Patent ID: 7174711

Claim:
A hydraulic control system comprising: a hydraulic pump; control valves for controlling a direction and flow rate of pressure oil discharged from said hydraulic pump; hydraulic actuators which the pressure oil is fed to and controlled by said control valves, said hydraulic actuators comprising hydraulic cylinders and a hydraulic motor; and a return passage adapted to conduct return oil from said hydraulic actuators to a tank, said return passage comprising: a first return passage adapted to conduct return oil present at a head side of one of said hydraulic cylinders to said tank, said first return passage being in communication with said tank; and a second return passage adapted to conduct return oil from each of the other hydraulic actuators including said hydraulic motor except for said one of said hydraulic cylinders to the tank, said second return passage having a back pressure check valve and a replenishing passage, said replenishing passage providing a back pressure developed by said back pressure check valve to a lower pressure side of said each of the other hydraulic actuators.