South African Class Experimental 3 2-8-0

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CGR Tandem Compound 2-8-0 1903
South African Class Experimental 3 2-8-0
SAR Class Exp 3 909 (2-8-0) CGR 839.jpg
CGR Tandem Compound no. 839
SAR Class Experimental 3 no. 909
Type and origin
Power type Steam
Designer Cape Government Railways
(H.M. Beatty)
Builder American Locomotive Company
Serial number 28638
Model CGR Tandem Compound
Build date 1903
Total produced 1
 • Whyte 2-8-0 (Consolidation)
 • UIC 1'Dnv4
Driver 3rd coupled axle
Gauge 3 ft 6 in (1,067 mm) Cape gauge
Leading dia. 28 12 in (724 mm)
Coupled dia. 48 in (1,219 mm)
Tender wheels 33 12 in (851 mm)
Wheelbase 46 ft 5 in (14,148 mm)
 • Engine 22 ft 2 in (6,756 mm)
 • Coupled 14 ft 6 in (4,420 mm)
 • Tender 14 ft 5 in (4,394 mm)
 • Tender bogie 5 ft (1,524 mm)
Wheel spacing
1-2: 4 ft 7 in (1,397 mm)
2-3: 4 ft 3 in (1,295 mm)
3-4: 5 ft 8 in (1,727 mm)
 • Over couplers 53 ft 8 12 in (16,370 mm)
Height 12 ft 10 in (3,912 mm)
Frame type Bar
Axle load 14 LT (14,220 kg)
 • Leading 7 LT 1 cwt (7,163 kg)
 • 1st coupled 14 LT (14,220 kg)
 • 2nd coupled 13 LT 2 cwt (13,310 kg)
 • 3rd coupled 13 LT 3 cwt (13,360 kg)
 • 4th coupled 12 LT 13 cwt (12,850 kg)
Adhesive weight 52.9 LT (53,750 kg)
Loco weight 59 LT 19 cwt (60,910 kg)
Tender weight 34 LT (34,550 kg)
Total weight 93 LT 19 cwt (95,460 kg)
Tender type 2-axle bogies
Fuel type Coal
Fuel capacity 6 LT (6.1 t)
Water cap 3,080 imp gal (14,000 l)
Firebox type Round-top
 • Firegrate area 31.3 sq ft (2.91 m2)
 • Pitch 7 ft 5 in (2,261 mm)
 • Diameter 4 ft 11 in (1,499 mm)
 • Tube plates 12 ft 5 58 in (3,800 mm)
 • Small tubes 200: 2 in (51 mm)
Boiler pressure 200 psi (1,379 kPa)
Safety valve Ramsbottom
Heating surface 1,413 sq ft (131.3 m2)
 • Tubes 1,306 sq ft (121.3 m2)
 • Firebox 107 sq ft (9.9 m2)
Cylinders Four
High-pressure cylinder 13 in (330 mm) bore
26 in (660 mm) stroke
Low-pressure cylinder 23 in (584 mm) bore
26 in (660 mm) stroke
Valve gear Stephenson
Valve type Piston
Couplers Johnston link-and-pin
Performance figures
Tractive effort 26,400 lbf (117 kN) @ 75%
Operators Cape Government Railways
South African Railways
Transvaal and Natal Collieries
Class SAR Class Experimental 3
Number in class 1
Numbers CGR 839, SAR 909
Delivered 1903
First run 1903
Withdrawn 1920
The 2nd and 3rd coupled axles had flangeless wheels

The South African Railways Class Experimental 3 2-8-0 of 1903 was a steam locomotive from the pre-Union era in the Cape of Good Hope.

