two unit locomotive

1) Military: articulated double-unit locomotive, articulated two-unit locomotive

2) Engineering: articulated locomotive, two unit locomotive

1) Engineering: twin unit

2) Railway term: double locomotive, two-unit locomotive

SUBJECT AREA: Land transport, Railways and locomotives, Steam and internal combustion engines

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Orphaned as a child, Hamilton went to work for Southern Pacific Railroad in his teens, and then worked for several other companies. In his spare time he learned mathematics and physics from a retired professor. In 1911 he joined the White Motor Company, makers of road motor vehicles in Denver, Colorado, where he had gone to recuperate from malaria. He remained there until 1922, apart from an eighteenth-month break for war service.

Upon his return from war service, Hamilton found White selling petrol-engined railbuses with mechanical transmission, based on road vehicles, to railways. He noted that they were not robust enough and that the success of petrol railcars with electric transmission, built by General Electric since 1906, was limited as they were complex to drive and maintain. In 1922 Hamilton formed, and became President of, the Electro- Motive Engineering Corporation (later Electro-Motive Corporation) to design and produce petrol-electric rail cars. Needing an engine larger than those used in road vehicles, yet lighter and faster than marine engines, he approached the Win ton Engine Company to develop a suitable engine; in addition, General Electric provided electric transmission with a simplified control system. Using these components, Hamilton arranged for his petrol-electric railcars to be built by the St Louis Car Company, with the first being completed in 1924. It was the beginning of a highly successful series. Fuel costs were lower than for steam trains and initial costs were kept down by using standardized vehicles instead of designing for individual railways. Maintenance costs were minimized because Electro-Motive kept stocks of spare parts and supplied replacement units when necessary. As more powerful, 800 hp (600 kW) railcars were produced, railways tended to use them to haul trailer vehicles, although that practice reduced the fuel saving. By the end of the decade Electro-Motive needed engines more powerful still and therefore had to use cheap fuel. Diesel engines of the period, such as those that Winton had made for some years, were too heavy in relation to their power, and too slow and sluggish for rail use. Their fuel-injection system was erratic and insufficiently robust and Hamilton concluded that a separate injector was needed for each cylinder.

In 1930 Electro-Motive Corporation and Winton were acquired by General Motors in pursuance of their aim to develop a diesel engine suitable for rail traction, with the use of unit fuel injectors; Hamilton retained his position as President. At this time, industrial depression had combined with road and air competition to undermine railway-passenger business, and Ralph Budd, President of the Chicago, Burlington \& Quincy Railroad, thought that traffic could be recovered by way of high-speed, luxury motor trains; hence the Pioneer Zephyr was built for the Burlington. This comprised a 600 hp (450 kW), lightweight, two-stroke, diesel engine developed by General Motors (model 201 A), with electric transmission, that powered a streamlined train of three articulated coaches. This train demonstrated its powers on 26 May 1934 by running non-stop from Denver to Chicago, a distance of 1,015 miles (1,635 km), in 13 hours and 6 minutes, when the fastest steam schedule was 26 hours. Hamilton and Budd were among those on board the train, and it ushered in an era of high-speed diesel trains in the USA. By then Hamilton, with General Motors backing, was planning to use the lightweight engine to power diesel-electric locomotives. Their layout was derived not from steam locomotives, but from the standard American boxcar. The power plant was mounted within the body and powered the bogies, and driver's cabs were at each end. Two 900 hp (670 kW) engines were mounted in a single car to become an 1,800 hp (l,340 kW) locomotive, which could be operated in multiple by a single driver to form a 3,600 hp (2,680 kW) locomotive. To keep costs down, standard locomotives could be mass-produced rather than needing individual designs for each railway, as with steam locomotives. Two units of this type were completed in 1935 and sent on trial throughout much of the USA. They were able to match steam locomotive performance, with considerable economies: fuel costs alone were halved and there was much less wear on the track. In the same year, Electro-Motive began manufacturing diesel-electrie locomotives at La Grange, Illinois, with design modifications: the driver was placed high up above a projecting nose, which improved visibility and provided protection in the event of collision on unguarded level crossings; six-wheeled bogies were introduced, to reduce axle loading and improve stability. The first production passenger locomotives emerged from La Grange in 1937, and by early 1939 seventy units were in service. Meanwhile, improved engines had been developed and were being made at La Grange, and late in 1939 a prototype, four-unit, 5,400 hp (4,000 kW) diesel-electric locomotive for freight trains was produced and sent out on test from coast to coast; production versions appeared late in 1940. After an interval from 1941 to 1943, when Electro-Motive produced diesel engines for military and naval use, locomotive production resumed in quantity in 1944, and within a few years diesel power replaced steam on most railways in the USA.

