PURPOSE: To enable a revolving motion irrespective of loads on an arm and to allow more than a given revolving force required to be obtained, by constituting an additional switch valve so that the valve can be changed-over due to the difference in pressure between at both sides of a throttle located at a pipe passage of an arm hydraulic cylinder.
CONSTITUTION: An additional pump 3a is connected to a prime mover 4, an additional switch valve 30a to the additional pump, an additional revolving switch valve 31a to a revolving hydraulic motor 50, and an additional arm switch valve 32a to an arm hydraulic cylinder 40. The additional revolving switch valve 31a, which is positioned upstream the additional arm 32a, and a revolving switch valve 21 are operated in conjunction with each other by means of a double-drawing mechanism Z, and the additional arm switch valve 32a is changed-over and controlled by virtue of the difference in pressure between at the front and the rear of a throttle E. Throttles F1 and F2 are situated in a pressured oil feed circuit which leads to the switch valve 32a and positions in the switch valve 31a. The pressured oil from a pump 3a is fed to the switch valve 32a through the throttles F1 and F2 by means of the switch valve 31a.
TAMURA SEIJI
YOSHIDA KUNIAKI
