J valves - question

[boogeywoogey]

I remember reading about something called a J valve....if I remember correctly, it released an extra supply of gas, from a reserve, when the tank was nearing empty.

I also read that if the switch hadn't been switched back, on filling, the diver thought he would have a full tank but only the reserve was filled and hence disaster.

Does anyone know more? Presumably these valves are no longer used.

Just interested to know more.

boogey

 

[scubajoe]

There are still some around. And they are being used safely. I can't believe I am saying this....do a search on J valves. It seems like I remember seeing a cutaway view of a J valve here a few years ago.

Joe

 

[boogeywoogey]

Joe...thanks for the info. When you said you can't believe you're saying they're being used safely. does that mean that you view them as odd/unsafe.

Never used/seen them myself but they do sound odd/unsafe.

Do you know why they were dreampt up in the first place? Was it a case of"..öh, I have no air left but, yes I do, I'll switch this lever thingy"???

Just checked after a search....it seems that they are ridiculous. "Leave the lever down"is the advice so why have it in the first place.

Question remains, if anyone can help, why were they invented?

boogey

 

[JMdiver]

If the J-valve is left open when being filled it is filled all the way, as a matter of fact that's how it's suppose to be filled. After it's filled is when you're suppose to close the valve to trap in the spare air.

Happy Diving

 

[Jeff Toorish]

I used one once or twice in a rental before I bought my own gear. Really not much different that a stardard valve...although I almost turned it to the 'reserve' position until the LDS owner explained it to me.

Frankly, I didn't like it.

Jeff

 

[PerroneFord]

They were apparently popular before the SPG caught on. From the ear of diving with no BC, and using the change in buoyancy swing of the tank to get neutral for surfacing

Gotta love vintage gear.

 

[captain]

There was a time before the SPG was invented (yes, there was a time when we dived without SPG's, BC's octos's, pony's and computers.) when the only thing to tell you your air was getting low was the J valve. At about 500 PSI it would start getting hard to breath, when that happened you pulled the reserve lever down and it released the last 500 psi in the tank. The tank had to be filled with the reserve lever down or air would not go in. They are still in use. if you have one just keep the lever down when using an SPG. I still use J valves during vintage equiptment dives.

 

[pt40fathoms]

I have a few tanks with J-Valves on them. The last time I tested the bypass on them, they all released the remaining 400 - 500 PSI without problem. It's very important to have the valve closed or UP if you are diving with vintage gear and are going to rely on it as your safe reserve. In many cases however, the J-Valve is modified so that the bypass no longer functions, and the valve essentially functions like a K-Valve.


Any old timers on the board still have a faded copy of the catalogue that listed the valves under the catalogue number that eventually became the name of the valve? I know of a museum that would like to get a copy.

 

[agilis]

There were no SPGs when I learned to dive, and for years after. I think submersible pressure gauges came along in the 1970s. A J valve is simply a standard valve with a spring powered stopper shutting off the air flow when pressure drops below a certain point. All J valves I used had a spring that took 500 pounds of pressure to hold it open. The spring block was removed when you pulled a rod attached to a big lever on the valve. It was simple: lever up, and the spring is engaged, lever down, spring pressure removed. If you carelessly began the dive with the lever down, you had no reserve air supply when you ran out of air. I'd check the lever connecting rod every few minutes while diving, to make sure it was up. When it got hard to breath, I'd pull the lever down, releasing the "reserve", the last 500 lbs, about 20% of the tank volume.

SPGs were the most important development in Scuba, I think. What a difference they made!

 

[Brewone0to]

What an excelent descripton of the operation of these valves.
The only thing you left out were the stats on the number of apparent diver/drowning that occurred when a diver would attempt to activate the remaining air pressure, only to discover that sometime during the dive it was, and the reserve is already
used up.
This being the reason the "gas gauge" SPG was so important in making diving a safe sport.

J-valves,Save em for display in a case,but don't put them in with your diving gear anymore than you would include a BCD with an inflater stuck open.
they have far too much of a chance for failure.Use a SPG,plan your dive,dive your plan

Brian