South African Class FD 2-6-2+2-6-2

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South African Class FD 2-6-2+2-6-2
Sar fd 1.jpg
Class FD no. 2323, later renumbered no. 674
Type and origin
Power type Steam
Designer North British Locomotive Company
Builder North British Locomotive Company
Serial number 23294-23297 [1][2]
Model Class FD
Build date 1925
Total produced 4
Specifications
Configuration 2-6-2+2-6-2 "Double Prairie" Modified Fairlie
Gauge 3 ft 6 in (1,067 mm) Cape gauge
Leading wheel
diameter
28.5 in (724 mm)
Driver diameter 46 in (1,170 mm)
Trailing wheel
diameter
28.5 in (724 mm)
Wheelbase Total: 58 ft 7 in (17.856 m)
Engines:
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 type Coal
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)
Heating surface:
– Tubes
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)
Cylinders Four
Cylinder size 15 in (381 mm) bore
24 in (610 mm) stroke
Valve gear Walschaerts [3]
Performance figures
Tractive effort 31,690 lbf (141 kN) at 75% pressure
Career
Operator(s) South African Railways
Class Class FD
Number in class 4
Number(s) 2320-2323, renumbered 671-674
Delivered 1926
First run 1926
Withdrawn 1949

The South African Class FD 2-6-2+2-6-2 of 1926 is a South African steam locomotive from the South African Railways era.

In 1926 the South African Railways placed four Class FD Modified Fairlie articulated steam locomotives with a 2-6-2+2-6-2 Double Prairie type wheel arrangement in service.[1][3]

Manufacturer[edit]

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.[1][3]

Characteristics[edit]

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.[1][3]

Shortcomings[edit]

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.[1][4]

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.[1][3][4]

Service[edit]

The locomotives joined the sole Class FC in service on the Cape Midland System, working on the Grahamstown branch. They were scrapped by 1949.[1][3]

See also[edit]

References[edit]

  1. ^ a b c d e f g 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. 
  2. ^ North British Locomotive Company works list, compiled by Austrian locomotive historian Bernhard Schmeiser
  3. ^ a b c d e f Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. p. 97. ISBN 0869772112. 
  4. ^ a b Durrant, A E (1989). Twilight of South African Steam (1st ed.). Newton Abbott, London: David & Charles. p. 31. ISBN 0715386387.