| 摘要 |
Load lifting apparatus comprises an extensible boom carrying a platform at its outer end and being pivotally mounted at its inner end on rotatable support structure. Hydraulic elevating and extending rams effect elevation and extension of the boom. The elevating ram acts at its bottom end on the support structure through a pivot arm which is seated at its free end on a spring pack. The coupling of the ram to the pivot arm preferably lies in the plane of the pivot axes of the arm and the boom, whereby the load on the spring pack can be independent of the boom elevation for a constant overturning moment of the boom. Hydraulic diverter valves, actuated by the pivot arm when it is deflected against the spring pack, operate to divert fluid flows from the elevating and/or extending rams to urge retraction of the boom upon a predetermined overturning moment being exceeded.
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