New CCRB Sentinel Rebreather aka Baby Boris

caveseeker7

Leon had a larger single counterlung with asymetrical hoses for a setup like that.
Even got an Armadillo from Curt for it.
Don't know if it ever went anywhere, but looked mighty good.

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Drmike

no - the side is the best CL position for wob

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dave t

My origional Inspiration had a single back mounted counterlung which I really liked and dived a lot but when it came to CE testing we could not get the WOB low enough to pass. so with my great disapointment we went to OTS lungs as the inspo is now. Having a good deal of experience with back mounted lungs both single and double it is VERY important where on the back they are placed and very difficult to find the position so it breathes good in all orientations. Jumping in the water and saying "oh that breathes fine" is sometimes very different from actual machine testing.

I would guess Kevin is solving the problem to a degree by widening the scrubber diameter, the wrong thing to do in my opinion but what works is what works!!

Dave

Nad

Hi Dave,
Could you explain why? Thanks

Nad

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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. A single counterlung does not provide this and may not be as good at insulating the gas either. Increasing the diameter of the scrubber should slow the gas down some and help with WOB due to potential less resistance, but increases the profile (in-water) and maybe more chance of channeling although this will not happen with the cartridge style scrubber packs. Most Rebreather builders have opted for twin counterlungs for good reason, an efficient system, low profile and good WOB/scrubber duration. I see no reason for a single counterlung. 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. but I know Kev Gurr very well and hes a smart guy who will do lots and lots of testing and experimenting and whatever his design ends up being I am sure it will work.

schford

I asked Kevin about this and he said his focus on the wider scrubber bed was to ensure decent duration at 40m on CE testing not just at 18m


I really dont understand the comment about insulating the gas - surely with 2 counter lungs then you have (roughly) double the surface area exposed to the cold water so heat loss will be much greater and infact some of the heat loss will occur before the scrubber so the scrubber will not be operating as efficiently as it should.

I have no idea about the mechanical issue though!

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dave t

I am surprised that widening the scrubber a bit would make much difference to duration a 40m, enough to warrant the extra profile anyway. I am assuming its an axial scrubber here, if its radial I reckon it would make a difference.

I guess it depends on what side of the scrubber the counter lung is but on a twin CL you have warm(er) gas and more volume either side of the scrubber especially if the lungs are made from an insulating material such as neoprene, as opposed to the gas running down a short thin hose. But anyway how much difference the insulating or not effect will have on scrubber efficiency is very debatable anyway

schford

Let me double check the reasoning we covered a lot in the conversation...

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silent running

Hello Dave, thanks for all the info. I'd like to ask you some more about it:

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?

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?

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

jhaaja

How could that work? How would you stop the gas in the inhale CL from flowing to the exhale CL? Pressure difference between those CLs would make the gas flow to the exhale lung. Or is there something that I don´t get?

JH