Hydraulic introduction of the hydraulic press effected a revolution in the various industries requiring compressing or expressing machines. It was invented in 1795 by Joseph Bramah, an English me chanic, and is usually designated the " Bramah " press. It is a machine in which the pressure of a piston on a body of water of relatively small sectional area is made to transmit the force to a cylinder of multiple area. The principle on which it acts is founded on one of the fundamental laws of hydrostatics—namely, that any non-elastic fluid, such as water, pos sesses the property of transmitting pressure exerted against it at any point equally in every direction. The operation of a hydraulic press will be comprehended from the following description of the illustration (fig. 9): a is a reservoir of water, on which are the pumps (b), whose piston-rods are worked by hand-levers (c). The water is conveyed by the pipe (a') to the cylinder of the press, where it elevates the piston and table (e), which rises. between guides that hold the upper plate or presser-head, against which the substance under pressure is driven. The elevation of the table is proportionate to the quantity of water injected, and the pres sure exerted is in proportion to the respective areas of the pinup and the cylinder.
The hydraulic press is adapted for a great variety of purposes in which a high and permanent pressure is required. Modified forms of machines, on the principle of the hydraulic press, have of late years been largely employed, and for a great variety of purposes that formerly were not thought of. Water, being nearly incompressible, is a convenient mode of conveying power to a distance, and in many cases of applying the force directly to machines. Hydraulic power is used for working lift ing-jacks, cranes, punching- and riveting-presses, etc., for engines as motors, and for operating warehouse hoists and passenger elevators, all of which are particularly described in the following pages under their appro priate heads.
Hydraulic constant increase in the production of loose materials, such as hay, cotton, etc., at a distance from the centres of their consumption, has led to the construction of special apparatus for compressing them into packages which can be more easily handled, more cheaply transported and stored, and be sold at more remunerative prices than if shipped in bulk. Several presses that have been invented in recent years are rendering efficient service to agriculture and the industries. This is especially evidenced in the baling of cotton (whose production in 1888 reached the large number of 6,935,082 bales), for which purpose the hydraulic press is eminently adapted. Figure 6 exhibits a powerful hydraulic cotton-compress operated by steam. This machine consists of a cast bed-piece with housings which support the press-head or upper platen, on which rests the hydraulic cylinders. There arc three cylin ders, each 2636 inches in diameter, with their rains or pistons working upward. These rains raise a cross-bead to which is attached strong steel
links carrying the table or lower platen. The water, on being forced into the hydraulic cylinders of the press, raises the rain-heads, which in turn raise the cross-head and lower platen, on which is placed the cotton-bale, and compresses it to the required density against the press-head. To ope rate the press there is provided a high- and a low-pressure steam-engine cylinder; to each cylinder there is attached a hydraulic rain, both rams being connected with the press cylinders by means of a pipe for transmit ting- the water. The low-pressure steam-cylinder has a diameter of 73 inches and a stroke of io feet; the high-pressure cylinder has a diameter of 73 inches with a stroke of i x feet, and uses steam at 125 pounds per square inch. The high-pressure ram has a diameter of 13;6 inches, and the low-pressure ram has a diameter of 291. inches. The initial pressure is given the bale by the ram of the low-pressure engine; the high-pressure engine ram is then brought into action, by which the pressing of the bale is completed, with a total pressure on the bale of 300o tons. There is thus obtained a power sufficient to permit of furnishing in a compact form a bale of 50o pounds and of a density of 5o pounds to the cubic foot. The capacity of the machine is one hundred bales per hour.
Hat-press.—All fibrous substances possess to some degree the property of being shapable—that is, the elementary fibres, and hence, also, the fabrics produced from them, assume under the action of heat any shape imprinted upon them, and retain it with a certain consistency. Of this property, which is also taken advantage of in ironing and pressing wash clothes, the hat-press (shown in Figure to) makes excellent use. It serves to give to felt and straw hats the shape prescribed by the prevailing fash ion. The press contains a cast-iron mould with thick sides heated from below by a charcoal fire or by gas, upon which the hat is placed and then pressed uniformly on all sides by an elastic membrane—the so-called "gum bag." The latter consists of a thick sheet of india-rubber shaped like a hood, which assumes the shape of the hat. The edges of this sheet are secured to a hemispherical metal lid in such a manner as to allow of a very high pressure (twenty to thirty atmospheres) being brought to bear upon the back by means of water-pressure. The water is forced into the dome by means of a small hand force-pump, and compresses the film on the hat and presses the latter on to its mould. In the figure the lid is shown turned up, in which position the hat to be shaped can be intro duced. Before the production of the high pressure the lid is turned down and closed with a strong bolt. Since the introduction of this machine the former customary pressing of the hats upon the mould has been almost entirely abandoned.