Technology

 Hydraulic 

Motors may produce either rotary or reciprocating motion in the load

In the operation and control of machine tools, farm machinery, construction machinery, and mining machinery, fluid power can compete successfully with mechanical and electrical systems (see fluidics). Hydraulics deals with such matters as the flow of liquids in pipes, rivers, and channels and their confinement by dams and tanks. The motor may be a counterpart of the pump, transforming hydraulic input into mechanical output. This continuous and irrecoverable change of position of one part of the material relative to another part when under shear stress constitutes flow, a characteristic property of fluids. Thus, kinetic energy, deriving from motion, can be partly converted to pressure energy by enlarging the cross section of a pipe, which slows down the flow but increases the area against which the fluid is pressing

Until the 19th century it was not possible to develop velocities and pressures much greater than those provided by nature, but the invention of pumps brought a vast potential for application of the discoveries of Pascal and Bernoulli. Hydraulic fracturing, better known as fracking, has allowed the extraction of natural gas and petroleum from previously inaccessible deposits.

fluid, any liquid or gas or generally any material that cannot sustain a tangential, or shearing, force when at rest and that undergoes a continuous change in shape when subjected to such a stress. In 1906 an important advance in hydraulic techniques was made when an oil hydraulic system was installed to raise and control the guns of the USS Virginia. Some of its principles apply also to gases, usually in cases in which variations in density are relatively small. The viscosity of non-Newtonian fluids either varies with the rate of shear or varies with time, even though the rate of shear is constant. The driver may be an electric motor or an engine of any type. Fluids in a class in this last category that become thinner and less viscous as they continue to be stirred are called thixotropic fluids. hydraulics, branch of science concerned with the practical applications of fluids, primarily liquids, in motion. In the hydraulic press, Pascal’s principle is used to gain an increase in force; a small force applied to a small piston in a small cylinder is transmitted through a tube to a large cylinder, where it presses equally against all sides of the cylinder, including the large piston.

Bernoulli’s theorem, formulated about a century later, states that energy in a fluid is due to elevation, motion, and pressure, and if there are no losses due to friction and no work done, the sum of the energies remains constant. In the 1920s, self-contained hydraulic units consisting of a pump, controls, and motor were developed, opening the way to applications in machine tools, automobiles, farm equipment, earth-moving machinery, locomotives, ships, airplanes, and spacecraft.

In hydraulic power systems there are five elements: the driver, the pump, the control valves, the motor, and the load. Automobiles use hydraulic power systems in their transmissions, brakes, and steering mechanisms. Mass production and its offspring, automation, in many industries have their foundations in the use of fluid power systems. In contrast, the shearing forces within an elastic solid, held in a twisted or flexed position, are maintained; the solid undergoes no flow and can spring back to its original shape. Consequently, the scope of hydraulics extends to such mechanical devices as fans and gas turbines and to pneumatic control systems.

Pascal's principle

Liquids in motion or under pressure did useful work for humanity for many centuries before French scientist-philosopher Blaise Pascal and Swiss physicist Daniel Bernoulli formulated the laws on which modern hydraulic power technology is based. Pascal’s principle, formulated about 1650, states that pressure in a liquid is transmitted equally in all directions; i.e, when water is made to fill a closed container, the application of pressure at any point will be transmitted to all sides of the container. Its chief advantages are flexibility and the ability to multiply forces efficiently; it also provides fast and accurate response to controls.

Hydraulic power systems have become one of the major energy-transmission technologies used by all phases of industrial, agricultural, and defense activity. It is related to fluid mechanics, which in large part provides its theoretical foundation. Modern aircraft, for example, use hydraulic systems to activate their controls and to operate landing gears and brakes. Virtually all missiles, as well as their ground-support equipment, use fluid power. In 1882 the city of London built a hydraulic system that delivered pressurized water through street mains to drive machinery in factories. The fluid exerts an outward pressure, called hydrostatic pressure, that is everywhere perpendicular to the surfaces of the container

Fluids of which the viscosity, or internal friction, must be taken into account are called viscous fluids and are further distinguished as Newtonian fluids if the viscosity is constant for different rates of shear and does not change with time. (See deformation and flow.) Compressed fluids can spring back to their original shape, too, but while compression is maintained, the forces within the fluid and between the fluid and the container are not shear forces. The pump acts mainly to increase pressure.