| 摘要 |
PURPOSE:To reduce the frictional resistance between a piston and a cylinder by a structure wherein a plurality of annular grooves, which form labyrinth together with the cylinder, are provided onto the outer periphery of the piston and yet communicating holes communicating to the discharge hole of a piston rod are provided at the middle of the piston in its axial direction. CONSTITUTION:A plurality of annular grooves 20a, between which and the inside surface of a cylinder tube labyrinth is formed, are provided onto the outer periphery of a piston 20. In addition, an annular groove 20b, which is communicated to the inner peripheral side of the piston 20 through the communicating holes 20d, is cut at the middle of the piston 20 in its axial direction. A hole, which communicates to the discharge hole provided by piercing the piston rod at its center, is provided at the part opposing to the communicating holes 20d in the piston rod piercingly inserted in the piston 20 so as to allow the oil leaked out along the outer peripheral surface of the piston 20 arrive through the annular groove 20b, the communicating holes 20d, and the communicating hole of the piston rod to the discharge hole of the piston rod and then to a drain tank in order to reduce the frictional resistance between the piston and the cylinder. |
