HYDRAULIC' MACHINERY, machinery which is operated by water pressure, either natural or transmitted: natural, as in a pipe leading down from an elevated reservoir; transmitted, when the pressure is produced by an engine, such as a pump or a hydraulic ram. The more poiverful hydraulic machines are worked through an which acts as a governor. This device substitutes a uni weight for the fitful variation of impulse inseparable from pumps and natural sources. It consists essentially of a piston held down by heavy weights, acting in a cylinder into which the water supply is led below the piston. The water under pressure pours into the cylinder, lifting the piston and its weights. If the impulse is much greater than the weight, the pressure in the cylinder does not change, but the piston is driven higher. The machine is operated by water taken from the cylinder at the constant pressure represented by the weight. The smaller the area of the piston in proportion to the weight the greater the pres sure per square inch available to run the machinery.
Hydraulic machines include metal working machinery like presses for corrugating and stamping, punches, shears, rivetters, bending machines, etc.; many kinds of cranes, lifts and elevators; hay and
presses; lacks, pumps, capstans, and winches; railway switches and turntables; drydocks; gun brakes to take up the recoil of guns when fired, and gun lifts to raise disappearing guns to the firing posi tion; door-closing mechanism for closing safety doors in bulkheads on shipboard; grain eleva tors and dredges; and similar power applica tions. (See HYDRAULICS; HYDRAULIC ENGINE; HYDRODYNAMICS). Consult Butler, E.,