JUSW

I quote you...

> Others say that it is an unlikely problem to occur, so an isolator is =

not necessary.>

Careful,...  it may be unlikely, but what's the price you'd pay if it =

happens? (And it will happen, we just don't know how nor when)

Ken Sallot has already explained the logic, now here's another set of =

questions:

a)-	Should the isolator valve be open or closed during a dive, if so why?=


	If it's open you can breathe from one regulator out of the two tanks, =

but depending on how quickly you can close the isolator, if at all, you =

may lose half your gas or all of it, in case of trouble.

	If it's closed you'll never lose more than half your remaining gas, =

provided you breathed from both regulators evenly, that is making =

switches every 10 bar/20 bar or so.  This is similar to using =

independent doubles.

b)-	What could happen if it were open & trouble happens?

	It happened to Exley's partner in a dive in the Atlantida lava hole in =

the Canary Islands.  The diver in question didn't realize the noise =

came from his own gear, thinking Exley had a problem, by the time the =

mistake had been cleared, almost all the gas in both tanks had been =

lost.   Only their great experience & training allowed them to get to =

the stage cylinders and eventually survive the dive.

c)-	What could happen if it were closed & trouble happens?

	In the previous example, exit from the cave would have been =

considerably less stressing, as Exley's partner would have had a full =

third in one of his tanks.

d)-	With a regular manifold, how redundant is your gear?

	Only as quick as you are in closing the valves... if they can be =

closed, and if the problem is not a tank neck O-ring.  I don't like the =

idea of using a regular manifold (without isolator) in an overhead =

environment or in a decompression dive.  For me it's either with =

isolator, or else independent doubles.

e)-	Are there any advantages/disadvantages to independent doubles?

	Advantage: It's very improbable that you will be left without gas =

provided you balance tank consumption.  It would require a double =

system failure something very improbable (has happened though! Partner =

provided gas to exit cave).  If a low cave ceiling forces you to =

side-mount your tanks, then you have no choice but to have independent =

tanks.  Also you KNOW for sure that both regs are in perfect working =

order, as you're switching from one to the other regularly. The nature =

of many caves/sumps  make the porterage of single tanks easier than =

manifolded ones through complicated extensive dry cave sections.

	Disadvantage: More task loading (frequent regulator changes), requires =

a diver that switches regulators instinctively, therefore training is =

longer. If you don't change regulators properly, then you'll not have a =

balanced redundancy in case of failure.  Some divers may have a hard =

time adjusting to perpetual exchange...  some argue that this produces =

excessive task load, but most tech divers and cave divers in Europe =

dive this way.

No system is pefect nor foolproof, just pick the one you think best =

suits you diving needs and use caution and common sense.


Conrad Daubanton


>----------
>De: Jsuw
>Para: ;
>Asunto: seeking opinions on isolator valves
>Fecha: Mi=E9rcoles 25 de Marzo de 1998 3:00
>
>Sender: owner-techdiver@aquanaut.com
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>From: Jsuw <Jsuw@ao*.co*>
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>Date: Tue, 24 Mar 1998 19:40:45 EST
>To: cavers@ww*.ge*.co*, techdiver@aquanaut.com
>Mime-Version: 1.0
>Subject: seeking opinions on isolator valves
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>
>I am in the market for doubles for cave diving and also for tech diving.=
  The
>one thing I still have a question about is whether to get a manifold wit=
h or
>without an isolator valve.
>
>Some people seem to like having a way to preserve the gas in at least on=
e
>cylinder in case of a problem.  Others say that it is an unlikely proble=
m to
>occur, so an isolator is not necessary.
>
>I'm interested in hearing opinions, along with your rationale.
>
>Thanks!
>--
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