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) 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 Firegrate area 36 sq ft (3.345 m2) 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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

• Class 20 no. 2485 (2-10-2).jpg

  No. 2485, as built, c. 1935

• Class 20 no. 2485 (2-10-2) condenser.jpg

  No. 2485 as experimental condensing locomotive, c. 1950