Methods of controlling an actuator during operation using a hydraulic circuit, and related apparatus, are described. The circuit has a first path section along which fluid is supplied to a first chamber of the actuator using a first valve and a second path section along which fluid is extracted from a second chamber of the actuator using a second valve. Pressure data associated with a pressure of the fluid supplied to the first side of the actuator are obtained, a pilot pressure pPilot is produced based on the data and the first and second valves are configured based on the pilot pressure pPilot.

A hydraulic system is disclosed for use with a machine. The hydraulic system may have a closed-loop, meterless hydraulic circuit with a first pump fluidly connected to a first actuator. The hydraulic system may also have a closed-loop, metered hydraulic circuit with a second pump fluidly connected to a second actuator. The hydraulic system may further have a combiner valve configured to selectively direct fluid from the closed-loop metered hydraulic circuit to the closed-loop meterless hydraulic circuit.

Provided is a hydraulic drive apparatus for working machine capable of preventing an excessive pressure reduction on a meter-in side and moving a load in a lowering direction at a stable speed requiring no counter balance valve. The apparatus includes a hydraulic pump, a hydraulic actuator for lowering the load, an operating device, a hydraulic circuit including a meter-in flow passage, a meter-out flow passage and a regeneration flow passage, a control valve, a meter-in-flow-rate controller for controlling a meter-in flow rate, a meter-out-flow-rate controller for controlling a meter-out flow rate to one not lower than the meter-in flow rate, a back pressure generator located downstream of the regeneration flow passage in the meter-out flow passage, and a meter-out-flow-rate limiter. The meter-out-flow-rate limiter minimizes a flow passage area of the meter-out orifice when a pressure in the meter-in flow passage falls to or below a permissible pressure.

A valve assembly having a supply fluid flow path which passes from a first supply point via a pressure reducing valve, further via a first control point, and further via a 2/2-way poppet valve to a discharge point. The pressure reducing valve is adjustable using a first actuating solenoid. The first control point is connected on the inlet side to a shuttle valve. A first 3/2-way switching valve is arranged in the supply fluid flow path between the pressure reducing valve and the first control point, and is configured such that the first control point is selectively connected to the pressure reducing valve or to the first return flow point. The first 3/2-way switching valve is adjustable at least indirectly using a second actuating solenoid. A second control point is arranged between the pressure reducing valve and the first 3/2-way switching valve in the supply fluid flow path.