| 摘要 |
In an articulated boom having a platform and comprised of upper and lower booms respectively, there are hydraulic actuators controlling the movements of the upper and lower booms. Control means are necessary in association with the lower boom to control its rate of movement, slowing such rate of movement as the lower boom approaches its retracted, or full rest, position. A position responsive valve permits unimpeded fluid pressure access to the actuator for lowering the lower boom at its regular rate until the lower boom reaches a critical angle as it approaches horizontal position, at which time the valve prevents further fluid access to its associated hydraulic actuator. Thereafter, a position responsive valve and a pressure reducing valve reduce the rate of descent of the lower boom until the lower boom is fully retracted to its rest position.
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