Re: [PSUBS-MAILIST] life support method?

["Sean T. Stevenson" <ststev@uniserve.com>]

On Thu, 3 Aug 2000 15:58:17 -0400, Alec Smyth wrote:

>	Guys,
>
>	I can see the obvious merit of having an O2 sensor to know whether
>the air you are breathing is good or bad. But why is it necessary to have it
>tied back to the replenishment system, with a solenoid, etc.? Surely you can
>just have a tank of O2 with a demand regulator attached (a scuba reg), which
>would replenish O2 automatically as it is absorbed by the scrubber. This
>would appear to be pretty simple. Am I overlooking something?
>
>	-Alec

Not sure what you mean by SCUBA reg, as to function there must be a
pressure differential between the ambient pressure (surrounding the
first stage) and the demand pressure (mouthpiece of second stage).  Of
course it is possible to implement passive oxygen addition, to maintain
a preset cabin pressure (1 ata), but are you overlooking something?

This depends on whether or not you consider scrubber malfunction to be
a possible mode of failure.  I do, taking into consideration the
possible loss of a fan motor, or channel development within the
scrubber material (due to poor packing) resulting in the passing of
unscrubbed gas.  In such an event, with the active addition system,
oxygen level is maintained, while CO2 level rises and raises cabin
pressure slightly.  With purely passive addition, the increasing CO2
pressure would fool the regulator into not adding O2, so you not only
need to be concerned with hypercapnia, but hypoxia as well.  The active
addition system, while more complex, permits changes in vehicle
interior pressure independently of life support system function.  This
may be moot for the majority of you, but is important for my sub
design.

My PSub design, which is admittedly purely conceptual, makes a
compromise between maximum operating depth and cost/weight issues, by
utilizing partial pressurization on deep dives.  Normally operating as
a 1 atmosphere vehicle, I have added the capability to (under
extenuating circumstances) extend its range to excursion depths below
the 1 atm test depth by internal pressurization, maintaining a maximum
pressure differential of the 1 atm test depth.  I don't know quite how
feasable this is, but it has made for an interesting design exercise.

-Sean