South African Class 5A 4-6-2

The South African Railways Class 5A 4-6-2 of 1903 was a steam locomotive from the pre-Union era in the Cape of Good Hope.

This article is about one of several different Cape Government Railways locomotive types to be designated "Karoo Class". For the others, see Cape Government Railways Karoo Class locomotives.

CGR Karoo Class 4-6-2 1903
South African Class 5A 4-6-2
CGR no. 903, SAR no. 721, Paardeneiland, c. 1940
Type and origin
Power typeSteam
DesignerCape Government Railways
(H.M. Beatty)
BuilderKitson and Company
Serial number4193-4194
ModelCGR Karoo
Build date1903
Total produced2
Specifications
Configuration:
​
 • Whyte4-6-2 (Pacific)
 • UIC2'C1'n2
Driver2nd coupled axle
Gauge3 ft 6 in (1,067 mm) Cape gauge
Leading dia.28 1⁄2 in (724 mm)
Coupled dia.60 in (1,524 mm)
Trailing dia.33 in (838 mm)
Tender wheels37 in (940 mm)
Wheelbase49 ft 1 1⁄8 in (14,964 mm)
 • Engine28 ft 2 1⁄2 in (8,598 mm)
 • Leading6 ft (1,829 mm)
 • Coupled10 ft 10 in (3,302 mm)
 • Tender10 ft (3,048 mm)
Wheel spacing
(Asymmetrical)		1-2: 5 ft 7 in (1,702 mm)
2-3: 5 ft 3 in (1,600 mm)
Length58 ft 9 in (17,907 mm)
Height12 ft 10 in (3,912 mm)
Frame typeBar
Axle load12 LT 15 cwt (12,950 kg)
 • Leading11 LT 7 cwt (11,530 kg)
 • 1st coupled12 LT 14 cwt (12,900 kg)
 • 2nd coupled12 LT 15 cwt (12,950 kg)
 • 3rd coupled12 LT 15 cwt (12,950 kg)
 • Trailing10 LT 12 cwt (10,770 kg)
 • Tender axleAxle 1: 10 LT 8 cwt (10,570 kg)
Axle 2: 10 LT 15 cwt (10,920 kg)
Axle 3: 10 LT 17 cwt (11,020 kg)
Adhesive weight38 LT 4 cwt (38,810 kg)
Loco weight60 LT 3 cwt (61,120 kg)
Tender weight32 LT (32,510 kg)
Total weight92 LT 3 cwt (93,630 kg)
Tender typeYE (3-axle)
Fuel typeCoal
Fuel capacity5 LT 10 cwt (5.6 t)
Water cap2,825 imp gal (12,800 l)
Firebox typeRound-top
 • Firegrate area26 sq ft (2.4 m2)
Boiler:
​
 • Pitch7 ft 1⁄2 in (2,146 mm)
 • Diameter4 ft 7 3⁄4 in (1,416 mm)
 • Tube plates14 ft 6 1⁄4 in (4,426 mm)
 • Small tubes154: 2 1⁄4 in (57 mm)
Boiler pressure180 psi (1,241 kPa)
Safety valveRamsbottom
Heating surface1,427 sq ft (132.6 m2)
 • Tubes1,317 sq ft (122.4 m2)
 • Firebox110 sq ft (10 m2)
CylindersTwo
Cylinder size18 1⁄2 in (470 mm) bore
26 in (660 mm) stroke
Valve gearStephenson
Valve typeRichardson balanced slide
CouplersJohnston link-and-pin
Performance figures
Tractive effort20,030 lbf (89.1 kN) @ 75%
Career
OperatorsCape Government Railways
South African Railways
ClassCGR Karoo Class
SAR Class 5A
Number in class2
NumbersCGR 903-904
SAR 721-722
Delivered1903
First run1903
Withdrawn1940
The centre coupled axle had flangeless wheels

In 1903, the Cape Government Railways placed two Karoo Class steam locomotives with a 4-6-2 Pacific type wheel arrangement in passenger service. In 1912, when they were assimilated into the South African Railways, they were renumbered and designated Class 5A.[1][2][3][4]

Design

The Karoo Class of the Cape Government Railways (CGR) was the first tender locomotive with a 4-6-2 Pacific type wheel arrangement to be introduced in Africa. It was the logical development of the CGR 6th Class 2-6-2 Prairie type which later became the Class 6Y on the South African Railways (SAR).[1][2]

