| Weight | Locomotive – 211t 1cwt |
| Length | 90ft 7⅞ins |
| Driving Wheels | 4ft 0ins |
| Boiler Pressure | 200psi Superheated |
| Cylinders | Four Outside – 22in x 26in |
| Tractive Effort | 78,650lbf |
| Valve Gear | Walschaert |
In the years before the First World War the South African Railways (SAR) experienced increasing loads on the Natal mainline. This line had gradients of 1 in 30 whilst the newer line, relocated to provide an easier route, still had 38 miles of near-uninterrupted 1 in 66.
The tight curvature of the line precluded the use of large, long wheelbased, non-articulated locomotives. This together with the ever-increasing train weights ensured that the line rapidly became a bottleneck.
The decision to electrify the line from Glencoe Junction to Durban had been taken in 1914, coincidentally the year in which the 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 end of First World War World War.
The SAR ordered eight class GL Garratt articulated steam locomotives with a 4-8-2+2-8-4 wheel arrangement which were built by Beyer, Peacock & Company at Gorton, Manchester. These entered service in 1929 and 1930. They were originally designed to work on the Durban to Cato Ridge section of the Natal mainline.
Electrification of the line between Glencoe and Pietermaritzburg was completed in 1926 and the heaviest freight trains were hauled on this section by three electric locomotives. The trains were then taken forward to Durban by a pair of class 14 locomotives.
The success of the class GA Garratt in proving the suitability of the Garratt design for South African conditions coupled with the economies in crew, fuel and water consumption it offered, provided an incentive for the SAR to consider a new Garratt class for use on the Natal mainline. The aim was to eliminate double-heading as a regular practice with such a locomotive to be equivalent to three of the electric locomotives which were then in use, or two Class 14 steam locomotives.
The specification of the locomotives to be supplied by Beyer, Peacock & Company covered these aims and restricted the maximum permitted axleload to 18tons owing to the use of 80 pounds per yard rail on both sections of the mainline, and a maximum weight of 215tons.
Since these locomotives would be some 48% larger and more powerful than any locomotive previously employed on the SAR and up to twice the track 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 workshops and placed in service in October. They proved to be so successful that the remaining six locomotives were quickly ordered for delivery in 1930. These six entered service in July 1930.
Test runs were undertaken which clearly demonstrated the power of the locomotives but also showed that their running qualities were exceptional and that they were smooth and free-running machines. In many ways, the class GL set a design standard which was followed later in the class GM, class GMA and class GO. At the time the GL class were the most powerful steam locomotives to be placed in service anywhere in the Southern Hemisphere.
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.
The boiler was of exceptional size with an inside diameter of 7 feet which was double the track gauge.
The locomotives were equipped with a powered fan blower to supply fresh air to the cab, sucked from ahead of the chimney and driven by a steam turbine in deference to the eleven tunnels on this section which totalled to almost 2 miles. This proved less than satisfactory, as did the smoke deflecting cowls over the chimneys of the second batch of locomotives. These cowls were controlled by steam-operated cylinders and, when not required, could be withdrawn longitudinally from the position over the chimney orifice. Since Garratts are designed to be bi-directional, the problem was eventually solved by simply
Preservation
Beyer Peacock Works no 6530 2351 Princess Alice
Beyer Peacock Works no 6531 2352Beyer Peacock Works no 6531 2352
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