Abstract: In a hydraulic circuit system, when pressurized oil discharged from a single hydraulic pump is supplied to a plurality of actuators: the pressurized oil is supplied to heavily-loaded ones of the actuators at gradually reducing flow rates to reduce a shock, while supplied to lightly-loaded ones of the actuators at gradually increasing flow rates to increase working speeds of these lightly-loaded actuators. The hydraulic circuit system comprises a plurality of directional control valves (2) one of which is provided with pressure-compensated flow control valves (18) each of which is provided with a load lead-in passage having a restriction means (R). In addition, further comprised in the system are: relief valves (22, 22) for relieving the pressurized oil under the influence of load pressure of the actuators (3) operated by the directional control valves (2); a restriction orifice (24) provided in a drain side of each of the relief valves so as to produce pressure therein.

Abstract: This invention provides a hydraulic circuit apparatus for operating a work-implement actuating cylinder arranged such that, during an earth compacting operation using a bucket, a work implement or boom is lowered by its own weight, and during other operations, a part of the fluid under pressure in a lifting chamber of the actuating cylinder is supplied together with pressurized fluid discharged by a pump into a lowering chamber to increase the retracting speed of a piston rod in the work-implement actuating cylinder. The apparatus comprises a spool slidably inserted in a valve bore formed in an operating valve body so that it may be moved between a first actuating position, where a second port connected to the lowering chamber is communicated with a second tank port and a first port connected to the lifting chamber is communicated with a first pump port; and a second actuating position, where the second port is communicated with a second pump port and the first port is communicated with a first tank port.