South African Class U 2-6-2+2-6-2
|South African Class U 2-6-2+2-6-2|
Class U Union Garratt, circa 1930
|Type and origin|
|Configuration||2-6-2+2-6-2 "Double Prairie" Union Garratt|
|Gauge||3 ft 6 in (1,067 mm) Cape gauge|
|30 in (762 mm)|
|Driver diameter||48 in (1,220 mm)|
|30 in (762 mm)|
|Wheelbase||Total: 66 ft 11 in (20.396 m)
9 ft (2.743 m) coupled
19 ft 8 in (5.994 m) total
|Length||74 ft 8 in (22.758 m)|
|Height||12 ft 11.4375 in (3.948 m)|
|Frame||Bar frame, 39 ft 1 in (11.913 m) between pivot centres|
|Axle load||18.6 long tons (18.9 t) on 5th driver|
|Weight on drivers||110 long tons (111.8 t)|
|Locomotive weight||266,756 lb (121.0 t) empty
164.8 long tons (167.4 t) w/o
|Fuel capacity||14 long tons (14.2 t)|
|Water capacity||2,640 imp gal (12,000 l) front
2,640 imp gal (12,000 l) underbelly
|Boiler||6 ft 1 in (1.854 m) inside diameter
18 ft 0.5 in (5.499 m) inside length
8 ft 0.75 in (2.457 m) pitch
|Boiler pressure||180 psi (1,240 kPa)|
|Firegrate area||60 sq ft (5.574 m2)|
|170 tubes 2.25 in (57.1 mm) diameter
30 tubes 5.5 in (140 mm) diameter
2,586 sq ft (240.247 m2)
|– Flues||25 sq ft (2.323 m2)|
|– Firebox||195 sq ft (18.116 m2)|
|– Total||2,806 sq ft (260.686 m2)|
|Superheater area||633 sq ft (58.808 m2)|
|Cylinder size||18.5 in (470 mm) bore
26 in (660 mm) stroke
|Valve gear||Walschaerts |
|Tractive effort||50,050 lbf (223 kN) at 75% pressure|
|Operator(s)||South African Railways|
|Number in class||10|
|Nicknames||U Boat |
The Class U Union Garratt, a variation on the Garratt principle, was designed and built for the South African Railways (SAR) by Maffei in Munich, Germany. Ten locomotives were delivered in 1927, numbered in the range from 1370 to 1379. They were superheated and had Walschaerts valve gear and bar frames.
During the design phase of the two Union Garratt types, they were designated classification letters in the regular SAR Garratt range as Classes GH and GJ. When orders were placed with the manufacturers, however, the Class designation of the Class GH 4-6-2+2-6-4 Double Pacific type was retained while that of the Class GJ was changed to Class U.
The Union Garratt was a hybrid locomotive, part Modified Fairlie and part Garratt. The front end of the locomotive was of a typical Garratt arrangement, with a water tank 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.
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 more than was usual on a pure Garratt locomotive. An additional underbelly water tank compensated for the resulting diminished water capacity of the front water bunker.
All its water was carried in the front bunker tank and in the large underbelly water tank under the boiler, each with a 2,640 imperial gallons (12,000 litres) capacity, while 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.
The Class U were large and powerful locomotives. With their 60 square feet (5.574 square metres) firegrate, they were originally equipped with mechanical stokers of the duplex type, but these were removed at the Germiston shops in 1937. Two reasons were given for the removal, first that the locomotives were being used in short-haul service on the Reef, and second that the stokers were difficult to clear in the event of a blockage.
Ironically, one reason that had been put forward for the construction of the rear end of the Union Garratt on the Modified Fairlie principle was actually 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.
The Modified Fairlies and the Union Garratt variations of it were not successful in South Africa and they suffered from the same shortcomings.
On the Union Garratt, as on the Modified Fairlie, the frame was also prone to metal fatigue and cracking, brought about by the long frame overhang at the rear beyond the engine pivot centre. The overhang, laden with the coal bunker of which about two-thirds extended beyond the rear engine unit’s pivot centre, was subjected to severe vertical vibration while the locomotive was in motion and this led to structural weakening of the frame.
In addition, as a result of the coal bunker that was mounted on the frame instead of on the engine unit, the rear pivot bearings were subject to quite rapid wear, since they carried a considerable additional vertical load compared to those on a pure Garratt. As was the case with the Modified Fairlie, this resulted in increased maintenance and, as a consequence, increased operating cost.
The Union Garratts were placed in service on the Witwatersrand, where they ended up being used mainly for pick-up work and local workings. Two locomotives were employed on the coal line between Vryheid and Hlobane in Natal. Even though the Class U proved to be less successful than the pure Garratts, some of them remained in service for more than thirty years. The Class U locomotives were all withdrawn from service by 1958.
The main picture and the following photographs offer views of both sides of the Class U locomotive.
- Articulated locomotive numbering and classification
- List of South African locomotive classes
- South African locomotive history
- The 2-6-2+2-6-2 "Double Prairie"
- South African Railways and Harbours Locomotive Diagram Book, 2’0” & 3’6” Gauge Steam Locomotives, 15 August 1941, as amended
- Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. pp. 96–97. ISBN 0869772112.
- Holland, D.F. (1972). Steam Locomotives of the South African Railways, Volume 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. p. 56. ISBN 978-0-7153-5427-8.
- Official Class U 2-6-2+2-6-2 drawing
- Durrant, A E (1989). Twilight of South African Steam (1st ed.). Newton Abbott, London: David & Charles. p. 31. ISBN 0715386387.