What is a fusible plug?

A fusible plug is a safety device designed to prevent overheating conditions within a boiler. Specifically, it functions by providing a means to relieve excess pressure when the temperature exceeds a certain threshold. When the temperature gets too high, the fusible plug begins to melt, allowing water or steam to escape, which helps to prevent a potential explosion or catastrophic failure. This feature is crucial for protecting the integrity of a boiler and ensuring safe operation.

The other options describe different components or safety measures in boiler systems. For example, a safety feature for low water levels is important, as low water conditions can lead to overheating. Blowdown valves are used to remove sediment buildup, and pressure gauges measure steam pressure to ensure operations remain safe and efficient. However, none of these serve the same protective function as a fusible plug in the context of extreme overheating scenarios.