| 摘要 |
PROBLEM TO BE SOLVED: To provide a counterweight mechanism of a check valve capable of easily opening a valve element for fluid to be controlled in the forward direction and easily closing the valve element when a small amount of fluid flows in the reverse direction. SOLUTION: The valve element 2 oscillating over a fully closed position and a fully opened position around a shaft core of a valve stem 3 is provided in a valve casing 1, a rail 7 which becomes down gradient in the direction of oscillation in accordance with the oscillation in the direction of fully opening of the valve element 2 is provided on one end side of an arm 4 oscillating around the shaft core in the valve stem 3, a counterweight 9 moving due to self-weight is provided on the rail 7, and an air cylinder 13 for receiving the counterweight 9 is provided in a tip part of the rail 7. The air cylinder 13 has a predetermined elastic modulus that allows it to come out and retract in the direction of shaft core of the rail 7 over the minimum shrinkage position for receiving the counterweight 9 at a lower end position of the rail 7 at a degree of fully opening of the valve element 2 and the maximum expansion position for receiving the counterweight 9 at a predetermined intermediate position of the rail 7 at a predetermined intermediate degree of opening of the valve element 2.
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