South African Class 20 2-10-2

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.

References

  1. 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.
  2. 1 2 South African Railways and Harbours Locomotive Diagram Book, 2’0” & 3’6” Gauge Steam Locomotives, 15 August 1941, as amended
  3. 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.
  4. 1 2 Durrant, A E (1989). Twilight of South African Steam (1st ed.). Newton Abbott, London: David & Charles. pp. 63–64. ISBN 0715386387.
  5. 1 2 Die Lokomotive der Klasse 20 der South African Railways
  6. Henschel & Son works list, compiled by Dietmar Stresow
  7. SAR Klasse 20 2485 on Kondenslok (German)
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