South African Class 20 2-10-2

The sole Class 20 2-10-2 no. 2485 as experimental condensing locomotive, c. 1950

Type and origin
Power type	Steam
Designer	South African Railways
Builder	South African Railways
Model	Class 20
Build date	1935
Total produced	1
Rebuilder	South African Railways
Rebuild date	1950
Number rebuilt	1 to condensing locomotive

Specifications
Configuration	2-10-2 "Santa Fe"
Gauge	3 ft 6 in (1,067 mm) Cape gauge
Leading dia	34 in (864 mm)
Driver diameter	48 in (1,219 mm)
Trailing dia	34 in (864 mm)
Wheelbase	Total: 59 ft 6.125 in (18,139 mm) as built 77 ft 8.875 in (23,695 mm) condensing Engine: 17 ft (5,182 mm) coupled 32 ft 8.25 in (9,963 mm) total MP1 tender: 4 ft 7 in (1,397 mm) bogie 16 ft 9 in (5,105 mm) total Condensing tender: 8 ft 8 in (2,642 mm) bogie 33 ft 5 in (10,185 mm) total
Length	68 ft 1 in (20,752 mm) as built 88 ft 5.5 in (26,962 mm) condensing
Height	12 ft 11.25 in (3,943 mm)
Frame	Bar frame
Axle load	11.5 long tons (11.7 t) on 2nd driver as built 13 long tons (13.2 t) on 2nd driver condensing
Adhesive weight	56.35 long tons (57.3 t) as built 60.6 long tons (61.6 t) condensing
Loco weight	73.35 long tons (74.5 t) as built 79.35 long tons (80.6 t) condensing
Tender weight	MP1 tender: 49,452 lb (22.4 t) empty 51.05 long tons (51.9 t) w/o Condensing tender: 78.8 long tons (80.1 t) w/o
Loco & tender weight	143,800 lb (65.2 t) empty 124.85 long tons (126.9 t) w/o as built 158.15 long tons (160.7 t) w/o condensing
Tender type	MP1, MX, MY, Condensing permitted MP1 tender: * 2 axle bogies * 34 in (864 mm) wheels * Length 25 ft 10.5 in (7,887 mm) Condensing tender: * 3 axle Buckeye bogies * Wheels 34 in (864 mm) dia
Fuel type	Coal
Fuel capacity	MP1 10 long tons (10.2 t) Condensing 11.5 long tons (11.7 t)
Water cap	MP1 4,250 imp gal (19,300 l) Condensing 3,900 imp gal (18,000 l)
Firebox: • Firegrate area	36 sq ft (3.345 m²)
Boiler	4 ft 10.25 in (1,480 mm) inside diameter 20 ft .375 in (6,106 mm) inside length 8 ft (2,438 mm) pitch
Boiler pressure	200 psi (1,380 kPa)
Heating surface	1,667 sq ft (154.869 m²)
• Tubes	86 tubes 2.25 in (57 mm) diameter 18 tubes 5.5 in (140 mm) diameter 1,527 sq ft (141.863 m²)
• Flues	15 sq ft (1.394 m²)
• Firebox	125 sq ft (11.613 m²)
Superheater: • Heating area	415 sq ft (38.555 m²)
Cylinders	Two
Cylinder size	21 in (533 mm) bore 24 in (610 mm) stroke
Valve gear	RC Poppet

Performance figures
Tractive effort	33,080 lbf (147 kN) at 75% pressure

Career
Operators	South African Railways
Class	Class 20
Number in class	1
Numbers	2485
Nicknames	Trapsuutjies (as Condenser)
Delivered	1935
First run	1935
Retired	1961

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The South African Railways Class 20 2-10-2 of 1935 is a steam locomotive.

