Venturi Meter:

It is an instrument used for measuring the rate of flow of a liquid and it works on the principles of Bernoulli's equation. As shown in Figure 12, it consists of two wide bore tubes A and B joined by a narrow tube C (known as the throat). A and C are fitted along with manometer tubes. The apparatus is interposed horizontally in the pipe in which the rate of flow of a liquid is to be measured. The horizontal placement of the apparatus ensures that the potential energy of the liquid remains the same at all points along the axis.

Now Let a₁ and a₂ be the areas of cross-sections of the tubes A and C and let v₁ and v₂ are the velocities of flow of the liquid through these tubes

Figure: A Venturi Meter

respectively.