| 摘要 |
PURPOSE:To increase sealing efficiency by providing a sealing device where a valve casing shifts relatively in the direction of a valve shaft and the valve shaft makes contact with a seal member to minimize the leakage of a fluid. CONSTITUTION:A cylinder 14 fixed to a part of a valve casing 1 and a piston 15 which shifts inside the cylinder in the shaft direction are provided and two ports are provided on respective sides of the piston 15 and air or oil is introduced into the cylinder through these ports. At the same time as the introduction of air or oil into a port 19 inside the cylinder 14, air or oil inside a port 20 is discharged and the piston 15 shifts outward from the center of a valve body. When the piston 15 shifts outward, a valve shaft 3 is pulled outward. A taper section provided on a part of the valve shaft 3 makes contact with the tapered surface of a fixed seal member 6 and moreover when hydraulic pressure or shifting degree outward grows larger, surface pressure is generated. Through this surface pressure, sealing effect is improved.
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