Brief History of the Steam Engine
Summary by Carl Lira
One of the most significant industrial challenges of the 1700's was the removal of water from mines. Steam was used to pump the water from the mines. Now, this might seem to have very little to do with modern steam-powered electrical power plants. However, one of the fundamental principles used in the development of steam-based power is the principle that condensation of water vapor can create a vacuum. This brief history discusses how condensation was used to create vacuum for operation of early steam-based pumps, and how James Watt invented the separate condenser. Although the cyclic processes presented in this history are not used in today's continuous flow steam turbines, current systems use separate condensers operating at subatmospheric pressure, adapting the principles explained here. Also, the stories of the inventors and their inventions offer insight into the process of technological discovery.
One of the most important priciples applied in the operation of steam power is the creation of vacuum by condensation. This link provides a simple illustration using a soft drink bottle and boiling water. The demo illustrates how condensation within a tank creates a vacuum. Savery's pump explained below uses a method very similar to the demonstrated method. Vacuum Demo.
In the early days, one common way of removing the water was to use a series of buckets on a pulley system operated by horses. This was slow and expensive since the animals required feeding, veterinary care, and housing. The use of steam to pump water was patented by Thomas Savery in 1698, and in his words provided an "engine to raise water by fire". Savery's pump worked by heating water to vaporize it, filling a tank with steam, then creating a vacuum by isolating the tank from the steam source and condensing the steam. The vacuum was used to draw water up from the mines. However, the vacuum could only draw water from shallow depths. Another disadvantage of the pump was the use of steam pressure to expel the water that had been drawn into the tank. In principle, pressure could be used to force the water from the tank upwards 80 feet, but boiler explosions were not uncommon since the design of pressurized boilers was not very advanced. This link has details of operation of the Savery Pump Description..
Newcomen Atmospheric Engine
Thomas Newcomen (1663-1729), a blacksmith, experimented for 10 years to develop the first truly successful steam engine to drive a pump to remove water from mines. His ability to sell the engine was hampered by Savery's broad patent. He was forced to establish a firm with Savery, despite the improved performance of his engine, the significant mechanical differences, the elimination of the need for steam pressure, and the use of vacuum in a very different manner. A schematic of a Newcomen engine is shown in Figure 1. The engine is called an "atmospheric" engine because the greatest steam pressure used is near atmospheric pressure.
Figure 1. Illustration of the Newcomen atmospheric engine for pumping water.
Principle of operation. The steam engine consists of a steam piston/cylinder that moves a large wooden beam to drive the water pump. The engine does not use steam pressure to push up the steam piston! Rather, the system is constructed so that the beam is heavier on the main pump side, and gravity pulls down the main pump side of the beam. Weights are added to the main pump side if necessary. The pumps in Figure 1 expel water on a upward pump piston stroke, in agreement with the pumps used in the equipment at the time, and the discussion follows that design. In order to draw water into the main pump on the right side of the diagram, consider a cycle that starts with the beam tipped down on the right. The cylinder below the steam piston is first filled with atmospheric pressure steam and then water is sprayed into the cylinder to condense the steam. The pressure difference between the atmosphere and the resulting vacuum pushes the steam piston down, pulling the main pump piston upwards, lifting the water above the main pump piston and filling the lower main pump chamber with water. At the bottom of the steam piston stroke, a valve opens to restore the steam cylinder to atmospheric pressure, and the beam tips down on the right by gravity, permitting the main piston to fall. As the main piston falls, the water from below the piston passes to the chamber above the piston as explained later. Atmospheric pressure steam enters the steam cylinder during this step, enabling the process to be repeated.
The Newcomen engine was the best technology for 60 years! Some Newcomen engines were used much longer, even though they were significantly inferior to the Watt engines that followed. For more details of operation and photos of the oldest existing Newcomen engine, see the Newcomen Engine Description.
Watt Atmospheric Steam Engine
Figure 2. Illustration of the Watt atmospheric engine for pumping water. The main pump is not shown. (Adapted from the engraving of Stuart, 1824, p 114.).
Newcomen engines were extremely inefficient. The users recognized how much energy was needed. The steam cylinder was heated and cooled repeatedly, which wasted energy to reheat the steel, and also caused large thermal stresses. James Watt (1736-1819) made a breakthrough development by using a separate condenser. Watt discovered the separate condenser in 1765. (See Watt's Experiment.) It took 11 years before he saw the device in practice! The greatest impediment to the implementation of the Watt engine was the technology to make a large piston/cylinder with close enough tolerances so that they would seal a moderate vacuum. The technology improved about the same time that Watt found the financial backing that he needed through a partnership with Matthew Boulton.
Principle of operation. The Watt engine, like the Newcomen engine, operated on the principle of a pressure difference created by a vacuum on one side of the piston to push the steam piston down. However, Watt's steam cylinder remained hot at all times. Valves permitted the steam to flow into a separate condenser and then condensate was pumped along with any gases using the air pump. (See Figure 2.)
For more details of operation and photos of a couple of Watt engines used for pumping water, see the Watt Engine Description.
The Double-acting Piston and the Rotative Engine
Figure 3. Illustration of the Boulton-Watt double-acting engine. (Adapted from the engraving of Stuart, 1824, p 128).
Watt and Boulton successfully applied their engine to pumping water from wells. Boulton was an industrialist of great vision, and took advantage of the opportunity to apply the engine to other industries. Moving the steam engine indoors, the device became useful for operating mills and textile factories, etc.
The engine pictured at left is an example of an engine from the late 1700s. Note the chain that connected the piston to the beam in earlier engines has been replaced with a parallel motion mechanism. Watt told his son that he was even more proud of this invention than he was of the engine itself. The mechanism made it possible for the piston to act in a perfectly aligned up/down motion while the beam traced an arc. The mechanism also made it possible to transfer work in the upward stroke! Steam is finally doing work by pushing upwards! The boilers used for this device are also atmospheric pressure boilers. The cylinder space above the piston is connected to the condenser vacuum in order to permit the steam to push up the piston.
The engine on the left also contains another improvement that was necessary to operate machinery at a constant speed - a speed governor connected to a throttle valve.
For more details on the double-acting engine, the parallel motion mechanism, the speed governor, as well as the sun and planet gear system (not pictured in Figure 3), including photos, see the Double-acting Engine Description.
Biography of James Watt and the History of the Engine
The story of James Watt and the development of the engine is extremely interesting. Use this link to find the Watt Biography. The story helps you understand how the engine became more than a water pump and how the above developments relate to the man and the times.
Important Dates in the Development of the Steam Engine
Brief Bibliography of Books and Resources for Studying Steam Engines and James Watt
For a directory of the site, click here.
Thank you for your interest!
© 2001-2013, Carl T. Lira, firstname.lastname@example.org
All rights reserved.
Prepared as a supplement to Introductory Chemical Engineering Thermodynamics.