South African Class 15A & 15AR 4-8-2
Class 15AR 1788, Graaff Reinet, 4 April 1978
Type and origin ♠ Class 15A as built with a Belpaire firebox ♥ Class 15AR rebuilt with a Watson Standard boiler ♣ Steel firebox - ♦ Copper firebox Power type Steam Designer South African Railways Builder North British Locomotive Company Beyer, Peacock & Company J.A. Maffei Serial number NBL 20556-20560, 20843-20850, 21054-21063, 21436-21441, 21502-21505, 21718-21737, 22736-22750 BP 5955-5974, 5978-5987 Maffei 5625-5645 Model Class 15A Build date 1914-1925 Total produced 119
Specifications Configuration: ​  • Whyte 4-8-2 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 60 ft 6+3⁄4 in (18,459 mm) ​  • Engine 33 ft 8 in (10,262 mm)  • Leading 6 ft 2 in (1,880 mm)  • Coupled 15 ft (4,572 mm)  • Tender 16 ft 9 in (5,105 mm)  • Tender bogie 4 ft 7 in (1,397 mm) Length: ​  • Over couplers 68 ft 11+1⁄8 in (21,009 mm) Height ♠ 12 ft 10 in (3,912 mm) ♥ 12 ft 11+3⁄4 in (3,956 mm) Frame type Plate Axle load ♠♥♣ 16 LT 11 cwt (16,820 kg) ♥♦ 16 LT 14 cwt (16,970 kg) ​  • Leading ♠ 15 LT 14 cwt (15,950 kg) ♥♣ 16 LT 1 cwt (16,310 kg) ♥♦ 16 LT 6 cwt (16,560 kg)  • 1st coupled ♠♥♣ 16 LT 10 cwt (16,760 kg) ♥♦ 16 LT 13 cwt (16,920 kg)  • 2nd coupled ♠ 16 LT 10 cwt (16,760 kg) ♥♣ 16 LT 9 cwt (16,710 kg) ♥♦ 16 LT 6 cwt (16,560 kg)  • 3rd coupled ♠♥♣ 16 LT 11 cwt (16,820 kg) ♥♦ 16 LT 14 cwt (16,970 kg)  • 4th coupled ♠♥♣ 16 LT 9 cwt (16,710 kg) ♥♦ 16 LT 11 cwt (16,820 kg)  • Trailing ♠ 12 LT 6 cwt (12,500 kg) ♥♣ 12 LT (12,190 kg) ♥♦ 12 LT 7 cwt (12,550 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 (67,060 kg) ♥♣ 65 LT 19 cwt (67,010 kg) ♥♦ 66 LT 4 cwt (67,260 kg) Loco weight ♠ 94 LT 16 cwt (96,320 kg) ♥♣ 94 LT 6 cwt (95,810 kg) ♥♦ 94 LT 17 cwt (96,370 kg) Tender weight 51 LT 1 cwt (51,870 kg) Total weight ♠ 145 LT 17 cwt (148,200 kg) ♥♣ 145 LT 7 cwt (147,700 kg) ♥♦ 145 LT 18 cwt (148,200 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 (10.2 t) Water cap. 4,250 imp gal (19,300 L) Firebox: ​  • Type ♠ Belpaire, combustion chamber ♥ Round-top  • Grate 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 1⁄2 in (2,451 mm)  • Diameter ♠ 5 ft 4+5⁄8 in (1,641 mm) ♥ 5 ft 7+1⁄2 in (1,714 mm)  • Tube plates ♠ 19 ft (5,791 mm) ♥♣ 21 ft 8 in (6,604 mm) ♥♦ 21 ft 7+5⁄8 in (6,594 mm)  • 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 ♠ 185 psi (1,276 kPa) ♥ 190 psi (1,310 kPa) Safety valve ♠ Ramsbottom - ♥ Pop Heating surface: ​  • Firebox ♠ 192 sq ft (17.8 m2) ♥ 142 sq ft (13.2 m2)  • Tubes ♠ 1,834 sq ft (170.4 m2) ♥ 2,171 sq ft (201.7 m2)  • Total surface ♠ 2,026 sq ft (188.2 m2) ♥ 2,313 sq ft (214.9 m2) Superheater: ​  • Heating area ♠ 478 sq ft (44.4 m2) ♥ 537 sq ft (49.9 m2) Cylinders Two Cylinder size 22 in (559 mm) bore 28 in (711 mm) stroke Valve gear Walschaerts Valve type Poppet (No. 2100), Piston (Others) Couplers Johnston link-and-pin AAR knuckle (1930s)
Performance figures Tractive effort ♠ 32,990 lbf (146.7 kN) @ 75% ♥ 33,880 lbf (150.7 kN) @ 75%
Career Operators South African Railways Swaziland Railway Class Class 15A & 15AR Number in class 119 Numbers 1571-1575, 1781-1828, 1839-1858, 1961-1970, 2011-2025, 2080-2100 Delivered 1914-1925 First run 1914 Withdrawn 1980s
Most leading coupled axles had flangeless wheels

