It is very important safety device, which protects the fire tube boiler against overheating.
- It is located just above the furnace in the boiler.
- It consists of gun metal plug fixed in a gun metal body with fusible molten metal.
Figure : Fusible Plug
- During the normal boiler operation, the fusible plug is covered by water and its temperature does not rise to its melting state.
- But when the water level falls too low in the boiler, it uncovers the fusible plug.
- The furnace gases heat up the plug and fusible metal of plug melts, the inner plug falls down
- The water and steam then rush through the hole and extinguish the fire before any major damage occurs to the boiler due to overheating.