Pressure Head

Manometers

A manometer (or liquid gauge) is a pressure measurement device which uses the relationship between pressure and head to give readings.

In the following, we wish to measure the pressure of a fluid in a pipe.

Piezometer

This is the simplest gauge. A small vertical tube is connected to the pipe and its top is left open to the atmosphere, as shown.

The problem with this type of gauge is that for usual civil engineering applications the pressure is large (e.g. 100 kN/m2 ) and so the height of the column is impractical (e.g.10 m).

Also, obviously, such a gauge is useless for measuring gas pressures.

U-tube Manometer

To overcome the problems with the piezometer, the U-tube manometer seals the fluid by using a measuring (manometric) liquid:

Notice that we have used the fact that in any continuous fluid, the pressure is the same at any horizontal level.

Differential Manometer

To measure the pressure difference between two points we use a u-tube as shown: