Quiz - Equipment - J-Valve

[Scuba-74]

I would say know. Those that got it wrong, including myself, either forgot or never knew the way J valves work.

If agencies don’t explain how the spring is triggered by low pressure and relieved by flipping the handle, then that’s on them. If they do, it’s on us.

I understand how J-valve works, although I never used one. I also answered wrong, and although I understand the reasoning behind A being the “right” answer, I do believe that question is quite fuzzy.

As others pointed out, the fuzziness is in the word “extra”. It can be argued that the J-valve doesn’t deliver extra air compared to what, say, K-valve would. But it also can be argued that it DOES deliver extra air compared to the lever being pulled up or down, air unavailable in the closed position becomes available in the open position. Since these exams do not leave room for arguing, IMO the questions should be more clear cut. Glad I don’t plan to take any of these any time soon

 

[Scuba-74]

It is also entirely possible, that the corresponding chapter in the text book contains a clear hint printed in bold to that extent, making the right answer rather obvious. And that the instructor would point that out to the students with a wink. It has happened in all PADI courses I took.

 

[wetb4igetinthewater]

I understand how J-valve works, although I never used one. I also answered wrong, and although I understand the reasoning behind A being the “right” answer, I do believe that question is quite fuzzy.

As others pointed out, the fuzziness is in the word “extra”. It can be argued that the J-valve doesn’t deliver extra air compared to what, say, K-valve would. But it also can be argued that it DOES deliver extra air compared to the lever being pulled up or down, air unavailable in the closed position becomes available in the open position. Since these exams do not leave room for arguing, IMO the questions should be more clear cut. Glad I don’t plan to take any of these any time soon

The problem is that it is difficult to make meaningful tests that are multiple guess ... ahem... multiple choice.

Imagine grading an exam where the question was: explain how J valves work?

scuba diving instruction is too quick and dirty for this.

 

[Scuba Lawyer]

Actually with a single stage DH reg breathing gets easier as tank pressure drops. The reason is the main spring has less pressure to overcome in order to open.

Yes, you are absolutely accurate with regard to a single stage DH like a USD Mistral with an upstream design - the lower the tank pressure, the easier it is to breath. However, with a downstream design such as the single stage Voit VCR-2 50 fathom, just the opposite is true. They get more difficult to breath as tank pressure drops.

As a side note, the single stage Healthways Gold Label DH (a upstream design) has a small disk with a hole in the center called a K-restrictor. It's purpose is to reduce the flow of air when tank pressure drops making it more difficult to draw air on each breath as a warning to end your dive. There is no "reserve" so to speak, you just go from a very very easy breathing reg as tank pressure drops to having to suck harder. It was designed to use on a K-valve tank (i.e. no reserve). Sorry for the history lesson, this stuff just facinates me.

 

[TMHeimer]

Beating Dead Horse-- 85% got it wrong, 72% got it wrong. Who cares!!!? Defining "extra air"? Talk about semantics. Discussing the mechanics of the J valve?
As stated, I think we all know what a J valve does.
Poorly worded multiple choice options!
Otherwise, why so much discussion???

 

[wetb4igetinthewater]

Yes, you are absolutely accurate with regard to a single stage DH like a USD Mistral with an upstream design - the lower the tank pressure, the easier it is to breath. However, with a downstream design such as the single stage Voit VCR-2 50 fathom, just the opposite is true. They get more difficult to breath as tank pressure drops.

As a side note, the single stage Healthways Gold Label DH (a upstream design) has a small disk with a hole in the center called a K-restrictor. It's purpose is to reduce the flow of air when tank pressure drops making it more difficult to draw air on each breath as a warning to end your dive. There is no "reserve" so to speak, you just go from a very very easy breathing reg as tank pressure drops to having to suck harder. It was designed to use on a K-valve tank (i.e. no reserve). Sorry for the history lesson, this stuff just facinates me.

It's great to get more history. Knowing how things work, both past and present, fascinates me.

 

[AfterDark]

Beating Dead Horse-- 85% got it wrong, 72% got it wrong. Who cares!!!? Defining "extra air"? Talk about semantics. Discussing the mechanics of the J valve?
As stated, I think we all know what a J valve does.
Poorly worded multiple choice options!
Otherwise, why so much discussion???

It could be said if one understands the function of a J valve, right off you know extra air is wrong. Think of a regulator like a Calypso J with a built in J valve, it couldn't possibly supply extra air, it can only warn of low pressure, the function of a J valve. It's more of a way of cross checking knowledge.

 

[scubadada]

They supply gas that is not available prior to releasing the valve, additional gas

 

[AfterDark]

They supply gas that is not available prior to releasing the valve, additional gas

No there's no extra air, it's 300psi held back, not somehow suddenly added to the tank. The tank stared with 2250psi no extra was added.

It's like a warning light on a car's fuel gauge it tells you have x amount of miles till you're empty.

 

[wetb4igetinthewater]

No there's no extra air, it's 300psi held back, not somehow suddenly added to the tank. The tank stared with 2250psi no extra was added.

It's like a warning light on a car's fuel gauge it tells you have x amount of miles till you're empty.

And that air is held back once the pressure approaches 300 psi. Is that not correct?