EIAT Mechanical Comprehension 4 — Questions and Answers
Question 1: A safety gear (progressive safety) on an elevator is activated by:
- The door operator sensing an obstruction
- Overspeed detected by the governor rope (Correct answer)
- The motor drawing excess current
- Manual activation by the elevator operator
Correct answer: Overspeed detected by the governor rope
The governor monitors cab speed and, if overspeed occurs, trips the governor rope which mechanically activates the safety gear to grip the guide rails.
Question 2: What is the primary purpose of a buffer at the bottom of an elevator pit?
- Reduce noise from the traveling cable
- Absorb the kinetic energy of the cab or counterweight at the end of travel (Correct answer)
- Support the weight of the cab when parked at the lowest floor
- Prevent water from entering the hydraulic cylinder
Correct answer: Absorb the kinetic energy of the cab or counterweight at the end of travel
Buffers (oil or spring type) are energy-absorbing devices designed to stop a descending cab or counterweight that travels beyond its normal limit.
Question 3: In a simple pulley system with a fixed pulley and a movable pulley, the mechanical advantage is:
- 1
- 2 (Correct answer)
- 3
- 4
Correct answer: 2
A system with one fixed and one movable pulley provides a mechanical advantage of 2, meaning half the effort is needed to lift the load.
Question 4: Viscosity of hydraulic oil in an elevator system affects:
- The electrical insulation of the motor windings
- The flow resistance and heat generation in the hydraulic circuit (Correct answer)
- The tensile strength of the hoisting ropes
- The alignment of the guide shoes
Correct answer: The flow resistance and heat generation in the hydraulic circuit
Higher viscosity increases flow resistance and heat generation; lower viscosity reduces efficiency and can cause leakage — proper viscosity ensures smooth, efficient operation.
Question 5: A driven gear has 60 teeth and the driving gear has 20 teeth. The gear ratio (output:input) is:
- 3:1 speed reduction (Correct answer)
- 1:3 speed increase
- 1:1 direct drive
- 6:1 speed reduction
Correct answer: 3:1 speed reduction
Gear ratio = driven teeth / driving teeth = 60/20 = 3:1, meaning the output shaft turns at one-third the speed of the input shaft.
Question 6: Thermal expansion is an important consideration in elevator guide rails because:
- Expanded rails conduct electricity more efficiently
- Rail length changes with temperature and must be accommodated to prevent buckling (Correct answer)
- Heat causes rails to become magnetically charged
- Thermal contraction weakens welds at rail joints
Correct answer: Rail length changes with temperature and must be accommodated to prevent buckling
Steel rails expand when heated; splice joints include expansion gaps so rails can grow without buckling or binding guide shoes.
Question 7: Which component converts the rotational motion of the elevator motor into the linear motion needed to raise the cab?
- The governor
- The drive sheave and ropes (Correct answer)
- The selector tape
- The landing zone vane
Correct answer: The drive sheave and ropes
The drive sheave (grooved pulley) rotates with the motor; the hoisting ropes wrapped over it convert that rotation into linear movement of the cab and counterweight.
EIAT Mechanical Comprehension 4
A safety gear (progressive safety) on an elevator is activated by: