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

Class GH at Monument Station, Cape Town, c. 1930

Type and origin
Power type	Steam
Designer	Maffei
Builder	Maffei
Serial number	5687-5688
Model	Class GH
Build date	1928
Total produced	2

Specifications
Configuration	4-6-2+2-6-4 (Double Pacific)
Driver	2nd & 5th coupled axles
Gauge	3 ft 6 in (1,067 mm) Cape gauge
Leading dia.	30 in (762 mm)
Coupled dia.	60 in (1,524 mm)
Trailing dia.	30 in (762 mm)
Wheelbase	76 ft 7 in (23,343 mm)
• Engine	25 ft 2 in (7,671 mm) each
• Leading	6 ft 2 in (1,880 mm) each
• Coupled	10 ft 9 in (3,277 mm) each
Pivot centres	39 ft 6 ¹⁄₂ in (12,052 mm)
Length:
• Over couplers	85 ft (25,908 mm)
Height	12 ft 11 ⁷⁄₁₆ in (3,948 mm)
Frame type	Bar
Axle load	18 LT 2 cwt (18,390 kg)
• Leading	25 LT 12 cwt (26,010 kg) front 25 LT 14 cwt (26,110 kg) rear
• 1st coupled	18 LT 2 cwt (18,390 kg)
• 2nd coupled	18 LT (18,290 kg)
• 3rd coupled	18 LT 2 cwt (18,390 kg)
• 4th coupled	17 LT 16 cwt (18,090 kg)
• 5th coupled	17 LT 14 cwt (17,980 kg)
• 6th coupled	17 LT 16 cwt (18,090 kg)
• Trailing	13 LT 2 cwt (13,310 kg) front 12 LT 17 cwt (13,060 kg) rear
Adhesive weight	107 LT 10 cwt (109,200 kg)
Loco weight	184 LT 15 cwt (187,700 kg)
Fuel type	Coal
Fuel capacity	13 LT 10 cwt (13.7 t)
Water cap	3,650 imp gal (16,600 l) front 2,350 imp gal (10,700 l) belly
Firebox type	Round-top
• Firegrate area	60 sq ft (5.6 m²)
Boiler:
• Pitch	8 ft 3 in (2,515 mm)
• Diameter	6 ft 11 in (2,108 mm)
• Tube plates	13 ft 8 in (4,166 mm)
• Small tubes	195: 2 ¹⁄₄ in (57 mm)
• Large tubes	43: 5 ¹⁄₂ in (140 mm)
Boiler pressure	180 psi (1,241 kPa)
Safety valve	Pop
Heating surface	2,655 sq ft (246.7 m²)
• Tubes	2,416 sq ft (224.5 m²)
• Arch tubes	25 sq ft (2.3 m²)
• Firebox	214 sq ft (19.9 m²)
Superheater:
• Heating area	665 sq ft (61.8 m²)
Cylinders	Four
Cylinder size	19 ¹⁄₂ in (495 mm) bore 26 in (660 mm) stroke
Valve gear	Walschaerts
Valve type	Piston
Couplers	AAR knuckle

Performance figures
Tractive effort	44,490 lbf (197.9 kN) @ 75%

Career
Operators	South African Railways
Class	Class GH
Number in class	2
Numbers	2320-2321
Delivered	1928
First run	1928
Withdrawn	c. 1958

The South African Railways Class GH 4-6-2+2-6-4 of 1928 was an articulated steam locomotive.

