Patent ID: 7178333

Claim:
A hydraulic control system for a hydraulic excavator, comprising: a boom control valve adapted to provide pressure oil from a first hydraulic pump with a boom cylinder in accordance with operation of a boom operating means, said boom control valve being disposed in a first path; an arm control valve adapted to provide pressure oil from a second hydraulic pump with an arm cylinder in accordance with operation of an arm operating means, said arm control valve being disposed in a second oil path; a confluence switching valve adapted to switch between a confluence position for joining said pressure oil from said first and second oil paths and a confluence stop position for stopping said joining; a flow control valve disposed in a return oil path for returning said pressure oil present in said first oil path to a tank; and a control means for controlling said confluence switching valve and said flow control valve by switching said confluence switching valve to the confluence position and making said flow control valve in a closed position when said arm operating means is operated independently, and by switching said confluence switching valve to the confluence stop position and making said flow control valve in an opened position when said arm operating means and said boom operating means are operated substantially simultaneously.