WTO Pumps and Motors 2 — Questions and Answers
Question 1: What is the primary purpose of a pump impeller in a centrifugal pump?
- To seal the pump casing
- To convert mechanical energy into fluid velocity (Correct answer)
- To regulate discharge pressure
- To prime the pump automatically
Correct answer: To convert mechanical energy into fluid velocity
The impeller rotates to impart velocity to the fluid, converting mechanical energy from the motor into kinetic energy in the water.
Question 2: A pump is experiencing cavitation. Which operational change would most likely resolve this issue?
- Increase the discharge pressure
- Reduce the suction lift or increase suction head (Correct answer)
- Increase the motor speed
- Close the discharge valve partially
Correct answer: Reduce the suction lift or increase suction head
Reducing suction lift or increasing suction head raises the pressure at the pump inlet above the vapor pressure of water, preventing vapor bubble formation.
Question 3: What does NPSH stand for in pump terminology?
- Net Positive Suction Head (Correct answer)
- Normal Pump Speed Head
- Net Pressure Surge Head
- Nominal Pump Suction Height
Correct answer: Net Positive Suction Head
NPSH (Net Positive Suction Head) is the total head of liquid at the pump suction, used to determine if cavitation will occur.
Question 4: A three-phase motor is running on two phases only due to a blown fuse. What will most likely happen?
- The motor will run normally at reduced speed
- The motor will overheat and may burn out (Correct answer)
- The motor will automatically switch to single-phase mode
- The motor will run faster than normal
Correct answer: The motor will overheat and may burn out
Single-phasing causes unequal current distribution, excessive heat buildup, and can destroy motor windings if not quickly corrected.
Question 5: Which type of pump is best suited for high-flow, low-head water transmission applications at a water treatment plant?
- Reciprocating piston pump
- Centrifugal pump (Correct answer)
- Peristaltic pump
- Gear pump
Correct answer: Centrifugal pump
Centrifugal pumps are ideal for high-flow, low-to-moderate head applications and are the most common pump type in water treatment.
Question 6: What is the function of a mechanical seal in a centrifugal pump?
- To balance the impeller
- To prevent leakage along the pump shaft (Correct answer)
- To regulate pump speed
- To protect the motor from overload
Correct answer: To prevent leakage along the pump shaft
A mechanical seal prevents water from leaking out along the rotating shaft where it passes through the pump casing.
Question 7: When reading a pump curve, what does the intersection of the pump curve and system curve represent?
- The maximum flow capacity of the pump
- The minimum operating efficiency
- The actual operating point of the pump (Correct answer)
- The shutoff head of the pump
Correct answer: The actual operating point of the pump
The intersection of the pump curve and system curve is the operating point, where the pump will naturally operate given the system's resistance.
WTO Pumps and Motors 2
What is the primary purpose of a pump impeller in a centrifugal pump?