ABC Pumping Systems and Hydraulics 1 — Questions and Answers
Question 1: What is the term for the total head a pump must work against, including static head plus friction losses?
- Net Positive Suction Head
- Total Dynamic Head (Correct answer)
- Discharge Pressure Head
- Velocity Head
Correct answer: Total Dynamic Head
Total Dynamic Head (TDH) is the total equivalent head the pump must overcome, including static head, friction losses, and minor losses.
Question 2: Cavitation in a centrifugal pump is most directly caused by which condition?
- Excessive discharge pressure
- Insufficient Net Positive Suction Head Available (NPSHa) (Correct answer)
- High motor amperage
- Over-sized impeller diameter
Correct answer: Insufficient Net Positive Suction Head Available (NPSHa)
Cavitation occurs when the available NPSH falls below the required NPSH, causing the liquid to vaporize at the impeller inlet.
Question 3: On a pump curve, the point where the pump curve intersects the system curve is called the:
- Shutoff Head
- Best Efficiency Point
- Operating Point (Correct answer)
- Maximum Flow Point
Correct answer: Operating Point
The operating point (or duty point) is where the pump curve crosses the system curve, defining the actual flow and head the pump will deliver.
Question 4: A centrifugal pump running at twice its original speed will produce approximately how many times its original flow rate?
- 4 times
- 8 times
- 2 times (Correct answer)
- 1.5 times
Correct answer: 2 times
By the affinity laws, flow rate varies directly with pump speed, so doubling the speed doubles the flow rate.
Question 5: Which type of pump is most commonly used for high-volume, low-pressure water distribution applications?
- Reciprocating piston pump
- Centrifugal pump (Correct answer)
- Peristaltic pump
- Gear pump
Correct answer: Centrifugal pump
Centrifugal pumps are preferred for high-volume, low-to-moderate pressure applications like water distribution due to their efficiency and simplicity.
Question 6: The pressure drop due to water flowing through a pipe is primarily a function of:
- Pipe color and material grade only
- Flow velocity, pipe diameter, and pipe length (Correct answer)
- Pump motor horsepower only
- Water temperature and color
Correct answer: Flow velocity, pipe diameter, and pipe length
Friction head loss in a pipe depends on flow velocity, pipe diameter, pipe length, and pipe roughness as described by the Hazen-Williams or Darcy-Weisbach equation.
Question 7: A water hammer event in a pipeline is best prevented by:
- Increasing pump speed rapidly
- Installing surge tanks or slow-closing valves (Correct answer)
- Reducing pipe diameter
- Using higher voltage motors
Correct answer: Installing surge tanks or slow-closing valves
Surge tanks and slow-closing valves absorb pressure transients, preventing the destructive pressure spikes associated with water hammer.
ABC Pumping Systems and Hydraulics 1
What is the term for the total head a pump must work against, including static head plus friction losses?