Understanding Boiler Mountings and Their Functions

Boiler mountings are essential components fitted to the boiler for its safe and efficient operation. They perform various functions, including safety, control, and measurement. Let's examine the given pairs of boiler mountings and their listed primary functions to identify the correctly matched one.

Analysing Boiler Mounting Functions

• (i) Manhole - Melts and releases steam if the water level in the boiler drops too down.

  A manhole (or mudhole) is primarily provided for inspection, cleaning, and maintenance purposes, allowing personnel to enter the boiler drum. The device that melts and releases steam when the water level drops too low is typically a fusible plug, which is a safety device to prevent overheating and potential explosion due to low water.

  Therefore, this pairing is incorrect.

• (ii) Feed check valve - Prevents backflow of water into the feed pump.

  The feed check valve is fitted in the feedwater line connecting the feed pump to the boiler. Its main function is to allow water to flow into the boiler but prevent it from flowing back into the feed pump when the pump is stopped or when the boiler pressure is higher than the pump pressure. It acts as a non-return valve.

  This pairing correctly describes the primary function of a feed check valve.

• (iii) Pressure gauge - Releases excess steam from the boiler to prevent overpressure.

  A pressure gauge is a measuring instrument used to indicate the steam pressure inside the boiler. The device responsible for releasing excess steam to prevent the boiler pressure from exceeding a safe limit is the safety valve.

  Therefore, this pairing is incorrect.

• (iv) Fusible plug - Allows the boiler to be drained for inspection and maintenance.

  A fusible plug is a safety device located below the lowest permissible water level. It contains a metal alloy that melts at a specific high temperature. If the water level drops dangerously low, the fusible plug gets exposed to steam and its temperature rises rapidly, causing the alloy to melt. This creates an opening through which steam escapes, alerting the operator and often extinguishing the furnace fire. The component used for draining water from the boiler for inspection and maintenance is the blow-off cock or valve.

  Therefore, this pairing is incorrect.

Identifying the Correct Boiler Mounting Pairing

Based on the analysis of the functions of each boiler mounting listed:

• (i) Manhole's function is incorrect.
• (ii) Feed check valve's function is correct.
• (iii) Pressure gauge's function is incorrect.
• (iv) Fusible plug's function is incorrect.

The only correctly paired boiler mounting and its primary function is the Feed check valve preventing backflow of water into the feed pump.