As the impeller wears, what happens to the pump efficiency?

• A. increases
• B. decreases
• C. remains the same
• D. varies unpredictably

Answer: (B)

Wear of the impeller reduces how effectively the pump transfers energy to the fluid. As the blades dull and the clearance between the impeller and the casing grows, the fluid slips more and turbulent losses rise. This means the pump delivers less hydraulic power for the same shaft power, so the efficiency—ratio of hydraulic output to input power—decreases. In practice, the performance curve shifts downward with wear, especially at design flow, rather than improving or staying the same.