What is a Pressure Gauge?
A pressure gauge is an equipment that measures pressure of fluids, gases, water or steam under pressure dependent systems.
When using a pressure gauge it is important to measure continuously for leaks or deviations in pressure as they could cause a function of an appropriate system to malfunction.
They work in ranges of pressure – to change the pressure often affects the efficiency of that system.
Over a century of history, pressure gauges have advanced based on what was required of them as applications changed. As previous innovations that created and utilized pressure systems have become normative within broader industrial applications, pressure gauges are now considered important tools.
What are the different types of pressure gauges?
Pressure gauges provide very important ways to measure and control pressure in industrial operations ensuring that safety, efficiency and process control can be achieved in any application.
Pressure gauges vary based on the the application to which they are used; with more variations occurring due to size, style, material and application of gauge based on industry requirements.
Pressure gauges can be defined and categorized in various ways, including by application (industrial pressure gauges, process gauges, HVAC gauges, or digital pressure gauges), means of measuring (gases, liquids, or steam), and method of gauging pressure.
Familiarizing operational technicians with each of these classifications of most commonly used pressure measuring devices is very important then when deciding which pressure measuring device to use on a system.
Pressure is understood as the amount of perpendicular force applied to some unit area of a surface depending on various techniques and methods.
There are a number of different types of ways to measure pressure and the accurate measurement of any type of pressure depends on the reference point against which the reading is taken due to design, reliability and selection issues.
There are two main classsifications for pressure gauges, hydrostatic and mechanical gauges. Both gauge types help to meet specific operational needs in industries such as oil and gas, chemical processing, manufacturing, pharmaceutical, and waste-water.
- Hydrostatic Pressure: Hydrostatic pressure is due to the weight of a fluid above a measurement point when the fluid is at rest. Hydrostatic pressure is affected by the height of the liquid. Hydrostatic conditions are not constant and are directly related to the density of the liquid and gravity (which together also determine hydrostatic pressure). Instruments used to determine hydrostatic pressure are typically employed in applications that deal with tanks, reservoirs, and groundwater monitoring.
- Mechanical Pressure: Mechanical pressure is measured by a bellows or a diaphragm or a Bourdon tube; each which convert the pressure of fluid into force. This mechanical motion will result in the cylinder (i.e. bellows, diaphragm, or Bourdon tube) moving either an analog needle on a dial or a digital display, based on the design of the gauge. Commonly, Mechanical pressure gauges are used for process automation, hydraulic systems, pneumatic controls, and general industrial maintenance.
- In discussing pressure, it is also important to know the dynamics of pressure as it relates to absolute, gauge, differential, and atmospheric pressure. Everyone is familiar with atmospheric pressure, which is communicated as part of weather reports, this is the pressure of the air surrounding us. Absolute, differential, and gauge pressure are styles of measuring pressure. It is important to know the differences between measuring styles to ensure proper sensor, transmitter, and gauge choices in various applications.
- Absolute Pressure: The absolute pressure is when pressure is measured against a perfect vacuum (zero reference point); which is important for scientific experiments, and vacuum systems, and barometric readings.
- Gauge Pressure: Gauge pressure is when pressure is measured against atmospheric pressure. This pressure is positive versus atmospheric pressure or negative versus atmospheric pressure. Common uses of gauge pressure measurement is for tire pressure, HVAC pressure, and industrial process application systems.
- Differential Pressure: Differential pressure measurement is measuring the difference between two applied pressures. This pressure measurement method does not have a reference, but rather the two applied pressures. Differential pressure gauges are common in monitoring filtration, flow measurement, and level measurement in pressurized tanks.
Types of Pressure Gauges
When selecting a pressure gauge for any application, you have to take into account the measurement range, process media, accuracy, operating conditions and industrial requirements. Below are the common types of pressure gauges, the different measuring principles and common applications:
Absolute Pressure Gauge
Absolute pressure gauges utilize a reference vacuum (constant zero pressure) and measure pressure free from atmospheric impact.
An isolated environmental reference void accomplishes the measurement, when the environmental chamber (pressure measurement) is referenced against the vacuum at the diaphragm. As pressure increases, the diaphragm deforms into the vacuum chamber.
When the diaphragm deforms into the vacuum chamber, it is encoded/converted to a pressure result by very sensitive mechanical and/or electronic inputs to read pressure over a wide range of values.
