Home Thermal Engineering Steam Engines: Parts, Types, Working Principle, and More

Steam Engines: Parts, Types, Working Principle, and More

In this post, you’ll learn what is a steam engine and different types of steam engines, it’s parts, working and more.

Steam Engines and Types

In steam engines, the steam is utilised as the working substance. Those engines operate on the principle of the first law of thermodynamics, i.e., heat and work are mutually convertible.

In a reciprocating steam engine, as the heat energy in the steam is converted into mechanical work by the reciprocating (to and fro) motion of the piston it is also called a reciprocating steam engine. Moreover, as the combustion of the fuel takes place outside the engine cylinder, it is also called an external combustion engine.

Types of Steam Engines

The steam engines have been classified by various scientists on a different basis.

But the following are the main types of steam engines:

  1. According to the number of working strokes
    1. Single-acting steam engine
    2. Double-acting steam engine
  2. According to the position of the cylinder
    1. Horizontal steam engine
    2. Vertical steam engine
  3. According to the speed of the crankshaft
    1. Slow-speed steam engine
    2. Medium-speed steam engine
    3. High-speed steam engine
  4. According to the type of exhaust
    1. Condensing steam engine
    2. Non-condensing steam engine
  5. According to the expansion of steam in an engine cylinder
    1. Simple steam engine
    2. Compound steam engine
  6. According to the method of governing employed
    1. Throttling steam engine
    2. Automatic cut off the steam engine

Read also: Steam Boilers: Parts, Types, Classification, Advantages, Application.

1. Single-acting Steam Engine

The steam is entered from one side of the piston, and during each revolution of the crankshaft one working stroke is produced, it is called a single-acting steam engine.

2. Double-acting Steam Engine

The steam is entered on both sides of the piston and during each revolution of the crankshaft two working strokes are produced it is known as a double-acting steam engine. The double-acting steam engine produces twice the power than produced by a single-acting steam engine.

3. Horizontal Steam Engine

When the axis of the cylinder is horizontal, it is known as a horizontal steam engine.

4. Vertical Steam Engine

When the axis of the cylinder is vertical it is called a vertical steam engine. The vertical steam engine requires less floor area than the horizontal engine.

5. Slow-speed Steam Engine

When the speed of the crankshaft is less than 100 revolutions per minute (r.p.m.), it is called a slow speed steam engine.

6. Medium-speed Steam Engine

When the speed of the crankshaft is between 25 r.p.m and 100 r.p.m. it is called a medium speed steam engine.

7. High-speed Steam Engine

Similarly, where the speed of the crankshaft is above 250 r.p.m, it is known as a high-speed steam engine.

9. Condensing Steam Engine

When steam after doing work in the cylinder passes into condenser, which condenses the steam into the water at a pressure less than the atmospheric pressure, it is said to be a condensing steam engine.

10. Non-condensing Steam Engine

When the steam after doing work in the cylinder is exhausted into the atmosphere, it is said to be a non-condensing steam engine. The steam pressure in the cylinder is, therefore, not allowed to fall below the atmospheric pressure.

11. Simple Steam Engine

When steam is expanded into a single cylinder and then exhausts into the atmosphere or condenser, it is known as a simple steam engine.

12. Compound Steam Engine

The expansion of the steam is performed in two or more cylinders, the engine is known as a compound steam engine. The compound steam engines are generally condensing engines. But some of them may be non-condensing also.

13. Throttling Steam Engine

When the engine speed is controlled by means throttle valve in the steam pipe, which regulates the pressure of steam to the engine, it is called a throttling steam engine.

14. Automatic cut off Steam Engine

With the help of an automatic cut-off governor, the speed is controlled by controlling the steam pressure, it is known as an automatic cut-off steam engine.

Parts of a Steam Engines

All the parts of a steam engine may be broadly divided into two groups i.e., stationary parts and moving parts. although a steam engine consists of many parts, both stationary and moving, yet

The following are important parts of a steam engine:

  1. Frame
  2. Cylinder
  3. Steam Chest
  4. D-Slide Valve
  5. Inlet and Exhaust Parts
  6. Piston
  7. Piston Rod
  8. Cross-head
  9. Connecting Rod
  10. Crankshaft
  11. Eccentric
  12. Eccentric Rod and Valve Rod
  13. Flywheel
  14. Governor

1. Frame

It is a heavy cast iron part, which supports all the s as well as moving parts and holds them in a proper position. It, generally, rests on engine foundations.

