Quote: (Originally Posted by
Hanssing)
Am I wrong?
You're not wrong, just not quite right. As you said in the first post, for a given pO2 there is a certain volume of O2 in the loop-22.05L for a pO2 of 2.1. You should have gone on to see that this is also true for the lower pO2 I used in my calculations [1.3] which gives a loop volume of O2 of 13.65L.
So at whatever depth you are at, to get down from 2.1 [22.05L] to 1.3 [13.65L] will take the 8 min 24 sec at a vO2 of 1. The amount of N2 in the loop makes no difference in this case, and you have to use 8.4 L of O2 to drop the pO2.
When you were looking at the lower pO2/fO2 figure did you remember to multiply back up to get the depth? I forgot when I first started running the figures
Of course, you need to remember that the CO2 produced will be absorbed, reducing lung volume as you allude to.
Quote: (Originally Posted by
Hanssing)
Yes, that I thought was implicit. I was writing that the constant-mass flow concept in theory works well at depth (If you can make a constant flow offcourse), but then can become wastefull when the same flow is used shallow with a new mix. Therefor its not enough to scale the flow only to the deep-part, you also need something to reduce it with for you decomixes.
I tend to go onto OC for deco. I haven't done a deco trimix dive on the Dolphin yet as I need more time in the shallows on a weak trimix before progressing. It is possible to switch gas mixes on the loop [an adaptor from Tecme to allow 2 mixes into the bypass is needed] by turning one tank off and another on for deco, but I prefer to know exactly what I am breathing on deco, and vO2 is never a constant.
It is also possible to deco on an OC reg connected to an H valve tank [when using nitrox] but the likelyhood is that the 'step' in fO2 is too small to be useful-see the bottom of this post:
http://www.rebreatherworld.com/semi-...tml#post121362