What Is Manometer? Features, Types, Uses

Pressure is force applied on the body, and for measuring the pressure applied on the body, different devices are used, such as manometers and barometers. A manometer is a device used for measuring fluid and liquid pressure, and a barometer is used for measuring fluid and air pressure. Here we will cover details for the manometer and its practical working with diagrams. Let’s get started.

What Is a Manometer?

The manometer is an instrument that has features to measure the pressure of a medium like liquid or gases. It’s working and also comes with checking the pressure of the cylinder, but it’s used to measure inner pressure as compared to outer pressure value.

Relative pressure measured; a barometer is used for measuring absolute pressure and then vacuum.
The basic monometer comes with a U-shaped glass tube having liquid material.
It is basically a pressure gauge and used for measuring the differenceof pressure applied at two different points of a glass tube.
A good manometer should provide some features before selection.
- It needed to be noncorrosive and not react with fluid where we are measuring pressure.
- It needed to have low viscosity and fast settings for pressure variations.
- It needed to have low surface tension and capillary effect.

Manometer Working

The working of a manometer relies on the principle of static fluid mechanics: that changes in pressure cause the liquid column in the tube to change.
This motion is due to the pressure of fluid. The formula for a manator working is shown as

P = ρgh,

In this question

‘P’ is pressure,
ρ’ (rho) is the density of fluid,
‘g’ is the acceleration due to gravity,
‘h’ is the height of the fluid column.

This equation explains that pressure applied at any point of static fluid has a direct relation with vertical fluid height over that point.
It is a constant relation and called the hydrostatic balance for static fluid. It is applicable for all types of manometers.

The easy working and applications of manometers are based on hydrostatic balance and help to easily use manometers in fluid mechanics. It helps measure the relation between fluid height and pressure.
Pascal’s law is the main factor for measuring values through manometers.
According to this law, pressure applied on fluid in a closed body is transmitted over the entire fluid and wall of the vessel.

Different types of pressure measured with a manometer

Absolute Pressure

It is pressure that is measured in a vacuum that denotes total pressure at a certain point.

Gauge Pressure

This pressure is measured for atmospheric pressure. such as if you connect one side of a U-tube manometer with an unknown pressure value and the other to face the atmosphere, the difference in height is called gauge pressure.

Differential Pressure

It is the pressure difference between two points. The distance between liquid columns for two sides of the manometer is differential pressure.

Selection of Fluid for Manometer

The use of proper manometer fluid is important for manometer design and application. Mercury is a commonly used fluid according to density, but its bad effect on the environment causes health issues, and it is not commonly used and is replaced with nonhazardous liquids.
The other common fluid is water and light oils; liquids are dyed for proper readability and fluid displacement tracking.
The use of fluid needed to have mechanical features and also provide safety-based applications.
The use is also based on chemical features of materials where fluid is used, and the temperature of the process is also important for avoiding vaporization of the manometer fluid.

Types of manometers

U-Tube Manometer

The U-tube manometer comes with a vertical U-column that has reference liquid like mercury for showing pressure level. If the columns are in the atmosphere, the liquid levels in the limbs are the same, and it shows atmospheric pressure.
One column is connected with the pressure level; there is a difference in the liquid level of limbs that defines the pressure of liquid in the vessel.
Here you can see a diagram of the U-tube manometer shown. This meter does not have moving components and does not need calibration.

In this diagram, when pressure is applied on the left side of the U-tube manometer, the left part shows the liquid lowering, and the liquid increases in the right leg.
The liquid moves until the unit weight of the liquid balances the pressure. that is denoted with h

Enlarged-Leg Manometer

This manometer comes with a float in an enlarged leg that is an indication point. In an enlarged leg manometer, two legs change for varying calculation spans.

Well-Type Manometer

The well-type manometer comes with a larger well in any one leg. Other legs come with a simple tube; the minor changes in displacement of the liquid level of the well cause larger changes in tube height.
A U-tube manometer is used for larger wells, so changes in level in the well are ignored, and for measuring the difference in height, a single height value is measured in the other column.
The area of the well is larger as compared to the tube area; this ratio is more than ten.

Barometer

A barometer comes with a glass tube where one end is sealed. The evacuated tube comes with an open end put in a mercury container.
Pressure applied with a column of mercury is balanced by the pressure of the atmosphere. Pressure units are used for tube calibration.
We can use any liquid for a barometer, but mercury is used since it has high specific gravity.
The mercury barometer needed to be about 30 inches tall; the water-filled barometer is higher than 33 feet in height.

Inclined manometer

The inclined manometer is configured at an angle from 15 to 45 degrees for providing high sensitivity. It is made with a well that comes with indicating liquid.
The vertical changes in height of the liquid column and the inclination show a larger length for the liquid moving vertically and a horizontal distance since amplification makes minor changes in pressure visible.
The inclined manometer, set up at an accurate position, makes highly accurate results for low pressure, like for slight differences.
It is made for measuring negative pressure; air and gas installation and glass flow measurement are low-pressure applications where there are not high liquid changes but high sensitivity is needed.
It comes with high accuracy, so it is used for standard calibration of other pressure tools.
It provides good results due to the limited U-tube manometer.

