SECR K and SR K1 Classes - Operational Details - Sevenoaks Disaster

Sevenoaks Disaster

The K and K1 classes suffered from stability problems when travelling at speed over points and curves. The locomotive would initially roll (briefly lean heavily) to one side, followed by several further rolls of gradually reducing amplitude, combined with a side-slipping movement that caused the driving wheels to mount the rails. Several minor derailments of members of the class culminated in the serious derailment of No. A800 River Cray at Sevenoaks, Kent, in August 1927, caused by a combination of a surge in the water tanks and the flanges of the locomotive's lead driving wheels mounting the rail at speed due to poor quality track-work. The locomotive was hauling a Cannon Street to Deal express with a Pullman carriage when the leading driving wheels derailed at 55 mph (89 km/h) over catch points in a cutting. Several carriages were flung against a road bridge, injuring 40 and killing 13 passengers.

In the days following the accident, two K and K1 class engines were trialled on the London and North Eastern Railway's (LNER) Great Northern mainline under the supervision of that company's CME, Nigel Gresley, to gain an unbiased review of their riding qualities. Locomotives No. A803 (K) and No. A890 (K1), and King Arthur class No. E782, were tested on the well-maintained LNER line between Huntingdon and St. Neots in October 1927, where few problems were found with locomotive stability. On runs between Kings Cross and Potters Bar with the LNER's dynamometer car, No. A890 was recorded at a top speed of 83 miles per hour (134 km/h) and A803 at 79 miles per hour (127 km/h), with no problems in riding. When these engines returned from the LNER, the Southern Railway's General Manager, Sir Herbert Walker ordered further trials to be led by Sir John Aspinall on the Western section main line near Woking. These were terminated by the Southern Railway's Operating Department, as the riding of the locomotives at speeds near 80 miles per hour (130 km/h) rendered the locomotives unsafe. The instability of No. A890 at speed was attributed to the helical springs on the Bissel truck and bogie.

The 1928 accident inquiry did not attach blame to the Southern Railway for track maintenance or locomotive performance issues, and noted that the prototype had run for eight years over the same stretch of line without complaint. However, it identified the Brighton batch and No. A890 as being more susceptible to rolling on sharp curves with weak rail joints, although the entire class operated without incident on the former LBSCR network. The management of the Southern Railway realised that to have any success in operating the K class tanks on other parts of the network, vast stretches of track would require upgrading. With the prospect of storing 20 locomotives whilst the necessary upgrading took place, the management recommended the class be fully withdrawn from service. To recoup the expense of constructing the engines, Maunsell was given permission to rebuild them to the new SR U class 2-6-0 tender engine design in 1928. This decision also reduced the adverse publicity generated by the accident. However, many of the components discarded during the rebuilding process would later be re-used on another 2-6-4 tank locomotive designed to haul heavy freight on short trips: the 3-cylinder W class of 1932.