In a steam system, what is the function of a sight glass?

A sight glass serves the critical function of visually indicating the water level in the boiler. This allows engineers to monitor the amount of water present directly without the need for complex measurement devices. Maintaining an appropriate water level is essential for safe boiler operation, as both low and high water levels can lead to operational issues. Low water conditions can cause overheating and damage to the boiler, while high water levels can lead to water carryover into the steam system, potentially causing damage to pipes and equipment.

The other options do not align with the primary role of a sight glass. It does not measure steam pressure, monitor temperature, or release excess steam; those functions are managed by other components of the steam system, like pressure gauges, thermometers, and safety valves, respectively. Understanding the specific role of the sight glass is vital for maintaining safe and efficient boiler operations.