HYDRAULIC PRESS. The action of the hydraulic press depends on two facts concern ing water: (1) that it is incompressible; (2) that when confined it will transmit equally in all directions any pressure to which it is sub jected. The hydraulic press by which these facts are put to economic use consists essen tially of two connected cylinders, one of large diameter and the other of small diameter. Each is fitted with a piston. The smaller cyl inder is operated as a pump, the larger one as a reservoir. Any pressure per square inch put upon the pump piston is transmitted to the res ervoir piston per square inch. Thus, if the pinup piston has an area of two square inches, and the reservoir piston an area of sixty square inches, a pressure of 80 pounds on the pump piston rod will exert a pressure of 2,400 pounds on the reservoir piston rod. As applied indus trially, the hydraulic press carries a platen, or platform, on the upper end of the reservoir pis ton rod—generally a plunger of large diam eter. A massive frame work extends from the base of the reservoir cylinder up and overhead, and upon this is fastened a fixed platen opposite the moving platen. The material to be pressed is placed on the movable platen below and is forced up against the upper platen by pumping water with the pump cylinder into the reservoir cylinder below its piston. The efficiency of the hydraulic press is very high — above 90 per cent; that is, less than 10 per cent of the power put into the machine is absorbed (by the friction developed in operating it.
The principle of the hydraulic press is made use of in the portable hydraulic jack, used in raising heavy vehicles, and even great build ings, bridges, etc. The hydraulic cranes used for lifting, heavy castings and machines, such as locomotives, is a development of the hy draulic press. Perhaps the most common appli cation of the hydraulic press is in the gaining of oil from oil-seeds and oil-nuts. These re quire the immense pressures long continued which the hydraulic press supplies. Another use is in forcing into place the metal hoops on large and strong barrels. A very interesting application of the hydraulic press is in the making of lead and tin pipes. These metals become plastic under the tremendous pressures exerted, and flow out of the prepared orifices in the same way that macaroni is forced from the machine in which it is made by a very mod erate pressure upon the soft dough. By an in genious device lead pipe lined with tin is as produced as the plain lead pipe. The hydraulic press is also used to coat electric cables with lead, the cable passing through the core stem which preserves the hollow when lead pipe is made. Still another application of major importance is the use by engineers of the hydraulic press in tunneling, the shield through which the excavations are made being forced forward into the new excavation (usually) hydraulic presses butting against false work in the completed part of the tunnel.