Question Bank • QB_IDE_PUMP_008 NAT • 2 Marks

Section 5: Irrigation and Drainage Engineering

Wells and Pumps

Subtopic: Pump characteristics

Question Statement:

A centrifugal pump running at $1450\text{ rpm}$ develops an operating head of $20.0\text{ m}$. If the pump motor is upgraded to run at $2900\text{ rpm}$ with the same impeller diameter, according to pump affinity laws ($H \propto N^2$), the new head developed in metres is ________ (answer in integer).

Answer Key:

80

Step-by-Step Solution & Explanation

By pump affinity laws for constant impeller diameter: $\frac{H_2}{H_1} = \left( \frac{N_2}{N_1} \right)^2$ Given: • $H_1 = 20.0\text{ m}$ • $N_1 = 1450\text{ rpm}$ • $N_2 = 2900\text{ rpm} = 2 N_1$ $H_2 = H_1 \times \left( \frac{2900}{1450} \right)^2 = 20.0 \times 2^2 = 20.0 \times 4 = 80.0\text{ m}$
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