Pascal's Law states that the "Pressure applied to any part of a confined fluid transmits to every other part with no loss. The pressure acts with equal force on all equal areas of the confining walls and perpendicular to the walls. This is the basic principle for any hydraulic system."
Earlier, weights were lifted using pulleys, levers, block and tackles, etc. Movements for a ship’s rudder or steering a vehicle where achieved by mechanical linkages like cams, levers, couplings, and gears which made the system complicated. These manual or mechanical methods of operation had several limitations. They also involved huge man power and long working hours for a particular job. As the population and technology increased exponentially, the demand for quicker and easier to operate equipment increased. To cater to this need, hydraulic machines were introduced.
A simple hydraulic system consists of hydraulic fluid, pistons or rams, cylinders, accumulator or oil reservoir, a complete working mechanism, and safety devices. These systems are capable of remotely controlling a wide variety of equipment by transmitting force, carried by the hydraulic fluid, in a confined medium. Modern developments in hydraulics have involved many fields in engineering and transportation. These systems transfer high forces rapidly and accurately even in small pipes of light weight, small size, any shape, and over a long distance. These systems play a vital role from small car's steering to supersonic aircraft’s maneuvering devices. More powerful and accurate systems are also used in maneuvering huge ships.
There are several other areas where hydraulics is applied. They are: i. Automobile garage ii. Petrol pumps iii. Measuring weights of heavy-lift trucks iv. Hydraulic cranes v. Automobile steering gears vi. Automobile brake, (disc brakes) vii. Ship's steering gear viii. Robotics ix. Aircraft's rudder and other maneuvering systems x. Industries and power plants xi. Servo mechanisms and control systems etc.