In water-supply mains, identify the most commonly used pump type for lifting and conveying water under typical municipal conditions.

Introduction / Context:
Selecting the appropriate pump for municipal water-supply mains is critical for reliable, energy-efficient operation. While many pump types exist, one class dominates distribution service due to its simplicity, cost-effectiveness, and ability to handle moderate to high flows at practical heads.

Given Data / Assumptions:

• Application: lifting and conveying potable water in public water-supply mains.
• Operating needs: continuous or near-continuous duty, moderate heads, wide flow ranges, reasonable efficiency, and easy maintenance.
• Pump options provided: axial-flow, reciprocating, rotary, and centrifugal.

Concept / Approach:
Centrifugal pumps convert rotational energy to hydraulic energy via an impeller, producing head by dynamic action. They are robust, relatively inexpensive per unit flow, tolerant of minor solids, and available in numerous configurations (end-suction, split-case, multistage). These traits make them the standard choice for municipal mains. Other pump types excel in niche roles but are not the common workhorses for distribution mains.

Step-by-Step Solution:
Step 1: Match pump characteristics to municipal distribution needs: steady flow, moderate head, efficiency, maintainability.Step 2: Recognize centrifugal pumps as industry-standard for these conditions due to dynamic head generation and scalability.Step 3: Eliminate less-suited types (axial-flow for very low head/high discharge, reciprocating for small high head/positive displacement duties, rotary for viscous fluids).Step 4: Conclude the most commonly used pump type is the centrifugal pump.

Verification / Alternative check:
Municipal standards and manufacturer catalogs for water utilities consistently show split-case and multistage centrifugal units for transmission mains and booster stations. Life-cycle cost analyses also favor centrifugal pumps for these duty points.

Why Other Options Are Wrong:
Axialflow pump: Best for very low head with extremely high discharge (e.g., flood control), not typical water-supply mains.Reciprocating pump: Positive displacement, suited for high-pressure/low-flow or dosing, not bulk distribution.Rotary type pump: Often used for viscous fluids or lubrication systems, not municipal water mains.None of these: Incorrect because centrifugal pumps are widely used.

Common Pitfalls:

• Oversizing pumps leading to operation far from best efficiency point (BEP), causing vibration and energy losses.
• Ignoring Net Positive Suction Head (NPSH) requirements, which may cause cavitation.
• Not considering variable-speed drives to match diurnal demand patterns.

Final Answer:
centrifugal pumps