A pump is a device that converts mechanical energy into fluid energy. The characteristics of the fluid pumped may vary considerably between one application and another. To meet this wide range of requirements, the manufacturers of fluid-power equipment offer pumps varying not only in design but also in capacity and adaptability - from capacities of a few cubic inches a minute to several hundred gallons a minute; from extremely low pressure to pressures in excess of 10,000 psi; with fixed or variable delivery; with constant pressure or intermittent pressure; and as hand-operated, electric-motor-operated, diesel and gasoline-engine-operated, or air-motor-operated units.