Boiler Mounting - Fusible Plug


Its function is to protect the boiler against damage due to overheating for low water level. It is fitted in the crown of the furnace or firebox at appropriate place.

In the normal working conditions of the boiler, the fusible plug is fully submerged under water. This is so because under normal condition, proper water level is maintained & can be checked by water level indicator. Under the circumstances, the heat from the fusible plug is being conducted to water. This keeps the fusible metal at an almost constant temperature, much below its melting point. When the water level falls below the fusible plug, the plug gets uncovered from water. The upper portion of the plug gets exposed to the steam space. The steam cannot keep the plug cool. This will over heat the fusible metal. The plug falls down along with the fusible metal making a hole. The steam and water, being under pressure immediately reach the firebox and extinguish the fire.

Fig. - Fusible Plug


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