The first piston of the first cylinder and the second piston of the second cylinder are connected so that the first piston and the second piston have the same displacement. The cross-section area of one side of the first piston is the smallest, and the cross-section area on the same side of the second piston is the third smallest. The two air chambers of the first cylinder and the two air chambers of the second cylinder are referred to as a first air chamber, a second air chamber, a third air chamber, and the fourth air in ascending order in the cross-section area. The control valve connects the air pressure source to the first air chamber, connects the second air chamber to the third air chamber, and opens the fourth air chamber to the atmosphere in the forward stroke.

Provided is a cylinder connection assembly comprising a ventilation connection sleeve sleeved on a piston shaft of the cylinder, the ventilation connection sleeve fixedly provided in a cylinder barrel of the cylinder and separates an inner cavity of the cylinder barrel to form front and rear air chambers, a first ventilation hole communicating with the front air chamber and a second ventilation hole communicating with the rear air chamber are provided on the ventilation connection sleeve, so that when the compressed gas is filled into the front air chamber through the first ventilation hole, or the compressed gas is filled into the rear air chamber through the second ventilation hole, the piston assembly in the cylinder barrel can move axially. Through the ventilation connection sleeve provided in the cylinder barrel, the compressed gas can directly enter the front air chamber or the rear air chamber through the ventilation hole thereon.

A hydraulic thruster system for providing an axial force. In one embodiment, the system comprises a pump, a motor for driving the pump, and a hydraulic thruster comprising: a cylinder comprising a plurality of cylinder pistons; a shaft comprising a plurality of shaft pistons; a plurality of first pressure chambers; and a plurality of second pressure chambers, wherein the plurality of shaft pistons are positioned inside the cylinder, between the cylinder pistons to form the plurality of first and a second pressure chambers, wherein the shaft further comprises a first fluid passage connected to the pump and to the first pressure chambers, and a second fluid passage connected to the pump and to the second pressure chambers, and wherein the pump may pump fluid into the first pressure chambers and suction fluid from the second pressure chambers providing an axial force between the shaft and the cylinder.

An actuator includes a casing having a first annular groove formed in an inner peripheral portion thereof; a piston having a second annular groove formed in an outer peripheral portion thereof, provided in the casing to form a pressure chamber together with the casing, and driven by a drive fluid from an outside of the actuator; and an annular seal member having a first fitting portion to be fitted into the first annular groove and a second fitting portion to be fitted into the second annular groove to seal the pressure chamber.

A cylinder device includes: a first piston (8) inserted in a first cylinder hole (4) so as to be movable in an axial direction, a piston rod (7) being hermetically inserted in the first piston (8), the first piston (8) being fixed to the piston rod (7); a second piston (10, 37) inserted in a second cylinder hole (5) so as to be movable in the axial direction, the piston rod (7) being inserted in the second piston (10, 37); and a partition wall (13) dividing a cylinder hole (6) into the first cylinder hole (4) and the second cylinder hole (5), the partition wall (13) being movable in the axial direction.

A hydraulic drive, preferably for a hydraulic press, having a first synchronized cylinder that comprises a piston between first and second pressure chambers; at least one hydraulic pump whereby the pump outlet is hydraulically connected with the first pressure chamber of the first synchronized cylinder and the pump inlet is hydraulically connected with the second pressure chamber of the first synchronized cylinder; at least a second synchronized cylinder that comprises a piston between first and a second pressure chambers; whereby the piston of the first synchronized cylinder is mechanically movably coupled with the piston of the second synchronized cylinder; whereby the first pressure chamber of the second synchronized cylinder is hydraulically connected with the pump outlet; and whereby the second pressure chamber of the second synchronized cylinder can be connected with the pump inlet when a pressure limit in the second pressure chamber of the second synchronized cylinder is exceeded.

A hydraulic system, for use under water with a hydraulic actuating drive, includes a hydraulic cylinder and at least one hydraulic machine. At least one rotary drive device and the hydraulic machine are coupled mechanically for a common rotating movement, and the hydraulic machine adjusts at least the hydraulic cylinder. The hydraulic cylinder has at least three cylinder chambers, and the hydraulic system includes a first hydraulic circuit and a second hydraulic circuit. The hydraulic system for use under water is set up, in particular, with a redundant hydraulic actuating drive for manual (mechanical) actuation.

A hydraulic thruster system for providing an axial force. In one embodiment, the system comprises a pump, a motor for driving the pump, and a hydraulic thruster comprising: a cylinder comprising a plurality of cylinder pistons; a shaft comprising a plurality of shaft pistons; a plurality of first pressure chambers; and a plurality of second pressure chambers, wherein the plurality of shaft pistons are positioned inside the cylinder, between the cylinder pistons to form the plurality of first and a second pressure chambers, wherein the shaft further comprises a first fluid passage connected to the pump and to the first pressure chambers, and a second fluid passage connected to the pump and to the second pressure chambers, and wherein the pump may pump fluid into the first pressure chambers and suction fluid from the second pressure chambers providing an axial force between the shaft and the cylinder.

Disclosed is a piston-cylinder assembly of a hydraulic press, which includes a basic cylinder and a first and second piston. A ring cylinder is formed above the basic cylinder as a continuation of the cylinder structure. The first piston is located inside the basic cylinder in the bottom part of the basic cylinder and the second piston is located above the first piston in the top part of the cylinder structure. The piston-cylinder assembly has a first hydraulic fluid space below the first piston and a second hydraulic fluid space below the second piston and the piston-cylinder assembly includes a unified hydraulic fluid channel in flow connection to the first hydraulic fluid space in order to provide a pressure effect in the first piston and to the second hydraulic fluid space in order to provide a pressure effect in the second piston.

A hydraulic system, for use under water with a hydraulic actuating drive, includes a hydraulic cylinder and at least one hydraulic machine. At least one rotary drive device and the hydraulic machine are coupled mechanically for a common rotating movement, and the hydraulic machine adjusts at least the hydraulic cylinder. The hydraulic cylinder has at least three cylinder chambers, and the hydraulic system includes a first hydraulic circuit and a second hydraulic circuit. The hydraulic system for use under water is set up, in particular, with a redundant hydraulic actuating drive for manual (mechanical) actuation.