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Kent Lind <klind@Al*.NE*> wrote: >Anthony DeBoer wrote: >> BTW, some people advocate having the valve just partway open, so that it >> can be closed more quickly in an emergency. It only has to be open a >> crack to keep both sides even, but because of the problems that can >> happen if it's a little bit closed instead of a little bit open, I'd be >> wary of this approach. > >What problems are you talking about? The ease at which you might >accidently roll the isolator shut and not realize it? Or is there some >other problem associated with leaving an isolator *mostly* closed? -KL You don't need too big a hole for HP air to get through, especially just enough to cover half your breathing rate. Closing it all the way is the problem. Mostly I was referring to point 5 in my posting; if the valve gets closed during a dive, then assuming a Hogarthian rig with SPG and primary on opposite firsts, your pressure stops going down. Hopefully you realize not too long afterwards that you shouldn't still have that much and you frown and twist the iso valve and all is right. Your dive plan should anticipate hitting thirds NN minutes into the dive, based on a known consumption rate, so you'd be suspicious if you had too much more than thirds at that point. Worst case is you suck dry on that reg, with no air left in your right tank. From the point you first get breathing resistance, you'll still have a few breaths left to make sure your buddy is near, look at your SPG, maybe think it's stuck, knock it, doublecheck the iso valve, swear at yourself, and you'd catch the problem but only have half your air left rather than two thirds. It would take a pretty wierd brush against the cave ceiling to turn the iso valve, but if you're only half a turn open it won't take much to shut it. Throw in that it should only take you a few seconds to close it even from full open, and the difficulty of proving that it's open by a few turns while setting up your gear, and it's probably not worth trying to get it to some magical midway point. At this point, however, I should disclaim that my wisdom on this is based on listening to prior discussions on Techdiver, listening to a reputable instructor on my tech nitrox course (Hi, Ian!), and putting my noggin in gear and thinking about the issue. My own iso manifold is on order even as we speak; the old pre-iso manifold is finally being retired. Anyone with actual experience of either having to close an iso in earnest during a dive or having experienced an inadvertent iso closure is invited to contribute some light on the topic. -- Anthony DeBoer http://www.onramp.ca/~adb/ adb@he*.re*.or* (here) adb@ge*.co* (work) #include "std.disclaimer" -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send list subscription requests to `techdiver-request@aquanaut.com'.
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