Quiz - Equipment - J-Valve

[TMHeimer]

But is IS intended to be used. It is the gas you use to ascend. You dive until you can't get any gas, pull the rod, ascend.

Thanks. I did not know that. I thought it was there in case you (with no SPG of course) miscalculated needed air for the dive, it was there to get you out of a jam.
Other than the "extra" discussion, I don't see how it being intended to be used changes my vote for "C" also being correct.

Question-- Someone said the reserve air the J valve releases can be 300-800 PSI. What was the most common amount? If it's say even as much as 800 and you are down 100', using that to ascend would get your tank pretty much empty, no? Safety stop? Never want a completely empty tank even if safely topside. Appreciate more info. on actually how the J valve was routinely used as it is way before my diving time.

 

[Scuba Lawyer]

Thanks. I did not know that. I thought it was there in case you (with no SPG of course) miscalculated needed air for the dive, it was there to get you out of a jam.

Speaking for myself, this is exactly what I was taught. The J-valve reserve was your backup if your gas management went haywire. One tried to account for the effects of added current, cold, depth, etc... on bottom time but if you needed it, the reserve air was there. That said, many (most) of the guys I would dive with just used the increased breathing resistance to single the end of the dive, pulled the reserve rod, and surfaced. The few times I actually had to activate my reserve involved heavy exertion (excitement?) trying to get lobster out of holes and loss of situational awareness. More than once I found the reserve has already been inadvertently activated so that is where my "blow and go" training kicked in. Overall, a SPG is a nice accessory to have.

Question-- Someone said the reserve air the J valve releases can be 300-800 PSI. What was the most common amount?

300 psi reserve on single tanks, 500 psi reserve on double tanks. Although that was spec, the actual spring tension on each valve was never uniform so there was fluctuation all over the board by around 100 psi in either direction when using different tanks.

My 2psi. M

 

[rhwestfall]

I had a relative who was a very active diver in the days of the j-valve being very prominent. He related a story of being in the engine room of the Keystorm (St. Lawrence River about 110' of depth) when he encountered the more difficult breathing indicative of being low on air. Reached to the release rod, only to find it already engaged!

They were darn crazy folks back then....

 

[TMHeimer]

But is IS intended to be used. It is the gas you use to ascend. You dive until you can't get any gas, pull the rod, ascend.

It seems Scuba Lawyer disagrees and mentions the reserve usually being 300 PSI for a single tank. I would figure if you purposely used that to ascend from any depth other than shallow, you'd risk emptying your tank. But, you guys have used those things and I'm just talking.

 

[tursiops]

It seems Scuba Lawyer disagrees and mentions the reserve usually being 300 PSI for a single tank. I would figure if you purposely used that to ascend from any depth other than shallow, you'd risk emptying your tank. But, you guys have used those things and I'm just talking.

Work it out: at the time, ascent rate was 60 ft/min with no safety stops. How much air do you need?
From 132 ft, an average depth of 66 ft, or 3 atm. SAC of (say) 0.7 cuft/min, 2 mins is 1.4 cuft, which is 55 psi in an AL80.

Added: I forgot to multiply by 3 atm in the example above. As scubadada points out in the next post, the answer is really 3 times as much air....sorry for the confusion, mea culpa.

 

[scubadada]

Work it out: at the time, ascent rate was 60 ft/min with no safety stops. How much as do you need?
From 132 ft, an average depth of 66 ft, or 3 atm. SAC of (say) 0.7 cuft/min, 2 mins is 1.4 cuft, which is 55 psi in an AL80.

I'm with my dolphin friend, but his example is actually 4.2 cu ft and 163 psi, it was not a problem ascending on the reserve Quiz - Equipment - J-Valve I used 130 ft, 2.17 min, and a RMV of 0.4.

 

[TMHeimer]

I'm sure the math confirms what you guys say. I guess there was just a difference of opinion way back then as to whether using the reserved was planned on not.
My Deep course instructor advised keeping 100 PSI for every 10 feet of depth, thus you ascend from 100' with 1000 PSI. Of course, they probably didn't do safety stops in 1960 and hear the DM say be back on board with 500 PSI.

 

[tursiops]

I'm with my dolphin friend, but his example is actually 4.2 cu ft and 163 psi, it was not a problem ascending on the reserve Quiz - Equipment - J-Valve I used 130 ft, 2.17 min, and a RMV of 0.4.

Oops, yes, thanks. Was hurrying to get to a 1:00 Zoom meeting. This working from home is tough.....

 

[scubadada]

Oops, yes, thanks. Was hurrying to get to a 1:00 Zoom meeting. This working from home is tough.....

I answered today's quiz question wrong because I hurried and didn't pay any attention

 

[Angelo Farina]

It seems Scuba Lawyer disagrees and mentions the reserve usually being 300 PSI for a single tank. I would figure if you purposely used that to ascend from any depth other than shallow, you'd risk emptying your tank. But, you guys have used those things and I'm just talking.

Here the reserve was set to 50 bars, in a 200 bars tank. This is 25% of total volume. Which indeed was 4000 liters, as the standatd tank, here, was a 10l+10l twin cylinder.
So 1000 liters of reservoir. And this for the one with higher SAC rate, as the rule was that as soon as one did pull the reserve, all the group has to end the dive and surface. And it was not possible to cheat, as the noise made by air going from one cylinder to the other ("tweeeiiing") was a clear indicator to everyone that it was time to ascend.