# What is a manometer and for what purpose it is used? A manometer is an instrument which is widely used for many industrial applications, this device can be used to measure the pressure difference between two points in a pipe or it can also be used to determine the pressure difference between two pipes. The manometer can measure the pressure by using the relation between the pressure and head. A manometer can be used to measure high pressures and negative pressure, it is also capable to measure differential pressure.

Manometer types

Types of pressure measurement

## What are the characteristics of a manometer?

• It can measure fluid pressure and this device has a tube which would be bent and it would have more than one liquid and their density would be different
• The measurement is done by using the known and unknown pressure of the liquid and it would be located at the different end of the tube
• The differential pressure manometer is only used when we need to know the difference between the two pressure
• This device can measure static pressure

## What are the properties of manometric fluids?

• It would have the good chemical stability
• Viscosity and capillary constant will be less
• The vapor pressure and volatility will be less
• Thermal expansion would have low co-efficient

### How does a manometer work, and what is the principle of manometer? How is a manometer used to measure pressure?

The manometer working is based on hydrostatic balance principle mostly a manometer would have a reservoir and it will contain liquid. The source will be connected to the reservoir so that the pressure can be measured. The reservoir will be connected to a column and the column will be exposed to the atmospheric pressure. Manometers could have sealed or unsealed columns, gauge pressure can be measured by using an open column manometer. Absolute pressure can be measured by using a sealed column manometer and these manometers can also be used to measure vacuum.

If we connect the manometer to a process there would be variations in the liquid level of the column, and these variations will be dependent on the pressure source that is to be measured. We should know the liquid type in the column, according to the type of the liquid used there could be a rise or fall according to the pressure, and we should also know the specific gravity to do the measurement properly.

### What are the types of manometer?

Classification of manometers

The manometers can be classified into two types they are simple manometer and differential manometer.

Simple manometer

This type of manometer can measure the pressure of the fluid at a point in the pipe the types of simple manometers are piezometer, U-tube manometer, and single column manometer.

Differential manometer

This type of manometer measures the pressure difference between two points, the types of differential manometers are U-tube differential manometer, Inverted U-tube differential manometer.

Piezometer

A piezometer is a simple manometer, it is used to measure the pressure inside the pipe that has liquid. This device has a vertical tube and its operation is based on the principle of hydrostatic equilibrium. The one end of this device glass tube will be connected to the point in which the pressure is to be measured and the other end will be opened to the atmosphere. The pressure rise will be according to the pressure at that point and this pressure can be measured by the liquid height in the tube.

What are the disadvantages of the piezometer?

• It can only measure the gauge pressure and cannot be used to measure the negative pressure
• The pressure of the gas cannot be measured by this device

U- tube manometer

This device is composed of a U-shaped glass and its one end is opened to the atmosphere and the other end is connected to the point in which the pressure is to be measured. This device is capable to measure the large pressures in the lighter liquids. This device tube will be filled with mercury or can be considered as the manometric fluid and this device can be used to measure the gas and liquid.

What are the applications of the U-tube manometer?

• It can be used for low range pressure measurement
• Widely used in laboratories
• It can also be used to detect the pressure drop in valves

Inverted U-tube manometer

In this type of manometer, an inverted U-tube is used, it can be used to measure the difference of low pressure. This can do accurate measurements, the both end of the tube will be connected to the point in which the pressure difference is to be determined.

#### What are the factors that affect the accuracy of the manometer?

• We must consider the type of liquid in the column for accurate measurement
• The specific gravity of the liquid in the column must be known
• The accuracy of the manometer is also depended on the liquid shape at the interference between the liquid and air in the column
• The column liquid quality is important
• The characteristic of the indicating fluid is an important factor the fluid must have good wetting characteristics

#### How is a simple manometer different from a differential manometer?

A simple manometer can only measure the pressure at a point, while the differential manometer is used to determine the pressure between two points. In a simple manometer, one of the limbs is open to the air and the other one is connected to the point, while in a differential manometer the limbs are connected to two points. In the case of a simple manometer, the pressure is determined by the difference of level of fluid flowing through the pipe, while in a differential manometer the difference of pressure is determined by measuring the difference of the levels of the manometer liquid.

#### What are the advantages of a manometer?

• It has good accuracy and sensitivity
• Maintenance is less
• Vibration is not a problem for this device
• It is easy to manufacture this device and it costs very less
• This device can be used for low pressure and low differential pressure
• The sensitivity of this device can be easily changed according to our need

#### What are the limitations of the manometer?

• It is not compact and has a big size
• It could be easily damaged because it is fragile
• The measurement of the manometer is affected by variations in temperature, gravity, and altitude
• Because of the surface tension of the manometric fluid, a capillary effect is created
• Dynamic response is not good

#### What are the applications of a manometer?

• It can be used for pressure monitoring applications
• It can also be used to monitor the air and gas pressure for the compressor
• A manometer can be used to measure the static pressure and vacuum
• Mercury absolute manometers are used in power plants
• This device is used for whether studies, research labs, gas analysis, etc
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