Pump affinity law check: Does delivery head vary inversely with impeller diameter at constant speed? Assume the same pump operating at a fixed rotational speed. State whether the given statement is correct. Choose the correct option.
Mechanical Engineering
Hydraulic Machines
Difficulty: Easy
Choose an option
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AYes — head is inversely proportional to impeller diameter
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BNo — at constant speed, head is proportional to the square of impeller diameter (H ∝ D²)
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CHead is independent of impeller diameter
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DTrue only for axial-flow pumps
Answer
Correct Answer: No — at constant speed, head is proportional to the square of impeller diameter (H ∝ D²)
Explanation
Affinity laws (for geometrically similar operation)
- Q ∝ D³ N
- H ∝ D² N²
- P ∝ D⁵ N³
Implication at constant NH ∝ D², so increasing impeller diameter increases the developed head; it is not inversely proportional.
Final AnswerFalse — delivery head increases with the square of impeller diameter at fixed speed.