| 摘要 |
PURPOSE:To improve sealing ability and seal responsiveness by forming a communicating passage extending from one of both end surfaces of a piston over as groove of the piston. CONSTITUTION:A piston 12 has a seal material 14 having a groove 13 extending over the whole periphery in the circumferential direction on the outer peripheral portion thereof, which can be elastically deformed, fitted thereto to form a communicating passage 15 extending from one of both end surfaces 12a, 12b to the groove 13. When the piston 12 is reciprocated in the direction of the shaft center, pressurized fluid in a chamber located in the moving direction passes through the communicating passage 15 and flows in the groove 13 to become static pressure. Whereupon, the seal material 14 is pressed to the bottom of the groove, and the force applied to the seal material 14 by fluid in the space between the seal material 14 and the bottom of the groove pushes the seal material 14 outward in the radial direction to be pressed to the inner surface of a cylinder 11. Furthermore, the force can be independently controlled by changing the sectional area of the communicating passage 15 to control the quantity of a fluid flowing through the passage, so that the sealing ability can be improved, and the responsiveness can be also improved.
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