Re: more cabin questions

["Alan D. Secor" <secor@btv.ibm.com>]

> At 02:54 PM 10/7/1997 -0400, Alan D. Secor wrote:
> >> Ok, the scrubber sounds pretty straight forward...but he's another
> >> silly question.  If oxygen is allowed to bleed into the cabin, eventually
> >> the pressure should rise past 1ATM.  What method is used to counter the
> >> buildup of atmospheric pressure in the cabin?  Is some sort of pressure
> >> relief valve used?
> >> Jon
> 
> 
> >Not silly at all....you bleed O2 in at the rate you metabolize it.  For
> >instance, a body at rest may metabolize something like .2-.5 liters per
> >minute of O2.  Therefore you just flow the O2 at that rate.  I plan on
> >having an onboard O2 analyzer (which I can show you how to build from a
> >sensor and voltmeter) to monitor if the concentration is too high or too
> >low. Also, I plan to have a barometer onboard to monitor changes in cabin
> >pressure.  You'll also need a vent valve for when you surface, if the cabin
> >pressure is slightly negative with respect to outside, you'll never get
> >you hatch open ;-)  Ray has asked me to send him a photo of all my parts
> >I have collected to date so you'll be able to see the various regs, flow
> >meters, scrubber parts, etc on the web page (hopefully in the not too
> >distant future)!
> >Al Secor
> >e-mail: secor@btv.ibm.com
> 
> 
>         Okay, you lost me on the metabolize thing (or I just didn't 'grok'
> it the first
> time around).  Even though you're metabolizing O2, you're giving off CO2, so
> the cabin pressure will still rise.  The 'partial pressure' of O2 becomes CO2
> (out of the entire atmosphere).  Am I way off here?
> 
> -Allan "CGK" Gaines
> 
The CO2 is absorbed by the scrubber. If you didn't inject O2, the net 
would
be a decrease of pressure in the cabin.  Think of how a fully closed 
circuit
rebreather works....CO2 is scrubbed (absorbed) out of the exhaled air, O2 
is
injected to account for the O2 metabolized (or used up) and the net is no
internal pressure change.  If there was, you'd either have exhaust bubbles
(which you don't) or your net bouyancy would increase (which it doesn't).
--
Alan D. Secor
e-mail: secor@btv.ibm.com