Great Central 0-8-4 Locomotives in Great_Britain

Class 8H/S1 (Locobase 4192)

Data from "Heavy 0-8-4 Three-Cylinder Shunting Tank-Engines; Great Central Railway", Volume 28, No 5 (May 1907), pp. 130-131 and "0-8-4 Three-Cylinder Shunting Tank Engines, GCR", Railway Engineer, Volume 29, No 3 (March 1908). pp 77) and No. 4 (April 1908, p. 111 for detail drawings); and "Heavy Tank Switching Locomotives for the Great Central Railway", Railroad Gazette, Volume XLIV [44], No 20 (15 May 1908). Works numbers were 5002-5005 in 1907-1908. (Thanks to Alexander Blessing for his 12 July 2023 email reporting the road numbers, correcting the driver diameter,

JG Robinson tank switcher of a very unusual arrangement. The 6 engines of this class went into service at the Wath yards pushing freight cars over the hump.

RG remarked on the Belpaire firebox and the fact that the engine used three cylinders, the outside pair driving on the third axle, the inside cylinder cranking on the second axle. Reflecting the limited scope of their duities, all three cylinders got their steam from slide valves.

RE explained in much greater detail why three cylinders were adopted. In the first place, the tonnage rating of these engines was 1,050 tons (70 cars) and the ruling grade was an adverse 1 in 109 (about 1%):

"[T]he engine, of course, gets no assistance from slack couplings, and must have great adhesion power and a constant and equal turning effort at the cranks. For these reasons three simple cylinders, with their cranks set at 120 degrees to each other, were adopted, as such an arrangement gives a more equal turning effort than either two or four cylinders do. The maximum variation in full gear is onlv about 5% on either side of the mean, so that the engine has the starting and non-slipping qualities of an electric locomotive."

Adopting the design he did allowed Robinson to use the boiler from an existing GCR Atlantic class, the running gear and outside motion from an 0-8-0, and the inside motion from an 0-6-0. The author explained why the boiler and grate are relatively small, but the tanks are sizable:

"The work is intermittent, and therefore it was not necessary to provide the boiler with more than sufficient heating and grate surface. The weight is made up by ample capacity for water and coal. It might be thought that such large tanks were not necessary for an engine intended to work in a yard well provided with water cranes, but it must be remembered that axle loads are of less moment on the Wath sidings than they are on the running lines."

The superheated modification is shown in Locobase 8916.