South African Class 20 2-10-2

The South African Railways Class 20 2-10-2 of 1935 was 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, designed and built at its Pretoria Mechanical Shops. In 1950, it was modified to an experimental condensing locomotive.^[1][2][3][4]

The Class 20 was the third locomotive type to be designed and built in South Africa, after the Natal Government Railways 4-6-2TT Havelock of 1888 and the Class 2C of 1910.^[4]

Construction

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. The locomotive was intended for use on the South West Africa system, where the tracks consisted of 40 ¹⁄₄ pounds per yard (20 kilograms per metre) section rail, laid in desert conditions and practically without ballast. This restricted Watson to a maximum axle load of 11 long tons (11.2 tonnes) and he decided upon a Santa Fe type wheel arrangement with 48 inches (1,219 millimetres) diameter coupled wheels and flangeless driving and intermediate coupled wheels.^{[2][3][4][5][6]}

A.G. Watson

The sole Class 20 locomotive was numbered 2485. It was a hybrid, with a boiler which had been inherited from a Class 19A locomotive which had been equipped with a Watson Standard no. 1A boiler. The driving wheels were from scrapped Class 8 locomotives. The trailing pony truck was similar to that of the Class 19C, but the leading Bissel truck was specially designed. The bar frames and cylinders were imported.^[1][2][3]

Even though it was not wholly a South African product with its imported frames and cylinders and its inherited boiler from a Swiss-built locomotive, this was the third recorded instance of steam locomotives designed and constructed in South African workshops, after the Natal Government Railways' engine Havelock of 1888 and the Class 2C of 1910.^[2][4][7][8]

Characteristics

The cylinders, with Rotary Cam Poppet valve gear, were identical to those of the Class 19C, but with the stroke reduced from 26 inches (660 millimetres) to 24 inches (610 millimetres). The modified cylinder covers had deep spigots to suit the reduction in stroke. The main drive and valve gear drive was from the third pair of coupled wheels. Grease lubrication was provided for all coupled wheel axle boxes. The ten-coupled wheel arrangement, in conjunction with the sharp curvature of the lines in South West, necessitated special side play for the leading coupled wheel axle boxes and spherical bearings for the leading crank pins.^[2][4]

The design of the leading Bissel truck necessitated certain proportions to suit the ten-coupled wheel arrangement, but the trailing Bissel truck was similar to that of the Class 19C. Its axle boxes were provided with end thrust pad bearings, attached to the axle box covers, which relieved the ends of the bearing from the effects of end thrust. This device proved successful in reducing the number of hot boxes on trailing Bissels.^[2]

The locomotive was tended by a Type MP1 tender, with a 10 long tons (10.2 tonnes) coal capacity, a 4,250 imperial gallons (19,300 litres) water capacity and a 13 long tons 15 hundredweight (13,970 kilograms) axle load. The total weight of the engine and tender in full working order was 124 long tons 8 hundredweight (126,400 kilograms).^[2]

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 resulting Class 20 could be considered as Watson's answer to the Class GCA 2-6-2+2-6-2 Garratt locomotive, which had very similar weight and tractive effort capacities. 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.^[2][3][9]

The construction of this sole Class 20 locomotive marked the beginning of a research process, which was continued two years later with the construction of the sole Class 21 2-10-4 and which eventually culminated in the procurement of the Class 23 4-8-2 fleet in 1939.^[5][6][9]

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 engine. It entered service there in 1935, but after some evidence that the engine was rather severe on the light track, it was returned to South Africa after comparatively short service. It was allocated to Pretoria for working on the Eastern Transvaal System, where its power capacity could be used more productively.^[1][2][3]

Photographs show that, after being returned to Pretoria, the engine's Type MP1 tender was replaced by a larger Type MT2 tender, with a 14 long tons (14.2 tonnes) coal capacity, a 6,000 imperial gallons (27,300 litres) water capacity and a 17 long tons 15 hundredweight (18,030 kilograms) axle load. The total weight of the engine and Type MT2 tender in full working order was 142 long tons 15 hundredweight (145,000 kilograms). 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]

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 the pre-war years, the SAR considered modifying a Class 12A into a condensing locomotive, but this never happened.^[3]

Buckeye bogie

In 1950, the Class 20 was modified to an experimental condensing locomotive, equipped with a Type CL condensing tender which had been ordered from Henschel in 1948. This condensing tender, with Henschel works no. 28388, was designed for a Deutsche Reichsbahn Class 52 condensing locomotive. It was modified slightly and regauged to Cape gauge. The tender rode on Buckeye three-axle bogies to reduce its axle load and had a 11 long tons (11.2 tonnes) coal capacity, a 3,900 imperial gallons (17,700 litres) water capacity and a 13 long tons 17 hundredweight 3 quarters (14,110 kilograms) axle load. The total weight of the modified engine and Type CL tender in full working order was 158 long tons 3 hundredweight (160,700 kilograms).^{[1][3][10][11]}

The Type CL 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 about 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.^[1][3][11]

At that time, no. 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.^[3][9]

Illustration

The pictures illustrate the Class 20 locomotive as built with a Type MP1 tender, then fitted with a larger capacity Type MT2 tender, and finally after modification to an experimental condensing locomotive with a Type CL tender. As on the later Class 25 4-8-4 condensing locomotives, the pipe to feed spent steam back to the condensing tender was mounted on the left side of the engine, as illustrated by the main picture.

