Comprehensive Guide For 7 Boiler Mountings And Accessories [PDF]

In today’s article, we shall study Boiler Accessories and mounting. We have also provided a PDF of the same.

Boiler Mountings and Accessories

Definition of 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.

what are the boiler mountings and accessories

  • 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
Boiler Mountings

Boiler mountings

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

The followings are the important mountings of a boiler

  • Water level indicator
  • Pressure gauge
  • Safety valve
  • Fusible plug
  • Steam stop valve
  • Blowoff valve or blowdown valve
  • Feed check valve

Water level indicator

The water level indicator is located in front of the boiler in such a position that the level of water can easily be seen by the attendant. There are two indicators present in a boiler 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.

water level indicator diagram
Water level indicator diagram

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

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 to its normal value. Thus, a safety valve ensures the safety of a boiler from being damaged due to excessive steam pressure. It also ensures the safety of a pipe or vessel containing water under high pressure. There are generally four types of safety valves which are as follows

  • Lever-type safety valve
  • Deadweight type of safety valve
  • Spring-loaded safety valve
  • High steam and low water safety valve
safety valve diagram
Safety valve diagram

Fusible plug

The function of a fusible plug is to ensure the safety of the boiler from being damaged by overheating due to the 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 the 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 being 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

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, which are as follows

  • Economizer
  • Superheater
  • Steam separator
  • Steam trap
  • Feed pump
  • Injector


The economizer is a accessory 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 are utilized to dry the wet steam and to make superheated by increasing its temperature. During the superheating of the steam, pressure remains constant, and its volume and temperature increase. A superheater consists of a set of small diameter U tubes in which steam flows and takes up the heat from hot flue gases.


  • There is a saving in fuel consumption.
  • 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 separate 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 to escape.

Feed pump

The feed pump delivers feed water at a pressure higher than that in the boiler. There are two types of feed pumps which are as follows

Reciprocating feed pump

  • These are positive displacement-type pumps. The most popular type 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 an 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

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

Video lecture on Boiler Mountings and Accessories

Video By NPTEL By: Prof. Ravi Kumar (IIT, Roorkee)


In conclusion, Boiler mountings and accessories are critical components that play a key role in regulating different aspects of boiler operations, ensuring their safe and efficient functioning. It is crucial for boiler operators and maintenance personnel to have a thorough understanding of these components, including their installation and maintenance, to prevent any accidents and optimize boiler performance. The smooth running of industrial processes greatly depends on the proper functioning of boiler mountings and accessories.

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