Patent ID: 8424657

Claim:
A cylinder assembly comprising: a piston rod having an end inserted into a cylinder and an end piece connected to the end of the piston rod; a piston being a hollow and cylindrical member and mounted to the piston rod, the piston movably received in the cylinder, an inside of the piston contacting an outside of the piston rod and an outside of the piston contacting an inside of the cylinder, an interior of the cylinder being defined into a first room and a second room by the piston, at least one first groove defined in the inside of the piston and at least one second groove defined in the outside of the piston, the at least one first groove being located longitudinally aligned with the at least one second groove, each of the at least one first groove and the at least one second groove having a seal ring received therein, the at least one first groove including a first inner surface, the at least one second groove including a second inner surface, a first distance defined between two respective extension lines of the at least one first groove and the at least one second groove, each of the two respective extension lines being defined by extending a line from the first/second inner surface of the at least one first/second groove; wherein the piston has a passage and communicates with the at least one first groove, the piston rod extends through the passage, the first and second inner surfaces are parallel with the passage, the first and second inner surfaces are parallel to each other and located alternatively to each other.