Pumps are required to displace fluids within a system of piping against the respective total friction head of the pipe system.

Typical example: The forced circulating system, e.g. of a central heating installation.

In the case of different liquid levels between system inlet and outlet the additional static head (H_geo) must be additionally overcome.

Typical example: Water displacement to a higher level ie. to fill and maintain a near constant level in an overhead tank.



Also see:
Basic Pump Designs