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At 09:37 AM 4/16/01 -0400, David E. Smith wrote: Hello David, > If you read my posts you will see that I have not advocated any of the >options for how to operate your valves. I have stated only that it is not >"common sense" that the valve should be fully open. It's "common sense" to me and from reading this thread, it appears to be "common sense" to nearly everyone participating in this discussion. >commenting on the "absolutist" posts that make statements of common sense or >fact because it suits someone's argument. Absolutism (is there such a word?) aside, the arguments presented for keeping the isolator fully open are based on logic and are not being made arbitrarily because it "suits someone's argument". The problem you propose to solve by leaving the isolator mostly closed, that of loss of gas due to a freeflow or valve disk or o-ring failure, is an invention of paranoia. These failures take far longer to drain a tank than it does to close the problem valve(s). If you practice these scenarios in a pool, you'll find it takes a very long time to drain your tanks and a very short time to close a fully open isolator. If you're diving with an adequate gas supply and reserve, a freeflow is a non-event. You simply handle it with the appropriate valve shutdowns, you signal your buddy that the dive is over, and you ascend normally. No big deal. Only paranoia would suggest otherwise. A recent post to this thread from someone missing most of his fingers suggests that even with that disability the poster can shut down his valve in a few seconds. How could it be otherwise for someone with all his fingers? >To this end, what is your source >on the design basis of scuba valves being several turns to shut as an >"intrinsic safety factor". David, this is common knowledge. In contrast, medical oxygen valves, such as those on DAN O2 systems, are fully open with just a single twist. This is because those valves are designed with different objectives than SCUBA valves. >on any of the arguments posed so far. I just take issue with the fact that >some have arrived at conclusions/statements of FACT, without any proof or >"authority". The "authority" is that of experience. You're hearing the same argument from numerous divers on this list, many of whom are probably more experienced than you. >If I am too stupid to open my isolator before mixing/filling, then that is >Darwin at work. David, people make mistakes. It behooves you to set up a system where the likelihood of mistakes is minimized, and the chances of catching them before they cause an accident is maximized. If someone mixes your gas with the isolator closed, you may end up with pure O2 in one tank and a very hypoxic heliair in the other. If the valve is opened during your analysis, you could come up with (nearly) the correct PO2 due to the cross-feed of gasses, and you'll never know about the mixing error. Should the isolator get bumped closed during the dive it will be a *death sentence* as pure O2 or hypoxic heliair is breathed. There is no logic in this. This is not "common sense". I'm done with this thread. Good luck and dive safe. -Mike Rodriguez <mikey@mi*.ne*> http://www.mikey.net/scuba Pn(x) = (1/(2^n)n!)[d/dx]^n(x^2 - 1)^n -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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