locomotive boiler

A locomotive boiler is a device which is used to create steam from water by using heat energy. It is a horizontal drum axis, multi-tubular, natural circulation, artificial draft, forced circulation, mobile, medium pressure, solid fuel fired fire tube boiler that has an internal fire furnace. It is capable of producing high steam rate and hence it is used for railway locomotive engines and in marines.

Construction of locomotive boiler-

A locomotive boiler comprises of various parts, and going through each part will make us understand the construction of a locomotive boiler. These parts are mentioned below:

locomotive boiler

1.Fire hole: This hole is used to insert solid fuel and ignite it in the furnace. It is located at the rear end of a boiler.

2.Fire box: In this box, burning of fuel takes place.

3.Grate: It is the platform on which fuel is kept and ignited.

4.Firebrick arch: It is placed over the grate in an inclined position to stop the entry of dust, ash, and burnt fuel particles into fire tubes. It allows the movement of fuel gases in such a way that they move in a definite path before going into the fire tubes of the boiler.

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5.Boiler tubes: Through these tubes, hot flue gases pass and exchange the heat with the surrounding.

6.Smokebox: The burnt fuel smoke, after passing through fire tubes, get collected in the smoke box and then released into the environment through the chimney.

7.Blast pipe: It is located above the steam engine and exhaust steam is passed through this pipe. It creates an artificial draft that pushes the smoke out through the chimney. Also, it creates suction for hotter flue gases in order to move forward through the fire tubed.

8.Steampipe: Steam is passed through the steam pipe. There are two types of steam pipes; one is used between superheater and dome which is called as main steam pipe and another is used between superheater end exit and steam engine.

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9.Superheater: The steam is superheated with the help of superheater at the desired temperature before entering into the steam engine cylinder.

10.Superheater element pipes: These pipes are present in the superheater through which steam moves and gets superheated.

11.Dome: It is used to regulate the steam generated through the steam pipe. It is located on the top.

12.Regulator valve: During the superheating process, this valve regulates the steam through the main steam pipe.

13.Safety valve: For a safe working steam pressure this valve is used. When pressure is more than the safety level, it blows off and prevents the boiler from blasting.

14.Superheater header: To accept the steam from the steam pipe, superheater header is used.

15.Chimney: To send out the exhaust smoke and gases from the boiler, a chimney is used which has a very small length.

Working of a locomotive boiler-

The locomotive boiler works with the insertion of solid fuel on the grate and then igniting it through the fire hole. As the fuel is burnt, it produces hot flue gases. These hot flue gases are moved through a definite path by firebrick arch into the long fire tubes and heat the water in the surrounding. As the heating continues, the water starts converting into saturated steam which gets collected at the top.

locomotive boiler

Then, from the dome, this saturated steam gets into the main steam pipe via regulator valve and reaches into the superheater header. The steam enters into the pipes of superheater element to get superheated and then transferred to the steam pipe of smoke box.

The steam from the superheater then enters into the cylinder which contains a piston. With the pressure exerted by the steam, the piston is moved. The piston is connected to the wheels of a locomotive, thus power is directly transferred to the wheels and they start rotating.

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The burnt gases and smoke are transferred to the smoke box through fire tubes and exhaust steam from the cylinder is transferred to the blast pipe. The exhaust steam pushes out the smoke from the boiler through the chimney, by coming out from the blast pipe. However, the smoke doesn’t move out from the boiler on its own, therefore artificial draft is made by exhaust steam that comes out of the steam engine. This artificial draft pushes the smoke out and simultaneously creates suction for hot flue gases.

Advantages and disadvantages of locomotive boiler-


  • It can meet the fluctuating need of steam and can be ported easily.
  • It provides high steam production rate.
  • Its operation is easy and it is cost effective along with a compact size.


  • Over time, it gets corroded and scale is formed.
  • Gets overheated when works under heavy load.
  • Cleaning of some water spaces is not easy.

Application of locomotive boiler-

The locomotive boiler has low efficiency and cannot be used under heavy load because of its overheating problem. They are commonly used in the railways and marines. In addition, they can be used in a portable steam engine, steam rollers, traction engines, and in other steam road vehicles.


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