Pressure Gauge: What Is It? How Is It Used? Types Of

30 Sep.,2022


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Pressure Gauges

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This article takes an in depth look at pressure gauges.

You will learn more about topics such as:

  • What is a pressure gauge?
  • How a pressure gauge works
  • Types of pressure gauges
  • How pressure gauges are used
  • And much more …

Chapter One: What is a Pressure Gauge?

A pressure gauge is a method of measuring fluid, gas, water, or steam intensity in a pressure powered machine to ensure there are no leaks or pressure changes that would affect the performance of the system. Pressure systems are designed to operate within a specific pressure range. Any deviation from the acceptable norms can seriously affect the workings of the system.

Pressure gauges have been used for more than a hundred years and have been constantly evolving to fit the needs of new applications. The implementation and use of pressure gauges has made them a necessity as more and more pressure systems become operational.

Chapter Two: Types of Pressure Gauges

The variations in pressure gauges are dependent on where the gauge will be used, with different sizes, styles, and materials designed to fit specific applications. There are several ways pressure gauges are categorized and defined, including by usage, media, and the method used to measure pressure.

Pressure is determined by the perpendicular force applied per unit area of a surface, a calculation that is determined through the use of different techniques and methods. The correct measurement of pressure is dependent on the reference the pressure reading is measured against. Pressure gauges are divided into hydrostatic and mechanical.

  • Hydrostatic Pressure: Hydrostatic pressure is generated by the weight of a liquid above a measurement point when the liquid is at rest. The height of the liquid influences the hydrostatic pressure. The hydrostatic properties of a liquid are not constant and are influenced by liquid density and gravity, (both of which determine hydrostatic pressure).
  • Mechanical Pressure: Mechanical pressure is measured by a bellows, diaphragm, or Bourdon tube that converts fluid pressure into force.

In the discussion of pressure, it is important to understand some of pressure‘s other dynamics, which are absolute, gauge, differential, and atmospheric. Everyone is familiar with atmospheric pressure; it is discussed as part of weather reports, it is the pressure of the air around us. Absolute, differential, and gauge pressure are methods for measuring pressure.

  • Absolute Pressure Absolute pressure is when pressure is measured relative to a vacuum.
  • Gauge Pressure: Gauge pressure is pressure relative to the atmospheric pressure. This form of pressure is positive when it is above atmospheric pressure and negative when it is below atmospheric pressure.
  • Differential Pressure: Differential pressure measurement is measuring the difference between two types of applied pressure. This form of pressure measurement does not have a reference but measures the two applied pressures.

Types of Pressure Gauges

Absolute Pressure Gauge

Absolute pressure gauges are used to measure pressure independent of the natural fluctuations in atmospheric pressure. A reference vacuum is attached to the side of the measuring element, which is not subject to pressure; it has zero pressure with no variation. A diaphragm separates the media chamber from the vacuum chamber and deforms into the vacuum chamber as pressure rises. The deformation and change is converted into a pressure value.

Unlike other pressure gauges, absolute pressure gauges are not influenced by changes in altitude, which makes them ideal for use in aeronautics, HVAC systems, and distillation processes.

Bellows Pressure Gauge

The bellows in a bellows pressure gauge is 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. As pressure is applied, it acts on the bellows on the free end, causing it to expand and produce movement. Bellows pressure gauges are very sensitive and used for low pressure applications.

There are two forms of bellows gauges. In one form, pressure is applied to the bellows, resulting in a deformation on a counterbalanced spring. Another form uses the differential pressure principle with the bellows sealed between the two chambers of differing pressures.

Bourdon Tube Pressure Gauge

A Bourdon tube pressure gauge has an elastic tube that is soldered or welded on one end into a socket. A change in pressure causes deflection in the tube; this is proportional to the applied pressure and is sent to a rotary gear with a pointer. The operating principle of a Bourdon pressure gauge is that a curved tube will straighten when pressure is applied; this is indicated by a dial or digital readout.

