Question

Which boiling mounting is used to extinguish the fire in the event of water level in the boiler shell falls below a certain limit?

• A. Blow off cock valve
• B. Safety valve
• C. Fusible plug
• D. Spring loaded safety valve

Hint:

Think of the Fusible Plug as the "boiler's fuse." Just like an electrical fuse melts to protect a circuit, the plug melts to protect the boiler shell from melting/overheating.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question refers to boiler safety devices (mountings) and asks for the specific component designed to prevent the boiler from overheating/exploding if the water level drops too low.

Step 2: Detailed Explanation:

• A steam boiler is a pressurized vessel. If the water level inside the shell falls below the heating surfaces, those surfaces will become "dry" and overheat rapidly, potentially leading to catastrophic failure.

• The fusible plug is a safety mounting located at the highest point of the furnace crown (the "fire side" part of the boiler).

• It consists of a hollow plug body with a core made of a low-melting-point alloy (usually tin, lead, or bismuth).

• Under normal conditions, the plug is covered by water, which keeps the alloy cool.

• If the water level falls below the plug, the plug is exposed to steam and the direct heat of the fire. The low-melting-point alloy melts away.

• Once the core melts, high-pressure steam and water from the boiler shell rush through the hole into the furnace. This blast of steam extinguishes the fire, alerting the operator and preventing the boiler from exploding.

• Other options: Safety valves release excess pressure; blow-off cocks are used to remove sludge.

Step 3: Final Answer: The fusible plug is the mounting that extinguishes the fire when the water level is dangerously low.