Watt steam engine
Watt steam engine (alternatively known as the Boulton and Watt
steam engine) was the first type of steam engine to make use of a
separate condenser. It was a vacuum or "atmospheric" engine using
steam at a pressure just above atmospheric to create a partial vacuum
beneath the piston. The difference between atmospheric pressure above
the piston and the partial vacuum below drove the piston down the
James Watt avoided the use of high pressure steam because of
safety concerns. Watt's design became synonymous with steam
engines, due in no small part to his business partner, Matthew
The Watt steam engine, developed sporadically from 1763 to 1775, was
an improvement on the design of the 1712
Newcomen steam engine
Newcomen steam engine and was
a key point in the Industrial Revolution. It was the first design to
use a separate condenser.
Watt's two most important improvements were the separate condenser and
rotary motion. The separate condenser, located externally to the
cylinder, condensed steam without cooling the piston and cylinder
walls as did the internal spray in Newcomen's engine. Watt's engine's
efficiency was more than double that of the Newcomen engine. Rotary
motion was more suitable for industrial power than the oscillating
beam of Newcomen's engine.
2 Separate condenser
3 The Partnership of
Matthew Boulton and James Watt
4 Later improvements
5 Preserved Watt engines
6 Watt engine produced by Hathorn, Davey and Co
7 Recent developments
8 See also
10 External links
In 1698, the English mechanical designer
Thomas Savery invented a
pumping appliance that used steam to draw water directly from a well
by means of a vacuum created by condensing steam. The appliance was
also proposed for draining mines, but it could only draw fluid up
approximately 25 feet, meaning it had to be located within this
distance of the mine floor being drained. As mines became deeper, this
was often impractical. It also consumed a large amount of fuel
compared with later engines.
The model Newcomen engine upon which Watt experimented
The solution to draining deep mines was found by
Thomas Newcomen who
developed an "atmospheric" engine that also worked on the vacuum
principle. It employed a cylinder containing a movable piston
connected by a chain to one end of a rocking beam that worked a
mechanical lift pump from its opposite end. At the bottom of each
stroke, steam was allowed to enter the cylinder below the piston. As
the piston rose within the cylinder, drawn upward by a counterbalance,
it drew in steam at atmospheric pressure. At the top of the stroke the
steam valve was closed, and cold water was briefly injected into the
cylinder as a means of cooling the steam. This water condensed the
steam and created a partial vacuum below the piston. The atmospheric
pressure outside the engine was then greater than the pressure within
the cylinder, thereby pushing the piston into the cylinder. The
piston, attached to a chain and in turn attached to one end of the
"rocking beam", pulled down the end of the beam, lifting the opposite
end of the beam. Hence, the pump deep in the mine attached to opposite
end of the beam via ropes and chains was driven. The pump pushed,
rather than pulled the column of water upward, hence it could lift
water any distance. Once the piston was at the bottom, the cycle
The Newcomen engine was more powerful than the Savery engine. For the
first time water could be raised from a depth of over 150 feet. The
first example from 1712 was able to replace a team of 500 horses that
had been used to pump out the mine. Seventy-five Newcomen pumping
engines were installed at mines in Britain, France, Holland, Sweden
and Russia. In the next fifty years only a few small changes were made
to the engine design. It was a great advancement.
While Newcomen engines brought practical benefits, they were
inefficient in terms of the use of energy to power them. The system of
alternately sending jets of steam, then cold water into the cylinder
meant that the walls of the cylinder were alternately heated, then
cooled with each stroke. Each charge of steam introduced would
continue condensing until the cylinder approached working temperature
once again. So at each stroke part of the potential of the steam was
The major components of a Watt pumping engine
James Watt was working as instrument maker at the University
of Glasgow when he was assigned the job of repairing a model Newcomen
engine and noted how inefficient it was.
In 1765, Watt conceived the idea of equipping the engine with a
separate condensation chamber, which he called a "condenser". Because
the condenser and the working cylinder were separate, condensation
occurred without significant loss of heat from the cylinder. The
condenser remained cold and below atmospheric pressure at all times,
while the cylinder remained hot at all times.
Steam was drawn from the boiler to the cylinder under the piston. When
the piston reached the top of the cylinder, the steam inlet valve
closed and the valve controlling the passage to the condenser opened.