Unlike other types of pressure gauges, absolute pressure gauges are unaffected by elevation or weather changes.
These differences (altitude or pressures relating atmospheric factors) make this gauge a good application for aeronautics, HVAC (heating ventilation and air conditioning), laboratory, vacuum, semiconductor processing, and distillation measurements where consistent and precision maintained, pressure reference measurements are important.
Absolute pressure gauges will often be specified in processes where enhanced accuracy and repeatability measurements are required (such as pharmaceutical, and food processing).
Bellows Pressure Gauge
Bellows pressure gauges are bellows made up of thin flexible metal tubes in an accordion-type shape and sealed at one end. When pressure is applied, pressure acts on the interior of the bellows expanding and causing movement.
Typically, bellows are very sensitive pressure gauges and used for low-pressure measuring applications like gas distribution systems, medical applications, or leak testing.
Bellows Gauges are available in two main types. For one type of gauge, the pressure acting on the bellows causes deformation of the bellows which is counterbalanced by a spring while the other type of gauge operates on the differential pressure principle with the bellows being sealed between two chambers with different pressures.
Bellows pressure gauges are suitable for accurately monitoring applications where it is critically important to detect minor pressure changes and may also be mandatory to do so in power generation applications or sensitive laboratory processes.
Bourdon Tube Pressure Gauge
A Bourdon tube pressure gauge uses a flexible, curved tube which is connected to a socket at one end. This tube deflects under applied pressure with its deflection depending on the amount of applied pressure (the gauge identifies the deflection).
The deflection is then transmitted through the rotary motion of a gear connected to either a pointer for analogue readings or sensor for electronic readings.
The Bourdon tube pressure gauge uses the principle that a curved tube will straighten when under pressure, and the deflection of this instrument is visually represented in either a needle or a digital display.
Bourdon tube pressure gauges are the most widespread and generic mechanical gauges in the world and can reliably measure pressure from vacuum (-1 bar) to 1000 bar for gases, steam, and fluids.
In terms of accuracy, Bourdon tube gauges are accurate to ±0.1% – ±2.5% of full scale deflection, and are made with standard materials of brass, stainless steel, or Monel (nickel alloy).
Bourdon tube pressure gauges are used in industrial and process applications such as oil refining, chemical processing, potable water, and hydraulic systems because of their robustness and reliability over a large detection range.
Capsule Pressure Gauge
A capsule pressure gauge consists of two closely spaced concentric circular corrugated diaphragms sealed around the edges. One of the two diaphragms has a central hole to allow the medium to come in.
The action of deflection of the diaphragm allows for rotation to be created. This rotation is then displayed on the indicator face of the gauge. The capsule pressure gauge is mainly developed for measuring low gas pressures which have an upper limit of 600 mbar (or about 8.7 psi) with an accuracy of ±1.6%.
It has been developed solely with the use of dry, clean gases for the purpose of measuring pressure in applications of ventilation, air monitoring and laboratory test.
Diaphragm Pressure Gauge
A diaphragm pressure gauge works on a similar principle to the Bourdon pressure gauge, in that the diaphragm is used to separate two separate pressure zones instead of a tube.
The diaphragm is usually made from some stiff elastomer or metal alloy and being located between two flanges, will move when subjected to pressure, determining the relationship between applied pressure and a reference pressure.
A diaphragm pressure gauge can measure an operating pressure range between -1 bar to 40 bar for gases, steam, and fluids, and provide more than adequate resistance to corrosive process media containing aggressive chemicals when built with appropriate wetted materials.
Diaphragm pressure gauges are commonly used in sanitary processing, chemical plants, and wastewater applications where plugging or crystallization of the pressure gauge is a consideration.
Differential (DP) Pressure Gauge
Differential pressure gauges measure the differences between two chambers separated by an element that is capable of moving back and forth with the changes in pressure.
As the element moves, it causes the pointer on the gauge face to also move, or it may provide a reading on the digital display. One port of the gauge is placed on the high side, a low side indicates pressure drop to register on the gauge face.
In many differential gauges, the element is a linear magnetic piston that is installed in between the two chambers of pressure. The piston is connected to a rotary magnet that moves the gauge pointer/indicator or displays a digital reading.
Differential pressure gauges are used to monitor filtration (i.e., across filters or membranes), flow tracking in piping, cleanroom pressure control, as well as for measuring liquid levels in pressurized vessels.
