i have had one failure, and was on a dive where a partner had one.
They were both rental tanks, so who knows what kind of care they were given.

the leak was s l o w, and not a problem at all.  in fact, neither of us had
isolation valves, and we still were able to exit the cave easily w/o any
major loss of air.
however, due to these incidents, i pretty much only dive now with isolator
valves, with the valve fully open, and from past experience know that i
probably have all the time in the world to close them and still be better
off than with no isolator at all.

Mark G.


> -----Original Message-----
> From: Paul Larrett [mailto:Paul_Larrett_at_LUC@co*.co*.uk*]
> Sent: Tuesday, April 28, 1998 2:59 AM
> To: techdiver@aquanaut.com
> Subject:
>
>
>      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
> --
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