| South African Class GL 4-8-2+2-8-4 | |
|---|---|
| Class GL 2351 "Princess Alice", circa 1930 | |
| Power type | Steam |
| Designer | South African Railways Beyer, Peacock and Company |
| Builder | Beyer, Peacock and Company |
| Serial number | 6530-6531, 6639-6644[1][2] |
| Build date | 1929–1930 |
| Total produced | 8 |
| Configuration | 4-8-2+2-8-4 "Double Mountain" Garratt |
| Gauge | 3 ft 6 in (1,067 mm) Cape gauge |
| Leading wheel diameter |
28.5 in (724 mm) |
| Driver diameter | 48 in (1,220 mm) |
| Trailing wheel diameter |
33 in (838 mm) |
| Wheelbase | Total: 83 ft 7 in (25.476 m) Engines: 6 ft 2 in (1.880 m) pilot 13 ft 3 in (4.039 m) coupled 27 ft 8 in (8.433 m) total |
| Length | 90 ft 7.875 in (27.632 m) |
| Height | 13 ft (3.962 m) |
| Frame | Bar frame, 41 ft 6 in (12.649 m) between pivot centres |
| Axle load | 18.75 long tons (19.1 t) on 6th driver |
| Weight on drivers | 144.85 long tons (147.2 t) |
| Locomotive weight | 211.05 long tons (214.4 t) |
| Fuel type | Coal |
| Fuel capacity | 12 long tons (12.2 t) |
| Water capacity | 4,650 imp gal (21,100 l) front 2,350 imp gal (10,700 l) rear |
| Boiler | 7 ft (2.134 m) int dia 14 ft 6.5 in (4.432 m) int length 8 ft 6 in (2.591 m) pitch |
| Boiler pressure | 200 psi (1,380 kPa) |
| Firegrate area | 75 sq ft (6.968 m2) |
| Heating surface: Tubes |
263 tubes 2 in (50.8 mm) ext dia 50 tubes 5.5 in (140 mm) ext dia 3,049 sq ft (283.261 m2) |
| Heating surface: Firebox |
347 sq ft (32.2 m2) including 2 Nicholson siphons & 2 arch tubes |
| Heating surface: Total |
3,396 sq ft (315.499 m2) |
| Superheater area | 835 sq ft (77.6 m2) |
| Cylinders | Four |
| Cylinder size | 22 in (559 mm) bore 26 in (660 mm) stroke |
| Valve gear | Walschaerts[3] |
| Tractive effort | 78,650 lbf (349.9 kN) at 75% boiler pressure[4] |
| Career | South African Railways |
| Class | Class GL |
| Number in class | 8 |
| Number | 2350-2357 |
| Delivered | 1929-1930 |
| First run | 1929 |
| Last run | 1972 |
| Disposition | Retired |
During 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" wheel arrangement in service. Constructed at Beyer, Peacock and Company's Gorton Foundry, they were originally designed to work on the Durban to Cato Ridge section of the Natal main Line. 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.[1][5]
Contents |
The Class GL had its origin in the steady increase in loads experienced by the Natal main line in the years prior to World War I. The old Natal main line had gradients of 1 in 30, whilst the newer line, relocated to provide an easier route, still had 38 miles (61 kilometres) of near-uninterrupted 1 in 66 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 rigid locomotives and restricted their length to a coupled wheelbase of 9 feet (2.7 metres). These factors, combined with ever-increasing train weights, ensured that the line quickly became a bottleneck.[1][6]
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 war’s end.[6]
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 consists 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 locomotives.[6]
Meanwhile, the success of the Class GA Garratt, which was approximately equivalent in power output to two Class 14 locomotives, in proving the basic suitability of the Garratt design for South African conditions, coupled with the economies in crew, fuel and water consumption it offered, provided a healthy incentive for the SAR to consider a new Garratt class for use on the Natal main Line. The aim was to eliminate double-heading as a regular practice, with such a locomotive to be equivalent to three of the Class 1E electric locomotives that were then in use, or two Class 14 steam locomotives.[1][6]
Colonel F.R. Collins, the Chief Mechanical Engineer (CME) of the SAR from 1922 to 1929, prepared the specifications and awarded the contract for the construction of these locomotives, the Class GL, to Beyer, Peacock and Company (BP). The design was to be approximately equal to two Class 14 locomotives in power output, with a maximum permitted axle loading of 18 long tons (18 tonnes) owing to the use of 80 pounds per yard (40 kilograms per metre) rail on both sections of the main line, and a maximum all-up weight of 215 long tons (218 tonnes).[1][3]
Since these locomotives would be some 48% larger and more powerful than any previously employed on the SAR and up to twice the rail gauge in width, the initial order was for two prototype locomotives only, with more to follow should they prove successful. They were delivered in September 1929 and were erected in the Durban shops, numbered 2350 and 2351, and placed in service in October. So successful did they prove to be that the remaining six locomotives were quickly ordered, for delivery in 1930 and numbered 2352 to 2357.[1][6]
The Class GL embodied comparatively few features of any particular novelty. Instead, they were designed to make the best possible use of existing technologies to produce a locomotive of great power, efficiency and reliability. Their all-up weight of 214.1 long tons (218 tonnes), coupled with their 18 long tons (18 tonnes) axle loading, was almost exactly within the limits laid down by the SAR and was considered by Lionel Wiener, author of Articulated Locomotives, to show "such mastery in general and detail design that we have pleasure on congratulating Messrs. Beyer, Peacock & Co. on this achievement."[7]
The main frames were 5 inches (127 millimetres) thick cut bar frames. On the SAR the bar frame had only been employed previously on the German-built Class GCA 2-6-2+2-6-2 Garratt.[6]