In 1935 the South African Railways placed one Class 20 steam locomotive with a 2-10-2 Santa Fe type wheel arrangement in service. In 1950 it was modified to an experimental condensing locomotive.^[1]^[2]^[3]

Manufacture

Design

The Class 20 2-10-2 Santa Fe type steam locomotive was designed in 1934 by A.G. Watson, Chief Mechanical Engineer (CME) of the South African Railways (SAR) from 1929 to 1936, and was built by the SAR at its Pretoria Mechanical Shops at Salvokop.^[3]

Watson disliked articulated locomotives and his aim with the Class 20 was to build an as powerful as possible non-articulated locomotive with a maximum 12 long tons (12.2 tonnes) axle load. The end result could be considered as Watson’s answer to the Class GCA 2-6-2+2-6-2 Garratt locomotive, having very similar weight and tractive effort capacities.^[3]^[4]

The Class 20 carried more water and coal than the Garratt and was about 20 long tons (20.3 tonnes) heavier with 33,080 pounds-force (147.1 kilonewtons) tractive effort, compared to the 28,470 pounds-force (126.6 kilonewtons) of the Class GCA. Even so, only one Class 20 was produced and the design was not repeated.^[4]

Construction

The sole Class 20 locomotive was numbered 2485. It was a hybrid with a boiler that had been inherited from a Class 19A locomotive after it was equipped with a Watson Standard no. 1A boiler. The driving wheels were from scrapped Class 8 locomotives. The bar frames and cylinders were imported, the cylinders with Rotary Cam Poppet valve gear being those of a Class 19C, but with the stroke reduced from 26 inches (660 millimetres) to 24 inches (610 millimetres) by means of deep spigots on the modified cylinder covers. The trailing pony truck was similar to that of the Class 19C, but the leading Bissel truck was specially designed.^[1]^[3]

Legacy

The construction of this sole Class 20 locomotive marked the beginning of a research process that was continued two years later with the construction of the sole Class 21 2-10-4 and that eventually culminated in the procurement of the Class 23 4-8-2 fleet in 1939.^[2]

Service

The locomotive was intended for goods traffic on light rail in South West Africa, even though freight traffic volumes in that territory were hardly enough to justify such a powerful locomotive. It entered service there in 1935 but was soon returned to South Africa and allocated to Pretoria, where its power capacity could be used more productively. The Pretoria enginemen considered the Class 20 to be one of their best locomotives since it was free-steaming, more than usually trouble-free and able to handle any load they gave it.^[1]^[3]^[5]

Condensing trials

The arid nature of a large part of South Africa and the consequent difficulty to ensure adequate and suitable water supplies for steam locomotives led to a decision to experiment with condensing locomotives. Such locomotives had by then already been built by Henschel and Son for use in Argentina and Germany. In pre-war days it was considered to modify a Class 12A into a condensing locomotive, but this never materealised.^[3]

In 1950 the Class 20 was modified to an experimental condensing locomotive, equipped with a condensing tender that had been ordered from Henschel in 1948. This condensing tender, with Henschel works number 28388, was designed for a Deutsche Reichsbahn Class 52 condensing locomotive. It was modified slightly and regauged to Cape gauge.^[1]^[3]^[6]^[7]

The tender was designed in such a way that it could also be used on a modified Class 19D or Class 24. This was never done, however. The tender was capable of condensing 27,000 pounds (12,000 kilograms) of exhaust steam per hour in maximum operating temperatures of between 100 and 110 degrees Fahrenheit (38 and 43 degrees Celsius).^[1]^[3]

Beginning in 1951, tests with the condensing Class 20 were conducted in the Eastern Transvaal and the Karoo. It proved the viability of condensing locomotives in South Africa by attaining a saving of between 88% and 93% on water as well as a lower coal consumption, the latter brought on by the higher temperature of the condensed feedwater. Depending on the operating conditions, a water range of between 400 and 680 miles (640 and 1,090 kilometres) was achieved.^[1]^[3]

At the end of 1951 the locomotive was relocated to Touws River, where it was used for further condensing tests and occasionally put to work in regular service. The positive results of the condensing trials led to the introduction of the Class 25 4-8-4 condensing locomotive fleet in 1953.^[3]

At that time number 2485 was again relocated, this time to De Aar, for service on the section via Prieska to Upington on the line to Windhoek in South West Africa. It remained in service there until 1958. Even though its service record and uniqueness justified preservation, it was scrapped in 1961.^[5]

Illustration

The main picture and the following show the Class 20 locomotive as built and after modification to an experimental condensing locomotive. As on the later Class 25 4-8-4 condensing locomotives, the pipe to feed spent steam back to the condenser was mounted on the left side of the engine.

