Counterlung Size/design .

colinicky

Digger
which lung is bigger ?

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Colin

I trust my rebreather completely ,
I just don't trust the user

onwards & downwards

pchanning

You need the o2 button - I was suggesting for those that wanted to better approximate the existing OTS CL design to their own lung volume.


A restriction means it can still get through. It might therefore become an air trap.

__________________
Cheers
Paul

The key to enlightenment... is survival.

colinicky

If you get round the O2 button in some way like you have or other is there a reason not to have them the same size ?

__________________
Colin

I trust my rebreather completely ,
I just don't trust the user

onwards & downwards

pchanning

I don't know. My experience is limited as I have not trifled with lung size.

Reading the Henmoor incident I would be wary of reducing the size. But thats me. I don't quite understand what happened there.

__________________
Cheers
Paul

The key to enlightenment... is survival.

jradomski

personally I doubt the accounts of the henmoor accident.. Something else was at work causing the venting.. Maybe the OPV wasnt operating properly??

I doubt there is a person on earth that could fill the medium counterlungs..

from APs manual

Medium - 11.4 litres (5.7 litres per counterlung)
Large - 14 litres (7 litres per counterlung)

The volume in a SINGLE counterlung should suffice most of the population!

If a person did manage to use the full counterlung that means they had almost 26 lbs of lift in the breathing bags alone! The diver would have had to have been severely overweighted to still stay down.

__________________
Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

colinicky

I personally have only heard stories/rumour of 1 time that someone needed to use every piece of boyancy they had to the limit which was to lift a buddy who's wing inflator detached from the wing at 75 metres somewhere in Egypt .As I say though it could only be a story as I have no personal knowledge of it .

__________________
Colin

I trust my rebreather completely ,
I just don't trust the user

onwards & downwards

AD_ward9

Sorry to differ, but the counterlungs could be much thinner and still get the inflates in the right place.

I am bit concerned about some of the things on this thread: there are some tiny little bits of detail which people may not have thought over before changing their kit. I will explain: sorry for the long post.

The reason the lungs are the size they are is to meet EN14143 WOB limits. To meet that on the Inspo design, the gas needs to move through the scrubber at half the peak rate. That is, the diver breathes from the inhale bag to the exhale bag and does not min or max either. For example, if a test is carried out at 75l/min, using Table 4 of EN14143, this is a flow rate of 150l/min from the inhale bag to the diver for half the cycle, and 150l/min for the second half of the cycle. If you put this flow rate through the Inspo scrubber, it would fail to meet the WOB requirement in EN14143, so APD's solution is make the bags big enough that there is always enough gas for a lung full and flow through the scrubber is averaged over the whole cycle, not half the breathing cycle as it would if a bag maxed or hit a min volume.

The figures I mention are for simplicity and assume the breathing machine provides a perfect square wave. When the drive waveform is modelling a human, the peak rate is over 220l/min, and this causes more problems: flow resistance increases with square of the area (hence to the 4th power of the tube diameter) so a sinusoid gives a high resistance peak.

All this being said, do not assume a rebreather with smaller breathing bags does not meet EN14143. The reason is not all rebreathers are limited by scrubber resistance in this way. We have one scrubber design for an ultra deep rebreather which achieves only 8mbar drop through the scrubber at depths 10 times that of the EN14143 tests. In this case, one could use a single breathing bag, or use two much smaller bags. More info later on, as the customer involved is willing for it to be one of the example units in the Open Revolution initiative.

Oversized breathing bags are a safety hazard. A good design gets these down as low as possible. However, if you restrict the lungs on the Inspo, you are likely to increase WOB and increased CO2 retention. This will cause an increased sensitivity to CNS, and generally do you no good . If you work hard with increased WOB, you could kill yourself .

So my bottom lines: Better not to tamper with breathing bags that have been designed and tested professionally. APD do not want oversized breathing bags any more than you do, but it is a product of their scrubber design. If you change the scrubber, then measure the advantage in breathing resistance, and you can then and only then, make a change.

Cheers,

Alex

colinicky

Thanks for the reply Alex does explain a bit more .
If you look in my original questions buried in the middle was the question :- "Or is it a case that it is the only way to get the inspiration through CE approval ?" which untill now nobody had answered .
I note from Joe's reply the size of the cl's is
Medium - 11.4 litres (5.7 litres per counterlung)
Large - 14 litres (7 litres per counterlung)

so what is the size of the small cl's that AP can do as a special order ? If its a proportional step down then it should be 8.8 litres (4.4 per cl)

Surely as well the inspo only needs one size to pass CE test which must be the smallest size otherwise they can't sell them ? Therefore it follows that in a way Beanie is correct that you only have the medium & large size purely for comfort & to get the inflator buttons in a comfortable position ? Which was what I was also told when I specced my unit with AP that the lung size didn't matter for breathing but only to get the buttons in the right place .

__________________
Colin

I trust my rebreather completely ,
I just don't trust the user

onwards & downwards