10HP, 12HP

The prototype 10 H.P. locomotive was slightly different in appearance to the production locos, with a curved top to the power unit covers and different brake rigging. The production 10 and 12 H.P. locos were externally similar to each other but with small details such as a lack of reinforcing strips on the water tank of 12 H.P. types. Buffer arrangements varied within the class with 2-slot block and pairs of small sprung buffers at each end being noted in addition to those illustrated. Both models were fitted with the Lister CS (cold start) series 10 or 12 H.P. two-cylinder diesel engine, the only difference being a higher rating on the 12 H.P. model. This engine used a two-part combustion chamber in the cylinder head, designed by Freeman-Sanders under the supervision of Harry Ricardo. A change-over valve was screwed in for starting, thus giving a higher compression ratio, and screwed out for running under load. Some mining locomotives differed from the surface version by having a flat topped engine cover vent and a flat (non-cylindrical) fuel tank. These differences being in addition to an exhaust conditioner (referred to by Rustons as a 'filter') in place of the toolbox at the rear as on surface versions. The first underground machine, (166027), had the filter placed on the left-hand side of the frame, forward of the front axle. This loco was despatched to Cafferata & Co. Ltd. for their Hawton Gypsum mine near Newark. A total of 108 10 and 12 H.P. locomotives were built but exact figures of how many of each are not clear since some are recorded as 10 H.P but are actually fitted with 12 H.P. engines.

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