Centrifugal pump - why term Head ?

What is Head?

The word Head is frequently spoken in the field of water working, pumping etc.

A column of water or any liquid in a vertical pipe exerts a certain pressure (force per unit area) on a horizontal surface at the bottom, this pressure is expressed in kg/cm2 or meters of liquid column (mlc). The height of a liquid column is known as HEAD.

Please refer the FIG 1 to understand the concept. A square container with 1m x 1m bottom and 10m height will exert a pressure of 1kg/cm2.

This means that any shaped container with water filled up to 10m height will exert a pressure of 1kg/cm2 and can be seen at pressure gauge attached at the bottom of the container.

Head and Pressure

The relation between Head in meters of liquid column and pressure in kg/cm2 can be expressed as under:-

H in mlc =(P x 10)/ r.

Where P = Pressure in Kg/cm2.

r = sp. gr. of liquid.

(1 kg/cm2 = 10 m of water column)

Why is head always measured in mlc?

Please refer FIG 2 to understand it. A centrifugal pump with a given speed in rpm and impeller dia will drive any liquid to the same height (Head)irrespective of its sp. gr. Please note:- Pressure gauge readings will vary according to sp.gr.

Figure is self explanatory, all the liquid having same height of column of 10 m, will have diff pressure based on sp.gr.