Hydraulic circuit system

A hydraulic circuit system including a hydraulic pump and hydraulic actuators, comprising:

• a plurality of operating valves provided in a discharge conduit of the hydraulic pump;
• pressure compensating valves disposed in connection conduits between said operating valves and respective hydraulic actuators, wherein each of the pressure compensating valves is set at a highest value of load pressures of the hydraulic actuators;
• a change-over valve controlling displacement of the hydraulic pump, said change-over valve being adapted to be actuated by a difference between pump discharge pressure and load pressure;
• a load pressure introduction circuit for introducing load pressure into a pressure receiving portion of said change-over valve;
• said load pressure introduction circuit introduces load pressure into pressure receiving portions of said pressure compensating valves for urging said pressure compensating valve to the high pressure set side;
• a bypass valve connected to said change-over valve, to selectively relieve pressure from said change-over valve introduced by said load pressure introduction circuit;
• said bypass valve is connected to said pressure compensating valves, to selectively relieve pressures from said pressure compensating valves introduced by said load pressure introduction circuit;
• a pilot control valve connected to at least one of said operating valves;
• an auxiliary pump having a delivery side connected to a discharge side of said bypass valve, for supplying a source pressure for actuating said pilot control valve.