South African Class 4AR 4-8-2

South African Class 4A & 4AR 4-8-2
No. 1559 at Hutchinson, Cape, 11 November 1916
Type and origin ♠ Class 4A as built with a round-topped firebox ♥ Class 4AR rebuilt with a Watson Standard boiler ♣ Steel firebox - ♦ Copper firebox Power type Steam Designer Cape Government Railways (H.M. Beatty) Builder North British Locomotive Company Serial number 20225-20234 Model CGR 4-8-2 Build date 1913 Total produced 10
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. 54 in (1,372 mm) Trailing dia. 33 in (838 mm) Tender wheels 33 1⁄2 in (851 mm) as built 34 in (864 mm) retyred Wheelbase 58 ft 5 3⁄8 in (17,815 mm)  • Engine 32 ft 2 in (9,804 mm)  • Leading 6 ft 2 in (1,880 mm)  • Coupled 14 ft 5 in (4,394 mm)  • Tender 16 ft 1 in (4,902 mm)  • Tender bogie 4 ft 7 in (1,397 mm) Wheel spacing (Asymmetrical) 1-2: 4 ft 10 in (1,473 mm) 2-3: 4 ft 9 in (1,448 mm) 3-4: 4 ft 10 in (1,473 mm) Length: ​  • Over couplers 66 ft 3 5⁄8 in (20,209 mm) Height ♠ 12 ft 10 in (3,912 mm) ♥ 12 ft 11 1⁄4 in (3,943 mm) Frame type Bar Axle load ♠ 15 LT 12 cwt (15,850 kg) ♥ 14 LT 11 cwt (14,780 kg)  • Leading ♠ 12 LT (12,190 kg) ♥ 13 LT 14 cwt (13,920 kg)  • 1st coupled ♠ 15 LT 2 cwt (15,340 kg) ♥ 14 LT 11 cwt (14,780 kg)  • 2nd coupled ♠ 15 LT 12 cwt (15,850 kg) ♥ 14 LT 9 cwt (14,680 kg)  • 3rd coupled ♠ 15 LT 10 cwt (15,750 kg) ♥ 14 LT 7 cwt (14,580 kg)  • 4th coupled ♠ 15 LT 10 cwt (15,750 kg) ♥ 14 LT 4 cwt (14,430 kg)  • Trailing ♠ 11 LT 14 cwt (11,890 kg) ♥ 10 LT 4 cwt (10,360 kg)  • Tender bogie Bogie 1: 23 LT 9 cwt (23,830 kg) Bogie 2: 23 LT 16 cwt (24,180 kg)  • Tender axle 11 LT 18 cwt (12,090 kg) Adhesive weight ♠ 61 LT 14 cwt (62,690 kg) ♥ 57 LT 11 cwt (58,470 kg) Loco weight ♠ 85 LT 8 cwt (86,770 kg) ♥ 81 LT 9 cwt (82,760 kg) Tender weight 47 LT 5 cwt (48,010 kg) Total weight ♠ 132 LT 13 cwt (134,800 kg) ♥ 128 LT 14 cwt (130,800 kg) Tender type XM (2-axle bogies) XC, XC1, XD, XE, XE1, XF, XF1, XF2, XJ, XM, XM1, XM2, XM3, XM4, XP1, XS permitted Fuel type Coal Fuel capacity 8 LT (8.1 t) Water cap 4,000 imp gal (18,200 l) Firebox type Round-top, combustion chamber  • Firegrate area ♠♥ 37 sq ft (3.4 m2) Boiler: ​  • Model ♥ Watson Standard no. 2  • Pitch ♠ 7 ft 6 in (2,286 mm) ♥ 8 ft (2,438 mm)  • Diameter ♠ 5 ft 6 3⁄8 in (1,686 mm) ♥ 5 ft 7 1⁄2 in (1,714 mm)  • Tube plates ♠ 18 ft 3 in (5,563 mm) ♥♣ 19 ft 4 in (5,893 mm) ♥♦ 19 ft 3 5⁄8 in (5,883 mm)  • Small tubes ♠ 144: 2 1⁄4 in (57 mm) ♥ 81: 2 1⁄2 in (64 mm)  • Large tubes ♠ 22: 5 3⁄8 in (137 mm) ♥ 30: 5 1⁄2 in (140 mm) Boiler pressure 180 psi (1,241 kPa) Safety valve Cole's Pop Heating surface ♠ 2,292 sq ft (212.9 m2) ♥ 2,075 sq ft (192.8 m2)  • Tubes ♠ 2,106 sq ft (195.7 m2) ♥ 1,933 sq ft (179.6 m2)  • Firebox ♠ 186 sq ft (17.3 m2) ♥ 142 sq ft (13.2 m2) Superheater: ​  • Heating area ♠ 554 sq ft (51.5 m2) ♥ 497 sq ft (46.2 m2) Cylinders Two Cylinder size 21 1⁄2 in (546 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 ♠♥ 32,360 lbf (143.9 kN) @ 75%
Career Operators South African Railways Class Class 4A, Class 4AR Number in class 10 Numbers 1551-1560 Delivered 1913-1914 First run 1913 Withdrawn 1974
The leading coupled axle had flangeless wheels

The South African Railways Class 4A 4-8-2 of 1913 was a steam locomotive.

In 1913 and 1914, ten Class 4A steam locomotives with a 4-8-2 Mountain type wheel arrangement were placed in service by the South African Railways.

The Class 4 Mountain type locomotive was designed at the Salt River shops as a heavy mixed traffic locomotive by H.M. Beatty, the last Chief Locomotive Superintendent of the Cape Government Railways (CGR).

Soon after the South African Railways (SAR) locomotive renumbering and classification scheme was carried out in 1912, an order was placed with North British Locomotive Company for a further ten locomotives of this type, built to an altered design. They were delivered late in 1913 and were designated Class 4A, numbered in the range from 1551 to 1560.

The Class 4A locomotive was an improved version of the predecessor Class 4. It had a superheater added, which further resulted in the slide valves and Stephenson valve gear having to be replaced with piston valves and Walschaerts valve gear. The boilers were similar to those of the Class 4, except for the superheater and the length between tube-plates, which was 3 inches (76 millimetres) longer. The bar frames were identical to that of the Class 4, but the cylinders were of a 1 inch (25 millimetres) larger bore. The engines were erected at the Salt River shops in Cape Town during November 1913. Like their two forerunners, they were excellent steamers and, with the design alterations, gave a much better performance.

The Class 4A were the only locomotives to be delivered with Type XM tenders, which had a coal capacity of 8 long tons (8.1 tonnes) and a water capacity of 4,000 imperial gallons (18,200 litres).

The locomotive was the prototype for the Rhodesia Railways 10th Class, a scaled-down version that, like the Class 4A, gave long service.

In the 1930s, many serving locomotives were reboilered with a standard boiler type designed by then Chief Mechanical Engineer 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 ten Class 4A locomotives were reboilered with Watson Standard no. 2 boilers during 1935 and reclassified to Class 4AR. No. 1554 was the first to be so modified and retained its original cab, which was cut back to accommodate the new boiler and wash-out plugs. It also initially retained its original cowcatcher. The other nine locomotives all had new Watson cabs fitted during reboilering, with their distinctive slanted fronts compared to the conventional vertical fronts of their original cabs.