No. 2485, as built, c. 1935
No. 2485 as experimental condensing locomotive, c. 1950

References

1 2 3 4 5 6 Holland, D.F. (1972). Steam Locomotives of the South African Railways, Volume 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 71, 107. ISBN 978-0-7153-5427-8.
1 2 South African Railways and Harbours Locomotive Diagram Book, 2’0” & 3’6” Gauge Steam Locomotives, 15 August 1941, as amended
1 2 3 4 5 6 7 8 9 10 Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. pp. 10–11, 73–74. ISBN 0869772112.
1 2 Durrant, A E (1989). Twilight of South African Steam (1st ed.). Newton Abbott, London: David & Charles. pp. 63–64. ISBN 0715386387.
1 2 Die Lokomotive der Klasse 20 der South African Railways
↑ Henschel & Son works list, compiled by Dietmar Stresow
↑ SAR Klasse 20 2485 on Kondenslok (German)

Wikimedia Commons has media related to South African Class 20 (2-10-2).

Locomotives of South Africa

Steam

7' ¼" gauge	East London Harbour 0-4-0 Table Bay Harbour 0-4-0ST Table Bay Harbour 0-4-0T Table Bay Harbour 0-4-0WT

4' 8½" gauge	Cape 0-4-0T Blackie Cape 0-4-2 Cape 2-4-0T CGR 0-4-0ST Aid Natal 0-4-0ST Durban Natal 0-4-0WT Natal Natal 4-4-0T Perseverance

3' 6" gauge Tank engines	CGR 0-4-0ST 1873 CGR 0-4-0ST 1874 CGR 0-4-0ST 1881 Coffee Pot CGR 0-6-0ST 1902 CGR 0-6-0T 1876 Back-to-Back CGR 2-6-0ST 1900 CGR 2-6-0ST 1902 CGR 1st Class 0-4-0ST 1875 CGR 1st Class 0-4-0ST 1876 CGR 1st Class 2-6-0ST 1876 CGR 1st Class 4-4-0T 1875 CGR 2nd Class 4-4-0T 1882 CGR 3rd Class 2-6-0T CGR Railmotor CSAR Class C CSAR Class E CSAR Rack CSAR Railmotor DSWA Eight-Coupled Tank 2-8-0T Durban's Congella Durban's Edward Innes Durban's John Milne Durban's Sir Albert Port Elizabeth Harbour 0-4-0ST Kowie Railway 0-6-0T Kowie Railway 4-4-0T Metropolitan & Suburban 4-6-2T NGR 2-6-0T Durban & Pietermaritzburg NGR Class I 2-6-2T NGR Class K 0-4-0ST NGR Class K 0-6-0ST NGR Class K 2-6-0T NZASM 10 Tonner NZASM 14 Tonner NZASM 18 Tonner NZASM 19 Tonner NZASM 32 Tonner NZASM 40 Tonner PPR 26 Tonner PPR 35 Tonner Portuguese SAR 0-4-0ST 1903 SAR 0-4-0T no. 69 SAR Class A SAR Class B SAR Class C SAR Class C1 SAR Class C2 SAR Class D SAR Class E SAR Class F SAR Class G SAR Class H SAR Class H1 SAR Class H2 SAR Class J SAR Class K SAR Clayton Railmotor

