Hello Dave, thanks for all the info. I'd like to ask you some more about it:
Quote: (Originally Posted by
dave t)
twin counterlungs either front or back mounted offer some mechanical "assist" when moving gas around the loop, this effectively lowers WOB and lengthens dwell time which helps to improve scrubber efficiency.
I'm asuming by "mechanical" you mean the hydrostatic head created by whatever position the CLs are relative to the diver's lungs, yes? And is it also true that the drive pressure needed to move the gas around the loop is lower with 2 CLs than with one due to this mechanical assist and thus increases dwell time by slowing the gas flow?
Quote: (Originally Posted by
dave t)
A single counterlung does not provide this and may not be as good at insulating the gas either.
I'm gessing that the reason for this is that in a single CL loop, the volume of gas outside the scrubber will be greater at any given moment than with a dual CL loop and thus be more directly exposed to the water temp longer, yes?
Quote: (Originally Posted by
dave t)
a twin back mounted counterlung correctly designed and placed will perform as well if not better than OTS lungs and give a clean front and low in-water profile.
I'm not sure how this is possible. My understanding about back mounted CLs placement is that it should be high and as close to the diver's body as possible, yes? This would explain why I found the Atlantis/Dolphin to have better WOB than the CK. But I have always been concious of the hydrostatic head while diving a BM CL unit in any postion other than the optimal one while I have not noticed any big difference in the hydrostatic head while diving the Prism. If my perception is accurate, is there any way to offset this difference btw OTS and BM units? I ask because I dive in places where I am sometimes tossed into odd positions and always at a time of stress and high exertion, when high RMVs make the WOB shoot up and create potential for CO2 retention. I have had some bad experiences on Drager units in high RMV situations and am thus wary of BM CL units, but happy to stand corrected as it gives me more options
.
And one last question if I may: Has anybody designed a dual CL unit with the inhale CL on the front and exhale CL on the back? I realize this design might be awkward, but it would seem to take maximum advantage of the hydrostatic head in all but the belly up position. And if we are maintaining mimimum loop volume as we should, the profile of any given CL placement other than one which wraps under the arm-ala Pelagian-should not be any more or less with BM or OTS CL units, volume is volume, yes?
Thanks, -Andy