Question

What type of lifts are used in high-rise buildings?

• A. Hydraulic lifts
• B. Vacuum lifts
• C. Traction machines
• D. Hydraulic and vacuum lifts

Hint:

- {Low-rise (<15 meters):} Hydraulic or Vacuum lifts are acceptable.
- High-rise (>30 meters): Traction Machines (Cable-driven systems with counterweights) are mandatory due to speed and height capabilities.

Answer 1

The Correct Option is C

Concept: Vertical transport solutions are selected based on the height of the building and the required travel speed. For tall structures and skyscrapers, the mechanical drive system must be capable of lifting heavy loads over long vertical distances while operating at high speeds and maintaining energy efficiency.

Step 1: Evaluating Traction Machine Elevators.
Traction elevators are the standard choice for medium- to high-rise structures because of their design and efficiency:
• They operate by passing heavy steel hoisting ropes or woven steel belts over a deeply grooved drive sheave turned by an electric motor.
• The weight of the elevator car is balanced by a counterweight, which reduces the amount of electrical power needed to move the cab.
• Because they rely on a balanced pulley system rather than a direct pushing piston, traction machines can serve buildings of unlimited heights and travel at high velocities (often exceeding $10\text{ m/s}$).

Step 2: Analyzing why other systems fail in high-rise applications.

• Hydraulic Lifts: These lifts use an electric pump to push a hydraulic piston that raises the elevator cab from below. Their travel distance is limited by the physical length of the cylinder piston, making them practical only for low-rise buildings up to 4–5 stories tall. They are also slower and require more power.
• Vacuum Lifts: These systems use air pressure differentials to move a lightweight cab inside a sealed cylinder. They operate via air pumps and are designed only for low-speed, single-family residential properties spanning 2–3 floors. They lack the capacity and speed required for commercial high-rises. Therefore, traction machines are the only viable choice for high-rise buildings.