Dual stroke cylinder

A dual stroke cylinder comprising:

• a cylinder tube having a head cover and a rod cover fitted to the opposite ends thereof;
• a first piston on the head cover side and a second piston on the rod cover side which slide airtightly in said cylinder tube, the second piston including a center hole;
• a first cylinder chamber partitioned between said first piston and said head cover;
• a second cylinder chamber partitioned between said two pistons;
• a third cylinder chamber partitioned between said second piston and said rod cover;
• first, second and third ports for individually supplying pressure fluid respectively to each cylinder chamber;
• a piston rod having a hollow portion, the piston rod including a piston base end portion being connected to said second piston such that the hollow area communicates with the center hole of the second piston, and a piston top end portion penetrating said rod cover airtightly, extending to the outside of the cylinder tube, and sealed from an exterior of the cylinder tube;
• a hollow rod for intermediate stop having a stopper at the top end portion, with which said second piston is engaged and stopped at a position of a most advancing end, the stopper providing a gap between the stopper and the second piston, with a rod base end portion being connected to said first piston, and a rod top end portion penetrating said second piston so as to be freely movable in the back and forth direction, and going into the inside of said piston rod;
• and
• a conduit shaft having a fluid passage connecting a hollow portion in said piston rod and said second port therein, with a shaft base end portion being connected to said head cover and airtightly and slidably penetrating said first piston and said rod for intermediate stop, and with a shaft top end portion extending into said hollow portion, such that fluid delivered to the second port flows through the stopper gap to the second cylinder chamber.