Editing Steam engine (section)

== Components and accessories of steam engines ==
There are two fundamental components of a steam plant: the [[boiler]] or [[boiler (steam generator)|steam generator]], and the "motor unit", referred to itself as a "steam engine". [[Stationary steam engine]]s in fixed buildings may have the boiler and engine in separate buildings some distance apart. For portable or mobile use, such as [[steam locomotive]]s, the two are mounted together.<ref>{{Harvnb|Hunter|1985|pp=495–96}} Description of the Colt portable engine</ref><ref>{{Harvnb|McNeil|1990|pp=}} See description of steam locomotives</ref>

The widely used reciprocating engine typically consisted of a cast-iron cylinder, piston, connecting rod and beam or a crank and flywheel, and miscellaneous linkages. Steam was alternately supplied and exhausted by one or more valves. Speed control was either automatic, using a governor, or by a manual valve. The cylinder casting contained steam supply and exhaust ports.

Engines equipped with a condenser are a separate type than those that exhaust to the atmosphere.

Other components are often present; pumps (such as an [[injector]]) to supply water to the boiler during operation, condensers to recirculate the water and recover the [[latent heat]] of vaporisation, and [[superheater]]s to raise the temperature of the steam above its saturated vapour point, and various mechanisms to increase the draft for fireboxes. When coal is used, a chain or screw stoking mechanism and its drive engine or motor may be included to move the fuel from a supply bin (bunker) to the firebox.<ref>{{cite book
 | last1 = Jerome
 | first1 = Harry
 | title = Mechanization in Industry, National Bureau of Economic Research
 | year = 1934
 | url = https://www.nber.org/chapters/c5238.pdf
 |pages=166–67
 }}</ref>

=== Heat source ===
The heat required for boiling the water and raising the temperature of the steam can be derived from various sources, most commonly from burning combustible materials with an appropriate supply of air in a closed space (e.g., [[combustion chamber]], [[firebox (steam engine)|firebox]], furnace).  In the case of [[model steam engine|model or toy steam engines]] and a few full scale cases, the heat source can be an [[heating element|electric heating element]].

=== Boilers ===
[[File:Dampfkessel für eine Stationärdampfmaschine im Textilmuseum Bocholt.jpg|thumb|right|An industrial boiler used for a [[stationary steam engine]]]]
{{Main|Boiler (steam generator)}}

Boilers are [[pressure vessel]]s that contain water to be boiled, and features that [[heat exchanger|transfer the heat to the water]] as effectively as possible.

The two most common types are:
; [[Water-tube boiler]]: Water is passed through tubes surrounded by hot gas.
; [[Fire-tube boiler]]: Hot gas is passed through tubes immersed in water, the same water also circulates in a water jacket surrounding the firebox and, in high-output locomotive boilers, also passes through tubes in the firebox itself (thermic syphons and security circulators).

Fire-tube boilers were the main type used for early high-pressure steam (typical steam locomotive practice), but they were to a large extent displaced by more economical water tube boilers in the late 19th century for marine propulsion and large stationary applications.

Many boilers raise the temperature of the steam after it has left that part of the boiler where it is in contact with the water. Known as [[superheating]] it turns '[[wet steam]]' into '[[superheated steam]]'. It avoids the steam condensing in the engine cylinders, and gives a significantly higher [[Heat engine#Efficiency|efficiency]].{{sfn|Hills|1989|p=248}}{{sfn|Peabody|1893|p=384}}

=== Motor units ===
{{further|#Types of motor units}}

In a steam engine, a piston or steam turbine or any other similar device for doing mechanical work takes a supply of steam at high pressure and temperature and gives out a supply of steam at lower pressure and temperature, using as much of the difference in steam energy as possible to do mechanical work.

These "motor units" are often called 'steam engines' in their own right. Engines using compressed air or other gases differ from steam engines only in details that depend on the nature of the gas although [[compressed air]] has been used in steam engines without change.{{sfn |Peabody|1893|p=384}}

=== Cold sink ===
As with all heat engines, the majority of [[primary energy]] must be emitted as [[waste heat]] at relatively low temperature.<ref name="energy.gov">{{cite web|url=http://fossil.energy.gov/programs/powersystems/turbines/turbines_howitworks.html |title=Fossil Energy: How Turbine Power Plants Work |publisher=Fossil.energy.gov |access-date=2011-09-25 |url-status=dead |archive-url=https://web.archive.org/web/20110812012523/http://fossil.energy.gov/programs/powersystems/turbines/turbines_howitworks.html |archive-date=12 August 2011 }}</ref>

The simplest cold sink is to vent the steam to the environment. This is often used on [[steam locomotive]]s to avoid the weight and bulk of condensers. Some of the released steam is vented up the chimney so as to increase the draw on the fire, which greatly increases engine power, but reduces efficiency.

Sometimes the waste heat from the engine is useful itself, and in those cases, very high overall efficiency can be obtained.