Hal Hamilton remained President of Electro-Motive Corporation until 1942, when it became a division of General Motors, of which he became Vice-President.

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SUBJECT AREA: Land transport, Railways and locomotives, Steam and internal combustion engines

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Trevithick's father was a tin-mine manager, and Trevithick himself, after limited formal education, developed his immense engineering talent among local mining machinery and steam-engines and found employment as a mining engineer. Tall, strong and high-spirited, he was the eternal optimist.

About 1797 it occurred to him that the separate condenser patent of James Watt could be avoided by employing "strong steam", that is steam at pressures substantially greater than atmospheric, to drive steam-engines: after use, steam could be exhausted to the atmosphere and the condenser eliminated. His first winding engine on this principle came into use in 1799, and subsequently such engines were widely used. To produce high-pressure steam, a stronger boiler was needed than the boilers then in use, in which the pressure vessel was mounted upon masonry above the fire: Trevithick designed the cylindrical boiler, with furnace tube within, from which the Cornish and later the Lancashire boilers evolved.

Simultaneously he realized that high-pressure steam enabled a compact steam-engine/boiler unit to be built: typically, the Trevithick engine comprised a cylindrical boiler with return firetube, and a cylinder recessed into the boiler. No beam intervened between connecting rod and crank. A master patent was taken out.

Such an engine was well suited to driving vehicles. Trevithick built his first steam-carriage in 1801, but after a few days' use it overturned on a rough Cornish road and was damaged beyond repair by fire. Nevertheless, it had been the first self-propelled vehicle successfully to carry passengers. His second steam-carriage was driven about the streets of London in 1803, even more successfully; however, it aroused no commercial interest. Meanwhile the Coalbrookdale Company had started to build a locomotive incorporating a Trevithick engine for its tramroads, though little is known of the outcome; however, Samuel Homfray's ironworks at Penydarren, South Wales, was already building engines to Trevithick's design, and in 1804 Trevithick built one there as a locomotive for the Penydarren Tramroad. In this, and in the London steam-carriage, exhaust steam was turned up the chimney to draw the fire. On 21 February the locomotive hauled five wagons with 10 tons of iron and seventy men for 9 miles (14 km): it was the first successful railway locomotive.

Again, there was no commercial interest, although Trevithick now had nearly fifty stationary engines completed or being built to his design under licence. He experimented with one to power a barge on the Severn and used one to power a dredger on the Thames. He became Engineer to a project to drive a tunnel beneath the Thames at Rotherhithe and was only narrowly defeated, by quicksands. Trevithick then set up, in 1808, a circular tramroad track in London and upon it demonstrated to the admission-fee-paying public the locomotive Catch me who can, built to his design by John Hazledine and J.U. Rastrick.

In 1809, by which date Trevithick had sold all his interest in the steam-engine patent, he and Robert Dickinson, in partnership, obtained a patent for iron tanks to hold liquid cargo in ships, replacing the wooden casks then used, and started to manufacture them. In 1810, however, he was taken seriously ill with typhus for six months and had to return to Cornwall, and early in 1811 the partners were bankrupt; Trevithick was discharged from bankruptcy only in 1814.

