CWEA MECHANICAL TECHNOLOGIST
GRADE 4 EXAM PREPARATION
QUESTIONS AND VERIFIED ANSWERS
1. According to the Pump Affinity Laws, if the speed of a centrifugal pump is reduced by 50%,
what is the resulting effect on the required brake horsepower (BHP)?
A. The BHP is reduced to 12.5% of the original.
B. The BHP is reduced to 25% of the original.
C. The BHP is reduced to 50% of the original.
D. The BHP remains unchanged.
Answer: A
Conceptual Explanation: According to Affinity Laws, power is proportional to the cube of
the speed ratio. (0.5)^3 = 0.125, or 12.5%.
2. Which vibration analysis technique is most effective for identifying early-stage rolling
element bearing defects before they become audible?
A. Overall Velocity Measurement
B. High-Frequency Enveloping (Demodulation)
C. Phase Analysis
D. Time Waveform Analysis
,Answer: B
Conceptual Explanation: Enveloping filters out low-frequency structural vibrations to
focus on high-frequency impacts typical of early bearing fatigue.
3. In the context of Reliability Centered Maintenance (RCM), what is a ‘Hidden Failure’?
A. A failure of a protective device that is not evident to the operating crew under normal
circumstances.
B. A failure that is not visible to the naked eye.
C. A failure that occurs during the ‘infant mortality’ phase of the bathtub curve.
D. A failure that has no operational consequences.
Answer: A
Conceptual Explanation: Hidden failures usually involve standby equipment or safety
systems (like a relief valve) that only show they have failed when they are needed to
perform.
4. When performing a laser alignment, what does the term ‘Soft Foot’ refer to?
A. A condition where the machine frame is made of inferior metal.
B. Improper contact between a machine casing foot and the baseplate.
C. Using rubber pads under the motor feet to reduce vibration.
D. The flexibility of the coupling under torque.
Answer: B
, Conceptual Explanation: Soft foot occurs when one or more feet do not sit flat on the
baseplate, causing frame distortion when bolts are tightened.
5. What is the primary purpose of a ‘Balanced’ mechanical seal in high-pressure applications?
A. To ensure the shaft is perfectly centered.
B. To reduce the net closing force on the seal faces.
C. To allow the seal to operate in both directions of rotation.
D. To eliminate the need for a seal flush (Plan 11).
Answer: B
Conceptual Explanation: Balanced seals are designed so that the pressure forces are
partially offset, reducing heat and wear at the seal faces in high-pressure environments.
6. A pump is exhibiting cavitation despite the static suction head being well above the pump’s
center line. Which of the following is the most likely cause?
A. NPSH Available is greater than NPSH Required.
B. The discharge valve is throttled too much.
C. Excessive friction losses in the suction piping.
D. The impeller is trimmed too small.
Answer: C
Conceptual Explanation: Friction losses (due to small pipe diameter or long runs) reduce
the NPSH Available at the pump inlet, leading to cavitation.
GRADE 4 EXAM PREPARATION
QUESTIONS AND VERIFIED ANSWERS
1. According to the Pump Affinity Laws, if the speed of a centrifugal pump is reduced by 50%,
what is the resulting effect on the required brake horsepower (BHP)?
A. The BHP is reduced to 12.5% of the original.
B. The BHP is reduced to 25% of the original.
C. The BHP is reduced to 50% of the original.
D. The BHP remains unchanged.
Answer: A
Conceptual Explanation: According to Affinity Laws, power is proportional to the cube of
the speed ratio. (0.5)^3 = 0.125, or 12.5%.
2. Which vibration analysis technique is most effective for identifying early-stage rolling
element bearing defects before they become audible?
A. Overall Velocity Measurement
B. High-Frequency Enveloping (Demodulation)
C. Phase Analysis
D. Time Waveform Analysis
,Answer: B
Conceptual Explanation: Enveloping filters out low-frequency structural vibrations to
focus on high-frequency impacts typical of early bearing fatigue.
3. In the context of Reliability Centered Maintenance (RCM), what is a ‘Hidden Failure’?
A. A failure of a protective device that is not evident to the operating crew under normal
circumstances.
B. A failure that is not visible to the naked eye.
C. A failure that occurs during the ‘infant mortality’ phase of the bathtub curve.
D. A failure that has no operational consequences.
Answer: A
Conceptual Explanation: Hidden failures usually involve standby equipment or safety
systems (like a relief valve) that only show they have failed when they are needed to
perform.
4. When performing a laser alignment, what does the term ‘Soft Foot’ refer to?
A. A condition where the machine frame is made of inferior metal.
B. Improper contact between a machine casing foot and the baseplate.
C. Using rubber pads under the motor feet to reduce vibration.
D. The flexibility of the coupling under torque.
Answer: B
, Conceptual Explanation: Soft foot occurs when one or more feet do not sit flat on the
baseplate, causing frame distortion when bolts are tightened.
5. What is the primary purpose of a ‘Balanced’ mechanical seal in high-pressure applications?
A. To ensure the shaft is perfectly centered.
B. To reduce the net closing force on the seal faces.
C. To allow the seal to operate in both directions of rotation.
D. To eliminate the need for a seal flush (Plan 11).
Answer: B
Conceptual Explanation: Balanced seals are designed so that the pressure forces are
partially offset, reducing heat and wear at the seal faces in high-pressure environments.
6. A pump is exhibiting cavitation despite the static suction head being well above the pump’s
center line. Which of the following is the most likely cause?
A. NPSH Available is greater than NPSH Required.
B. The discharge valve is throttled too much.
C. Excessive friction losses in the suction piping.
D. The impeller is trimmed too small.
Answer: C
Conceptual Explanation: Friction losses (due to small pipe diameter or long runs) reduce
the NPSH Available at the pump inlet, leading to cavitation.