The condenser being at a lower pressure, drew the steam from the
cylinder into the condenser where it cooled and condensed from water
vapor to liquid water, maintaining a partial vacuum in the condenser
that was communicated to the space of the cylinder by the connecting
passage. External atmospheric pressure then pushed the piston down the
The separation of the cylinder and condenser eliminated the loss of
heat that occurred when steam was condensed in the working cylinder of
a Newcomen engine. This gave the Watt engine greater efficiency than
the Newcomen engine, reducing the amount of coal consumed while doing
the same amount of work as a Newcomen engine.
In Watt's design, the cold water was injected only into the
condensation chamber. This type of condenser is known as a jet
condenser. The condenser is located in a cold water bath below the
cylinder. The volume of water entering the condenser as spray absorbed
the latent heat of the steam, and was determined as seven times the
volume of the condensed steam. The condensate and the injected water
was then removed by the air pump, and the surrounding cold water
served to absorb the remaining thermal energy to retain a condenser
temperature of 30°C to 45°C and the equivalent pressure of 0.04 to
0.1 bar 
At each stroke the warm condensate was drawn off from the condenser
and sent to a hot well by a vacuum pump, which also helped to evacuate
the steam from under the power cylinder. The still-warm condensate was
recycled as feedwater for the boiler.
Watt's next improvement to the Newcomen design was to seal the top of
the cylinder and surround the cylinder with a jacket. Steam was passed
through the jacket before being admitted below the piston, keeping the
piston and cylinder warm to prevent condensation within it. The second
improvement was the utilisation of steam expansion against the vacuum
on the other side of the piston. The steam supply was cut during the
stroke, and the steam expanded against the vacuum on the other side.
This increased the efficiency of the engine, but also created a
variable torque on the shaft which was undesirable for many
applications, in particular pumping. Watt therefore limited the
expansion to a ratio of 1:2 (i.e. the steam supply was cut at half
stroke). This increased the theoretical efficiency from 6.4% to 10.6%,
with only a small variation in piston pressure. Watt did not use
high pressure steam because of safety concerns.:85
These improvements led to the fully developed version of 1776 that
actually went into production.
The Partnership of
Matthew Boulton and James Watt
Main article: Boulton and Watt
The separate condenser showed dramatic potential for improvements on
the Newcomen engine but Watt was still discouraged by seemingly
insurmountable problems before a marketable engine could be perfected.
It was only after entering into partnership with
Matthew Boulton that
such became reality. Watt told Boulton about his ideas on improving
the engine, and Boulton, an avid entrepreneur, agreed to fund
development of a test engine at Soho, near Birmingham. At last Watt
had access to facilities and the practical experience of craftsmen who
were soon able to get the first engine working. As fully developed, it
used about 75% less fuel than a similar Newcomen one.
In 1775, Watt designed two large engines: one for the Bloomfield
Colliery at Tipton, completed in March 1776, and one for John
Wilkinson's ironworks at Willey, Shropshire, which was at work the
following month. A third engine, at Stratford-le-Bow in east London,
was also working that summer.
Watt had tried unsuccessfully for several years to obtain an
accurately bored cylinder for his steam engines, and was forced to use
hammered iron, which was out of round and caused leakage past the
piston. Joseph Wickham Roe stated in 1916: "When [John] Smeaton saw
the first engine he reported to the Society of Engineers that 'Neither
the tools nor the workmen existed who could manufacture such a complex
machine with sufficient precision'".
In 1774, John Wilkinson invented a boring machine in which the shaft
that held the cutting tool was supported on both ends and extended
through the cylinder, unlike the cantilevered borers then in use.
Boulton wrote in 1776 that "Mr. Wilkinson has bored us several
cylinders almost without error; that of 50 inches diameter, which we
have put up at Tipton, does not err on the thickness of an old
shilling in any part".
Boulton and Watt's practice was to help mine-owners and other
customers to build engines, supplying men to erect them and some
specialised parts. However, their main profit from their patent was
derived from charging a licence fee to the engine owners, based on the
cost of the fuel they saved. The greater fuel efficiency of their
engines meant that they were most attractive in areas where fuel was
expensive, particularly Cornwall, for which three engines were ordered
in 1777, for the Wheal Busy, Ting Tang, and
Watt's parallel motion on a pumping engine
The first Watt engines were atmospheric pressure engines, like the
Newcomen engine but with the condensation taking place separate from
the cylinder. Driving the engines using both low pressure steam and a
partial vacuum raised the possibility of reciprocating engine
development. An arrangement of valves could alternately admit low
pressure steam to the cylinder and then connect with the condenser.
Consequently, the direction of the power stroke might be reversed,
making it easier to obtain rotary motion. Additional benefits of the
double acting engine were increased efficiency, higher speed (greater
power) and more regular motion.
