Articulated Steam Locomotives
An articulated or jointed locomotive is one in which there are two or more independent groups of wheels, at least one of which can turn relatively to the boiler, in a manner similar to a bogie or to a bissel.
The purpose of the articulated design is to provide an engine of considerable power but with comparatively low axle loading. The difficulty of restricted axle load can be overcome by the coupling together of several pairs of wheels. The curvature of the tracks is still a denominator, especially to the length of the rigid wheel base, and therefore to the number of pairs of wheels of any given size which can be coupled together. To overcome the problem of providing sufficient coupled wheels to transmit the required power, the wheels are seperated into two groups; each group driven by an independent pair of cylinders. This arrangement also lowers the axle load. This is the principle behind the articulated locomotive, flexible enough to run on severely curved track, yet powerful. Each group of wheels is usually referred to as a “unit”.
The four types of articulated locomotives used by the South African Railways are the Mallet, the Garratt, the Modified Fairlie and the Union-Garratt. All these types have two sets of frames and wheel arrangements with one boiler. In this way the number of coupled wheels can be doubled and correspondingly high tractive effort developed. The rigid wheelbase is limited to that of one unit only, and the engine could therefore traverse existing curves without difficulty.
The policy of the South African Railways at that time was to incorporate standard frames, wheels, cylinders and accessories in the design of these locomotives. The boiler is carried in a cradle suspended on pivot centres attached to the frames each is free to align itself to the curvatures of the track. Flexible connection are required for the steam and exhaust pipes. The use of such articulated locomotives enables the capacity of a line to be doubled without strengthening the track, bridges and culverts or to improve the curvature. These engines are capable of safe speeds, equally as track worthy and immune from breakdown as non-articulated locomotives. The Garratt runs equally well in either direction. The design and shape of the firebox can be extremely simple, and a greater depth of firebox can be obtained. Also as an added advantage is that with the simplest forms of construction maximum boiler power is obtained. Another added advantage is the operating economy, only one engine crew required to operate what is practically a double engine.
In 1914 an order for five locomotives of the Garratt articulated type was placed with Beyer, Peacock & Co., but it was not completed until 1920 due to the Great War. The five locomotives comprised three different designs, namely a narrow gauge (2 feet), a light type for 45lb rail and one for main line working. The ordering of three different sizes had the added advantage that the Garratt principle could be studied under three different conditions. All these types had two sets of frames and wheel arrangements with one boiler.
The Mallet
The locomotive has two groups of coupled wheels with the rear group mounted on the main frame of the engine, and thus rigid. The front group of wheels is mounted on a separate frame, and this group is coupled to the rear group by means of a hinged joint. The firebox of the boiler is carried on the main frame, and the smoke box rests on a flat slide on the front frame. The tender is coupled the usual manner. The front end buffer and draw gear are mounted on the frame of the front unit.
The four cylinders of the engine works on the compound expansion principle. Two high pressure cylinders are fitted on the main frame and drive the rear group of coupled wheels. The exhaust steam from these cylinders is taken through a system of pipework to the low pressure cylinders, which is mounted on the front unit, thus driving the front group of coupled wheels. Thus the steam is used, economically, twice before emitted into the atmosphere.
The Mallet was the only type of engine on the SAR to use compound expansion. The exhaust steam from the low pressure cylinders is led through passages in the saddle between the cylinders, from which it is taken via a pipe to the blast pipe in the smoke box. Each of the high and low pressure cylinders has its own set of Walschaerts valve gear. The arrangement of the valve gears is as such that while the die blocks of the low pressure unit are in the lower portion of the expansion links in fore gear, the die blocks of the high pressure unit are in the upper portion of the expansion links in fore gear. The effect obtained from this arrangement is that of balancing the weight of the motion coupled to the reversing gear, thus makes the notching up and reversing very easy.
The Garratt
The Garratt locomotive differs completely from the Mallet. It consists of two units, each driven by a pair of cylinders at its outer end, and these are connected together by the cradle, which carries the boiler. A water tank is attached to the frame of the front unit, while a combined coal bunker and water tank is carried on the frame of the back unit. No tender is used because the locomotive is entirely self contained. To ensure maximum rotation of each unit on curved tracks, the units are coupled to the cradle by means of pivots.
The four cylinders all take high pressure superheated steam direct from the superheated header, the pipe on the left hand side supplying the front unit and that on the right hand side supplying the rear unit. Each unit has its own set of Walschaerts valve motion and is completely independent of each other except that the regulator controls the supply of steam to both units simultaneously. The steam pipe to each pair of cylinders is fitted with ball and socket joints. As each unit is in effect an independent locomotive (except for the boiler) any breakdown which will put one cylinder out of action is not as serious as it is on an ordinary locomotive, because there are still three cylinders left. The tractive force thus reduced by a quarter and not by half as in the case of the ordinary class of locomotive.
The buffer and draw gear at each end are carried on the main frame. An electric headlamp is mounted on the water tank in front and on the coal bunker at the back.
