Patent ID: 7487609

Claim:
A hydraulic circuit system for a hydraulic working machine, said hydraulic circuit system comprising: at least one hydraulic pump, plural actuators driven by a hydraulic fluid delivered from said hydraulic pump, plural flow control valves for feeding the hydraulic fluid, which has been delivered from said hydraulic pump, to said plural actuators, respectively, a pilot hydraulic pressure source, plural pilot operating units for producing operation signal pressures from said pilot hydraulic pressure source to change over the corresponding flow control valves, shuttle valves for selecting maximum pressures from plural groups of operation signal pressures among the operation signal pressures produced by said plural pilot operating units, a hydraulic selector valve arranged in association with at least one of said plural operation signal pressure groups and operated based on said maximum pressure to produce a corresponding control signal pressure from the pressure of the pilot pressure source, and a shuttle block with all of said shuttle valves and hydraulic selector valve built therein such that said control signal pressures are produced in said shuttle block to operate at least one control device arranged in association with any one of said hydraulic pump, said actuators and said flow control valves, wherein in addition to said hydraulic selector valve operated based on said maximum pressure, at least one of a boom-lowering, hydraulic selector valve, which is operated based on an operation signal pressure relating to a single boom-lowering operation among said operation signal pressures produced by said pilot operating units, and a superstructure-swinging, hydraulic selector valve, which is operated based on an operation signal pressure relating to a swing revolving operation to produce a swing control signal pressure from the pressure of said pilot pressure source, is built in said shuttle block, wherein said control signal pressures produced from said boom-lowering, hydraulic selector valve and superstructure-swinging, hydraulic selector valves comprise a pressure signal for operating said control device arranged in association with said hydraulic pump, and wherein with respect to equal operation signal pressures from said pilot operating units, a delivery flow rate from said hydraulic pump based on control signal pressures produced from said boom-lowering selector valve and superstructure-swinging, hydraulic selector valves are smaller than a delivery flow rate from said hydraulic pump based on a control signal pressure produced from another hydraulic selector valve for operating said control device arranged in association with said pump.