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> Isn't this an *advantage* since nasal venting is one of the > commonly quoted complaints about shifting to CC? It's only a problem until you learn how to breathe without exhaling through the nose (doesn't take too much time). Once this has been mastered, exhaling through the nose becomes a very convenient and hands-free way to dump excess gas from the loop during ascents. > Surely the loop has an overpressure valve to dump through; just > run the loop at or near the top end of the cycle. Yes, but there are a whole slew of other problems when you maintain the loop near maximum capacity. In order for gas to escape through the overpressure valve, you need to force it out with your exhale. Unless you have a very lightly-loaded valve (not a good idea if you're trying to keep water out of the loop), then this requires some prettey decent effort. I suspect with a FFM, the gas would vent from the mask seal before it cracked the overpressure valve, so backpressure may not be as big a problem. But there are a number of other reasons why it's good to leave some "breathing room" in the counterlungs. Furthermore, the loop becomes your fine-tune buoyancy control. To get slightly negative, it's nice just to exhale a little from your nose. > Mark me up for an FFM on the 'breather. :-) (Dream on!) Don't get me wrong, FFMs can make rebreather diving more pleasant and safer (in case PO2 drifts out of paramters). We use them on about half our dives. I'd recommend a half-mask, though. Aloha, Rich
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