Figure 12-20.—House assembly.Figure 12-21.—Lattice boom crane control levers.2. The left drum brake pedal is used to hold andlower loads placed on the hoist line. When locked, itprevents the hook block and wire rope from unwindingon the hoist drum. Figure 12-22 shows a typical hoistbrake assembly.Figure 12-22.—Hoist brake assembly.3. The main drum lever engages power to raise and,on some models, support lowering of loads placed onthe main hoist drum.4. The master clutch engages the power from thepower source to the hoist and swing mechanisms.5. The secondary drum lever engages power toraise and, on some models, support lowering of loadsplaced on the secondary hoist drum.6. The right drum brake pedal is used to hold andlower loads placed on the hoist line. When locked, itprevents the hook block and wire rope from unwindingon the hoist drum.7. The boom hoist lever allows for the raising andlowering of the boom.HOISTING MECHANISM.— The hoistingmechanism provides the mechanical power to lift andlower loads. The hoisting mechanism usually has twohoist drums that are mounted side by side on one shaftor in tandem. A separate clutch and brake controls eachhoist. The control levers, operating the clutches andbrakes, are normally power-assisted with hydraulics orair pressure. A lifting operation requires the use of onedrum; whereas the clamshell, dragline, and pile-drivingoperations require the use of two.ENGINE.— The engine provides power to thehoisting mechanism through a gearbox or, in some12-11
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