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.

The invention relates to a hydraulic cylinder, for example for use with a hydraulic tool, which hydraulic tool is provided with a frame and an element which is movable with respect to the frame by means of the hydraulic cylinder.

A hydraulic tool which is operated by means of a hydraulic cylinder as described above is known from, for example, European patent no. 0641618. This patent discloses a frame which is coupleable to a jib of an excavator or the like and to which an assembly of two jaws can be coupled. One of the jaws is pivotable with respect to the other jaw by means of a hydraulic adjusting cylinder (a double-acting piston/cylinder combination).

A hydraulic machine unit that can be operated with various working forces, in which working medium is selectively delivered, via a pump-piston accumulator system, to a main cylinder and at least one driving cylinder, wherein at least for one working stroke a pump system of the pump-piston accumulator system is used to provide working medium to a piston accumulator of the pump-piston accumulator system, and then at least for the working stroke at least the main cylinder is charged with a working pressure from the piston accumulator, and wherein at least for a return stroke the at least one driving cylinder is charged with a return stroke pressure from the pump-piston accumulator system, can be of structurally simple configuration if, at reduced working forces, the working pressure is reduced with respect to the piston accumulator pressure prevailing in the piston accumulator.

A hydraulic cylinder (1) which acts as a cylinder hollow rod in an outer hydraulic cylinder (10) is disclosed comprising an inner rod (4) with a piston (2) and piston-gland (3) wherein the cylinder hollow rod (1) is held longitudinally displaceably in the cylinder housing (10). The system additionally has a cylinder base (5) and a fibre cover (14) on the outer casing of hydraulic cylinder (10). The system also has ports for fluid (11, 12 and 13) corresponding to four chambers, (67, 8 and 9 respectively). According to the invention, when pressure is applied to chamber (7), the internal rod (4) extends into the chamber (6), displacing its mass and dramatically increases the pressure in Chamber (6). This displacement is effectively an internal pump which can be activated multiple times within a given stroke of rod (1).

A hydraulic control circuit operable to selectively hydraulically link first and second hydraulic actuators and to bypass that hydraulic link.

A hydraulic actuator includes two or more cylinder parts that nest inside each other, each cylinder part including a piston and piston rod forming an operating element and a cylindrical component, inside which the operating element is arranged, the piston of the inner cylinder part being inside the piston rod of the outer cylinder part, chambers formed for each cylinder part, a pressure-medium feed arrangement creating work-movement in the operating element by the pressure medium led to the chambers, a pressure-difference-controlled valve controlling operation of the hydraulic actuator between a first ducting and a second ducting, controlling the feed of the pressure medium among the chambers and a pressure-difference-controlled spool valve including a housing, connecting chambers and a spool arranged to move backwards and forwards in the housing to open and close the connections creating a work movement alternately by the operating element of the inner or outer cylinder part.

A hydraulic system includes: a cylinder in which an interior of a tube is divided by a piston into a first pressure chamber and a second pressure chamber; a first bidirectional pump connected to the first pressure chamber by a first supply/discharge line; a second bidirectional pump connected to the second pressure chamber by a second supply/discharge line and coupled to the first bidirectional pump in a manner enabling torque to be transmitted between the first and second bidirectional pumps; a relay line connecting the first and second bidirectional pumps such that a hydraulic liquid discharged from one of the first and second bidirectional pumps is introduced into the other of the first and second bidirectional pumps; and an electric motor that drives the first or second bidirectional pump. At least one of the first and second bidirectional pumps is a variable displacement pump whose delivery capacity per rotation is freely variable.

A hydraulic system includes: a cylinder that moves a moving object in a vertical direction by extension and retraction of a rod; a first bidirectional pump connected to a head-side chamber of the cylinder by a first supply/discharge line; a second bidirectional pump connected to a rod-side chamber of the cylinder by a second supply/discharge line and coupled to the first bidirectional pump in a manner enabling torque to be transmitted between the first and second bidirectional pumps; a relay line connecting the first and second bidirectional pumps such that a hydraulic liquid discharged from one of the first and second bidirectional pumps is introduced into the other of the first and second bidirectional pumps; and a servomotor that drives the first or second bidirectional pump. At least one of the first and second bidirectional pumps is a variable displacement pump whose delivery capacity per rotation is freely variable.

A hydraulic cylinder comprising a cylinder, a piston element movably guided in the cylinder in a working direction and comprising an active surface, and a first opening for feeding a fluid into a cylinder chamber by the active surface. A working pressure of the fluid acting on the active surface drives the piston element in the working direction. The active surface includes a first partial surface and at least one second partial surface, the cylinder chamber being divided into a first sub chamber with the first opening by the first active surface and a second partial surface with a second opening by the second partial surface, and the partial surfaces are hydraulically separated from each other at least in a selectable operating mode.

A portable hydraulic power unit includes a frame, a fluid tank supported by the frame, and a manifold supported by the frame. The fluid tank is configured to store a supply of hydraulic fluid for powering a hydraulically-driven tool. A reciprocating pump is mounted on the exterior of the fluid tank and on the exterior of the manifold. The reciprocating pump is secured to the fluid tank and the manifold with fasteners extending through a cylinder body of the reciprocating pump.