Conrad,

I have to give you credit for at least trying to think the logic 
through, which is a lot better then most. However, one real simple 
thing to remember is that with any sort of independent system you'll 
never be able to access all of your gas. Independents have so much 
more convolution to them beyond just the "task loading" aspect to 
them.

Overall I like a lot of the CDAA policies for cave training, except 
the requirement for independents.. Once again, the logic wasn't all 
thought through. Remember, if you have a first stage failure on a 
manifolded system (and the handwheel is intact), you can still access 
all of your gas in doubles.

You might hope, think, and pray you'll never need to get to all of 
that gas, but there have been recorded Charlie Foxtrots where if 
people had the added problems of independents there would have been 
multiple fatalities (the McFadden fatality comes to mind, if those 
guys were diving independents and had a failure then more then just 
Bill McFadden would have died).

Ken


> Date:          Wed, 25 Mar 1998 15:42:38 -0500
> From:          Conrad Daubanton <100774.1625@co*.co*>
> Subject:       RE: seeking opinions on isolator valves
> To:            Jsuw <Jsuw@ao*.co*>
> Cc:            "'Cave Diving list'" <cavers@ww*.ge*.co*>,
>                "' techdiver@aquanaut.com '" <techdiver@aquanaut.com>

> 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*>
> >Message-ID: <e2d30005.3518528f@ao*.co*>
> >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
> >Content-type: text/plain; charset=3DUS-ASCII
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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 wi=
th or
> >without an isolator valve.
> >
> >Some people seem to like having a way to preserve the gas in at least o=
ne
> >cylinder in case of a problem.  Others say that it is an unlikely probl=
em to
> >occur, so an isolator is not necessary.
> >
> >I'm interested in hearing opinions, along with your rationale.
> >
> >Thanks!
> >--
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