J-Valve on vintage twinset.

[Ghost95]

Morning all. I have a question for you vintage twin manifold divers.

On a set of twins connected by a manifold, with a single regulator attachment point, does the J-Valve provide a reserve for both tanks or only for the tank that the J-Valve is attached to?

The set of twins I recently acquired has a White Stag dual manifold that can isolate either tank by a valve but only the left tank (when worn) has a J-Valve.

I'm just guessing but if you had a set of twin 50's you'd only have a reserve on a single 50, and that would equalize between tanks when it was activated.

PS. Any idea of the capacity? of these tanks. 2250 psi, 6.9" Dia., 2/3 the height of a steel 72.
They were Hydro'ed and VIP'ed, Valve manifold rebuilt, filled, and now waiting to dive. Shop tech said they were excellent inside and out and that the J-Valve worked great.

Thanks for your info.

 

[AfterDark]

Nice set! The reserve works for both tanks when both valves are opened.

 

[Ghost95]

Thanks for the reply.

So am I to understand that when I actuate the reserve lever an "extra" 500psi. +/- is released from each tank? If not it seems that the "extra" 500 psi would cross fill to the other tank and instead of the gauge reading 500 psi it would only read 250 +/-. Twice the volume, half the pressure.

The reason I ask is that I understand there are parts in the left valve that hold back pressure and are manipulated by moving the lever, but there was nothing going through the crossover to activate anything on the right side. If there is a reserve on the right side tank as well, I'm just curious as to how it's activated.

Best I can tell one valve is a "J" and one valve is a "K". So one with reserve and one without.

I am at work and don't have the tanks in front of me to play with at the moment.

Thanks again.

 

[AfterDark]

Thanks for the reply.

So am I to understand that when I actuate the reserve lever an "extra" 500psi. +/- is released from each tank? If not it seems that the "extra" 500 psi would cross fill to the other tank and instead of the gauge reading 500 psi it would only read 250 +/-. Twice the volume, half the pressure.

The reason I ask is that I understand there are parts in the left valve that hold back pressure and are manipulated by moving the lever, but there was nothing going through the crossover to activate anything on the right side. If there is a reserve on the right side tank as well, I'm just curious as to how it's activated.

Best I can tell one valve is a "J" and one valve is a "K". So one with reserve and one without.

I am at work and don't have the tanks in front of me to play with at the moment.

Thanks again.

With both valves opened you have one big tank. If you closed off one tank and breath other down to a lower pressure, then opened the valve on the closed tank the tanks would equalize. With both tank valves opened there is no left or right. If you closed off the valve on the right side tank and breath the left down to 300 psi then yes the reserve would work on the left side only. If after pulling the reserve you opened the other tank, the tanks would equalize and your left tank would then have more than 300psi in it. It's simple but hard to describe in writing..

 

[Ghost95]

Ok, thanks. I think I got it.

Only one tank has the reserve. So, the actual amount of reserve gas is whatever volume 500 psi of that left tank equals. Not both tanks.

500 psi x 1 tank not 500 psi x 2 tanks.

Seems like you would want to shut down the "K" valve so as not to cross fill and lower the working pressure, which can be important for regulator function.

Pressure gauges must have been a great leap forward in safety.

 

[James79]

Ok, thanks. I think I got it.

Only one tank has the reserve. So, the actual amount of reserve gas is whatever volume 500 psi of that left tank equals. Not both tanks.

500 psi x 1 tank not 500 psi x 2 tanks.

Seems like you would want to shut down the "K" valve so as not to cross fill and lower the working pressure, which can be important for regulator function.

Pressure gauges must have been a great leap forward in safety.

I agree, right up until you say shutting a tank down. A first stage is held closed by intermediate pressure... you inhale, IP drops, 1st stage opens, IP recovers. So low IP will effect cracking pressure (be a bit harder to draw on the second stage), but the reg will function all the way down to ambient pressure in the tank (once tank pressure gets below IP setting, the 1st stage just stays open). Easy way to verify that is breathe off your reg with the dust cap off and the reg not attached to a tank. Works, but you gotta pull on it pretty good. If you shut down the right tank when you feel it first start to get harder to breath off of, it's still probably between 75 and 100 PSI still. That means there's a minimum of 4 times the tank's water volume of use-able air in it you are shutting off.

Respectfully,
James

 

[James79]

And for the record, I believe those are 50 cf tanks. Terribly dangerous old stuff... you should give them to me for proper disposal! lol
Respectfully,
James

 

[Ghost95]

I agree, right up until you say shutting a tank down. A first stage is held closed by intermediate pressure... you inhale, IP drops, 1st stage opens, IP recovers. So low IP will effect cracking pressure (be a bit harder to draw on the second stage), but the reg will function all the way down to ambient pressure in the tank (once tank pressure gets below IP setting, the 1st stage just stays open). Easy way to verify that is breathe off your reg with the dust cap off and the reg not attached to a tank. Works, but you gotta pull on it pretty good. If you shut down the right tank when you feel it first start to get harder to breath off of, it's still probably between 75 and 100 PSI still. That means there's a minimum of 4 times the tank's water volume of use-able air in it you are shutting off.

Respectfully,
James

Thanks, I guess I was thinking that even though the volume of air would be the same, it would be easier to use if the pressure were higher.

And you know something, you're the third person who has mentioned how dangerous the tanks are and tried to take them off my hands for my own protection! If I didn't like living dangerously I might take you up on the offer.

I did strip the paint. It was not original and the tanks are galvanized anyway. They look cool but seem really heavy. It will be interesting as to what kind of weighting I'll need.

 

[James79]

Thanks, I guess I was thinking that even though the volume of air would be the same, it would be easier to use if the pressure were higher.

And you know something, you're the third person who has mentioned how dangerous the tanks are and tried to take them off my hands for my own protection! If I didn't like living dangerously I might take you up on the offer.

I did strip the paint. It was not original and the tanks are galvanized anyway. They look cool but seem really heavy. It will be interesting as to what kind of weighting I'll need.

No worries... with an unbalanced first stage (flow by pistons are about the only ones now) the IP fluctuation over tank pressure is more pronounced (maybe 20-25 psi)... but not enought that I would isolate that 75 to 100 psi in one tank and loose access to it. Particularly when J-valve diving (vintage, no spg style) is generally predicated on "when you hit the reserve it's time to surface".
Regarding weighting, I don't know what you normally use... but when I went to single old school 72s from AL80s, I dropped 5 lb off my belt.
If you decide you don't like them, let me know... I might make you an offer!
Respectfully,
James

 

[Angelo Farina]

My Aralu twins (by Technisub) have the reserve on the right tank. It is tuned to 100 bar (half of the standard filling pressure of 200 bar).
The two regs are mounted one on the manifold, one on the left tank.
When you breath down to 100 bar, the spring-loaded reserve kick in: you hear the click.
At that point your are breathing only from the left tank, until it is empty. Now you pull the rod, opening the reserve: pressure equalizes, and you end with approximately 50 bars in both tanks, which is 1/4 of the total capacity.
Last point: when filling the tank, remenber that the reserve rod must be pulled down. If not, there is the risk that one of two cylinders is not filled.
The tank looks full, but if you pull down the rod, the pressure will equalize and you suddenly discover that the tank is just half filled.
Nowadays most shops are not used anymore to these old valves, so be sure of instructing them properly when you give them the tank for being filled.
And when you get the tank back, check the pressure both before and after pulling the reserve.