Short Answer:

Manometers are devices used to measure fluid pressure using a column of liquid. They work on the principle that the pressure difference in a fluid column is proportional to its height. The types of manometers are mainly divided into two categories — Simple Manometers and Differential Manometers.

In simple words, simple manometers measure pressure at a single point (like a U-tube or piezometer), while differential manometers measure the pressure difference between two points in a fluid system (like U-tube and inverted U-tube manometers). These types are selected based on pressure range, fluid type, and accuracy required.

Detailed Explanation :

Types of Manometers

A manometer is an instrument used to measure the pressure of a fluid (liquid or gas) by balancing the fluid column against a known pressure or atmosphere. It works on the hydrostatic principle, which states that the pressure difference between two points in a fluid is proportional to the product of the fluid’s density, gravitational acceleration, and height difference.

The different types of manometers are generally divided into two broad categories based on their function and construction:

Simple Manometers
Differential Manometers

Let us discuss both types in detail.

Simple Manometers

A simple manometer is used to measure the pressure at a single point in a fluid system with respect to the atmospheric pressure. It consists of a glass tube filled with a manometric fluid (like mercury, water, or oil). One end of the tube is connected to the point where pressure is to be measured, and the other end is open to the atmosphere.

Common types of simple manometers include:

(a) Piezometer

A piezometer is the simplest form of a manometer. It consists of a vertical glass tube connected to a point in a liquid container or pipe. The liquid rises in the tube until the pressure at the measuring point is balanced by the weight of the liquid column.

Working Principle:
The height of the liquid column in the tube directly represents the pressure head.

where is the pressure, is the density of the liquid, is gravity, and is the height of the column.

Limitations:
- Can measure only gauge pressure.
- Suitable only for liquids (not gases).
- Cannot measure negative pressure or high pressures.
Applications:
Commonly used in laboratories and small water systems to measure low pressures in liquids.

(b) U-Tube Manometer

A U-tube manometer consists of a transparent glass tube bent in a U-shape, partially filled with a manometric fluid such as mercury or water.

One limb is connected to the pressure source, while the other limb is open to the atmosphere.
The difference in fluid levels in the two limbs indicates the pressure at the point of measurement.
Formula:

where is the height difference between the fluid columns.

Advantages:
- Can measure both positive and negative pressures.
- More accurate than the piezometer.
Applications:
Used for measuring low and medium pressures in pipelines and fluid tanks.

(c) Inclined Tube Manometer

An inclined tube manometer is a modified version of the U-tube manometer in which one limb is inclined at an angle to the horizontal.

The inclination increases the accuracy for measuring small pressure differences.
The height difference is measured along the inclined limb.
Formula:

where is the angle of inclination.

Advantages:
- High sensitivity for small pressure differences.
- Easy to read due to larger scale movement for small pressure changes.
Applications:
Used in laboratories and low-pressure applications such as airflow measurements.

Differential Manometers

A differential manometer is used to measure the pressure difference between two points in a fluid system. It contains a U-shaped glass tube filled with a manometric liquid and both ends connected to the two points whose pressure difference is to be measured.

Common types of differential manometers are:

(a) U-Tube Differential Manometer

In this type, both ends of a U-tube are connected to two different points in a pipe or system. The difference in heights of the liquid columns gives the pressure difference between the two points.

Formula:
If the manometric liquid has a density and the fluid in the pipes has a density , then

Advantages:
- Can measure small pressure differences accurately.
- Suitable for both gases and liquids.
Applications:
Used in Venturi meters and orifice meters to measure pressure drop and flow rate in pipelines.

(b) Inverted U-Tube Differential Manometer

An inverted U-tube differential manometer is used when the pressure difference to be measured is very small. In this case, a light manometric fluid such as oil is used instead of a heavy one like mercury.

Both ends of the inverted U-tube are connected to the two points in the system.
The lighter fluid collects at the top of the inverted tube, and the difference in column levels indicates the pressure difference.
Formula:

Advantages:
- Suitable for small pressure differences.
- Used for measuring low-pressure differences in gases or air systems.
Applications:
Used in ventilation systems, gas flow systems, and low-pressure gas pipelines.

Comparison of Simple and Differential Manometers

Feature	Simple Manometer	Differential Manometer
Measures	Pressure at one point (relative to atmosphere)	Pressure difference between two points
Example	Piezometer, U-tube, Inclined	U-tube, Inverted U-tube
Application	Low-pressure systems	Flow and pressure difference in pipes
Fluid Type	Usually heavier liquids	Light or heavy depending on range

(Note: No graph or chart should be drawn if not required in exams.)

Applications of Different Types of Manometers

Piezometer: Used for measuring static fluid pressure in open tanks.
U-Tube Manometer: Used in laboratory experiments and fluid flow measurement setups.
Inclined Manometer: Used for precise measurement of very low pressures.
Differential U-Tube Manometer: Used for measuring pressure drops in flow systems.
Inverted U-Tube Manometer: Used for measuring low pressure differences in gases.

Importance of Manometers

They provide accurate and reliable pressure readings.
Manometers are easy to design, operate, and maintain.
They are essential tools in fluid mechanics experiments, industrial flow systems, and pressure calibration processes.

Conclusion

In conclusion, the types of manometers are broadly classified into simple manometers and differential manometers. Simple manometers such as piezometers, U-tube, and inclined manometers measure pressure at a single point, while differential manometers like U-tube and inverted U-tube types measure the pressure difference between two points. Each type operates on the hydrostatic principle and is selected based on the pressure range, accuracy, and fluid type. Manometers are widely used because of their simplicity, accuracy, and reliability in fluid pressure measurement.