Digital Manometers

Digital manometers are advanced tools used for measuring pressure using an electronic pressure sensor instead of a mechanical liquid column.
Pressure measurement sent electronically to digital display for electronic pressure signal that is shown as a gauge reading in the closest hundredth of value.
Digital manometer used for industrial and commercial uses. Digital manometers measure different pressure values in different mediums.
The main feature of a digital manometer is that it has a configuration with Industrial Internet of Things (IoT) systems.
IoT configuration digital manometers come with a data logging system for getting data through testing.
Provide accurate monitoring of pressure and can make a connection with any programmable control device.

Selection factor for manometer

Follow these points for the selection of manometers.

Check the pressure value that can be easily handled through the manometer. pressured measured not higher than 2/3 of the manometer scale so the meter can absorb any leaking pressure.
Not all manometers can be used for all types of fluid or gas for measuring pressure. It is based on material.
There is a need to measure ambient temperature and fluid temperature.

Factors for Manometer Accuracy

Some factors affect the accuracy of the manometer and must be considered to get error-free readings.

First of all, consider fluid density changes; the temperature changes affect density which directly affects the manometer equation P = ρgh, and we get faulty results. So use fluid that has stable density to avoid any error.
Capillary action also affects the readings; concave or convex menisci occur in readings due to surface tension. Capillary action is bad for narrow tubes, so use of a wide tube reduces capillary action.
if we use an inclined manometer it causes a small pressure reading to be amplified. For vertical manometers, faulty angles cause errors. The inclination is the main factor for getting an accurate reading.
If there are any impurities or air bubbles existing in the manometer fluid column, it causes changes in reading. If there are air bubbles in the manometric fluid, the fluid column shows an erroneous result. To solve this error properly, clean and maintain the manometer from air bubbles.
If you are forming a manometer rain in such conditions, varying temperature changescan affect the color of the dial or filling liquid, discoloring components, and also cause filled gauges. As a result, we can get inaccurate readings or damage to instruments.

Advantages of Manometer

The main features and advantages of manometers are as

It is a low-cost meter with a simple design.
It has sensitivity at a high level with high accuracy.
It is used for low pressure and is easy to operate.
It is not needed to be calibrated against a standard value and used for different liquids.

Limitations of Manometers

It is a larger size and does not work without leveling.
It does not come with a fixed reference and error due to condensation.
If it does not provide accurate work, then define the range.
Its operating range is small and provides bad dynamic response.
It has zero portability due to its fragile nature.
It also comes with error due to temperature changes and slow response.

Applications of Manometers

It is used for measuring pressures of different fluids through measuring their mechanical features.
It is used for vacuum measurement and also the flow of fluid.
It is used to measure filter pressure losses of fluid.
It is used for meter calibration and used for measuring leak testing.
It measured the liquid level existing in the tank.

Summary

Manometer is the best option to use for low-range pressure measurements. Manometers are used for measuring pipe fluids, HVAC pressure, and gas pressure.
All manometer work is done through variations in pressures that increase or decrease liquid levels. Manometers normally use liquids like mercury, water, and light oils. To use them, one end of the U-tube manometer is connected with unknown pressure, and the other end is open to atmospheric pressure. The difference in height of liquid on two sides of the tube shows different pressure. The other manometer comes with a barometer and the inclined manometer

FAQs

What are the uses of a manometer?

The manometer used for measuring the pressure of fluid or gas in confined spaces such as in boilers that measures the pressure value with respect to atmospheric pressure

What is the main factor a manometer measures?

The manometer measures the pressure of fluid or gas.

What pressure does a manometer measure?

The common type of sealed tube A manometer, is a mercury barometer that measures atmospheric pressure. The manometer made for measuring direct absolute pressure

What is the measuring unit of a manometer?

The manometer used for measuring the pressure difference between column height and is measured in unit of millimeters or centimeters of Hg or liquid

Who invented the manometer?

Otto von Guericke invented the manometer.

What is the formula of a manometer?

The mathematical expression for a manometer is written as P=ρ×g×h.
‘P’ is pressure,
ρ’ (rho) is the density of fluid,
‘g’ is the acceleration due to gravity,
‘h’ is the height of the fluid column.

Which Manometer Is Most Common?

The U-tube differential manometer is a commonly used type of manometer.

What Is the Difference Between a Manometer and a Pressure Gauge?

The pressure gauge, also called a pressure meter or vacuum gauge. It uses the surface area and weight of a liquid column for measuring pressure, called a manometer.
Gauges measure pressure based on atmospheric pressure at 0 points.