The invention relates to a hydraulic drive (1) comprising a working cylinder (2) and a travel cylinder (3) which is mechanically connected to the working cylinder (2). The working cylinder (2) and the travel cylinder (3) each comprise an upper and a lower cylinder chamber (21, 22, 31, 32), and all four cylinder chambers (21, 22, 31, 32) of the working and travel cylinder (2, 3) are connected to one another in a suitable manner in a closed pressure circuit (4) which is filled and prestressed with a hydraulic fluid (F). A rotational speed-variable hydraulic machine (5) with a first and second pressure connection (51, 52) is arranged in the pressure circuit (4) in order to conduct the hydraulic fluid (F) between the individual cylinder chambers (21, 22, 31, 32) of the working and travel cylinder (2, 3) during the operation (B) of the hydraulic drive (1). At least one first and second distributing valve (6, 7) are arranged in the pressure circuit (4) such that the respective valve switch positions (61, 62, 71, 72, 73) which are suitable for the different operating phases of the hydraulic drive (1) together with the suitably driven hydraulic machine (5) allow a common movement of the work and travel cylinder (2, 3) in one or the other piston movement direction (R1, R2). For this purpose, preferably only the first and the second distributing valve (6, 7) are arranged in the pressure circuit (4). The hydraulic drive (1) requires a minimum number of components, maintains a low installation complexity, improves the energy efficiency, can be constructed in a compact manner, and can be operated in a sufficiently variable manner.

The pump discharge volume of a bi-directional piston pump is set to a reference pump discharge volume Qa in condition where the actuation state of lift cylinders is a no-load state, and is set to a small-discharge pump discharge volume Qb smaller than the reference pump discharge volume Qa in condition where the actuation state of the lift cylinders is a high-load state. Qb.Math.Pb which is the product of the pump discharge volume Qb and a pump discharge pressure Pb of the bi-directional piston pump in condition where the actuation state of the lift cylinders is the high-load state is set to be equal to or less than or approximately equal to a Qa.Math.Pa which is the product of the pump discharge volume Qa and a pump discharge pressure Pa of the bi-directional piston pump in condition where the actuation state of the lift cylinders is the no-load state.

A hydraulic forming machine, includes a hydraulic cylinder with a piston guided in a cylinder tube and divides the cylinder tube into a first cylinder chamber, and a second cylinder chamber. A hydraulic circuit with a control unit for controlling the operation of the hydraulic cylinder includes a first hydraulic valve coupled to the control unit and is connected to the second cylinder chamber via the second hydraulic connection. The control unit regulates an opening width of the first hydraulic valve such that the first hydraulic valve is open in a first phase and the bear) is accelerated to a target speed in the first phase, while, in a following second phase the opening width of the first hydraulic valve is reduced to an inflow opening width, and the first hydraulic valve is closed during a return stroke running in the opposite direction to the working stroke.

A solar-powered waste compactor comprises a waste container for housing waste, a compactor ram actuated by a hydraulic cylinder and piston assembly for compacting the waste in the waste container, and a hydraulic power unit operably associated with the hydraulic cylinder and piston assembly for powering the compactor ram. The hydraulic power unit comprises a motor/pump assembly including a pump unit, a single-phase electric motor driving the pump unit and a flow control valve operating the motor/pump assembly at first or second flow rate depending on an operating pressure. The hydraulic power unit further comprises a battery unit, a solar panel to charge the battery unit, a DC-to-AC inverter, a single-phase AC power inlet connectable to a source of a single-phase electrical power grid, and a reversing contactor providing the electric current only from the inverter or the power inlet at any given time.

A machine press is provided in which at least one hermetically sealed hydraulic drive unit is switchable from a working mode, in which a base pressure above ambient pressure is continually exceeded, into a rest mode. To this end, in parallel with a pressure converter, to the high-pressure side of which a pressure store and a raising working chamber of a cylinder piston unit are connected, a bypass is provided, having a first blocking valve that is controllable by a control unit and, in its blocking position, blocks the through-flow direction from the high-pressure side of the pressure converter to the low-pressure side. Furthermore, the low-pressure side is connectable to a lowering working chamber via a second blocking valve controllable by the control unit. The pressure output of the hydraulic unit is connectable to the raising working chamber via a third blocking valve controllable by the control unit.