ABC Pumping Systems and Hydraulics 2 — Questions and Answers
Question 1: According to the affinity laws, if pump speed is doubled, the power (brake horsepower) required changes by a factor of:
- 2
- 4
- 8 (Correct answer)
- 1.5
Correct answer: 8
By the third affinity law, power varies as the cube of speed, so doubling the speed increases power requirements by 2³ = 8 times.
Question 2: What does the specific speed of a pump indicate?
- The rpm at maximum power consumption
- The type of impeller design best suited for given flow and head conditions (Correct answer)
- The minimum suction head required
- The horsepower at shutoff head
Correct answer: The type of impeller design best suited for given flow and head conditions
Specific speed is a dimensionless index that classifies pump impeller geometry and is used to select the best impeller design for specific flow and head requirements.
Question 3: In a parallel pump configuration, what happens to total flow and head compared to a single pump?
- Flow doubles, head doubles
- Flow increases, head remains approximately the same (Correct answer)
- Head doubles, flow remains approximately the same
- Both flow and head remain the same
Correct answer: Flow increases, head remains approximately the same
Pumps in parallel add their flows at the same head, increasing total flow capacity while the total head remains approximately constant.
Question 4: What instrument is used to measure the flow rate in a pressurized water main using pressure differential?
- Ultrasonic flow meter
- Venturi meter or Pitot tube (Correct answer)
- Rotameter
- Weir box
Correct answer: Venturi meter or Pitot tube
A Venturi meter or Pitot tube measures flow by detecting pressure differential created by flow velocity in a pressurized pipe.
Question 5: The volute casing of a centrifugal pump is designed to:
- Increase impeller rotation speed
- Convert velocity head to pressure head as water exits the impeller (Correct answer)
- Filter suspended solids from the water
- Cool the pump motor
Correct answer: Convert velocity head to pressure head as water exits the impeller
The volute's gradually expanding cross-section converts kinetic energy (velocity head) from the impeller into potential energy (pressure head).
Question 6: Which of the following conditions would cause a centrifugal pump to operate at a lower-than-expected flow rate?
- Lower than designed system friction losses
- Larger than specified impeller diameter
- Air binding or air entrainment in the suction line (Correct answer)
- Lower discharge static head
Correct answer: Air binding or air entrainment in the suction line
Air binding reduces the effective liquid column in the suction line, preventing the pump from priming and significantly reducing or stopping flow.
Question 7: The wire-to-water efficiency of a pumping system accounts for losses in which components?
- Only the pump impeller
- Only the motor windings
- The motor, mechanical drive, and pump hydraulic efficiency combined (Correct answer)
- Pipe friction losses only
Correct answer: The motor, mechanical drive, and pump hydraulic efficiency combined
Wire-to-water efficiency is the overall system efficiency from electrical input to hydraulic output, accounting for motor, drive, and pump losses together.
ABC Pumping Systems and Hydraulics 2
According to the affinity laws, if pump speed is doubled, the power (brake horsepower) required changes by a factor of: