Boiler mountings and accessories | The Mechanical post


A boiler is a closed vessel used extensively for steam generation. The boiler is a very important part of the Steam power plant. It is used for steam generation at a desired pressure and temperature. 

This steam is then used for various purposes like power generation, heating and drying purposes and many more industrial applications.

Boiler mountings and accessories | The Mechanical post

Read about What is a boiler? its types, applications and much more in detail here.

To download the PDF on Boiler mountings and accessories click on the button provided at the end of the article.

What is boiler mounting?

Boiler mountings are the essential devices mounted on the boiler and are responsible for the safe and smooth operation of the boiler.

Following are the boiler mountings:

  • Safety valve
  • Fusible plug
  • Water level indicator
  • Feed check valve
  • Steam pressure gauge
  • Steam stop valve
  • Blow-off cock

Now let's discuss the boiler mountings in detail

1. Safety valve.

Sometimes, when there is a sudden drop in the requirement of steam, the steam pressure in the boiler increases as a consequence. This increase in pressure is dangerous.

MbeychokCC BY-SA 3.0, via Wikimedia Commons

Therefore, a safety valve is used. Its main function is to discharge the steam to the atmosphere when the pressure inside the boiler exceeds a certain limit. The safety valve is mounted at the top of the boiler. 

The different types of safety valve used are:

1. Dead weight safety valve.

2. Lever safety valve.

3. Spring-loaded safety valve.

2. Water level indicator

As the name suggests, the function of the water level indicator is to indicate the level of water inside the boiler. It also warns the operator if the water level in the boiler goes below a certain limit, so that accidents can be prevented.

Image by- Learn and Grow youtube channel

Watch the video of the construction and working of water level indicator by Learn and grow here. (* not sponsored)

Water level indicator consists of three cocks and a glass tube. The steam cock 1 keeps the glass in connection with the steam space and cock 2 puts the glass tube in connection with the water space in the boiler.

The drain cock 3 is used to drain out the water from the glass at intervals to ascertain that the steam and the water cocks are clear in operation. The glass tube is protected with a shield. 

3. Fusible plug 

The main function of the fusible plug is to protect the firebox crown plate or fire tubes from burning when the water level in the boiler falls down suddenly to unsafe level and thus to prevent any accident.

Image by -

It consists of a hollow gunmetal body screwed into the crown plate. In this hollow gunmetal body, second hollow gunmetal is screwed. In this second hollow gunmetal body fusible plug is locked with a fusible metal.

Fusible metal is made up  of a low point melting temperature metal, which acts as bonding material under normal working condition but when the water level decreases in the boiler, the fusible plug gets exposed to the high temperature steam.

This high temperature steam melts the fusible metal i the fusible plug.

By melting fusible material, fusible plug drops in creating a passage to allow steam to rush the water into the furnace and extinguish the fire. Thus, the fusible plug protects the boiler from the danger of overheating due to low water levels.

4. Steam pressure gauge

Image source - Pixabay

The function of pressure gauge is to display the pressure of steam inside the boiler. It is mounted on the top of shell in the front portion. It acts as an indicator and warning sign when the pressure in the boiler exceeds a certain limit.

5. Feed check valve

Image from -

The function feed check valve is to regulate the supply of feed water to the boiler at high pressure at a continuous rate and to prevent the backflow of water when pump pressure is less than the boiler pressure or when the pump fails.

6. Steam stop valve 

The function of the steam stop valve is to control the flow of steam from the boiler to the turbine or for any other application and shut-off the steam flow when not required. This valve can be manipulated manually or automatically. 

7. A blow-off cock

Blow off cock

The function of blow-off cock is as follows: 

1. To empty the boiler whenever necessary for cleaning, repair and inspection.

2. To remove the mud and sediments collected in the bottom part of the boiler.

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What are boiler accessories?

Boiler accessories are the devices which are used for smooth operation and for improving efficiency of the boiler.

Sm faysalCC BY-SA 3.0, via Wikimedia Commons

The different types of boiler accessories are:

1. Economiser.

2. Superheater.

3. Steam injection.

4. Air preheater.

Air preheater

Air preheater is used to heat gas/air entering the combustion chamber by recovering the heat from flue or waste gases when it comes out of economiser. 

Air preheater is installed between the economiser and chimney. This helps in reducing thermal stresses within the boiler.

Air pre-heater

Advantages of air preheater:

1. Preheated air helps in achieving higher furnace temperature.

2. Better combustion is achieved.

3. Preheated air helps achieve more stable flame which reduces smoke.

4. It allows low-grade coal to be burnt with less surplus of air.


The function of economiser is to recover some of the heat from flue or waste gases up the chimney and use it for the heating feed water supplied to the boiler.

Image by - Learn and Grow youtube channel

Watch its working animation by Learn and Grow here. (* not sponsored)

Advantages of economiser:

1. Increase in the thermal efficiency of the boiler. Every 6°C rise in temperature increase the thermal efficiency by 1%.

2. Increase in evaporative capacity of the boiler.


The function of superheater in the boiler is to increase the temperature of steam above its saturation temperature. This is achieved by passing the steam through a small set of tubes while hot flue gases flow over the them. 

Advantages of superheater:

1. Superheated stream helps reduce the specific steam consumption of engine or turbine.

2. It reduces the condensation losses in the pipe.

3. Superheating eliminates the turbine blade's erosion in the last stage

Feed pump

The feed pump is used to deliver the feed water in the boiler against the boiler pressure. It continuously feeds the water equal to the evaporating capacity of the boiler and maintains the water level in the boiler almost constant. 

Steam injector

The injector is a water feeding apparatus to the boiler by utilizing steam at high pressure to feed water. It makes use of the kinetic energy of steam to increase the pressure and velocity of the water.

Johannes RösselCC BY 3.0, via Wikimedia Commons

Advantages of steam injector:

1. Less initial expense.

2. Maintenance costs are low.

3. Compact size.

4. Easy to operate.

5. Simple in construction

Some FAQ

Can a boiler work without mounting?

No, mountings are a essential part of the boiler without which the boiler can't operate safely and efficiently.

What is the difference between boiler mountings and accessories?

The main difference between boiler mountings and accessories is that the boiler can function without accessories whereas without boiler mountings a boiler cannot function.

What is the use of boiler accessories?

Boiler accessories are used to increase the efficiency of the boiler.


So that's all about Boiler moutings and accessories. Do follow The Mechanical post on social media to never miss an update. Follow links are give in the footer!

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