CET Traction Elevator Mechanics 2 — Questions and Answers
Question 1: What is the primary function of the deflector sheave in a traction elevator?
- To increase rope tension
- To redirect the hoist ropes to a different angle (Correct answer)
- To act as a secondary brake
- To balance the counterweight
Correct 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.
Question 2: In a 2:1 roping arrangement, how does the car speed compare to the rope speed at the drive sheave?
- Car speed equals rope speed
- Car speed is twice the rope speed
- Car speed is half the rope speed (Correct answer)
- Car speed is four times the rope speed
Correct 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.
Question 3: What causes 'creep' in elevator hoist ropes on a traction sheave?
- Insufficient lubrication on the sheave
- Differential elongation of ropes under varying loads (Correct answer)
- Overloading the elevator car
- Worn brake shoes
Correct 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.
Question 4: Which type of hoist rope construction is most commonly used in modern traction elevators?
- 6x7 fiber core
- 8x19 Seale pattern
- 6x19 independent wire rope core (IWRC) (Correct answer)
- 4x36 Warrington
Correct 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.
Question 5: What is the minimum number of hoist ropes required by ASME A17.1 for a traction elevator?
- One
- Two (Correct answer)
- Three
- Four
Correct answer: Two
ASME A17.1 requires a minimum of two hoist ropes for traction elevators to ensure redundancy in case of one rope failure.
Question 6: What is the purpose of the compensation ropes or chains in a high-rise traction elevator?
- To provide emergency braking
- To balance the weight of the hoist ropes between car and counterweight (Correct answer)
- To limit car travel speed
- To connect the governor to the safety device
Correct 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.
Question 7: Which component determines the maximum traction force available between the hoist ropes and the drive sheave?
- Rope diameter
- Groove angle and rope tension ratio (Correct answer)
- Motor horsepower
- Counterweight mass
Correct 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.
CET Traction Elevator Mechanics 2
What is the primary function of the deflector sheave in a traction elevator?