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The Jumbos

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March 2002
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THE JUMBOS

Rodney Weaver

These were a series of general express passenger locomotives which over the years coalesced to become two very similar classes noted for their remarkable performance in relation to size, their neat appearance and, like almost all LNWR locomotives in the Webb Explain 'Webb, Francis William (1836—1906)' era, giving when under load a vivid impression of the Biblical ‘Pillar of fire by night and pillar of cloud by day’. Behind this rather general introduction to the classes one finds an excellent example of Webb’s method of working – a policy of progressive improvement whereby a satisfactory original is over a period of years transformed into a totally different locomotive looking essentially like the first but upon investigation totally new and quite different. Move to the photographs page

When he took over from Ramsbottom (behind which move lies a fascinating and quite typical story of someone committing hari kiri in front of the great Richard Moon with no malice or harsh words on either side while everybody involved remained the best of friends) he inherited the existing Ramsbottom 2-4-0s: the Newtons Explain 'Newton Class 2-4-0 Locomotive Class' and their lighter brethren the Samsons Explain 'Samson Class 2-4-0 Locomotive Class'. The latter, according to the late E.L. Ahrons Explain 'Ahrons, Ernest Leopold (1866—1926)' were the most inappropriately named locomotives imaginable. Webb was in no hurry to develop anything new and continued building his predecessor’s classes. It was 1874 before his first two designs appeared which bore the significant names PRECEDENT and PRECURSOR. The former, with 6ft 6in wheels was a real express engine; the latter with wheels only 5ft 6in was intended for more steeply graded lines; at this time Richard Moon laid down that ‘fast’ trains must not exceed 60 mph.

 

The new locomotives embodied the classic cylinder and valve chest layout seen in the Bloomers. The V-shaped valve chest enabled the cylinder centres to be brought closer together and to achieve this Allan straight link gear Explain 'Allan Valve Gear' was used which gave excellent valve events. The boiler was virtually identical with that already used on the Coal Engine Explain 'Coal Engine 0-6-0 Locomotive Class' and like all Crewe boilers was an effective steam generator. The use of 5ft 6in wheels on express engines surprised some observers but Webb knew what he was doing and on trial the locomotive developed 484 IHP Explain 'Indicated Horse Power (IHP)' at 28 mph up a 1 in 75, gradient (i.e. Shap), 592 IHP at 33 mph up 1 in 125 and could reach its ‘permitted maximum’ on level track without seriously overtaxing the boiler. In service, the Precursors ran freely up to 74 mph and did a lot of work over the steeply graded line to Leeds. The draughting Explain 'Draughting' of these early Webb designs left something to be desired: 74 mph on a Precursor was equal to 87.5 mph on a Precedent, and while the mechanical side of the locomotives would stand that, the boilers would be hard pressed to do so. That is why the larger-wheeled Precedents took over on the Shap route. Ahrons’s Explain 'Ahrons, Ernest Leopold (1866—1926)' wild statement that the Precursors were withdrawn because they ‘knocked themselves to pieces’ was an early example of ‘Practice & Performance’ Explain '‘Practice & Performance’' idiocy.

In the later 1880s Webb re-thought the designs and the true Jumbos emerged. The Precursors and Samsons were reconstructed as the 6ft 3in Whitworths Explain 'Whitworth 2-4-0 Locomotive Class' or Small Jumbos Explain 'Small Jumbo 2-4-0 Locomotive Class' while the Newtons and Precedents were rebuilt as the Precedents or Large Jumbos Explain 'Large Jumbo 2-4-0 Locomotive Class'. Many detail improvements were made in the new locomotives, steam passages were

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