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J Valve

Discussion in 'Vintage Equipment Diving' started by 2Bobbyo, Apr 11, 2020.

  1. Scuba Lawyer

    Scuba Lawyer Manta Ray

    # of Dives: 5,000 - ∞
    Location: Laguna Beach, California
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    :thumbsup:
     
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  2. AfterDark

    AfterDark Solo Diver

    # of Dives: 1,000 - 2,499
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    I do with my dbl hose.
     
  3. John C. Ratliff

    John C. Ratliff Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Beaverton, Oregon
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    Situational awareness, including awareness of the equipment configuration at all times, would be the first skill. The second would be, for me, relaxing and enjoying the dive, while ensuring your safety by watching depth/time and ensuring you aren't pushing up against the "knife edge" of the no-decompression limits. That's right, I'm a NDL diver. Getting into decompression diving, in my opinion, is technical diving and requires a whole different set of skills.

    Depth gauge that works (some don't) and a functional dive watch or dive timer.

    Now, I'm going to show you some of my gear. It shows how I handle the J-valve pull rod (or don't). The first several of my sets of doubles has a reversed J-valve configuration, so that the valve is facing my back instead of facing away. In this configuration, it is much more difficult to trip accidentally.

    Now, last night before going to sleep I was doing the math in my head to figure out how much in cubic feet of air a 300 psig J-valve on a 71.2 cubic foot of tank actually reserves for the diver. Here's the calculation:

    300 psig / 2475 psig = X / 71.2 cubic feet

    X = 0.12 x 71.2 cubic feet = 8.63 cubic feet of air

    That's the reserve for a steel 71.2 cubic foot tank. Now, if you look at the photos you'll see that I use double tank systems a lot. The double J-valve manifold has a 500 psig reserve spring, and so holds back 500 psig from one tank. I'll use my twin 52s as an example (I also have twin 40s and twin 45s). The calculation for this set is:

    500 psig / 1800 psig = 0.28
    0.28 X 52 = 14.44 cubic feet of air held back.

    Of course, this happens in one cylinder, and when I trip the J-reserve, it equalizes to 250 psig.

    Now look at that same set with a J-reserve Calypso regulator on it. This regulator has a 300 psig spring, but it is set in the center, and not on one tank. So two tanks feed it. Here's that calculation for the center post Calypso-J regulator:

    300 psig / 1800 psig = 0.17
    0.17 X 104 cubic feet = 17.33 cubic feet of air held back.

    So having the regulator J-valve on twin tanks is an advantage over the J-valve twin manifold. But then consider what if both valves were used, the one on the cylinder and the one on the Calypso-J regulator? Well, we'd have 14.44 cubic feet held back in one cylinder, and

    0.17 X 52 cubic feet = 8.84 cubic feet held back in the other cylinder.

    .....14.44
    ....+.8.84
    .....17.68 held back by both J-valves

    Now, look at the J-valve pull rods. I have several different ways of holding the pull rods. One is on the tank band, which was pretty universal for harnesses. I have another which is a simple "L" shaped piece of metal with a hole drilled into the shorter part; it hooks into the tank band at the appropriate place.

    There are two "unconventional" methods, and one simple one is on my twin 40s (the AL 3000 psig tanks). It is simply a piece of duct tape with another piece (shorter) on the adhesive side to form the loop. The adhesive side is much longer, and allows the tape to stick onto the tank. In the USAF, we used masking tape for a lot of things, as it would come off easily. We put it over the manifold guard to keep our parachute harness or risers from inadvertently hanging up on either the manifold or the regulator yolk. We basically formed a "covering" with masking take to ensure no protruding piece of the scuba would hang up on the parachute as it deployed in parascuba jumps.

    The other is a birdnest coil of 550 cord, with enough end to tie to the J-valve on the Calypso-J regulator. The birdnest coil gives a handhold, and allows you to easily access the J-valve without reaching behind to trip it. Note that with this regulator, the J-reserve is also pointed toward the diver's back, so that is is very difficult to trip, and is protected by the manifold itself.

    Finally, I figure not too many people have ever seen or heard of a birdnest coil. I have it here on 550 pound test cord (parachute cord), and the coil is very convenient to keep this line from tangling. You start with about six coils of cord, then start making loops across these coils. As you progress, you make a loop, go behind the cord and make another loop through the loop you just made, and continue that process until all the cord has been used. When that is complete, put the end through the last look and it is "safetied," and cannot be untied until that end comes out of the loop. The birdnest coil is a very convenient way of keeping cords, or in our case in pararescue, our 250 foot letdown tape (one-inch nylon tubular tape that is made into a birdnest coil, and stored in the pocket of our tree-jump suit).

    SeaRat
     

    Attached Files:

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  4. Luis H

    Luis H Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Maine
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    Those are not even close to the answers I was looking for... So you flunked... :D

    Even after I gave you the answers. :confused:


    I thought my point was fairly clear: A reserve valve only give you enough warning to make a direct ascent to the surface.

    There are many things in diving that are debatable, but the point about the limited air supplied by the reserve mechanism is not really up for debate. :wink:

    Depending on starting depth the reserve doesn't provide enough air to do a safety stop, which now-a-days I consider mandatory (OK only for dives deeper than 20 feet).

    Keep in mind that breathing the last 100 psi really sucks (pun intended), even close to the surface.
     
  5. John C. Ratliff

    John C. Ratliff Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Beaverton, Oregon
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    Hi Luis,

    The reserve in a set of twin 72s is adequate for a 10 foot safety stop, but we never did that as it wasn't even in the protocol in the 1960s and 1970s.

