Personnel who operate, service or design fluid power systems should have a complete understanding of the physics and properties of fluids and their behavior under different circumstances. Liquids and gases have tendency to flow freely, and for that reason both are called fluids (from the Latin fluidus, meaning flow). A fluid may be defined as a substance which changes its shape easily and adapts to the shape of its container. This applies to both liquids & gases.

The fluid serves as the medium by which power is transferred in hydraulic machinery. Common hydraulic fluids are based on mineral oil or water. Because hydraulics can transmit high forces rapidly along lightweight pipes of any size, shape and length, they are the prime source of power in aircraft systems such as flying controls, flaps, retractable undercarriages, wheelbrakes, etc.

Since the first use of water as a hydraulic medium in the late 18th century, hydraulics has become an indispensable discipline of engineering science. This reference text bring different components and principle of hydraulics to provide the readers deeper insight to the subject. Basics of hydraulics such as transmission of force, atmospheric pressure, vacuum pressure, gas laws, etc are discussed in detail to provide a better and precise understanding of the complexities involved.