Re: [PSUBS-MAILIST] L.S.S.-Life Support System

[Phil Nuytten <pnuytten@compuserve.com>]

Hi, Rick!
 Forwarding an old post - Ray and Jon combined efforts to get me back in
cyberland - I changed my email adress slightly and the clever automation
gremmies kept kicking back my posts - As you know, I'm an 'intermittent'
poster at best, so after a few had got kicked back, I didn't bother - but
now I;m back in 'Show biz' !
Thanks Jon & Ray!
Phil Nuytten

-------------Forwarded Message-----------------

From:   Phil Nuytten, 72020.572
To:     INTERNET:personal_submersibles@psubs.org,
INTERNET:personal_submersibles@psubs.org
        
Date:   12/16/2004  8:36 PM

RE:     Re: [PSUBS-MAILIST] L.S.S.-Life Support System

Hey, Rick!
        Long time no 'talk' to  . . .yeah, the loss of pressure on phase
change is a concept that a lot of otherwise pretty savvy types have trouble
with  . . .it is counter-intuitive, certainly. It's unusual for the sub to
have exactly surface pressure when surfaced - ( usually it's a bit higher)
- for two main reasons:1.) the sub hits the warm surface water and the
cabin gas expands and the cabin pressure goes up - normally ( on a
bellows-add system) the bellows would just stay contracted until you had
metabolized the excess O2 . In DeepWorker, (and Aquarius, Deep Rover,
etc.,) we have an 'equalizing vent system' which is a fancy name for a
sensitive check valve with a through-hull and cabin valve to activate. Any
excess gas is lost thru' this system. 2.) The hull is compressed at depth
and re-expands to it's original, 'surface' dimension during a direct bottom
to surface ascent - as it does. the pressure falls. the bellows-add will
make it up to the sealed bellows setting, but it takes a little bit of
time. The degree depends on depth attained, cabin volume, rated depth of
hull,  hull material - all of these are pretty . .well  . . .material ! As
an example, Deep Rover loses 90lbs of buoyancy at  a 1000 meters - from
hull compression.
        On a simple continuous liter-flow system, the surfaced cabin
pressure can be pretty far off the mark if you haven't been paying
attention and manually adjusting flow or hitting a by-pass valve to make up
for cabin pressure fall due to temperature change, level of exertion of
occupant(s), etc. A common problem ( that can take some sleuthing to
uncover) is too high a flow-rate on your continuous-flow calibrated
orifice. ( you are all using one, aren't you?? - could save your ass!). For
some, the usual .25 lpm will only keep your super-active soul attached to
your body- for others with a lower metabolic rate, .25 may be too much and
can raise the cabin pressure over time. 
        The long and short of it is that LS is a most inexact science
because of the number of variables and their inconsistency over time. You
need to understand your particular system completely, do what seems to make
sense and see what happens. When you find a set of settings/procedures that
works for you - stay with it! Or . .use a bellows-add and your starting
point will likely well be very close to your final tweak! 
        Finally: on 'burping' : In my humble opinion, you should  avoid
hatch burping like the effing plague!!! Sounds cool. but there's nothing
quite so bowel - loosening as the hatch sticking in the burp position while
you're still submerged, or the burp blowing the hatch o-ring out of its
groove on surfacing - then slamming partially shut on it as you sink back !
Do the math on the flow rate of a quarter inch gap 60 inches long with a 
few pound head - the hull buoyancy is negated in a shocking short period! A
properly designed and engineered 'burpable' hatch or dome port -  with
return springs, annular guides, mechanically fastened seals, etc., is
expensive and introduces a host of problems of its own. Though, come to
think of it, there is at least one thing more bowel - affecting; I had a
hatch blow off at the surface - while the aft tank was still flooded (
which meant the back of the hatch/dome was still underwater). Oh, man! the
water, she come in very fast!  - and the worst part was that it was being
filmed for a TV special.  Did they use the footage? you bet your loosened
bowel they did! 
Best of the season to Psubbers
Phil Nuytten




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