    500 psig / 2475 psig = 0.20
    0.20 x 71.2 = 14.24 cubic feet, or about 14 cubic feet of air.

    It was even greater in the 1960s when we were using the twin 90 cubic foot U.S. Navy AL tanks, and the amount was about 15 cubic feet of air.

    Of course, you'd have to deplete the air supply to below the currently recommended 500 psig, as that's what one cylinder's J-valve is set to retain, and it would equalize to 250 psig.

    The first time I did a safety stop was when I worked with Larry Murphy and Sonny Cockrell at the Warm Mineral Springs Underwater Archaeological Project in Florida. There, we were essentially under cave diving rules, and because we were wearing twin 80s decompression was a significant possibility. We had a setup for oxygen decompression, starting on I think the 20 foot stop. Warm Mineral Springs was quite deep, for that time at least, at about 220 feet at the deepest part. We didn't have computers at the time, and so decompression had to be planned and executed well. Oxygen was used for decompression in the upper stages, and then they actually had a 5-minute stay in the water at least chest deep too. It helped that the water was 87 degrees F.

    For many, many years there was no safety stop. I think it's no coincidence that the safety stop, cave diving with decompression, and the use of computerized SPGs came almost simultaneously. The dive computer depends upon algorithms that are many times not U.S. Navy approved. Here is a paper from the 2011:

    http://dspace.rubicon-foundation.or...dle/123456789/10147/VDC_2012_6.pdf?sequence=1

    Also, Appendix 2B of the U.S. Navy Diving Manual is a chapter about the U.S. Navy Dive Computer.
    https://www.navsea.navy.mil/Portals/103/Documents/SUPSALV/Diving/US DIVING MANUAL_REV7.pdf?ver=2017-01-11-102354-393

    My reading of this is that the U.S. Navy is allowed to use regular, commercial off-the-shelf diving computers in their diving if they have been validated to follow the same recommended profile as the Navy diving Computer.

    This leads me to believe that there is sufficient variability in the algorythms that the safety stop was mandated as a safety precaution. In "the ol' days," we actually used the U.S. Navy Dive Tables, and because we use the total dive time (time from starting descent to time off the bottom) and the deepest depth we achieved to calculate either the NDL or decompression times, we built in the safety factor by having already ascended from our deepest depth. In my current diving, my dive site on the Clackamas River is only about 25 feet deep at the deepest. I have found the J-valve, on any of my tanks, adequate for my diving.

    SeaRat
     
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  6. happy-diver

    happy-diver Skindiver Just feelin it

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    full.jpg

    With a pressurised tank when the tank valve is off you are able to remove or install a hose
    and spg despite the position of the J valve, the same applies to Dacor twin tank manifolds.
     
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  7. Angelo Farina

    Angelo Farina Marine Scientist

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    All the J-valves used here in Italy, both the spring-loaded Technisub model, and the normal Cressi or Mares ones, were always designed to be on the side close to your back, not external as I see in some of your photos.
    Now I understand why with American valves it was so easy to open the valve inadvertently...
     
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  8. JamesBon92007

    JamesBon92007 Great White

    # of Dives: 2,500 - 4,999
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    I wasn't considering a snorkel to be a skill, but I'm never without one. As for watches, I was a poor kid with a part-time job making $1.50/hour which was just enough to eat and get my tank filled 2-3 times a week. I always managed to have a working dive watch. They were selling for around $13 at drug stores etc and were rated to 5 atm. I never had one fail on a dive, but they never lasted more than a couple of years. I can dive without a BC, a SPG, or a depth gauge, but I always wanted to know my bottom time. I supposed you could get a pretty good idea when your air was getting low by the shift in buoyancy, especially if diving with no BC. But, of course, what it all comes down to is being able to get back to shore at the end of the dive. Many times I emptied my tank, knowing I would be snorkeling back all the way, but my endurance level was a bit higher than it is now :wink: So, after considering everything, snorkeling skills do seem to be very important. I am confident that I could dive without a watch if using a J-valve, and of course I would be checking it regularly to make sure it didn't get knocked down. :wink:

    When I took my course in '69 they had us put our J-valve in the down position so we would not count on it. Their thinking was that if it accidently got knocked down something bad might happen if you were expecting 300 psi to be there and it wasn't. They taught us to calculate how long our air would last which is why I felt that a watch or bottom timer is of utmost importance. Having said all that, I had no way to check how much air was in my tank at the beginning of a dive so much of it was faith in the dive shop that filled it. But then, running out of air was just not something that I ever worried about. :)
     
  9. AfterDark

    AfterDark Solo Diver

    # of Dives: 1,000 - 2,499
    Location: Rhode Island, USA
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    My buddy used light monofilament fishing line on his J valve to keep it up. He just pulled hard broke the line. He never had a problem at least when we dove together and we did a lot of dives. He said he was pretty sure if he got the rod hung up enough to break the line he'd know the lever was down.

    He'd wrap the line around the lever at the rod then do the same on the valve and tie it off, leaving one line between the valve and the lever the to break. He went on to become a commercial diver and is now retired.
     
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  10. captain

    captain Captain

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    All 6 of my tanks have J valves. One other benefit a of J valve is it is a better carrying handle than a K valve.
    In my experience I have never had a steel 2450 psi 72 get me anywhere near the no deco limit on the old Navy tables on the first dive.
     

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