Differential pressure gauges can be easy and convenient to use and valuable to avoid potentially large financial failures and ongoing system effectiveness.
Manometer Pressure Gauge
Manometer pressure gauges measure pressure using the two columns of fluid. Generally, this simple gauge consists of a transparent “U”-shaped tube, which is partially filled with a manometric fluid, such mercury or water.
One side of the tube is connected to the pressure source, while the other side is open to the atmosphere. This allows the fluid at the connected side to rise or fall, but most importantly, it allows the difference between the two levels of fluid to give an indicator of the pressure.
Industrial and laboratory manometers are popular due to their simplicity, durable design, reliability and good performance for calibrating or verifying accuracy on other pressure instruments.
Piezometer Pressure Gauge
The piezometer which is a commonly used manometer measures the pressure of liquids within a moderate range of pressure. The piezometer is simply a glass tube with both ends open.
One open end of the piezometer is connected to a pipeline where the pressure of the fluid was to be monitored, while the other open end is exposed to the atmosphere. The piezometer is oriented vertically so that liquid could rise into the tube, and the reading would be the height.
Piezometer pressure gauges are used mainly as a relatively simple pressure gauge for measuring pressure head and the fluid in geotechnical engineering, groundwater studies, and hydrologic studies.
Specialty and Digital Pressure Gauges
To improve measurement devices, we now see the emergence of digital pressure gauges and process transmitters used in many high accuracy applications.
Digital pressure gauges and process transmitters offer electronic sensing elements, digital displays, advanced data logging, and the ability to communicate with SCADA systems and other automation networks.
Digital gauges (often referred to as smart gauges) are becoming more favored for a majority of industrial settings because they are more durable, more accurate, more flexible to changes in the validation field, and have the added benefit of remote access and communicating with other digital gauges via common industrial protocols like HART or Modbus.
The choice between digital and analog, will ultimately be based on the specific application requirements of accuracy, durability, visibility, and maintenance.
Digital pressure gauges are available in explosion-proof, sanitary, and corrosion resistant models to meet specific specifications, such as withstanding extreme environments offshore oil platforms, beverage industries, and pharmaceutical manufacturing while still allowing safe and accurate pressure readings from extreme conditions.
How are pressure gauges manufactured?
Pressure gauges are critical devices for determining and monitoring pressure levels in pipelines, equipment and process systems in an industrial and commercial context.
These instruments are vital for ensuring the safe functioning of required gases, liquids and steam in chemical plants, refineries, HVAC system, water treatment facilities, and any type of manufacturing plant.
Pressure gauges immediately communicate real-time accurate pressure readings of gases and liquids and thereby are used to determine abnormal conditions, such as drops in pressure or spikes in pressure, that can damage equipment, or compromise process safety.
Active and ongoing monitoring using pressure gauges is the primary role of the pressure gauge to provide important information to an operator.
What’s more, while a gauge can provide an operator with insights into the system, this ultimately enables quicker detection of an abnormal condition that may result in an equipment failure or failure to contain a surface or subsurface leak.
A continuous monitoring capability using high quality pressure measurement instruments on a periodic basis will minimize the possibility of unplanned downtime, therefore extending the life of pumps and valves, and reduced repair and maintenance costs to the end user.
Whether you have hydraulic systems, pneumatic systems, refrigeration systems or some type of general process controls, it is important to recognize the importance of purchasing a quality precision calibrated pressure gauge to ensure accurate measurement, long-term reliability and establish compliance with safety regulations.
How Pressure Gauges Are Made
Various styles of pressure gauges are available commercially – these include: bourdon tube gauges; diaphragm gauges; capsule gauges; digital gauges; and, differential pressure gauges. Each of these has its own individual operating mechanism to sense and display pressure.
This section will focus on the manufacture of Bourdon pressure gauges and the materials and processes involved, as the Bourdon pressure gauge is the most commonly used mechanical pressure gauge and demonstrates mechanical simplicity and mechanical reliability at a low cost.
Case
The outer casing of pressure gauges protects the internal pressure sensing mechanism from environmental risks such as moisture, dust, and chemicals. Cases can be made from plastic, steel, brass, or most often, stainless steel, depending on the use.
The nature and degree of complexity of the case are usually understood as an indicator of the gauge’s potential resistance to corrosion and overall service life.