2. Cylinder

It is a cast-iron cylindrical hollow vessel, in which the piston moves back and forth under steam pressure. Both ends of the cylinder are sealed and made steam tight. In small steam engines, the cylinder forms an integral part of the frame.

3. Steam Chest

It is cast as an integral part of the cylinder. It supplies steam to the cylinder with the movement of the D-slide valve.

4. D-slide Valve

D-slide valve moves in the steam chest with simple harmonic motion. Its function is to throw out the exhaust steam from the cylinder at the proper moment.

5. Inlet and Exhaust Parts

Inlet and exhaust are holes provided in the body of a cylinder for the movement of steam. The steam is admitted from the steam chest alternately to either side of the cylinder through the inlet ports. After doing its work in the cylinder, the steam is exhausted through the exhaust port.

6. Piston

It is a cylindrical disc, Moving back and forth, in the cylinder because of the steam pressure. Pistons working is to convert the heat energy of steam into mechanical work. Piston rings are made up of cast iron and are fitted in the grooves in the piston. Their purpose is to prevent the leakage of steam.

7. Piston Rod

It is a circular rod, which is connected to the piston on one side and crosshead to the other. Its function is to transfer motion from a piston to the cross-head.

8. Cross-head

It is a link between the piston rod and the connecting rod. Its function is to control the motion of the piston rod and to prevent it from bending.

9. Connecting rod

It is made of forged steel, whose one end is connected to the crosshead and the other to the crank. Its function is to convert the reciprocating motion of the piston (or crosshead) into rotary motion of the crank.

10. Crankshaft

It is the shaft of the engine that has a crank. The crank operates on the lever principle and produces rotary motion of the shaft. The crankshaft is held on main bearings of the engine.

11. Eccentric

It is generally made of cast iron and is fitted to the crankshaft. Its working is to produce reciprocating motion to the slide valve.

12. Eccentric Rod and Valve Rod

The eccentric rod is made up of forged steel, one end is fixed to the eccentric and other to the valve rod. Its function is to convert the rotary motion of the crankshaft into to and fro motion of the valve rod. The valve rod attaches the eccentric rod and the D-slide valve. Its function is to provide a simple harmonic motion to the D-slide valve.

13. Flywheel

The flywheel is a heavy cast iron wheel, attached on the crankshaft. Its function is to prevent the fluctuation of the engine. It also prevents the jerks from the crankshaft.

14. Governor

Governor is a device which keeps the engine speed, more or less, uniform at load conditions. This is done by either controlling the amount of pressure of steam supplied to the engine.

Working Principle

Working principle of a single cylinder double acting horizontal reciprocating steam engine:

The principal parts of a single-cylinder, double-acting horizontal reciprocating steam engine are shown in the figure.

Single cylinder double acting horizontal reciprocating steam engine

The superheated steam at high pressure (about 20 atmospheres) from the boiler is led into the steam chest. After that, the steam makes its way into the cylinder through any of the ports ‘a’ or ‘b’ depending upon the position of the D-slide valve.

When port ‘a’ is open, the steam rushes to the left side of the piston and forces it to the right. At this stage, the slide valve covers the exhaust port and the other steam port as shown in the figure. Since the pressure of steam is greater on the left side than that on the right side, the piston moves to the right.

When the piston reaches near the end of the cylinder, it closes the steam port ‘a’ and exhaust port. The port ‘b’ is now open, and the steam passes to the right side of the piston.

This forces the piston to the left and at the same time the exhaust steam goes out through the exhaust pipe, and thus completes the cycle of operation. The same process is repeated in other cycles of operation, and as such the engine works.


At the end of each stroke, the piston changes its direction of motion and is momentarily stopped. The crank comes in line with the piston rod. The extreme left and right positions of the crank, where the piston rod exerts no turning tendency on the main shaft, are called dead centres of the crank.

That’s it, Thanks for reading if you like this article on “Types of Steam Engines” please share with your friends. Have any questions to ask leave a comment.

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Saif M
Saif M. is a Mechanical Engineer by profession. He completed his engineering studies in 2014 and is currently working in a large firm as Mechanical Engineer. He is also an author and editor at theengineerspost.com


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