Boiler feed system: Before feedwater enters the boiler, its pressure must be raised to exceed boiler pressure for safe delivery. Name the device primarily used to raise the feedwater pressure.

Introduction / Context:
Every steam generator requires a mechanism to deliver water into the boiler against the internal steam pressure. Selecting and understanding the correct device ensures reliable operation and prevents starvation or water hammer.

Given Data / Assumptions:

• Boiler operates at positive pressure relative to atmosphere.
• Feedwater source is at low pressure (tank or condenser hotwell).
• Continuous, controllable delivery into the boiler is required.

Concept / Approach:
A feed pump (reciprocating, rotary, or centrifugal multistage) raises the pressure of feedwater to a value higher than boiler pressure so the feed check valve opens and water enters the drum or once-through circuit. An injector can also lift and force feedwater using a steam jet, but the generic and primary device specified by practice and codes is the feed pump. The feed check valve merely prevents backflow; it does not raise pressure. A pressure gauge only indicates pressure; it adds no energy to the water.

Step-by-Step Solution:
Identify need: p_feed > p_boiler at entry.Select device that adds hydraulic head to water: feed pump.Confirm ancillary roles: feed check valve prevents backflow; injector is an alternative jet device, not the baseline answer.Hence, the correct choice is feed pump (feedpump).

Verification / Alternative check:
Plant P&IDs show feed pumps upstream of the feed check valve; injectors are used on some locomotives and small boilers but are still categorized as feed-pumping devices driven by steam jets.

Why Other Options Are Wrong:
Injector: can serve the same purpose in specific setups but the generic term requested is feed pump.

Feed check valve: non-return isolation, no pressure rise.

Pressure gauge/air preheater: measurement and air-heating devices, not pumping equipment.

Common Pitfalls:
Assuming the check valve raises pressure or that the injector is the universal solution across all plants.

Final Answer:
feedpump