Bourdon tube pressure gauges are used to measure pressure up to 1000 bar and down to -1 bar of gas, steam, or fluids. They have accuracy between ± 0.1% and ± 2.5% of full scale deflection and are made of brass, stainless steel, or monel, a nickel alloy.

Capsule Pressure Gauge

A capsule pressure gauge has two thin, concentric corrugated diaphragms that are sealed tightly together around their circumferences. One of the diaphragms has a hole in the center that allows the medium to enter. When pressure is applied, the diaphragms expand or contract. This change in shape creates rotary movement that appears on the face of the gauge. Capsule pressure gauges are used for the measurement of substances with pressures up to 600 mbar with an accuracy of ± 1.6%, and they are used exclusively for measuring the pressure of gases.

Diaphragm Pressure Gauge

A diaphragm pressure gauge is elastic and becomes displaced when pressure is applied. This type of pressure gauge works on the same principle as a Bourdon pressure gauge but measures pressure using a diaphragm instead of a flexible tube. The diaphragm, which is placed between two flanges, is used to determine the difference between the applied pressure and the reference pressure. It can measure pressure as high as 40 bar to -1 bar of gas, steam, and fluids. The main use of a diaphragm pressure gauge is for measurement of low level pressure.

Differential (DP) Pressure Gauge

Differential pressure gauges measure the difference between the pressure in two chambers that are separated by an element that moves back and forth according to the changes in pressure. The movement of the element causes a movement in the pointer on the gauge face or provides a digital display reading. One of the ports of the gauge is installed on the high side, while the other is placed on the low side that shows a pressure drop on the gauge.

In some cases, a linear magnetic piston is placed between the two pressure chambers that tugs at a rotary magnet connected to the gauge pointer or digital display. Differential pressure gauges are popular due to their simplicity.

Manometer Pressure Gauge

Manometer pressure gauges measure pressure on a fluid by balancing one column of fluid against a second column of fluid. This type of pressure gauge is the simplest type and consists of a transparent tube in the form of a "U" that is partially filled with a manometric fluid like mercury. In its simplest form, one end of the tube is connected to the location in which pressure is to be measured, while the other end is open to the atmosphere; this can be seen in the diagram below.

Piezometer Pressure Gauge

A piezometer is a type of manometer that is used to measure the medium pressure range of liquids; it is a simple glass tube that is open at both ends. One end is connected to a pipe line where the pressure of a fluid is to be measured, while 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.

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Chapter Three: How Pressure Gauges Are Made

Pressure gauges are a commonplace measuring device used to monitor pressure in pipelines and ensure the safe movement of gases, fluids, and steam. The performances of pumps, conveying systems, and various types of spray nozzles are evaluated using pressure gauges.

The main purpose of pressure gauges is to provide information regarding the status of a system and prevent damage to equipment and leakages. A properly placed high quality pressure gauge, regardless of its cost, saves on time and expenditures.

How Pressure Gauges Are Made

Because there are so many types of pressure gauges, it would be impossible to describe the construction of each type. For the sake of brevity, this discussion will focus on the Bourdon pressure gauge construction.


The cases for pressure gauges are made of plastic, steel, brass, or, most commonly, stainless steel. The complexity and type of case is a good indication of how expensive the gauge is. Phenolic, a resin made from phenols and aldehydes, cases are used in aggressive and harmful environments such as those for chemical and petrochemical production.

Cases can be filled with glycerin or silicone to prevent condensation and provide protection from corrosive environments that could damage the internal mechanism. Rubber gauge covers are available to protect the gauge‘s case from impact damage.


The socket is the first part of the pressure gauge the pressurized fluid contacts. Inexpensive gauges have a hole drilled at the outlet connection, while more expensive gauges have a threaded hole for a restrictor orifice. The insertion of a restrictor orifice prevents particles from entering the gauge and jamming the gauge.

Welding Style

One end of the Bourdon tube is welded where the linkage is attached. Less expensive pressure gauges use a stamping or a mechanical device to attach the linkage.


