🪛Mechanical & Machinery Principles · 6 min read

Pulleys & Rope Systems

Mechanical advantage from pulleys and how elevator roping works

Pulleys are the second critical mechanical concept for elevator work. The entire hoist rope system in a traction elevator is a pulley arrangement. You need to know how to find mechanical advantage from a pulley system and how different roping configurations affect speed and load.

On the Test

Pulley questions on the EIAT ask which setup requires less effort, or how many rope segments support the load. No calculation is needed — count the ropes and reason from there.

•Fixed pulley: MA = 1 (direction change only, no force reduction). Movable pulley: MA = 2. Each rope segment supporting the moving block adds 1 to MA.
•More rope segments = less force needed, but you pull more rope. Force and distance always trade off — there is no free advantage.
•"Sheave" is the elevator-industry word for a grooved pulley wheel. The test uses both words interchangeably.
⚠Common trap: Counting the total number of pulleys instead of counting only the rope segments supporting the moving load. A fixed (overhead) pulley does not contribute to mechanical advantage.

Fixed vs. Movable Pulleys

A fixed pulley is anchored to a stationary surface. It only changes the direction of the force — it does not reduce the force required. Pull down to lift up. Mechanical advantage = 1.

A movable pulley is attached to the load and moves with it. It has a mechanical advantage of 2: you apply half the weight as force, but you must pull twice as much rope. The load is supported by two rope segments.

The key insight: mechanical advantage comes from the number of rope segments supporting the moving load, not from the number of pulleys in the system.

Calculating Mechanical Advantage

Rule: count the number of rope segments directly supporting the movable block (the one attached to the load). That number is the mechanical advantage.

A fixed pulley at the top does not count — it only redirects the pull rope. Only segments that bear the load weight contribute to MA.

Example: A system has 4 rope segments holding the lower block. MA = 4. A 800 lb load needs only 200 lbs of pull. Trade-off: you must pull 4 feet of rope for every 1 foot the load rises.

Block and tackle: the classic multi-pulley arrangement used to lift very heavy loads with modest force. The upper block is fixed, the lower block attaches to the load. More sheaves in each block = more rope segments = more MA.

Elevator Roping Configurations

1:1 roping: One end of the hoist rope attaches to the car, the other to the counterweight. The rope passes once over the drive sheave. Car speed equals rope speed. The drive sheave must support the full rope tension.

2:1 roping: The rope end is anchored to the overhead structure. The rope runs down under a sheave on the car, back up over an overhead deflector sheave, back down under a sheave on the counterweight, and back up to another overhead anchor. The car moves at half the rope speed. The motor carries half the rope tension per rope, but the sheave turns twice as far per foot of car travel. Used for heavier, slower service elevators.

The number after the colon (1:1, 2:1) represents the roping ratio — how many rope segments support the car. Higher number = slower car, less tension per rope, easier on the machine.

Sheaves in Traction Elevators

Drive sheave: the grooved wheel connected to the motor. The rope does not wrap around it — it sits in the groove and is driven by friction between rope and groove. The groove shape (undercut or semicircular) is designed to maximize this traction.

Deflector sheave: a non-driven sheave that redirects the ropes from the drive sheave down into the hoistway at the correct angle. Does not add mechanical advantage.

Secondary sheave (in 2:1 roping): attached to the car or counterweight frame. This sheave is what creates the 2:1 mechanical advantage — it moves with the load.

Key Takeaways

✓Count rope segments supporting the load to find MA — not the number of pulleys.
✓Fixed pulley: MA = 1, direction change only. Movable pulley: MA = 2.
✓High MA = less force required, but more rope to pull and slower movement.
✓2:1 roping: car moves at half the rope speed; each rope carries half the load.
✓"Sheave" is the elevator industry word for a grooved pulley wheel.

Key Terms

Fixed pulley

Stationary pulley that changes rope direction only. MA = 1.

Movable pulley

Pulley attached to the load; provides MA = 2.

Block and tackle

System of multiple pulleys giving high mechanical advantage for lifting heavy loads.

Mechanical advantage (MA)

Factor by which a machine multiplies the input force.

1:1 roping

Standard traction roping; car speed equals rope speed.

2:1 roping

Roping where car travels at half rope speed; reduces load per rope segment.

Drive sheave

Motor-driven grooved wheel that moves hoist ropes via friction.

Deflector sheave

Non-driven sheave that redirects rope path.

Traction

The friction between rope and sheave groove that drives rope movement.

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