| 摘要 |
<p>PROBLEM TO BE SOLVED: To prevent torque from being increased and durability of a piston from being deteriorated by reducing the slide resistance of the piston. SOLUTION: A rotation preventing projecting part 23 for stopping the rotation of a piston 7 around a central shaft C is provided on the front side end of a piston 7, the radius of curvature of a sliding curved surface 23 on one end in the circumferential direction of the rotation preventing part 23 and the radius of curvature of an inner peripheral surface 4a of a front head are equalized to each other, and the center of curvature of the sliding curved surface 23a and the center of curvature of the inner peripheral surface 4 of the front head are deviated from each other so that the sliding curved surface 23a of the rotation preventing projecting part 23 may be brought into surface-contact with the inner peripheral surface 4a of the front head when the piston 7 is rotated.</p> |
