Allied & ICAR Exam Bank • ALLIED_0569 MCQ • 1 Mark

Section 5: Irrigation and Drainage Engineering

Centrifugal Pumps and Cavitation

Subtopic: Centrifugal Pumps and Cavitation

Question Statement:

Priming of a centrifugal pump is necessary prior to starting when installed above water level because:

Options:

  • (A) Air trapped in the casing cannot generate enough centrifugal pressure rise to draw water up the suction line due to the low density of air
  • (B) The motor cannot spin in air
  • (C) Air melts the impeller
  • (D) The foot valve closes permanently

Answer Key:

A

Step-by-Step Solution & Explanation

Pressure head rise $H = \Delta P / (\rho g)$ is similar for air and water, but since air density is $\sim 800$ times lower than water, pressure generated in air is negligible ($\\sim 1/800\text{ atm}$).
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