Plant Operator Selection System Test Plant Operator Selection System Mechanical Concepts 3 — Questions and Answers
Question 1: A compound gear train has a driving gear with 10 teeth meshed with an intermediate gear of 50 teeth. The intermediate gear is on the same shaft as a 10-tooth gear driving a final gear with 40 teeth. What is the overall gear ratio (input to output)?
- 5:1
- 10:1
- 20:1 (Correct answer)
- 40:1
Correct answer: 20:1
Overall ratio = (50/10) × (40/10) = 5 × 4 = 20:1, meaning the output shaft turns once for every 20 input turns.
Question 2: Which type of bearing is specifically designed to handle axial (thrust) loads along a shaft's axis?
- Radial ball bearing
- Cylindrical roller bearing
- Thrust bearing (Correct answer)
- Needle bearing
Correct answer: Thrust bearing
Thrust bearings are engineered to support loads parallel to the shaft axis, unlike radial bearings that handle perpendicular loads.
Question 3: A manometer reads 25 inches of water column. Approximately how many PSI does this represent?
- 0.9 PSI (Correct answer)
- 1.8 PSI
- 2.5 PSI
- 25 PSI
Correct answer: 0.9 PSI
Water column converts at 27.7 inches H₂O per PSI, so 25 ÷ 27.7 ≈ 0.9 PSI.
Question 4: In a steam system, which device removes condensed water (condensate) from the steam lines without allowing steam to escape?
- Pressure regulator
- Steam trap (Correct answer)
- Check valve
- Strainer
Correct answer: Steam trap
A steam trap automatically drains condensate while keeping steam in the system, preventing water hammer and efficiency loss.
Question 5: A centrifugal pump is running but producing no flow. Which condition is MOST likely the cause?
- The discharge valve is fully open
- The pump is air-bound (cavitating on air) (Correct answer)
- The suction strainer is clean
- The motor is running at full speed
Correct answer: The pump is air-bound (cavitating on air)
If a centrifugal pump is air-bound, it cannot create suction because air does not produce enough centrifugal force to move liquid.
Question 6: What is the mechanical advantage of a single fixed pulley used to lift a load?
- 0
- 1 (Correct answer)
- 2
- 4
Correct answer: 1
A single fixed pulley only changes the direction of force; the mechanical advantage is 1 because you still pull with the full weight of the load.
Question 7: Heat transfer that occurs through direct physical contact between two objects is called:
- Convection
- Radiation
- Conduction (Correct answer)
- Evaporation
Correct answer: Conduction
Conduction is heat transfer through direct contact, as heat energy moves from molecule to molecule within or between materials.
Plant Operator Selection System Test Plant Operator Selection System Mechanical Concepts 3
A compound gear train has a driving gear with 10 teeth meshed with an intermediate gear of 50 teeth.
The intermediate gear is on the same shaft as a 10-tooth gear driving a final gear with 40 teeth.
What is the overall gear ratio (input to output)?