Few basic CCR questions.....

Campbell · 8th October 2006, 20:17

Hello all,

I am now the proud owner of a yellow box and am looking at doing the course within the next few months. I won't be using the unit until I have full training but have a few basic questions that I was hoping that someone could help with.

I understand the rebreather concept, how it works etc but I have a bit of a query:

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?
I hope that makes sense what I'm trying to ask? Obviously if the counter lung volume increases at times the ecess is going to have to be purged.

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?

I hope that these questions aren't stupid ones and I thank you all in advance.

John

Janos · 8th October 2006, 20:25

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

8th October 2006, 20:17	#1 (permalink)
Campbell New Member Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Oct 2006 Location: Portsmouth, UK Posts: 88	Few basic CCR questions..... Hello all, I am now the proud owner of a yellow box and am looking at doing the course within the next few months. I won't be using the unit until I have full training but have a few basic questions that I was hoping that someone could help with. I understand the rebreather concept, how it works etc but I have a bit of a query: 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? I hope that makes sense what I'm trying to ask? Obviously if the counter lung volume increases at times the ecess is going to have to be purged. 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? I hope that these questions aren't stupid ones and I thank you all in advance. John
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8th October 2006, 20:25	#2 (permalink)
Janos "Two Sheds" Current Rebreather/s: Classic Kiss Other Rebreather/s: Classic Kiss Join Date: Feb 2005 Location: East Surrey Posts: 581	Re: Few basic CCR questions..... 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 __________________ You can lead a horse to water but you can't climb a ladder with a large bell in both hands - Vic Reeves www.hellfins.com/shed
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