It is often of essential importance to be able to arrest the progress of a carriage on a railway with great promptitude; and the breaks in ordinary use by pendulous links z from a centre pin or bolt e, fixed to the frame. The breaks are caused to apply to the circumference of the tires of the wheels K and M, by means of links, which are interposed between the two breaks, and which links, when put down into an angle, as shown in the figure, leave the breaks free of the wheels K and M; but when, by opening the cock c, the steam from the boiler is admitted through the pipe b b, into the hollow cylinder a, it raises up the plunger therein; and the latter, by its lever y, and rod f, draws up the links towards a straight line, and then they force the two breaks apart from each other, against the wheels K and M, with an increased force beyond that which the plunger exerts; that increase of force being in consequence of the leverage at y, and the oblique direction of the links. When the handle of the cock c is turned the other way, it allows the steam to issue through an upright spout, and escape from the cylinders into the open air.
for this purpose have not always been found sufficiently potent. As a remedy for this inconvenience, Mr. Robert Stephenson, under the same patent, proposes to employ the force of steam acting upon pistons or plungers in small cylinders; so that when it is required to stop the train it is only necessary to turn a small cock, which allows the steam to flow instantaneously through a pipe into the cylinder, and by its pressure on the piston give motion to a system of levers, which cause two breaks or clogs to be forced against the peripheries with great energy, and to arrest the motion of the vehicles very quickly. These clogs or breaks, and their mode of action, are shown in the side elevation on the preceding page. a is the hollow cylinder into which a plunger is fitted, to act by a lever y, and an upright rod f, upon the two brakes d 3, which are suspended End Elevation.
The following letters have reference to the other parts of the engine. At h is the fire-box; i the ash-grate; j is the boiler, cylindrical in shape through the lower part of the transverse sectional area of which are passed longitudinally a great number of small brass tubes, proceeding from the furnace chamber, which serve as the hot-air flues, and conduct the same into the smoke-box /, at the other end, whence the gases resulting from the combustion of the fuel ascend the chimney n; p is the steam-head; q a safety-valve; r another valve, the extremity of the lever of which is held down by the elastic force of a spring steel-yard at s; t is a man hole; u the working geer; v v v the springs; w w the iron brackets that connect the machinery to the wooden frame; x the fire-door; y the throttle-cock, provided with a lever and graduated scale. In the end elevation it will be observed that the axes of the running wheels M, like those at O, are straight; the form of the axles to the wheels K, is represented in the annexed cut, and they are forged with great care from the toughest quality of iron, and are turned and centered, as well as the running wheels, in the lathe.
Locomotive engines, constructed according to the description of the foregoing, Mr. Stephenson says, have the effect of preventing the boilers being burnt out so soon as usual, by allowing them to be made of greater magnitude and strength; the additional wheels supporting the extra weight. The bearing springs are used for the extra small wheels, the same as is now done for other wheels in ordinary engines; the six springs used causing all the six wheels to apply and bear fairly on the rails, and ease all jolts and concussions; the relative weights, or portions of the whole weight of the engine, which is to be borne by each of the six wheels, being regulated by the strength and setting of their respective bearing springs. The main wheels, which are impelled by the power of the engine, are, in all cases, left loaded with as much of the weight of the engine as will cause sufficient adhesion of those wheels to the rails, to avoid slipping thereon. The larger the entire capacity of a boiler is, the more metallic heating surface it will contain; and, consequently, render unnecessary that intensity of heat which is so prejudicial to the metal.
And the jet of eduction steam which is thrown into the chimney to produce a rapid draught therein, may be greatly diminished in its velocity, which will permit the eduction steam to escape from the working cylinders with greater freedom than could be permitted with smaller boilers, wherein a greater heat and a more rapid generation of steam are indispensable to furnish the requisite power.
The annexed cut exhibits another form of Mr. Stephenson's locomotive engine, but with the foregoing improvement added thereto. The foremost wheels, at the chimney end of the boiler, are, in this, however, impelled by means of outside cranks and connecting rods, as well as the two middle wheels K, which are on the cranked axle; in other respects, the improvement is the same as in the other engine. The breaks, or clogs, are, of course, applicable to this or any other engine, but they are left out in this instance, as being unnecessary to our illustration.