| 摘要 |
PROBLEM TO BE SOLVED: To reduce rotational opening and closing torque at the time of normal operation by making the manufacture and processing of valve seats on the valve box side easy to suppress a rise in cost, and achieve the improvement in a water-stopping ability when water leakage occurs by increasing the amount of bite only by the rotation of a valve body in closed state. SOLUTION: With elastic ringlike valve seats 8 mounted to the inner peripheral surface of a passage 1A of a valve box 1, out of both side parts facing each other in the diametrical direction perpendicular to the rotary shaft center of a valve body 5, the inner surface 8b1 of one side part (A part) has an inclined angle ofαrelative to a tangent t1 of a locus-circle of rotation of the valve body, and the inner surface 8b2 of the other side part (B part) has an inclined angle ofβrelative to a tangent t2 of a locus-circle of rotation of the valve body. The elastic ringlike valve seat 8 is formed into a pseudo-cone shape so that the amount of bite on it is increased as the valve body 5 is clamped deeper, the whole inner surface of the elastic ringlike valve seat is sequentially and integrally mold-formed so that it becomes circular.
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