Md. Mohiuddin

Lecturer

Department of Mechanical Engineering

ME 1105

Boiler Mountings

Basic Mechanical Engineering

Boiler Mountings

• Mountings are the fittings that are mounted on the boiler for its proper and safe functioning.

• Some important boiler mountings are
• Water level indicators/Water Gauge
• Pressure gauge
• Safety valves 
• Fusible plug    
• Steam stop valve or Junction Valve     
• Feed check valve
• Blow off cock
• Manhole and Hand hole
• Steam Scrubbers/Anti-priming pipe

Water Level Indicator

Function:

• Indicates the water level inside the boiler to an operator
• Helps in regulating the supply of feed water to maintain the correct water level.

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Location: Usually two indicators are located at the front of the boiler.

Safety Valve

Function:

• The function of a safety valve is to prevent the accumulation of excessive pressure within a steam boiler.
• When the steam pressure inside the boiler drum exceeds the designated working pressure, the safety valve allows the release of steam into the atmosphere until the boiler's safe working pressure is reached again.
• Additionally, the safety valve alerts the boiler operator by providing a signal of the release of steam.

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Principle of Operation: A valve is pressed against its seat by an external force. When the pressure within the boiler exceeds the designed safe limit, the force exerted by the steam pressure on the valve causes it to lift off from its seat, creating an opening that allows steam to be discharged from the boiler until the pressure returns to the safe level.

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Numbers and Location: Each boiler must be fitted with at least two safety valves. Safety valves are located above the steam space in the boiler.

Safety Valve

Safety Valve

Types of Safety Valves:

• Dead weight safety valve   
• Spring loaded safety valve
• Lever safety valve
• High steam and low water safety valves.

Pressure Gauge

• Number and Location: 
• All boilers must be fitted with at least one pressure gauge
• it is  usually mounted at the front top of the boiler shell or drum so that attendant can easily read the pressure reading.

Fusible Plug

Function:

• The purpose of the fusible plug is to protect the heating surface of the boiler from overheating when the water level inside the boiler falls below the safe limit.
• Its objective is to put off the fire in the furnace of the boiler when the level of water in the boiler falls to an unsafe limit and thus, avoid explosion.

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Location: It is fitted to the crown plate of the furnace.

Fusible Plug

Working:

• Under normal water level conditions:
• The fusible plug attached to the furnace is submerged in water.
• Since water is always present for heat transfer from the hot gases in the furnace, the temperature of the fusible metal remains below its melting point.
• This ensures that the solid copper plug stays in place which allows the normal steam generation process in the boiler to proceed.

Fusible Plug

Working:

• In situations where the water level drops below the lower limit in the boiler:
• The fusible plug becomes uncovered and is exposed to steam only.
• Without water as a heat transfer medium for the hot gases in the furnace, both plugs 'B' and 'C' become overheated.
• This overheating leads to the initial melting of the fusible metal, causing the release of the copper plug 'C,' which falls as shown in the figure.
• This opening creates a passage between the steam space and the furnace, thus, allowing steam to go into the firebox
• The steam extinguishes the fire and halts the steam generation process.

Steam Stop Valve

Function:

• To control the flow of steam from the boiler to the main steam pipe.
• To shut off the steam completely when required.
• To regulate the flow of steam from one steam pipe to another.

Location:

• In the boiler, it is usually located to the highest part of the shell.
• Between steam pipes to regulate flow from one steam pipe to another.

Steam Stop Valve

Working:

• During regular boiler operation:
• The valve is in an open position, allowing steam to flow from the boiler to the steam pipe, as illustrated in Figure (a).

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• When the boiler is shut down or when steam is not needed from the boiler:
• The valve is closed by turning the handwheel, as shown in Figure (b). This closing halts the steam flow from the boiler to the steam pipe.

Function:

• To control the supply of feed water to the boiler from the feed pump
• To prevent any water escaping back from the boiler in the event of failure of the feed pump or when the pump pressure is less than the boiler side.

Feed Check Valve

Working:

• During regular boiler operation when the feed pump functions correctly:
• The water supply to the boiler is regulated by manually adjusting the feed valve by raising or lowering it from its seat using a handwheel, as illustrated in Figure (a).
• In this state, the higher water pressure on the feed pump side of the check valve causes the valve to lift from its seat thus allowing water to enter the boiler and maintain a consistent water level.

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• In the event of feed pump failure or insufficient pump pressure compared to the boiler side:
• The feed valve remains in the open position, as shown in Figure (b).
• However, due to the lower water pressure on the feed pump side of the check valve, the valve is pressed onto its seat thus preventing the backflow of water from the boiler to the water pump.

Feed Check Valve

Function:

• To blow out sediments, precipitated sludge, loose scale, or other impurities periodically when the boiler is in operation.
• To empty the boiler when necessary for cleaning, repair, and inspection.
• To permit rapid lowering of water level in the boiler if accidentally it becomes too high.

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Location: It is located at the bottom of the boiler shell.

Blow-off Cock

Working

Blow-off Cock

Some Additional Components

Manhole and Handhole

• Man holes and hand holes are required for cleaning, inspection, and repairing of the boiler. The manhole is provided for the entrance of a man inside the boiler shell whereas the hand hole is for a hand.

Steam Scrubbers/Anti-priming pipe

• The steam in contact with the water surface always contains water particles.
• A steam scrubber also known as a steam drier is used in a boiler to remove the water particles contained in steam.

Air vent/Vacuum breaker

• It is used to eliminate air from steam space of the boiler.

Soot blowers

• It is used to blow soot and the combustion products from the tube surfaces.

Thank You