South African Class U 2-6-2+2-6-2

South African Class U 2-6-2+2-6-2

Class U Union Garratt, c. 1930

Type and origin Power type Steam Designer Maffei Builder Maffei Model Class U Build date 1927 Total produced 10

Specifications Configuration 2-6-2+2-6-2 (Double Prairie) Driver 3rd & 4th coupled axles Gauge 3 ft 6 in (1,067 mm) Cape gauge Leading dia. 30 in (762 mm) Coupled dia. 48 in (1,219 mm) Trailing dia. 30 in (762 mm) Wheelbase 66 ft 11 in (20,396 mm)  • Engine 19 ft 8 in (5,994 mm) each  • Coupled 9 ft (2,743 mm) each Pivot centres 39 ft 1 in (11,913 mm) Length: ​  • Over couplers 74 ft 8 in (22,758 mm) Width 10 ft (3,048 mm) Height 12 ft 11 7⁄16 in (3,948 mm) Frame type Bar Axle load 18 LT 12 cwt (18,900 kg)  • Leading 16 LT (16,260 kg) front 11 LT 1 cwt (11,230 kg) rear  • 1st coupled 18 LT 9 cwt (18,750 kg)  • 2nd coupled 18 LT 2 cwt (18,390 kg)  • 3rd coupled 18 LT 1 cwt (18,340 kg)  • 4th coupled 18 LT 10 cwt (18,800 kg)  • 5th coupled 18 LT 12 cwt (18,900 kg)  • 6th coupled 18 LT 6 cwt (18,590 kg)  • Trailing 12 LT 12 cwt (12,800 kg) front 15 LT 3 cwt (15,390 kg) rear Adhesive weight 110 LT (111,800 kg) Loco weight 164 LT 16 cwt (167,400 kg) Fuel type Coal Fuel capacity 14 LT (14,220 kg) Water cap 2,640 imp gal (12,000 l) front 2,640 imp gal (12,000 l) belly Firebox type Round-top  • Firegrate area 60 sq ft (5.6 m2) Boiler: ​  • Pitch 8 ft 3⁄4 in (2,457 mm)  • Diameter 6 ft 1 in (1,854 mm)  • Tube plates 18 ft 1⁄2 in (5,499 mm)  • Small tubes 170: 2 1⁄4 in (57 mm)  • Large tubes 30: 5 1⁄2 in (140 mm) Boiler pressure 180 psi (1,241 kPa) Safety valve Pop Heating surface 2,806 sq ft (260.7 m2)  • Tubes 2,586 sq ft (240.2 m2)  • Arch tubes 25 sq ft (2.3 m2)  • Firebox 195 sq ft (18.1 m2) Superheater: ​  • Heating area 633 sq ft (58.8 m2) Cylinders Four Cylinder size 18 1⁄2 in (470 mm) bore 26 in (660 mm) stroke Valve gear Walschaerts Valve type Piston Couplers AAR knuckle

Performance figures Tractive effort 50,050 lbf (222.6 kN) @ 75%

Career Operators South African Railways Class Class U Number in class 10 Numbers 1370-1379 Nicknames U Boat Delivered 1927 First run 1927 Withdrawn c. 1958

The South African Railways Class U 2-6-2+2-6-2 of 1927 was an articulated steam locomotive.

In 1927, the South African Railways placed ten Class U Union Garratt articulated steam locomotives with a 2-6-2+2-6-2 Double Prairie type wheel arrangement in service. The locomotive design embodied the Garratt design at the front end and the Modified Fairlie design at the rear end.

Specifications for the Class GJ 2-6-2+2-6-2 Garratt locomotive were prepared by Colonel F.R. Collins DSO, Chief Mechanical Engineer of the South African Railways (SAR) in 1925, but the class designation was changed to Class U when orders for its design and construction were placed with Maffei in Munich, Germany. The locomotive design deviated from the Garratt principle, the patent of which was held by Beyer, Peacock and Company, and the end result was a hybrid locomotive, part Garratt and part Modified Fairlie. Ten locomotives were delivered in 1927, numbered in the range from 1370 to 1379.

The front end of the locomotive was of a typical Garratt arrangement, with a water bunker mounted on the front engine unit's frame, while the rear end was constructed in the Modified Fairlie fashion, with the coal bunker mounted on a rigid extension of the locomotive's main frame and with the pivoting rear engine unit positioned beneath the coal bunker. One reason which had been put forward for the construction of the rear end on the Modified Fairlie principle was to enable the coal bunker to be rigidly in line with the boiler frame, to ensure a satisfactory arrangement for the installation of the mechanical stoker. Since the locomotive was neither Garratt nor Modified Fairlie, its unique configuration was dubbed Union Garratt.

The locomotives were superheated and had round-topped fireboxes, Walschaerts valve gear and bar frames. In order to enable the longest boiler possible without increasing the overall length of the locomotive, the front engine unit was tucked in underneath the boiler frame somewhat further than was usual on a purebred Garratt locomotive. An additional underbelly water tank compensated for the resulting diminished water capacity of the front water bunker.

All the engine's water was carried in the front bunker tank and in the large underbelly tank, each tank with a capacity of 2,640 imperial gallons (12,000 litres; 3,170 US gallons). The rear bunker carried only coal and had a capacity of 14 long tons (14.2 tonnes). The main frame therefore carried the smokebox, boiler, firebox, cab, coal bunker, as well as the underbelly water tank.