How did the old J valves work?

[John C. Ratliff]

I've retired mine since the last time I took it in for a hydro they wouldn't do it unless I replaced the valve.

Dr. Bill,

How can the LDS dictate the choice of valve you put on the cylinder. That has nothing to do with the hydro, or the visual inspection. Do they simply want to sell another valve?

I still use my J-valves. I have two that I use, on my twin 45s and my UDS-1 system. I have, on my twins, reversed the valve so that it is on the other side, and therefore points toward my body rather than away from it. That way, it is not easy to bump it into the "off" position (no reserve--various people use different terminology for whether the valve is "on" or "off"). I am currently also using a Suunto computer, and that gives me a different type of redundancy.

John

 

[PerroneFord]

Dr. Bill,

How can the LDS dictate the choice of valve you put on the cylinder. That has nothing to do with the hydro, or the visual inspection. Do they simply want to sell another valve?

Umm, the valve IS part of the Visual Inspection. Or at least it was in my PSI class.

 

[Brewone0to]

Not as well as an SPG,
or at least not as reliable.
When given the chance to use the valve without the gauge,
Don't walk away......RUN

 

[stas]

Is the debate in this thread (not the original question, but the modes of failure for an iso manifold) about iso manifold vs independent doubles,iso manifold vs single outlet manifold, or iso manifold vs single tank w/J valve? The first case has been discused till no end. In the secondor third cases, it seems like there isnt much of a debate.
Stas

 

[PerroneFord]

it seems like there isnt much of a debate.

Stas

Bingo.

 

[Thalassamania]

They worked poorly. When inspected by the Naval Safety Center, less than 10% of those in active lockers met spec. If you breathed gently you could often go right through the reserve without activating in (enough got past the seat).

I have a DACOR 300-J that I sometimes dive, it had the J-Valve built into the regulator. I dive it with a DACOR tank valve that has a high pressure port built into the neck of the valve itself and a home made SPG from the mid 1960s. Combine that with a intermediate pressure "direct feed" screwed into the CO2 detonator and controlled by a plumbing valve and your time machine is complete<G>.

 

[Walter]

Is the debate in this thread (not the original question, but the modes of failure for an iso manifold) about iso manifold vs independent doubles,iso manifold vs single outlet manifold, or iso manifold vs single tank w/J valve? The first case has been discused till no end. In the secondor third cases, it seems like there isnt much of a debate.
Stas

There wasn't a debate, but there was a bit of a comparison, but it wasn't of any of those combinations. It was a comparison of a manifold with an isloator vs one without the isolator. Other than the isolator, the manifolds are identical. The isolator is only useful in the event of a tank neck o-ring failure, a burst disk failure or the failure of the o-ring in the manifold connections. All of those are less likely to fail than is the isolator.

 

[jonnythan]

The isolator is only useful in the event of a tank neck o-ring failure, a burst disk failure or the failure of the o-ring in the manifold connections. All of those are less likely to fail than is the isolator.

Care to offer some data to back that up?

 

[Thalassamania]

According to Jeff Bozanic in his 2005 article:

During the twenty or so years in which the dual valve manifold design was in use, there was only one recorded failure … a Sherwood manifold incorporating a metal-to-metal seal … prior to the dive, the double cylinders were accidentally knocked off the preparation platform. They fell about three feet to the ground, landing on the manifold. The manifold was closely examined prior to diving, but was not leaking, and the divers elected to dive. After the cylinder pressure had been reduced to about 1500 psi, the manifold catastrophically failed, and both divers exited successfully sharing gas from the remaining rig. It was suggested at the time that the fall caused a displacement cylinders relative to each other, which did not manifest itself until the pressure reduction allowed the metal-to-metal seal to shift and lose integrity.
… in 30 years of accident data collection, there are two instances of in-water burst disk failure recorded. Both events occurred with cylinders that had been pressurized beyond the working pressure of the cylinders (in one case almost to the hydrostatic test pressure!), and occurred within minutes of the cylinders being placed in the water … in both instances, the burst disks had not been replaced in many years. As both of these incidents occurred at the surface, prior to beginning the dive, an isolation manifold would not have benefited the divers, since they would have called the dive anyway.
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-drill prior to descending, indicating that both regulators were working fine. About 15 minutes into the dive, he noted that the pressure on his SPG was not dropping as expected. He reached up, opened the isolation manifold, and watched as his pressure dropped from 2,700 psi (180 bar) to 1,700 psi (110 bar). He called the dive, and exited the cave with no further incidents.
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-drill usage, BC and drysuit inflation, and cylinder cooling after being placed into the water.

1. 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.

1. 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-shutdown” of the valve, as the hand wheel turned shut off as it scraped across the ceiling.
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.

 

[stas]

Jeff Bozanic was advocating/debating isolation manifold vs independent doubles. This is a debate as old as the isolation manifold.

The third case has nothing to do with the isolator but with a left post roll-off.

People keep on saying that burst disk failures and necks cracking are uncommon. Yes they are. The problem is that uncommon things can happen, often at quite inconvinient moments.

I believe that if one agrees with the task-loading argument given against independent doubles, the isolation manifold on a set of doubles is the most redundant/safest choice for open circuit scuba.
Stas