Editing Steam engine (section)

=== Multiple-expansion engines ===
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{{Main|Compound steam engine}}
[[File:Triple expansion engine animation.gif|thumb|upright=1.35|An animation of a simplified triple-expansion engine. High-pressure steam (red) enters from the boiler and passes through the engine, exhausting as low-pressure steam (blue), usually to a condenser.]]

It is a logical extension of the compound engine (described above) to split the expansion into yet more stages to increase efficiency. The result is the '''multiple-expansion engine'''. Such engines use either three or four expansion stages and are known as ''triple-'' and ''quadruple-expansion engines'' respectively. These engines use a series of cylinders of progressively increasing diameter. These cylinders are designed to divide the work into equal shares for each expansion stage. As with the double-expansion engine, if space is at a premium, then two smaller cylinders may be used for the low-pressure stage. Multiple-expansion engines typically had the cylinders arranged inline, but various other formations were used. In the late 19th century, the [[Compound steam engine#The Yarrow-Schlick-Tweedy system|Yarrow-Schlick-Tweedy balancing "system"]] was used on some [[Marine steam engine#Triple or multiple expansion|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 four-cylinder triple-expansion engine popular with large passenger liners (such as the [[Olympic class ocean liner|''Olympic'' class]]), but this was ultimately replaced by the virtually vibration-free [[#Turbine engines|turbine engine]].{{citation needed|date=January 2013}} It is noted, however, that triple-expansion reciprocating steam engines were used to drive the World War II [[Liberty ship]]s, by far the largest number of identical ships ever built. Over 2700 ships were built, in the United States, from a British original design. {{Citation needed|date=February 2020}}

The image in this section shows an animation of a triple-expansion engine. The steam travels through the engine from left to right. The valve chest for each of the cylinders is to the left of the corresponding cylinder.{{Citation needed|date=February 2020}}

Land-based steam engines could exhaust their steam to atmosphere, as feed water was usually readily available. Prior to and during [[World War I]], the expansion engine dominated marine applications, where high vessel speed was not essential. It was, however, superseded by the British invention [[steam turbine]] where speed was required, for instance in warships, such as the [[dreadnought battleship]]s, and [[ocean liner]]s. {{HMS|Dreadnought|1906|6}} of 1905 was the first major warship to replace the proven technology of the reciprocating engine with the then-novel steam turbine.<ref>Brooks, John. ''Dreadnought Gunnery at the Battle of Jutland''. p. 14.</ref>