Mechanical Components, Hoisting, and Roping Systems
Domain 3 covers the machinery between the motor and the car: sheaves, ropes, counterweights, guides and buffers. Exam items are usually ratio and load questions rather than vocabulary.
Roping and ratios
In 1:1 roping the ropes dead-end at the car and counterweight, so car speed equals rope speed. In 2:1 roping the rope passes around a sheave on the car or counterweight and dead-ends at the structure, so the car moves half the rope travel: rope speed is twice car speed, and the car hangs on two rope falls. Drum machines store rope on a drum and are not traction-limited; traction machines depend on groove shape, rope tension and sheave condition for adhesion.
Counterweight and components
Counterweight is sized to the car plus a percentage of rated load - commonly 40% to 50% - which sets the unbalanced load the machine must lift. Guide rails and guide shoes (sliding) or roller guides maintain alignment. Compensation chains or ropes offset rope weight on high-rise jobs. Buffers are spring type for car speeds up to 200 ft/min and oil type above that.
Worked example
A 2:1 traction job has a machine sheave rope speed of 350 ft/min. Car speed = 350 ÷ 2 = 175 ft/min, and 120 in of car travel requires 240 in of rope travel. Counterweight check: car 3,000 lb and rated load 2,500 lb at 40% balance gives 3,000 + 1,000 = 4,000 lb.
Traps
Reporting rope speed as car speed; forgetting 2:1 doubles rope travel; balancing the counterweight to 100% of rated load; mixing up which buffer type is permitted above 200 ft/min.