Piezometer Tube
The direct proportional relation between gauge pressure and the height h for a fluid of constant density enables the pressure to be simply visualized in terms of the vertical height, 
.
The height h is termed as pressure head corresponding to pressure p. For a liquid without a free surface in a closed pipe, the pressure head
at a point corresponds to the vertical height above the point to which a free surface would rise, if a small tube of sufficient length and open to atmosphere is connected to the pipe
. The height h is termed as pressure head corresponding to pressure p. For a liquid without a free surface in a closed pipe, the pressure head
at a point corresponds to the vertical height above the point to which a free surface would rise, if a small tube of sufficient length and open to atmosphere is connected to the pipe |
Fig 4.2 A piezometer Tube
Such a tube is called a piezometer tube, and the height h is the measure of the gauge pressure of the fluid in the pipe. If such a piezometer tube of sufficient length were closed at the top and the space above the liquid surface were a perfect vacuum, the height of the column would then correspond to the absolute pressure of the liquid at the base. This principle is used in the well known mercury barometer to determine the local atmospheric pressure.
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