In 1903, the Cape Government Railways placed a single experimental 2-8-0 Consolidation type tandem compound steam locomotive in service, based on its Schenectady-built 8th Class of 1901. It was similar to the tandem compound locomotive which had been delivered a year earlier, but with a larger firegrate and an increased heating surface. In 1912, when the locomotive was assimilated into the South African Railways, it was renumbered and designated Class Experimental 3.[1][2][3][4]


H.M. Beatty

In the first few years of the twentieth century, Cape Government Railways (CGR) Chief Locomotive Superintendent H.M. Beatty experimented with various forms of compound steam locomotives. The second of these experimental locomotives was delivered by the American Locomotive Company (ALCO) in 1903. Like CGR no. 804, the first experimental CGR tandem compound locomotive which had been delivered the year before, it was based on the CGR’s Schenectady-built 8th Class of 1901. It was numbered 839, but it was not classified by the CGR and was simply referred to as the Tandem Compound.[1][2][4]

Compound expansion[edit]

Compound locomotive[edit]

In a compound locomotive, steam is expanded in phases. After being expanded in a high-pressure cylinder and having then lost pressure and given up part of its heat, it is exhausted into a larger-volume low-pressure cylinder for secondary expansion, after which it is exhausted through the smokebox. By comparison, in the more usual arrangement of simple expansion (simplex), steam is expanded just once in any one cylinder before being exhausted through the smokebox.[5]

Tandem compound[edit]

The tandem compound locomotive first appeared on the American Erie Railroad in 1867. In a tandem compound engine, each pair of high- and low-pressure cylinders drove a common crosshead, connecting rod and crank. The high-pressure cylinders were bolted onto the fronts of the low-pressure cylinders, which were usually each cast integrally with one half of the smokebox saddle. The hollow piston valves were mounted on the same valve spindle in a common steam chest, with the high-pressure valves arranged for inside admission and the low-pressure valves for outside admission.[1][4][6]


The locomotive was similar to CGR no. 804, the tandem compound which had been delivered to the CGR in 1902 and which was later designated Class Experimental 2, but it had a larger and improved firebox design and an increased heating surface which enhanced its steaming ability. The firegrate area had been increased from 20 to 31.3 square feet (1.858 to 2.908 square metres) and the total heating surface from 1,409.4 to 1,413 square feet (130.938 to 131.272 square metres). However, it suffered from similar mechanical weaknesses as its predecessor.[2][4]

The high-pressure cylinders were 13 inches (330 millimetres) and the low-pressure cylinders 23 inches (584 millimetres) in diameter, with a common stroke of 26 inches (660 millimetres). The steam was admitted to the same side of each piston simultaneously by means of an intricate system of crossed ports in the high-pressure cylinder casting to convey its spent steam to the low-pressure cylinder, from where it was then exhausted after use.[1][4]


Considerable trouble was experienced with the tandem arrangement, since the piston rod packing between the high- and low-pressure cylinders could not be inspected or serviced without removing the high-pressure cylinder. In addition, as a result of high levels of condensation, the low-pressure cylinders were inefficient since the drain cocks had to be opened frequently enough to detract from the locomotive’s otherwise good performance.[1]


The locomotive was placed in service on the lower section of the Cape mainline.[1][4]

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][7]

In 1912, the locomotive was designated Class Experimental 3 and renumbered to 909 on the SAR. Unlike the predecessor Class Experimental 2, it was never modified and remained in service as a tandem compound until it was withdrawn and sold to the Transvaal and Natal Collieries in 1920.[1][2][3][4][8]


  1. ^ a b c d e f g Holland, D.F. (1971). Steam Locomotives of the South African Railways. 1: 1859–1910 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 67–68. ISBN 978-0-7153-5382-0. 
  2. ^ a b c d 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, March 1944. pp. 169-173.
  3. ^ a b c Classification of S.A.R. Engines with Renumbering Lists, issued by the Chief Mechanical Engineer’s Office, Pretoria, January 1912, pp. 9, 12, 15, 36 (Reprinted in April 1987 by SATS Museum, R.3125-6/9/11-1000)
  4. ^ a b c d e f g Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. p. 82. ISBN 0869772112. 
  5. ^ van Riemsdijk, John T. (1970). "The Compound locomotive, Parts 1, 2, 3". Transactions of the Newcomen Society (2). 
  6. ^ van Riemsdijk, John T. (1994). Compound Locomotives: An International Survey. Penryn: Atlantic Books. pp. 36–40. ISBN 0-906899-61-3. 
  7. ^ The South African Railways - Historical Survey. Editor George Hart, Publisher Bill Hart, Sponsored by Dorbyl Ltd., Published c. 1978, p. 25.
  8. ^ Holland, D. F. (1972). Steam Locomotives of the South African Railways. 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. p. 140. ISBN 978-0-7153-5427-8.