HYDRAULIC CIRCUIT FOR WORKING MACHINE

摘要

PROBLEM TO BE SOLVED: To provide a hydraulic circuit which is capable of ensuring a necessary speed for a special attachment, according to the type of attachment, without requiring controls on the revolution speed of an engine. SOLUTION: A hydraulic circuit for a working machine is equipped with a first oil-hydraulic pump 2 and a second oil-hydraulic pump 3 driven by an engine 1, permanent actuators like a boom cylinder 11, an arm cylinder 7, etc., an auxiliary actuator 8 to be arranged selectively as occasion demands for driving a special attachment like a mowing machine, etc., an auxiliary directional control valve 8a arranged on a center bypass line for the first oil- hydraulic pump 2 for controlling the flow of pressure oil to be supplied to the auxiliary actuator 8, and a converging line 21 connected to a center bypass line connecting to the second oil-hydraulic pump 3 and available for joining pressure oil from the second oil-hydraulic pump 3 with pressure oil from the first oil-hydraulic pump 2 and supplying the joined pressure oil to the auxiliary directional control valve 8a. A selector valve 20 for changing the converging line 21 from the state of opening to the state of shutoff and vice versa is provided.