In the chemical and petrochemical industry, high-quality gauges often are manufactured with phenolic resin cases for extreme applications involving harsh and aggressive process conditions.
Many industrial pressure gauges can be purchased with liquid-filled cases (usually using either glycerin or silicone oil) to minimize internal condensation and protect sensitive parts from vibration due to corrosive atmospheres.
Liquid-filled pressure gauges are especially applicable when the operating conditions are demanding and include exposure to chemicals, ice or heat, and impact.
All rubbers covers are also available to provide further protection to gauges from mechanical shock, and in the case of needle gauges, define where the added mechanical protections are permissible.
All gauges should be protected from damage due to routine maintenance processes and/or fall during daily operations.
Socket
The socket, or pressure connection, is the portion of the gauge which directly comes into contact with the pressurized process fluid.
Low-cost gauges have a simple drilled path at the process connection; however, high-performance industrial pressure gauges utilize a precision-threaded socket that accepts restrictor orifices to protect the bourdon tube and internal mechanism from particulate matters while also dampening rapid pressure fluctuations (pulsation damping).
Determining the socket material for compatibility with the process and corrosion resistance is essential as with brass and stainless steel.
Welding Style
Bourdon tube pressure gauges are assembled such that one extremity of the bourdon tube, (a curved, flattened tube that flexes under pressure) is attached by precision weld to the mechanisms linkage.
The method of connection has a significant bearing on the performance and service life of the gauge. High quality gauges utilize modern welding techniques to achieve leak proof seals with high integrity, while lower quality gauges may mechanically fasten or stamped connect the bourdon tube that provides low strength corrosion etc. under high cycle or vibro-mechanical conditions.
Pointer
The pointer interprets the movement of the bourdon tube into a way of visually representing system pressure in the dial scale.
Pointers can take on a variety of designs; from simple fixed pointers to high-accuracy adjustable pointers which allow for calibration adjustments to account for the effects of altitude, as well as repairs for wear due to pressure cycling, vibration, and mechanical drift.
Many high-accuracy gauges offer micrometer or knife-edge pointers to enhance readability, improve resolution, and reduce parallax error.
Display
Pressure gauges provide a variety of display formats to accommodate different process monitoring requirements. The most common display formats include analog dial display formats (mechanical pressure gauges) and digital read-out formats (electronic pressure gauges).
Each format presents the pressure in a different level of resolution and scale range indicated in different styles.
Selecting the correct type of display for your application (for example, a backlit LCD to be used in low lighting, or an analog dial for convenient precision and at-a-glance referencing) can have a large impact on both operator efficiency and ability to control the system.
Dial or analog pressure gauges
Analog pressure gauges consist of a circular dial with a marked scale, with a pointer rotating over the dial in response to the systems pressure. The field of the reference pressure gauge will increase as the range of pressure readings increases.
It is important to note that a gauge in order to maintain accuracy must always be in the mid-range of the gauge. The center one-third of the dial range is called the “sweet spot” and is where the gauge will have the least errors and pointer deflection.
Whenever possible, you should try to keep the normal operating pressure in the mid-range of the dial section. Several precision pressure gauges can achieve full-scale accuracy to the 1% level, which is good repeatability for pressure-related processes.
Analog gauges are commonly used in industrial environments for continuous monitoring, instant visual reference, and durability under process settings. Analog gauges can be configured for a wide variety of pressure ranges, accuracy classes and sizes associated with the diameter of the dial.
Digital pressure gauge
Digital pressure gauges operate by an internal electronic pressure sensor, such as a piezoresistive, strain gauge or capacitive transducer, to sense applied pressure and convert it to an electrical signal, which is digitally processed and displayed on an LCD or LED screen.
Digital pressure gauges can be customized with high precision, programmed set-points, data logging, and remote monitoring capabilities.
Digital gauges are used for advanced automation, calibration in the field, and process control where continuous or exact pressure readings, output signal integration, or rapid data collection is required.
Digital pressure gauges rely on a while a battery or other external power supply since they require current to operate, whereas mechanical analog pressure gauges are self-powered and require very little maintenance.
Digital models provide real time pressure data with improved accuracy and alarms for overpressure or vacuum in both bench- and field-testing; integration with industrial control systems is seamless.
Window
The face window is a critical component of a pressure gauge. It protects the dial and pointer from the environmental hazards of dust, moisture, and corrosive gases. At the same time, the window must allow for easy viewing of the pressure.