Before the development of the double acting piston, the linkage to the
beam and the piston rod had been by means of a chain, which meant that
power could only be applied in one direction, by pulling. This was
effective in engines that were used for pumping water, but the double
action of the piston meant that it could push as well as pull. This
was not possible as long as the beam and the rod were connected by a
chain. Furthermore, it was not possible to connect the piston rod of
the sealed cylinder directly to the beam, because while the rod moved
vertically in a straight line, the beam was pivoted at its centre,
with each side inscribing an arc. To bridge the conflicting actions of
the beam and the piston, Watt developed his parallel motion. This
masterpiece of engineering uses a four bar linkage coupled with a
pantograph to produce the required straight line motion much more
cheaply than if he had used a slider type of linkage. He was very
proud of his solution.
Watt steam engine
Having the beam connected to the piston shaft by a means that applied
force alternately in both directions also meant that it was possible
to use the motion of the beam to turn a wheel. The most simple
solution to transforming the action of the beam into a rotating motion
was to connect the beam to a wheel by a crank, but because another
party had patent rights on the use of the crank, Watt was obliged to
come up with another solution. He adopted the epicyclic sun and
planet gear system suggested by an employee William Murdoch, only
later reverting, once the patent rights had expired, to the more
familiar crank seen on most engines today. The main wheel attached
to the crank was large and heavy, serving as a flywheel which, once
set in motion, by its momentum maintained a constant power and
smoothed the action of the alternating strokes. To its rotating
central shaft, belts and gears could be attached to drive a great
variety of machinery.
Because factory machinery needed to operate at a constant speed, Watt
linked a steam regulator valve to a centrifugal governor which he
adapted from those used to automatically control the speed of
windmills. The centrifugal was not a true speed controller because
it could not hold a set speed in response to a change in load.
These improvements allowed the steam engine to replace the water wheel
and horses as the main sources of power for British industry, thereby
freeing it from geographical constraints and becoming one of the main
drivers in the Industrial Revolution.
Watt was also concerned with fundamental research on the functioning
of the steam engine. His most notable measuring device, still in use
today, is the Watt indicator incorporating a manometer to measure
steam pressure within the cylinder according to the position of the
piston, enabling a diagram to be produced representing the pressure of
the steam as a function of its volume throughout the cycle.
Preserved Watt engines
The oldest surviving Watt engine is Old Bess of 1777, now in the
Science Museum, London. The oldest working engine in the world is the
Smethwick Engine, brought into service in May 1779 and now at
Birmingham (formerly at the now defunct Museum of Science
and Industry, Birmingham). The oldest still in its original engine
house and still capable of doing the job for which it was installed is
Boulton and Watt
Boulton and Watt engine at the Crofton Pumping Station. This
was used to pump water for the Kennet and Avon Canal; on certain
weekends throughout the year the modern pumps are switched off and the
two steam engines at Crofton still perform this function. The oldest
extant rotative steam engine, the
Whitbread Engine (from 1785, the
third rotative engine ever built), is located in the Powerhouse Museum
in Sydney, Australia. A Boulton-Watt engine of 1788 may be found in
the Science Museum, London., while an 1817 blowing engine,
formerly used at the Netherton ironworks of M W Grazebrook now
decorates Dartmouth Circus, a traffic island at the start of the
A38(M) motorway in Birmingham.
The Henry Ford Museum
The Henry Ford Museum in
Dearborn, Michigan houses a replica of a 1788
Watt rotative engine. It is a full-scale working model of a
Boulton-Watt engine. The American industrialist Henry Ford
commissioned the replica engine from the English manufacturer Charles
Summerfield in 1932. The museum also holds an original Boulton and
Watt atmospheric pump engine, originally used for canal pumping in
Birmingham, illustrated below, and in use in situ at the Bowyer
Street pumping station from 1796 until 1854, and afterwards
removed to Dearborn in 1929.
