Patent ID: 8403335

Claim:
A liquid-operated cylinder that is extended by a pressurized hydraulic fluid guided into a drive pressure chamber, comprising: a cylinder tube; a piston that defines the drive pressure chamber and a cushion pressure chamber inside the cylinder tube; and a piston seal that is disposed at an outer circumference of the piston and slidably contacts an inner circumferential surface of the cylinder tube, the piston seal comprising: a main seal ring that slidably contacts the inner circumferential surface of the cylinder tube, the main seal ring being constituted of a resin material; an O-ring configured to impart a force causing an outer circumference of the main seal ring to move closer to the inner circumferential surface of the cylinder tube by pressing onto an inner circumference of the main seal ring; and a sub-seal ring that is disposed parallel to the main seal ring at a position further toward the cushion pressure chamber and is pressed by the main seal ring, as pressure from the drive pressure chamber is applied to the main seal ring, to slidably contact the inner circumferential surface of the cylinder tube, the sub-seal ring being constituted of a resin material having a hardness that is equal to or greater than a hardness of the resin material constituting the main seal ring; the piston seal being disposed inside a housing groove formed at an outer circumference of the piston; the housing groove including a main housing groove in which the main seal ring is housed and a sub-housing groove in which the sub-seal ring is housed; and along a longitudinal axis of the liquid-operated cylinder, the sub-seal ring having a ring width greater than a groove width of the sub-housing groove, the sub-seal ring being pushed in a direction along the groove width by the main seal ring that is housed inside the main housing groove as the pressure from the drive pressure chamber is applied to the main seal ring.