How did the old J valves work?

[Walter]

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

True, it could happen with any configuration.

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.

How do you come to that conclusion? You are ignoring non-isolation manifolds.

 

[PerroneFord]

I think I like the idea of being able to preserve half my remaining backgas.

 

[Thalassamania]

There are two ways to do that: Independent and isolation valve. Each has its advantages and drawbacks.

Isolation valves introduce the problems that Jeff covered as well as the potential failure at the connectors (never heard of the double captive o-rings going, but I guess there's always a chance).

Independents add a bit of complexity to gas management issues.

I have more experience with independents and don't really find the additional task load that great.

Independents add a bit of complexity to to gas management issues.

I have more experience with indepentents and don't really find the additional task load that great.

 

[Walter]

I think I like the idea of being able to preserve half my remaining backgas.

You'll be able to save it all by shutting down the side that has a regulator failure. It doesn't matter if you have an isolator or not.

 

[PerroneFord]

Yes it does.

 

[Under Pressure]

Interesting thread. Not exactly sure how it went from J valves to dual manifolds. But we have a tendency to wander from time to time.

 

[jonnythan]

Yes it does.

Any particular reason?

The critical question here is which is more likely:

1) A failure of the isolator itself.

2) A failure of the right tank burst disc, left tank burst disc, right tank neck o-ring, or left tank neck o-ring.

"It's just better" is not an answer.

Walter appears to be arguing that failure #1 is more likely, and introducing this failure to deal with any of the #2 failures is foolish.

 

[Walter]

Yes it does.

Well, if you have a regulator freeflow and you close off the isolator instead of shutting down that side, you're right, it does matter. You save half your gas instead of all of it. Other than making a poor choice, the result would be the same - you'd save all your gas..

 

[Walter]

Walter appears to be arguing that failure #1 is more likely, and introducing this failure to deal with any of the #2 failures is foolish.

Foolish is a tad strong. Chances of an isolator failing are also pretty remote (operator error is the most likely problem).

I just don't believe we need to introduce a potential problem to solve a problem that does not exist.

 

[Walter]

Interesting thread. Not exactly sure how it went from J valves to dual manifolds. But we have a tendency to wander from time to time.

Did you ever have a conversation (over 10 minutes) that didn't? Especially when the original question was answered in the opening rounds.