How did the old J valves work?

[PerroneFord]

Right post first stage
Left post first stage
Right post second stage
Left Post second stage
BC/Drysuit inflator

 

[jonnythan]

I don't understand how an isolation valve solves the problems of first or second stage failures. You simply shut down the offending post.

The only things I can think of an isolator solving are tank neck O-ring failures and manifold O-ring failures.

 

[drbill]

Many if not most J-valve divers had at least one dive where, when things got hard to breathe, reached back and discovered the J-vave had already been accidently pulled earlier in the dive meaning they were in fact just plain out of air. Emergency swimming ascents were more common back then.

Yep, happened to both me and my buddy at almost the same time on a 90 ft dive back in the 60's. Fortunately there was "enough" air in my tank to get us both to the surface buddy breathing on my reg.

 

[jonnythan]

Oh, and burst disc failures.

 

[drbill]

But Walters point is still valid, mine still works although I rarely use in as intended.

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.

 

[PerroneFord]

I don't understand how an isolation valve solves the problems of first or second stage failures. You simply shut down the offending post.

The only things I can think of an isolator solving are tank neck O-ring failures and manifold O-ring failures.

Jonnythan,

Have you used a j-bar? They don't (or at least the one I used) have knobs to shut down the posts. So with the isolator manifold you get that option as well as the isolator itself.

 

[jonnythan]

Do you mean the manifold with only one output? If so, then there is no left or right post.

Show me a picture?

 

[PerroneFord]

Yes, you are right. In thinking about it, there was only 1 reg connection. In my mind, I confused the straightbar (which has posts but no isolator) with the single outlet j-bar.

So the failures would be tank o-ring on either side.

Good catch.

 

[roakey]

The only things I can think of an isolator solving are tank neck O-ring failures and manifold O-ring failures.

That's it, plus as someone else mentioned, burst disk failures.

Roak

 

[jonnythan]

That's it, plus as someone else mentioned, burst disk failures.

Roak

That was me too