Power Plant Engineering

What is a Locomotive Boiler? How Does It Work?


A Locomotive Boiler is a Fire tube Boiler, why? Because the hot flue gas passes through the tubes, which are surrounded by water or emerged in water. As fire is present inside the tube, hence it is called so. In this article, we will cover the various parts, applications, specifications, working principles, advantages, and disadvantages of a Locomotive Boiler.

What is a Locomotive Boiler?

A Locomotive Boiler is a horizontal boiler (which means the body is parallel to the plane), multi-tubular (it has more than one flue tube), portable (means can be easily moved from one place to another), internally fired (the combustion chamber is present inside the boiler), naturally circulated (means water is distributed by a natural process e.g. convection currents, not by any centrifugal pump) and low-pressure boiler (means the operating/ working pressure is less than 15 psi) respectively.

In the most straightforward way, it can be stated that Here, the heat or Thermal energy is generated by the burning of fuel (coal), which superheats the saturated steam to get superheated steam. And it drives the wheel of a steam engine in the form of Mechanical energy.

Diagram of Locomotive Boiler

Locomotive Boiler Diagram

Locomotive Boiler Main Parts

The important parts of a Locomotive boiler are given below.

  • Grate: It is like a base or floor section inside the combustion chamber, where the fuel (solid fuel e.g. coal) is burnt. This base plate is made up of cast iron. Why? Because of its high heating capacity. You can see that there is some space between them so that air can pass through them. The whole surface area of a grate where the fuel is burnt is known as a great surface.
  • Fire hole: The small hole is provided at the bottom section of this boiler and is attached to the firebox to place fuel (e.g. coal, oil). Also through this hole, the air is entered into the firebox and combustion chamber, which helps for burning the fuel easily.
  • Firebox (Furnace): Normally the firebox is placed over the grate in this boiler. Practically it plays a mediator role in between the fire holes and the combustion chamber. This furnace is designed in such a way that it deflects back the un-burnt charge particle and directs the flue gases into the combustion chamber.
  • Safety Valve: The safety valve is a mechanical device and also the most important part of this boiler’s construction. It preserves human life as well as the property of the Railway. Normally it prevents the explosion when there is an excessive internal pressure of steam inside this boiler. This mechanical device is designed in such a way that it automatically opens and releases excess internal steam pressure. Similarly, it closes automatically when the internal pressure decreases to the prescribed value.
  • Regulator valve: The driver/ operator turns the lever which is attached to the regulator valve, allowing the saturated steam to move through the main pipe for superheating. In other words, you can say through this valve, an operator can easily operate saturated steam inside the Locomotive Boiler.
  • Superheater element pipe: The saturated steam and the superheated steam is carried out through a series of pipes called superheater element pipe. Then it reaches the superheater header where the saturated steam is again heated to get superheated steam. These are the pipes having a small diameter as compared to the fire tubes.
  • Blast pipe: This is connected above the steam engine through which the exhaust steam is released and creates an artificial draft that pushes the smoke out through the chimney. This creates suction for the hot flue gases.
  • Superheater header: This is the head of the superheater which accepts the saturated steam through the steam pipe from one end. And released Superheated steam to the steam engine through the steam pipe at another end.
  • Chimney: This is an open chamber provided at the upper portion of this boiler. Generally, the lower part of the chamber is attached to the smoke-box and the upper part is opened to the atmosphere. The hot flue gases are coming out from fire tubes to the smokebox and exhausted out through this open chamber which is called a chimney. [Note:- The length of the chimney is shorter because it reduces the air resistance acting on it when the train is at high speed.]
  • Firebrick arch: This is placed inclined over the grate and prevents the entry of ash, dust, and burnt fuel particles into the fire tubes. Also, it deflects the hot flue gases to travel a definite path before entering into the fire tubes of the boiler.
  • Smokebox: This is nothing but a box-like structure where the smoke of burnt fuel and exhaust steam from the shell gets collected. These are exhausted into the atmosphere through the short chimney.