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. The Union Garratt design embodied the Garratt design at the front end and the Modified Fairlie design at the rear end.^[1]^[2]^[3]^[4]^[5]

Manufacturer

The Class GH, the heavy passenger version of the Class U Union Garratt, was designed and built by Maffei in Munich, Germany, to the specifications of Colonel F.R. Collins DSO, Chief Mechanical Engineer of the South African Railways (SAR). Two locomotives were delivered in 1928, numbered 2320 and 2321, and were erected at the Salt River shops in Cape Town.^[1]^[3]^[4]^[5]

If the same classification practice as that which was used for Garratt and Mallet locomotives had been followed, the Classes GH and U Union Garratts should have been designated Class UA and Class UB respectively. 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 respectively. When orders were placed with the manufacturers, however, the Class designation of the Class GH was retained while that of the Class GJ Double Prairie type was changed to Class U. The reasoning behind this inconsistency is not known.^[6]^[7]

Characteristics

The locomotives were superheated and had round-topped fireboxes, Walschaerts valve gear and bar frames. The design of the two Union Garratt types deviated from the Garratt principle, the patent of which was held by Beyer, Peacock and Company, and the end results were hybrid locomotives, part Garratt and part Modified Fairlie. 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]^[5]

Since the rear bunker carried only coal, an additional large underbelly water tank under the boiler compensated for the resulting diminished water capacity. All the engine's 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 long tons 10 hundredweight (13.7 tonnes). The main frame therefore carried the smokebox, boiler, firebox, cab, coal bunker, as well as the underbelly water tank.^[1]^[2]^[5]

The Class GH were massive and powerful locomotives and, having been designed for passenger service, they were built for speed with their large 60 inches (1,524 millimetres) diameter coupled wheels. With their 60 square feet (5.6 square metres) firegrates, they were equipped with mechanical stokers of the duplex type. One reason which was put forward for the construction of the rear end of the Union Garratts on the Modified Fairlie principle was 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. The subsequent designs of the Classes GL and GM Garratts showed that this precaution was unnecessary.^[1]^[2]

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, which extended completely beyond the rear engine unit's pivot centre, was subjected to severe vertical oscillation while the locomotive was in motion and this led to structural weakening of the frame over time.^[1]^[6]

In addition, since the coal bunker 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 purebred Garratt. As was the case with the Modified Fairlies, this resulted in increased frequency of maintenance and, as a consequence, increased operating cost.^[1]^[5]^[6]

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 shedded 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.^[2]^[5]

Illustration

Class GH Union Garratt staged at Glencoe, Natal, c. 1950

References

1 2 3 4 5 6 7 8 9 Holland, D.F. (1972). Steam Locomotives of the South African Railways, Volume 2: 1910-1955 (1st ed.). Newton Abbott, Devon: David & Charles. pp. 56–57. ISBN 978-0-7153-5427-8.
1 2 3 4 Espitalier, T.J.; Day, W.A.J. (1945). The Locomotive in South Africa - A Brief History of Railway Development. Chapter VII - South African Railways (Continued). South African Railways and Harbours Magazine, December 1945. p. 969.
1 2 South African Railways & Harbours/Suid Afrikaanse Spoorweë en Hawens (15 Aug 1941). Locomotive Diagram Book/Lokomotiefdiagramboek, 3'6" Gauge/Spoorwydte. SAR/SAS Mechanical Department/Werktuigkundige Dept. Drawing Office/Tekenkantoor, Pretoria. p. 32.
1 2 South African Railways & Harbours/Suid Afrikaanse Spoorweë en Hawens (15 Aug 1941). Locomotive Diagram Book/Lokomotiefdiagramboek, 2'0" & 3'6" Gauge/Spoorwydte, Steam Locomotives/Stoomlokomotiewe. SAR/SAS Mechanical Department/Werktuigkundige Dept. Drawing Office/Tekenkantoor, Pretoria. p. 32.
1 2 3 4 5 6 Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. p. 93. ISBN 0869772112.
1 2 3 Durrant, A E (1989). Twilight of South African Steam (1st ed.). Newton Abbott, London: David & Charles. p. 31. ISBN 0715386387.
↑ Drawing: 2-6-2-2-6-2 Type Garratt Engine, Class GJ (Ordered as Class U). S.A.R. Mechanical Department, Drawing Office, Pretoria, 29-10-25. Approved by F.R. Collins, Chief Mechanical Engineer, 31-10-25. (Class U 2-6-2+2-6-2 drawing).

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

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