In the meantime he continued as a steam engineer and produced a single-acting steam engine in which the cut-off could be varied to work the engine expansively by way of a three-way cock actuated by a cam. Then, in 1813, Trevithick was approached by a representative of a company set up to drain the rich but flooded silver-mines at Cerro de Pasco, Peru, at an altitude of 14,000 ft (4,300 m). Low-pressure steam engines, dependent largely upon atmospheric pressure, would not work at such an altitude, but Trevithick's high-pressure engines would. Nine engines and much other mining plant were built by Hazledine and Rastrick and despatched to Peru in 1814, and Trevithick himself followed two years later. However, the war of independence was taking place in Peru, then a Spanish colony, and no sooner had Trevithick, after immense difficulties, put everything in order at the mines then rebels arrived and broke up the machinery, for they saw the mines as a source of supply for the Spanish forces. It was only after innumerable further adventures, during which he encountered and was assisted financially by Robert Stephenson, that Trevithick eventually arrived home in Cornwall in 1827, penniless.

He petitioned Parliament for a grant in recognition of his improvements to steam-engines and boilers, without success. He was as inventive as ever though: he proposed a hydraulic power transmission system; he was consulted over steam engines for land drainage in Holland; and he suggested a 1,000 ft (305 m) high tower of gilded cast iron to commemorate the Reform Act of 1832. While working on steam propulsion of ships in 1833, he caught pneumonia, from which he died.

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See also: Blenkinsop, John

SUBJECT AREA: Land transport, Mechanical, pneumatic and hydraulic engineering, Railways and locomotives, Steam and internal combustion engines

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Matthew Murray was apprenticed at the age of 14 to a blacksmith who probably also did millwrighting work. He then worked as a journeyman mechanic at Stockton-on-Tees, where he had experience with machinery for a flax mill at Darlington. Trade in the Stockton area became slack in 1788 and Murray sought work in Leeds, where he was employed by John Marshall, who owned a flax mill at Adel, located about 5 miles (8 km) from Leeds. He soon became Marshall's chief mechanic, and when in 1790 a new mill was built in the Holbeck district of Leeds by Marshall and his partner Benyon, Murray was responsible for the installation of the machinery. At about this time he took out two patents relating to improvements in textile machinery.

In 1795 he left Marshall's employment and, in partnership with David Wood (1761– 1820), established a general engineering and millwrighting business at Mill Green, Holbeck. In the following year the firm moved to a larger site at Water Lane, Holbeck, and additional capital was provided by two new partners, James Fenton (1754–1834) and William Lister (1796–1811). Lister was a sleeping partner and the firm was known as Fenton, Murray \& Wood and was organized so that Fenton kept the accounts, Wood was the administrator and took charge of the workshops, while Murray provided the technical expertise. The factory was extended in 1802 by the construction of a fitting shop of circular form, after which the establishment became known as the "Round Foundry".

In addition to textile machinery, the firm soon began the manufacture of machine tools and steam-engines. In this field it became a serious rival to Boulton \& Watt, who privately acknowledged Murray's superior craftsmanship, particularly in foundry work, and resorted to some industrial espionage to discover details of his techniques. Murray obtained patents for improvements in steam engines in 1799, 1801 and 1802. These included automatic regulation of draught, a mechanical stoker and his short-D slide valve. The patent of 1801 was successfully opposed by Boulton \& Watt. An important contribution of Murray to the development of the steam engine was the use of a bedplate so that the engine became a compact, self-contained unit instead of separate components built into an en-gine-house.

Murray was one of the first, if not the very first, to build machine tools for sale. However, this was not the case with the planing machine, which he is said to have invented to produce flat surfaces for his slide valves. Rather than being patented, this machine was kept secret, although it was apparently in use before 1814.

In 1812 Murray was engaged by John Blenkinsop (1783–1831) to build locomotives for his rack railway from Middleton Colliery to Leeds (about 3 1/2 miles or 5.6 km). Murray was responsible for their design and they were fitted with two double-acting cylinders and cranks at right angles, an important step in the development of the steam locomotive. About six of these locomotives were built for the Middleton and other colliery railways and some were in use for over twenty years. Murray also supplied engines for many early steamboats. In addition, he built some hydraulic machinery and in 1814 patented a hydraulic press for baling cloth.

Murray's son-in-law, Richard Jackson, later became a partner in the firm, which was then styled Fenton, Murray \& Jackson. The firm went out of business in 1843.

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