RE: [PSUBS-MAILIST] pressure hull sizing

[Alec Smyth <Asmyth@changepoint.com>]

This is correct, if you are releasing O2 at a constant flow. An alternative
is to release it only upon demand. As you metabolize CO2, the compartment
pressure will drop. Via a simple demand valve (think a scuba second stage)
you can then release O2 automatically to restore the original pressure. This
sounds complicated but is straight forward and entirely automatic.

Another idea is to do a combination of constant flow AND demand flow. The
constant flow can be set at a level compatible with consumption by a crew
that is unconscious, and the demand valve can provide whatever you need
beyond that. The advantage is redundancy without having a heavy constant
flow. 

The above are Phil's ideas, I don't want to steal his thunder.

Of course one could also put in all sorts of gas analyzers, a
microcontroller, electrically actuated valves, etc. But it seems to me a
simple mechanical approach has fewer failure points.


Alec
 

-----Original Message-----
From: Al Secor [mailto:wreckdiver@usadatanet.net]
Sent: Sunday, May 05, 2002 9:11 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] pressure hull sizing


This has been covered before in the list archives.  You input O2 at the
rate your body metabolizes it...somewhere between .8 and 1.0 liters per
min at rest.  You circulate the cabin air through a CO2 scrubber which
extracts the CO2 from the air.  As a result there should be no net
increase or decrease in cabin pressure and it remains at 1 atm.  A
simple baramoter can be used to keep track of the cabin air creeping up
or down.  A valve to vent the cabin environment to the outside at the
surface will equalize and small pressure differential to avoid any
difficulties in opening the main hatch.

Al

DBACKIDS@aol.com wrote:
> 
> It seems that whether you put the excess air into a tank, or vent it
> (which seems a better idea), you will still need a pump, because as
> Adam said, the surrounding pressure also increases. A valve would only
> equalize the pressure, would it not?

-- 
Al Secor  ARS: WA3PWX  Scuba Instructor SSI DCSI #5528 TDI #1413
http://www.geocities.com/SubDiverI