John Speller's Web Pages Maunsell "River" Class

John Speller's Web Pages - SE&CR
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For handling its express traffic Richard Maunsell originally proposed an enlarged version of the "L" Class 4-4-0, but it was found that this would have too heavy an axle loading for many of the SE&CR's rather flimsy bridges and light, poorly maintained track. His assistants Harold Holcroft, formerly of the GWR, and James Clayton, formerly of the Midland Railway, had both experience of designing powerful tank locomotives, and suggested a 6-coupled tank locomotive as the answer to the SE&CR's express needs. The locomotives had 6 ft. 0 in. diameter driving wheels and were fitted with tapered Belpaire boilers and outside Walschaerts' valve gear. One locomotive was built in 1915 by the SE&CR, but because of the First World War the remaining 19 did not follow until 1925 and were built under the auspices of the Southern Railway. The desire for a slightly narrower engine capable of operating on the Hastings line resulted in building the prototype three-cylinder "K-1" Class locomotive "River Frome" in 1925. This had three 16 inch diameter cylinders in place of two 19 inch diameter cylinders of the "K" Class. The engine made used of the conjugated motion with 2:1 lever, developed by Holcroft under Churchward on the Great Western Railway, and widely used by Gresley on the Great Northern and LNER. With its carefully designed tolerances the version in use on the Southern Railway does not seem to have suffered from the same problems with the middle cylinder overrunning that afflicted some LNER locomotives. The demise of the "River" Class tanks came in the aftermath of the Sevenoaks disaster of 24 August 1927. No. 800 "River Cray" derailed at 55 mph over badly maintained catch points while heading a Canon Street to Deal Pullman express. Thirteen passengers were killed. Although poor track was officially held to be responsible for the accident, there was some feeling that the "River" Class tanks were unsteady at speed. Maunsell sent "K" Class No. 803 and "K-1" Class No. 890 to be independently tested by Sir Nigel Gresley with the dynamometer car on the LNER. The "K" Class ran at up to 79 mph and the "K-1" Class at up to 83 mph, and neither locomotive showed any signs of unsteadiness. When, however, further tests were organized by Sir John Aspinall on the Southern Railway near Woking, they showed that the locomotives could become unstable at around 80 mph. This, like the accident, was probably due to poor track, but the Southern Railway decided to rebuild all the "River" Class locomotives as tender engines to be on the safe side. Thus all 21 were rebuilt as 2-6-0 tender locomotives in 1928.
The prototype Maunsell "K" Class 2-6-4T No. 790, later "River Avon," in SE&CR livery. Image courtesy of Wikipedia Commons
In 1925 the Metropolitan Railway ordered five "K" Class 2-6-4T locomotives, similar to Maunsell's "River" Class design, from Armstrong, Whitworth & Co. These locomotives were later taken into LNER stock and became LNER Class "L-2". Image courtesy of Wikipedia Commons
The prototype "K-1" Class No. 890 "Fiver Frome" in SR livery at Bricklayers Arms in July 1927. Note the modifield front end. Image courtesy of Wikipedia Commons
Aftermath of the Sevenoaks Disaster of 24 August 1927, showing the derailed "K" Class locomotive No. 800 "River Cray"
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