Cotton mouth is real, more of a problem for some people. The metal 2nd do work. It's not a miracle, but it is a help and can make a difference to susceptible people.
A dive friend was bothered enough he got one of those Apollo in line hydration units. I let him try a metal 2nd. He bought one. It convinced him, and he already had a reg so he didn't need the additional expense.
In respiratory therapy there is a small device called an "artificial nose" technically a [heat moisture exchanger]. They are not very big for the job they do (neither is you nose but the work it does is flat out remarkable) but are effective enough that they are used extensively for short term mechanical ventilation over a heated moisturizer due to lower cost, simpler maintenance, and reduced probability of infection. Metal 2nds work in a similar fashion but with (much?) lower efficiency.
Thank you for that. I am going to read up on the artificial nose then, if it makes sense to me, ask the ScubaPro guy what he thinks of it, as it relates to the question at hand.
It has become somewhat of a moot issue for me. I will be buying new, current model regs. I was debating between the G260 and the A700. The reality of metal regs and cotton mouth is of lower priority, to me, than some other things I have learned that have now sold me on the G260 over the A700 anyway.
The "real" answer is simple. It's a matter of feel and personal preference. Evaluating second stages on some level is a little like wine tasting; there are norms but it's also subjective. The ANSI numbers are almost meaningless in terms of giving a picture of how the reg actually feels in the water.
Using the exhaust valve size as an example, it's true that a bigger valve will lower exhale effort and this lowers the WOB numbers, but most people don't care too much about small variations in exhale effort. There's much more psychological attachment to the sensation of how easy it is to take in air than there is to expelling it. Our perception of breath is VERY sensitive, just like our sense of taste (to further the wine analogy).
There are other examples but the bottom line is to try out different regs and see which YOU like. The mumbo-jumbo provided by the dive gear companies is often misleading and hyped, even if it's packaged along with helpful info about service procedures and techniques. Their goal is to sell new regulators above all else.
Well stated. Got it.
The other thing the SP guy said is that the easier exhalation contributes a good amount to reduction of CO2 retention and also to lowering SAC. Any thoughts on that? I understand that a reg with a higher WOB might still "feel" better. But, it seems like a reg that doesn't feel as good could still give objective performance that is better - at least for some situations. E.g. maybe it doesn't matter on a recreational drift dive. But, on a working technical dive, one might choose the one that is objectively better, even though it doesn't give as nice a feel.
Is my thinking on the right track here?
As a side note, I observed something that I thought was interesting. As part of my class, I tuned several 2nds. An R195, an S600, a G260, a C350, and an A700. Part of the "check" was to verify that with the VIVA in the Pre-dive position, hitting the purge did not start a freeflow, but putting VIVA in the Dive position and hitting the purge did start a freeflow.
Generally, in the Pre position, hitting the purge was done without doing anything with the mouthpiece, which was installed. After putting it in the Dive position, we would spread the mouthpiece wings out wide to clear the opening of any possible extra back pressure. All of the 2nds would freeflow with the VIVA in Dive, the mouthpiece spread like that, and a solid push on the purge ... except the A700. We could tuned and re-tuned it and could not get it to freeflow ... until we just took the mouthpiece completely off. With the mouthpiece removed, VIVA in Pre would not freeflow and VIVA in Dive freeflowed no problem.
It left me wondering if the A700 mouthpiece is actually done cleverly, to provide just the right amount of back pressure so that you can tune it very light and still not freeflow. Or is the mouthpiece very UNclever and overly restrictive. I.e. it will feed you PLENTY of gas at 1 ATA ambient, but perhaps it would actually give less-then-ideal performance if you were using it on a deep dive with extra high gas density.
