Question:
A device fitted on the crown plate of fire box and used to prevent damage of heating surface in case of low water level is
A device fitted on the crown plate of fire box and used to prevent damage of heating surface in case of low water level is
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The fusible plug is a reliable thermal safety fuse for steam boilers. It uses a low-melting-point alloy that melts when uncovered by water, allowing steam to escape and extinguish the furnace fire before the boiler plates overheat.
Updated On: Jul 23, 2026
- Water level indicator
- Safety valve
- Fusible plug
- Steam trap
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Verified By Collegedunia
The Correct Option is C
Solution and Explanation
Step 1: Understanding the Concept:
Steam boilers operate under high pressures and temperatures, requiring safety mountings to prevent structural failure or explosions during operation.
If the water level inside the boiler falls below a critical level, the heating surfaces can overheat, causing severe structural damage.
Step 2: Detailed Explanation:
Let us analyze the function of each boiler mounting:
- Water level indicator: A glass tube that allows operators to visually monitor the water level inside the boiler shell, but does not actively prevent damage.
- Safety valve: Releases excess steam pressure to prevent over-pressurization of the boiler.
- Steam trap: Discharges condensed water from steam lines without letting steam escape.
- Fusible plug: This safety device is fitted on the crown plate of the furnace or firebox, directly above the combustion chamber.
- Under normal conditions, the plug is fully submerged in water, which keeps its temperature below the melting point of its low-melting-point alloy core (made of tin, lead, or bismuth).
- If the water level drops dangerously low, the plug is uncovered.
- The dry crown plate heats up rapidly, melting the fusible alloy core.
- This allows high-pressure steam and water to escape from the boiler into the firebox, extinguishing the fire and preventing catastrophic damage to the boiler.
Therefore, the fusible plug is the device used for this purpose.
Step 3: Final Answer:
The safety device used to prevent damage due to low water levels is the fusible plug. Hence, the correct option is (C).
Steam boilers operate under high pressures and temperatures, requiring safety mountings to prevent structural failure or explosions during operation.
If the water level inside the boiler falls below a critical level, the heating surfaces can overheat, causing severe structural damage.
Step 2: Detailed Explanation:
Let us analyze the function of each boiler mounting:
- Water level indicator: A glass tube that allows operators to visually monitor the water level inside the boiler shell, but does not actively prevent damage.
- Safety valve: Releases excess steam pressure to prevent over-pressurization of the boiler.
- Steam trap: Discharges condensed water from steam lines without letting steam escape.
- Fusible plug: This safety device is fitted on the crown plate of the furnace or firebox, directly above the combustion chamber.
- Under normal conditions, the plug is fully submerged in water, which keeps its temperature below the melting point of its low-melting-point alloy core (made of tin, lead, or bismuth).
- If the water level drops dangerously low, the plug is uncovered.
- The dry crown plate heats up rapidly, melting the fusible alloy core.
- This allows high-pressure steam and water to escape from the boiler into the firebox, extinguishing the fire and preventing catastrophic damage to the boiler.
Therefore, the fusible plug is the device used for this purpose.
Step 3: Final Answer:
The safety device used to prevent damage due to low water levels is the fusible plug. Hence, the correct option is (C).
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