Boom Angle Indicators

Boom angle indicators are normally mounted on the boom butt, visually readable by the operator. On most models in the NCF, the boom angle indicator is a metal plate with degree numbers (0 to 90 degrees) and a freely swinging arm that reacts as the boom angle changes (fig. 12-14). The numbers and arm should remain clean and visually readable at all time.

The capacities that are listed on the crane load charts are also based on and vary with the boom angle of the crane. On hydraulic cranes, the boom angle is the angle between the bottom of the boom butt and the horizontal

Figure 12-13.-Boom sections connection.

Figure 12-14.-Boom angle indicator.

while the boom is under load (fig. 12-15, view A). The boom angle on lattice boom cranes is the angle between the center line of the boom (from the boom butt pins to the boom tip sheave) and the horizontal while the boom is under load (fig. 12-15, view B).

To check the accuracy of the boom angle indicator, place a 3-foot builders level on the center boom section and raise or lower the boom until the level indicates the boom is level (fig. 12-16). At this point the boom angle indicator

Figure 12-15.-Boom angle configurations.

Figure 12-16.-Check accuracy of boom angle indicator.

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

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.

Boom Pendants

A pendant line is a fixed-length ^{of wire rope,} forming part of the boom suspension ^{system. Each} section of boom has two boom pendants. ^{Both pendants} 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 or strain.