GWR Dean experimental locomotives
During the 1880s and 1890s, William Dean constructed a series of experimental locomotives to test various new ideas in locomotive construction for the Great Western Railway.
Locomotives
No. 1
This locomotive was built at Swindon in 1880 as a 4-4-0T. It had double frames, and the bogie had no central pivot. Principal dimensions included: boiler diameter ; pressure ; cylinders ; coupled wheel diameter ; total wheelbase. It was rebuilt in 1882 as a 2-4-0T, the wheelbase now being. A new boiler was fitted in 1899, having a diameter of and a working pressure of ; this had a round-topped firebox. A further new boiler fitted in 1914 had a Belpaire firebox. It was withdrawn in 1924.No. 7
Number 7 was built in 1886 at Swindon as a tandem compound 2-4-0 with coupled wheels and outside frames. The diameter low pressure cylinders were in front of the high pressure cylinders, the pistons being carried on the same piston rod. Valves for the low pressure cylinders were below, and those for the high pressure cylinders above the cylinders. One set of valve gear drove each pair of valve spindles. This setup proved difficult to access for maintenance, and the locomotive was relegated to minor routes. It was broken up in 1890. The wheel centres were used in building No. 7 of the Armstrong class.No. 8
Number 8 was built in 1886 as a broad gauge convertible 2-4-0 tandem compound, the low- and high-pressure piston rods sharing a common crosshead. It had driving wheels, six plate frames and a high-pressure boiler rated at. The frames consisted of a double frame supporting the driving axleboxes, and an external frame from which the hornblocks for the leading wheels projected. Unsuccessful in its trials, it was never taken into stock or converted to . In 1894 the wheel centres were used in a conventional standard gauge 4-4-0, No. 8 of the Armstrong class.No. 9
This unit started out in 1881 as a 4-2-4T, with two diameter driving wheels and unusually large cylinders. The valves were above the cylinders, and operated by Stephenson link motion via rocking shafts; although the cylinders were between the frames, the motion was mounted outside the driving wheels. The wheelbase was. It was the only 4-2-4T locomotive built by the Great Western Railway. It did little work as it was prone to derailing, indeed it did this in front of William Dean on its first trial move out of the shed. The order had been for two locomotives ; the second 4-2-4T, intended to be numbered 10, would have differed from no. 9 in being fitted with Joy valve gear, but it was cancelled following the problems with no. 9. The cylinders and Joy valve gear were not wasted, as they were used in a different experimental locomotive, no. 1833.In 1884, no. 9 was rebuilt as an unconventional 2-2-2 tender locomotive. Some of the old components were retained, such as the frames, cylinders, outside Stephenson valve gear and driving wheels, but the round-top boiler and carrying wheels were new. The wheelbase was. In 1890, it was again rebuilt, this time with more standard double frames, driving wheels and inside valve gear similar in style to the Queen Class. The wheelbase was increased to. In this guise it was named Victoria in honour of Queen Victoria. A Belpaire boiler was fitted in 1902, and the locomotive was withdrawn in 1905.
No. 10
A 2-2-2 locomotive built in 1886 that, as with number 9, was rebuilt in 1890 to be similar to the Queen class. In this latter guise it was named Royal Albert in honour of Prince Albert, husband of Queen Victoria. It was withdrawn in 1906.No. 13
Tank locomotive number 13 first appeared in 1886 as a 2-4-2WT, or well tank: the two water tanks were mounted one below the boiler and between the frames, the other at the back under the coal bunker. In this form it worked on the St Ives branch and also on the Abingdon branch.In 1897, it was rebuilt as a 4-4-0ST, or saddle tank. The large bunker and rear water tank were reduced in size. This allowed the rear carrying wheels to be removed, and a saddle tank fitted over the boiler. The frames were shortened at the rear and extended at the front to allow the fitting of a bogie instead of the leading axle. It continued to work on various branch lines, being loaned to the Liskeard and Looe Railway and later continuing to work on the Looe branch. It was also recorded on the Highworth branch line, before finally moving to Swindon Works, where it shunted for three or four years, and from where it was withdrawn in 1926.
Nos. 14 and 16
Two rather more conventional 2-4-0 express locomotives were turned out in 1888 and ran on the broad gauge. They were similar to the standard gauge 3206 Barnum' Class turned out in 1889 but with larger in driving wheels. They were built for the 3 p.m. express from Bristol to, and although they ceased work after broad gauge ended in May 1892, they were put into store instead of withdrawn.They were renewed as standard gauge 4-4-0 locomotives in 1894, nos. 14 and 16 of the Armstrong class.