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J valves

Discussion in 'Vintage Diving & Equipment' started by bryon, Jul 6, 2004.

  1. bryon

    bryon Guest

    Hi Lisa and Co.

    Is it possible/necessary to rebuild old J valves so they work as originally intended? Is there any easy way to accurately test - on dry land - an old J valve to see if it still works at the prescribed tank pressures? Obviously, I can just drain the tank down to 500 psi and see what happens. For example, is there a way to accurately verify if its actually at 500 psi (as opposed to 520 psi or 490 psi) on any given tank when the J valve reserve should be activated?

    Many thanks in advance. bryon

  2. Turtleguy9

    Turtleguy9 Instructor, Scuba

    # of Dives:
    Location: Honolulu , Hawaii
    Aloha Byron. I usually use a somwhat similar method to check activation pressure. I use a modern reg with Submersible pressure guage, and bleed down to where I get no more air. Then I check for activation by operating the j-valve . I have had some activate as low as 350 psi.
    Aloha Turtleguy
  3. ScoobieDooo

    ScoobieDooo Contributor

    Thats what I have also done this past week.

    I used a modern reg to bleed my tank down to where it REALLY became impossible to breathe off the reg. I then checked my PSI level with my modern SPG. I then opened the J-valve and easy breathing resumed.

    I was testing at the time to see if the valve even worked properly - not so much as to the actual PSI this occurred at.
  4. captain

    captain Captain

    I have made new J valve seats out of nylon to replace deteriorated ones. I check them the same way turtleguy does. None of them will close at an exact pressure. Some never shut off completely but enough that the breathing gets hard and you will know you have reached the reserve point.

  5. bryon

    bryon Guest

    Thanks turtleguy, captain, and Scoobie dooo! It sounds like the technique is to just run the tank down with a reg/SPG hooked onto the valve and assess it that way!

    Have any of you ever had a J-valve quit working - as in fail to provide the 300-500 psi after activating the valve?
  6. aseeker2

    aseeker2 Registered

    # of Dives: I just don't log dives
    Location: Stockholm Sweden,
    Does anyone still make J-valves?

  7. pescador775

    pescador775 Contributor

    The J valve is no longer manufactured. Sometimes, the spring which sets the cut off pressure gets weak and the valve does not deliver the full reserve pressure when the rod is pulled. The USD check valve body was made from brass with a hard material called 'phenolic' as the seat. This stuff would get brittle and crack. In rare instances a piece of the material could come adrift and block the air flow downstream or wherever it lodged in the manifold. It would be quite a trick to refit this with a piece of teflon but I suppose it could be done. It depends on the exact type of seat I think. I've done it with defunct seats used on condensators (compressor filter). Maybe the 'captain' could tell us more. The valve seat in the USD double manifold must be accessed by removing a brass plug inside the female oxygen fitting. This may be jammed, and the plug cracks when removal is attempted.

  8. captain

    captain Captain

    I have a small metal lathe that I use to make the J valve seat and and other parts for regulators and valves.
    It's not easy but it can be done. I replace the original material with nylon, teflon is too soft. If the J valve is shuting at too low a pressure shims can be placed behind the spring to increase reserve pressure. Generally US divers used a 300 psi spring in the twin tank J valve and a 500 psi spring in the single tank valve.


  9. John C. Ratliff

    John C. Ratliff Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Beaverton, Oregon
    Just one slight correction to the Captain's post above. USD and other manufacturers used a 300 psi spring for a single tank, and a 500 psi spring for the twins. They also had a triple J valve, and it was a 700 psi spring (see Basic Scuba by Fred Roberts, Table 3-31 "Air Remaining After Reserve Action in Single, Twin and Triple Cylinder Blocks, "J" Type Reserve"). My UDS-1 has a very well-designed triple J valve, and it is set at 1000 psi, which with the 35 cubic foot tanks at 3000 psi amounts to 12 cubic feet held in the reserve.

    These springs could loose tension over the years, but my experience is that they last pretty well (at least for USD valves). If there is a problem, it's more likely a seat problem, or a corroded valve mechanism.

  10. captain

    captain Captain

    Thanks for the correction, John. Sometimes I put the cart before the horse. Must have been a "senior moment"


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