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J-valve question

Discussion in 'Vintage Equipment Diving' started by broncobowsher, Jul 14, 2019.

  1. KWS

    KWS ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: SE TEXAS
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    From the looks of the video it appears to function like a Back Pressure regulator on a conpressor and teh ull rod over rides teh spring shutdown. I know to fill the tank you had to pull the rod to force the J portion open until you got above say 7-800 psi.
     
  2. captain

    captain Captain

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    The J valve is basically a relief valve (aka safety valve) that opens at any pressure above its setting, either 300 or 500 psi. It is over ridden when the lever is pulled down. There are only two situations when it would read below tank pressure on an spg. 1- when the tank pressure drops below the J set pressure and the lever is up. 2- When the tank pressure is above the J valve set point briefly during inhalation. As soon as inhalation stops the pressure reading goes back to tank pressure.
    Think of a J valve as the relief valve on a water heater. If the pressure in the water heater goes above the set pressure water would blow out (tank pressure is above set pressure). If the water pressure is below the set pressure and you pull the lever on the relief valve water will blow out. The J lever is the same as the lever on the water heater relief valve.
    It's simple folks.
     
  3. captain

    captain Captain

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    No is a relief valve set at 300 or 500 psi, pulling the lever holds it open.
    The J has to remain down thought out the filling process. If at anytime it is raised it will stop the filling process.
     
  4. JackD342

    JackD342 Dive Shop

    # of Dives: 500 - 999
    Location: Highland Park, IL
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    From Sherwood maintenance guide:

    When filling cylinders equipped with a reserve valve, make sure the reserve lever is in the reserve position (down). If the lever is in the dive position (up) when filling, the cam and block assembly could be damaged. The fill rate may also be extremely slow.
     
    oly5050user and John C. Ratliff like this.
  5. KWS

    KWS ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: SE TEXAS
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    Come to think of it I had to have the J rod pulled through out the fill and we closed it when done. Relooking at it i see why. the fill whip is higher pressure than the tank at all times. 2000 psi on the whip plus the 500 of the spring was higher than the 2000 in the tank.

    Sorry about that I got that fill part wrong.
     
    John C. Ratliff likes this.
  6. george_austin

    george_austin Manta Ray

    # of Dives: 5,000 - ∞
    Location: Los Angeles,CA. Alcoi, Espana, Los Barilles, Baja
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    J valves are the very definition of a solution in search of a problem IMO. Why complicate life? If the diver isn’t “aware” enough to manage his or her gas, simply, they’re just kind of the non serious types that might be better off in safer pursuits. IMO.

    Incidentally, not to be a nooj, but a relief valve and a safety valve - if we’re using strict ASME lingo, are two separate pieces of equipment in pressure vessels and piping installations.
    A relief valve lifts (opens) at a set point and immediately returns to its closed position as soon as P drops below whatever the setting is

    A safety valve typically lifts (opens) at a set pressure and stays open until pressure drops (usually in a pressure vessel) below another set pressure defined by adjusting rings inside the valve huddling chamber (body)
     
  7. captain

    captain Captain

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    Using those definitions it is a relief valve.
     
    george_austin and Sam Miller III like this.
  8. george_austin

    george_austin Manta Ray

    # of Dives: 5,000 - ∞
    Location: Los Angeles,CA. Alcoi, Espana, Los Barilles, Baja
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    I just leave the J valve open at all times and remove the pull rod actuator.
     
  9. JackD342

    JackD342 Dive Shop

    # of Dives: 500 - 999
    Location: Highland Park, IL
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    Your comment on the utility of j-valves almost sounds like you think they are a new feature. Just in case it needs to be said, they were the standard and definitely needed before the SPG became a standard item. Even today it has a very specialized need, for divers who work in blackout conditions unable to see and read an SPG, and who require the reserve air supply for safety. I think it might even be OSHA mandated for some situations?
     
  10. Ghetto Diver

    Ghetto Diver Solo Diver

    # of Dives: I just don't log dives
    Location: Beerfield Beach, FL
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    Reserves on doubles + are fun when filling....
    "Doh, forgot to open"...swooosh.
     
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