Editing Compound steam engine (section)

==Applications==
===Pumping engines===
{{Main|Cornish engine}}

===Mill engines===
{{Main|Stationary steam engine}}
[[File:Steam engine at Craven Mills - geograph.org.uk - 388255.jpg|thumb|right|A Marchent & Morley horizontal tandem compound engine built 1914, at Craven Mills, Cole. The air pump and jet condenser are nearest with the LP cylinder beyond. It is fitted with Morley's patent piston drop valves]]
Though the first mills were driven by [[water power]], once steam engines were adopted the manufacturer no longer needed to site the mills by running water. Cotton spinning required ever larger mills to fulfil the demand, and this drove the owners to demand increasingly powerful engines. When boiler pressure had exceeded 60 psi, compound engines achieved a thermo-dynamic advantage, but it was the mechanical advantages of the smoother stroke that was the deciding factor in the adoption of compounds. In 1859, there was 75,886&nbsp;ihp (indicated horsepower{{cref|ihp}}) of engines in mills in the Manchester area, of which 32,282 ihp was provided by compounds though only 41,189 ihp was generated from boilers operated at over 60psi.{{sfnp|Hills|1989|p=160}}

To generalise, between 1860 and 1926 all Lancashire mills were driven by compounds. The last compound built was by [[Buckley & Taylor|Buckley and Taylor]] for [[List of mills in Shaw and Crompton#V to Z|Wye No.2 mill, Shaw]]. This engine was a cross-compound design to 2,500 ihp, driving a 24&nbsp;ft, 90 ton flywheel, and operated until 1965.{{sfnp|Hills|1989|p=281}}

===Marine applications===
{{Main|Marine steam engine}}
[[Image:TripleExpansion.jpg|thumb|upright|Model of a triple-expansion engine]]
[[File:Christopher Columbus whaleback ccengine crop.jpg|thumb|upright|1890s triple-expansion (three cylinders of 26, 42 and 70&nbsp;inch diameters in a common frame with a 42-inch stroke) marine engine that powered the [[Christopher Columbus (whaleback)|SS ''Christopher Columbus'']].]]
[[File:SS Ukkopekka steam engine.jpg|thumb|upright|[[S/S Ukkopekka|SS ''Ukkopekka'']] triple-expansion marine engine]]
[[File:Liberty ship 140-ton VTE engine.jpg|thumb|right|140-ton &ndash; also described as 135-ton &ndash; vertical triple expansion steam engine of the type used to power [[World War II]] [[Liberty ship]]s, assembled for testing prior to delivery. The engine is 21 feet (6.4 meters) long and 19 feet (5.8 meters) tall and was designed to operate at 76 [[Revolutions per minute|rpm]] and propel a Liberty ship at about 11 knots (12.7 mph; 20.4&nbsp;km/h).]]
In the marine environment, the general requirement was for autonomy and increased operating range, as ships had to carry their coal<!--and water?--> supplies. The old salt-water boiler was thus no longer adequate and had to be replaced by a closed fresh-water circuit with condenser. The result from 1880 onwards was the '''multiple-expansion engine''' using three or four expansion stages (''triple-'' and ''quadruple-expansion engines''). These engines used a series of double-acting cylinders of progressively increasing diameter and/or stroke (and hence volume) designed to divide the work into three or four, as appropriate, equal portions for each expansion stage. Where space is at a premium, two smaller cylinders of a large sum volume might be used for the low-pressure stage. Multiple-expansion engines typically had the cylinders arranged in-line, but various other formations were used. In the late 19th century, the Yarrow-Schlick-Tweedy balancing 'system' was used on some marine triple-expansion engines. Y-S-T engines divided the low-pressure expansion stages between two cylinders, one at each end of the engine. This allowed the crankshaft to be better balanced, resulting in a smoother, faster-responding engine which ran with less vibration. This made the 4-cylinder triple-expansion engine popular with large passenger liners (such as the [[Olympic class ocean liner|Olympic class]]), but was ultimately replaced by the virtually vibration-free [[steam turbine]].

The development of this type of engine was important for its use in steamships as by exhausting to a condenser the water could be reclaimed to feed the boiler, which was unable to use [[seawater]]. Land-based steam engines could simply exhaust much of their steam, as feed water was usually readily available. Prior to and during [[World War II]], the expansion engine dominated marine applications where high vessel speed was not essential. It was superseded by the steam turbine when speed was required, such as for warships and [[ocean liner]]s. [[HMS Dreadnought (1906)|HMS ''Dreadnought'']] of 1905 was the first major warship to replace the proven technology of the reciprocating engine with the then-novel steam turbine.

===Application to railway locomotives===
{{Main|Compound locomotive}}
For railway locomotive applications the main benefit sought from compounding was economy in fuel and water consumption plus high power/weight ratio due to temperature and pressure drop taking place over a longer cycle, this resulting in increased efficiency; additional perceived advantages included more even torque.

While designs for compound locomotives may date as far back as [[James Samuel]]'s 1856 patent for a "continuous expansion locomotive",<ref>{{Citation
  |title=Compound Engines facsimile reprint
  |publisher=Scholarly Publishing Office, University of Michigan Library    |location=Ann Arbor, MI
  |year=2005
  |pages=16;17
  |isbn=1-4255-0657-7
}}</ref> the practical history of railway compounding begins with [[Anatole Mallet]]'s designs in the 1870s. [[Mallet locomotive]]s were operated in the United States up to the end of mainline steam by the [[Norfolk and Western Railway]]. The designs of [[Alfred George de Glehn]] in France also saw significant use, especially in the rebuilds of [[André Chapelon]]. A wide variety of compound designs were tried around 1900, but most were short-lived in popularity, due to their complexity and maintenance liability. In the 20th century the [[superheater]] was widely adopted, and the vast majority of steam locomotives were simple-expansion (with some compound locomotives converted to simple). It was realised by engineers that locomotives at steady speed were worked most efficiently with a wide-open regulator and early cut-off, the latter being set via the reversing gear. A locomotive operating at very early cut-off of steam (e.g. at 15% of the piston stroke) allows maximum expansion of the steam, with less wasted energy at the end of the stroke. Superheating eliminates the condensation and rapid loss of pressure that would otherwise occur with such expansion.

Large American locomotives used two cross-compound steam-driven air compressors, e.g. the Westinghouse 8 1/2" 150-D,<ref>1941 Locomotive Cyclopedia of American Practice, Eleventh Edition, Simmons-Boardman Publishing Corporation, 30 Church Street, New York p.813</ref> for the train brakes.