Hydraulic, << hy DRAW lihk, >> engine, or fluidic engine, is a machine that produces motion by means of pressure from water or some other fluid. This type of engine can be used to drive machinery or move heavy loads. Examples of hydraulic engines include jacks, hoists, the power steering and brake mechanisms of automobiles, and the control systems of aircraft.
There are two basic types of hydraulic engines–reciprocating engines, such as hydraulic elevators and suction pumps; and turbines, such as those that turn electric generators. Reciprocating engines operate at slow speeds. Turbines usually function at higher speeds.
Early hydraulic engines used water to produce power. Today, engines that use water are rare except for water turbines in hydroelectric plants. Modern hydraulic engines use fluids that do not freeze at low temperatures. Such fluids include oil, certain silicones, and some gases. The fluid in some hydraulic engines is put under pressure mechanically. In other engines, the pressure comes from the weight of the fluid stored in a reservoir above the engine.
