Short Answer:

A venturimeter is a device used to measure the flow rate of a fluid, such as water, gas, or oil, flowing through a pipe. It works on the principle of Bernoulli’s theorem, which relates pressure and velocity of a flowing fluid. The venturimeter has three main parts — a converging section, a throat, and a diverging section. The pressure difference between the inlet and the throat helps determine the flow rate.

It is widely used in industries, water supply systems, and laboratories because it provides accurate results with minimum energy loss. Its smooth design allows smooth fluid flow without major obstruction or pressure drop.

Detailed Explanation :

Venturimeter

A venturimeter is an important flow measuring instrument used to determine the discharge (flow rate) of a fluid passing through a pipe. It is based on Bernoulli’s theorem, which states that an increase in the velocity of a fluid results in a decrease in its pressure and potential energy. This device is mainly used where accurate measurement of flow is required, especially in water supply systems, oil refineries, and chemical industries.

Construction of Venturimeter

A venturimeter consists of three main parts:

Converging Section:
This is the part where the diameter of the pipe gradually decreases. The fluid velocity increases as it enters this section, and the pressure decreases according to Bernoulli’s principle.
Throat:
The throat is the narrowest part of the venturimeter. Here, the velocity of the fluid is maximum, and pressure is minimum. The pressure difference between the inlet and the throat is the key factor used to calculate the flow rate.
Diverging Section:
In this section, the diameter of the pipe gradually increases again. The velocity of the fluid decreases, and the pressure recovers. This design helps minimize energy losses due to friction.

The venturimeter is usually made of materials such as brass, stainless steel, or cast iron, depending on the type of fluid and pressure conditions.

Working Principle of Venturimeter

The working of the venturimeter is based on the principle of Bernoulli’s theorem and the continuity equation.

When a fluid flows through a pipe fitted with a venturimeter, it enters the converging section, where the velocity increases and pressure decreases.
As the fluid passes through the throat, the pressure reaches its minimum value while velocity becomes maximum.
The difference in pressure between the inlet and throat is measured using a differential manometer.
This pressure difference is used to calculate the flow rate using Bernoulli’s equation:

However, in simple terms, the discharge (Q) is directly proportional to the square root of the pressure difference between the inlet and the throat.

Here,

= Coefficient of discharge,
= Areas of inlet and throat,
= Pressure difference,
= Flow rate or discharge.

Applications of Venturimeter

The venturimeter is widely used in many practical areas, such as:

Water supply systems to measure the flow of water in pipelines.
Chemical and process industries for accurate measurement of fluid flow.
Oil and gas industries for monitoring fuel and lubricant movement.
Irrigation systems to measure the discharge of water.
Hydraulic laboratories for experimental analysis and calibration work.

Advantages of Venturimeter

Provides high accuracy in flow measurement.
Has low energy loss compared to orifice meters.
Suitable for both liquids and gases.
Can handle large flow rates efficiently.
The smooth design reduces turbulence and pressure loss.

Limitations of Venturimeter

High cost due to complex manufacturing and installation.
Bulky in size, requiring more space in the pipeline.
Not suitable for very small pipes or low flow conditions.
Difficult to install and maintain in existing pipelines.

Precautions and Installation

The venturimeter should be installed horizontally or vertically with proper alignment.
It should be placed in a straight section of the pipe, away from bends and valves to ensure smooth flow.
The pipe should be completely filled with fluid during operation to get accurate readings.

Conclusion

A venturimeter is a highly reliable and accurate device for measuring the flow rate of fluids in pipelines. It works on Bernoulli’s principle, utilizing the pressure difference between the inlet and the throat to calculate discharge. Due to its simple working and high precision, it is commonly used in water treatment, chemical, and oil industries. Though expensive and large in size, it remains one of the most efficient flow measuring devices with minimal energy loss.