GATE AG 2014 • Q27 NAT • 1 Mark

Section 5: Irrigation and Drainage Engineering

Wells and Pumps

Subtopic: Classification of pumps

Question Statement:

The brake power of a centrifugal pump having an impeller diameter of 200 mm is 1.86 kW. If the impeller is replaced with another impeller of 180 mm diameter, the brake power of the pump in kW will be _________.

Official Answer Key:

1.35 to 1.36

Step-by-Step Solution & Explanation

Pump affinity laws for an impeller-diameter change at constant speed: Q ∝ D, H ∝ D², P ∝ D³. P₂ = P₁(D₂/D₁)³ = 1.86 × (180/200)³ = 1.86 × (0.9)³ = 1.86 × 0.729 = 1.356 kW, within the accepted range.

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