Liquid fluid energy transmission

Summary: Water- and oil-based fluids in closed systems or in motion are used to transmit energy from source to point of application.

The term fluids refers to both liquids and gases. With regard to energy transmission, however, the most common referents are water- and oil-based transmission media. Liquids, unlike gases, are incompressible, and this allows smooth transmission of the input energy.

Along with electrical and mechanical power transmission, fluid power is one of the popular means of transmitting energy in industries. Force and power are transmitted through fluids when pressure is applied to a liquid in a closed system or by increasing the kinetic energy of the liquid. Fluid energy transmission is flexible and widely preferred where power or forces have to be transferred in different directions through different angles from one place to another. Such transmission has a source where energy originates and an actuator or end effector where it is applied. Machines that utilize energy transmission through fluids are called hydraulic machines. Commonly used actuators are cylinders and rotating devices.

Fluid transmission is typically used for transmitting large power over short distances, for example, in aircraft, ground vehicles, cranes, construction equipment, industrial machines, and within buildings or industrial setups. Hydraulic transmission has the ability to convert small input forces into large output force or power, and this property is used in controlling machines, automobiles, and aircraft. For example, fluids containing glycol ethers are used to transmit force in braking systems in order to stop the motion of wheels. These brakes are called hydraulic brakes, and they are very effective in converting the small forces applied to a brake pedal into the large forces needed to stop spinning wheels. Lockheed Martin, which started as the Lockheed Hydraulic Brake Company, first made these brakes. Since hydraulic power can be stored, auxiliary or backup power in aircraft, to rotate turbines and start engines, is provided through hydraulics. For long distances, electrical transmission is convenient and more economical as compared to fluid transmission.

Fluid power transmission has been in use since ancient times for tasks such as lifting heavy loads, rotating objects, and facilitating agriculture. Force and power transmission was achieved almost entirely using fluids in the early part of the 1900s. The typical application was lifting loads. The basis for fluid energy transmission comes from 17th-century developments in the fields of hydrostatics and hydrodynamics. Blaise Pascal, in the year 1647, discovered an important property of fluids that pressure applied to a fluid at rest is transmitted in all directions. This law, known as Pascal’s law, was the basis for development of hydrostatic power transmission using fluids. One of the first hydraulic machines, called the Bramah press, was based on Pascal’s law. An English inventor, Joseph Bramah, invented the press. It can convert small forces acting on a small area into large forces acting on larger areas by transmitting pressure through a fluid in a closed system. This feature is an integral part of most hydraulic applications even today.

The scientific basis for hydrodynamic power transmission, or the use of fluids in motion for transmitting energy, can be explained by the Bernoulli principle, first stated in 1738 by mathematicianDaniel Bernoulli, although hydrodynamic transmission was in use long before. This type of transmission imparts kinetic energy to the liquid, and the momentum of the liquid is used to transmit power. The kinetic energy, or flow of liquid, is obtained with the help of a pump. The choice of pump used depends on the operating conditions. Such systems are used primarily for obtaining rotational motion. The long history of fluid power transmission has resulted in the establishment of well-known engineering standards in hydraulics today. Numerous flow-control and pressure-control valves are available and routinely used to control fluid transmission.

The first hydraulic fluid used was water. The increasing use of metallic piping and mechanical actuators led to the replacement of this fluid with oil-based or synthetic liquids, as water causes corrosion and freezes at lower temperatures. Mineral-oil-based liquids that provide lubrication and can be used over a larger temperature range replaced were superior. Hydraulic transmission liquids today can contain a wide range of chemical compounds, including water-soluble oils, silicons, esters, water-glycol mixtures, and complex hydrocarbons. The recent introduction of ceramics and water-resistant materials for transmission equipment has restored the feasibility of water as a medium.

The advantages of fluid-based energy transmission are its safety in hazardous applications such as areas with harmful radiation, the consistency of the force and power output, and easy control. Such systems can produce a wide range of rotation speeds and have high accuracy. The advent of modern electronics and its combination with fluid transmission have led to the development of smart actuators such as robotic hands, arms, and precision machines with sensors.

One of the major disadvantages of fluid energy transmission is the leakage of fluids. Oil-based fluids are dangerous to use in applications where there is a possibility of leakage in high-temperature areas or around electrical equipment. Hydraulic transmission is also accompanied by a consistent and loud hissing sound.

Bibliography

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