The types of pointers vary according to the types of fine adjustments that the pointer permits and the pointer‘s complexity. More complex and refined pointers allow for adjustments for changes in altitude or wear from pulsations and vibrations.


The readings on a pressure gauge can appear in a dial fashion analog display or as a digital readout. As other factors, the types of displays vary depending on the type and design of the pressure gauge. A pressure gauge‘s dial scale is calibrated to the design and type of pressure gauge. In the case of the Bourdon tube, the dial is calibrated to the Bourdon tube.

Dial or analog pressure gauges

The scale on a pressure gauge can be divided into three sections with the first and third sections being the least accurate and the middle or second section being the most accurate. When selecting an analog pressure gauge, you want the normal pressure range to fall within the middle section of the dial.

Though the middle of the dial has the most accurate pressure readings, there are pressure gauges that have high accuracy readings throughout the full scale of the dial at 1%.

Digital pressure gauge

A digital pressure gauge displays the pressure on an LCD screen and makes use of a transducer that converts the pressure value into an electrical signal. There are a wide variety of designs and styles of digital pressure gauges, with types that can be carried for field testing and types that are installed on a pipeline.

A requirement of digital pressure gauges is a power source, which is normally a battery. Analog pressure gauges operate mechanically without a need for a power source.


The front or face of a pressure gauge is the window that protects it from the environment and protects the internal mechanism. It can be made of glass, tempered glass, or plastic. Windows made of soft plastic flex for thermal compensation and allow the glycerin or silicone fill to expand without bleeding. The window serves as a clear membrane that permits the user to see the dial of the gauge and read the data.

The three basic types of windows are safety glass, polycarbonate, and acrylic. Safety glass can be tempered and laminated; this means it is hardened and toughened for durability and breakage avoidance. Polycarbonate is 250 times stronger than glass, 30 times stronger than acrylic, and can withstand any form of possible negative impact. Acrylic is also stronger than glass, exceptionally resistant to stress, and does not shatter.

Pressure Measurement Units

Pressure is a physical and measurable force, per area, that is exerted against an object by a substance, material, other object, or gas that is in contact with it. In the case of liquids or gases, their weight exerts increased pressure as the amount increases.

  • Pascals (Pa) is the unit of pressure or stress applied over an area of one meter squared and is equal to one Newton (1N). Pascals serve as the base unit of pressure for the International System of Units (SI), the modern form of the metric system.
  • Bar or Millibar is a metric unit of pressure that is equal to 100,000 Pa.
  • Atmosphere (atm) is a unit of measure that is equal to the average air pressure at sea level at a temperature of 15° C or 59° F. One atmosphere is 1013 millibars or 760 mm or 30 inches of mercury. It is measured by a barometer.
  • Torr is a unit of measure that is named after Evangelista Torricelli, the discoverer of the barometer. A Torr is 1/760 of a standard atmosphere or 101,325 Pa.
  • Pounds Per Square Inch (psi) is a unit of measure that is expressed in pounds of force per square inch of area, which is equal to 6894 Pa or 0.07 atm or 51.175 torr. PSI is based on the avoirdupois system of measurement, which uses pounds and ounces as units of measure.
  • Millimeters of Mercury (mm Hg) is a unit of measure that once stood for the pressure created by one millimeter of mercury. It is not an SI unit but is used in certain industries and scientific studies. Its modern definition is 133.322387415 Pa, which is equal to one Torr.
  • Inches of Water (in H2O) is a unit of measure that is determined by the pressure exerted at the base of a column of fluid that is one inch high and has a fluid density of 1.004514556 grams per cubic centimeter at a location where the gravity acceleration is at 9.80665 m/sec2.

The conversion chart below can assist in converting the various forms of pressure units as well as offer an understanding of each type.

Chapter Four - How Pressure Gauges Are Used

Pressure gauges are an essential instrument used by industry to measure the pressure in a system as a quality check measure and to ensure the consistency of products. For reasons of safety, pressure gauges monitor fluids, gases, and steam for leaks or a build up of pressure in a system.