The windows are typically made of glass, tempered glass, or special plastics (polycarbonate and/or acrylic), all of which are chosen based on criteria related to the needed chemical resistance, impact strength, and available optical clarity.
For liquid gauges, flexible plastic windows will accommodate the inevitable expansion of the liquid caused by temperature changes, allowing for fail-safe leak performance in extreme or variable climates.
The three basic types of gauge windows (safety glass, polycarbonate, and acrylic) all provide an advantage over a bare dial. Safety or tempered glass (window) offers exceptional scratch resistance and protection against shattering.
Polycarbonate is a utilitarian window that is lightweight, extremely impact- resistant (250 times stronger than glass), and often the product of choice in extreme service or for portable applications.
Acrylic also provides excellent clarity and is lower stress resistant than glass (but more than polycarbonate) and is the low cost, general industrial option. Selecting the appropriate window materials gives the you a level of confidence in the durability of the gauge and reliability of readings over time.
Pressure Measurement Units
Pressure is defined as the force per unit area exerted on an object from a fluid (liquid/gas). Pressure is measured and quantified in force by various sensors and gauges, and expressed in a number of engineering units.
The extensive list of pressure units, including psi, bar, Pascals, atmosphere, Torr, and inches of H20, is dependent on geographic conventions and specific applications, (i.e. HVAC pressure measurement, hydraulics, or lab vacuum pressure testing).
- Pascals (Pa): The International System of Units (SI) has its own ways of measuring pressure, and the base unit is called Pascal. One Pascal is one Newton of force per square meter. Regardless of how you value the mix of meaning, a Pascal is accepted one way or another in the science of studying pressure. It is used for standard applications in scientific and industrial formats.
- Bar or Millibar: The bar is acceptable for use around Europe and many of the meteorological services use bar units, and is a unit of pressure equal to 100,000 Pa. There is also, pressure transmitters, pressure gauges and process gauges that use the litre or bar as the main unit of measure or scale.
- Atmosphere: (atm) it indicates the average atmospheric pressure at sea level. The unit is used in science and meteorology, and the flying applications and research.
- Torr: 1 Torr is equal to 1/760 of a standard atmosphere, the use of this unit is preferred when using vacuum measurement, and is most often used lab science pressure measurement.
- Pound Per Square Inch (psi): The unit is the most used and accepted unit of pressure in North America, and is combined with the pounds of force acting on the area of one square inch, and is defined for general measurement in pressure in industrial, automotive, and hydraulic applications.
- Millimeter of Mercury (mm Hg): This is a sometimes assigned to medical instrumentation, lab pressure measurement and it is equal to 1 Torr.
- Inches of water H2O: This is a common measurement of pressure when a contractor uses some diagnostic method e.g., when using a manometer during an air conditioning equipment and it is troubleshooting, or the method becomes part of an environmental and monitoring air changes protocol (refer to the table above for an example of this, as part of clean room, or process controls in a low-pressure application that are pressure differential or measuring changes in pressure differential).
Choosing a pressure gauge requires the proper selection of pressure measurement with respect to your process to meet system functional requirements and safety standards.
The pressure unit conversion table below lets you easily cross reference some common pressure units used in instrumentation, calibration and other process applications.
| Pascal (Pa) | Bar (bar) | Pounds per Square Inch (psi) | Technical Atmosphere (at) | Standard Atmosphere (atm) | Torr (Torr) | |
| 1 Pa | = N / m² | 10-5 | 1.450377 x 10-4 | 1.0197 x 10-5 | 9.8692 x 10-5 | 7.5006 x 10-3 |
| 1 bar | 105 | = 100kPa | 14.50377 | 1.0197 | 0.98692 | 750.06 |
| 1 psi | 6.8948 x 103 | 6.8948 x 10-2 | = 1 lbf / in² | 7.03069 x 10-2 | 6.8046 x 10-2 | 51.71493 |
| 1 at | 9.80665 x 104 | 0.980665 | 14.22334 | = 1 kp / cm² | 0.9678411 | 735.5592 |
| 1 atm | 1.01325 x 105 | 1.01325 | 14.69595 | 1.0332 | 1 | = 760 |
| 1 Torr | 133.3224 | 133.3224 x 10-3 | 1.933978 10-2 | 1.359551 x 10-3 | ≈1.315789 x 10-3 | ≈1mm Hg |
Knowing how pressure gauges are made and the differences between the different types of pressure gauge, materials, display methods, and measuring units means you can make a more informed selection and find the optimal pressure measurement solution for your industry and application.
