Operation of a steam locomotive

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Operation of a steam locomotive

We will examine the main elements of a steam locomotive , we can see in the diagrams below one of the potent locomotives that were the most important means of transport in the beginnings of the XX century and in these days remain available in countries with scarce electricity production or as a tourist attraction , it can be appreciated that the boiler is assembled seated on an armor that at the same time is sustained on the axes of the wheels by means of springs . A solid armor of strained iron connects one end of the boiler with the frame of the vehicle and it also takes the cylinders of the machine. In the figure it has been separated the wall of the cylinder, to show the circular piston that moves back and forward inside the cylinder. The steam is admitted in the bomb body by a valve that obeys the machinist's action. Inside the bomb body exists another valve that is not shown in the figure which works due to the action of one of the axes . When the axis gives entrance to the vapor, it forces the piston to move from an end to the other of the cylinder , first toward a side of the piston and then toward the other one, it is then ejected to escape after it has transmitted its pressure on the piston . The shaft of the piston is articulated with a connecting rod that at the same time acts on a fastener of one of the moving wheels, so that the movement of sway of the piston and its shaft puts in movement the connecting rod and impels the displacement of it so that it makes that the wheel rotates in the same way that works the pedal of old mechanic sewing machines , producing the rotational movement of its motive wheels . When the machine has more than a set of driving wheels, with the object of making greater contact between the wheels and the track , all the wheels of a side are connected by means of a lateral bar that forces them to turn to the unisonous .

1 - boiler, 2 - steam box , 3 - forward set of auxiliary wheels, 4 - piston, 5 - cylinder, 6 - articulation of the shaft of the piston with the connecting rod, 7 -lateral bar that couples the wheels, 8-connecting rod, 9-frame , 10 - rail, 11-rear set of auxiliary wheels, 12 - smoke box, 13 - tubes, 14 - water, 15 - armor, 16-locomotive's suspension, 17 - supports , 18 - bearing, 19 - rail, 20 - grill of the firebox , 21 - mouth of the firebox .

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To each side of the locomotive works a cylinder with its corresponding piston coupled to the same set of wheels; but the connecting rods of each side work with a quarter of turn of difference, so that the two lateral machines are never at the same time at the end of a piston blow, and one of them, consequently, is always in disposition of acting on the locomotive. The mechanism to make work the steam admission valve in the bomb body allows the change of direction of the steam jet with the object of also reversing the direction of movement of the locomotive when it is wanted that the engine marches backwards.

In the lower picture of the diagram the wheels are suppressed to show how the great weight of the whole machine is supported. Its boiler ,the most compact of all types of boiler in relation to the amount of steam that it produces. Suitable for pressures up to about 300 pounds per square inch, it is usually fired by coal although oil has also been widely used. In some countries, the fuel can also be wood, sugar cane waste or even peat .The boiler, represented in the picture , rests on the frame which is supported on the suspension system by means of links or hook rings. The bearings in the axis , finally, transmit the weight to the wheels which rest on the rails. In the American locomotives, in those that there were several set of motive wheels, the enclosed ends of the suspension were connected with the opposed ends of a common lever, as it is shown in the picture , giving bigger elasticity to the connection between the frame and the axis. This allowed to the big machines to move on places not so evened in the track , without necessity of forcing the frame or the boiler to suffer an excessive effort.

When the locomotive is very long as the one that is shown in the figure it should be provided with sets of auxiliary wheels in one or in the two ends, and they are denominated forward set and rear set of wheels respectively. The locomotives are sometimes mounted in two wheels; other , in four, and the frame that takes the axes should be able to rotate around a central fastener, allowing to the locomotive to keep steady in the curves.
In the lower picture of the diagram it has also been suppressed a part of the cover of the boiler, to show how the fuel is burned on the grate of the inner firebox. This firebox is surrounded by water in the outer firebox shell and so absorbing radiant heat from the fire. The gap between the inner and outer fireboxes is maintained by hundreds of rigid stays.

To support combustion, air is admitted into two areas:
1, Primary air enters via damper doors in the ash pan and is drawn through the fire bed. This makes the fuel incandescent but it is not sufficient to burn all of the elements of the coal.
2, Secondary air is drawn through the fire hole door or small flaps.
The brick arch within the inner firebox is constructed firebrick or refractory concrete and serves three purposes. As its material is incandescent, it encourages combustion of gas distilled from the fire bed; it lengthens the path of those gases to give additional time for combustion and it prevents cool air reaching the fire tubes as it enters the fire hole door.

Then long tubes surrounded by water in the boiler barrel draw the flames and the hot gases from this firebox to the smokebox in to the front end of the of the engine, where they escape by the chimney. The saturated steam that is generated collects above the water in the boiler . On later locomotive boilers, these tubes are of two types, small ones of about 1¾ - 2¼ inches in diameter and large flues of 5 - 5½ inches diameter.
The water that surrounds the tubes and the home evaporates for the action of the hot gases and the steam passes to the bomb body; its journey to the cylinders is controlled by the regulator valve operated from within the cab by the regulator handle. It travels through the main steam pipe to the superheater header, which is divided into two separate areas. The saturated steam at a temperature of about 200ºC passes through the superheater elements and increasing its temperature to about 350ºC. Returning to the other side of the superheater header, the superheated steam flows via steam pipes to the valves and then on to the cylinders ,after having acted there, this steam is exhausted by means of a tube that drives it to the chimney, causing a strong shot through the tubes and in the firebox , the steam from the cylinders passing through the reduced orifice of the blastpipe at high speed, and capturing the gases on the way, stimulate the combustion of the coal vastly. If it was not for this reason, the steam locomotive would not be as potent as it is it, considering its size.

The main parts of a locomotive are, consequently, the boiler, the frame or armor that sustains it, the machines, or be the bomb bodies, with their pistons and valves, and the motive wheels. Contrasting with some other forms of the steam machines,. the locomotive is comparatively simple, and at first sight it can cause strangeness that it has taken so long in being perfected. It should be regarded that the conditions in that the steam locomotive works are very different from those engines that operate the fixed machines and even those that were used in the sailing vessels. The reason is that the fixed machines always rest on very solid foundations, and the marine ones also have quite stable supports; but the locomotive constitutes a total mechanism of around 21 meters of longitude and five of height that weighs more than 300 tons, with a boiler of about three meters of diameter , containing vapor to 200 pounds of pressure by square inch, mounted on wheels separated by spaces of more than a meter, and marching on a steel rail that compared with the size of the machine, it appears like a true tape, and that the locomotive not only rests on the track , but even it drags on it big loads at a high speed, ascending and lowering slopes, with more security certainly and less interferences and cares that those that demand most of the machines.

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