• 
  No. 2485 with Type MP1 tender, c. 1935
• 
  No. 2485 with Type MT2 tender, c. 1945

• 
  No. 2485 as experimental condensing locomotive with Type CL tender, c. 1950

References

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

Locomotives of South Africa
Steam	7' ¼" gauge East London 0-4-0VB Table Bay 0-4-0ST Table Bay 0-4-0T Table Bay 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 CGR 0-4-0ST 1881 Coffee Pot CGR 0-6-0ST CGR 0-6-0T 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 CGR 1st Class 4-4-0T CGR 2nd Class 4-4-0T CGR 3rd Class 2-6-0T CGR Railmotor CSAR Class C CSAR Class E CSAR Rack 4-6-4RT CSAR Railmotor Durban's Congella Durban's Edward Innes Durban's John Milne Durban's Sir Albert Port Elizabeth 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 13 Tonner NZASM 14 Tonner NZASM 18 Tonner NZASM 19 Tonner NZASM 32 Tonner NZASM 40 Tonner PPR 26 Tonner PPR 35 Tonner Portuguese 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 Railmotor SAR Dock 0-4-0ST SAR Dock 0-4-0T SWA 2-8-0T 3' 6" gauge Tender engines CGR 1st Class 2-6-0 1876 BP 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 CGR 1st Class 4-4-0TT CGR 2nd Class 2-6-2TT 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 1882 Joy CGR 4th Class 4-6-0TT 1884 CGR 5th Class 4-6-0 1890 CGR 5th Class 4-6-0 1891 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 1st SAR Class 14C 2nd SAR Class 14C 3rd SAR Class 14C 4th 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 1928 SAR Class 16DA 1930 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 SAR Katanga SWA 2-8-0 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 John King & Miner Cape Copper Britannia Cape Copper Caledonia Cape Copper Clara Cape Copper Condenser Cape Copper Scotia Namaqua Copper Pioneer Walvis Bay 2-4-2T Hope 2' & 600mm gauges ACR Class NG-G16A CGR NG 0-4-0T CGR NG 0-6-0T CGR NG 4-6-2T CGR Type A 2-6-4T CGR Type C 0-4-0T NGR Class N 4-6-2T SAR Dutton SAR NG 0-4-0T 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 SWA Class Ha SWA Class Hb SWA Class Hc SWA Class Hd SWA Jung SWA Zwillinge
Electric	Amcoal Class E38 SAR Class ES SAR Class ES1 SAR Class Exp-AC SAR Class 1E SAR Class 2E SAR Class 3E SAR Class 4E SAR Class 5E s1 SAR Class 5E s2 SAR Class 5E s3 SAR Class 5E1 s1 SAR Class 5E1 s2 SAR Class 5E1 s3 SAR Class 5E1 s4 SAR Class 5E1 s5 SAR Class 6E SAR Class 6E1 s1 SAR Class 6E1 s2 SAR Class 6E1 s3 SAR Class 6E1 s4 SAR Class 6E1 s5 SAR Class 6E1 s6 SAR Class 6E1 s7 SAR Class 6E1 s8 SAR Class 6E1 s9 SAR Class 6E1 s10 SAR Class 6E1 s11 SAR Class 7E SAR Class 7E1 SAR Class 7E2 s1 SAR Class 7E2 s2 SAR Class 7E3 s1 SAR Class 7E3 s2 Spoornet Class 7E4 SAR Class 8E SAR Class 9E s1 SAR Class 9E s2 SAR Class 10E SAR Class 10E1 s1 Spoornet Class 10E1 s2 SAR Class 10E2 SAR Class 11E SAR Class 12E Spoornet Class 14E Spoornet Class 14E1 TFR Class 15E Spoornet Class 16E Spoornet Class 17E Spoornet Class 18E s1 TFR Class 18E s2 TFR Class 19E TFR Class 20E TFR Class 21E TFR Class 22E
Gas-electric	SAR Gas-electric
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 TFR Class 35-800 SAR Class 36-000 SAR Class 36-200 SAR Class 37-000 Spoornet Class 39-000 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
List of South African locomotive classes South African locomotive numbering and classification

South African steam locomotive tenders
Cape gauge	Type CL Type CZ Type ET Type ET1 Type EW Type EW1 Type EW2 Type FT Type GT Type HT Type JT Type JT1 Type JV Type KT Type LP Type MP Type MP1 Type MR Type MS Type MT Type MT1 Type MT2 Type MX Type MY Type MY1 Type SH Type SK Type TJ Type TL Type TM Type WE Type WG Type X-17 Type X-20 Type XC Type XC1 Type XD Type XE Type XE1 Type XF Type XF1 Type XF2 Type XJ Type XM Type XM1 Type XM2 Type XM3 Type XM4 Type XP1 Type XS Type YB Type YC Type YE Type YE1 Type ZA Type ZB Type ZC Type ZE
List of South African locomotive classes South African locomotive history