should show the boom is at zero degrees or adjusted to
read zero degrees.
The boom angle indicator is a quick reference for
the operator to know what angle the boom is at.
However, do NOT rely on the boom angle indicator for
radius accuracy especially when the lift exceeds 75
percent of the rated capacity. Use the radius
measurement to determine the capacity of the crane
from the load charts and to avoid any possibility of error.
Sheaves are located in the hook block boom tip,
boom bridle, gantry, and boom mast. Sheaves rotate on
either bearings, or bushings, and are installed basically
anywhere wire rope must turn or bend.
A pendant line is a fixed-length
forming part of the boom suspension
section of boom has two boom pendants.
of wire rope,
must stay with the section of the boom they came with.
When storing a boom section, secure the two pendants
to the boom section with tie wire or rope. If a pendant
is bad, both pendants must be replaced. If you only
replace the one bad pendant, the new or replaced
pendant could be of a different length or be different in
manufacture. This difference will cause an uneven pull
or twist on the boom when the boom is put under a load
Jib and Extension
Figure 12-17 shows one type of jib and boom
extension. A jib is an extension of a boom capable of
being 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 mast
is connected to the boom tip. The jib backstay pendant
is normally manually adjustable to change the angle of
On most cranes the function of the jib is to increase
the lift height and to aid in increasing load radius. The
operators manual will have instructions on how to
install a jib or extension. You must remember if lifts are
made with the main hook block the weight of the jib
assembly will reduce the lifting capacity of the crane;
therefore, you must deduct the effective weight of the
jib assembly from the gross capacity of the crane.
The gantry, or A-frame, is a structural frame,
extending above the revolving superstructure (fig.
12-18). The gantry supports the sheaves in which the
Figure 12-17.Jib and boom extension mounted on a