The hydraulic system of the working machine

Closed circuit hydraulic pumps 2a, the arm / boom cylinder 7a the discharge port 2b, and connected to the head side chamber and the rod side chamber of 7b, the cylinder head side chamber and the open-circuit hydraulic pumps 1a, on-off valve 12a between 1b of the discharge port, place 12b, the cylinder head side chamber and the oil reservoir between the proportional control valve 14a, arranged 14b, when the cylinder extension and both pumps so that the discharge flow rate of both pumps for the open circuit closed circuit is fed into the head side chamber off valve controls, when the cylinder retracted some outflow rate from the head-side chamber is returned to the closed circuit pump, another part controls the closed circuit pump proportional control valve so as to be returned to the oil tank .