hydraulic machine

Also found in: Acronyms.

hydraulic machine,

machine that derives its power from the motion or pressure of water or some other liquid.

Hydraulic Engines

Water falling from one level to a lower one is used to drive machines like the water wheelwater wheel,
device for utilizing the power of flowing or falling water. The Norse wheel is the oldest type known. Despite its name it probably originated in the Middle East, where the swift stream required by this type of wheel is common.
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 and the turbineturbine,
rotary engine that uses a continuous stream of fluid (gas or liquid) to turn a shaft that can drive machinery.

A water, or hydraulic, turbine is used to drive electric generators in hydroelectric power stations.
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. The difference in height between the highest and the lowest level is called the head. The amount of workwork,
in physics and mechanics, transfer of energy by a force acting to displace a body. Work is equal to the product of the force and the distance through which it produces movement.
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 produced per pound of falling water is proportional to the head. Water power can be produced in this way from many natural sources, such as waterfalls and dammed rivers. Where no natural sources are available, an artificial reservoir can be made. When energy is plentiful, it is used to pump water into the reservoir; the water is then available as a power source to drive turbines when energy becomes scarce.

In driving certain industrial hydraulic machines an apparatus called an accumulator is employed to supply high power for short periods of time. One type consists essentially of a cylinder enclosing a piston loaded with weights. When water is slowly pumped into the cylinder, the piston and weights are forced up to a position where they are held. When they are released, they force the water out of the cylinder rapidly, providing the machine with hydraulic power.

Hydrostatic Devices

Water or oil under pressure is commonly used as a source of power for many types of presses, riveting machines, capstans, winches, and other machines. The hydraulic press, or hydrostatic press, was invented by Joseph Bramah and is therefore sometimes called the Bramah press. It consists essentially of two cylinders each filled with liquid and each fitted with a piston; the cylinders are connected by a pipe also filled with the liquid. One cylinder is of small diameter, the other of large diameter. According to Pascal's lawPascal's law
[for Blaise Pascal], states that pressure applied to a confined fluid at any point is transmitted undiminished throughout the fluid in all directions and acts upon every part of the confining vessel at right angles to its interior surfaces and equally upon equal
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, pressure exerted on the smaller piston is transmitted undiminished through the liquid to the surface of the larger piston, which is forced upward. Although the pressure (force per unit of area) is the same for both pistons, the total upward force on the larger piston is as many times greater than the force on the smaller piston as the area of the larger piston is greater than the area of the smaller piston. If, for example, the smaller piston has an area of 2 sq in. and a force of 100 lb is exerted on it, then the force on the larger piston having an area of 50 sq in. would be 2,500 lb (100× 50-2=2,500). However, when the pistons move, the distance the smaller piston travels is proportionately greater than the distance the larger piston travels, satisfying the law of conservation of energy. If the smaller piston moves 25 in., the larger one will only move 1 in. The hydraulic press is used, for example, to form three-dimensional objects from sheet metal and plastics and to compress large objects.

The hydraulic jack, also an application of Pascal's law, is used to exert large forces or to lift heavy loads. Like the hydraulic press it consists essentially of two different-sized pistons contained in cylinders that are connected by a pipe. When the smaller piston is moved back and forth by a handle connected to it, it pumps a liquid into the cylinder of the larger piston, forcing the larger piston to move. In this way a weak force applied to the smaller piston can raise a heavy load on the larger one. The hydraulic elevatorelevator,
in machinery, device for transporting people or goods from one level to another. The term is applied to the enclosed structures as well as the open platforms used to provide vertical transportation in buildings, large ships, and mines; it is also applied to devices
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 is also an application of Pascal's law.

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hydraulic machine

[hī′drȯ·lik mə′shēn]
(mechanical engineering)
A machine powered by a motor activated by the confined flow of a stream of liquid, such as oil or water under pressure.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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