A fluid power system transmits and controls energy through the use of pressurized fluid. The term fluid power applies to both hydraulics and pneumatics. With hydraulics, that fluid is a liquid such as oil or water. With pneumatics, the fluid is typically compressed air or inert gas. Hydraulics uses oil or liquid as the medium that cannot be compressed and pneumatics, which involves gases, uses air or gas as the medium that can be compressed.
It is a term, which was created to collect the generation, control, and application of smooth, effective power of pumped or compressed fluids (either liquids or gases). This power is used to provide force and motion to various mechanisms. This force and motion may be in the form of push, pull, rotate, regulate, or drive.
Fluid power is one of three commonly used methods of transmitting power in an industry; the others are electrical and mechanical power
transmission. Electric power transmission uses an electric current flowing through a wire to transmit power. Mechanical power transmission uses gears, pulleys, chains, etc. to transmit power. Fluid power’s motive force comes from the principle that pressure applied to a confined fluid is transferred uniformly and undiminished to every portion of the fluid and to the walls of the container that holds the fluid. A surface such as a cylinder piston will
move if the difference in force across the piston is larger than the total load plus frictional forces. The resulting net force can then accelerate the load proportionately to the ratio of the force divided by the mass.
Fluid power encompasses most applications that use liquids or gases to transmit power in the form of mechanical work, pressure, and/or volume in the system. This definition includes all systems that rely on pumps and compressors to transmit specific volumes and pressures of liquids or gases within a closed system. Fluid power is used in the steering, brake system,and automatic transmissions of cars and trucks. In addition to the automotive
industry, fluid power is used to control airplanes and spacecraft, harvest
crops, mine coal, drive machine tools, and process food. Fluid power can be
effectively combined with other technologies through the use of sensors, transducers, and microprocessors.
BASIC ELEMENTS OF FLUID POWER SYSTEM
The basic elements of fluid power system are:
1.Power device
2.Pump or Compressor
3.Control valves
4.Actuators: Cylinders or Motors
Figure 3.1 shows the basic elements of a fluid power system connected by fluid power lines. These elements are discussed in detail in next chapters.
FLUID POWER
There are few advantages, which make fluid power so popular. These
are listed below:
No need of intermediate equipment: They eliminate the need for complicated systems of gears, cams, and levers. Motion can be
transmitted without the slack inherent in the use of solid machine parts.
Less wear and tear: The fluids used are not subject to breakage as are mechanical parts, and the mechanisms are not subjected to great wear.
Multi-function control: A single hydraulic pump or air compressor can
provide power and control for numerous machines or machine functions
when combined with fluid power manifolds and valves.
Constant force or torque: This is a unique fluid power attribute.
Flexibility: Hydraulic components can be located with considerable flexibility. Pipes and hoses instead of mechanical elements virtually eliminate location problems.
Comparatively small pressure losses: The different parts of a fluid power system can be conveniently located at widely separated points, because the forces generated are rapidly transmitted over considerable
distances with small loss. These forces can be conveyed up and down or around corners with small loss in efficiency and without complicated mechanisms.
Multiplication and variation of force: Very large forces can be controlled by much smaller ones and can be transmitted through
comparatively small lines and orifices. Linear or rotary force can be multiplied from a fraction of an ounce to several hundred tons of output.
Accurate and easy to control: We can start, stop, accelerate, decelerate,reverse, or position large forces with great accuracy.
High horsepower and low weight: Pneumatic components are compact and lightweight.
Smoothness: Fluid systems are smooth in operation. Vibration is kept to
a minimum.
Overload protection: In case of an overload, an automatic release of pressure can be guaranteed; automatic valves guard the system against a breakdown from overloading so that the system is protected against
breakdown or strain.
Wide variety of motions: Fluid power systems can provide widely variable motions in both rotary and straight-line transmission of power.
Low speed torque: Unlike electric motors, air or hydraulic motors can produce large amounts of torque (twisting force) while operating at low speeds. Some hydraulic and air motors can even maintain torque at zero
speed without overheating.
Less human intervention: The need for control by hand can be minimized.
Low operating costs: Fluid power systems are economical to operate their high efficiency with minimum friction loss keeps the cost of a
power transmission at a minimum.
Safety in hazardous environments: Fluid power can be used in mines, chemical plants, near explosives, and in paint applications because it is inherently spark-free and can tolerate high temperatures.
Better force control: Force control is much easier with fluid systems than for electric motors. Fluid actuators, either hydraulic or pneumatic, are well suited to walking robots because they are high force, low speed
actuators. They provide much higher force densities than electricsystems.
Simpler design: In most cases, a few pre-engineered components will
replace complicated mechanical linkages.
Disadvantages
The main disadvantage of a fluid system is maintaining the precision parts when they are exposed to bad climates and dirty atmospheres. Protection against rust, corrosion, dirt, oil deterioration, and other adverse environmental conditions is very important.
APPLICATIONS OF FLUID POWER
Mobile
Fluid power is used to transport, excavate, and lift materials, as well as
control or power mobile equipment. End use industries include construction,
agriculture, marine, and the military. Applications include backhoes, graders,
tractors, truck brakes and suspensions, spreaders, and highway maintenance
vehicles.
Industrial
Fluid power is used to provide power transmission and motion control
for the machines of industry. End use industries range from plastics to paper
production. Applications include metal working equipment, controllers,
automated manipulators, material handling, and assembly equipment.
Aerospace
Fluid power is used for both commercial and military aircraft,
spacecraft, and related support equipment. Applications include landing gear,
brakes, flight controls, motor controls, and cargo loading equipment.