South African Class 20 2-10-2

South African Class 20 2-10-2

No. 2485 as experimental condenser, c. 1950

Type and origin ♠ Type MP1 tender - ♥ Type MT2 tender ♣ Type CL condensing tender Power type Steam Designer South African Railways (A.G. Watson) 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) Driver 3rd coupled axle Gauge 3 ft 6 in (1,067 mm) Cape gauge Leading dia. 28 1⁄2 in (724 mm) Coupled dia. 48 in (1,219 mm) Trailing dia. 34 in (864 mm) Tender wheels ♠♥♣ 34 in (864 mm) Wheelbase ♠ 59 ft 6 1⁄8 in (18,139 mm) ♣ 77 ft 8 7⁄8 in (23,695 mm)  • Engine 31 ft 7 1⁄2 in (9,639 mm)  • Coupled 17 ft (5,182 mm)  • Tender ♠ 16 ft 9 in (5,105 mm) ♥ 20 ft 5 in (6,223 mm) ♣ 33 ft 5 in (10,185 mm)  • Tender bogie ♠ 4 ft 7 in (1,397 mm) ♥ 6 ft 2 in (1,880 mm) ♣ 8 ft 8 in (2,642 mm) Length: ​  • Over couplers ♠ 68 ft 1 in (20,752 mm) ♣ 88 ft 5 1⁄2 in (26,962 mm) Height 12 ft 11 1⁄4 in (3,943 mm) Frame type Bar Axle load ♠♥ 11 LT 14 cwt (11,890 kg) ♣ 13 LT (13,210 kg)  • Leading ♠♥ 8 LT 2 cwt (8,230 kg) ♣ 9 LT 5 cwt (9,398 kg)  • 1st coupled ♠♥ 11 LT 6 cwt (11,480 kg) ♣ 12 LT 16 cwt (13,010 kg)  • 2nd coupled ♠♥ 11 LT 10 cwt (11,680 kg) ♣ 13 LT (13,210 kg)  • 3rd coupled ♠♥ 11 LT 14 cwt (11,890 kg) ♣ 11 LT 12 cwt (11,790 kg)  • 4th coupled ♠♥ 11 LT 4 cwt (11,380 kg) ♣ 11 LT 12 cwt (11,790 kg)  • 5th coupled ♠♥ 11 LT 3 cwt (11,330 kg) ♣ 11 LT 12 cwt 3 qtr (11,820 kg)  • Trailing ♠♥ 8 LT 18 cwt (9,043 kg) ♣ 9 LT 9 cwt 1 qtr (9,614 kg)  • Tender bogie Bogie 1: ♠ 27 LT 10 cwt (27,940 kg) ♥ 33 LT 18 cwt (34,440 kg) ♣ 41 LT 13 cwt 1 qtr (42,330 kg) Bogie 2: ♠ 23 LT 11 cwt (23,930 kg) ♥ 35 LT 10 cwt (36,070 kg) ♣ 37 LT 3 cwt 1 qtr (37,760 kg)  • Tender axle ♠ 13 LT 15 cwt (13,970 kg) ♥ 17 LT 15 cwt (18,030 kg) ♣ 13 LT 17 cwt 3 qtr (14,110 kg) Adhesive weight ♠♥ 56 LT 17 cwt (57,760 kg) ♣ 60 LT 12 cwt 3 qtr (61,610 kg) Loco weight ♠♥ 73 LT 7 cwt (74,530 kg) ♣ 79 LT 7 cwt (80,620 kg) Tender weight ♠ 51 LT 1 cwt (51,870 kg) ♥ 69 LT 8 cwt (70,510 kg) ♣ 78 LT 16 cwt (80,060 kg) Total weight ♠ 124 LT 8 cwt (126,400 kg) ♥ 142 LT 15 cwt (145,000 kg) ♣ 158 LT 3 cwt (160,700 kg) Tender type ♠ MP1 (2-axle bogies) ♥ MT2 (2-axle bogies) ♣ CL (Buckeye 3-axle bogies) CL, MP1, MT2, MX, MY permitted Fuel type Coal Fuel capacity ♠ 10 LT (10.2 t) ♥ 14 LT (14.2 t) ♣ 11 LT 10 cwt (11.7 t) Water cap ♠ 4,250 imp gal (19,300 l) ♥ 6,000 imp gal (27,300 l) ♣ 3,900 imp gal (17,700 l) Firebox type Round-top  • Firegrate area 36 sq ft (3.3 m2) Boiler: ​  • Pitch 8 ft (2,438 mm)  • Diameter 4 ft 10 1⁄4 in (1,480 mm)  • Tube plates 20 ft 3⁄8 in (6,106 mm)  • Small tubes 86: 2 1⁄4 in (57 mm)  • Large tubes 18: 5 1⁄2 in (140 mm) Boiler pressure 200 psi (1,379 kPa) Safety valve Pop Heating surface 1,667 sq ft (154.9 m2)  • Tubes 1,527 sq ft (141.9 m2)  • Arch tubes 15 sq ft (1.4 m2)  • Firebox 125 sq ft (11.6 m2) Superheater: ​  • Heating area 415 sq ft (38.6 m2) Cylinders Two Cylinder size 21 in (533 mm) bore 24 in (610 mm) stroke Valve gear Rotary Cam Poppet Valve type Poppet Couplers AAR knuckle

Performance figures Tractive effort 33,080 lbf (147.1 kN) @ 75%

Career Operators South African Railways Class Class 20 Number in class 1 Numbers 2485 Nicknames Trapsuutjies (Chameleon) Delivered 1935 First run 1935 Withdrawn 1958 Scrapped 1961

The 3rd & 4th coupled axles had flangeless wheels

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.

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.

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.

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.

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.

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.