Purpose of pumps
Every fluid-power system uses one or more pumps to pressurize the hydraulic fluid. THE Fluid under pressure, in turn, performs work in the output section of the fluid-power system. Thus, the pressurized fluid may be used to used to move a piston in a cylinder or to turn the shaft of a hydraulic motor.
The purpose of a pump in a fluid-power system is to pressurize the fluid so that work may be performed .Some fluid-power systems use low pressures-1000 psi or more-may be used. So we find that every modern fluid-power system uses at least one pump to pressurize the fluid.