You know, all this talk of super-redundant rebreathers for cave 
diving, going to open circuit long enough to change to alternate 
rebreathers, etc. remind me of a quote which goes something along the 
lines of "if it takes more then a sentance to explain it's too 
complicated"... 

Of course, what do I know? Proud to say I've never dove a rebreather 
and for the diving I do, I do not see the need... 

Of course, Will Smithers, I'm sure, is a much more accomplished cave 
diver then most of the subscribers to this list (well as soon as he 
completes a full cave course that is).

Ken

> Date:          Mon, 21 Dec 1998 09:50:49 -1000 (HST)
> From:          Richard Pyle <deepreef@bi*.or*>
> To:            "William M. Smithers" <will@tr*.co*>
> Cc:            H2Ocaver <ezimmerm@ch*.ca*.us*.ed*>, rebreather@nw*.co*,
>                cavers <cavers@cavers.com>
> Subject:       Re: Cave diving RB setup.

> > I imagine a switchover going like this: you grab the OC reg on the
> > necklace and start breathing that immediately.  Then you deploy
> > one of the bag rebreathers and start to inflate it, dumping gas
> > from your wings at the same time.  When you've got about the 
> > right volume in the bag counterlung, you drop the OC and switch
> > to the bailout RB.  Not too bad, on the task-loading front.
> 
> 
> Will, question:  are the bailout RB's connected to some sort of automatic
> pressure compensation device so that internal pressure is kept at ambient?
> If not, wouldn't you worry about 'sorb compression (and possible
> channeling complications therefrom) as the bag collapsed around it?  If
> you do have a pressure compensating system, does the bag have an OP relief
> valve to dump the excess gas on ascent without expanding displacement?
> Finally, if the SC bailout RB has sensors (or does it?), why not plumb a
> quick-disconnect with manual valve to your MK 15.5 O2 supply so that even
> the simple bailout RB can be run fully-closed? The way I see it, with
> clever plumbing, you really need only four cylinders total: two Dil and
> two O2 (for redundancy of O2, and for momentary OC supply of Dil). One of
> each is already inside your MK 15.5, so you'd onle need two external
> cylinders. The idea is to allow for cross-over redundancy: all RB's can
> access all gas supplies. Then problem, of course, is the need to be very
> clever about the plumbing to: 1) minimize extraneous failure points; and
> 2) minimize probability of a diver cluster.
> 
> Aloha,
> Rich
> 
> 
"Say, is that your Captain Marvel secret decoder lunchbox you got
hanging back there?" - Anon E. Mouse

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