The steam generated in the boilers is conveyed to the engine, where it is to do its work, by what is called the steam pipe. The steam pipe of the larboard engine, that is, of the one nearest the spectator, is not represented in the engraving, as it would have intercepted too much the view of the other parts. That belonging to the starboard engine, however, may be seen passing across from the boiler to the engine, on the back side of the room. The destination of the steam is the cylinder.
GENERAL VIEW OF A MARINE ENGINE.
The cylinder, marked C, is seen on the extreme right, in the view. It may be known, too, by its form, which corresponds with its name. The cylinder is the heart and soul of the engine, being the seat and centre of its power. The steam is generated in the boilers, but while it remains there it remains quiescent and inert. The action in which its mighty power is expended, and by means of which all subsequent effects are produced, is the lifting and bringing down of the enormous piston which plays within the cylinder. This piston is a massive metallic disc or plate, fitting the interior of the cylinder by its edges, and rising or falling by the expansive force of the steam, as it is admitted alternatively above and below it.
The round beam which is seen issuing from the centre of the head of the cylinder is called the piston rod. The piston itself is firmly secured to the lower end of this rod within the cylinder. Of course, when the piston is forced upward by the pressure of the steam admitted beneath it, the piston rod rises, too, with all the force of the expansion. This is, in the case of the largest marine engines, a force of about a hundred tons. That is to say, if in the place of the cross head—the beam marked H in the engraving which surmounts the piston—there were a mass of rock weighing a hundred tons, which would be, in the case of granite, a block four feet square and eighty feet high, the force of the steam beneath the piston in the cylinder would be competent to lift it.
The piston rod, rising with this immense force carries up the cross head, and with the cross head the two side rods, one of which is seen in full, in the engraving, and is marked S. There is a side rod on each side of the cylinders. The lower ends of these rods are firmly connected with the back ends of what are called the side levers. One of these side levers is seen in full view in the engraving. It is the massive flat beam, marked L, near the fore-ground of the view. It turns upon an enormous pivot which passes through the centre of it, as seen in the drawing, in such a manner that when the cylinder end is drawn up by the lifting of the cross head, the other end is borne down to the same extent, and with the same prodigious force. There is another side beam, on the other side of the cylinder, which moves isochronously with the one in view. The forward end of this other beam may be seen, though the main body of it is concealed from view. These two forward ends of the levers are connected by a heavy bar, called the cross tail, which passes across from one to the other. From the centre of this cross tail, a bar called the connecting rod rises to the crank, where the force exerted by the steam in the cylinders is finally expended in turning the great paddle wheels by means of the main shaft, S, which is seen resting in the pillow block, P, above. These are the essential parts of the engine, and we now proceed to consider the mode of manufacturing these several parts, somewhat in detail.
THE CUTTING ENGINE.
The boilers are formed of wrought iron. The material is previously rolled into plates of the requisite thickness, and then the first part of the process of forming these plates into a boiler is to cut them into proper forms. The monster that fulfills the function of shears for this purpose, bears a very slight resemblance to any ordinary cutting implement It resembles, on the other hand, as represented in the adjoining engraving, an enormous letter U, standing perpendicularly upon one of its edges. Through the centre of the upper branch of it there passes a shaft or axle, which is turned by the wheels and machinery behind it, and which itself works the cutter at the outer end of it by means of an eccentric wheel. This cutter may be seen just protruding from its place, upon the plate which the workmen are holding underneath. The iron plates thus presented are sometimes nearly half an inch thick, but the monstrous jaw of the engine, though it glides up and down when there is nothing beneath it in the most gentle and quiet manner possible, cuts them through, as if they were plates of wax, and apparently without feeling the obstruction.
