Quiz - Equipment - J-Valve

[wetb4igetinthewater]

But, but, but, an AI computer might warn you if you have your alarms on

I don’t know why we are discussing AI computers which are not relevant to the question. While I agree that an AI dive computer can be programmed to warn you when gas pressure is low, we are taking about a valve that has a lever to open another small chamber. That’s it. It doesn’t do anything else, certainly not warn you. It is the lack of gas available that tells you to open up the reserve

 

[TMHeimer]

Maybe you are trying too hard to have black-and-white, unambiguous exactitude and clarity.
Consider: What is 2+2?
(a) 4.
(b) less than 5.
(c) more than 3.
(d) all of the above.
I guess there is always the accountant's answer: What do you want it to be?

OK. I'm just being picky I guess. In this question all of the answers are correct. Is this one you'd put on an exam? I guess it's OK if all answers are marked and credited as correct.
I may word it like this:
A. 4
B. 6
C. less than 3
D. all of the above.
Would seem just as easy to me to word it so there can only be one correct answer.

In today's posted question A and C can both be correct.
Wrong answers could easily be:
B. J Valve allows diver to monitor air during the dive.
C. J Valve alerts diver has exceeded no stop limits.
--Probably a few more that are clearly wrong. Not hard to do.

 

[tursiops]

OK. I'm just being picky I guess. In this question all of the answers are correct. Is this one you'd put on an exam? I guess it's OK if all answers are marked and credited as correct.
I may word it like this:
A. 4
B. 6
C. less than 3
D. all of the above.
Would seem just as easy to me to word it so there can only be one correct answer.

In today's posted question A and C can both be correct.
Wrong answers could easily be:
B. J Valve allows diver to monitor air during the dive.
C. J Valve alerts diver has exceeded no stop limits.
--Probably a few more that are clearly wrong. Not hard to do.

I guess my point was not clear. In my artificial example, yes, (d) is correct. But (a) is more correct than any of the others. It is a way to get people to think rather than overthink....or underthink.

 

[agilis]

A is the only correct answer. The J valve does not give any 'extra' air and certainly does not allow 'monitoring' of the air supply. I dived with J valves for a couple of decades. I still have one, a Dacor. What a J valve does is create a spring blockage to the air supply at pressures below five or six hundred PSI. As you got close to that level of pressure you could feel some difficulty in drawing a breath. You then pulled the lever downward with the attached actuating rod, removing the spring blockage and enabling you to use the remaining volume which was always there anyway. No 'extra' involved. No monitoring either. You had no idea of how much air you were using or still had until the spring blockage kicked in.

The J valve simply let you know when you were down to the last roughly 20% of the cylinder's volume. The biggest problem with these J valves was an accidental lowering of the lever during the dive, thereby removing the warning pressure block, so users learned to check the actuating rod regularly by reaching behind their back and pushing upward on the rod. I sometimes still, after all these decades, automatically reach behind me at the start of a dive to check that the non-existent rod is in the up position. I fail to understand how anyone familiar with these devices could come up with any answer other than 'A'.

 

[Must_dash]

I learnt with a 'J' and as has been commented you do develop a twitch to ensure it's correctly stowed, bit like a gauge check....

 

[wetb4igetinthewater]

A is the only correct answer. The J valve does not give any 'extra' air and certainly does not allow 'monitoring' of the air supply. I dived with J valves for a couple of decades. I still have one, a Dacor. What a J valve does is create a spring blockage to the air supply at pressures below five or six hundred PSI. As you got close to that level of pressure you could feel some difficulty in drawing a breath. You then pulled the lever downward with the attached actuating rod, removing the spring blockage and enabling you to use the remaining volume which was always there anyway. No 'extra' involved. No monitoring either. You had no idea of how much air you were using or still had until the spring blockage kicked in.

The J valve simply let you know when you were down to the last roughly 20% of the cylinder's volume. The biggest problem with these J valves was an accidental lowering of the lever during the dive, thereby removing the warning pressure block, so users learned to check the actuating rod regularly by reaching behind their back and pushing upward on the rod. I sometimes still, after all these decades, automatically reach behind me at the start of a dive to check that the non-existent rod is in the up position. I fail to understand how anyone familiar with these devices could come up with any answer other than 'A'.

Now that’s an excellent explanation and now makes a lot more sense. Then yes, I’d change my answer to A.

 

[scubadada]

A is the only correct answer. The J valve does not give any 'extra' air and certainly does not allow 'monitoring' of the air supply. I dived with J valves for a couple of decades. I still have one, a Dacor. What a J valve does is create a spring blockage to the air supply at pressures below five or six hundred PSI. As you got close to that level of pressure you could feel some difficulty in drawing a breath. You then pulled the lever downward with the attached actuating rod, removing the spring blockage and enabling you to use the remaining volume which was always there anyway. No 'extra' involved. No monitoring either. You had no idea of how much air you were using or still had until the spring blockage kicked in.

The J valve simply let you know when you were down to the last roughly 20% of the cylinder's volume. The biggest problem with these J valves was an accidental lowering of the lever during the dive, thereby removing the warning pressure block, so users learned to check the actuating rod regularly by reaching behind their back and pushing upward on the rod. I sometimes still, after all these decades, automatically reach behind me at the start of a dive to check that the non-existent rod is in the up position. I fail to understand how anyone familiar with these devices could come up with any answer other than 'A'.

If the rod was never pulled, would you be able to breath the cylinder to near empty, albeit with increased resistance, or would it quit delivering gas until you pulled the rod. I never tried this myself, so do not know the answer. I always pulled the rod when the resistance increased and did my ascent. If the latter is true, then it does, indeed, make more gas available.

 

[Angelo Farina]

I guess my point was not clear. In my artificial example, yes, (d) is correct. But (a) is more correct than any of the others. It is a way to get people to think rather than overthink....or underthink.

Actually it could the opposite. While in abstract math 2+2 makes exactly 4, in the real world it makes approximately 4. The chance that the result is bounded between 4-epsilon and 4+epsilon diminishes as epsilon goes towards zero.
On the other side, the chances that 2+2 makes something larger than 3, or smaller than 5, are order of magnitude larger.
Hence B and C are much more true (or, better, probable) than A.

 

[Altamira]

Although my steel 72 with J-valve is long gone, I still have the J-valve activation rod. Whenever I see it, fond memories and a smile magically appear. I never had an inadvertent activation, but really had to pay attention to making sure the valve was open when having the tank refilled.
Edited to add: With the advent of the SPG, I can't imagine going back to the J-valve for the reason cited above about needing to insure the valve was open during air fills.

 

[Angelo Farina]

Although my steel 72 with J-valve is long gone, I still have the J-valve activation rod. Whenever I see it, fond memories and a smile magically appear. I never had an inadvertent activation, but really had to pay attention to making sure the valve was open when having the tank refilled.
Edited to add: With the advent of the SPG, I can't imagine going back to the J-valve for the reason cited above about needing to insure the valve was open during air fills.

As said, the Technisub valve was avoiding entirely the risk of pulling the rod inadvertidely.
This is how I did learn diving, in the seventies, and this type of valve was alteady the standard. I do not know why this was not standard also on your side of the pond...