The design, style, type, and configuration of a pressure gauge is determined by the application it serves or the industry in which it is used. There are innumerable uses for pressure gauges, from measuring the pressure in a swimming pool pump to measuring the pressure in a hydraulic line for manufacturing equipment.

Pressure Gauge Usages


When discussing pressure gauges for a car, the first thing that comes to mind is the air pressure gauge for the tires. Though an air pressure gauge is important, there are several other pressure gauges that monitor various car systems, such as the air conditioning, oil, and engine coolant. Modern cars have gauges and meters on almost every critical component.


There are a wide variety of instruments that inform a pilot of an aircraft's condition and pressure variances. Pressure sensing devices can be found in the flight group and engine group. They are the most critical and essential aspects of an airplane's operation, as they are a means of preserving its safe functioning. Each type of pressure gauge is designed to fit a specific application.

The types of aeronautical pressure gauges include Bourdon tube, bellows, and diaphragm.

Oil Production

In the oil industry, flow lines, separators, and stock tanks are all under some form of pressure. Every aspect of an oil operation, from the wellhead to the tank, is monitored and overseen by a pressure gauge. All gauges for the oil industry have safety measures built into them for the protection of workers since they can blow out when the pressure gets too high.

Food Industry

Pressure gauges for the food industry are required to be exceptionally hygienic and are made of stainless steel grade 316, which is allowed to be exposed to the media.

Food grade pressure gauges are able to withstand the regular rigorous cleaning that is a necessary part of the food preparation process.

For safety and sanitary reasons, food processing pressure gauges must have an extremely smooth surface so that contaminants, bacteria, and residue are unable to be trapped on the surface of the pressure gauge.

Chemical Industry

Pressure gauges for the chemical industry are specially designed to meet the needs of a variety of mediums and highly aggressive environments. Chemical industry pressure gauges require frequent repair and replacement. For protection of the instrument, chemical industry pressure gauges are coated in Tantalum, Halar, or Polytetrafluoroethylene (PTFE), which are exceptionally corrosion resistant.


A hydraulic pressure gauge is a critical part of the operation of a hydraulic device. Inadequate pressure gauges can adversely affect the system‘s performance and can be damaging to the flow of a manufacturing process. Any detectable pressure changes can indicate leaks in the system or damage to a hydraulic component. Hydraulic pressure gauges must be exceptionally accurate and capable of functioning in harsh and hazardous conditions.

Chapter Five - How to Choose a Pressure Gauge

Pressure gauges are widely used by several industries to monitor and calibrate pressure functions and applications. In most cases, they are designed, configured, and produced to exactly meet the specific needs of an industry as well as provide accurate and precise data.

Regardless of the wide use of pressure gauges, it is important to carefully consider all of the factors about a pressure gauge when making the decision to install one. The selection of the right gauge for accurate measurement of the needs of the process can help to avoid the many problems associated with pressure gauge malfunctions.

Pressure Gauge Choosing


According to the American Society of Mechanical Engineers (ASME), the accuracy of pressure gauges ranges from 4A to D, which is outlined in ASME 40.1. For mechanical pressure gauges, accuracy is determined by a percentage of the full scale or the span. As the accuracy increases, so does the price.

The determination of the required accuracy depends on the function of the pressure gauge; pressure gauge functions range from simple testing to the monitoring of complex industrial processes. In general, testing pressure gauges should have an accuracy of 0.25% to 0.10% on the full scale, while critical processes need an accuracy of 0.5%. Less critical processes can have an accuracy of 2%.


The dials of pressure gauges vary as much as the types of pressure gauges, with the sizes ranging between 1.5 inches and 16 inches. The determining factor for the size of the dial is where it will be placed and the required accuracy. The general rule is that larger dials are used in areas of the operation that are somewhat inaccessible, while smaller dials can be used in easily accessible spaces.

When a pressure gauge has to be read frequently and must be exceptionally accurate, the rule of thumb is to have a dial with a large face for quick and easy readings.