H.M. Beatty

Designed by CGR Chief Locomotive Superintendent H.M. Beatty at the Salt River shops in Cape Town, it was acquired to cope with the increasing weight of passenger trains on the one-in-eighty gradients between Beaufort West and De Aar.[1][2]

The locomotive had a bar frame, Stephenson valve gear and used saturated steam. At the time, there was a general belief that any appreciable raising of the boiler pitch would result in a top-heavy locomotive. Since Beatty was very cautious about raising the boiler's centre line to more than twice the rail gauge, or 7 feet (2,134 millimetres), and in this case also to accommodate the large 60 inches (1,520 millimetres) diameter coupled wheels, he resorted to cutting the boiler shell and installing specially shaped pockets to obtain the required clearance.[1][2][4]

Manufacturer

In 1903, two of these locomotives were built by Kitson and Company, immediately after building the two 6th Class 2-6-2 Prairie locomotives since their works numbers follow in sequence. They were numbered 903 and 904, but were not allocated class numbers by the CGR and instead became known as the Karoo Class after the region of the Western System which they were designed to work in.[1]

Kitson’s later used the Karoo design as basis for a batch of Pacific type locomotives which it built for the Midland Railway of Western Australia.[5]

Characteristics

One of the most striking features of the Karoo Class was the length of its boiler, which was accentuated by the extended smokebox. The length of the smokebox was over 8 feet (2,438 millimetres) and the distance between the boiler's tube-plates was 14 feet 6 1⁄4 inches (4,426 millimetres).[2]

The engine used Richardson slide valves, arranged above the cylinders and actuated by the Stephenson motion and rocker shafts. The eccentrics were fitted to the trailing coupled wheel axle, which resulted in exceptionally long valve connecting rods of 7 feet 10 1⁄4 inches (2,394 millimetres).[2]

South African Railways

When the Union of South Africa was established on 31 May 1910, the three Colonial government railways (CGR, Natal Government Railways and Central South African Railways) were united under a single administration to control and administer the railways, ports and harbours of the Union. Although the South African Railways and Harbours came into existence in 1910, the actual classification and renumbering of all the rolling stock of the three constituent railways were only implemented with effect from 1 January 1912.[3][6]

In 1912, these two locomotives were renumbered 721 and 722 and designated Class 5A on the SAR.[3][7][8]

Service

In service, the Class 5A locomotives performed excellently. Beatty's annual report for 1905 stated that they ran 159,000 miles (256,000 kilometres) before a failure occurred, that failure being a hot box. They spent most of their working lives in the Karoo until they were displaced by larger locomotives. They were then placed in suburban service working out of Cape Town, where they remained until they were withdrawn from service c. 1940.[1][2]

Illustration
  • Working a suburban train, c. 1930
  • Ex CGR Karoo Class no. 903, SAR Class 5A no. 721, Paardeneiland, Cape Town, c. 1940

References
  1. Holland, D.F. (1971). Steam Locomotives of the South African Railways. 1: 1859–1910 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 69–71. ISBN 978-0-7153-5382-0.
  2. Espitalier, T.J.; Day, W.A.J. (1944). The Locomotive in South Africa - A Brief History of Railway Development. Chapter II - The Cape Government Railways (Continued). South African Railways and Harbours Magazine, February 1944. pp. 97-101.
  3. Classification of S.A.R. Engines with Renumbering Lists, issued by the Chief Mechanical Engineer's Office, Pretoria, January 1912, pp. 8, 12, 14, 34 (Reprinted in April 1987 by SATS Museum, R.3125-6/9/11-1000)
  4. Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. p. 39. ISBN 0869772112.
  5. Durrant, A. E. (1989). Twilight of South African Steam (1st ed.). Newton Abbott, London: David & Charles. p. 13. ISBN 0715386387.
  6. The South African Railways - Historical Survey. Editor George Hart, Publisher Bill Hart, Sponsored by Dorbyl Ltd., Published c. 1978, p. 25.
  7. Holland, D. F. (1972). Steam Locomotives of the South African Railways. 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. p. 137. ISBN 978-0-7153-5427-8.
  8. South African Railways and Harbours Locomotive Diagram Book, 2'0" & 3'6" Gauge Steam Locomotives, 15 August 1941, as amended
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