mild+adhesion

SUBJECT AREA: Land transport, Mining and extraction technology, Railways and locomotives

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The Wylam wagonway passed Newburn, and Hedley, who went to school at Wylam, must have been familiar with this wagonway from childhood. It had been built c.1748 to carry coal from Wylam Colliery to the navigable limit of the Tyne at Lemington. In 1805 Hedley was appointed viewer, or manager, of Wylam Colliery by Christopher Blackett, who had inherited the colliery and wagonway in 1800. Unlike most Tyneside wagonways, the gradient of the Wylam line was insufficient for loaded wagons to run down by gravity and they had to be hauled by horses. Blackett had a locomotive, of the type designed by Richard Trevithick, built at Gateshead as early as 1804 but did not take delivery, probably because his wooden track was not strong enough. In 1808 Blackett and Hedley relaid the wagonway with plate rails of the type promoted by Benjamin Outram, and in 1812, following successful introduction of locomotives at Middleton by John Blenkinsop, Blackett asked Hedley to investigate the feasibility of locomotives at Wylam. The expense of re-laying with rack rails was unwelcome, and Hedley experimented to find out the relationship between the weight of a locomotive and the load it could move relying on its adhesion weight alone. He used first a model test carriage, which survives at the Science Museum, London, and then used a full-sized test carriage laden with weights in varying quantities and propelled by men turning handles. Having apparently satisfied himself on this point, he had a locomotive incorporating the frames and wheels of the test carriage built. The work was done at Wylam by Thomas Waters, who was familiar with the 1804 locomotive, Timothy Hackworth, foreman smith, and Jonathan Forster, enginewright. This locomotive, with cast-iron boiler and single cylinder, was unsatisfactory: Hackworth and Forster then built another locomotive to Hedley's design, with a wrought-iron return-tube boiler, two vertical external cylinders and drive via overhead beams through pinions to the two axles. This locomotive probably came into use in the spring of 1814: it performed well and further examples of the type were built. Their axle loading, however, was too great for the track and from about 1815 each locomotive was mounted on two four-wheeled bogies, the bogie having recently been invented by William Chapman. Hedley eventually left Wylam in 1827 to devote himself to other colliery interests. He supported the construction of the Clarence Railway, opened in 1833, and sent his coal over it in trains hauled by his own locomotives. Two of his Wylam locomotives survive— Puffing Billy at the Science Museum, London, and Wylam Dilly at the Royal Museum of Scotland, Edinburgh—though how much of these is original and how much dates from the period 1827–32, when the Wylam line was re-laid with edge rails and the locomotives reverted to four wheels (with flanges), is a matter of mild controversy.

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See also: Stephenson, George