What is the purpose of gauge glasses in a boiler?

• A. To indicate the boiler water level.
• B. To measure steam temperature.
• C. To monitor flue gas composition.
• D. To control boiler pressure.

Answer: (A)

Gauge glasses provide a direct visual indication of the boiler water level by showing the boundary between water and steam in a transparent sight tube connected to the boiler. This visibility lets the operator ensure the water is covering the heat transfer surfaces and stays within safe limits; if the level drops too low, the tubes can overheat and the boiler can be damaged or pose a danger. Readings can be affected by deposits or air leaks, so keeping the gauge glass clean and functional is important. This tool is not used to measure steam temperature, monitor flue gas composition, or control boiler pressure. In short, gauge glasses are used to indicate the boiler water level.