Quote: (Originally Posted by
Campbell)
When I breathe in from the counterlung, I breathe whatever the PP setpoint is (basically) but when I breathe out I have used about 4% of the O2 and expell CO2 from my body. The CO2 is removed from my expelled air by the scrubber. It's then analysed and the reduced O2% is then topped up from the O2 cylinder. My question is, does this mean that the counter lung volume slowly increases or does the scrubber absorb the correct volume of CO2 expelled by my body?
Pretty much yes. Although 4% is only true at the surface. At 30m, (4 bar) it's 1%, 70m (8 bar) 0.5%. Think molecules not percentages. On my KISS, which is a Manual CCR, if I work hard then I use more O2 so the counterlung volume decreases. No problem I just add a bit more. The scrubber removes all the CO2 produced by the body, and I (with the constant-flow of a MCCR) add the oxygen that's been used so the volume stays the same. The Electronic CCR fellers have electrics that do this for them.
Quote: (Originally Posted by
Campbell)
My second question (sorry guys) is more to do with no-stop times. Because I'm going to be breathing from a closed loop, does my body absorb the same amount of Nitrogen as if I was on Open Circuit? I mean if I have a set-point of 1.5 Bar on CC and compare it to an Open Circuit of 30% at 40M (PPO2 = 1.5Bar) is the no-stop time the same, or because it's closed loop is the no-stop time longer?
Think of the Rebreather giving you the ideal blend of Nitrox for your depth. The no-stop time is the same, but CCR gives you the advantage of 1.5 all the way up. So your stops are slightly shorter. In practice it doesn't make much difference. I run my RB on 1.2-ish on the bottom
Janos