The South African Railways Handbook on the Steam Locomotive commments: “If it is essential to use two Garratts on a train, it is better where possible to place one of them in the middle or at the rear of the train, rather than to marshal both at the front. To avoid damage to the pivots and other parts of the locomotive, a Garratt should normally be the leading engine when double-heading is necessary.
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Classification and brief description Garratt-type locomotives:
Class GA 2-6-0+0-6-2
Ordered in 1914 from Beyer, Peacock & Co., but only delivered in 1920 due to the First World War. This was the first Garratt locomotive for the Cape gauge. Due to excessive flange wear (caused by incorrect wheel arrangement) no more engines of this class were ordered. The only one of this class ordered, were being withdrawn from service in 1938.
Locomotive Number: 1649/2140.
Class GB 2-6-2+2-6-2
Initially ordered as an experimental locomotive for use on the Cape gauge, and put to service in 1921. It proved so successful that a further six were ordered and placed in service in 1924. These six locomotives differed from the original prototype in boiler proportions and cab design. The locomotives were in service at the tortuous Aliwal North—Barkley East line until withdrawn in 1967.
Locomotive Numbers: 1650/2166, 2160—2165.
Class GC 2-6-2+2-6-2
Developed from the class GB, it was more powerful and heavier. Supplied by Beyer, Peacock & Co. They were similar to the Class GK supplied to the New Cape Central Railway. They were to service in the Natal area and withdrawn from service in 1962.
Locomotive Numbers: 2180—2185.
Class GCA 2-6-2+2-6-2
Built in 1927 and 1928 to the same specification as the Class GC by Krupp of Essen. Their appearance differ from the Class GC in that they had bar frames and a round-topped firebox. There were 39 engines of this class in service on the Natal south coast and in the Eastern Transvaal. They were all withdrawn in 1978.
Locomotive Numbers: 2190—2202, 2600—2625.
Class GD 2-6-2+2-6-2
Specification wise it was a heavier and slightly more powerful machine than the GC. Beyer, Peacock & Co. delivered 14 engines of this class in 1925 and 1926. Initially destined for use on the Cape Town—Caledon, Natal North coast, the Pietermaritzburg—Franklin lines, and the Montagu Pass between George and Oudtshoorn. They were all withdrawn from service by 1967.
Locomotive Numbers: 2220—2223, 2228—2237.
Class GDA 2-6-2+2-6-2
They were build to the same specifications as the GD, fitted with bar frames and round-topped fireboxes, but were not as successful as the GCA. Build by Linke-Hofmann-Werke, Breslau, these 5 GDA locomotives were placed in service at Cape Town in 1929. Not found to be successful, they were sent to Natal to work the Stanger area and later a pair were sent to the Port Elizabeth area. Withdrawn by 1972.
Locomotive Numbers: 2255—2259.
Class GE 2-8-2+2-8-2
Beyer, Peacock & Co. build 18 in total of the Class GE. The first 6 were delivered in 1925, and these engines were larger than the Class GD. A second order for 10 were placed in 1926. Mechanically identical to the first two, but were fitted with a revised design for the coal bunkers and the water tanks. The final order for 2 engines were made in 1931. Similar in appearance of the previous order except the cab was wider and the engine more powerful due to larger cylinders and many refinements to the boiler design. Withdrawn by 1979 after successfully used on the Transvaal, Natal lines and on the Montagu Pass line.
Locomotive Numbers: 2260-2277.
Class GEA 4-8-2+2-8-4
Build by Beyer, Peacock & Co. during the period between 1945 and 1947 from the design of Dr M.M. Loubser. Streamlined tanks were the main distinction in the naked eye design of these engines. There was no mechanical stoker incorporated in the Class GEA. Initially used on the Natal line and the Montagu Pass and later on the Cape Town—Caledon branch till the withdrawn in 1976.
Locomotive Numbers: 4001—4050.
Class GF 4-6-2+2-6-4
Specifications laid down by Col. Collins led to the Class GF, produced by the German firm of Hannomag in 1927. It was suitable either for passenger and goods trains. The order was for 37 of these locomotives in 1927, and for a further 18 in 1928. The GF were the second most numerous Garratt on the SAR list. They were very useful engines and were in service on many lines in Natal, Transvaal, Free State and the Eastern Cape till the last one was withdrawn in 1979.
Locomotive Numbers: 2370—2434.
Class GG 2-6-2+2-6-2
The primarily function of this design was for passenger working. It was the only Garratt design on the SAR to pull passenger trains. It were introduced for use on the Union Limited and Union Express and build by Beyer, Peacock & Co. in 1925. The engine could achieve a maximum speed of 55 mph, but was not stable at those high speeds, and was withdrawn in 1947.
Locomotive Number: 2290.
Class GK 2-6-2+2-6-2
Beyer, Peacock & Co. were the supplier of the Class GK to the SAR in 1921, and to the New Cape Central Railway in 1923. When the NCCR were affiliated with the SAR in 1925, these Garratt became the Class GK. Initially they worked the Caledon line, then were sent to Natal. They were scrapped in 1957.