Specification of Locomotive Boiler

The Locomotive boilers are made at Chitranjan Works in India. These data may slightly vary according to the Boiler Manufacturing Companies.

  • No. Of superheater tubes- 38
  • Size of the Superheater tubes- 14 cm
  • Steam generation capacity- 9000 kg/ hr
  • Operating/ working pressure- 14 bar
  • Maximum Steam pressure- 20 bar
  • Rate of evaporation- 55 to 70 kg/ sec
  • Heating surface- 271
  • Grate Area- 4.2 m²
  • Size of fire tubes- 5.72 cm
  • No. Of Fire tubes- 116
  • Barrel/ shell diameter- 8.5 m

Locomotive Boiler Application

  • Locomotive boilers are generally used in Railways and Marines.
  • Apart from that these boilers are used in Steam Rollers, Traction Engines, and Portable Engines.

Locomotive Boiler Working

The solid fuel e.g. coal is fed through the fire hole and burns on a base-like plate e.g. grate. Below the grate, there is an ash pit that collects the waste after burning. Air is supplied through the damper hole into the Ash pit to burn the coal efficiently. The flue gases are formed due to the combustion of coal in the presence of air. These hot flue gases rise from the grate and are deflected by a firebrick arch for their proper distribution to the smoke tubes.

The hot flue gases while passing through the fire tubes transferred their heat energy from the surface of the flue tube to the surrounding water. Then the water is converted into saturated steam. This moves towards the steam dome which is provided to increase the steam release capacity. Then it enters into the main steam pipe through the regulator valve which the driver is operated by turning a lever and reaches the Superheater header.  Here the saturated steam enters into the Superheater element pipes which have a lesser diameter tube inserted into the fire tube. The Superheater reheats the steam again and finally, the Superheated steam flows into the steam pipe of the smoke-box. Then it enters into the cylinder which contains a piston allowing it to move within the cylinder. The piston is connected to the wheels of the steam engine and it starts rotating. The exhaust steam from the cylinder enters the blast pipe and pushes the smoke that is released from the fire tubes through the chimney. However the smoke cannot be released from the boiler on its own, so it is used to create an artificial draft that pushes the smoke out of the smoke-box and creates a suction for the hot exhaust gases.

Locomotive Boiler Advantage

The Locomotive boiler advantages are given below.

  • It is compact in size and its operation is easy.
  • The defective tubes can be replaced easily.
  • The draught loss is minimal compared with other boilers.
  • It provides a high steam production rate.
  • It is a portable boiler.
  • Installation cost is low because it is free from brickwork, special foundation, and chimney.
  • This boiler is capable of meeting sudden and fluctuating demands of steam.

Locomotive Boiler Disadvantage

The Locomotive boiler disadvantages are given below.

  • The overall efficiency is less.
  • Some of its water space is difficult to clean.
  • Due to the overheating issues, it can’t work under heavy load conditions.
  • Corrosion chances are more due to the accumulation of sediments and mud particles.

This is all about “Locomotive Boiler”. Thanks for giving your valuable time. If you have any doubts please don’t hesitate, to ask in the comments section below. If you have any prior experience related to this boiler and know more about it, please share it with us. We promise that we will solve your doubts as soon as possible. If you find this article helpful, consider sharing it with colleagues and friends. Best of luck!

MechStudy Team

MechStudy Team

About Author

Leave a comment

Your email address will not be published. Required fields are marked *

You may also like

Power Plant Engineering

What is a Steam Boiler? How Does it Work?

A steam boiler represents a closed vessel designed to transform fluid, typically water, into steam through the utilization of heat
Power Plant Engineering

What is a Fire Tube Boiler? How Does It Work?

In a Fire Tube Boiler, hot flue gases typically flow through small tubes that are surrounded by or immersed in