South African Railways GL class Garratt

Infobox Locomotive Auto

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caption = SAR GL no. 2352 at the Manchester Museum of Science and Industry
name = South African Railways GL class Garratt
powertype = Steam
railroad = South African Railways Administration
whytetype = 4-8-2+2-8-4T
uicclass = 2'D'1+1'D'2
gauge = RailGauge|cape|al=on
firstrundate = 1929
lastrundate = 1972
locale = South Africa
builder = Beyer, Peacock & Co. Ltd.
boiler = 7 ft 7⅜ in (2.32 m) outer diameter
tractiveeffort = 89,130 lbs
wheelbase = 83 ft 7 in (25.5 m)
driversize = 4 ft (1.22 m) diameter
firearea = 74½ ft² (7.58 m²)
fireboxarea = 340 ft² (103 m²)
tubesandflues = 3,036 ft² (920 m²)
superheaterarea = 809 ft² (245.2 m²)
cylindersize = 22 in (558.8 mm) diameter × 26 in (660.4 mm) stroke
fuelc

waterc

locobrakes =
trainbrakes = The S.A.R. GL class were Beyer-Garratt articulated steam locomotives, constructed at Beyer, Peacock & Co.'s Gorton Foundry between 1928 and 1930 and operated by the South African Railways Administration (S.A.R.) from 1929 to 1972. Originally designed to work the Durban - Cato Ridge section of the Natal Main Line, the GLs were eventually displaced to the Glencoe - Vryheid route, before ending their lives operating on the line from Stanger to Empangeni.

Genesis

The GLs had their origins 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 possessed mi to km|38 of near-uninterrupted 1 in 66 gradients. Moreover, the tight curvature of the line, with curves of as little as ft to m|275|wiki=yes radius, precluded the use of large, long-wheelbase rigid locomotives and restricted their length to a coupled wheelbase of ft to m|9; these factors, combined with ever-increasing train weights, ensured that the line fast 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 S.A.R. ordered their first Garratt, the GA class), only to be placed in abeyance, along with the delivery of the GA, until the war’s end. 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 three electric locomotives being used on the heaviest freights. These trains were then hauled onward to Durban by a pair of 14th class 4-8-2s.

Meanwhile, the success of the GA class (which was approximately equivalent in power output to two 14th class) in proving the basic suitability of the Garratt design for South African conditions, coupled with the economies in crew wages, fuel and water consumption it offered, provided a healthy incentive for the S.A.R. 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 being equivalent to three electric locomotives then in use, or two 14th class 4-8-2s.

Colonel Collins, the then-CME of the S.A.R., awarded the contract for the construction of these locomotives, classed GL, to Beyer, Peacock & Co. Ltd. The design was to be approximately equal to two 14th class in power output, with a maximum permitted axle loading of 18.5 tons (owing to the use of 80 lb rail on both sections of the main line) and a maximum all-up weight of 215 tons. Since these engines would be some 48% larger and more powerful than any previously employed on the S.A.R. 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. The first GL, no. 2350, (BP works no. 6350) was placed in service in 1929; so successful did 2350 and 2351 prove that the remaining six engines were quickly ordered, for delivery in 1930.

Design

The GLs 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 tons 2cwt, coupled with their 18.5 ton axle loading, was almost exactly within the limits laid down by the S.A.R., 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.” The main frames were 5 in (127 mm) thick cut bar frames, this being the first use of bar frames for a South African Beyer-Garratt, although the bar frame had been employed previously on the German-built GCA class.

The valves were modern, straight-ported types with long-lap, long-travel valves, used for the first time in a South African Garratt, thus making the GLs very free-running and more efficient than their predecessors. The cylinders, of the same bore and stroke as those of the 14th class, drove the third coupled axle using long connecting rods, which stabilised the engine by reducing to a minimum any vertical forces at the crosshead. This method of design was standardised on most Beyer-Garratts hereafter. Meanwhile, in order to allow for the tight curves, including ft to m|300 radius bends with 4.5 in (114.3 mm) superelevation lacking any intermediate tangent, and steep, twisting nature of the line, the front pivot bearing connecting boiler framing to engine unit was spherical, with its alignment controlled by sprung rollers. The rear pivot was of the normal, Beyer, Peacock & Co. flat adjustable type.