The South African Railways Class 15A 4-8-2 of 1914 was a steam locomotive.

Between 1914 and 1925, the South African Railways placed 119 Class 15A steam locomotives with a 4-8-2 wheel arrangement in service, delivered in ten batches from three manufacturers.^[1][2][3]

The Classes 15 and 15A were the final development of the plate-framed 4-8-2 Mountain locomotive designed by D.A. Hendrie, Chief Mechanical Engineer (CME) of the South African Railways (SAR) from 1910 to 1922. Of the whole Hendrie Mountain family, the Class 15A was the most numerous and proved to be his most useful.^[1][4]

The predecessor Class 15 locomotives had one flaw, their excessively long fire tubes. When more locomotives of the type were ordered, Hendrie improved the boiler by adding a combustion chamber in the firebox, which shortened the distance between tube plates from 21 feet 9 inches (6,629 millimetres) to 19 feet (5,791 millimetres). When the first five of these redesigned locomotives were delivered in 1914, they were designated Class 15A. Altogether 119 were ultimately built in ten batches by three manufacturers. Being wartime, initial production and delivery occurred in dribs and drabs.^[1][2]

• Five were delivered by the North British Locomotive Company (NBL) in July 1914, numbered in the range from 1571 to 1575.^[2][5]
• Eight more were delivered by NBL, also in 1914, numbered in the range from 1781 to 1788. Like the Class 15, these first thirteen locomotives had narrow cabs, rear end running boards which curved down below their cabs and Belpaire fireboxes, but unlike the Class 15, the firebox had a combustion chamber.^[5]
• Ten more were delivered by NBL in 1915, numbered in the range from 1789 to 1798. While the first two batches were delivered with all coupled wheels flanged, beginning with this third batch the leading coupled wheels were flangeless to cope with the sharp curves on the Hex River Pass. These and subsequent locomotives had rear end running boards which continued straight through underneath their cabs.^[1][2][5]
• Six more were delivered by NBL in 1916, numbered in the range from 1799 to 1804.^[2][5]
• Four more were delivered by NBL in 1917, numbered in the range from 1805 to 1808.^[2][5]
• Twenty more were delivered by NBL in 1920, numbered in the range from 1809 to 1828. These twenty and all subsequent Class 15A locomotives were delivered with wider cabs.^[5]
• Twenty were delivered by Beyer, Peacock & Company in 1920, numbered in the range from 1839 to 1858.^[6]
• Ten more were delivered by Beyer, Peacock in 1921, numbered in the range from 1961 to 1970.^[6]
• Fifteen were delivered by NBL in 1921, numbered in the range from 2011 to 2025.^[5]
• Twenty-one were delivered by J.A. Maffei in 1925, numbered in the range from 2080 to 2100.^[1][4]

The locomotives had 1+1⁄4 inches (32 millimetres) thick plate frames and piston valves, actuated by Walschaerts valve gear.^[2]

To reduce the weight on the trailing wheels, steel fireboxes were originally used instead of copper. Some locomotives in Natal had been fitted with steel fireboxes years previously and the results were fairly good, but wherever water supplies were of poor quality, steel fireboxes gave a lot of trouble and necessitated the introduction of water treatment plants to prevent corrosion. This reintroduction of steel fireboxes eventually led to its widespread use on all the larger locomotive types, but it also forced the SAR to adopt locomotive water treatment as a general policy.^[1][3][4][7]

