| 摘要 |
A three-part boom for a crane or the like has the usual pair of hydraulic cylinders, one for the forward boom section and one for the intermediate boom section. Fluid connections for the forward cylinder is through the rear piston rod and cylinder so as to use no hose reel. Extension of the forward section only when desired is achieved by a solenoid valve between cylinders, the electric cord for which requires only a small reel.
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