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The piston rods, by means of their crosshead, and the connecting rods actuate on the levers of the driving axle (which links two wheels, one on each side), transmitting to it a rotatory movement with the consequent rotation of the wheels on the rails. In the first locomotives there was only one driving axle; the need to drag increasingly heavier convoys required to transmit the rotatory movement to additional axles, to increase adherence on the rails, a factor that, as mentioned in a previous chapter, was of great concern for the first railway engineers. Later it was introduced an auxiliary system - which remains in use in modern locomotives - to improve adherence in difficult situations: it consists of dropping sand in the very point where the rails make contact with the wheels. To this effect, steam locomotives carry sand in one or more domes attached to the upper part of the boiler.

The characteristics of the wheel arrangement can be indicated with three digits: the first one indicating the number of leading axles (the increase in speed required the addition of a fore "leading bogie" fitted with small wheels, which were able of a certain steering, to facilitate the march of the locomotive when entering curves and switching tracks), the second one indicating the number of driving axles and the third one indicating the number of trailing axles (the rear "trailing bogie" uses similar wheels as the leading bogie, but it serves the purpose of supporting the weight of the cab and the fire box). In Anglo-Saxon countries the number of wheels is used instead of the number of axles. The letter "T" at the end of the numeration indicates that the locomotive has the tender incorporated to itself instead of as a separate vehicle.

Steam locomotive wheel arrangement
Driving wheels and different wheel arrangements used in steam locomotives. Increasing the diameter of the driving wheels is the easiest way to achieve a greater speed. Note how driving wheels have an added weight to increase inertia, facilitating so the movement of the running gear.
Rails joint system
Binding systems for rails: old system (to the left) and new system (to the right).

To the locomotive is attached a vehicle called tender for transporting fuel and water. Actually, the tender together with the machine is what constitutes the locomotive. Another important part is the driving cab. To the left, where the machinist is placed, are all the controls and indicators that affect the march of the locomotive: the speed shift, the steam regulator, the command for the compressed-air brakes, the water level in the boiler and diverse manometers. The largest one indicates the pressure in the boiler while smaller ones indicate the pressure in the compressed-air deposits. Of great help for the stoker, and required in the most powerful machines, is the mechanical device - known as stocker - which transports the coal from the tender to the fire box, typically by means of a duct which has an auger - rotating screw - inside and along it.

Steam locomotive cab
Interior of the driving cab of a steam locomotive Beyer-Garratt, type GMAM, in service in the South African railways. In the center it can be seen the hatch through which the coal is fed, by means of a mechanical loader, and to the right is the feeding device.

Now that we have an idea on how these machines work, it would be interesting to mention that the locomotives built by Robert Stephenson could march at an average speed of 50 kilometers per hour, and already in 1839 the trains of the South Western achieved a speed of 80 kilometers per hour while towing convoys weighing 50 tonnes. To increase the speed without altering the cylinders and running gear engineers resorted to building locomotives with very tall driving wheels. In fact, in June 1846 the Great Western introduced a locomotive whose wheels had 2.44 meters in diameter. This powerful machine effectuated the route between London and Swindon at an average speed of 95 kilometers per hour while towing a load of 100 tonnes.

This same line, circa 1850, was the scene of another episode on the race for speed: a powerful machine of the type "Iron Duke" covered the 124 kilometers of the route in one hour and 12 minutes, at an average speed of 102 kilometers per hour. These speeds could be possible thanks as well to the width of the track (the spacing between the internal faces of the rails, technically known as track gauge), which was larger than normal to allow the utilization of these locomotives, whose dimensions prevented them from operating on tracks of normal width.

The first manufacturers of railway equipment

The first industry that built a steam locomotive in England were the workshops led by Robert Stephenson, in Newcastle. From there departed the locomotives that inaugurated railroads all around the world, in France, Austria, Egypt, Australia or Canada. A direct competitor of Stephenson was Edward Bury & Company, who had in Liverpool a factory specialized in building locomotives of two driving wheels. Another very important manufacturer was Sharp Robert's & Company, which after being refounded several times took the name North British Locomotive Company. In 1940 existed in England more than 30 manufacturers.

In America, the production was initially localized in the Eastern States. In Philadelphia it was founded the first establishment of Matthias W. Baldwille, from which emerged that type of locomotive known as the "American type". This factory produced in just one year (1836-37) 80 locomotives, a truly remarkable production in those times in which the railway industry was taking its first steps. In the continental Europe, France was the first country in producing locomotives, and it would be convenient now to remember Marc Seguin and his factory Chemins de Fer de Saint-Étienne.

Locomotive Norris, 1846
American locomotive "Norris" built in 1846. Maximum speed: 55 kilometers/hour.

In Belgium, in 1839, from the factory of John Cockerill, a British manufacturer living there, emerged the locomotive called "Belgium", acquired by the state railways. In Germany, the first manufacturers were the workshops Borsing, followed by the factories in Munich, among others. In Italy the first machines of national construction departed from the workshops Ansaldo di Sampierdarena, in 1854. Regarding the cars, those reserved for first-class passengers in the starters of the railway travels reminded, regarding their construction, the conventional stagecoaches, while those reserved for third-class passengers were fully uncovered, leaving the passengers exposed to the weather. Very soon these cars suffered notable transformations, and while in 1854 the locomotives were still of "free design", the cars had already acquired their classic look, with two or three wheel axles supporting a box-shaped wooden structure.

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