Dolgoch is a narrow gauge

Narrow gauge

A narrow gauge railway is a railway that has a track gauge narrower than the of standard gauge railways. Most existing narrow gauge railways have gauges of between and .- Overview :...

 0-4-0

0-4-0

Under the Whyte notation for the classification of steam locomotives, 0-4-0 represents one of the simplest possible types, that with two axles and four coupled wheels, all of which are driven...

 well tank steam locomotive

Steam locomotive

A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...

. It was built by Fletcher, Jennings & Co.

Fletcher, Jennings & Co.

Fletcher, Jennings & Co. was an engineering company at Lowca near Whitehaven, Cumbria, England.-Overview:Fletcher and Jennings took over the business of Tulk and Ley in 1857...

 in 1866 and is one of the oldest locomotives still in active service. It was delivered to the Talyllyn Railway

Talyllyn Railway

The Talyllyn Railway is a narrow-gauge preserved railway in Wales running for from Tywyn on the Mid-Wales coast to Nant Gwernol near the village of Abergynolwyn. The line was opened in 1866 to carry slate from the quarries at Bryn Eglwys to Tywyn, and was the first narrow gauge railway in Britain...

 in 1866 and continues to run on this railway.

The fictional Rheneas in The Railway Series

The Railway Series

The Railway Series is a set of story books about a railway system located on the fictional Island of Sodor. There are 42 books in the series, the first being published in 1945. Twenty-six were written by the Rev. W. Awdry, up to 1972. A further 16 were written by his son, Christopher Awdry; 14...

 by the Rev. W. Awdry was based on this engine.

Design

The design is unusual for a 0-4-0. The well tank engine has a long wheelbase and the driving axle is behind the firebox, which prevents the use of a conventional valve gear

Valve gear

The valve gear of a steam engine is the mechanism that operates the inlet and exhaust valves to admit steam into the cylinder and allow exhaust steam to escape, respectively, at the correct points in the cycle...

 layout. Consequently, the Allan valve gear is driven from the leading coupled axle and doubled back to connect to the valve rods.

The engine was renamed "Pretoria" between about 1900 and 1914 in celebration of the relief of the township of Pretoria in South Africa by Lord Roberts during the Boer war. It then reverted to the original name "Dolgoch", which it retains to this day. It is likely that, in the top left photograph, the engine carries the name "Pretoria" - the freshly painted appearance hints that this photograph was taken after the repainting and name change (records indicate it was repainted and renamed around 1900^[1], and would have been a bit paint-weary prior to that. Zoom in on the high resolution picture option and you can just make out very faintly ".....ria" painted on the boiler side between the chimney and the side-tank). For most of the Railway's life, engine names were painted only on one side of the engines - the North side (the side facing the station platforms which were also only on this side for the whole line). Polished brass nameplates are a feature of current preservation.