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>From: Richard Pyle <deepreef@bi*.bi*.Ha*.Or*> > >> Using a front/back bag, it seems like the front bag would almost always >> be empty, with all of the gas naturally migrating to the back when the >> diver was horizontal. If this were the case, the front/back issue seems >> to disappear; either put it on the front (so gas *can't* go back) or put it >> on the back (because it *will* go there if you let it). I don't see the >> point of the over the shoulder front/back configuration unless the diver >> is vertical. Perhaps this is the normal position for cave divers? >> >> Any experiences that could clarify this? > >As far as I know, no rebreather design has both a front and back >counterlung. The Cis-Lunar Mk-4 has two counterlungs, left and right, both >up front. I have found that changing my orientation in the water has >almost no effect on the breathing resistance (I don't understand it >either). Breathing "back-pressure" (as I prefer to call the hydrostatic >pressure component of rebreather breathing "resistance") depends more on >the total volume of gas in the loop (i.e., how full the counterlungs are >at a given lung volume). Learning to maintain optimal loop volume is >a significant skill when training for rebreather diving. > Richard, Having just done an intro course to the Prism, I know what you mean about back pressure! I found at first, I was swimming around with cheeks puffed out like a chipmunk! It seems the positioning of the breathing bag is fairly critical in reducing this effect. As we were only using it in a swimming pool, it was rather shallow. Do you find this effect is independent of depth or less noticable down deeper ? I found it significantly less comfortable to use than open circuit because of this effect. How do you find the rebreather compared to open circuit now that you have a significant number of hours on it ? The Prism is an attractive proposition for technical diving in my opinion as it is a versatile system with a relatively low cost. Cheers, David. ______________________________________________________________________________ David Giddy, | Voice: +61 3 253 6388 Telstra Research Laboratories, | Fax: +61 3 253 6144 P.O. Box 249, Rosebank MDC, 3169, AUSTRALIA | Internet: d.giddy@tr*.oz*.au* ------------------------------------------------------------------------------
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