J Valve justification

[Nemrod]

I saw them in the Marvel website I do believe.

There are plenty on ebay all of the time. For practical purposes they are no longer needed because the spg is widely used now. This was not always the case as Dr Miller and Captain point out. I think as Captain mentions, military and commercial divers may still use them due to OSHA rules etc. Of which speaking, if you have noticed commercial divers and rescue divers don't generally use the type of scuba gear sold in your LDS exactly.

I like them for simple diving like from my kayak or boat. Just toss on the tank and grab the flippers and away you go, no BCs or complicated stuff. You don't need the pull rod, just reach back and check that the valve lever is up occasionally and when you feel the effort increasing, pull it down and go to the surface. You can adjust the cutting in pressure by shimming the reserve spring with washers. When you reassemble it make sure you install the lever with correct orientation--otherwise it is on when down and off when up (opposite of correct)--ask me what sort of a problem that might cause--doh!!!!! or maybe not.

N

 

[GrumpyOldGuy]

I learned to dive with a J valve and an SPG in the late 70's. Scuba Pro also had a regulator that started honking when you ran low on air. I think the bottom line is a small fixed reserve is no subsitute for gas planning. This became more of an issue as ascent rate was reduced from 60FPM to 30FPM and safety stops became more common, both of which required more gas and more variance based on your dive plan. Just like spare air, the actual J valve may not be the culprit, but that it becomes all to easy to rely on it and ignore proper gas management, thus becomming a liability.

 

[Sam Miller III]

I was a staff member for the LA County three month long UW Instructor course for several years during the mid 1960s. Prior to the course we discussed if we should use SPGs and/or require the student to be so equiped...The answer was No. The market and the percevied and/or actual need for an SPG had not yet been established.

In about 1967 (before PADI) NAUI & LA County presented the first IQ aka the ICUE or International Conference on Underwater Education at Santa Ana College (Now Rancho Santa Ana.) A major theme of many presentations was diver pre occupation resulting in not monitoring the J rod and SPG if so equiped. A short time later Scuba Pro warmed up an old Healthways audio reserve reg and marketed it as the Mark Seven. This was one of the many contributions to the demise of the J valve.

sdm

 

[DA Aquamaster]

The Mk 7's audio feature along with it's Mk 5 internals performance made it a top of the line Scubapro regulator for into the early 1980's. As an added benefit you could use about 4 lbs less weight with it attached as it was large and heavy.

Another auditory warning approach used a tank valve with a small steel ball and lever inside that would literally bang on the inside of your tank when the air supply got low.

After the first time I reached back to pull a J-valve pullrod and discovered it had already gotten pulled, I found my self checking it fairly often, particulary during the last half of the dive.

J-valves varied with some of them shutting the gas off quite sharply, and others just making it progressively harder to breathe but still giving you something. I suppose with a hard breathing regulator and low gas consumption, a diver could the miss the cue that the gas supply was low with some J-valves, but they'd have to work at it.

On single tanks the reserve was normally set around 500 psi and it was around 300 psi on doubles. Scubapro however marketed a Depth Compensating Automatic Reserve valve
that used ambient pressure to increase the reserve pressure based on depth, which was a pretty nice idea.

 

[Luis H]

On single tanks the reserve was normally set around 500 psi and it was around 300 psi on doubles. Scubapro however marketed a Depth Compensating Automatic Reserve valve
that used ambient pressure to increase the reserve pressure based on depth, which was a pretty nice idea.

Actually most single tank reserves were 300 psi. Many double tanks reserve were 500 psi and only on one tank (usually the left one). When you pulled the reserved in a double tank you would immediately hear the air rushing to equalize both tanks. You actually ended up with close to 300 psi once the tanks equalized after pulling the reserve. At least that was the intention and it kind of worked.

The Scubapro DCAR (Depth Compensating Automatic Reserve) valve was very clever. It not only was depth compensated, but on the top it has a spot that you can push down with a flat blade screwdriver and turn 90degrees to adjust the reserve from 300 to 600 psi (above ambient). They also had a little rod pressure gauge on the back that would tell you if the tank was full or empty. Not very accurate, but somewhat helpful (if it wasn't leaking).

The DCAR also came standard with the lever pointing forward towards the diver to reduce the chance of accidental activation. The lever could be easily changed to point back (in the conventional mater) if it interfere with the regulator, like it was the case with a double hose regulator.

The reserve had a brass cone plunger with no real seat to fail, just metal to metal flow restriction. There was a lot of thought put into that valve. I still have a couple of them, but I don’t use them anymore.

 

[Luis H]

The Mk 7's audio feature along with it's Mk 5 internals performance made it a top of the line Scubapro regulator for into the early 1980's. As an added benefit you could use about 4 lbs less weight with it attached as it was large and heavy.

Another auditory warning approach used a tank valve with a small steel ball and lever inside that would literally bang on the inside of your tank when the air supply got low.

If you want to have some fun, put a diver equipped with a Mk-7 (or any other audio reserve) among a bunch of spear fisherman. An OOA situation is going to be the least of his concerns.

 

[Sam Miller III]

...

Another auditory warning approach used a tank valve with a small steel ball and lever inside that would literally bang on the inside of your tank when the air supply got low.
~~~~~~~~~
US Divers Audio Reserve Valve, part number 0523 price $39.95, introduced in 1963.
It was not a steel ball.but a peice of hard plastic.

It could be activated at any time during the dive at a any tank pressure.

It was on the market only a short time.

~~~~~~~~~~~~~~~~~~~~~~~~~~~


On single tanks the reserve was normally set around 500 psi and it was around 300 psi on doubles.
QUOTE]

~~~~~~~~~~~~~~~~
There were three springs;
300 pounds for the single tank
500 for the doubles
750 for the tripple 44 USN tanks

sdm

 

[Wayward Son]

When I started diving, J valves & no SPG was the common configuration. During the 1970's that changed & SPG's became common. I saw a large drop off in buying J valves even before extra 2nd stages became common. Once we had SPG's, we just didn't need J valves.

I still have 2 old tanks with J's on them. The only reason is that I can't bring myself to spend cash to replace 2 vales that work. But I always dive them with the J down, they are, for all practical purposes, used as K valves.

 

[agilis]

oxyhacker, how can an octopus/ safe second provide an "actual backup"? Only a redundant system can do that. All the extra second stages in the world are worthless if the tank is empty. My recollection is that it was SPGs that made the J valve unnecessary in most situations. The SPG was revolutionary when it was introduced. Safe seconds are basically just a better way to buddy breathe.

I think Jvalves are still available, and are certainly still used. Until SPGs became available, the J valve was all there was as an emergency backup. I was trained (long long ago) to not depend on it, and to plan each dive conservatively.

 

[Thalassamania]

There are a few things being missed in this conversation, perhaps I became more aware of the major J-valve problem then most, because I was a child (small lungs and time SAC rate) when I used them: It was easy to breathe right through the reserve. The seats were not very good and air weeped by, if you breathed slow and easy you could empty the tank even with the lever in the up position. Lt. Fitzgerald's findings bore this out and the Navy stopped using them.

With respect to the DCAR, what did the added complexity and such give you? 300 or 500 PSI over ambient rather than 300 or 600 PSI absolute, that's what. So lets figure you're at 130, thats about 60 psi, or for the tanks of the day, a bit less than 2 cubic feet ... like a spare air. It was a ScubaPro sales gimmick, nothing more.