3' 6" gauge Tender engines	CGR 1st Class 2-6-0 1876 Beyer, Peacock CGR 1st Class 2-6-0 1876 Kitson CGR 1st Class 2-6-0 1879 CGR 1st Class 2-6-0 1891 CGR 1st Class 4-4-0 1879 CGR 1st Class 4-4-0TT 1881 CGR 2nd Class 2-6-2TT 1875 CGR 3rd Class 4-4-0 1883 CGR 3rd Class 4-4-0 1884 CGR 3rd Class 4-4-0 1889 CGR 3rd Class 4-4-0 1898 CGR 3rd Class 4-4-0 1901 CGR 3rd Class 4-4-0 1903 CGR 4th Class 4-4-2 CGR 4th Class 4-6-0TT 1880 CGR 4th Class 4-6-0TT 1882 CGR 4th Class 4-6-0TT 1884 CGR 5th Class 4-6-0 1890 CGR 5th Class 4-6-0 1891 DSWA Eight-Coupled Tender 2-8-0 NGR Havelock NGR Class I SAR Class Exp 1 SAR Class Exp 2 SAR Class Exp 3 SAR Class Exp 4 SAR Class Exp 5 SAR Class Exp 6 SAR Class S SAR Class S1 SAR Class S2 SAR Class 1 SAR Class 1A SAR Class 1B SAR Class 2 SAR Class 2C SAR Class 3 SAR Class 3A SAR Class 3B SAR Class 4 SAR Class 4A SAR Class 5 SAR Class 5A SAR Class 5B SAR Class 6 SAR Class 6A SAR Class 6B SAR Class 6C SAR Class 6D SAR Class 6E SAR Class 6F SAR Class 6G SAR Class 6H SAR Class 6J SAR Class 6K SAR Class 6L SAR Class 6Y SAR Class 6Z SAR Class 7 SAR Class 7A SAR Class 7B SAR Class 7C SAR Class 7D SAR Class 7E SAR Class 7F SAR Class 8 SAR Class 8A SAR Class 8B SAR Class 8C SAR Class 8D SAR Class 8E SAR Class 8F SAR Class 8R SAR Class 8X SAR Class 8Y SAR Class 8Z SAR Class 9 SAR Class 10 SAR Class 10A SAR Class 10B SAR Class 10C SAR Class 10D SAR Class 11 SAR Class 12 SAR Class 12A SAR Class 12B SAR Class 13 SAR Class 14 SAR Class 14A SAR Class 14B SAR Class 14C SAR Class 15 SAR Class 15A SAR Class 15B SAR Class 15C SAR Class 15CA SAR Class 15E SAR Class 15F SAR Class 16 SAR Class 16A SAR Class 16B SAR Class 16C SAR Class 16D SAR Class 16DA SAR Class 16E SAR Class 17 SAR Class 18 SAR Class 19 SAR Class 19A SAR Class 19B SAR Class 19C SAR Class 19D SAR Class 20 SAR Class 21 SAR Class 23 SAR Class 24 SAR Class 25 SAR Class 25NC SAR Class 26 Red Devil

3' 6" gauge Articulated engines	CGR Fairlie CGR Kitson-Meyer SAR Class FC SAR Class FD SAR Class GA SAR Class GB SAR Class GC SAR Class GCA SAR Class GD SAR Class GDA SAR Class GE SAR Class GEA SAR Class GF SAR Class GG SAR Class GH SAR Class GK SAR Class GL SAR Class GM SAR Class GMA SAR Class GO SAR Class HF SAR Class KM SAR Class MA SAR Class MB SAR Class MC SAR Class MC1 SAR Class MD SAR Class ME SAR Class MF SAR Class MG SAR Class MH SAR Class MJ SAR Class MJ1 SAR Class U

2' 6" gauge	Cape Copper 0-6-0T 1871 Cape Copper Britannia Cape Copper Caledonia Cape Copper Clara Class Cape Copper Condenser Cape Copper Scotia Class Namaqua Copper Pioneer

2' & 600mm gauges	ACR Class NG-G16A CGR NG 0-6-0T CGR NG 4-6-2T CGR Type A 2-6-4T CGR Type C 0-4-0T DSWA Class Ha DSWA Class Hb DSWA Class Hc DSWA Class Hd DSWA Jung DSWA Zwillinge NGR Class N 4-6-2T SAR NG 0-4-0T 1899 SAR Class NG1 SAR Class NG2 SAR Class NG3 SAR Class NG4 SAR Class NG5 SAR Class NG6 SAR Class NG7 SAR Class NG8 SAR Class NG9 SAR Class NG10 SAR Class NG-G11 SAR Class NG-G12 SAR Class NG-G13 SAR Class NG-G14 SAR Class NG15 SAR Class NG-G16

Electric

Amcoal Class E38

Diesel

3' 6" gauge Diesel-electric	PRASA Class Afro 4000 SAR Class DS SAR Class DS1 SAR Class 31-000 SAR Class 32-000 SAR Class 32-200 SAR Class 33-000 SAR Class 33-200 SAR Class 33-400 SAR Class 34-000 SAR Class 34-200 SAR Class 34-400 SAR Class 34-500 SAR Class 34-600 SAR Class 34-800 SAR Class 34-900 SAR Class 35-000 SAR Class 35-200 SAR Class 35-400 SAR Class 35-600 SAR Class 36-000 SAR Class 36-200 SAR Class 37-000 Spoornet Class 39-000 TFR Class 35-800 TFR Class 39-200 TFR Class 43-000 TFR Class 44-000

2' gauge Diesel-electric	SAR Class 91-000

3' 6" gauge Diesel-hydraulic	SAR Class 61-000

3' 6" gauge Electro-diesel	Spoornet Class 38-000

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