Pumping engines Mill engines 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 ihp (indicated horsepower) 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. To generalise, between 1860 and 1926 all Lancashire mills were driven by compounds. The last compound built was by
Buckley and Taylor for
Wye No.2 mill, Shaw. This engine was a cross-compound design to 2,500 ihp, driving a 24 ft, 90 ton flywheel, and operated until 1965.
Marine applications . triple-expansion marine engine
Liberty ships, assembled for testing prior to delivery. The engine is long and tall and was designed to operate at 76
rpm and propel a Liberty ship at about . In the marine environment, the general requirement was for autonomy and increased operating range, as ships had to carry their coal 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 ), 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 liners. 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 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", the practical history of railway compounding begins with
Anatole Mallet's designs in the 1870s.
Mallet locomotives 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, for the train brakes. == The Yarrow–Schlick–Tweedy system ==