What are boiler mountings and accessories?

Definition of Boiler:

In today’s article, you are gonna get a brief knowledge on Boiler Accessories and Mountings. So at first let’s look at what is a boiler? A boiler is a closed vessel in which water is heated, vaporized and converted into steam at a pressure higher than the atmospheric pressure. The heat energy required for steam generation is produced by burning fuel in the furnace.

Let’s see what are the boiler mountings and accessories?

So these are the important boiler accessories and mountings we will discuss today:

  • Water level indicator
  • Pressure gauge
  • Safety valve
  • Fusible plug
  • Steam stop valve
  • Blow off valve or blowdown valve
  • Feed check valve
  • Economizer
  • Superheater
  • Steam separator
  • Steam trap
  • Feed pump
  • Injector

Let’s discuss them one by one.

Boiler mountings and accessories

Boiler mountings:

What are the boiler mountings? Boiler mountings are those mechanical appliances which are considered essential for operating a boiler smoothly and safely which are usually mounted on the surface of a boiler.

The followings are the important mountings of a boiler:

  1. Water level indicator
  2. Pressure gauge
  3. Safety valve
  4. Fusible plug
  5. Steam stop valve
  6. Blowoff valve or blowdown valve
  7. Feed check valve

Let me discuss all.

Water level indicator:

The water level indicator located in front of the boiler in such a position that the level of water can easily be seen by the attended.

There are two indicators:

A water level indicator consists of a metal and a strong glass tube with marking. The upper and lower ends of these tubes are connected to two gunmetal hollow pipes.

The upper pipe has a steam valve and the lower pipe has a water valve which is bolted to the boiler plated by two flanges. The upper pipe is opened to the steam and the lower pipe is open to the water with the help of steam and water valves, respectively.

In case of glass gauge breaks accidentally, the water and steam simultaneously rush out through the gunmetal pipe and they are carried away by water and steam and passages are closed. The water and steam valves are then closed and the glass gauge is replaced.

water level indicator diagram
Water level indicator diagram

Pressure gauge:

A pressure gauge is fitted in front of a boiler in such a position that the operated can conveniently read it. It reads the pressure of steam in the boiler and is connected to the steam space by a siphon tube.

pressure gauge diagram
Pressure gauge diagram

Safety valve:

The safety valve is a relief valve that prevents the boiler pressure from raising over its normal working pressure by automatically opening when the boiler pressure exceeds the normal working pressure, thus allowing excess steam to escape into the atmosphere until the pressure comes down on its normal value.

Thus, a safety valve ensures safety to a boiler from being damaged due to excessive steam pressure.

It also ensures safety to a pipe or vessel containing water under high pressure.

There are generally four types of safety valve.

These are:

  1. Lever-type safety valve
  2. Deadweight type of safety valve
  3. Spring-loaded safety valve
  4. High steam and low water safety valve
safety valve diagram
Safety valve diagram

Fusible plug:

The function of a fusible plug is to ensure safety to the boiler from being damaged by overheating due to water level falling very low in the boiler.

fusible plug diagram
Fusible plug diagram

Steam stop valve:

The function of a steam stop valve (this is called main stop valve) is to control the flow of steam from within the boiler and to stop it completely when required.

steam stop valve diagram
Steam stop valve diagram

Blow-off valve or blow-down valve:

The function of a blowoff valve is to remove periodically the sediments deposited at the bottom of the boiler while the boiler is in operation and to empty the boiler while it is to be cleaned or inspected. When the blow-off valve is opened the water which is under the pressure of steam, rushes out with tremendous velocity thus crying out the sediments along with it.

blow off valve diagram
Blow off valve diagram

Feed check valve:

The function of a feed check valve is to control the flow of water from the feed pump to the boiler and to prevent the backflow of water from the boiler to the pump when the pump pressure is less than the boiler pressure or when the feed pump ceases to work.

feed check valve diagram
Feed check valve diagram

Boiler accessories:

What are the boiler Accessories? Boiler accessories are those appliances and plants which are installed along with a boiler to improve the operating condition and overall efficiency of the boiler plant.

There are several boiler accessories, and those are:

  1. Economizer
  2. Superheater
  3. Steam separator
  4. Steam trap
  5. Feed pump
  6. Injector

Let’s discuss them all.


The economizer is a plant in which the feed water is preheated before it enters into a boiler, the heat is taken from the waste flue gases of the boiler


  • Saving of fuel
  • The increase in the evaporative capacity of the boiler.
  • The long life of the boiler.
economizer diagram
Economizer diagram


It is a heat exchanger in which products of the heat of combustion is utilized to dry the wet steam and to make superheated by increasing its temperature.

During superheating of the steam, pressure remains constant and its volume and temperature increase. A superheater consists of a set of small diameter U tube in which steam flows and takes up the heat from hot flue gases.


  1. There is a saving in fuel consumption.
  2. The overall efficiency is increased.
super heater diagram
Superheater diagram

Steam separator:

Saturated steam obtained from all types of industrial boilers contains some water particles which decries the economy and efficiency of steam engines and steam turbines. For this, a steam separator is fitted before the steam engine or steam turbine to separated water particles from steam.

Steam separator diagram
Steam separator diagram

Steam trap:

The function of a steam trap is automatically to drain away or return to the boiler, the water collected in the steam pipe or steam jacket due to partial condensation of steam without allowing steam escape.

Feed pump:

Feed pump delivers feed water at a pressure higher than that in the boiler.

There are two types of feed pumps.

  1. Reciprocating feed pump
  2. Rotary feed pump
  • Reciprocating feed pump:

These are positive displacement type pumps. The most popular types of reciprocating feed pump used in a boiler is a duplex feed pump. It consists of a steam engine and a water pump side by side.

  • Rotary feed pump:

It is a high-speed centrifugal pump and is used to deliver a large quantity of water into the boiler. It consists of impeller and casing.


An injector is a simple device used to supply feed water into the boiler. It has no moving parts and water is supplied into the boiler by the action of steam flowing through nozzles. This type of feed pump is used in locomotives.

Difference between boiler mountings and accessories:

Mountings Accessories
1. Boiler mounting is an essential apparatus without which a boiler cannot be operated. 1. Boiler accessory is not an essential apparatus.
This is used to improve the operating condition and overall efficiency of the boiler plant.
2. Boiler mountings are mounted on the boiler. 2. Boiler accessories are not generally mounted on the boiler but installed within or near the boiler.
3. Boiler mounting occupies less floor space. 3. Boiler accessory occupies comparatively greater floor space.

Also, read the article on

Lathe Machine: Definition, Parts, Types, and Operations”

Boiler: Definition, Types, Parts, Mounting, Accessories, Function, Application with PDF

Video lecture on Boiler Mountings and Accessories:

Source: nptel By: Prof. Ravi Kumar (IIT, Roorkee)


On a concluding note, I hope you are able to understand what are the boiler mountings and accessories and why we need mountings and accessories to run a boiler. I also mentioned a video by Prof Ravi Kumar from IIT, Roorkee, and I encourage you to see his lecture to clear your concepts.

So, If you have any queries or doubts about the lathe machine tool, you can ask me in the comment section or we have a dedicated Q&A platform for you where you directly post your question: Click here to post your question, and also you can join our facebook group. I will love to hear from you and glad to help you. Till then enjoy rest your day. Cheers

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Anup Kumar Dey

A Mechanical Engineer with 19 years of working experience in various renowned MNCs.

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