ABSTRACT
The function of the fluid in a fluid power system is to transmit power, provide lubrication, provide cooling, and seal clearances between moving parts. Pneumatic systems use air as the working fluid, and hydraulic systems use either an oil-based or water-based liquid.
In a hydraulic system, the establishment and maintenance of a lubricant film between the moving parts in a pump or motor is essential, thus, the properties of the fluid are very important. A hydraulic system is designed to operate in a given temperature range in order to maintain viscosity, a key property, in the range needed to ensure that the lubrication film between parts is continuous. Other properties of interest are oxidation potential and corrosion resistance. Fire resistance is a key consideration in some applications.
When a pressure drop is created and no mechanical work is done, all the fluid energy is converted to heat energy. For the vast majority of circuits, this source of heat is greater than the heat produced by pressure drops in the lines and fittings.
