What is the purpose of a gauge glass in a boiler?

The purpose of a gauge glass in a boiler is to provide a visual indication of the water level within the boiler. This is crucial for safe and efficient boiler operation. The gauge glass allows operators to directly observe the water level, ensuring that it remains within safe operating limits. Maintaining the correct water level is essential to preventing damage to the boiler, such as overheating or potentially causing a failure due to low water levels which can lead to a dangerous situation.

Other options mentioned, such as displaying boiler pressure, measuring fuel efficiency, or indicating temperature fluctuations, are functions typically associated with other instruments in a boiler system. Pressure gauges monitor the steam pressure, various sensors and meters assess fuel efficiency, and thermometers or thermocouples track temperature changes. However, the gauge glass is specifically dedicated to showing the water level, making option B the appropriate choice.