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In my own personal experience, I have never had a first stage or regulator failure under water. This is probably due to the fact that I keep them maintained very well, but with today's regs and such, yes there is still a posibility. I dive with option 2, with the manifold open and breathing off the long hose. In my belief, that if following the rule of thirds, and a major failure occurs, one is not supposed to just switch regs and go on, that is the end of the dive, and you abort!.. In diving via option 2, you should have sufficient air to turn off your valve, and ascend to whatever stop or to the surface as required by your present profile. Now again, I have never experienced a major failure that has caused me to abort a dive, but I still carry not only my duals, but a third independant pony, usually mixed for deco, but still something that can support me at a given depth. I like redundancy.... Keep it simple, the other options require you to think too much during the dive, thus not concentrating on the dive itself.. As a what if clause, what if by some chance you get narced at depth and forget to either switch regs, equalize your valve, or worse yet turn off a tank because you turned the valve the wrong way.. If anything, using method 2, you really only have to turn off one valve instead of trying to deal with three valves at a time. Thats why one dosen't use their BC underwater with a drysuit.. It gets too complicated. Paul Larrett wrote: > > I have given this some thought but would like some input from others > on the matter: > > The way I see it is this, I can think of 4 ways of using an isolation > manifold: > > 1) Have isolation valve closed and dive independents, swapping over > left and right regs frequently and abiding by the rule of thirds. The > benefit of this is that you have protected at least one half of your > back gas no matter if there is a delay in closing down the offending > first stage or manifold leak. Disadvantages would be having to swap > regs and not always breathing from the long hose (Hogarthian, which I > personally think is a good idea). Also, I like the idea of only using > 1 contents gauge for the twin set, thus minimising the number of hoses > and reducing potential failure points. Having them independent usually > means having 2 contents gauges. > > 2) Have isolation valve fully open. Advantages to my mind being that > you can always breathe off the long hose and only need 1 contents > gauge. I like to think that I can shut down my valves pretty quickly > (ie. a few seconds as I don't have to adjust my harness or pull the > set up or do any other "wrestling"). But you never know what might > prevent you from easily reaching behind and shutting down, so I guess > the disadvantage that this method has is the *potential* for losing a > lot of gas from both sides. > > 3) Have isolation valve just open. Same comments as 2) above except > that some people say that they can therefore shut the isolation valve > faster. Although I have "clockwise to close" permanently engraved in > my brain, having a valve partially open or closed does bring the > possibility of turning it the wrong way. > > 4) Have isolation valve closed, breathe from the long hose on the > right, have contents gauge off the right and periodically open the > isolation valve to equalise the pressure across the two cylinders. You > therefore don't have to swap regs and still have the fail safe of > independents. It does require discipline in opening the isolation > valve periodically, but if you can reach this with ease is that a big > hassle? If you are not a very disciplined diver you should not be > doing this type of diving anyway. Using this method you must have the > contents gauge off the right if your long hose is off the right. I > know in a strict Hogarthian set-up the contents gauge comes off the > left, away from the long hose and light canister, but is the contents > gauge off the right so bad in view of the above redundancy? > > I suppose that my preference would be method 2) above, however, if gas > loss was extremely sudden & fast I may lean towards method 4). Has > anybody out there suffered a serious first stage/manifold failure? How > fast was the gas loss? > > > Constructive comments would be appreciated, for information purposes > the isolation manifold I am referring to is the Scubapro (yes with DIN > fittings, balanced across the manifold and with barrel o-rings!). > > TIA > > Paul Larrett > -- > Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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