What should consistently be visible in the gauge glass during boiler operation?

During the operation of a boiler, it is essential for the gauge glass to consistently display water. The gauge glass provides a visual indication of the water level within the boiler. This is crucial for safe operations because maintaining the appropriate water level is necessary to prevent overheating and possible damage to the boiler components. If the water level is too low, parts of the boiler could be exposed to steam, leading to overheating, while too much water can cause improper steam formation.

Having a visible water level helps operators to monitor and ensure that the boiler is functioning correctly and that it is within operational safety limits. In contrast, steam, oil, and pressure are not typically represented in the gauge glass; steam indicates a change in state, oil is not part of the water level monitoring, and pressure is monitored through pressure gauges, not the gauge glass. Therefore, seeing water in the gauge glass is the best indicator of safe and proper boiler operation.