CET CET Roping & Counterweight Systems 2 — Questions and Answers
Question 1: What type of wire rope construction is most commonly used for elevator hoist ropes?
- 6×7 fiber core
- 8×19 Seale, independent wire rope core (IWRC) (Correct answer)
- 4×31 Warrington
- 1×7 strand
Correct answer: 8×19 Seale, independent wire rope core (IWRC)
8×19 Seale construction with IWRC is the most common elevator hoist rope, offering a good balance of flexibility, strength, and fatigue resistance.
Question 2: What is the purpose of the counterweight guide rails?
- Support the weight of the counterweight sheave
- Keep the counterweight traveling in a straight vertical path within the hoistway (Correct answer)
- Connect the counterweight to the hoist ropes
- Provide a surface for the counterweight safeties to engage
Correct answer: Keep the counterweight traveling in a straight vertical path within the hoistway
Counterweight guide rails constrain the counterweight to a precise vertical path, preventing lateral movement that could cause contact with hoistway walls or the car.
Question 3: What is 'rope creep' in a traction elevator system?
- Gradual rope elongation under constant load
- Slow slippage of hoist ropes relative to the drive sheave under traction (Correct answer)
- Movement of ropes through the sheave grooves due to overloading
- Lateral movement of ropes across the sheave face
Correct answer: Slow slippage of hoist ropes relative to the drive sheave under traction
Rope creep is the slow, controlled slippage of hoist ropes relative to the drive sheave, which occurs due to the difference in tension between the car and counterweight sides.
Question 4: Which condition would most likely cause loss of traction in a traction elevator?
- Sheave groove wear causing increased rope contact
- Overloaded car creating too large a traction ratio between loaded and unloaded rope sides (Correct answer)
- Excessive rope tension on both sides equally
- Proper lubrication of drive sheave grooves
Correct answer: Overloaded car creating too large a traction ratio between loaded and unloaded rope sides
An overloaded car creates an extreme tension ratio between the car-side and counterweight-side ropes, exceeding the traction limit and causing the ropes to slip on the sheave.
Question 5: What is the purpose of 'compensating ropes' or 'compensating chains' in a tall-rise traction elevator?
- Provide a backup rope system in case primary ropes fail
- Compensate for the weight imbalance caused by hoist rope weight shifting as the car travels (Correct answer)
- Connect the car safety to the governor rope
- Limit the travel speed on long rises
Correct answer: Compensate for the weight imbalance caused by hoist rope weight shifting as the car travels
Compensating ropes or chains loop under the car and counterweight to compensate for the changing weight of hoist ropes as the car moves up and down in high-rise applications.
Question 6: What is the minimum bend ratio (D/d ratio) required for elevator hoist rope sheaves under ASME A17.1?
- 20:1
- 40:1
- 60:1 (Correct answer)
- 80:1
Correct answer: 60:1
ASME A17.1 requires a minimum sheave diameter to rope diameter (D/d) ratio of 40:1 for traction elevator drive sheaves to limit rope fatigue from bending.
CET CET Roping & Counterweight Systems 2
What type of wire rope construction is most commonly used for elevator hoist ropes?