>I've discussed this question with a couple of dive buddies and we couldn't 
>reach
>a consensus.  Assuming you have a fully closed rebreather, and ignoring 
>venting
>of the breathing loop, what would happen to the pressure in the loop as O2 
>is being metabolized if no dilutent or external O2 were added? Would the 
>pressure
>remain the same or would it decrease?  Also, if the pressure remains the 
>same,
>what would the makeup of gasses in the loop look like assuming the CO2 is 
>being
>absorbed by a scrubber?  Thanks in advance for no flames and intelligent
>responses.

Purely theoretical - I've got no experience with rebreathers:

0. The partial pressure of a certain gas in a mix is equal to its 
relative proportion times the total pressure. E.g. 20% O2, 1bar total 
pressure -> ppO2=0.2bar

1. The total gas pressure in the rebreather system remains the same as 
the external water pressure because of the flexible counterlung.

2. If pure O2 is used the ppO2 equals the total pressure and therefore 
remains constant at a given depth (but the volume decreases).

3. If O2 is mixed with inert gas, the proportion of O2 decreases as it is 
consumed.  Consequently, the ppO2 decreases at a given depth.

Does that answer the question? (I've had a glass of excellent wine, well 
maybe two...)

blu



-----------------------------------------------------
Beat Ludin, FMI, PO Box 2543, 4002 Basel, Switzerland
Tel. +41 61 697 6697 / FAX +41 61 697 3976
Internet:ludin@fm*.ch* / Compuserve:100102,1527

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