THE Great Western Railway has relied for a long period on the single-expansion 4-6-0 type of locomotive as most suitable for the haulage of its express trains. This policy is the fruit of careful experiments with simple and compound engines having various wheel arrangements.
Experiments were made many years ago by the Great Western Railway with Swindon-built locomotives converted to the 4-4-2 or Atlantic type, which were run concurrently with its contemporary 4-6-0s. In addition, the company bought in 1903 a French compound Atlantic, working on the De Glehn-Du Bousquet system, and in 1905 two similar but larger locomotives were imported from France.
In 1908 there was turned out from Swindon works the first Pacific, or 4-6-2 locomotive, to run in Great Britain. This was called The Great Bear.
The data obtained front these experiments suggested to the company that neither Atlantics nor Pacifics - at any rate, those of the period - were suitable for its line. The Swindon-built Atlantics were reconverted into 4-6-0s, the French Atlantics were scrapped after some years of service, and the Pacific was converted into a 4-6-0.
Since then the Great Western Railway has built a number of 4-6-0 express and mixed traffic locomotives, all having single expansion. Some of them have two cylinders, others four. Of the four-cylinder 4-6-0s the most powerful are those of the King class - so called because the engines are named after kings. No. 6000, the first of the series, appeared in 1927 and was called King George V.
A typical King is No. 6028, King George VI, illustrated above. This locomotive has four cylinders, each 16¼ in diameter by 23 in stroke. The outside cylinders drive the second pair of driving wheels, and the inside cylinders the leading pair. The driving wheels are of 6 ft 6 in diameter, 2½ in less than that of the Castles, the Great Western 4-6-0s next in order of power to the Kings. The diameter of the bogie wheels is 3 feet.
The taper boiler barrel, characteristic of modern Great Western locomotives, has a length of 16 feet. The outside diameter tapers from 6 feet to 5 ft 6¼ in. The total heating surface is 2,514 square feet, including 313 square feet of superheating surface. In conformity with Great Western practice, the boiler of No. 6028 works with a moderate degree of superheat. The working pressure is 250 lb per square inch - a high figure for British locomotives. The firegrate area is 34.3 square feet. Tractive effort, at 85 per cent boiler pressure, is 40,300 lb.