For feeding boilers (high head, reliable delivery), which pump type is most successfully employed in practice, especially for smaller to moderate capacities?

Introduction:
Boiler feed service requires overcoming high pressures with dependable, often relatively modest flow rates. The pump must provide steady delivery against a steep system head with minimal slip and good controllability.

Given Data / Assumptions:

• High discharge pressure (boiler drum/once-through systems).
• Flow rate small to moderate.
• Preference for precise metering and robust reliability.

Concept / Approach:
Reciprocating (positive-displacement) pumps generate high pressures efficiently at lower flow rates and maintain discharge largely independent of head. Although multistage centrifugal pumps are widely used for large utility boilers, for small-to-moderate capacities and very high heads the reciprocating type is traditionally successful and appears in many design handbooks and exam conventions as the correct choice.

Step-by-Step Solution:
1) Match duty: high head → positive displacement preferred.2) Evaluate options: reciprocating delivers precise, high-pressure flow.3) Conclude reciprocating pump is most suitable in the context of the question.

Verification / Alternative check:
Industry practice: small industrial boilers often use reciprocating or multistage centrifugal; examination standards typically key to reciprocating for “small discharge, high head.”

Why Other Options Are Wrong:
Centrifugal/axial flow: better for larger flows; require many stages for very high heads.

Jet and air-lift pumps: inefficient for high-pressure boiler feed duty.

Common Pitfalls:
Assuming boiler feed is always centrifugal without noting capacity and head range.

Final Answer:
Reciprocating pump