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Trying to determine the inlet valve type on my hot water radiators

Just inherited an old house with 12 hot water radiators (circa 1920's). Was trying to understand what kind of valves these all have on the inlet side of the radiator. They are all identical in look. The knob on the top of each one turns exactly 180 degrees (1/2 turn). The heigth of the knob doesn't change when they are rotated through this 1/2 turn. What type of valve do you think these are? Thanks much!


    JUGHNE Member Posts: 11,021
    My guess is they are what I call a "spool" valve.
    You are rotating a cylinder with half on one side open to pass water into the rad.
    The water comes up in the center of the spool.
    When you close it then the other complete half closes off the inlet to the rad.

    They are not 100% shut off and even when "closed" there may be a small 1/4" hole in the closed section that will flow some water to prevent freeze up the the rad.

    A picture might get you other answers.
  • hot_rod
    hot_rod Member Posts: 21,898
    Plug valve is another term used. Gas cocks are often plug style, but 1/4 turn from onto off.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • bobperetti
    bobperetti Member Posts: 2
    Oh Thanks so much for the insights! I believe I understand the mechanics involved in the 1/2 cylinder spool - this would confirm the full 1/2 turn range. Here's a picture of one of them (the turning knob is removed) that might confirm the valve is the spool type?
  • mattmia2
    mattmia2 Member Posts: 9,475
    There are also ways to build globe valves that are 1/2 turn and non rising stem by using 2 intertwined spirals on the threads and a second spline arrangement between the stem an the shaft.
  • bburd
    bburd Member Posts: 893
    Spool valves were standard on gravity hot water systems, and if yours is from the 1920s that is probably what it was. Most gravity systems have been converted to forced circulation. The differential pressure across the valve was much lower when the system ran on gravity.

    Spool valves are not much use for forced circulation, I had them in a similar house once.