What is typically the last warning indicator for low water in a boiler?

The fusible plug serves as a crucial safety device in a boiler system, particularly regarding low water levels. It is typically made of a metal alloy with a low melting point that melts when the temperature reaches a certain threshold, usually due to insufficient water levels. When the water in the boiler drops below a safe level, the temperature will rise significantly, causing the fusible plug to melt and create an opening. This allows steam to escape, which can provide a last-minute warning that the water level is too low before more severe damage occurs, such as overheating or a potential explosion.

This mechanism acts as a final fail-safe, designed to function when other indicators, like visual gauges or alarms, may fail or not be heeded. It is an essential feature in the boiler's safety design, protecting not just the equipment but also ensuring the safety of personnel in the area.