Quiz - Equipment - J-Valve

[wetb4igetinthewater]

I read it all, .

Hmmmm..,,,

Iwhat post are you referring to.

when I changed my answer to a

 

[captain]

My answer was A to begin with, I feel A is the only truly correct answer.

 

[captain]

Now my understanding is that when the pressure of the cylinder reaches a low pressure, it then engages the spring, so it does take an action (restricting air flow) when a condition occurs (low pressure). Pulling the lever disengages the spring and you can resume breathing as effortlessly as previously.

Look at the pressure relief valve on your home water heater, it is constructed the same as a J valve. If the water pressure is above whatever the valve is set at it will be forced open and water will flow out. It also has a manual opening lever that manually compresses the spring and allows water to flow out.
The J valve is not held open constantly when the tank pressure is above the 300 or whatever pressure the valve is set to hold in reserve. Each time you inhale you create a lower pressure down stream of the J valve and tank pressure forces it open. When you exhale pressure is equalized upstream and downstream of the J valve and it closes. In a way it acts as a demand valve until tank pressure no longer can force it open at each inhalation because you can not create enough differential pressure with your lungs..
An empty tank to a diver at 100' still has pressure in it but the diver can not create enough differential pressure to get air. If the diver goes up he is essentially pulling the lever to free up the air available by increasing the pressure differential between himself and the tank pressure.

 

[AfterDark]

Extra air IMO is air that a diver carries but is not part of diver's gas management usage plan. As someone posted the 300psi is part of that planning, for ascending.

 

[TMHeimer]

Extra air IMO is air that a diver carries but is not part of diver's gas management usage plan. As someone posted the 300psi is part of that planning, for ascending.

That gets back to the question from before about whether that 300 PSI is/was part of the planning and routinely used on purpose when ascending-- or, is it for emergency use and not originally planned to be used.
There is disagreement and I would like to read if anyone has found something on the internet that is more than an opinion--something saying exactly what the 300 PSI was intended for back then, or even what the majority of J valve divers used it for. I was unable to find anything.

 

[rhwestfall]

"The New Science of Skin and Scuba Diving" - 1968 edition:

interpret as you wish...

 

[tursiops]

That gets back to the question from before about whether that 300 PSI is/was part of the planning and routinely used on purpose when ascending-- or, is it for emergency use and not originally planned to be used.
There is disagreement and I would like to read if anyone has found something on the internet that is more than an opinion--something saying exactly what the 300 PSI was intended for back then, or even what the majority of J valve divers used it for. I was unable to find anything.

From "The Complete Illustrated Guide to Snorkel and Deep Diving," by Owen Lee, Forward by Jacques-Yves Cousteau, copyright 1963, page 145:

 

[captain]

View attachment 579549

That gets back to the question from before about whether that 300 PSI is/was part of the planning and routinely used on purpose when ascending-- or, is it for emergency use and not originally planned to be used.
There is disagreement and I would like to read if anyone has found something on the internet that is more than an opinion--something saying exactly what the 300 PSI was intended for back then, or even what the majority of J valve divers used it for. I was unable to find anything.

Speaking for my myself when you reached the reserve point the dive was over and you began the accent. There was no planning involved. In shallow water less than 25 or 30 feet you might delay the accent several minutes after pulling the reserve.

 

[Couv]

The operative word is "Reserve." The valve does exactly that-it reserves some of the air in the tank. It does not supply any extra air. I've only had a couple of motorcycles-they both had a reserve fuel valve. When activated, the valves allow the remaining fuel to be used from the tank-they don't port to a separate tank.

 

[AfterDark]

That gets back to the question from before about whether that 300 PSI is/was part of the planning and routinely used on purpose when ascending-- or, is it for emergency use and not originally planned to be used.
There is disagreement and I would like to read if anyone has found something on the internet that is more than an opinion--something saying exactly what the 300 PSI was intended for back then, or even what the majority of J valve divers used it for. I was unable to find anything.

I used it most of the time, I knew the air was there and "counted" on the J valve to tell me when the dive was over. Can't speak for everyone, but that was my training.