Traction Elevator Mechanics Flashcards

What is the primary function of the deflector sheave in a traction elevator?

Answer: To redirect the hoist ropes to a different angle

A deflector sheave redirects the hoist ropes so they hang vertically from the drive sheave to the car and counterweight.

In a 2:1 roping arrangement, how does the car speed compare to the rope speed at the drive sheave?

Answer: Car speed is half the rope speed

In 2:1 roping, the car moves at half the speed of the rope because the mechanical advantage doubles the lifting force while halving the speed.

What causes 'creep' in elevator hoist ropes on a traction sheave?

Answer: Differential elongation of ropes under varying loads

Creep occurs when ropes stretch unequally under load changes, causing slight slippage relative to the sheave groove.

Which type of hoist rope construction is most commonly used in modern traction elevators?

Answer: 6x19 independent wire rope core (IWRC)

6x19 IWRC ropes are standard because they offer a good balance of flexibility, strength, and fatigue resistance for elevator service.

What is the minimum number of hoist ropes required by ASME A17.1 for a traction elevator?

Answer: Two

ASME A17.1 requires a minimum of two hoist ropes for traction elevators to ensure redundancy in case of one rope failure.

What is the purpose of the compensation ropes or chains in a high-rise traction elevator?

Answer: To balance the weight of the hoist ropes between car and counterweight

Compensation ropes or chains counteract the changing weight imbalance of hoist ropes as the car travels through long hoistways.

Which component determines the maximum traction force available between the hoist ropes and the drive sheave?

Answer: Groove angle and rope tension ratio

Traction capacity is governed by the Euler-Eytelwein equation, where groove angle and the tension ratio of the loaded to unloaded rope side determine grip.