page_title: SECR N class
section_title: Experiments
hierarchical_section_title: SECR N class / Operational details / Experiments
caption_attribution_description: English: An image of SECR N class No. 1850 with experimental J. T. Marshall valve gear from the Ian Allan Ltd. collection, now under the custodianship of the British National Railway Museum, with which the copyright currently rests. The museum is a non-departmental public body sponsored by the Department for Culture. See: http://www.nationalarchives.gov.uk/a2a/records.aspx?cat=756-ialc&amp;cid=0&amp;kw=ian%20allan#0 The image was taken c. February 1934 at Eastleigh Works. (Source: Haresnape, Brian: Maunsell Locomotives: A Pictorial History (Hinckley: Ian Allan, 1963), p. 28)
context_page_description: The SECR N class was a type of 2-6-0 steam locomotive designed in 1914 by Richard Maunsell for mixed-traffic duties on the South Eastern and Chatham Railway. Built between 1917 and 1934, it was the first non-Great Western Railway type to use and improve upon the basic design principles established by GWR Chief Mechanical Engineer George Jackson Churchward. The N class was based on the GWR 4300 Class design, improved with Midland Railway concepts.
  The N class was mechanically similar to the SECR K class 2-6-4 passenger tank engine, also by Maunsell. It influenced future 2-6-0 development in Britain and provided the basis for the 3 cylinder N1 class of 1922. Production was delayed by the outbreak of the First World War in 1914, and the first N class rolled out of Ashford Works in 1917, three years after design work was completed. The class replaced obsolete 0-6-0s as part of the SECR's fleet standardisation, as they used parts interchangeable with those of other classes.
  Eighty N class locomotives were built in three batches between the First and Second World Wars.
context_section_description: Although sufficient for the Southern Railway's needs, the N class was an ideal test-bed for experiments with new steam technology. The first experiment entailed fitting a Worthington feed pump to No. A819 in 1924. The trial was moderately successful, and the pump remained in use until removal in 1927. In June 1930, No. A816 was withdrawn from service for the application of experimental Anderson steam conservation equipment at Eastleigh Works. This was designed by a Scottish marine draughtsman, Mr. A.P.H. Anderson, who proposed the use of a fan system to condense spent steam and improve draughting of the fire on long-distance runs in regions with poor access to water.
  No. A816 emerged from Eastleigh in August 1931 for trials, but was stopped when temperature variations within the condensing equipment caused water leakage. Modifications were made to improve the draughting of the locomotive, incorporating a box-like chimney attached to the condenser array by pipes. No. A816 was released for more trials, and produced performances well-below those displayed by the unmodified members of the class. The experiment was ended when the system's developers ran out of money, and the locomotive was converted back to standard form between May and August 1935, re-entering service as No. 1816.
  The final experiment with performance enhancement began in October 1933, when No. 1850 had its Walschaerts valve gear replaced with J.T. Marshall valve gear at Eastleigh Works. The engine was trialled on the Western section, where the gear showed promise at slower speeds, with reduced consumption of coal and water. Problems were encountered at speeds over 50 mph (80 km/h), at which a severe "knocking" sound was reported by the footplate crew. When trialled on a Basingstoke–Waterloo semi-fast (a high-speed passenger train that stops at selected intermediate stations), the valve gear disintegrated near Woking. After immediate withdrawal from traffic, the locomotive had its Walschaerts valve gear re-fitted and No. 1850 re-entered traffic in April 1934.
caption: An official photograph of Woolwich-built No. 1850, which was fitted with Marshall valve gear for trials in 1934. Note the complex layout of the motion, which disintegrated at speed near Woking. The locomotive was subsequently rebuilt with standard Walschaerts valve gear in April 1934.
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