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Bi 2x10L 200b + Apeks 200, la solution pour 85% des plongées.
Pour des plongées jusqu'à -
Isolation centrale ? Je ne l'ai jamais fermée !
En fait, si je dois plonger en totale autonomie et l'esprit tranquille, je prévoie plutôt d'emporter en latéral un ou deux blocs en alu respirable à la profondeur donnée. Je me souviens d'un essai assez scabreux à Thun-
Droite: la plaque inox et son lest de 2.5kg / Gauche: plongeur "tek" fin années '60
Utilité de la vanne centrale ? Voici un avis parmi d'autres...
“Ideal” Manifolds… Not So Ideal?
By Jeffrey Bozanic, NSS-
The Benjamin Conversion manifold, or as it is more popularly called, the dual valve manifold, was utilized for cave diving and other environments in which regulator redundancy was deemed beneficial throughout the late 1970s to the mid-
* Burst disk failure
* Sudden, massive failure of one of the cylinder neck o-
* Loss of integrity of the manifold itself
These concerns lead to the development of the “Ideal” or isolation manifold, which allowed the two cylinders to be isolated from each other, maintaining at least part of the gas in the event of one of the failures listed above. It was considered a vast improvement, and very quickly replaced the use of the “unsafe” dual valve manifold. It is the primary manifold used today for all forms of technical open circuit diving. Yet, my opinion is this valve does not add safety, rather it significantly reduces it.
During the twenty or so years in which the dual valve manifold design was in use, there was only one recorded failure of the type listed above that occurred while diving. This event occurred during a cave dive while using a Sherwood manifold incorporating a metal-
In addition, in 30 years of accident data collection, there are two instances of in-
In contrast, since the isolation manifold was introduced in the early 1990’s, there have been many, many incidents related to misuse of the manifold. Most of these have been rectified without harm to the divers involved, but all of them had the potential for very serious consequences. The types of problems associated with this design of manifold along with representative case histories include:
1. The isolation valve being closed prior to the dive
Case #1: This involved a cave diver who began the dive with 3,000 psi (200 bar) in his doubles. He and his buddy did a S-
What happened was that the diver was in the practice of always leaving his isolation manifold open. However, when he had it filled, apparently the fill station operator closed it. Thus, only one cylinder was being utilized during the dive. The diver using the cylinders did not check the isolation valve, since it was “always” open. The pressure drop seen was due to the S-
2. The isolation valve being closed during filling of the cylinders
Case #2: A cave diver planned a nitrox dive to a depth of 110 ffw. Prior to the dive he analyzed his cylinders and found that he had EAN32, as expected. He proceeded to a depth of 50 ffw, whereupon he began to experience symptoms of CNS oxygen toxicity. He immediately began sharing gas from his buddy, and aborted the dive.
After examining the cylinders on the surface, the team found EAN32 in one cylinder, and 100% oxygen in the second. Apparently, at some time during the blending process, the isolation valve was shut, resulting in only one cylinder being properly prepared. This was the cylinder that was analyzed, and so everything appeared normal prior to the dive. At no time prior to the dive did the diver check the isolation valve.
3. Roll off of the left manifold valve
Case #3: A cave diver swimming through a tight cave passage experienced a sudden failure of his gas supply. He switched regulators, and aborted the dive. After surfacing, he found that left manifold valve was closed. It had been open prior to the dive, as evidenced by his utilization of that regulator for the entire period up to the sudden supply failure. His forward movement through the overhead environment resulted in the “auto-
These failures are only representative of those in the files, and related to me anecdotally from other sources. Cases like this are very numerous, and any of them could have resulted in a fatality. In my opinion, it is only a matter of time until one does.
One might argue that these incidents did not need to occur, and that it was the divers’ fault for not checking the isolation valve prior to their dives. I do not disagree with this. However, when a piece of equipment opens itself up to a multitude of cases of “pilot error,” while not providing any concrete improvement in other areas of safety, then the net result is one of additional risk with a commensurate reduction in safety. For this reason, and the history of misuse of the manifolds in the field, my belief is that we should go back to using the standard dual valve manifold of the 1980’s or adopt another type of technology.
NOTE: This is one of a series of articles planned for Underwater Speleology, NACD News, and other journals of interest to the technical diving community which will discuss findings from the combined accident analysis files collected by the cave diving community.
About the Author
P.O. Box 3448
Huntington Beach, CA 92605-
Jeff was certified as a NAUI Instructor in 1978, and for the NSS-
Article Copyright 2005 Jeffrey Bozanic, All Rights Reserved
Source: http://iucrr.org/manifolds1.htm + http://iucrr.org/manifolds2.htm