| 摘要 |
A crane having a boom pivotally mounted mesially thereof to a mast which is itself pivotally mounted on a base platform. A generally horizontally disposed control beam is line attached to the free, rear end of the boom and includes a hydraulic fluid-compression spring control assembly in place of conventional counterweights. Thus, all three units making up the crane have a rough "Z" profile. Mercury switches and pressure actuated switches are provided to activate appropriate warning devices and prevent further operation of the crane in the event of improper boom positioning and/or an overload, respectively.
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