| 摘要 |
PURPOSE:To lower a working bed onto a safe area where no obstacles are present, by connecting the bottom chamber of a rising cylinder with a hydraulic circuit for a turning motor upon failure of an engine or the like during a high level working. CONSTITUTION:During a high level working, if a working bed 5 cannot be lowered onto the ground under normal control operation due to failure of an engine E or a pump P, a directional control valve 16 is changed over to the right position, and as well a solenoid valve 20 is opened to feed hydraulic oil in a chamber 7a of a rising cylinder 7 to a pipe line 12a so that a hydraulic turning motor 3 is normally rotated. As a result, the rising cylinder 7 retracts to lower the working bed while the latter turns. At this time, since hydraulic oil is fed from a tank T to a chamber 7c of the rising cylinder 7 through the valve 20, the lowering of the working bed is made smooth. When the working bed turns to a predetermined position, a solenoid valve 17 is changed over to the left position so that hydraulic oil in the chamber 7a is discharged into the tank T. With this arrangement the working bed stops its turn, but is continued to be lowered. |
