How did the old J valves work?

[slackercruster]

How did the old J valves work? I know their purpose, but how about mechanics?

 

[Tom Smedley]

It had a spring with about 300 to 400 pounds tension on it. When the tank pressure dropped to below 300 to 400 psi the spring closed the seat and shut off air supply. When the handle was pulled down it defeated the spring and allowed the remaining air to reach the regulator. The handle had to be in the down position to fill the tank.

 

[DA Aquamaster]

The orifice was a lot smaller than 1 square inch so the spring pressure requiredwas a lot less than 300-400 lbs but Tom is otherwise right on the money .

Most were set to leave about a 300-400 psi reserve, but the work of breathing noicably increased at 500-500 psi.

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.

 

[Walter]

One more point, it's not how did they work, it's how do they work.

 

[Greg Barlow]

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.

Yeah, back in my early days of diving I had a habit of checking its position a few times every dive. When I make vintage dives with a J-Valve I still have that tendency. I generally use a banjo fitting now whenever the yoke permits.

Greg Barlow

 

[PerroneFord]

One more point, it's not how did they work, it's how do they work.

Come on Walter. We have backup regs and SPGs these days. You don't have to "flip the bar" any more.

Interestingly, I borrowed a set of j-bar doubles last winter for a dive. Very cool actually, but I think I prefer my isolator.

 

[Walter]

Come on Walter. We have backup regs and SPGs these days. You don't have to "flip the bar" any more.

No you don't. I also don't have to dive with a double hose, Duck Feet, oval mask and no BC, but sometimes I do it anyway. The vast majority of my dives are with modern gear, but I love diving vintage as well.

Why do you prefer the isolator? Isn't it just an extra failure point?

 

[herman]

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

 

[PerroneFord]

Why do you prefer the isolator? Isn't it just an extra failure point?

Yes, it's an extra failure point. But I like the tradeoffs. It's a single failure point that solves 5 others. Take the good with the bad.

 

[Walter]

5 others? I can think of 2. 2 that are much more unlikely than an isolator failure. What are the other 3?