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

["Rick and Marcia" <empiricus@telus.net>]

William - thanks for that outstanding repost.

Peter - I've just learned something new!  Since "barometric activation"
actually works, I've got to get  my head around the concept that, even in a
closed system (cockpit), pressure will indeed drop due to chemical
absorption.  Will have to study that one.  It's the one area that, over the
years, I've had little interest in (scrubbers).  I've always been interested
in using regs in an ambient boat, wet or dry.

Now I'd like to know, as Peter so correctly pointed out, whether net cabin
pressure equalization (burping the cabin on surfacing) is due to positive or
negative pressure (relative to starting pressure from the beginning of the
dive).  I suppose that would depend on how finely tuned the equalization
"thermostat" was set.

Rick
Vancouver, Canada


----- Original Message -----
From: "William Alford" <walford@dbtech.net>
To: <personal_submersibles@psubs.org>
Sent: Wednesday, December 15, 2004 10:55 AM
Subject: Re: [PSUBS-MAILIST] L.S.S.-Life Support System


>
> >> > Hi, Peter . . . in what way is carbon dioxide consumed?  And why
would
> >> > pressure be lost?
>
> repost from the expert: Dr. Nuytten--
>
> In an ideal situation, you capture a
> volume of air in a rigid container (your sub) when you close the hatch.
> With no increase in pressure, there is no uptake of inert gas (nitrogen)
so
> it acts a filler or diluent gas - ( be careful of the term 'inert' -
> nitrogen is only inert in the context of metabolic oxidation, not in it's
> ability to affect neurons under elevated pressures - as all you deep air
> divers are well aware!) As the O2 is metabolized and - for all practical
> purposes - converted entirely into Co2  . . .and the Co2 is chemically
> bound to the scrubber alkalai - the cabin pressure falls and the
barometric
> device ( 'bellows-add', or such) is triggered and O2 inflows until the
> cabin pressure reaches the set point of the barometric device and the O2
> flow ceases . .and so on.  What actually happens with a sensitive enough
> barometric device/add valve is that the add valve achieves a 'just
cracked'
> position, commensurate with O2 uptake- and will only shut off entirely if
> breathing ceases ( R.I.P.) or open 'more' if respiratory rate increases (
> Jeez! - it's a Giant Squid!). Don't forget the constant-flow safety device
> ( 'steady-rate by-pass', 'fixed-orifice', or similar) This is fixed at a
> rate that will support life but not high-normal respiratory rate.
>          So . . after much divergence . . .why have an O2 sensor?? Well .
.
> .what if the O2 stops? ( runs out, swerf or debris jams orifice, hul- stop
> accidentally turned off, etc., etc.,) Air flows into lungs, O2 is
converted
> to Co2, Scrubber snatches Co2, next breath of 'air' (cabin gas) is
> deficient in O2 . . . as you can tell. Yeah? how do you tell? The increase
> in Co2 which would normally warn you of decreased O2, is not present.
Since
> our primitive design specifications never  envisioned a situation where
the
> oxygen could diminish without an increase in carbon-dioxide, there is
> virtually NO warning until the bod suddenly realizes that death is next on
> the dance card,shuts you down, and shunts what little O2 is left to the
> brain.  Would have been nice to have an O2 meter read-out when you
started
> to feel a bit peculiar or noticed gas draining from your eustachion tubes
> and sinuses!
>         Probably the best argument for an O2 sensor is that they're 'cheap
> like borscht' and bring a peace of mind that is far more than their cost.
A
> good unit should run about $300 -  more with hi/lo audio/visual alarms. Be
> careful of the cheapies that 'get you by the sensor-cells' - much like the
> printers that offer high quality at a low entry price and then gore you
> unmercifully on 'proprietary' ink cartridges for the life of the device!
If
> the vendor wont direct you to the sensor cell's EOM, go somewhere else. We
> (Nuytco) make a unit called the 'Newtrox' ( what else!) which was designed
> for sub use - runs over a week steady on a regular little 9 volt battery.
A
> shameless commercial - BUT - it is just more rugged than usual - it is
> functionally almost identical to a bunch of other, cheaper, models. So, go
> with the best deal - but make sure you can buy the cells direct from the
> cell manufacturer!
>         I did a paper on barometric activation on sub life-support, years
> ago. I think there is a copy on/in P-subs archives. Probably worth a look
> if you're going to use this type of system.
> Phil Nuytten
>
>
>
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