The evil J valve ?

[herman]

the only prob you run into running a j valve without the rod
is forgetting to flick it down prior to dive...
...then thinking that you still have 500 lbs,maybe stay a bit longer...
then noticing that it's sucking hard...and you don't have the rod to pull...
then trying to be "gumby" and bend enough to reach the freakin' valve....
just saying!
remember to flick valve down first...DOH!!!!
have fun
yaeg

If you make it to 500 psi with the lever up and don't notice it, you really should not be diving. If you dive a J valve with the lever up and a SPG, the SPG needle bounces like crazy with every breath. Any diver that ignores a bouncing SPG needle an entire dive either is stupid and in line for a Darwin award or knows exactly what is going on, in which case it's not a big deal.

 

[agilis]

Commercial divers using scuba sometimes use J-valves when working in zero visibility. An spg is useless when working under conditions that involve more feel than vision.

There is nothing mysterious about a J-valve; a spring that requires about 500 lbs.of pressure to hold open is engaged when the lever is up. Pull the rod down and that spring block is removed. I dived for years with J-valves and developed a habit of reaching behind me with my left hand every 5 or 10 minutes and making sure the pull rod was in the up position. Diving solo at night tends to create these kinds of habits.

 

[Diver0001]

One of the dive charters used by our club had a DM on board from a local dive shop who warned me about my tank and its valve.

I'm kind of curious what he said about it? Everyone seems ready to declare the DM an idiot for having an opinion but what did he actually tell you?

R..

 

[j yaeger]

If you make it to 500 psi with the lever up and don't notice it, you really should not be diving. If you dive a J valve with the lever up and a SPG, the SPG needle bounces like crazy with every breath. Any diver that ignores a bouncing SPG needle an entire dive either is stupid and in line for a Darwin award or knows exactly what is going on, in which case it's not a big deal.

hmmm.....
ive never noticed my needles bouncing with a j valve
how odd...
the only time it bounces is when i'm at the point to pull the rod- 300-500# depending on the valve set

 

[Couv]

Well, it's been a long time since I dived with both an SPG and a J valve, but you can count me in the group who never noticed the bouncing needle.....or at least I don't remember.

I do remember reaching back to check the valve position intermittently just as I now check my SPG.

 

[herman]

Well, it's been a long time since I dived with both an SPG and a J valve, but you can count me in the group who never noticed the bouncing needle.....or at least I don't remember.

I do remember reaching back to check the valve position intermittently just as I now check my SPG.

You did this just to make me go look, didn't you.

I just checked 4 J valves I use, tank pressures ranged from almost 3000 to around 800. All 4 shifted the SPG by around 400 psi with each breath with the lever UP, with it down, no movement. Now there is one exception to this and it's the old style manifolds. Because the reg is always connected directly to one of the tanks and only the one with the J valve beside it actually holds the reserve you will not see the SPG deflect on them. One other possibility, a lot of rental valves had the reserve seats removed, in which case, the needle would not move since there is no reserve seat to restrict flow.

If you think about it for a minute, the SPG needle must move if the J valve seat is working. A reserve works by blocking the air passage with a spring loaded seat. For air to flow past the seat, there must be a pressure differential across the seat which is at least equal to the spring load (the reserve pressure). As tank pressure on the down stream side is reduced by breathing, the seat opens when the differential gets to the reserve pressure, pulling down the pressure on the SPG side of the J valve. You don't notice the pressure drop until you get close to the reserve pressure of the valve, at which time (pressure) it gets hard to breathe from because you must supply a little of the pressure differential with your lungs. When you move the lever to the reserve, the spring pressure is removed from the seat allowing full flow with no need for a pressure differential to open the valve.

 

[oldschoolto]

You did this just to make me go look, didn't you.

I just checked 4 J valves I use, tank pressures ranged from almost 3000 to around 800. All 4 shifted the SPG by around 400 psi with each breath with the lever UP, with it down, no movement. Now there is one exception to this and it's the old style manifolds. Because the reg is always connected directly to one of the tanks and only the one with the J valve beside it actually holds the reserve you will not see the SPG deflect on them. One other possibility, a lot of rental valves had the reserve seats removed, in which case, the needle would not move since there is no reserve seat to restrict flow.

We can always count on Herman.......

Jim...

 

[scubamitch]

'' Still have that f'n valve on there I see", is what he said to me the 2nd. time I saw him, we used the same charter boat that summer at least twice together. As I recall, he told me I may forget to turn the knob down, or it may get turned up some how just prior to going over. Not being able to reach the knob quickly at depth was the concern.

 

[herman]

'' Still have that f'n valve on there I see", is what he said to me the 2nd. time I saw him, we used the same charter boat that summer at least twice together. As I recall, he told me I may forget to turn the knob down, or it may get turned up some how just prior to going over. Not being able to reach the knob quickly at depth was the concern.

Which just shows his/her lack of knowledge....or excessive coolaid drinking. I love these kinds of know it alls, it is so fun making them look like fools. My first question would have been, exactly why is it necessary to get to the knob quickly? You have almost the entire dive to move the knob before the reserve function starts to be noticable, plenty of time. And so what if it gets turned up, that is the way it's designed to be used. Most divers can easily reach the valve if necessary but unless you plan/do pull the tank down below the reserve pressure (usually 500 on a single tank) it will have no effect on the dive. At worst, just educate your buddy...if I show you a bouncing SPG and point to this lever, turn it down...problem solved... or better and much more fun...offer to educate the DM on how to operate simple dive gear....something he should of learned in OW.

 

[j yaeger]

...besides,having the j-valve makes it easier to grip the tank,tell him!!!
my brother-in-law used one of my tanks with the jay valve up
after about 20 min.s he showed me his spg going up and down with each breath...
i just figured that the "air pig" had sucked it down to 500# already
he may have,but i flicked it down,we were at safety stop,and that was the end of it
my bad for not telling him to turn it down
i have never noticed it,but it makes perfect sense!!!!
my j-valve on the twins i can reach easily,but only forgot once...
have fun and thanks herman!!
yaeg