L&YR Class 32

From 1903 with the introduction of Henry Ivatt's Class L1,[2] several of the UK railway companies introduced extremely large tank engines that were eight- or even ten-coupled,[lower-roman 1] with few carrying axles, so as to achieve the maximum adhesive weight over their driving wheels. Although limited in their maximum speed by the lack of any pilot truck, their size was the maximum permitted by the loading gauge and their axle loading specifications, and so they could achieve a high tractive effort. On some lines this was put to use for accelerating suburban passenger services, in competition with the new electric railways. Other railways required heavy shunters, to cope with the increasing weight of freight trains. These were particularly needed for the new technology of hump shunting. Although the tank engine layout restricted the coal and water capacity that could be provided (their large boilers left little space for side tanks), all of these uses were relatively short ranged, and so the engines did not require long endurance.

In 1908, Hughes produced a locomotive of this type for the Lancashire and Yorkshire. These tank engines were based on the previous Aspinall Class 30 0-8-0 tender engines, although their similarities have often been over-emphasised.[1] Their coupled wheelbase was extended by two feet to 24 feet 6 inches (7.47 m), requiring the two centre drivers to be flangeless, with widened tyre treads, to allow them to negotiate a tight radius curve within a marshalling yard.[3][4] This was more successful than similar flangeless drivers had been with Hoy's Class 26 2-6-2Ts, where they had shown a tendency for the centre drivers to drop between the rails if track in a siding wasn't maintained as well as main-line track. The two inside cylinders were 21+1⁄2 by 26 inches (546 mm × 660 mm) and were the largest in size of any non-compound engine in the country.[2]

The type 'L' boiler was again substantially different to any other class. It was 5 feet 9.5 inches in diameter (6 ft 1 in over the outer wrapper), a foot larger than the 'J' boiler of the previous engines. A Belpaire firebox and Ramsbottom safety valves were used. A similar boiler was fitted to Hughes' 1910 large-boilered Class 9, a development of the Class 30. Although this was another feature often described as being in common with the 0-8-0s, they were actually longer than the L boiler. The L boiler was unique to the Class 32, although they were made on the same flanging plates as Hughes' Dreadnought class. This unique boiler would eventually lead to the class' early withdrawal, when the boilers were due for replacement at twenty years old.[1]

Superheating was an innovation at this time and not yet firmly established, mostly owing to difficulties in providing adequate cylinder lubrication. Hughes was an advocate of superheating and used it when rebuilding the 7 ft 3 in Class 4 express 4-4-0s, fitting Schmidt superheaters and piston valves, along with Walschaerts valve gear. Despite this, he recognised that an intermittently worked shunting engine such as the 0-8-2Ts would not allow the superheater elements to reach their optimum working temperature, and so retained a simpler saturated boiler.[1][5]

Other detail fittings included vacuum brakes and oval buffers, to avoid locking of buffer heads when working around tight curves with the engine's long overhang at each end.[1]