Overview
The tank and tender locomotive versions of the 4-8-2 Mountain wheel arrangement both originated in the Colony of Natal in South Africa.
In 1888 the Natal Government Railways (NGR) placed the first five of its eventual one hundred Class Dübs A 4-8-2T tank locomotives in service. The locomotive was designed by W. Milne, the Locomotive Superintendent of the NGR from 1877 to 1896, and was built by Dübs and Company. This was the first known use of the 4-8-2 wheel arrangement in the world.
In 1906 six NGR Class Hendrie B 4-8-0 Mastodon locomotives, designed by D.A. Hendrie, Locomotive Superintendent of the NGR from 1903 to 1910, were modified to a 4-8-2 wheel arrangement by having trailing bissel trucks added below their cabs to improve their stability when hauling fast passenger trains. These Class Altered Hendrie B locomotives were the first 4-8-2 tender locomotives in the world.
The first locomotive to be designed and built as a 4-8-2 tender locomotive was the X class, designed by A. L. Beattie and built by the New Zealand Railways Department's Addington Workshops in Christchurch in 1908. It was designed to haul heavy freight trains on the mountainous central section of the North Island Main Trunk Railway and it is believed that this was the source of the "Mountain" name of the 4-8-2 type, although it is also possible that the name was originated by the Chesapeake and Ohio Railway in the United States of America, who named the type after the Allegheny Mountains. The X class was, however, not considered to be a true Mountain type, since its trailing truck served to spread the axle load rather than to allow a larger and wider firebox. The trailing wheels were positioned well behind a narrow firebox, which itself sat above the driving wheels, necessitating the same design compromise between driving wheel diameter and grate size as on a 2-8-0 Consolidation or 4-8-0 Mastodon. A true 4-8-2 design was a progression of the classic 4-6-2 Pacific layout, which featured a wide firebox positioned above the trailing truck and behind the driving wheels, allowing for a wide and deep firebox as well as large driving wheels.
In 1909 the NGR placed the world’s first true Mountain type locomotive in service when five Class Hendrie D 4-8-2 tender locomotives were commissioned. It was designed by Hendrie to handle coal traffic on the upper Natal mainline and, while it was based on the Class Hendrie B 4-8-0, it had the firebox positioned to the rear of the driving wheels to make a larger grate and ashpan possible. To accomplish this, the plate frame was equipped with a cast bridle at the rear to accommodate the improved firebox design, which also necessitated the addition of a trailing truck. Five locomotives were built by the North British Locomotive Company and delivered in 1909. The 4-8-2 type went on to become the most widely used wheel arrangement in South Africa, with altogether thirty classes of both tank and tender versions eventually seeing service on the South African Railways.
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