We know that force per unit of the surface area gives the pressure. Pressure is a scalar quantity and the SI unit of pressure is Pascal. It is denoted by the symbol ‘p’. Pressure is measured using various devices. There are many types of pressure: absolute pressure, gauge pressure, differential pressure, and sealed pressure or vacuum pressure. In this session, let us learn about a pressure measuring device known as a pressure gauge. Let us know the working and uses of the pressure gauge.
What is Pressure Gauge
The devices that are used for measuring pressure are called pressure gauges. Gauge pressure is the pressure relative to atmospheric pressure. For the pressures above atmospheric pressure, gauge pressure is positive. For the pressures below atmospheric pressure, gauge pressure is negative. The pressure gauge is also known as pressure meters or vacuum gauges. A device that uses the surface area and weight of a liquid column to measure and indicate pressure is known as a manometer.
Most gauges calculate the pressure relative to atmospheric pressure as the zero point. Hence, this form of reading is known as gauge pressure. Pressure gauges are analog as well as digital.
The pressure difference between the system and the atmosphere is given by the formula:
P=Pa+ ρgh
Where,
P= pressure at any point
Pa = atmospheric pressure
From this, we can make out that the pressure at any point is always greater than the atmospheric pressure by ρgh amount.
When P-Pa=ρgh
Where,
P =pressure of the system
Pa=atmospheric pressure
(P-Pa) = pressure difference between the system and atmosphere.
hρg = Gauge pressure
The difference between two pressures measured using the gauge is known as gauge pressure. Now, let us know more about the types of pressure gauges.
Types of Pressure Gauges
Depending on the usability and purpose whether it is for commercial purpose or industrial purpose, most common pressure gauges are designed. Some of the pressure gauges are:
- Bourdon Tube Pressure Gauge
- Diaphragm Pressure Gauge
- Capsule Pressure Gauge
- Absolute Pressure Gauge
- Differential Pressure Gauge
- Bellows Pressure Gauge
- Manometer Pressure Gauge
- Piezometer Pressure Gauge
Bourdon Tube Pressure Gauge
A bourdon tube is the most commonly used pressure gauge. It is a mechanical instrument that measures the pressure without an electric supply. It is made of steel to resist wear and corrosion. A bourdon tube pressure gauge can measure pressure from 0.6 to 7000 bar (8 to 10000 psi). It is compatible with liquid or gaseous media for vacuum, as well as low and high-pressure applications. It is a compact instrument that is ideal for heavy vibration application and dynamic pressure load. The bourdon tube pressure gauge is as shown below.
Diaphragm Pressure Gauge
It is the device used to measure the pressure of fluid in a system. It is purposefully designed to measure low-pressure intensities. A diaphragm pressure gauge is also known as a membrane pressure gauge. This device uses the deflection of a flexible thin membrane known as the diaphragm. The pressure is indicated by using a needle, which is moved with the help of pinion arrangement with the diaphragm.
Capsule Pressure Gauge
In this type of pressure gauge, two corrugated diaphragms are welded together at their periphery to form a capsule. This capsule is the main element in sensing the pressure. A hole is present in one of the diaphragms in the center which lets the medium enter. The diaphragms expand or contract upon the application of pressure. The capsule pressure gauge is used for calculating the pressure of gases and is utilised for calculating the pressure of substances with up to 600 mbar.
Absolute Pressure Gauges
These are the instruments ideally used to measure the pressure independent of the natural fluctuations in atmospheric pressure. A reference measure of vacuum is fixed to the side of the measuring element and is not subject to pressure. Hence, it has zero pressure with no variation. They are mainly used in scientific laboratories. Altitude does not affect the absolute pressure gauges, hence they are used in aeronautics, Heating, ventilation, and air conditioning systems, and distillation processes.
Differential Pressure Gauge
The difference between the pressure in two chambers separated by an element that moves back and forth according to the changes in pressure is measured by the differential pressure gauge. A diaphragm present in the differential pressure gauge separates the media chamber from the vacuum chamber. When the pressure increases, the diaphragm deforms into the vacuum chamber. The deformation and change are converted into a pressure value.
Bellows Pressure Gauge
Bellows pressure gauges are the devices used to measure low-pressure applications. The bellows in the devices are made of thin-walled springy metal connected tubes that form a shape similar to an accordion; this is sealed in the free end of the gauge.
Manometer Pressure Gauge
It is a device that is used to measure pressure on a fluid by balancing one column of fluid against the second column of fluid. One end of the tube in the manometer pressure gauge is connected to the place where pressure is to be measured, while the other end is open to the atmosphere.
The below figure depicts the simplest type of manometer pressure gauge that consists of a transparent tube in the form of a “U” partially filled with a manometric fluid like mercury.
Piezometer Pressure Gauge
A piezometer is a type of manometer that is designed to calculate the medium pressure range of liquids. A Piezometer pressure gauge is a simple glass tube that is opened at both ends. One end of the glass tube is connected to a pipeline where the pressure of a fluid is to be measured and the other end is open to the atmosphere. The tube is attached vertically such that the liquid in the pipe can rise into the tube. The pressure reading is indicated by the height of the fluid in the tube.
Applications of Pressure Gauge
Pressure gauges are used in various sectors in different applications.
- Pressure gauges are used to measure the pressure of liquids, vapors, solids, and gases.
- It is used for the inspection of air brakes on trucks.
- Pressure gauges are used in chemical, petrochemical, sanitary, pharmaceutical, and process industries.
- Pressure gauges are used in HVAC, refrigeration, ventilation, food, and beverage industries
- They are also used in eliminating the potential leak paths.
Frequently Asked Questions – FAQs
Pressure is scalar or vector quantity?
Pressure is a scalar quantity since it has only magnitude and no direction.
What are the types of pressure gauges?
The following are the types of pressure gauges:
- Bourdon Tube Pressure Gauge
- Diaphragm Pressure Gauge
- Capsule Pressure Gauge
- Absolute Pressure Gauge
- Differential Pressure Gauge
- Bellows Pressure Gauge
- Manometer Pressure Gauge
- Piezometer Pressure Gauge
What is the range of pressure, bourdon tube pressure gauge can measure?
Bourdon tube pressure gauge can measure pressure from 0.6 to 7000 bar.
What is a piezometer?
What is the diaphragm pressure gauge also known as?
A diaphragm pressure gauge is known as a membrane pressure gauge.
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