Abstract: A hydraulic fluid circuit of a hydraulic shovel including a first directional control valve group connected to a first hydraulic pump and including a first directional control valve and a second directional control valve respectively connected to a first hydraulic cylinder and a second hydraulic cylinder. A second directional control valve group, connected to a second hydraulic pump, includes a third directional control valve having a first working port connected to one cylinder chamber of the first hydraulic cylinder and a second working port connected to one cylinder chamber of the second hydraulic cylinder.

Abstract: A hydraulic circuit for a hydraulic power shovel of the type having a swingable boom, swingable arm and a bucket attached to the end of the arm. The hydraulic circuit includes a levelling cylinder adapted to extend and contract in response to the swinging of the arm, and a switching valve device movable between a first position where it provides a communication between the levelling cylinder and a boom cylinder and a second position where it provides a communication between the levelling cylinder and an arm cylinder. When the switching valve device takes the first position, the levelling cylinder is communicated with the boom cylinder so that the boom is swung downwardly in response to the upward swinging of the arm, thereby to move the bucket horizontally. On the other hand, when the switching valve device takes the second position, the levelling cylinder and the boom cylinder are disconnected hydraulically so that the arm is allowed to swing independently of the boom.