CWEA Mechanical Technologist Grade 3
Exam Questions with Correct Answers
and explanations LATEST THIS YEAR -
JUST RELEASED.pdf
Question 1: A large centrifugal pump at a water reclamation facility experiences repeated
cavitation damage on the impeller. What is the most likely root cause?
A) Excessive discharge pressure
B) Low net positive suction head available (NPSHa)
C) High specific gravity of the pumped fluid
D) Worn mechanical seal
Correct Answer: B
Explanation: Cavitation occurs when the pressure at the pump suction falls below the vapor
pressure of the liquid, causing vapor bubbles to form and collapse on the impeller surface. This
happens when the Net Positive Suction Head Available (NPSHa) drops below the Net Positive
Suction Head Required (NPSHr) by the pump. Common causes include a clogged suction
strainer, high fluid temperature, or inadequate submergence .
Question 2: When performing lockout/tagout (LOTO) on a sludge pump driven by a 480V motor,
which step must occur immediately before applying the lock?
A) Notify affected employees
B) Verify isolation by attempting to start the pump
C) Shut down the equipment using normal stop procedures
D) Remove stored energy (e.g., discharge pressure)
Correct Answer: C
Explanation: Per OSHA and standard LOTO procedures, the equipment must be shut down using
its normal stopping controls before isolating the energy source. Applying a lock while the
equipment is running could damage the lock or cause an arc flash. After shut down, you isolate
the energy source, apply the lock, then verify zero energy .
Question 3: A hydraulic cylinder fails to extend fully under load. System pressure at the pump is
normal. What is the most probable cause?
A) Worn cylinder piston seal (internal bypass)
,B) Low hydraulic fluid viscosity
C) Clogged return line filter
D) Air in the pilot line
Correct Answer: A
Explanation: If system pressure is normal but the cylinder won't extend fully under load, the
issue is likely internal leakage. A worn piston seal allows pressurized fluid to leak from the piston
side to the rod side, bypassing the piston and reducing its effective force. This is often referred
to as "bypass" or "crossport leakage" .
Question 4: What is the correct procedure for tightening bolts on a split-case pump's bearing
housing cover?
A) Tighten one bolt fully, then move to the opposite side
B) Use a star pattern in three incremental torque steps
C) Tighten sequentially clockwise to final torque
D) Hand-tighten only, then use impact gun for final pass
Correct Answer: B
Explanation: A "star" or crisscross pattern with incremental torque steps (e.g., 30%, 60%, 100%
of final torque) ensures even gasket compression and prevents housing distortion. Uneven
tightening can misalign the bearing journals, leading to premature bearing failure or shaft
contact with seals .
Question 5: A SCADA trend shows a centrifugal pump's discharge pressure slowly decreasing
over 3 days while flow remains constant. What is the most likely cause?
A) Worn impeller or wear rings
B) Increasing suction pressure
C) Motor speed increasing
D) Discharge valve closing
Correct Answer: A
Explanation: With flow held relatively constant, a slow decline in discharge pressure indicates
the pump is losing its ability to generate head. This is a classic symptom of internal recirculation
due to increased clearances from worn wear rings or an impeller. Constant flow rules out
system blockage or speed change .
Question 6: A 3-phase induction motor trips on overload after 30 seconds of running a belt
press. The motor draws locked rotor current for 2 seconds then slowly drops but remains 20%
above FLA. Most likely cause?
A) Single phasing condition
, B) Mechanical binding in the belt press
C) Low voltage at motor terminals
D) Failed start capacitor
Correct Answer: B
Explanation: Prolonged high running current (above Full Load Amps - FLA) indicates an overload
condition, not an electrical fault inside the motor. A mechanical bind in the driven load (belt
press) forces the motor to work harder, drawing excess current. Low voltage would also cause
high current, but it typically affects starting torque immediately .
Question 7: When repacking a centrifugal pump stuffing box with ½-inch square PTFE packing,
how many rings are typically used for a standard-depth box?
A) 2 rings
B) 4 to 6 rings
C) 8 to 10 rings
D) Only 1 ring with lantern ring
Correct Answer: B
Explanation: Most standard-depth stuffing boxes hold 4 to 6 packing rings. This provides
sufficient sealing surface against the shaft while leaving room for the lantern ring (if used) and
gland follower. Each ring should be cut at a 45-degree angle and the gaps staggered 90-120
degrees to prevent a straight leak path .
Question 8: A mechanic is troubleshooting a centrifugal pump that delivers low flow at shutoff
head. The most likely cause is:
A) Worn impeller
B) Air leak in suction line
C) Reverse rotation
D) Discharge valve closed
Correct Answer: C
Explanation: A pump running backwards (reverse rotation) will still generate some head and
flow, but significantly less than designed. If the discharge valve is closed, you would have no
flow at shutoff head. Reverse rotation often occurs after motor maintenance if phases are
swapped and is a critical check on three-phase systems .
Question 9: When replacing a bearing on a critical process pump, which information is most
important to record in the maintenance log for future predictive maintenance planning?
