South African Class 15B 4-8-2

South African Class 15B & 15BR 4-8-2
Class 15BR no. 1982 at Bonnievale, February 1974
Type and origin ♠ Class 15B as built with a Belpaire firebox ♥ Class 15BR rebuilt with a Watson Standard boiler ʘ 22 in (559 mm) bore - ʘ 21 3⁄4 in (552 mm) bore Power type Steam Designer Montreal Locomotive Works Builder Montreal Locomotive Works Serial number 58440-58449, 61424-61443 Model Class 15B Build date 1918-1922 Total produced 30
Specifications Configuration: ​  • Whyte 4-8-2 (Mountain)  • UIC 2'D1'h2 Driver 2nd coupled axle Gauge 3 ft 6 in (1,067 mm) Cape gauge Leading dia. 28 1⁄2 in (724 mm) Coupled dia. 57 in (1,448 mm) Trailing dia. 33 in (838 mm) Tender wheels 34 in (864 mm) Wheelbase 62 ft 7 1⁄4 in (19,082 mm)  • Engine 33 ft 9 in (10,287 mm)  • Leading 6 ft 2 in (1,880 mm)  • Coupled 15 ft (4,572 mm)  • Tender 17 ft 11 in (5,461 mm)  • Tender bogie 4 ft 7 in (1,397 mm) Length: ​  • Over couplers 70 ft 5 1⁄8 in (21,466 mm) Height ♠ 12 ft 10 in (3,912 mm) ♥ 13 ft 3⁄4 in (3,981 mm) Frame type Bar Axle load ♠ 16 LT 11 cwt (16,820 kg) ♥ 16 LT 11 cwt (16,820 kg)  • Leading ♠ 16 LT 4 cwt (16,460 kg) ♥ 16 LT 6 cwt (16,560 kg)  • 1st coupled ♠ 16 LT 1 cwt (16,310 kg) ♥ 16 LT 11 cwt (16,820 kg)  • 2nd coupled ♠ 16 LT 2 cwt (16,360 kg) ♥ 15 LT 16 cwt (16,050 kg)  • 3rd coupled ♠ 16 LT 8 cwt (16,660 kg) ♥ 16 LT 7 cwt (16,610 kg)  • 4th coupled ♠ 16 LT 11 cwt (16,820 kg) ♥ 16 LT 9 cwt (16,710 kg)  • Trailing ♠ 10 LT 8 cwt (10,570 kg) ♥ 10 LT 6 cwt (10,470 kg)  • Tender axle 12 LT 14 cwt 2 qtr (12,930 kg) av. Adhesive weight ♠ 65 LT 2 cwt (66,140 kg) ♥ 68 LT 3 cwt (69,240 kg) Loco weight ♠ 91 LT 14 cwt (93,170 kg) ♥ 94 LT 15 cwt (96,270 kg) Tender weight 50 LT 18 cwt (51,720 kg) Total weight ♠ 142 LT 12 cwt (144,900 kg) ♥ 145 LT 13 cwt (148,000 kg) Tender type LP (2-axle bogies) Fuel type Coal Fuel capacity 10 LT (10.2 t) Water cap 4,250 imp gal (19,300 l) Firebox type ♠ Belpaire ♥ Round-top  • Firegrate area ♠ 40 sq ft (3.7 m2) ♥ 37 sq ft (3.4 m2) Boiler: ​  • Model Watson Standard no. 2A  • Pitch ♠ 7 ft 9 in (2,362 mm) ♥ 8 ft 1 1⁄2 in (2,476 mm)  • Diameter ♠ 5 ft 4 13⁄16 in (1,646 mm) ♥ 5 ft 7 1⁄2 in (1,714 mm)  • Tube plates ♠ 19 ft (5,791 mm) ♥ 21 ft 8 in (6,604 mm) steel ♥ 21 ft 7 5⁄8 in (6,594 mm) copper  • Small tubes ♠ 113: 2 1⁄4 in (57 mm) ♥ 87: 2 1⁄2 in (64 mm)  • Large tubes ♠ 21: 5 1⁄2 in (140 mm) ♥ 30: 5 1⁄2 in (140 mm) Boiler pressure ♠♥ʘ 185 psi (1,276 kPa) ♠♥ʘ 190 psi (1,310 kPa) Safety valve ♠ Ramsbottom - ♥ Pop Heating surface ♠ 2,028 sq ft (188.4 m2) ♥ 2,313 sq ft (214.9 m2)  • Tubes ♠ 1,840 sq ft (171 m2) ♥ 2,171 sq ft (201.7 m2)  • Firebox ♠ 188 sq ft (17.5 m2) ♥ 143 sq ft (13.3 m2) Superheater: ​  • Heating area ♠ 446 sq ft (41.4 m2) ♥ 537 sq ft (49.9 m2) Cylinders Two Cylinder size ♠♥ʘ 22 in (559 mm) bore ♠♥ʘ 21 3⁄4 in (552 mm) bore ♠♥ 28 in (711 mm) stroke Valve gear Walschaerts Valve type Piston Couplers Johnston link-and-pin AAR knuckle (1930s)
Performance figures Tractive effort ♠♥ʘ 32,990 lbf (146.7 kN) @ 75% ♠♥ʘ 33,130 lbf (147.4 kN) @ 75%
Career Operators South African Railways Caminhos de Ferro de Moçambique Tweefontein United Collieries Randfontein Estates Gold Mine Class Class 15B & 15BR Number in class 30 Numbers 1829–1838, 1971-1990 Delivered 1918-1922 First run 1918 Withdrawn 1976
The leading coupled axle had flangeless wheels

The South African Railways Class 15B 4-8-2 of 1918 was a steam locomotive.

Between 1918 and 1922, the South African Railways placed thirty Class 15B steam locomotives with a 4-8-2 Mountain type wheel arrangement in service.

The Class 15B was ordered at a time when further orders of the earlier Class 15 models were unobtainable from manufacturers in the United Kingdom as a result of wartime disruption in Europe. The first batch of ten Class 15B 4-8-2 steam locomotives for the South African Railways (SAR) was therefore ordered from the Montreal Locomotive Works (MLW) in Canada, who undertook to supply engines of equivalent power, wheelbase and weight to that of the Class 15A, but built to their own design. They were built and delivered in 1918, numbered in the range from 1829 to 1838. A second batch of twenty locomotives was ordered from the same builders and delivered in 1922, numbered in the range from 1971 to 1990.

They were built to the general specifications of the Class 15A, but with 4 inches (102 millimetres) thick bar frames instead of plate frames and some other typical North American features, and they were equipped with Belpaire fireboxes with combustion chambers. Many of the parts of these engines were similar to those of the Class 14C which was built by the same manufacturers in that same year.

The first ten locomotives were modified on similar lines as the earlier versions of the Class 14C. As they went in for major overhauls, they had their cylinders bushed to reduce the bore from the as-built 22 to 21 ³⁄₄ inches (559 to 552 millimetres). At the same time, their operating boiler pressure was adjusted upwards from 185 to 190 pounds per square inch (1,276 to 1,310 kilopascals) to keep their tractive effort more or less unaffected by the reduction in piston diameter.

During the 1930s, many serving locomotives were reboilered with a standard boiler type designed by A.G. Watson, CME of the SAR at the time, as part of his standardisation policy. Such Watson Standard reboilered locomotives were reclassified by adding an "R" suffix to their classification.

Eventually all thirty Class 15B locomotives were reboilered with Watson Standard no. 2A boilers and reclassified to Class 15BR. The number plate of no. 1972, as illustrated, had the "B" omitted in error.