2-8-2+2-8-2

SAR Class GE no. 2269, circa 1930

In the Whyte notation for the classification of steam locomotives by wheel arrangement, a 2-8-2+2-8-2 is an articulated locomotive using a pair of 2-8-2 power units back to back, with the boiler and cab suspended between them. The 2-8-2 wheel arrangement has a single pair of leading wheels in a leading truck, followed by four coupled pairs of driving wheels, with a pair of trailing wheels in a trailing truck. Since the 2-8-2 type was known as Mikado, the corresponding Garratt and Modified Fairlie types were usually known as Double Mikado.

Other equivalent classifications are:

Overview

The 2-8-2+2-8-2 wheel arrangement was used on Garratt and Modified Fairlie locomotives.

Garratt locomotives

The Double Mikado was the fourth most common Garratt type, with 144 examples constructed, 114 built by Garratt patent owner Beyer, Peacock and Company (BP) and thirty built by others under license. Only ten, six for Chile and four for Peru, were built to 4 ft 8 1⁄2 in (1,435 mm) standard gauge. Ninety were built to 3 ft 6 in (1,067 mm) for a number of different railways. For Spain sixteen were built to 5 ft 6 in (1,676 mm).[1][2]

Modified Fairlie locomotives

The South African Railways (SAR), where the Modified Fairlie concept was conceived as an alternative to the Garratt, was the only user. The Modified Fairlie was in essence an adaptation of the Kitson-Meyer concept. It was similar in appearance to a Garratt, but with the boiler, cab, coal and water bunkers all mounted on a single rigid frame which pivoted on the engine units, with the pivot centers located approximately at the centre of the rigid wheelbase of each unit. In the Garratt design, by comparison, the coal and water bunkers are mounted directly on the engine units and swivel with them, while the boiler, firebox and cab are mounted on a rigid frame that is suspended between the two engine units.[3][4][5]

Usage

South Africa

Between 1925 and 1931 the SAR placed eighteen 3 ft 6 in (1,067 mm) Class GE Garratts in service, all built by BP. The first six entered service in 1925 and proved so successful that a second order for ten was placed in 1926. Another two locomotives entered service in 1931. All of them had Belpaire fireboxes, plate frames, Walschaerts valve gear and were superheated. The locomotive was an enlargement of the Class GD 2-6-2+2-6-2 Double Prairie and was designed as a heavy goods locomotive for use on light 60 pounds per yard (30 kilograms per metre) rail. They were the first eight-coupled Garratts to be built for the SAR and, on a tractive effort basis at the time of their introduction, they were the most powerful locomotives operating on light track in Africa and the Southern Hemisphere.[3][4][6][7]

Class HF no. 1386, circa 1940

In 1927 the SAR placed ten Class HF Modified Fairlie Double Mikados in service, followed by an eleventh one in 1928. The locomotive was designed by the SAR under the direction of Colonel F.R. Collins, Chief Mechanical Engineer from 1922 to 1929, and built by Henschel & Son in 1926 and 1927, hence the designation of Class HF for "Henschel Fairlie". Designed for main line work, it was the Modified Fairlie equivalent of the Class GE Garratt, which was similar in both size and mechanical respects. It had Walschaerts valve gear, a bar frame and was superheated, with a round top firebox.[3][4][8]

The Class HF proved to be a powerful locomotive but it was less successful than its Garratt equivalent. The pivot bearings were subject to quite rapid wear since they carried a considerable additional load compared to those on the Garratt as a result of the water and coal bunkers that were mounted on the main frame instead of on the engine units. This resulted in increased maintenance and, as a consequence, increased operating cost. No more locomotives of the Modified Fairlie design were acquired by the SAR.[3][7]

References

  1. 1 2 Hamilton, Gavin N., The Garratt Locomotive - Garratt Locomotives produced by Beyer, Peacock, retrieved 10 November 2012
  2. 1 2 Hamilton, Gavin N., The Garratt Locomotive - Garratt Locomotives from Other Builders, retrieved 10 November 2012
  3. 1 2 3 4 Holland, D.F. (1972). Steam Locomotives of the South African Railways, Volume 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 43–45, 52–53. ISBN 978-0-7153-5427-8.
  4. 1 2 3 Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. pp. 12, 91, 98. ISBN 0869772112.
  5. ↑ The Fairlie locomotive
  6. ↑ South African Railways and Harbours Locomotive Diagram Book, 2’0” & 3’6” Gauge Steam Locomotives, 15 August 1941, as amended
  7. 1 2 Durrant, A E (1989). Twilight of South African Steam (1st ed.). Newton Abbott, London: David & Charles. pp. 31–32, 111. ISBN 0715386387.
  8. ↑ Henschel-Lieferliste (Henschel & Son works list), compiled by Dietmar Stresow
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