| 摘要 |
PURPOSE:To reduce the cost of an oil-pressure device for working vehicles by a method in which a throttle valve is provided between a switch valve an a safety valve in such a way as to enable an oil path to be closed by the throttle valve. CONSTITUTION:Before a tractor is held for long time by stopping vertically movable front and back arms at adequate rising positions, a throttle valve 57 provided between a safety valve 60 and a switch valve 55 is contracted to close a throttling hole 70. The discharge of oil pressure from a cylinder 22r is interrupted by the throttle valve 57 and the fixed condition of the verti cally movable back arm is kept even when a back output port 71r connected to the back oil-pressure cylinder 22r for operating the vertically movable back arm is led through the valve 55 to the central port 68. A front output port 71f connected to the front oil-pressure cylinder 22f for operating the front verti cally movable arm is closed by the valve 55 to keep even the vertically movable front arm in the fixed condition.
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