The time difference in shutting down a fully vs. partially open valve is so
miniscule that you either have an adequate gas supply to survive or not.
Fully open or partially open WILL NOT have a meaningful impact on the outcome.
Regards,
Bob Decker
www.SportDiverHQ.com
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