GARRATT LOCOTIVES

Broadly speaking a" Garratt" consists of an ordinary locomotive-type boiler slung between two sets of driving units, over which are placed water tanks and coal bunkers. As there are no axles beneath the boiler, this arrangement has several advantages. The boiler can be of the maximum diameter allowed by the loading gauge, for it is not restricted by the space required for the frames and wheels. A good steaming boiler can therefore be mounted, comparatively short in the barrel, for the efficiency of tubes decreases with their length, of large diameter, and with a wide deep fire-box. The main frames, which carry the boiler, have their points of support close to the inner ends of the bogies, but by placing the cylinders at the outer ends, and by a proper distribution of the fuel bunker and tanks, a satisfactory adjustment of weight is obtained. This type of articulated locomotive is greatly favoured throughout the British Empire, and appears to be particularly successful in working on narrow gauge lines. It is ccapable. of traversing the most difficult curves with perfect ease, owing to its weight being slung between the two motor bogies, in much the same manner as the load is carried by a "crocodile" wagon.
The " Garratt" locomotive owes its inception to the British engineer after whom it is named. The first one was built for a Tasmanian railway in 1909, and since that time the use of such engines has spread rapidly on railways of all gauges. Particularly notable are those on the 3 ft. 6 in. gauge South African Railways.
some have the 4-8-2 : 2-8-4 wheel arrangement, or "double Mountain" as it might be called. Weighing over 214 tons in working order these engines develop a tractive effort of 78,650 lb. at 75 per cent. working pressure, and they regularly haul loads of 1,000 tons over gradients as severe as l in 66. They were built by Beyer-Peacock & Co. Ltd., of Manchester, who hold the 'Garratt' manufacturing rights, and are the most powerful engines ever built outside the American Continent.
There are some fine "Garratt" express locomotives in New Zealand. They are notable for having three cylinders in each driving unit, and two sets of outside Walschaerts valve gear, operating all three valves by means of the Gresley system of levers, as used on many L. N. E. R. locomotives. In South America "Garratts" are in service on metre and standard gauge lines, and they are found in India on the broad or 5 ft. 6in. gauge, and also on other systems laid with narrow gauge tracks. Of the last named, the Darjeeing Himalayan Railway is of special interest, for the line is of 2 ft. 6 in. gauge and is sharply curved and graded throughout its length of 51 miles.

The first "Garratt" locomotive built for service in England was also the first of the type to be used on standard gauge lines. This was not for a railway company, but for service about the Hafod Copper works of Vivian & Sons Ltd., of Swansea. The works are situated in a valley, and connected with the G.W.R. and the canal, both of these being at a higher level. The gradient is 1 in 20, and the line is sharply  graded at the actual connection with the G.W.R. system, where the radius is 97 ft. The "Garratt" locomotive showed itself capable of dealing successfully with these difficulties, and at the same time its coal consumption was found to be some 25 per cent. less than that of two standard shunting tank engines working together, and this with loads 33 1/3 per cent. greater.
Considerable interest was arroused in 1925 at the Stockton and Darlington Railway centenary celebrations at Darlington when a "Garrett" locomotive built for the L. N. E. R. made its first public appearance. This engine, the now well-known No. 2395, has the 2-8-O : 0-8-2 wheel arrangement, and is equal in capacity to two of the L.N.E.R. three-cylinder "Consolidation" mineral engines. Each engine unit has three cylinders, and following Mr. Gresleys usual plan, two sets of outside Walschaerts gear actuate the three valves. The cylinders and motion are standard with those of the 2-8-0 locomotives previously mentioned, and where possible the details are interchangeable with that class. The boiler is comparatively enormous, and its size is only made possible by the fact that the locomotive is built upon the "Garratt" system. It has a diameter of 7 ft., and a total heating surface of 3,640 sq. ft. With its tractive effort of 72,940 lb. at 85 per cent. working pressure, and its weight of 168 tons, it is the largest, heaviest and most powerful locomotive in Great Britain. Its duties are to bank heavy coal trains on the Worsborough branch between Wath and Penistone, where two successive miles are inclined at 1 in 40. Some two years afterwards the L.M.S.R. took delivery from Messrs. Beyer-Peacock of three engines of the 2-6-U: 0-6-2 type. After some experience with these between Toton and Cricklewood on coal trains that previously required the services of two locomotives, 30 more of the type were ordered and were delivered in 1930. These are Nos. 4967 to 4996, the earlier engines being 4997-99.
An extremely interesting feature was introduced on No. 4986 in connection with the firing of the engine. As a boiler of the size possible in "Garratt designs makes hard work for the fireman with a large fuel capacity being necessary, considerable attention has to be given to trimming the coal down to the shovel plate, with the result that the fire may be neglected to some extent, and moreover this trimming involves extremely hard work. In order to render this extra work unnecessary engine No. 4986 was fitted with the BeyerPeacock patent self-trimming bunker. The coal is carried in a closed container, which has opening doors on top to allow of coaling. This container is circular in form and becomes wider towards the cab end. It is pivoted so that the top side is practically horizontal, and thus the lower side of the bunker is well sloped. The bunker is revolved periodically by a small steam engine driven from the boiler of the locomotive, and in this manner, owing to the shape and inclination of the container, the coal is caused to slide forward. The bunker may thus be revolved between periods of firing, and no labour in the matter of trimming the coal is called for on the part of the fireman. The fact that the container can be completely closed prevents dust from being blown into the cab, particularly when the engine is running bunker first; and owing to its circular form the look-out when running in this direction is improved. This scheme was so successful that the other engines of the class have been similarly provided.

are each pivoted at the centre of the rigid wheelbase. This system reduces the wear between the flanges and the rails. Locomotives of this kind are in use in South Africa, and in addition to these 2-6-2 : 2-6-2 engines, some large and powerful 2-8-2: 2-8-2 modified "Fairlies" are also in use. A later development is the "Garratt-Union" type, which is found on the South African Railways. In this type certain characteristics are found both of the " Garrett " design and of the modified "Farlie".