HYDRAULIC CIRCUIT DEVICE

PURPOSE:To enable acceleration control according to an operational rate and efficient complex operations by controlling the set pressure of a pressure control valve according to the operational rate, detecting the escaping flow rate which is returned from the pressure control valve to a low pressure circuit, and according thereto, controlling the compensation differential pressure of the pressure compensation valve. CONSTITUTION:Pressure compensating flow rate control valves 8, 9 composed of directional changeover valves 4, 5 and pressure compensation valves 6, 7 are arranged between a hydraulic pump 1 and hydraulic motors 10, 11, and the directional changeover valves 4, 5 are operated in proportion to the operation rate of operational levers 14, 15 of operational devices 12, 13. A pilot relief valve 22 is provided on circuits 20, 22 between the directional changeover valve 4 and the rotary motor 10, and the certain amount of flow escaping from the low pressure side returns to the low pressure sides of the circuits 20, 21 through a check valve 25 or 26. A throttle 28 is arranged between the relief valve 22 and the check valves 25, 26, and then pressure of the upstream side thereof is introduced to the pressure compensation valve 6 as a signal of passing flow rate. It is thus possible to reduce energy loss and prevent delay of cycle time of multiple operations.