The /I 'estinghouse Engine has among its essential features—many of which are peculiar to it—single-acting inverted cylinders, having no piston-rods, but the piston driving the crank-shaft through a connect ing-rod pivoted to the piston-head. The valves are cylindrical pistons. The crank case constitutes a receptacle for oil, in which the crank dashes at each revolution, thereby effecting lubrication of the crank-pin, man bearing, and wrist-pin. This type exists in three varieties, of which the most recent and important is the compound engine shown in lon gitudinal vertical section in Figure 6 05/. 93), a perspective being given in Figure 5. The functions of the working portions may be readily studied in Figures i to 4; Figure r showing the position of the valve and piston at the moment when the steam is being admitted into the high-pressure cylinder; Figure 2, when the steam in the high-pressure cylinder has been cut off; Figure 3, when the high-pressure cylinder is exhausting and the low-pressure cylinder is getting the exhaust there from; and Figure 4, when the exhaust of the high-pressure cylinder (which is the supply for the low-pressure cylinder) has been cut off so as to cause cushion or compression, this leaving the low-pressure cylinder to work on expansion alone until stroke-end. Steam is admitted at s and finally exhausted at E; the space C between the valve-beads forms a clear ance volume which is constantly in communication with the high-pressure cylinder through the annular port P. Steam is admitted to and cut off from the high-pressure cylinder by the valve-edge a, a; this being the only func tion performed by that end of the valve. The valve does not cut off on the port P to the cylinder, but upon another port (111), communicating only with the steam-pipe. Since the valve never reaches the port P, the latter is always uncovered, and the clearance volume C is therefore always in communication with, and a part of, the high-pressure cylinder during both the upward and the downward stroke of the piston. This clearance space bears the same relative proportion to the high-pressure cylinder that the latter does to the low-pressure cylinder. The remaining functions of the valve motion are all performed by the short end of the valve, of which the inner edge b, b effects release and compression in the high-pressure cylinder coincidently with the admission and secondary expansion in the low-pressure cylinder; the outer edge c, c effecting the release and com pression in the low-pressure cylinder.
Afiseellaneous Reeijn-acating Engines. —The principal types of recip rocating engines having been illustrated and described, it now remains in this class only to give a few more examples of various types of construc tion, both ordinary and unusual. Figure 3 (bl. 94) represents a German engine of large, and Figure i one of small, capacity. In these the cyl inder and guides and one of the fly-wheel pillow-blocks are fastened to an iron bed-plate, which is bolted to a stone foundation. In Figure 2, a medium engine, the pillow-block is passed hi one piece with the iron bed-plate, no masonwork foundation being used. Figure 4 shows a double-cylinder twin engine. In Figure 4 (ft/. 95) we have an inclined double-cylinder engine. Figure 3 shows an engine attached to the boiler, thus saving the expense and room of a separate frame. Figure 6 shows a curious type of engine (Sulzer's), in which the fly-wheel is not on the crank-shaft, but is driven by a pinion upon that shaft; of course at a slower rate of speed than that of the engine. Figure 5 shows a three-cylinder engine in which there are
three single-acting cylinders, with their axes 12o° apart, driving a com mon shaft. Such machines, having no dead-point, start easily, and are used for direct-driving high-speed machines, such as saws, dynamos, etc.
Figure i (AZ 96) shows a steam-engine and boiler contained in a rail way-car for convenience in doing construction-work along the line of the road. Figures 3 and 4 show forms of German " locomobiles" or traction engines. Figure 2 illustrates a German semi-portable engine, with loco motive fire-box.
Geared Engines are those in which the screw or other rotating part driven by the engine is given, by means of gear, greater rotation speed than the engine. They were in use for marine work long after engines were known which could have been run at even a greater speed than the screw might have been run at had the latter been made large enough. The term is usually restricted to marine engines.
hoisting purposes there arc generally used small double-acting reciprocating engines, geared to a drum upon which a rope or chain is wound and unwound ( f/. 95, fig. 2). These engines must be quickly reversible, and as such machines arc most often used in exposed situations, they need be of extreme simplicity. Usually they are attached to, as in the figure, or arc in close connection with, a portable boiler.
Sector Cylinders arc very rarely seen. The ordinary cylinder is replaced by a cylindrical sector in which a rectangular piston oscillates, as on a hinge, on a rock-shaft which drives the crank.
The Disc Engine (fig. 1) has, instead of a regular cylinder, a spher ical zone having for its ends a pair of cones the apices of which coin cide with the centre of the sphere. The piston is a flat circular disc, which fits the interior of the spherical zone around its edge, and has in it a radial slit which fits a partition fixed in the cylinder and shaped like the cylinder sector. The disc is fixed to a ball, from which projects (perpen dicular to the plane of the disc) a rod which acts as a crank-pin, its end fitting into a hole in the end of the crank. The disc and partition divide the cylinder into four spaces, two of which enlarge as the others contract, steam being let into the two former, and discharged from the two latter, by ports near the partition.
The Tendency of Modern Practice is toward higher and higher piston speed and rotation speed, as well as higher pressure and earlier cut-off. This tendency is by reason of the fact that the more rap idly the steam is used, the less it is wasted by condensation from radia tion; the higher the pressure, the earlier the cut-off, and the greater the amount of work done with a given weight of steam; and the higher the rotation speed, the less countershafting, pulleys, etc. are needed to drive the machinery, the greater part of which is high speed. Of course the cost of small engines is less than that of large ones to do the same work. We must not, however, lose sight of the fact that in any steam-engine the fluid must enter the cylinder at as high a pressure as possible and leave at as low a pressure, this reduction of pressure being by expan sion, not by condensation in the cylinder; and that there must be no waste of heat by conduction and radiation. Within certain limitations, the engine which expands steam at from one hundred to twenty pounds pressure is doing more work than that which expands it only at from one hundred to fifty pounds.