Maybe I should post this in the tech section, but I am curious as to what one of these looks like. Early cave divers used them, and they are incorrectly listed in many books as being the first manifold with which to double up tanks (even though Aqualung did that in 1953). Does anyone have a picture of what the Benjamin manifold looks like?
Benjamin manifold?
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vintagediver
Contributor
vintagediver
Contributor
Two outlets with independant knobs and no isolator? That is what I always understood it to be, no matter who manufactures it.
I don't think anyone ever manufactured them. The Benjamin conversion was two K valves that were drilled and tapped to accommodate a piece of stainless steel tubing between them to equalize the gas between tanks.
It allowed two independent regs to be used on separate valves, either of which could be shut off yet still access the gas in both tanks. The NACD cave diving manual (vintage 1971) references it, but per Bret Gilliam's "Deep Diving" (1992) it was developed by Dr. George Benjamin and Ike Ikehara a few years before that. The major objections to it were related to reliability and the potential for leaks related to the tubing and two extra connections.
But, home brewed reliability issues aside, functionally it was equivalent to a modern day two outlet non-isolator manifold and while it was certainly not the first manifold that allowed two tanks to be connected, it was the first to allow two regs to be independently shut down where each of them could still access all the gas in both tanks.
Given the difficulty in saying "two outlet non-isolator manifold", calling one of those a "Benjamin Conversion" is just a lot easier even if it is not 100% accurate from a vintage perspective.
It allowed two independent regs to be used on separate valves, either of which could be shut off yet still access the gas in both tanks. The NACD cave diving manual (vintage 1971) references it, but per Bret Gilliam's "Deep Diving" (1992) it was developed by Dr. George Benjamin and Ike Ikehara a few years before that. The major objections to it were related to reliability and the potential for leaks related to the tubing and two extra connections.
But, home brewed reliability issues aside, functionally it was equivalent to a modern day two outlet non-isolator manifold and while it was certainly not the first manifold that allowed two tanks to be connected, it was the first to allow two regs to be independently shut down where each of them could still access all the gas in both tanks.
Given the difficulty in saying "two outlet non-isolator manifold", calling one of those a "Benjamin Conversion" is just a lot easier even if it is not 100% accurate from a vintage perspective.
The Benjamin Rig was developed by Dr. George Benjamin in the late 50s/early 60s. It wasn't a commercial product. It was a modification of two single valves on two tanks to share the same air source. It was usually done by machining an extension, about 1.5" long, to go between the valve and the tank with a stainless steel HP tube going between the extensions. Slightly less common was to connect the valves with fittings installed in place of the burst disks or in holes machined into the valve bodies.
Functionally, they were equivalent to a modern isolation manifold but with the isolation valve locked open. Many people now feel that non-isolation manifolds are safer than isolation manifolds because of slightly less failure points and far less operator error induced incidents.
Functionally, they were equivalent to a modern isolation manifold but with the isolation valve locked open. Many people now feel that non-isolation manifolds are safer than isolation manifolds because of slightly less failure points and far less operator error induced incidents.
Jeff Bozanic was one of the people pushing that argument 4-5 years ago. I agree to an extent in that it is a bit more idiot proof as without the isolator, a diver can't close it at the wrong time, fail to check it pre-dive, etc.
But that is also a bit like saying that firing a gun with a safety is more problematic as the gun has a safety that can be left on, left off, or fail. That's all true, but it must be balanced with the greater overall safety that is attained and any added faults can be addressed with better training and/or maintenance.
Instances of neck o-ring extrusion, burst disc failure, or manifold failure have a very low incidence of occurring - but the total gas loss that results creates a significant risk of a fatality, especially in a two person team diving thirds and near the point of max penetration.
On the other side of the coin, actual failure of the isolator valve itself is equally rare - I have never actually heard of one. At worst, it adds one more potential very low incidence failure to the existing list of three, but it makes those three much more surviveable.
