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LSWR N15 class
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===Maunsell's "Eastleigh Arthurs": Drummond rebuilds=== Maunsell's projected design of express passenger locomotive was not ready for introduction during the summer timetable of 1925, so a third batch of 10 N15s was ordered for construction at Eastleigh. This batch was part of an outstanding LSWR order to rebuild 15 of Drummond's unsuccessful 4-cylinder [[LSWR F13 class|F13]], [[LSWR G14 class|G14]] and [[LSWR P14 class|P14 classes]] 4-6-0s into 2–cylinder H15 class locomotives.<ref name=Clarke-49 /> Only the five F13s were converted to H15s; the remaining 10 G14 and P14s classes (Nos. 448–457, renumbered E448–E457) were rebuilt as N15s, implementing modifications to Urie's original design.<ref name=Bradley99 /> The modifications are attributed to Maunsell's Chief Draughtsman [[James Clayton (engineer)|James Clayton]], who had transferred to [[Ashford railway works]] in 1914 from [[Derby Works]]. They were the result of cooperation between the [[South Eastern and Chatham Railway]] (SECR) and the [[Great Western Railway]] (GWR) when Maunsell was seconded to the Railway Executive Committee during the First World War.<ref name=Bradley99 /> The aim was to create a series of standard freight and passenger locomotives for use throughout Britain, and meant that Clayton was privy to the latest GWR developments in steam design. These included streamlined steam passages, long-travel valves, the maximisation of power through reduced cylinder sizes and higher boiler pressure.<ref name=Bradley99 /> Maunsell initiated trials with Urie N15 No. 442 in 1924, and proved that better performance could be obtained by altering the steam circuit, valve travel and draughting arrangements.<ref name=Clarke-49 /> As a result, Clayton reduced the N15 cylinder diameter to {{convert|20.5|in|mm}} and replaced the safety valves with Ross pop valves set to {{convert|200|psi|MPa|2|abbr=on}} boiler pressure.<ref name=Bradley101>Bradley (1987), p. 101</ref> The Urie boiler was retained, though the Eastleigh superheater was replaced by a Maunsell type with 10 per cent greater superheating surface area.<ref name=Clarke-49 /> This was supplemented by a larger [[Steam locomotive components|steam chest]] and an increased-diameter chimney casting specially designed for the rebuilds.<ref name="Haresnape54" /> It incorporated a rim and [[Capuchon (chimney)|capuchon]] to control exhaust flow into the atmosphere.<ref name="Haresnape54" /> Valve events (the timing of [[valve gear|valve]] movements with the piston) were also revised to promote efficient steam usage and the wheels were re-balanced to reduce hammerblow.<ref name=Bradley101 /><ref name=Nock1976>Nock (1976), Section "N15 class"</ref> When rebuilding was complete, only the numbers, smokebox doors with centre tightening handles and the flat-sided cabs remained of the G14 and P14 classes.<ref name=Haresnape54>Haresnape (1983), p. 54</ref> The rebuilds retained their distinctive Drummond "watercart" tenders, which were modified with the removal of the complex injector feedwater heating equipment.<ref name=Clarke-49 /> The "watercart" tenders were of {{convert|4300|impgal|L|sigfig=3|abbr=on}} water and {{convert|5.00|LT|t|1|abbr=on}} coal capacity.<ref name=Bradley101 /> The 10 rebuilds became the first members of the King Arthur class upon entering service.<ref name=Bradley99>Bradley (1987), p. 99</ref>
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