Locomotive Numbers: 2340—2341.
Class GL 4-8-2+2-8-4
The GL were designed with specifications to be as powerful as two Class-14 locomotives. In 1929 Beyer, Peacock & Co. delivered 2 engines of this class, and in 1930 a further 6 were delivered. They were the most powerful steam engines on the SAR roster, but their great weight (in excess of 211 tons) and high axle load limited them to operate only on the main lines laid with heavy tracks. They were withdrawn from service in 1972.
Locomotive Numbers: 2350—2357.
Class GM 4-8-2+2-8-4
In 1938 Beyer, Peacock & Co. delivered 16 of these locomotives. To obtained maximum power while not exceeding the permissible axle load limit on the particular line, an auxiliary water tank trailed behind the engine. This successful system was later also applied to other classes like the GMA/M and the GO. One power unit was equal to that of a Class 19D, thus the GM was twice as powerful as a Class 19D. The class GM were in service till 1972, when they were replaced by diesel electric units, on the track between Johannesburg—Zeerust—Mafeking. Till 1974 they were in service on the Pietersburg line.
Locomotive Numbers: 2291-2306.
Class GMA & GMAM4-8-2+2-8-4
Between 1954 and 1956 orders for 150 of these engines were placed with Beyer, Peacock & Co., the North British Locomotive Co. and Henschel. The coal and water capacities were the only difference between the two classes. Class GMA had a capacity for 11.6 tons of coal and 1650 gallons of water; the Class GMAM 14 tons of coal and 2100 gallons of water. The M from GMAM indicates that it were used on main lines only. They trailed an auxiliary water tank, just like the Class GM. They were suitable for use on 60lb rails. They were in service till 1984.
Locomotive Numbers: 4051—4170.
Class GO 4-8-2+2-8-4
A variation from the GMA for use on 45-lb rails. A smaller boiler were fitted, the cylinder diameter were reduced, thus reduced steaming capacity. Coal and water capacity were lessened to reduce the overall weight. Henschel delivered 25 of these engines in 1954. Allocation were to different areas in South Africa and the final allocation before withdraw in 1975 was Natal.
Locomotive Numbers: 2572—2596.
The Modified Fairlie
It is very similar to the Garratt, the main difference being that the front water tank and the combined coal bunker and water tank at the rear are carried on extensions of the boiler cradle and not on the unit frames. The units act as bogies and have jointed steam and exhaust pipes as in the Garratt.
Classification and brief description Modified Fairlie-type locomotives:
Class FC 2-6-2+2-6-2
This locomotive were developed by the North British Locomotive Co. The front and rear coal bunkers and water tanks were attached on one rigid frame together with the boiler and cab, thus they did not swivel with the front and rear power units. This was an unsuccessful design with a lot of overhang on the curves, metal fatigue and tremendous wear on the pivot bearings. A single unit was delivered in 1925 and worked the Cape midlands section until withdrawn by 1939.
Locomotive Number: 2310/670.
Class FD 2-6-2+2-6-2
Four Class FD’s were delivered by the North British Locomotive Co. in 1926, they compared to the Class GD. They did service until 1949 when scrapped. The Class HF [ HF = Henschel Fairlie ] was a Modified Fairlie equivalent to the Class GE Garratt. Henschel delivered 10 units by 1928. Modifications improved the working of this class and they were in service till withdrawn in 1951.
Locomotive Numbers: 2323—2326/671—674.
The Union-Garratt
This is a combination of the Garratt and the Modified Fairlie designs. The front unit carries a water tank on the unit frame, as thus the Garratt do, while the boiler cradle is extended over the back unit to carry the coal bunker. No water tank is fitted at the back, but a tank is fitted to the cradle underneath the boiler barrel.
Classification and brief description Union-Garratt-type locomotives:
Class GH 4-6-2+2-6-4
Built by J.A. Maffei in 1926 as passenger train versions of the Union-Garratt. Working the main line to the north from Cape Town they were found to be in excess of the loading gauge, and thus were stripped from certain trimmings. Transferred to Natal and withdrawn in 1958.
Locomotive Numbers: 2320—2321.
Class U 2-6-2+2-6-2
With the rear coal bunker attached to an extension of the boiler frame, and the rear power unit that could swivel below it, while the front power units arrangement was like that of a Garratt one could see the resemblance with the conventional Garratt. In order to maintain the long boiler, without increasing the overall length of the unit, the front water tank was tucked in under the boiler frame more than that of the conventional Garratts. An additional water tank was fitted to the underside of the boiler frame. Ten Class U locomotives were delivered by J.A. Maffei in 1927. A distinct feature of the Class U was its mechanical stoker, but strangely, that was removed from all units in 1938. They worked the Reef area in Transvaal and in Natal till their withdrawal in 1958.
Locomotive Numbers: 1370—1379.