A centrifugal pump is required to lift water to a total head of 40 m at the rate of 50 L/s. If its overall efficiency is 62%, the power required for the pump will be
- A25·6 kW
- B28·4 kW
- C31·6 kWCorrect
- D34·4 kW
Solution
Concept
Input power of a pump
Formula
P = ρ g Q H / η
Step-by-step solution
1. P = 9.81 × 0.05 × 40 / 0.62 = 31.6 kW.
Explanation
The input power equals the water power divided by the overall efficiency.
Why the other options are wrong
19.6 kW is the water power; 25.6, 28.4 and 34.4 kW come from other efficiencies.
Shortcut
P = γ Q H / η.
Common mistake
Multiplying by η instead of dividing.
Correct answer: C) 31·6 kW