OTS lung sizing

eXile

Hi all. I have recently test dived my modified drager ray homebuild and found that the counterlungs seem to be too small for me to get a full breath from without activating the adv. Does anyone know the capacity of the front portions of the lungs as i have the back sections behind the back of the diver restricted by my backplate assembly. Also what is a common size for the OTS lungs on homebuilds. I am thinking of getting two 2L bags but I am not sure if they will be big enough. Any information is welcomed. Thanks

Paul

divepig2

Early on in by building I used the water displacement method with a couple soda bottles to find my approximate lung vulome. As it turned out, my volume was roughly 3 liters and I'm an "average" sized guy. You may need to adjust accordingly.

Harrison

OceanOpportunity

counterlung sizing is somewhat arbitrary. Most of today's CCRs have grossly oversized lungs. This allows one unit to be sold to a variety of sized divers. Since we dive as close to minumum lung volume as possible, it doenst equate to much more than extra material to carry around during the dive.

the minimum size for a buld project is somewhat critical, and is related to a person's lung tidal volume. An average adult male has a vital capacity of about 4liters. In most cases, this volume cannot be exchanged since it requires full inhalation and collapse of the lungs. Todal volume for an average breathe is rarely more than 1liter when relaxed. Certainly not more than 2-2.5 liters. In any case, counterlungs that match your vital capacity should be more than suficient. after all, if you are hyperventilating (overworking), you're better off venting gas (activating OPV) since chances are you are blowing CO2 through the scrubber and overworking the rig.

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Oceans of Opportunity
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Dave Sutton

CL's that match your lung capacity are fine as long as you never ascend a few feet over an obstruction and then redescend. But if you tune the lungs too closely, you will vent gas and then need to re-add gas more often. 150% of personal lung capacity is about right. Run them at minimum volume as a matter of course, but use the extra volume as a short-term buffer for slight depth changes.


Dave

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jaap

And how does it work when you test it without the ADV? Perhaps the ADV is set too light so that it adds gas too easily?

When I did some tinkering with my Ray I modified it in such a way that the back sections of the counterlungs could still be used. The way I did it was to use two backplates back to back like an X. One with a harness for the diver, the other with the scrubber in the middle and the tanks on the sides. I used spacers on the bolts so there was about 1 inch between the backplates to make room for the rear counterlungs, OPV and ADV.

I manage with 2x2l lungs but its really on the small side. Even more so if something can restrict the lungs from being fully inflated. Also think about what shape the lungs get when they are full. If you go for small lungs its likely they will inflate fully quite often. "Short & fat" lungs could build quite alot on your profile when full.

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Dave Sutton

Don't forget that SCC rebreathers are built with deliberately small CL's as well, as they are designed to have the lungs filled to 100% of their capacity 100% of the time. Unlike a CCR, they cannot be optionally run at a volume lower than completely filled. This is one of the things that causes several common SCC rigs to be less than optimal CCR conversion platforms.


Dave

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eXile

Thanks for the info guys. JAAP without the ADV I stil have the same problem. I cannot get it to take a full exhale without activating the OPV and I cant get a full inhale when the lungs are full. The ray harness is quite restrictive to the counterlungs and i have never really liked it anyways so i will just strip it for now and use the fittings and DSV for the new unit.

Dave1w

I tried putting a backplate into my Ray, but found it moved it away from my back, and was a bit cumbersome, so I went back to the Ray harness (in SCR) and it was a bit better. (This is in a wetsuit) But either way, the front counterlungs don't come too far down my chest (if at all)

How are you hanging the bottles off? Also have you got ride of the BC bladder in the ray and replaced with a wing?

I also worried that trying to strap the ray to my big frame pulled it tight and restricted the lungs, so maybe tighten the waist strap and leave a little on the shoulders.

Have you removed the foam padding to cut down the weight also?

Dave

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