Editing Watt steam engine (section)

{{Short description|Industrial Revolution era stream engine design}}
{{Use British English|date=August 2017}}
{{Use dmy dates|date=August 2017}}
[[File:Maquina vapor Watt ETSIIM.jpg|thumb|300px|A late version of a Watt [[double-acting cylinder|double-acting]] [[steam engine]],  built by [[D. Napier & Son]] (London) in 1832, now in the lobby of the Superior Technical School of Industrial Engineers of the [[Technical University of Madrid|UPM]] ([[Madrid]]). Steam engines of this kind propelled the [[Industrial Revolution]] in Great Britain and the world.]]

The '''Watt steam engine''' design was an invention of [[James Watt]] that became synonymous with steam engines during the [[Industrial Revolution]], and it was many years before significantly new designs began to replace the basic Watt design.

The [[Newcomen atmospheric engine|first steam engine]]s, introduced by [[Thomas Newcomen]] in 1712, were of the "atmospheric" design. At the end of the [[power stroke (engine)|power stroke]], the weight of the object being moved by the engine pulled the piston to the top of the cylinder as steam was introduced. Then the cylinder was cooled by a spray of water, which caused the steam to condense, forming a [[partial vacuum]] in the cylinder. Atmospheric pressure on the top of the piston pushed it down, lifting the work object. [[James Watt]] noticed that it required significant amounts of heat to warm the cylinder back up to the point where steam could enter the cylinder without immediately condensing. When the cylinder was warm enough that it became filled with steam the next power stroke could commence.

Watt realised that the heat needed to warm the cylinder could be saved by adding a separate condensing cylinder. After the power cylinder was filled with steam, a valve was opened to the secondary cylinder, allowing the steam to flow into it and be condensed, which drew the steam from the main cylinder causing the power stroke. The condensing cylinder was water cooled to keep the steam condensing. At the end of the power stroke, the valve was closed so the power cylinder could be filled with steam as the piston moved to the top. The result was the same cycle as Newcomen's design, but without any cooling of the power cylinder which was immediately ready for another stroke.

Watt worked on the design over a period of several years, introducing the condenser, and introducing improvements to practically every part of the design. Notably, Watt performed a lengthy series of trials on ways to seal the piston in the cylinder, which considerably reduced leakage during the power stroke, preventing power loss. All of these changes produced a more reliable design which used half as much coal to produce the same amount of power.<ref>{{Cite web
 | last1 = Ayres
 | first1 = Robert
 | author1-link = Robert Ayres (scientist)
 | title =Technological Transformations and Long Waves
 | year = 1989
 |page=13
 | url = http://pure.iiasa.ac.at/id/eprint/3225/1/RR-89-001.pdf
 }}</ref>

The new design was introduced commercially in 1776, with the first example sold to the [[Carron Company]] ironworks. About the same time, Watt encountered a business problem that led him to introduce a new unit of measurement of power, or the rate at which work is done: the [[horsepower]]. His earlier business agreements framed his earnings in how much coal the customer of the steam engine saved, but when discussing installing a steam engine for a London brewer, that business did not use coal - it used horses to drive the mills.<ref>{{Cite web |url= http://www.pballew.net/arithm17.html#hp |title= Math Words — horsepower |publisher= pballew.net |access-date= 2007-08-11 |archive-date= 2018-09-20 |archive-url= https://web.archive.org/web/20180920001001/http://www.pballew.net/arithm17.html#hp |url-status= usurped }}</ref> 

Watt continued working to improve the engine, and in 1781 introduced a system using a [[sun and planet gear]] to turn the linear motion of the engines into rotary motion. This made it useful not only in the original pumping role, but also as a direct replacement in roles where a [[water wheel]] would have been used previously. This was a key moment in the industrial revolution, since power sources could now be located anywhere instead of, as previously, needing a suitable water source and [[topography]]. Watt's partner [[Matthew Boulton]] began developing a multitude of machines that made use of this rotary power, developing the first modern industrialized factory, the [[Soho Foundry]], which in turn produced new steam engine designs. Watt's early engines were like the original Newcomen designs in that they used low-pressure steam, and all of the power was produced by atmospheric pressure. When, in the early 1800s, other companies introduced high-pressure steam engines, Watt was reluctant to follow suit due to safety concerns.<ref name="Dickinson">
{{cite book |title=A Short History of the Steam Engine |last1=Dickinson |first1= Henry Winram |author-link=Henry Winram Dickinson |year=1939 |publisher = Cambridge University Press |isbn= 978-1-108-01228-7 |page=87}}
</ref> Wanting to improve on the performance of his engines, Watt began considering the use of higher-pressure steam, as well as designs using multiple cylinders in both the double-acting concept and the multiple-expansion concept. These double-acting engines required the invention of the [[parallel motion]], which allowed the [[piston rod]]s of the individual cylinders to move in straight lines, keeping the piston true in the cylinder, while the walking beam end moved through an arc, somewhat analogous to a [[crosshead]] in later steam engines.