The boiler, which had an outside diameter of some 7 ft 7⅜ in (2.32 m), used a top feed and contained 263 small and 50 large tubes, plus superheater flues of 1½ in (38.1 mm) diameter, while the round-top firebox was fired by a duplex mechanical stoker - Beyer, Peacock & Co. estimated the GLs’ economical coal consumption rate at 3½ tons per hour - and contained two Nicholson thermic syphons and four arch tubes. The GLs made use of the standard, lever-actuated Beyer, Peacock & Co. Sterling-type, steam-operated power reverser and a Pyle National Co. turbogenerator, along with a rocking grate and self-cleaning hopper ashpan with water/steam sprayers to dampen down the ash, preventing it from entering axleboxes, motion and other friction-sensitive areas.

Crew comfort was also considered, with engines no. 2352 - 2357 (BP works nos. 6639 - 6644) given smoke-deflecting cowls over their chimneys and a turbine-powered fan blower to supply fresh air to the cab in deference to the almost two miles of tunnels to be found on this difficult section of line.

The GLs in service

As has been mentioned, the GLs were intended to approximately equal the power output of two 14th class locomotives. However, on their first test run and despite the cut-off being limited on these engines to 65%, 1,117 tons were hauled from Durban to Cato Ridge in 163 min., as against 500 tons in 184 min. for a 14th class. Moreover, this was performed on half-throttle (i.e. in first valve) and with the cut-off set at 45%; this suggested that the GLs had still more to give, a suggestion confirmed on the following day’s testing when a load of 1,205 tons was hauled over the same stretch of track. The GLs were eventually marshalled to standard loads of between 950 and 1,000 tons, despite having shown themselves capable of greater loads, in order to correspond with the load hauled by three electric locomotives. These tests, as well as demonstrating the GLs’ prodigious power and capacity for hauling heavy trains, also showed that their running qualities were exceptional, being smooth and free-running machines. It was as a result of these tests that the remaining six GLs were ordered, for delivery in 1930.

These eight engines were then displaced from the Durban section upon completion of the electrification project in 1938, and were transferred to the gruelling run between Glencoe and Vryheid with the latter’s coal trains. This work entailed the regular haulage of 1,200 tons up gradients of 1 in 50, taxing the GLs even more heavily than the work for which they were designed, despite which they maintained an effective service along this line until its electrification in 1968. From Glencoe, the GLs were then transferred to work the Stanger-Empangeni line; however, the loads on this route did not fully justify the use of the mighty GLs, and they were eventually replaced by less powerful, more modern and more economical GMAM class locomotives. Though briefly considered, somewhat improbably, as hump shunters at Bloemfontein, the GLs had outlasted their use, and were withdrawn, after some forty-two years of S.A.R.’s most difficult working, in 1972.

Preservation

Of the eight locomotives, two survived: 2351, named "Princess Alice" and preserved, in working order, at De Aar, and 2352, which waited at Germiston for some eight years before being removed, shorn of around 200 parts including its right-hand-side ashpan and much of its brick arch, to the Museum of Science and Industry in Manchester.

Additional specifications

* Weight in working order: 214t 2cwt.
* Axle loading (max.): 18.5t
* Adhesion weight: 145t

References

* Durrant, A.E., (1981), "Garratt Locomotives of the World", David & Charles, ISBN 0-7153-7641-1
* Durrant, A.E., (1989), "Twilight of South African Steam", David & Charles, ISBN 0-7153-8638-7
* Lewis, C.P. and Jorgensen, A.A., (1978), "The Great Steam Trek", C. Struik Publishers, ISBN 0-86977-101-9
* Wiener, L., (1970), "Articulated Locomotives", Kalmbach

External links

* [http://users.powernet.co.uk/hamilton/ A Complete List of All Garratt Locomotives "Gavin Hamilton]
* [http://users.powernet.co.uk/hamilton/pics3.html Garratt Photos including 2351 in preservation]
* [http://mysite.wanadoo-members.co.uk/hotmetal/sa/images/J0804.jpgA GL at work]
* [http://emu.msim.org.uk/education/navigate.php?irn=2364 The MSIM’s page on 2352]