Hydraulic Machines MCQ with answer and solution

Concept

In a multistage pump, impellers are connected in series on one shaft, so the head (pressure) adds up stage by stage.

Formula

Total head H_m = n × H, where n = number of impellers in series and H = head per impeller

Step-by-step solution

1. A single-stage pump has one impeller, so its head is limited. 2. In a multistage pump, impellers are in series on the same shaft. 3. Each stage adds head, so total head = n × head of one stage. 4. So a multistage pump can deliver discharge against a high pressure (high head). 5. Answer: B.

Explanation

A multistage pump has many impellers in series. The same discharge passes through every stage and pressure increases at each stage. So it can deliver water at a high pressure, for example as a boiler feed pump or a deep well pump.

Why the other options are wrong

A: A single impeller gives only limited head. C: Rotary pumps are positive displacement pumps for small discharge and viscous liquids; they are not the standard textbook answer. D: Mono-block only describes the motor and pump on one shaft; it does not mean high pressure.

Shortcut

High head means impellers in series (multistage). High discharge means impellers in parallel.

Common mistake

Mixing up series and parallel arrangement. Parallel impellers increase discharge, not head.