CPE Mechanical Systems & Equipment 5 — Questions and Answers
Question 1: Which maintenance strategy uses real-time condition monitoring data to schedule repairs only when needed?
- Preventive maintenance
- Corrective maintenance
- Predictive (condition-based) maintenance (Correct answer)
- Run-to-failure maintenance
Correct answer: Predictive (condition-based) maintenance
Predictive maintenance uses sensor data (vibration, temperature, oil analysis) to detect deterioration and schedule intervention before failure occurs.
Question 2: A plant engineer must select a pump for a high-viscosity fluid. Compared to water, operating with a viscous fluid will:
- Increase pump head and efficiency
- Decrease flow, head, and efficiency (Correct answer)
- Increase flow capacity with no efficiency loss
- Have no effect if the impeller is unchanged
Correct answer: Decrease flow, head, and efficiency
Higher viscosity increases internal fluid friction losses, reducing pump flow, head, and efficiency compared to the water-based pump curve.
Question 3: What is the purpose of dynamic balancing (two-plane balancing) vs. static balancing?
- Dynamic balancing corrects couple imbalance in wide rotors; static balancing only corrects static imbalance (Correct answer)
- Static balancing is used at high speeds; dynamic balancing at low speeds
- Dynamic balancing removes mass; static balancing adds mass only
- They are interchangeable for all rotor geometries
Correct answer: Dynamic balancing corrects couple imbalance in wide rotors; static balancing only corrects static imbalance
Two-plane dynamic balancing corrects both static and couple (dynamic) imbalance, which is essential for wide rotors where imbalance planes are axially separated.
Question 4: In a screw conveyor design, increasing the screw pitch will primarily:
- Decrease conveying capacity for the same speed
- Increase conveying capacity for the same speed (Correct answer)
- Reduce power consumption at all conditions
- Increase the conveyor's ability to handle sticky materials
Correct answer: Increase conveying capacity for the same speed
A larger screw pitch moves more material per revolution, increasing volumetric conveying capacity at the same rotational speed.
Question 5: An engineer notices a pump's performance curve has shifted left (reduced flow at given head). The MOST likely cause is:
- Worn impeller reducing effective diameter and clearance (Correct answer)
- Increased motor speed above nameplate RPM
- Reduced system resistance due to valve opening
- Increased fluid temperature lowering viscosity
Correct answer: Worn impeller reducing effective diameter and clearance
Impeller wear increases running clearances and reduces effective diameter, causing the pump curve to shift downward and to the left.
Question 6: Which type of valve is BEST for throttling (flow control) service in a plant piping system?
- Gate valve
- Ball valve
- Globe valve (Correct answer)
- Butterfly valve
Correct answer: Globe valve
Globe valves are designed for throttling because their plug-and-seat design provides fine, controllable flow regulation across a wide range of positions.
Question 7: The term 'mechanical efficiency' of a pump refers to:
- The ratio of hydraulic power output to shaft power input (Correct answer)
- The ratio of actual flow to theoretical flow at zero head
- Losses due to bearing friction and seal drag vs. total power
- The efficiency of converting electrical energy to shaft rotation
Correct answer: The ratio of hydraulic power output to shaft power input
Mechanical efficiency is the ratio of useful hydraulic power delivered to the fluid to the shaft brake power input, accounting for all mechanical and volumetric losses.
CPE Mechanical Systems & Equipment 5
Which maintenance strategy uses real-time condition monitoring data to schedule repairs only when needed?