Hydraulic Press

Hydraulic Press is a machine employed extensively for the compression of merchandise, various products in process of manufacture, and the like, for such purposes as the economy of space, the extraction of oil or other derivatives by the compression, or the improvement of the material under treatment. A thick cast-iron or steel hollow cylinder is fitted with a ram or cylindrical piece of metal that can slide freely into the hollow. When water is forced in under pressure, it presses on every portion of the ram that is open to the interior of the vessel, and the resultant force is one tending to drive the ram out. So that the ram shall be watertight, and yet move easily, Bramah introduced a collar of leather into a groove cut in the neck of the press. Water tending to pass outwards fills the collar and presses it against the ram, and so exit is prevented; the greater the water-pressure the more tightly will the collar cling to the ram. The characteristic property of a fluid - that it will transmit pressure equally in all directions - enables us to increase indefinitely the total available pressure of the ram, e.g. by doubling the sectional area of the ram the total liquid pressure thereon is doubled without increasing the pressure of the water, the larger dimensions of the press demanding, however, a greater quantity of pressure-water each stroke. [Hydraulics.]