PURPOSE: To reduce the cost of fuel by a method in which a two-position switch valve provided to the discharge pipeline of a pump for turning and connected branch pipeline is switched to the opening position in interlocking manner with the operation of an actuator.
CONSTITUTION: The pump 1 for turning of a turning motor 2 is controlled by a control valve 3 for turning, and the first and second main pumps 7 and 8 are controlled by the first and second main control valves 9 and 10, thereby permitting such actuators as a boom and an arm cylinder 14 and 16 to be controlled. At least one of a communication pipeline 23 between the pump and the valve 9 and a communication pipeline 23' between the pump 8 and the valve 10 is connected with the discharge pipe 32 of the pump 1 by a branched pipeline 31. A two-position switch valve 33 and a check valve 34 are provided to the pipeline 31, and the valve 33 is connected through a shuttle valve 36, etc., to a pilot valve 28 of signals for boom and the valve 9, thereby suppressing the relief loss.
OOTSUBO KAZUHIKO
ASAI KOUJI
| JP54176203B |