CWEA MECHANICAL TECHNOLOGIST
GRADE 6 EXAM QUESTIONS AND
VERIFIED ANSWERS
1. When calculating Net Positive Suction Head Available (NPSHa), which variable is most
affected by an increase in the elevation of a plant located in a mountainous region?
A. Vapor Pressure
B. Friction Loss
C. Atmospheric Pressure
D. Static Head
Answer: C
Conceptual Explanation: Atmospheric pressure decreases as altitude increases, directly
reducing the NPSHa according to the standard formula NPSHa = Ha + Hs - Hvp - Hf.
2. According to the Pump Affinity Laws, if the speed of a centrifugal pump is reduced by 50%,
what is the resulting effect on the brake horsepower (BHP) requirement?
A. Reduced to 12.5%
B. Reduced to 50%
C. Reduced to 75%
D. Reduced to 25%
,Answer: A
Conceptual Explanation: Brake horsepower varies with the cube of the speed ratio.
(0.5)^3 = 0.125, or 12.5%.
3. In vibration analysis, a peak occurring at exactly twice the rotational speed (2X) with a high
axial component is most characteristic of which mechanical fault?
A. Misalignment
B. Unbalance
C. Mechanical Looseness
D. Bent Shaft
Answer: A
Conceptual Explanation: Angular misalignment typically generates a strong 2X vibration
in the axial direction, whereas unbalance is primary 1X radial.
4. What is the primary purpose of a ‘balance hole’ in a centrifugal pump impeller?
A. To reduce axial thrust on the bearing frame
B. To increase the discharge pressure
C. To prevent cavitation at the eye
D. To improve the hydraulic efficiency
Answer: A
, Conceptual Explanation: Balance holes allow high-pressure fluid behind the impeller to
flow back to the suction side, equalizing pressure and reducing axial load.
5. Which mechanical seal face material combination offers the highest resistance to thermal
shock and abrasive wear in wastewater applications?
A. Silicon Carbide vs. Silicon Carbide
B. Carbon vs. Ceramic
C. Tungsten Carbide vs. Carbon
D. Stainless Steel vs. Bronze
Answer: A
Conceptual Explanation: Silicon Carbide (SiC) is extremely hard and has high thermal
conductivity, making a SiC vs SiC pair ideal for abrasive wastewater conditions.
6. A bearing designated as C3 denotes what characteristic?
A. High precision tolerance
B. Internal clearance greater than normal
C. Three rows of rolling elements
D. Stainless steel construction
Answer: B
Conceptual Explanation: C3 is a standard designation for internal radial clearance that is
greater than the ‘Normal’ (CN) clearance to allow for thermal expansion.
GRADE 6 EXAM QUESTIONS AND
VERIFIED ANSWERS
1. When calculating Net Positive Suction Head Available (NPSHa), which variable is most
affected by an increase in the elevation of a plant located in a mountainous region?
A. Vapor Pressure
B. Friction Loss
C. Atmospheric Pressure
D. Static Head
Answer: C
Conceptual Explanation: Atmospheric pressure decreases as altitude increases, directly
reducing the NPSHa according to the standard formula NPSHa = Ha + Hs - Hvp - Hf.
2. According to the Pump Affinity Laws, if the speed of a centrifugal pump is reduced by 50%,
what is the resulting effect on the brake horsepower (BHP) requirement?
A. Reduced to 12.5%
B. Reduced to 50%
C. Reduced to 75%
D. Reduced to 25%
,Answer: A
Conceptual Explanation: Brake horsepower varies with the cube of the speed ratio.
(0.5)^3 = 0.125, or 12.5%.
3. In vibration analysis, a peak occurring at exactly twice the rotational speed (2X) with a high
axial component is most characteristic of which mechanical fault?
A. Misalignment
B. Unbalance
C. Mechanical Looseness
D. Bent Shaft
Answer: A
Conceptual Explanation: Angular misalignment typically generates a strong 2X vibration
in the axial direction, whereas unbalance is primary 1X radial.
4. What is the primary purpose of a ‘balance hole’ in a centrifugal pump impeller?
A. To reduce axial thrust on the bearing frame
B. To increase the discharge pressure
C. To prevent cavitation at the eye
D. To improve the hydraulic efficiency
Answer: A
, Conceptual Explanation: Balance holes allow high-pressure fluid behind the impeller to
flow back to the suction side, equalizing pressure and reducing axial load.
5. Which mechanical seal face material combination offers the highest resistance to thermal
shock and abrasive wear in wastewater applications?
A. Silicon Carbide vs. Silicon Carbide
B. Carbon vs. Ceramic
C. Tungsten Carbide vs. Carbon
D. Stainless Steel vs. Bronze
Answer: A
Conceptual Explanation: Silicon Carbide (SiC) is extremely hard and has high thermal
conductivity, making a SiC vs SiC pair ideal for abrasive wastewater conditions.
6. A bearing designated as C3 denotes what characteristic?
A. High precision tolerance
B. Internal clearance greater than normal
C. Three rows of rolling elements
D. Stainless steel construction
Answer: B
Conceptual Explanation: C3 is a standard designation for internal radial clearance that is
greater than the ‘Normal’ (CN) clearance to allow for thermal expansion.