How are pressure gauges used?
Pressure gauges are essential devices used in industry and are used to measure system pressure, as part of quality control to ensure consistency of products. They are used to ensure safety by monitoring fluids, gasses, and steam for leakage or pressure scalds in a system.
Pressure gauges are designed, styled, configured and manufactured the way they are for the individual application or industry, as there are countless possible designs for measuring pressure.
There are different types of pressure gauges for varying potential uses, examples ranging from pressure monitoring in a swimming pool pump, all the way to measuring in hydraulic lines in manufacturing equipment.
Pressure Gauge Usages
Automobiles
When thinking about pressure gauges for a car, the first thought is the air pressure gauge that measures air pressure in the tires.
While an air pressure gauge is important; there are other pressure gauges monitoring other various car systems such as the air conditioning, oil, and engine coolant. Almost every critical aspect of a modern automobile has some measuring device and gauges or meters.
Aeronautics
Pilots can use a number of instruments to provide useful information about the condition of the aircraft and changes in pressure. From the flight group, there are pressure sensing devices in determining flight parameters for the safe operation of the aircraft.
Pressure gauges are in both the flight instrumentation group and engine group for even greater accuracy regarding pressure changes within multiple systems. Each type of pressure gauge must be evaluated based on the intended measurement.
There are also several types of aeronautical pressure gauges: Bourdon tube, bellows, and diaphragm gauges.
Oil Production
Pressure is present in the oil industry in a variety of ways, including flow lines, separators, and stock tanks. Each component of the oil operation, from the wellhead down to the tank, can be monitored and controlled using pressure gages.
All gages for the oil industry have inherent safety built in to ensure worker safety in the event of blowout due to too much pressure being applied.
Food Industry
Pressure gauges used in the food industry must conform to hygiene specifications, and they are made from stainless steel grade 316, which is suitable for direct contact with food media.
Food grade pressure gauges take into account the vigorous cleaning practices common in food preparation, providing the user with cleanliness and proper function without concern.
For safety and sanitary purposes; food processing pressure gauges ought to have a very smooth surface, so contaminants, bacteria, and residue do not get trapped.
Chemical Industry
Pressure gauges that are found in the chemical industry are designed to be exposed to a range of mediums and very aggressive conditions.
They tend to be in repair or replacement more often than not. To protect any instrumentation, they are covered with materials including Tantalum, Halar, or Polytetrafluoroethylene (PTFE) which are, in most circumstances, corrosion resistant.
Hydraulic
The hydraulic pressure gauge is a mechanical component inherent in hydraulic systems. If the gauge incorrectly reads or is not calibrated accurately, the gauge potentially could disable an entire manufacturing process, or have performance consequences in a hydraulic system.
Apparent pressure variations in systems indicate loss of capability and possible leak or damage to a hydraulic component. By their very nature, hydraulic pressure gauges need to be accurate and durable with high reliability in very hostile and hazardous working conditions.
How do you choose a pressure gauge?
Pressure gauges are designed and made with regulations and applications based on the need for accuracy in any type of measurement.
Pressure gauges are developed and fabricated in various Industries based on utilization by industry-specific existing data.
However, regardless of the requirement, it is always essential to consider all aspects when selecting a pressure gauge for installation.
If an accurate measurement takes place with the right gauge, this should eliminate all tension to the respect of the common pressure gauge failure modes and allow the process to go as intended.
Pressure Gauge Choosing
Accuracy
According to the American Society of Mechanical Engineers (ASME), pressure gauge accuracy is categorized from 4A to D in ASME B40.1. Accuracy for mechanical gauges is given as a percentage of full-scale or span. In most cases, higher accuracy also increases cost.
The level of accuracy required for a pressure gauge will depend on the function of the gauge, which can vary from low complexity testing activities to high complexity industrial monitoring.
For testing applications, the percentage would range from 0.25% to 0.10% full scale, while critical processes will typically require gauges at 0.5%. For pressure gauges in limited applications, 2% will likely be accurate enough.
Dial
Pressure Gauge dials are available in a wide variety of sizes (1.5 inches to 16 inches) and are selected based on placement and accuracy needed. A larger dial is typically used in more inaccessible areas. Smaller dials are used in less inaccessible locations.