The first five locomotives of 1914 were delivered with steel fireboxes. In the case of the Classes 15 and 15A, it was still early days for water treatment and enough trouble was experienced to result in their steel fireboxes being replaced with copper fireboxes. Hendrie followed a conservative policy in this respect and the majority of the rest of the Class 15A fleet were originally fitted with copper fireboxes. Steel fireboxes were only to be fitted in large numbers by his successor, Colonel F.R. Collins DSO, and only the last batch of 1925, supplied by Maffei, were delivered with steel fireboxes.^[2][7]

The last Class 15A locomotive, Maffei-built no. 2100, was fitted with Lentz Rotary Cam Poppet valve gear as an experiment, but this was later replaced with Walschaerts valve gear and piston-valve cylinders, thereby turning no. 2100 into a standard Class 15A.^[1][2][4]

During the 1930s, many serving locomotives were reboilered with a standard boiler type designed by A.G. Watson, CME of the SAR from 1929 to 1936, as part of his standardisation policy. Such Watson Standard reboilered locomotives were reclassified by adding an "R" suffix to their classification.^[3][8][9]

When Class 15A locomotives were reboilered with Watson Standard no. 2A boilers, they were therefore reclassified to Class 15AR. Early conversions were equipped with copper and later conversions with steel fireboxes. 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, while the cab platform was extended over the front end of the tender underframe. Many of the reboilered engines were later fitted with Type MR or Type MT tenders.^[2][8][9]

Since the only difference between the as-delivered Class 15 and Class 15A lay in the length of their boilers and whether they were built with or without combustion chambers, both models were reclassified to Class 15AR when they were reboilered with Watson Standard boilers. In the case of the Class 15A engines, reboilering replaced their combustion-chambered Belpaire boilers with less efficient Watson Standard boilers without combustion chambers and it was found that the rebuilds were inferior steamers compared with their non-rebuilt sister engines.^[3][7][10]

Their original Belpaire boilers were fitted with Ramsbottom safety valves, while the Watson Standard boiler was fitted with Pop safety valves. Another obvious difference between an original and a Watson Standard reboilered locomotive is usually a rectangular regulator cover, just to the rear of the chimney on the reboilered locomotive. In the case of the Class 15A and Class 15AR, two even more obvious differences are the Watson cab and the absence of the Belpaire firebox hump between the cab and boiler on the reboilered locomotives. In addition, during reboilering the early Class 15A models with curved down rear end running boards and narrow cabs were altered to straight rear end running boards with Watson cabs.^[8][9]

The Class 15A, one of the best classes of mainline mixed traffic locomotives to see service in South Africa, was placed in service on the Cape mainline to Kimberley where they formed the mainstay of motive power for many years. The engine was a good utility type and gave a good account of itself on goods and passenger working alike. It is noted for reducing the running time of the Union Limited by 2½ hours in March 1922. When they were superseded on this section by more powerful types, they ended up working in all parts of the country and proved to be reliable, free-steaming locomotives which ran up high mileage figures between major overhauls.^[1][2]

As the reboilered Class 15AR, many ended up working in the Eastern Transvaal around Waterval Boven, in the Western Transvaal, Eastern Cape and the Orange Free State. During the 1960s, many were transferred to the Cape Midland and used mainly on the section from Port Elizabeth to Klipplaat and in passenger service on the Uitenhage suburban.^[3]

Near the end of their service lives in the early 1980s, they were all relegated to shunting work at centres all around the country, except for some which were hired out to Swaziland and which were still employed in mainline service on the Swaziland Railway until they were eventually replaced by diesel traction and retired. By the time they were withdrawn after more than sixty years in service, many of these locomotives had completed three million miles of heavy-duty mainline work.^[4][11]

The table lists the Class 15A engine numbers, builders, years built, works numbers and eventual classifications.^[8][9]

Media related to South African Class 15A (4-8-2) at Wikimedia Commons