South African Class GH 4-6-2+2-6-4

The South African Class GH 4-6-2+2-6-4 of 1928 is a South African steam locomotive from the South African Railways era.

In 1928 the South African Railways placed two Class GH 4-6-2+2-6-4 Double Pacific type passenger versions of the Class U Union Garratt articulated steam locomotive in service.^[1][2][3]

Manufacturer

The Class GH, the heavy passenger version of the Class U Union Garratt, was designed and built for the South African Railways (SAR) by Maffei in Munich, Germany. Two locomotives were delivered in 1928, numbered 2320 and 2321, and were erected at the Salt River shops in Cape Town. They were superheated and had Walschaerts valve gear and bar frames.^[1][2][3]

It has been surmised that, if the same classification practice as that which was used for Garratt and Mallet locomotives had been followed, the Class U and the Class GH should have been designated Class UA and Class UB respectively.^[4]

Truth is that 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 was retained while that of the Class GJ 2-6-2+2-6-2 Double Prairie type was changed to Class U.^[5]

Characteristics

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.^[1][3]

Since the rear bunker carried only coal, an additional large underbelly water tank under the boiler compensated for the resulting diminished water capacity.^[3]

All its water was carried in the front bunker tank and in the underbelly water tank, with a combined capacity of 6,000 imperial gallons (27,000 litres), while the rear bunker had a coal capacity of 13.5 long tons (14 tonnes). The main frame therefore carried the smokebox, boiler, firebox, cab, coal bunker, as well as the underbelly water tank.^[1]

These were massive and powerful locomotives and, having been designed for passenger service, they were built for speed with their large 60 inches (1,520 millimetres) driving wheels. With their 60 square feet (5.574 square metres) firegrates, they were equipped with mechanical stokers of the duplex type. One reason that had been put forward for the construction of the rear end of the Union Garratts on the Modified Fairlie principle was actually to enable their coal bunkers to be rigidly in line with their boiler frames, to ensure a satisfactory arrangement for the installation of mechanical stokers.^[1]

Shortcomings

The Modified Fairlies and the Union Garratt variations of it were not successful in South Africa and they suffered from the same shortcomings.^[1]

On the Union Garratts, as on the Modified Fairlies, the frames were 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.^[1][4]

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 Fairlies, this resulted in increased maintenance and, as a consequence, increased operating cost.^[1][3][4]

Service

The Class GH was acquired for working the named fast passenger trains of the era, the Union Express and Union Limited, and was initially stationed in Cape Town. The service career of the Class GH had a rough start, however, since on the first trip it was discovered that it exceeded the loading gauge in width. It returned to Salt River minus its steps and sundry fittings after having scraped the platforms of every station along its route. Considerable modifications had to be carried out before the two locomotives could be placed back in regular service.^[1]

The Class GH made several trips working the two Union trains out of Cape Town, but they were not as successful as had been hoped and they were soon taken off that duty. Their mechanical stokers also proved to be troublesome and were eventually removed. They were transferred to Natal and worked on the Natal mainline north of Glencoe for the rest of their service lives. Both were withdrawn from service by 1958.^[3]

Sides illustrated

The main picture and the following illustrate both sides of the Class GH Union Garratt.

• 

  Class GH Union Garratt staged at Glencoe, Natal, circa 1950

See also

• Articulated locomotive numbering and classification
• List of South African locomotive classes
• South African locomotive history
• The 4-6-2+2-6-4 "Double Pacific"

References

Wikimedia Commons has media related to: South African Class GH (4-6-2+2-6-4)

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