should show the boom is at zero degrees or adjusted toread zero degrees.The boom angle indicator is a quick reference forthe operator to know what angle the boom is at.However, do NOT rely on the boom angle indicator forradius accuracy especially when the lift exceeds 75percent of the rated capacity. Use the radiusmeasurement to determine the capacity of the cranefrom the load charts and to avoid any possibility of error.SheavesSheaves are located in the hook block boom tip,boom bridle, gantry, and boom mast. Sheaves rotate oneither bearings, or bushings, and are installed basicallyanywhere wire rope must turn or bend.Boom PendantsA pendant line is a fixed-lengthforming part of the boom suspensionsection of boom has two boom pendants.of wire rope,system. EachBoth pendantsmust stay with the section of the boom they came with.When storing a boom section, secure the two pendantsto the boom section with tie wire or rope. If a pendantis bad, both pendants must be replaced. If you onlyreplace the one bad pendant, the new or replacedpendant could be of a different length or be different inmanufacture. This difference will cause an uneven pullor twist on the boom when the boom is put under a loador strain.Jib and ExtensionFigure 12-17 shows one type of jib and boomextension. A jib is an extension of a boom capable ofbeing mounted on either a hydraulic or lattice boom.The jib is equipped with its own forestay pendant lines,connected from the jib tip to the jib mast. The jib mastis connected to the boom tip. The jib backstay pendantis normally manually adjustable to change the angle ofthe jib.On most cranes the function of the jib is to increasethe lift height and to aid in increasing load radius. Theoperator’s manual will have instructions on how toinstall a jib or extension. You must remember if lifts aremade with the main hook block the weight of the jibassembly will reduce the lifting capacity of the crane;therefore, you must deduct the effective weight of thejib assembly from the gross capacity of the crane.GantryThe gantry, or A-frame, is a structural frame,extending above the revolving superstructure (fig.12-18). The gantry supports the sheaves in which theFigure 12-17.—Jib and boom extension mounted on ahydraulic boom.Figure 12-18.-Gantry.12-9
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