On Mon, 21 Dec 1998, Richard Pyle wrote:

> Will, question:  are the bailout RB's connected to some sort of automatic
> pressure compensation device so that internal pressure is kept at ambient?

Yeah, I forgot to mention that - I'm thinking of having a modified
OC 2nd stage for the gas addition and depth compensation.  Pretty
simple and reliable.

> does the bag have an OP relief valve to dump the excess gas on ascent 
> without expanding displacement?

Definitely - for now, I'm thinking a simple drysuit exhaust valve
will do nicely.

> 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? 

Funny, I was just thinking of that while I was walking to the office, 
although I was thinking that I'd just have a spare bottle of
O2 with a quick-disconnect - that way, as you
say, you can either run the units SC or CC, or at least start
SC, then switch to CC by plugging in the quick-disconnect.

> 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). 

I wanted to have each (for lack of a better term) "hand-off" unit
have it's own SC gas supply, so that if you had to pass it to
someone, they wouldn't have to fart around with locking in
quick disconnects before using it.  Plus, if they (or you) somehow did
have a total gas supply failure, they could get out with nothing
but the self-contained unit.

> One of each is already inside your MK 15.5, so you'd only need two external
> cylinders. 

The way I'm thinking about it right now, rather than dealing
with cross-connects, you'd have the two SC tanks for the 
hand-off units, which would be rolled inside the units
when not in use, a bottle of O2 (maybe an AL13 - a good
3-4 hours of gas), and a bottle of inflation/short bailout OC.
Plus, that way, the units can take care of themselves
when it comes to depth compensation, without having to
be constantly plumbed into anything.  If they are rolled
firmly enough, you won't waste much gas during normal
sawtooth activity.

This does amount to four (small) external cylinders, but
the extra two cylinders strip off a bit of complexity.  I'm
figuring the external O2 and inflation/temporary OC bottles
would be affixed to the primary unit, and the two hand-off
units would each be tucked under an arm.  This still doesn't
address the issue of trimix and suit inflation, though.  I guess
if you weren't worried about static discharge, you could 
inflate your drysuit with the O2, and have trimix in the
BC inflation/short bailout bottle.  Of course, at say 10ATA
of pure O2, it wouldn't take a very big spark to make
you uncomfortably warm. ;)

BTW, the way I'm thinking of deploying the hand-off unit
is this:  The unit is normally rolled up and attached
to your left (or right) shoulder D-Ring.  When you need it,
you pull one side to unroll it, and attach the top corner
to your right D-ring, and the bottom to your crotch-strap
scooter D-ring (the roll up and soft cannister ideas, again,
are 100% Tracy's).

-Will

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