GWR Dean experimental locomotives
During the 1880s William Dean constructed a series of experimental locomotives to test various new ideas in locomotive construction for the Great Western Railway.
This locomotive appeared in 1880 as a 4-4-0T, but was rebuilt in 1882 as a 2-4-0T. It was withdrawn in 1924.
Number 7 was built in 1886 at Swindon as a tandem compound 2-4-0 with 7 ft 0 1⁄2 in (2.146 m) coupled wheels and outside frames. The 23 in (584 mm) 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.
Number 8 was built in 1886 as a 7 ft 1⁄4 in (2,140 mm) broad gauge convertible 2-4-0 tandem compound, the low- and high-pressure piston rods sharing a common crosshead. It had 7 ft 0 1⁄2 in (2.146 m) driving wheels, six plate frames and a high-pressure boiler rated at 180 lbf/in2 (1.2 MPa). 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 4 ft 8 1⁄2 in (1,435 mm) standard gauge. In 1894 the wheel centres were used in a conventional standard gauge 4-4-0, No. 8 of the Armstrong class.
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