Fluid is that deforms continuously on the application of shear stress, no matter how much small is it. Fluid comprises both gases and liquid. The technique of using liquid for power transmission is called as hydraulics while which uses gases for power transmission is called Pneumatics.In most hydraulics system mineral oils will be used while in most pneumatic system atmospheric air will be used.
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Principle behind fluid power
The basic principle which governs any fluid system is the pascal law. The law applies to fluid power transmission. The other laws which will be used in the analysis, design and manufacturing of any fluid system are Boyle's law, Charles's law and Bernoulli theorem.
Property of fluid
For reliable and proper working of hydraulic system the fluid used should have the following certain qualities. Some of them are
Some of the most commonly used fluid for power transmission are water,emulsions,Water glycol, Synthetics, air and compressed gases
Parts of fluid system
The most of fluid system will employ some or all of the following parts
Cylinders are primary type of actuators used in fluid circuit. The cylinder used in fluid circuit will consist the following parts
Whenever fluid is supplied to the cylinder the piston will move. This movement of piston is called as stroke. The piston can move in forward or reverse direction. The cylinders can be classified as double acting or single acting. In single acting cylinder work will be performed only in the forward stroke. The fluid will be supplied to the cylinder only during the forward stroke. The return stroke is achieved by the spring mounted in the cylinder. In double acting cylinder there will be two ports for the supply of fluid. Work can be obtained both at forward and reverse strokes. Directional control valves required for the easy operation of double acting cylinder.
The transmission of power through fluid has following advantages compared to the other modes
Use of fluid power
The hydraulic press, invented by Englishman John Brahmah, was one of the first workable pieces of machinery developed that used hydraulics in its operation. Today, hydraulic power is used to operate many different tools and mechanisms. some of the devices which uses hydraulic power are
Some devices which uses Pneumatics are
Difference between Hydraulics and Pneumatics
Precise control of velocity is achievable in hydraulics while due to compressible nature of gas, Pneumatics cannot have precise control over velocity. In Hydraulics, self-regulation action of oil can be used while in pneumatics oil mist has to be used for lubrication. The pressure range for hydraulics is 500-5000 psi while the pressure range for pneumatics is below 100 psi The air after performing work can be sent into atmosphere, whereas oil has to be discharged into a tank.