J-Valve question

[boulderjohn]

I have never used a tank with a J-valve, nor do I personally know anyone who has. I have a question about it, so I hope someone out there with some experience with it can help me.

Can you describe what it felt like as you depleted the main air and switched to the reserve? Could you feel a difference in the air flow prior to the need, and, if so, to what extent and for how long?

 

[SteveAD]

it feels just like running out of air, or more accurately, having your air shut off (pool training, air depletion exercise) breathing normally, then one breath comes a little harder, another breath or 3 with increasing resistance, then NO AIR! after pulling the reserve rod performance returns to normal until you run out of air for real.

 

[H2Andy]

this is just hearsay, since i never used a J-valve (WAY before my time), but
once you were pretty close to 300 psi, you'd feel the reg getting hard to breathe.

from what i hear, this happened quickly, maybe 3 or 4 breaths before you'd
have to switch the reserve on. you'd then not be able to breathe unless
you pulled the reserve.

you then pulled the reserve, and you had 300 psi to finish the dive

 

[DennisW]

I have two tanks with J-Valves. I keep them in the down, or reserve always on, position.

 

[Walter]

Stevead is exactly correct.

 

[boulderjohn]

Thanks for the help on this, but I have an additional question.

I was actually asking because of the air depeletion exercise. I am frequently a demonstratee (if that is a word) for this exercise, so I am very familiar with it. In that exercise, I don't sense any warning at all. I am breathing at a very relaxed pace, and then suddenly I don't have any air. I have been wondering about the point of the exercise because of that. I was wondering if you got more of a warning with the J-valve, and I was theorizing that the exercise makes more sense with that equipment.

 

[Gary D.]

I have two tanks with J-Valves. I keep them in the down, or reserve always on, position.

Only two?

I still have a half a dozen at home and 5 at work.

Leave em down and they are just like any other valve.

Gary D.

 

[Nemrod]

This thread should have been in the vintage section. I have modern equipment but alos dive vintage gear in vintage configurations--because it is safer and more functional--lol--!
I own numerous tanks with J valve and one regulator with a built in J valve. The spring tension can be varied to effect the point at which the reserve becomes active. The J valve came into being before the SPG was in common use. I have mine set to activate at approx. 500 psi. As the 500 psi poit is reached breathing becomes diffucult--like running out of air--it become increasingly diffucult if you insist because the spring increasingly has more net force against the dwindling air supply. Pulling the lever down releases the spring pressure and breathing returns to normal. J valve tanks should be filled with the lever down, some times they will not fill with it up. The J valve is very reliable, it is how I learned to dive, "gas" managment was a science back then and much time and class room study went into air consumption calculations. Cousteu, himself, was never big on the SPG, and he used various reserve mechanisms for his divers. This may account for the early resistence to the SPG. That and early regulators had no means of attaching them without using a banjo bolt or attaching to the tank itself via a port some valves had and yes, some of those valves released pressure on the SPG when shut off.
Obviously there are limits to such equipment, now with doubles being used for diving routinely, but down to say 40/45 feet diving a J valve is very practical. Training other than what you get today is useful as well. It was a different world then and the methods and practices were considerably different. N

 

[Diver0001]

Thanks for the help on this, but I have an additional question.

I was actually asking because of the air depeletion exercise. I am frequently a demonstratee (if that is a word) for this exercise, so I am very familiar with it. In that exercise, I don't sense any warning at all. I am breathing at a very relaxed pace, and then suddenly I don't have any air. I have been wondering about the point of the exercise because of that. I was wondering if you got more of a warning with the J-valve, and I was theorizing that the exercise makes more sense with that equipment.

Yeah. Modern regs with balanced 1st and 2nd stages give you virtually no warning in an OOA situation. The "best" ones will breathe totally normally until the tank is completely empty and then *BANG* no air. One breath, maybe two....

Older regs didn't do that. I had a J valve with an Aqualung Aquarius (unbalanced piston) with a kind of stiff unbalanced 2nd and if you were alert you would get ample warning that the tank was running dry, maybe 5 or 6 breaths, more if you could keep yourself calm and inhale very slowly.

But it wasn't the J valve that made the difference, it was the regulator.

R..

 

[boulderjohn]

Yeah. Modern regs with balanced 1st and 2nd stages give you virtually no warning in an OOA situation. The "best" ones will breathe totally normally until the tank is completely empty and then *BANG* no air. One breath, maybe two....

Older regs didn't do that. I had a J valve with an Aqualung Aquarius (unbalanced piston) with a kind of stiff unbalanced 2nd and if you were alert you would get ample warning that the tank was running dry, maybe 5 or 6 breaths, more if you could keep yourself calm and inhale very slowly.

But it wasn't the J valve that made the difference, it was the regulator.

R..

Great information. Thanks!