Steam engines in stationary power plants use [[surface condenser]]s as a cold sink. The condensers are cooled by water flow from oceans, rivers, lakes, and often by [[cooling tower]]s which evaporate water to provide cooling energy removal. The resulting condensed hot water (''condensate''), is then pumped back up to pressure and sent back to the boiler. A dry-type cooling tower is similar to an automobile radiator and is used in locations where water is costly. Waste heat can also be ejected by evaporative (wet) cooling towers, which use a secondary external water circuit that evaporates some of flow to the air.

River boats initially used a [[jet condenser]] in which cold water from the river is injected into the exhaust steam from the engine. Cooling water and condensate mix.  While this was also applied for sea-going vessels, generally after only a few days of operation the boiler would become coated with deposited salt, reducing performance and increasing the risk of a boiler explosion.  Starting about 1834, the use of surface condensers on ships eliminated fouling of the boilers, and improved engine efficiency.<ref>Nick Robins, ''The Coming of the Comet: The Rise and Fall of the Paddle Steamer'', Seaforth Publishing, 2012, {{ISBN|1-4738-1328-X}}, Chapter 4</ref>

Evaporated water cannot be used for subsequent purposes (other than rain somewhere), whereas river water can be re-used. In all cases, the steam plant boiler feed water, which must be kept pure, is kept separate from the cooling water or air.

[[File:Boiler Feed Injector Diagram.svg|thumb|right|An [[injector]] uses a jet of steam to force water into the boiler. Injectors are inefficient but simple enough to be suitable for use on locomotives.]]

=== Water pump ===
Most steam boilers have a means to supply water whilst at pressure, so that they may be run continuously. Utility and industrial boilers commonly use multi-stage [[centrifugal pump]]s; however, other types are used. Another means of supplying lower-pressure (typically about 5 to 10 atmospheres pressure) boiler feed water is an [[injector]], which uses a steam jet usually supplied from the boiler. Injectors became popular in the 1850s but are no longer widely used, except in applications such as steam locomotives.{{sfn|Hunter|1985|pp=341–43}} It is the pressurization of the water that circulates through the steam boiler that allows the water to be raised to temperatures well above {{convert|100|C}} boiling point of water at one atmospheric pressure, and by that means to increase the efficiency of the steam cycle.

=== Monitoring and control ===

[[File:Steam indicator (Steam and the Steam Engine - Land and Marine, 1875).jpg|thumb|upright=0.8|right|Richard's indicator instrument of 1875. See: Indicator diagram (below)]]

For safety reasons, nearly all steam engines are equipped with mechanisms to monitor the boiler, such as a [[pressure gauge]] and a [[sight glass]] to monitor the water level.

Many engines, stationary and mobile, are also fitted with a [[governor (device)|governor]] to regulate the speed of the engine without the need for human interference.

The most useful instrument for analyzing the performance of steam engines is the steam engine indicator. Early versions were in use by 1851,{{sfn|Hunter|Bryant|1991|p=123|loc = 'The Steam Engine Indicator' Stillman, Paul (1851)}} but the most successful indicator was developed for the high speed engine inventor and manufacturer Charles Porter by Charles Richard and exhibited at London Exhibition in 1862.<ref name="Thomson 2009" /> The steam engine indicator traces on paper the pressure in the cylinder throughout the cycle, which can be used to spot various problems and calculate developed horsepower.<ref>{{cite web
 |last1       = Walter
 |first1      = John
 |title       = The Engine Indicator
 |year        = 2008
 |url         = http://www.archivingindustry.com/Indicator/chapterzero.pdf
 |pages       = xxv–xxvi
 |url-status=dead
 |archive-url  = https://web.archive.org/web/20120310071206/http://www.archivingindustry.com/Indicator/chapterzero.pdf
 |archive-date = 10 March 2012}}</ref> It was routinely used by engineers, mechanics and insurance inspectors. The engine indicator can also be used on internal combustion engines. See image of indicator diagram below (in ''Types of motor units'' section).

===Governor===
{{Main|Governor (device)}}
[[File:Boulton and Watt centrifugal governor-MJ.jpg|thumb|upright=0.8|right|[[Centrifugal governor]] in the [[Boulton & Watt engine]] 1788 [[Lap Engine]].]]

The [[centrifugal governor]] was adopted by James Watt for use on a steam engine in 1788 after Watt's partner Boulton saw one on the equipment of a flour mill [[Boulton & Watt]] were building.<ref>
{{cite book
|title=A History of Control Engineering 1800–1930
 |last1=Bennett
 |first1= S.
|year=1979 |publisher =Peter Peregrinus Ltd.
|location= London
|isbn= 978-0-86341-047-5
}}
</ref> The governor could not actually hold a set speed, because it would assume a new constant speed in response to load changes. The governor was able to handle smaller variations such as those caused by fluctuating heat load to the boiler. Also, there was a tendency for oscillation whenever there was a speed change. As a consequence, engines equipped only with this governor were not suitable for operations requiring constant speed, such as cotton spinning.<ref>{{Harvnb|Bennett|1979|pp=}}</ref> The governor was improved over time and coupled with variable steam cut off, good speed control in response to changes in load was attainable near the end of the 19th century.