John Speller's Web Pages GCR Smith Compounds

John Speller's Web Pages

GCR Smith Compounds Great Central Horizontal Menu Great Central Horizontal Menu
The Smith System

Developed by Walter M. Smith (1842-1906), the arrangement makes use of one H.P. cylinder and two L.P. cylinders. In most cases all three cylinders drive one axle with the L.P. cranks 90 apart and the H.P. crank dividing the obtuse angle; but two engines have just been placed in service wherein the H.P. cylinder drives one axle and the L.P. cylinders drive another, the two axles being coupled.

The main object of Mr Smith's system is not so much to obtain direct economy by compounding pure and simple, but rather, while obtaining some advantage in this way, to produce an engine which can be adapted in a very considerable degree to the work required of it, so that it can work trains single-handed, which, owing to difficulties occurring on one section only of a journey, would otherwise require an assisting engine, and it can at other times deal with its train in a way which would be difficult or well-nigh impossible for a non-compound engine of corresponding or greater power.

The starting arrangements introduced by Mr Smith comprise a duplex valve, one part of which is of an automatic character, whereby an engine, after starting non-compound, is automatically changed to compound as soon as there is sufficient pressure in the receiver from the exhaust of the high-pressure cylinder for operation in the low- pressure cylinder, this automatic valve automatically reintroducing non-compound working should the receiver pressure fall below the required (but variable) pressure for non-compound working; the second portion of the mechanism comprises a reducing steam admission valve, which can be regulated by the driver to admit boiler steam at any desired pressure to the receiver, so as to cause the automatic valve to reintroduce non-compound working, and to supply steam at a pressure suitable for variable requirements to the low-pressure cylinders, or to reinforce the receiver steam with live steam to assist work in the low-pressure cylinders. By this means the mechanism allows of working as follows: (a) Three-cylinder non-compound, for starting with three large cylinders (in engines built the H.P. cylinder is 19 in. diameter, and the L.P. cylinders 21 in. diameter). (b) Three-cylinder compound. (c) As compound, the low-pressure steam being reinforced in a variable degree with live steam. (d) As a two-cylinder non-compound engine with large cylinders, larger than could be well supplied with steam did the engine always have to work in this way. The last-mentioned method of working results when the steam- reducing valve is adjusted so that full or nearly full pressure steam is admitted to the receiver, in which case the high-pressure piston is nearly balanced, and therefore floats, while the two L.P. pistons (21 in. diameter) work with steam at full or nearly full boiler pressure. [J. F. Gairns, Locomotive Compounding and Superheating (1907), pp. 96f].

J. G. Robinson seems to have been pleased with the results of the Smith compounds he tried on the Great Central. As well as their added flexibility, he claimed a fuel saving of 2 to 2 lb. of coal a mile. He planned experimenting with higher pressures, and it is unclear why he did not proceed.
Front-end arrangement of a Smith Compound
In 1905-06 Robinson built four Class "8" (LNER Class "C-5") 3-cylinder compounds. They were Nos. 258 "Viscount Cross (illustrated)," 259 "King Edward VII," 364 "Lady Henderson" (later "Lady Faringdon"), & 365 "Sir William Pollitt
3-cylinder compound Atlantic No. 358 "The Rt. Hon. Viscount Cross, G.C.B., G.C.S.I" (to give it its full, and somewhat verbose, name -- though unlike the others it was not named until 1927, so the GCR cannot be blamed for this!) in works gray
"C-5" Class Compound Atlantic No. 259 "King Edward VII" with a Sheffield express of teak clerestory stock
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