(A) The head generated by a centrifugal pump at zero discharge is the 'shutoff head'.
(B) To avoid cavitation in centrifugal pumps, the net positive suction head should be more than the theoretical atmospheric pressure.
(C) According to the affinity laws of centrifugal pumps, the head varies with the square of the impeller speed.
(D) Most of the turbine pumps have operational characteristics closer to those of the centrifugal pumps than the propeller pumps.
Official Answer Key:
B
Step-by-Step Solution & Explanation
(A) is correct by definition — head at Q = 0 is the shut-off head.
(C) is correct — affinity law H ∝ N².
(D) is correct — vertical turbine (mixed-flow) pumps behave more like radial (centrifugal) pumps than axial (propeller) pumps.
(B) is wrong: the available NPSH must exceed the required NPSH of the pump, and NPSH_avail is always less than atmospheric pressure head (it equals atmospheric head minus suction lift, friction losses and vapour pressure head). Requiring NPSH > atmospheric pressure is physically impossible on a suction lift.
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