South African Class GL 4-8-2+2-8-4

South African Class GL 4-8-2+2-8-4
No. 2351 Princess Alice, c. 1930
Type and origin Power type Steam Designer Beyer, Peacock and Company Builder Beyer, Peacock and Company Serial number 6530-6531, 6639-6644 Build date 1929–1930 Total produced 8
Specifications Configuration: ​  • Whyte 4-8-2+2-8-4 (Double Mountain)  • UIC 2'D1'+1'D2'h4t Driver 3rd & 6th coupled axles 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. 33 in (838 mm) Wheelbase 83 ft 7 in (25,476 mm)  • Engine 27 ft 8 in (8,433 mm) each  • Leading 6 ft 2 in (1,880 mm) each  • Coupled 13 ft 3 in (4,039 mm) each Pivot centres 41 ft 6 in (12,649 mm) Wheel spacing (Asymmetrical) 1-2: 4 ft 3 in (1,295 mm) 2-3: 4 ft 3 in (1,295 mm) 3-4: 4 ft 9 in (1,448 mm) Length: ​  • Over couplers 90 ft 7 7⁄8 in (27,632 mm) Height 13 ft (3,962 mm) Frame type Bar Axle load 18 LT 14 cwt (19,000 kg)  • Leading 21 LT 10 cwt (21,850 kg) front 19 LT 12 cwt (19,910 kg) rear  • 1st coupled 17 LT 18 cwt (18,190 kg)  • 2nd coupled 18 LT (18,290 kg)  • 3rd coupled 18 LT (18,290 kg)  • 4th coupled 17 LT 11 cwt (17,830 kg)  • 5th coupled 18 LT 6 cwt (18,590 kg)  • 6th coupled 18 LT 14 cwt (19,000 kg)  • 7th coupled 18 LT 5 cwt (18,540 kg)  • 8th coupled 18 LT 3 cwt (18,440 kg)  • Trailing 12 LT 6 cwt (12,500 kg) front 12 LT 16 cwt (13,010 kg) rear Adhesive weight 144 LT 17 cwt (147,200 kg) Loco weight 211 LT 1 cwt (214,400 kg) Fuel type Coal Fuel capacity 12 LT (12.2 t) Water cap 4,650 imp gal (21,100 l) front 2,350 imp gal (10,700 l) rear Firebox type Round-top  • Firegrate area 75 sq ft (7.0 m2) Boiler: ​  • Pitch 8 ft 6 in (2,591 mm)  • Diameter 7 ft (2,134 mm)  • Tube plates 14 ft 6 1⁄2 in (4,432 mm)  • Small tubes 263: 2 in (51 mm)  • Large tubes 50: tubes 5 1⁄2 in (140 mm) Boiler pressure 200 psi (1,379 kPa) Safety valve Pop Heating surface 3,396 sq ft (315.5 m2)  • Tubes 3,049 sq ft (283.3 m2)  • Firebox 347 sq ft (32.2 m2) Superheater: ​  • Heating area 835 sq ft (77.6 m2) Cylinders Four Cylinder size 22 in (559 mm) bore 26 in (660 mm) stroke Valve gear Walschaerts Valve type Piston Couplers AAR knuckle
Performance figures Tractive effort 78,650 lbf (349.9 kN) @ 75%
Career Operators South African Railways Class Class GL Number in class 8 Numbers 2350-2357 Delivered 1929-1930 First run 1929 Withdrawn 1972

The South African Railways Class GL 4-8-2+2-8-4 of 1929 was an articulated steam locomotive.

In 1929 and 1930, the South African Railways placed eight Class GL Garratt articulated steam locomotives with a 4-8-2+2-8-4 Double Mountain type wheel arrangement in service. Built at Beyer, Peacock and Company's Gorton Foundry, they were originally designed to work on the Durban to Cato Ridge section of the Natal mainline. The Class GL was eventually displaced to the route between Glencoe and Vryheid before spending their final working years operating on the line from Stanger to Empangeni.

The Class GL had its origin in the steady increase in loads experienced by the Natal mainline in the years prior to the First World War. The old Natal mainline had gradients of 1 in 30 (3⅓%) whilst the newer line, relocated to provide an easier route, still had 38 miles (61 kilometres) of near-uninterrupted 1 in 66 (1½%) gradients. Moreover, the tight curvature of the line with curves of as little as 275 feet (84 metres) radius precluded the use of large, long wheelbased, non-articulated locomotives and restricted them to a coupled wheelbase of 9 feet (2,743 millimetres). These factors combined with ever-increasing train weights ensured that the line rapidly became a bottleneck.

The decision to electrify the line from Glencoe Junction to Durban had been taken in 1914, coincidentally the year in which the South African Railways (SAR) ordered its first Cape gauge Garratt, the Class GA 2-6-0+0-6-2. Electrification was placed in abeyance along with the delivery of the Class GA until the end of the First World War.

Despite this delay, the process of electrification began in earnest in 1922 and by 1926 full electrified haulage had been instituted between Glencoe and Pietermaritzburg, with lashups of three electric locomotives being used on the heaviest freights. These trains were then hauled onward to Durban by a pair of Class 14 4-8-2 steam locomotives.