A fluid machine is a device which converts the energy stored by a fluid into mechanical energy or vice versa . The energy stored by a fluid mass appears in the form of potential, kinetic and intermolecular energy. The mechanical energy, on the other hand, is usually transmitted by a rotating shaft. Fluid Mechanics is a branch of Continuum Mechanics and deals with the study of fluids under rest and motion. Fluid Machinery deals with the machines that operate on fluids or operated by the fluids like compressors or turbines.