South African Class FD 2-6-2+2-6-2
|South African Class FD 2-6-2+2-6-2|
Class FD no. 2323, later renumbered no. 674
|Type and origin|
|Designer||North British Locomotive Company|
|Builder||North British Locomotive Company|
|Serial number||23294-23297 |
|Configuration||2-6-2+2-6-2 "Double Prairie" Modified Fairlie|
|Gauge||3 ft 6 in (1,067 mm) Cape gauge|
|28.5 in (724 mm)|
|Driver diameter||46 in (1,170 mm)|
|28.5 in (724 mm)|
|Wheelbase||Total: 58 ft 7 in (17.856 m)
8 ft 6 in (2.591 m) coupled
18 ft 7.5 in (5.677 m) total
|Length||65 ft 7.75 in (20.009 m)|
|Height||12 ft 9.25 in (3.893 m)|
|Frame||Plate frame, 36 ft 6 in (11.125 m) between pivot centres|
|Axle load||12.35 long tons (12.5 t) on 1st driver|
|Weight on drivers||72.85 long tons (74.0 t)|
|Locomotive weight||114.1 long tons (115.9 t) w/o|
|Fuel capacity||5 long tons (5.1 t)|
|Water capacity||2,500 imp gal (11,000 l) front
1,300 imp gal (5,900 l) rear
|Boiler||6 ft (1.829 m) inside diameter
10 ft 8 in (3.251 m) inside length
7 ft 6.25 in (2.292 m) pitch
|Boiler pressure||180 psi (1,240 kPa)|
|Firegrate area||41 sq ft (3.809 m2)|
|190 tubes 2 in (50.8 mm) diameter
32 tubes 5.5 in (140 mm) diameter
1,552 sq ft (144.186 m2)
|– Firebox||178 sq ft (16.537 m2)|
|– Total||1,730 sq ft (160.722 m2)|
|Superheater area||371 sq ft (34.467 m2)|
|Cylinder size||15 in (381 mm) bore
24 in (610 mm) stroke
|Valve gear||Walschaerts |
|Tractive effort||31,690 lbf (141 kN) at 75% pressure|
|Operator(s)||South African Railways|
|Number in class||4|
|Number(s)||2320-2323, renumbered 671-674|
The Class FD Modified Fairlie locomotive was designed and built for the South African Railways (SAR) by the North British Locomotive Company (NBL) in 1925. Four locomotives were delivered in 1926, numbered in the range from 2320 to 2323. They were later renumbered in the range from 671 to 674.
The Class FD was a larger and more powerful version of the experimental Class FC that was placed in service in 1924. It was the Modified Fairlie equivalent of the Class GD 2-6-2+2-6-2 Garratt, which was similar in both size and mechanical respects, hence the Class FD designation of these Modified Fairlies. The Class FD locomotives had Walschaerts valve gear, plate frames and were superheated. They proved to be powerful locomotives and good steamers, but they were less successful than their Garratt equivalent.
They suffered from the same shortcomings as their Class FC predecessor. The 65 feet (19.8 metres) long rigid frame resulted in severe overhang on sharp curves and was also prone to metal fatigue and cracking, brought about by the long frame overhangs at the front and back beyond the engine pivot centres. The overhangs, laden with the water and coal bunkers of which about two-thirds of each extended beyond the respective pivot centres, tended to vibrate in an up-and-down motion while the locomotive was in motion.
In addition to this rather serious defect, the pivot bearings were also 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 frame instead of on the engine units. This resulted in increased maintenance and, as a consequence, increased operating cost.
- Articulated locomotive numbering and classification
- List of South African locomotive classes
- South African Class FC 2-6-2+2-6-2
- South African Class GD 2-6-2+2-6-2
- South African locomotive history
- The 2-6-2+2-6-2 "Double Prairie"
- Holland, D.F. (1972). Steam Locomotives of the South African Railways, Volume 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 50–51. ISBN 978-0-7153-5427-8.
- North British Locomotive Company works list, compiled by Austrian locomotive historian Bernhard Schmeiser
- Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. p. 97. ISBN 0869772112.
- Durrant, A E (1989). Twilight of South African Steam (1st ed.). Newton Abbott, London: David & Charles. p. 31. ISBN 0715386387.