The 1817 engine in Birmingham, England
Watt atmospheric pump engine (1796) at The
Henry Ford Museum
Watt engine produced by Hathorn, Davey and Co
In the 1880s, Hathorn Davey and Co / Leeds produced a 1 hp / 125 rpm
atmospheric engine with external condenser but without steam
expansion. It has been argued that this was probably the last
commercial atmospheric engine to be manufactured. As an atmospheric
engine, it did not have a pressurized boiler. It was intended for
Daveys Engine 1885
Watt's Expansion Engine is generally considered as of historic
interest only. There are however some recent developments which may
lead to a renaissance of the technology. Today, there is an enormous
amount of waste steam and waste heat with temperatures between 100 and
150 °C generated by industry. In addition, solarthermal
collectors, geothermal energy sources and biomass reactors produce
heat in this temperature range. There are technologies to utilise this
energy, in particular the Organic Rankine Cycle. In principle, these
are steam turbines which do not use water but a fluid (a refrigerant)
which evaporates at temperatures below 100°C. Such systems are
however fairly complex. They work with pressures of 6 to 20 bars, so
that the whole system has to be completely sealed.
The Expansion Engine can offer significant advantages here, in
particular for lower power ratings of 2 to 100 kW: with expansion
ratios of 1:5, the theoretical efficiency reaches 15%, which is in the
range of ORC systems. The Expansion Engine uses water as working fluid
which is simple, cheap, not toxic, nonflammable and not corrosive. It
works at pressure near and below atmospheric, so that sealing is not a
problem. And it is a simple machine, implying cost effectiveness.
Researchers from the University of Southampton / UK are currently
developing a modern version of Watt's engine in order to generate
energy from waste steam and waste heat. They improved the theory,
demonstrating that theoretical efficiencies of up to 17.4% (and actual
efficiencies of 11%) are possible.
The 25 Watt Experimental Condensing Engine built and tested at
In order to demonstrate the principle, a 25 watt experimental model
engine was built and tested. The engine incorporates steam expansion
as well as new features such as electronic control. The picture shows
the model built and tested in 2016.
Currently, a project to build and test a 2 kW engine is under
Corliss steam engine
Preserved beam engines
Ivan Polzunov made a powerful non-condensing steam engine in 1776, but
died before he could mass-produce it
^ a b Dickinson, Henry Winram (1939). A Short History of the Steam
Engine. Cambridge University Press. p. 87.
^ Rosen, William (2012). The Most Powerful Idea in the World: A Story
of Steam, Industry and Invention. University of Chicago Press.
p. 137. ISBN 978-0226726342.
^ Landes, David S. (1969). The Unbound Prometheus: Technological
Change and Industrial Development in Western Europe from 1750 to the
Present. Cambridge, New York: Press Syndicate of the University of
Cambridge. ISBN 0-521-09418-6.
^ Ayres, Robert (1989). "Technological Transformations and Long Waves"
^ a b Rosen 2012
^ "Model Newcomen Engine, repaired by James Watt". University of
Glasgow Hunterian Museum & Art Gallery. Retrieved 1 July
^ a b Farey, John (1827-01-01). A treatise on the steam engine :
historical, practical, and descriptive. London : Printed for
Longman, Rees, Orme, Brown and Green. pp. 339 ff.
^ Hulse David K (1999): "The early development of the steam engine";
TEE Publishing, Leamington Spa, U.K., ISBN, 85761 107 1 p. 127 et seq.
^ R. L. Hills, James Watt: II The Years of Toil, 1775–1785
(Landmark, Ashbourne, 2005), 58–65.
^ a b Roe, Joseph Wickham (1916), English and American Tool Builders,
New Haven, Connecticut: Yale University Press,
LCCN 16011753 . Reprinted by McGraw-Hill, New York and
London, 1926 (LCCN 27-24075); and by Lindsay Publications, Inc.,
Bradley, Illinois, (ISBN 978-0-917914-73-7).
^ Hills, 96–105.
^ Hulse David K (2001): "The development of rotary motion by the steam
power"; TEE Publishing, Leamington Spa, U.K., ISBN 1 85761 119
5 : p 58 et seq.
^ from 3rd edition Britannica 1797
^ James Watt: Monopolist
^ Rosen 2012, pp. 176–7
^ Thurston, Robert H. (1875). A History of the Growth of the
Steam-Engine. D. Appleton & Co. p. 116. This is the
first edition. Modern paperback editions are available.
^ Bennett 1979
^ Bennett, S. (1979). A History of Control Engineering 1800-1930.
London: Peter Peregrinus Ltd. pp. 47, 22.
^ "Rotative steam engine by Boulton and Watt, 1788". Science
Henry Ford Museum".
Henry Ford Museum".
^ "Rowington Records".
^ "Davey's engine of 1885".
^ Müller, Gerald (2015). "Experimental investigation of the
atmospheric steam engine with forced expansion" (PDF). Renewable
Energy. 75: 348–355. doi:10.1016/j.renene.2014.09.061. Retrieved 5
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