Hydraulics
From Wikipedia, the free encyclopedia
Table of Hydraulics and Hydrostatics, from the 1728 Cyclopaedia.
Hydraulics is a topic of science and engineering dealing with the mechanical properties of liquids. Hydraulics is part of the more general discipline of fluid power. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties. Hydraulic topics range through most science and engineering disciplines, and cover concepts such as pipe flow, dam design, fluid control circuitry, pumps, turbines, hydropower, computational fluid dynamics, flow measurement, river channel behavior and erosion.
The word "hydraulics" originates from the Greek word ὑδραυλικός (hydraulikos) which in turn originates from ὕδραυλος meaning water organ which in turn comes from ὕδωρ (water) and αὐλός (pipe).
Contents
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1 History
2 Hydrostatic power transmission
3 See also
4 References
5 External links

History
The earliest masters of this art were Ctesibius (flourished c. 270 BC) and Hero of Alexandria (c. 10–70 AD) in the Greek-Hellenized West. In ancient China there was Sunshu Ao (6th century BC), Ximen Bao (5th century BC), Du Shi (circa 31 AD), Zhang Heng (78 - 139 AD), and Ma Jun (200 - 265 AD), while medieval China Su Song (1020 - 1101 AD) and Shen Kuo (1031 - 1095). The ancient engineers focused on sacral and novelty uses of hydraulics, rather than practical applications. In ancient Sri Lanka, the Sinhalese used hydraulics in many applications, in the ancient kingdoms of Anuradhapura and Polonnaruwa. The discovery of the principle of the valve tower, or valve pit, for regulating the escape of water is credited to Sinhalese ingenuity more than 2,000 years ago. By the first century A.D, several large-scale irrigation works had been completed. Macro- and micro-hydraulics to provide for domestic horticultural and agricultural needs, surface drainage and erosion control, ornamental and recreational water courses and retaining structures and also cooling systems were in place in Sigiriya, Sri Lanka.
In 1690 Benedetto Castelli (1578–1643), a student of Galileo Galilei, published the book Della Misura dell'Acque Correnti or "On the Measurement of Running Waters", one of the foundations of modern hydrodynamics. He served as a chief consultant to the Pope on hydraulic projects, i.e., management of rivers in the Papal States, beginning in 1626.[1]
Blaise Pascal (1623–1662) study of fluid hydrodynamics and hydrostatics centered on the principles of hydraulic fluids. His inventions include the hydraulic press, which multiplied a smaller force acting on a smaller area into the application of a larger force totaled over a larger area, transmitted through the same pressure (or same change of pressure) at both locations. Pascal's law or principle states that for an incompressible fluid at rest, the difference in pressure is proportional to the difference in height and this difference remains the same whether or not the overall pressure of the fluid is changed by applying an external force. This implies that by increasing the pressure at any point in a confined fluid, there is an equal increase at every other point in the container, i.e., any change in pressure applied at any point of the fluid is transmitted undiminished throughout the fluids.

Hydrostatic power transmission
A hydrostatic power transmission system makes use of fluid under pressure to drive a mechanical load. In this sense, hydrostatic means that energy transfer is brought about by fluid flow and pressure, but not from the kinetic energy of the flow (the latter would be characteristic of a hydrodynamic drive, such as a fluid coupling or torque converter).
A basic hydrostatic power transmission system consists of a positive displacement pump driven by the prime mover, a positive displacement hydraulic motor, interconnecting piping (which may be a combination of steel tubing, actual pipe and hoses), and a reservoir. Additional components, such as valves and filters, are often part of such a system, the former to provide control of the transmission system and the latter to protect precision machined parts from damage due to oil-borne contaminants.
Motion is transmitted by the pump drawing oil from the reservoir, pumping it into the motor, with the discharge returning to the reservoir. The flow of oil causes the motor to rotate at a speed that is proportional to the pump speed. Any resistance to motor rotation will cause system pressure to rise due to the use of the positive displacement pump, which will translate as torque at the motor.
The maximum torque that can be exerted by the motor is determined by the maximum pressure in the system, as well as the ratio between the displacement of the pump and the displacement of the motor, displacement being expressed in cubic inches or cubic centimeters per revolution. For example, a pump specified as displacing 10 cubic inches per revolution will (in theory) pump exactly 10 cubic inches of oil for each revolution (the actual output will be lower due to internal leakage in the pump). If said pump is mated with a motor that displaces 20 cubic inches per revolution, the drive ratio will be 2:1 and the motor will run at one half the speed of the pump, but develop approximately twice the torque applied to the pump. Hence hydrostatic power transmission behaves in a fashion similar to that of a purely mechanical equivalent of gears and shafts.
Hydrostatic power transmission is widely used in industrial machinery and earthmoving equipment, and has found some application in transportation. A principal advantage of hydrostatic power transmission systems is the flexibility of pump and motor positioning within the equipment. Since the only connection between the pump and motor is through the piping, which can be routed in whatever fashion is convenient for the machine designer, hydrostatic motors can often be used to drive machinery placed in difficult to access areas.
The main disadvantage of hydrostatic drive is its inefficiency relative to other power transmission systems. Most of the inefficiency is brought about by resistance to fluid flow through the piping and fittings. The resulting turbulence wastes some of the energy imparted to the fluid as heat.

Hydraulic press
Hydraulic force increase.
A hydraulic press is a hydraulic mechanism for applying a large lifting or compressive force. It is the hydraulic equivalent of a mechanical lever, and is also known as a Bramah press after the inventor, Joseph Bramah. Hydraulic presses are the most commonly-used and efficient form of modern press.

How it works
The hydraulic press depends on Pascal's principle: the pressure throughout a closed system is constant. At one end of the system is a piston with a small cross-sectional area driven by a lever to increase the force. Small-diameter tubing leads to the other end of the system. A fluid, such as oil, is displaced when either piston is pushed inward. The small piston, for a given distance of movement, displaces a smaller amount of volume than the large piston, which is proportional to the ratio of areas of the heads of the pistons. Therefore, the small piston must be moved a large distance to get the large piston to move significantly. The distance the large piston will move is the distance that the small piston is moved divided by the ratio of the areas of the heads of the pistons.
For example, if the ratio of the areas is 5, a force of 100 newtons on the small piston will produce a force of 500 newtons on the large piston, and the small piston must be pushed 50 cm to get the large piston to rise 10 cm. This is how energy, in the form of work in this case, is conserved. Work is force times distance, and since the force is increased on the larger piston, the distance the force is applied over must be decreased. The work of the small piston, 100 newtons multiplied by 0.5 meter (50 cm) is 50 joules (J}, which is the same as the work of the large piston, 500 newtons multiplied by 0.1 meter (10 cm).