It also adds some potential failures due mis-handling of the isolator valve such as starting a dive with it closed, breathing off the right tank and reading the SPG on the un used left tank. However in that case and in most others, good pre-dive checks and good situational awareness - a truly attentive diver will not go far before they notice they are using a lot less gas than normal and check the isolator to discover it is closed. In that regard, I think the early problems with isolator manifolds were due to existing pre-isolator habits and and training protocols based on older non-isolator techniques.
Personally, I check my valves at least twice in the pre-dive phase, can reach them underwater and am alert to any oddities in gas usage that may suggest a closed isolator, so I would rather have the ability to isolate in the event of one of the unlikely failure modes than to have a more idiot proof manifold that cannot be isolated.
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In regard to when it was first invented, Gilliam states "late 1960's".
But that is also a bit like saying that firing a gun with a safety is more problematic as the gun has a safety that can be left on, left off, or fail. That's all true, but it must be balanced with the greater overall safety that is attained and any added faults can be addressed with better training and/or maintenance.
Instances of neck o-ring extrusion, burst disc failure, or manifold failure have a very low incidence of occurring - but the total gas loss that results creates a significant risk of a fatality, especially in a two person team diving thirds and near the point of max penetration.
On the other side of the coin, actual failure of the isolator valve itself is equally rare - I have never actually heard of one. At worst, it adds one more potential very low incidence failure to the existing list of three, but it makes those three much more surviveable.
It also adds some potential failures due mis-handling of the isolator valve such as starting a dive with it closed, breathing off the right tank and reading the SPG on the un used left tank. However in that case and in most others, good pre-dive checks and good situational awareness - a truly attentive diver will not go far before they notice they are using a lot less gas than normal and check the isolator to discover it is closed. In that regard, I think the early problems with isolator manifolds were due to existing pre-isolator habits and and training protocols based on older non-isolator techniques.
Personally, I check my valves at least twice in the pre-dive phase, can reach them underwater and am alert to any oddities in gas usage that may suggest a closed isolator, so I would rather have the ability to isolate in the event of one of the unlikely failure modes than to have a more idiot proof manifold that cannot be isolated.
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In regard to when it was first invented, Gilliam states "late 1960's".
Hi DA,
I think both of us got our training when it had more substance and preperation and problem solving was a more in depth part of training. These days, I see very few equipment errors but many operator errors. The rig that I mostly use has the operation ease of a non isolator "Benjamin" manifold with bailout even if the manifold fails. I dive triples with two tanks on a non-isolated manifold with two regulators with independant shut off and the third tank independant. So if my manifold fails totally, I still have 1/3 of my air without having to operate any valves. With only doubles and my training I would slightly lean toward an isolator manifold but with triples (or doubles and a pony) I prefer non-isolator manifolds.
The first "Benjamin Manifold" that I ever saw was in 1969 but the diver said he had been using it for a few years.
I think both of us got our training when it had more substance and preperation and problem solving was a more in depth part of training. These days, I see very few equipment errors but many operator errors. The rig that I mostly use has the operation ease of a non isolator "Benjamin" manifold with bailout even if the manifold fails. I dive triples with two tanks on a non-isolated manifold with two regulators with independant shut off and the third tank independant. So if my manifold fails totally, I still have 1/3 of my air without having to operate any valves. With only doubles and my training I would slightly lean toward an isolator manifold but with triples (or doubles and a pony) I prefer non-isolator manifolds.
The first "Benjamin Manifold" that I ever saw was in 1969 but the diver said he had been using it for a few years.
Gilldiver
Contributor
I have always known the Sherwood double outlet manifold as the "Benjamin Crossover". Who told me this name in the late 70's or early 80's I haven't a clue.
VooDooGasMan
Contributor
I feel that my us divers barrel manifold is the most reliable manifold I have. Still have J valve capability on it also, not at vintage point of view, but spare air for deep diving. It has been on al's for the last few decades, yet I have some newer steels that I have been considering on hooking them to.
Never had any problems with my genisis manifolds with Isolator, 300 bar. only other vintage manifolds have I had leaking from, which are in vintage storage.
Happy Diving
Never had any problems with my genisis manifolds with Isolator, 300 bar. only other vintage manifolds have I had leaking from, which are in vintage storage.
Happy Diving
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