The valves were modern straight-ported types with long-lap, long-travel valves, used for the first time in a South African Garratt, making the Class GL very free-running and more efficient than its predecessors. The cylinders, of the same bore and stroke as those of the Class 14, drove the third coupled axle using long connecting rods, which stabilised the locomotive by reducing to a minimum any vertical forces at the crosshead. This method of design became the standard on most Beyer-Garratts thereafter.[5][6]
In order to allow for the tight curves, including 300 feet (91 metres) radius bends with 4.5 inches (114 millimetres) superelevation lacking any intermediate tangent, and the steep, twisting nature of the line, the front pivot bearing connecting the boiler framing to the engine unit was spherical, with its alignment controlled by sprung rollers. The rear pivot was of the normal Beyer, Peacock flat adjustable type.[6]
The boiler, which had an inside diameter of 7 feet (2.134 metres), used a top feed and contained 263 small and 50 large tubes, plus superheater flues of 1.5 inches (38.1 millimetres) diameter, while the round-top firebox was fired by a duplex mechanical stoker and contained two Nicholson thermic syphons and two arch tubes. Beyer, Peacock estimated the Class GL locomotive’s economical coal consumption rate at 3.5 long tons (4 tonnes) per hour.[6]
The Class GL made use of Beyer, Peacock’s standard lever-actuated Sterling-type steam-operated power reverser and a Pyle National Company turbo-generator, along with a rocking grate and self-cleaning hopper ashpan with water and steam sprayers to dampen down the ash, preventing it from entering axle boxes, motion areas and other friction-sensitive places.[6]
Crew comfort was also considered. They were equipped with a "Sturtevant" steam turbine powered fan blower to supply fresh air to the cab, sucked from ahead of the chimney, in deference to the almost 2 miles (3 kilometres) of tunnels to be found on this difficult section of the line. This proved less than satisfactory, as did the smoke deflecting cowls over the chimneys of the second batch of locomotives. Since Garratts are designed to be bi-directional, the problem was eventually solved by simply running them with the chimney trailing on the ascending legs of the tunneled routes.[1][3][5][6]
Their tractive effort of 78,650 pounds-force (349.9 kilonewtons) at 75% boiler pressure made them the most powerful steam locomotives to be placed in service anywhere in the Southern Hemisphere at the time and attained the objective of constructing a locomotive to approximately equal the power output of two Class 14 locomotives. On their first test run and despite the cut-off on these locomotives being limited to 65%, 1,117 long tons (1,135 tonnes) were hauled from Durban to Cato Ridge in 163 minutes, as against 500 long tons (508 tonnes) in 184 minutes for a Class 14. Moreover, this was performed on half throttle (i.e. in first valve) and with the cut-off set at 45%.[1][6]
This suggested that the Class GL had still more to give, a suggestion confirmed on the following day’s testing when a load of 1,205 long tons (1,224 tonnes) was hauled over the same stretch of track. It was as a result of these tests that the further six Class GL locomotives were ordered for delivery in 1930.[1][6]
The Class GLs were eventually marshalled to standard loads of between 950 and 1,000 long tons (965 and 1,016 tonnes), despite having shown themselves capable of greater loads, in order to correspond with the load that could be hauled by a consist of three electric locomotives. Apart from demonstrating the Class GL’s prodigious power and capacity for hauling heavy trains, these tests also showed that their running qualities were exceptional, being smooth and free-running machines. In many ways, the Class GL set a design standard that was followed later in the Class GM, Class GMAM and Class GO.[5][6]
Upon completion of the electrification project between Durban and Pietermaritzburg in 1938, the eight locomotives were transferred from the Durban section to the gruelling run between Glencoe and Vryheid, with the latter’s coal trains. This work entailed the regular haulage of 1,200 long tons (1,219 tonnes) up gradients of 1 in 50, taxing the Class GL even more heavily than the work for which it was designed. Despite this they maintained an effective service along this line until its electrification in 1968.[1][5][6]
From Glencoe the Class GL was then transferred to work the line between Stanger and Empangeni. However, since the loads on this route did not fully justify the use of the mighty GL while their great weight and high axle loading restricted them to main lines laid with heavy rail, they were eventually replaced by less powerful, more modern and more economical Class GMAM locomotives. Though briefly considered, somewhat improbably, as hump shunters at Bloemfontein, the Class GL had outlasted its use and, after some forty-two years of working the most difficult terrain on the SAR, they were withdrawn from service in 1972.[3][6]
Of the eight locomotives only two survived. Number 2351, named Princess Alice, is preserved at the Outeniqua Transport Museum. Number 2352, which waited at Germiston for some eight years before being shipped, shorn of around two hundred parts including its right-hand-side ashpan and much of its brick arch, resides at the Museum of Science and Industry in Manchester.[6][8]
The main picture shows Class GL 2351 "Princess Alice", circa 1930. The smoke deflecting cowl on the chimney was later removed.
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