IA Pumping Systems & Pump Selection 1 — Questions and Answers
Question 1: Total Dynamic Head (TDH) in a pump system is the sum of which components?
- Static head + friction losses + velocity head + pressure head at discharge (Correct answer)
- Flow rate + pipe diameter + elevation
- Pump horsepower + motor efficiency
- Operating pressure + static water level only
Correct answer: Static head + friction losses + velocity head + pressure head at discharge
TDH = static head + friction head losses + velocity head + any pressure required at the point of delivery, representing total energy the pump must supply.
Question 2: On a centrifugal pump curve, what is the 'best efficiency point' (BEP)?
- The maximum flow rate on the curve
- The point on the pump curve where the pump operates at its highest efficiency (Correct answer)
- The shutoff head with zero flow
- The intersection of the pump curve and system curve
Correct answer: The point on the pump curve where the pump operates at its highest efficiency
The BEP is the flow and head combination where the centrifugal pump converts the most shaft power into hydraulic energy with minimal losses.
Question 3: Cavitation in a centrifugal pump is caused by:
- Excessive discharge pressure
- Low suction pressure causing liquid to vaporize inside the pump (Correct answer)
- Over-lubrication of pump bearings
- Impeller running at too low a speed
Correct answer: Low suction pressure causing liquid to vaporize inside the pump
When suction pressure drops below the liquid's vapor pressure, bubbles form and collapse violently inside the pump, causing noise, vibration, and impeller damage.
Question 4: Net Positive Suction Head Available (NPSHa) must always be:
- Equal to total dynamic head
- Greater than NPSHr (required) to prevent cavitation (Correct answer)
- Less than NPSHr to maximize flow
- Equal to static suction lift
Correct answer: Greater than NPSHr (required) to prevent cavitation
NPSHa must exceed NPSHr by at least 2–3 feet of safety margin to ensure the pump does not cavitate.
Question 5: Which type of pump is most commonly used in municipal and agricultural irrigation mainline applications?
- Gear pump
- Diaphragm pump
- Centrifugal pump (Correct answer)
- Peristaltic pump
Correct answer: Centrifugal pump
Centrifugal pumps are the most widely used irrigation pump type due to their high flow capacity, reliability, and suitability for clean water service.
Question 6: Brake horsepower (BHP) of a pump is calculated using which formula?
- BHP = Flow (GPM) × TDH / 3,960 × pump efficiency (Correct answer)
- BHP = Voltage × Amperage
- BHP = TDH × pipe diameter
- BHP = Flow (GPM) / pressure (PSI)
Correct answer: BHP = Flow (GPM) × TDH / 3,960 × pump efficiency
BHP = (GPM × TDH) / (3,960 × Ep), where 3,960 converts GPM and feet of head to horsepower and Ep is pump efficiency.
IA Pumping Systems & Pump Selection 1
Total Dynamic Head (TDH) in a pump system is the sum of which components?