Environmental factors play a significant role in any monitoring, calibrating, or data gathering device. In addition to the type of medium being checked, environmental factors include temperature, particulate matter in the medium and atmosphere, condensation, and humidity.

A major factor in the environment is the temperature, which dramatically affects pressure gauge readings. There are pressure gauge models that are designed to compensate for temperature. Where there are extreme temperature variances, the gauge should be isolated for its protection.

In environments with corrosive materials, particulate matter, or wet and humid conditions, a weather proofed hermetically sealed and fluid filled pressure gauge should be used.


The selection of a pressure gauge should be aligned with the media to be monitored and to which it will be subjected. Manufacturers offer a wide selection of pressure gauges for corrosive conditions, various types of chemicals and gases, and conditions where there is the danger of impacts, pulsations, or vibrations.

The popular choice for corrosive conditions, such as wastewater plants, petrochemical processing, or chemical manufacturing, are gauges made from stainless steel, which provides excellent protection from shocks, vibrations, and temperature extremes.

Other things used to protect a pressure gauge against hazardous media are various forms of seals, such as a diaphragm seal that can be fitted on any type of pressure gauge. Manufacturers also offer custom sealing materials such as Tantalum and PTFE.


When choosing the connection, it is important to consider the process pressure, gauge size and weight, space, and leak integrity. Pressure gauges have either a national pipe thread (NPT) or G type connection. Whether a connection is NPT or G usually is decided by the geographical location of the pressure gauge. In the United States or Canada, the connection is normally NPT, which is a standard thread type for the American National Standards Institute (ANSI) and the ASME.

Male NPT connections are conical, with the thread diameter decreasing from the tip to the socket since tapered threads form a better seal.

G connections are found in Europe, Asia, and Latin America and can be found anywhere else in the world except Canada and the United States. The threads will be straight following the pattern of the British Standard Pipe Parallel (BSPP) connector, which is distinguished by the letter "G". The parallel thread design of G connectors allows for regular installation and removal of gauges without damaging the threads, but a sealing washer is required to seal the connection.

Aside from the NPT and BSPP connection types, other types include Deutsches Institut für Normung (DIN), Japanese Industrial Standard (JIS), and SAE.

Connection Location

An obvious factor regarding the connection is that it is designed to connect the gauge to the application. The placement and size of the connection can allow for more versatility. A lower mount gauge can be attached to an upward facing female connection, while backward facing connection makes it awkward to read the gauge.

The types of mounting choices are direct stem lower connect, remote surface mount lower connect, panel surface mount back connect, panel hole U clamp flush mount back connect, or panel hole front flange flush mount back connect.

Pressure Range

The maximum operating pressure should not be more than 75% of the full scale range. Selecting a pressure gauge that exceeds this range can result in pressure gauge fatigue and failure.


The pressure sensor elements are made from a variety of metals, which include brass, bronze, steel alloys, stainless steel, Monel, and Inconel. Much like many other factors in choosing a pressure gauge, the choice of elements is dependent on the media to be monitored. The types of elements must be compatible with the media and be able to withstand all aspects of the media that may harm or damage them.


For many years, analog displays have been the first and most popular choice. In recent years, digital displays have become sufficient, which has caused a shift in display selection.

Again, the type of application is the ultimate deciding factor regarding the type of display. Two directives from the ASME, 40.1 and 40.7, offer a detailed guide for the use of analog and digital pressure gauge displays.


  • A pressure gauge is a method for measuring fluid, gas, water, or steam intensity in a pressure powered machine to ensure there are no leaks or pressure changes that would affect the performance of the system.
  • Pressure gauges have been used for more than a hundred years and have been constantly evolving to fit the needs of new applications.
  • The variations in pressure gauges are dependent on where the gauge will be used with different sizes, styles, and types of materials designed to fit specific applications.
  • The performances of pumps, conveying systems, and various types of spray nozzles are evaluated using pressure gauges.
  • Pressure gauges are a critical and essential instrument used by industry to measure the pressure in a system as a quality check measure and to ensure the consistency of products.

Leading Manufacturers and Suppliers