HYDRAULIC CONTROL APPARATUS

摘要

A hydraulic control apparatus (1) includes a switch valve (11) , a valve support chamber (35) , a flow control valve (12) movable therein, an on-off valve (13) movable within a communication path chamber (12a) located inside the flow control valve (12)', and a valve control device 14. The on-off valve (13) can open and shut off a communication path X between a cylinder line (32) and a switch valve line (33) . A restrictor formed between the flow control valve (12) and a wall defining the valve support chamber (35) connects the cylinder line (32) and the communication path chamber (12a) . The restrictor opening is changed in correspondence with movement of the flow control valve (12) . When the switch valve (11) is located at the drainage position, the valve control device (14) applies a pilot pressure lower than the pressure in the cylinder line (32) to a back pressure chamber (12d) of the flow control valve (12) , thereby moving the on-off valve (13) in a direction for opening the communication path X.