Hydraulics

Hydraulics is the general term for applied hydrodynamics. The chief applications of this science are either in the direction of water supply (q.v.) or of the utilisation or transformation of energy possessed by water under certain circumstances. In both these directions much has been done of late years, so much so that hydraulic engineering has separated itself from ordinary civil engineering, and now demands special training and experience. The question of the utilisation of natural forces, as it is generally expressed, demands for its discussion an intimate knowledge of hydraulic principles; for the two best known instances are those of tides and of waterfalls, and in various parts of the world successful attempts have already been made to prevent entire waste of such energy. The practical machines dependent upon hydraulic principles are described separately. The chief of these are the hydraulic press, for producing a great intensity of pressure by means of a large bearing surface of water upon a ram enclosed in a suitable strong cylinder; the waterwheel, which is driven either by impact of running water or by the weight of water that is carried down in suitable buckets arranged round the circumference of the wheel; the turbine, which is the modern development of the water-wheel, and by stricter guidance of the descending water compels a greater percentage of its energy to be given to the wheel than before; the pump, force-pump, and fire-engine, for lifting water by a reciprocating motion of a piston in a cylinder; and the centrifugal pump for effecting the same result by a rotary motion of a water-wheel. Hydraulic presses are variously applied in the arts: for punching holes in metal plates, for riveting such plates together by squeezing wrought-iron rivets into shape after they have been dropped into the proper rivet holes, for working steel shears to cut metal, and the like. The well-known hydraulic lifts are precisely similar in principle, and are used extensively for domestic Durposes, as well as for heavy work in engineering. Canal-locks are frequently worked now by hydraulic lifts; heavy guns are raised, lowered, or otherwise moved by the same means; and in large shipbuilding and repairing docks arrangements are made by which huge vessels are elevated on a series of powerful hydraulic lifts.