A) Bearing manufacturer and number
B) Name of the supervisor on duty
Exam Questions with Correct Answers
and explanations LATEST THIS YEAR -
JUST RELEASED.pdf
Question 1: A large centrifugal pump at a water reclamation facility experiences repeated
cavitation damage on the impeller. What is the most likely root cause?
A) Excessive discharge pressure
B) Low net positive suction head available (NPSHa)
C) High specific gravity of the pumped fluid
D) Worn mechanical seal
Correct Answer: B
Explanation: Cavitation occurs when the pressure at the pump suction falls below the vapor
pressure of the liquid, causing vapor bubbles to form and collapse on the impeller surface. This
happens when the Net Positive Suction Head Available (NPSHa) drops below the Net Positive
Suction Head Required (NPSHr) by the pump. Common causes include a clogged suction
strainer, high fluid temperature, or inadequate submergence .
Question 2: When performing lockout/tagout (LOTO) on a sludge pump driven by a 480V motor,
which step must occur immediately before applying the lock?
A) Notify affected employees
B) Verify isolation by attempting to start the pump
C) Shut down the equipment using normal stop procedures
D) Remove stored energy (e.g., discharge pressure)
Correct Answer: C
Explanation: Per OSHA and standard LOTO procedures, the equipment must be shut down using
its normal stopping controls before isolating the energy source. Applying a lock while the
equipment is running could damage the lock or cause an arc flash. After shut down, you isolate
the energy source, apply the lock, then verify zero energy .
Question 3: A hydraulic cylinder fails to extend fully under load. System pressure at the pump is
normal. What is the most probable cause?
A) Worn cylinder piston seal (internal bypass)
,B) Low hydraulic fluid viscosity
C) Clogged return line filter
D) Air in the pilot line
Correct Answer: A
Explanation: If system pressure is normal but the cylinder won't extend fully under load, the
issue is likely internal leakage. A worn piston seal allows pressurized fluid to leak from the piston
side to the rod side, bypassing the piston and reducing its effective force. This is often referred
to as "bypass" or "crossport leakage" .
Question 4: What is the correct procedure for tightening bolts on a split-case pump's bearing
housing cover?
A) Tighten one bolt fully, then move to the opposite side
B) Use a star pattern in three incremental torque steps
C) Tighten sequentially clockwise to final torque
D) Hand-tighten only, then use impact gun for final pass
Correct Answer: B
Explanation: A "star" or crisscross pattern with incremental torque steps (e.g., 30%, 60%, 100%
of final torque) ensures even gasket compression and prevents housing distortion. Uneven
tightening can misalign the bearing journals, leading to premature bearing failure or shaft
contact with seals .
Question 5: A SCADA trend shows a centrifugal pump's discharge pressure slowly decreasing
over 3 days while flow remains constant. What is the most likely cause?
A) Worn impeller or wear rings
B) Increasing suction pressure
C) Motor speed increasing
D) Discharge valve closing
Correct Answer: A
Explanation: With flow held relatively constant, a slow decline in discharge pressure indicates
the pump is losing its ability to generate head. This is a classic symptom of internal recirculation
due to increased clearances from worn wear rings or an impeller. Constant flow rules out
system blockage or speed change .
Question 6: A 3-phase induction motor trips on overload after 30 seconds of running a belt
press. The motor draws locked rotor current for 2 seconds then slowly drops but remains 20%
above FLA. Most likely cause?
A) Single phasing condition
, B) Mechanical binding in the belt press
C) Low voltage at motor terminals
D) Failed start capacitor
Correct Answer: B
Explanation: Prolonged high running current (above Full Load Amps - FLA) indicates an overload
condition, not an electrical fault inside the motor. A mechanical bind in the driven load (belt
press) forces the motor to work harder, drawing excess current. Low voltage would also cause
high current, but it typically affects starting torque immediately .
Question 7: When repacking a centrifugal pump stuffing box with ½-inch square PTFE packing,
how many rings are typically used for a standard-depth box?
A) 2 rings
B) 4 to 6 rings
C) 8 to 10 rings
D) Only 1 ring with lantern ring
Correct Answer: B
Explanation: Most standard-depth stuffing boxes hold 4 to 6 packing rings. This provides
sufficient sealing surface against the shaft while leaving room for the lantern ring (if used) and
gland follower. Each ring should be cut at a 45-degree angle and the gaps staggered 90-120
degrees to prevent a straight leak path .
Question 8: A mechanic is troubleshooting a centrifugal pump that delivers low flow at shutoff
head. The most likely cause is:
A) Worn impeller
B) Air leak in suction line
C) Reverse rotation
D) Discharge valve closed
Correct Answer: C
Explanation: A pump running backwards (reverse rotation) will still generate some head and
flow, but significantly less than designed. If the discharge valve is closed, you would have no
flow at shutoff head. Reverse rotation often occurs after motor maintenance if phases are
swapped and is a critical check on three-phase systems .
Question 9: When replacing a bearing on a critical process pump, which information is most
important to record in the maintenance log for future predictive maintenance planning?
A) Bearing manufacturer and number
B) Name of the supervisor on duty
