Head Requirements

Head describes pressure in terms of feet of lift. It is calculated by the expression:

Pressure (psi) X 2.31 Head in feet = Specificgravity

The discharge head on a pump is a sum of the following contributing factors:

STATIC HEAD (hd)—The vertical distance through which the liquid must be lifted (see Figure 7.12.3).

FRICTION HEAD (hf)—The resistance to flow caused by friction in the pipes. Entrance and transition losses can also be included. Because the nature of the fluid (density, viscosity, and temperature) and the nature of the pipe (roughness or straightness) affect friction losses, a careful analysis is needed for most pumping systems although tables can be used for smaller systems. VELOCITY HEAD (hv)—The head required to impart energy into a fluid to induce velocity. Normally this head is quite small and can be ignored unless the total head is low.

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