What is a manometer?
A Manometer is a scientific instrument used for Pressure measurement of liquids and gases.
U tube manometer
The U tube manometer is the simplest version of Manometers. A U tube manometer consists of a constant bore glass tube in the form of a long U, partly filled with a suitable liquid such as water, alcohol or mercury. A U tube manometer is shown below.
Figure 5: U Tube Manometer
How to use a U tube manometer to measure Pressure
To measure the Pressure of a fluid which is less dense and immiscible with the manometer fluid, a connection is made to one limb of the U-tube while a suitable reference Pressure is applied to the other limb. The vertical displacement z of the manometer fluid gives an indication of the applied Pressure difference Dp. If Pm is the density of the manometric fluid, Pf that of the fluid whose Pressure is to be measured and g is the gravitational acceleration, then
Dp = (Pm – Pf)gz