If a pressure gauge is going to be read accurately and frequently, it is a good idea to select a gauge with a large dial face so that it is easy to read and quick to interpret.
Environment
Monitoring, calibration, and data collection devices can be significantly affected by environmental factors. Aside from considerations of the medium’s type being measured, temperature, particulate matter within the medium and atmosphere, condensation, and humidity are important considerations.
Temperature is a primary environmental factor affecting pressure gauge readings. Certain elements of the device can be compensated for by certain pressure gauge models.
However, in cases where there are extremes in temperature fluctuations, it is best practice to isolate the gauge, which protects the protective device from damage.
In the case of corrosive materials, particulates, or high humidity, the preferred gauge is a weatherproofed, hermetically sealed, and fluid-filled pressure gauge to ensure reliable performance in difficult situations.
Media
When selecting a pressure gauge, the medium being measured and the environment must be considered. Manufacturers sell a variety of gauges to cover corrosive environments, different chemicals and gases, and applications where shock, pulsation, or vibration would be a concern.
In corrosive environments such as wastewater treatment plants, petrochemicals processing, or in chemical manufacturing, gauges are typically made from stainless steel, which withstands shocking, vibration and high/low temperatures relatively well.
There are many types of seals that will protect a gauge in hazardous media, including diaphragm seals that can be fitted to any gauge. There are alternative sealing materials that manufacturers can customize, i.e., Tantalum, PTFE, etc. to help protect against corrosive and extreme environment.
Connections
Selecting the correct connection is a matter of considering the process pressure, the gauge’s size and weight, available space, and leak integrity. Pressure gauges typically use either national pipe thread (NPT) or a G connection.
The selection of NPT or G connections is typically based on the geography (region of the world) in which the gauge is used. NPT would be most typical in the United States and Canada since both are in accordance with the standards of the American National Standards Institute (ANSI) and the ASME.
Male NPT connections are tapered threads of varying thread diameter that decrease from the tip to the socket, which is designed to improve the seal quality.
The G connections are pretty common in Europe, Asia, Latin America, and other areas, other than Canada and the United States. The G connections follow the British Standard Pipe Parallel (BSPP) pattern, and the connections are identified by the letter “G” and must be straight threads.
G connections allow for ease of installation and removability of gauges without damage from the threads but require a sealing washer to seal securely.
There are also other connection types aside from NPT and BSPP. Other connection types include DIN, JIS, SAE etc.
Connection Location
One key consideration for the connection is the function it serves to connect the gauge to the application; as with any design, the connection to the application will be dependent on design and size for versatility. A lower mount gauge can be connected to an upward-facing female connection or made backward-facing, but both can cause the gauge to be difficult to read.
The mounting options are direct stem lower connect, remote surface mount lower connect, panel surface mount back connect, panel hole U clamp flush mount back connect, and panel hole front flange flush mount back connect.
Pressure Range
The maximum working pressure should not exceed 75% of the full-scale range. Using a pressure gauge that is pushed beyond this limit can lead to gauge fatigue, eventually causing gauge failure.
Press
Pressure sensor elements are manufactured from a variety of metals. Common metals are brass, bronze, steel alloys, stainless steel, Monel and Inconel.
The choice of these elements relies on the media being monitored. The elements have to be compatible with the media, and they must be able to withstand any corrosive or destructive effects the media may cause.
Display
For a long time, analog displays have been the preferred option for an application. Due to modern advances, digital displays have become acceptable, and display preferences are shifting among the community.
In the end, the application determines the use of either analog or digital displays. The ASME standards 40.1 and 40.7 provide detailed guidelines for when to use the types of displays.
Conclusion
- A pressure gauge is a device in which measures fluid, gas, water or steam energy in a pressure operating machine to determine acceptable leaks or variations in energy to verify system performance.
- Pressure gauges have been in existence for more than a century and have continuously evolved to satisfy new applications over the years.
- There are numerous variations of pressure gauge depending upon the application where it will be used because pressure gauges are available in many sizes, styles, and types of material for a specific application.
- Pressure gauges are used in measuring the performance of pumps and conveying systems and also a variety of spray nozzles.
- Pressure gauges are an important and necessary tool used by industry to measure pressure in a system as a quality check measure to ensure consistency in products.