HYDRAULIC CIRCUIT FOR CONSTRUCTION MACHINE AND URGENT DRIVE METHOD FOR ATTACHMENT

摘要

PROBLEM TO BE SOLVED: To enable a front attachment to be driven safely in an emergency with a simple structure. SOLUTION: In the hydraulic circuit provided with a hydraulic pump 11 driven by an engine, an actuator 1 driving a front attachment FA, driven by the delivery hydraulic oil of the hydraulic pump 11, and a hydraulic pilot control valve 12 controlling inflow/outflow of the hydraulic oil to the actuator 1, a hydraulic oil injection port 25 to which a manual hydraulic pump 30 can be connected is provided in a pilot pipe line 23b leading the pilot hydraulic pressure to the control valve 12 to supply the hydraulic oil to the pilot pipe line 23b from the port 25 by the manual hydraulic pump 30 to make it possible to switch over the control valve 12.