South African Class 12B 4-8-2

South African Class 12B & 12R 4-8-2

Class 12R no. 1931 at Port Elizabeth sheds, with Belpaire firebox, c. 1930

Type and origin ♠ Class 12B as built with a Belpaire firebox ♥ Class 12R rebuilt with a Watson Standard boiler Power type Steam Designer South African Railways (D.A. Hendrie) Builder Baldwin Locomotive Works Serial number 52476, 52558-52559, 52583-52584, 52649-52651, 52690-52693, 52712-52713, 52723-52724, 52754-52767 Model Class 12B Build date 1920 Total produced 30

Specifications Configuration 4-8-2 (Mountain) Driver 2nd coupled axle Gauge 3 ft 6 in (1,067 mm) Cape gauge Leading dia. 28 1⁄2 in (724 mm) Coupled dia. 51 in (1,295 mm) Trailing dia. 33 in (838 mm) Tender wheels 34 in (864 mm) Wheelbase 58 ft 3 3⁄4 in (17,774 mm)  • Engine 31 ft 9 1⁄2 in (9,690 mm)  • Leading 6 ft 2 in (1,880 mm)  • Coupled 13 ft 6 in (4,115 mm)  • Tender 16 ft 9 in (5,105 mm)  • Tender bogie 4 ft 7 in (1,397 mm) Length: ​  • Over couplers 66 ft 8 in (20,320 mm) Height ♠ 12 ft 10 in (3,912 mm) ♥ 12 ft 7 1⁄2 in (3,848 mm) Frame type Plate Axle load ♠ 16 LT 15 cwt (17,020 kg) ♥ 17 LT 9 cwt (17,730 kg)  • Leading ♠ 15 LT 13 cwt (15,900 kg) ♥ 16 LT 2 cwt (16,360 kg)  • 1st coupled ♠ 16 LT 13 cwt (16,920 kg) ♥ 16 LT 15 cwt (17,020 kg)  • 2nd coupled ♠ 16 LT 15 cwt (17,020 kg) ♥ 17 LT 9 cwt (17,730 kg)  • 3rd coupled ♠ 16 LT 14 cwt (16,970 kg) ♥ 16 LT 17 cwt (17,120 kg)  • 4th coupled ♠ 16 LT 15 cwt (17,020 kg) ♥ 16 LT 15 cwt (17,020 kg)  • Trailing ♠ 12 LT 4 cwt (12,400 kg) ♥ 11 LT 16 cwt (11,990 kg)  • Tender bogie Bogie 1: 27 LT 10 cwt (27,940 kg) Bogie 2: 23 LT 11 cwt (23,930 kg)  • Tender axle 13 LT 15 cwt (13,970 kg) Adhesive weight ♠ 66 LT 17 cwt (67,920 kg) ♥ 67 LT 16 cwt (68,890 kg) Loco weight ♠ 94 LT 14 cwt (96,220 kg) ♥ 95 LT 14 cwt (97,240 kg) Tender weight 51 LT 1 cwt (51,870 kg) Total weight ♠ 145 LT 15 cwt (148,100 kg) ♥ 146 LT 15 cwt (149,100 kg) Tender type MP1 (2-axle bogies) MP, MP1, MR, MS, MT, MT1, MT2, MX, MY, MY1 permitted Fuel type Coal Fuel capacity 10 LT (10,160 kg) 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. 2  • Pitch ♠ 7 ft 7 in (2,311 mm) ♥ 7 ft 8 1⁄4 in (2,343 mm)  • Diameter ♠♥ 5 ft 7 1⁄2 in (1,714 mm)  • Tube plates ♠ 20 ft (6,096 mm) ♥ 19 ft 4 in (5,893 mm) steel ♥ 19 ft 3 5⁄8 in (5,883 mm)  • Small tubes ♠ 139: 2 1⁄4 in (57 mm) ♥ 87: 2 1⁄2 in (64 mm)  • Large tubes ♠ 24: 5 1⁄2 in (140 mm) ♥ 30: 5 1⁄2 in (140 mm) Boiler pressure ♠♥ 190 psi (1,310 kPa) Safety valve ♠ Ramsbottom - ♥ Pop Heating surface ♠ 2,488 sq ft (231.1 m2) ♥ 2,075 sq ft (192.8 m2)  • Tubes ♠ 2,328 sq ft (216.3 m2) ♥ 1,933 sq ft (179.6 m2)  • Firebox ♠ 160 sq ft (15 m2) ♥ 142 sq ft (13.2 m2) Superheater: ​  • Heating area ♠ 574 sq ft (53.3 m2) ♥ 492 sq ft (45.7 m2) Cylinders Two Cylinder size 22 1⁄2 in (572 mm) bore 26 in (660 mm) stroke Valve gear Walschaerts Valve type Piston Couplers Johnston link-and-pin AAR knuckle (1930s)

Performance figures Tractive effort ♠♥ 36,780 lbf (163.6 kN) @ 75%

Career Operators South African Railways Class Class 12B & 12R Number in class 30 Numbers 1931-1960 Delivered 1920 First run 1920 Withdrawn c. 1984

The leading coupled axle had flangeless wheels

The South African Railways Class 12B 4-8-2 of 1920 was a steam locomotive.

In 1920, the South African Railways placed thirty Class 12B steam locomotives with a 4-8-2 Mountain type wheel arrangement in service.

In May 1920, an additional thirty locomotives, built to the Class 12 design of SAR Chief Mechanical Engineer (CME) D.A. Hendrie, were delivered to the South African Railways (SAR) from Baldwin Locomotive Works in the United States of America. Most of them were erected in the SAR workshops, but a few were contracted to James Brown and Company at Durban for erection. Even though they were very similar to the second and subsequent orders of the Class 12 which was also designed specifically for the Midland System, they were classified separately as Class 12B and numbered in the range from 1931 to 1960. Like the Class 12, they were also built with plate frames, Walschaerts valve gear and Belpaire fireboxes.

The separate 12B classification has been ascribed to the fact that the wheelbase of the leading bogie was 2 inches (51 millimetres) longer than on the original Class 12 locomotives. This was probably not the reason, bearing in mind that only the first eight out of altogether 46 Class 12 locomotives were built with leading bogies with a 6 feet (1,829 millimetres) wheelbase, while the other thirty-eight all had leading bogies with a 6 feet 2 inches (1,880 millimetres) wheelbase, the same as the Class 12B. More likely, the separate classification was simply based on the fact that the Class 12 was British-built while the Class 12B was American-built.

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

All thirty Class 12B locomotives were eventually reboilered with Watson Standard no. 2 boilers. In the process, they were also equipped with Watson cabs with their distinctive slanted fronts, compared to the conventional vertical fronts of their original cabs. Upon reboilering, the unknown original reason for the separate classification was ignored and instead of becoming Class 12BR, the reboilered locomotives were reclassified to Class 12R along with the reboilered Class 12 locomotives.