Pressure gauges are a group of devices that measure and display fluid pressure levels (of liquid or gas) inside enclosed vessels or systems. Pressure is nothing more than the measurement of the amount of force applied over a specific unit area. Read More…
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Meriam offers a wide variety of mechanical and digital pressure gauges for process measurement and indication. Terrific accuracy specifications and little-to-no temperature effect set these instruments apart from the competition. Many of our digital gauge products have multiple output options to increase their versatility in today’s changing control schemes.
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Various pressure measurement devices convert readings into electric signals, which can be displayed by data acquisition devices (DAQ). In contrast, pressure gauges directly measure and display pressure readings without electronic conversion. Known for their simplicity, accuracy, cost-effectiveness, and low maintenance, pressure gauges are highly valued in the industrial sector.
History
The origins of pressure gauges can be traced back to the early modern era, specifically to the scientific discoveries of Evangelista Torricelli, an Italian mathematician and physicist. In 1644, Torricelli discovered the existence of vacuums in nature and demonstrated that air has weight. His work laid the foundation for other scientists, such as the Frenchman Blaise Pascal, to build upon. However, pressure gauges as we know them today truly emerged during the Industrial Revolution. In the 1840s, Frenchman Eugene Bourdon sought a solution to the high fatality rates caused by highly-pressurized locomotive engines. His efforts led to the invention of the Bourdon gauge in 1849. Initially intended for railroad use, Bourdon’s invention had a significant impact on various industries by allowing the measurement of much higher pressure levels than previously possible and paving the way for further advancements in gauge technology. Today, the Bourdon gauge remains the most commonly used type of pressure gauge.
Importance
The measurement of pressure is essential for the safe and effective operation of various industrial systems, such as those based on water, oil, or gas. This is also true for industrial products like water heaters, fire extinguishers, and medical gas cylinders. Without accurate pressure measurement and adjustment, fluid power systems would be unpredictable, unreliable, and ultimately useless. Measuring pressure is vital not only for maintaining mechanisms that require precise pressure control but also for operating mechanisms that rely on pressure-dependent values, such as flowmeters where pressure levels impact flow rates. In modern industry, pressure measurement is so critical that it ranks among the most frequently measured phenomena in commerce, second only to temperature.
Materials
Pressure gauges can be made from various materials, depending on the requirements of their specific applications. Here are some examples:
- Chemical and Harsh Environments: Gauges used in the chemical, petrochemical, refining, power, and pharmaceutical processing industries are often exposed to harsh substances or chemicals. These gauges need to be corrosion-resistant and are typically made of stainless steel. Conversely, for applications involving only non-corrosive fluids or gases, gauges constructed from brass or bronze are usually sufficient.
- Pressure Conditions: The pressure conditions a gauge will operate under also influence material selection. High-pressure environments generally necessitate the use of very durable materials like steel. In contrast, low-pressure environments can often be accommodated by gauges made from bronze or similar materials.
The internal mechanisms of pressure gauges are typically made from materials such as beryllium copper, phosphor bronze, and various steel alloys. The internal tubes, which will be discussed in the following section, usually undergo a specific heat treatment known as spring tempering. This process enhances the tubes’ elasticity while maintaining their original shape.
Pressure gauges also vary significantly in size. Regardless of their material composition, both standard and custom gauges are designed to fit into a range of spaces, from very tight spots to spanning large tanks.
How They Work
The simplicity of pressure gauges lies in the fact that the pressure they measure is the only energy source required for their operation. At the end of the production process, pressure gauges are calibrated against a pre-existing “master” gauge. Once calibrated, the gauge is ready for use. They can be installed at various points in a fluid power system, such as near a hydraulic pump’s pressure port or at a stand-alone regulator in a pneumatic system. Sometimes, pressure gauges measure “sub-circuits” within a fluid power system that operate at different pressures than the overall system, such as circuits occurring after a reducing valve.
Pressure gauges are divided into two main categories: analog and digital, which operate and display information differently. Analog gauges, considered “traditional,” use a needle that moves on a clock-like face to show pressure changes.
Analog Pressure Gauges
The essential component of analog gauges is an inner, elastic chamber that deforms or moves as pressure changes. This motion is translated into the movement of a needle across a scale through a system of gears known as the movement.
Elastic chambers typically come in three forms:
- Bourdon tubes: The most common type of elastic chamber, a Bourdon tube is a C-shaped, elastic metal chamber that uncoils or straightens when pressurized fluid enters. This motion activates the gear and shaft assembly, moving the needle on the gauge’s display. Bourdon tubes may also come in spiral or helical forms.
- Bellows: These chambers expand and contract in response to pressure changes. They consist of thin-wall tubing and are usually supplemented by a coil spring to enhance fatigue life.
- Diaphragms or Stacks: These chambers consist of thin metal sheets within a cup and move as pressure is applied. Unlike bellows, diaphragms do not use supporting spring structures.
Digital Pressure Gauges
Digital gauges are increasingly replacing analog gauges due to their ease of reading and accuracy. They require an external power source, such as batteries, to operate. Digital gauges use sophisticated sensors and microprocessors to measure pressure and display a numerical reading.
Digital gauges use either strain gauge technology or piezoelectric technology. Strain gauge sensors measure mechanical pressure indirectly by detecting changes in the electric resistivity of conducting materials, like silicon or bonded metal foil. When pressure deforms the chamber, changes in resistivity occur, which are electronically converted and displayed. Piezoelectric sensors, on the other hand, measure electric charges that develop in response to mechanical pressure changes.
Types and Applications
To accommodate various applications, manufacturers produce different types of pressure gauges. These include a href=”https://pressure-gauges.com/water-pressure-gauge”>water pressure gauges, air pressure gauges, oil pressure gauges, temperature gauges, gas pressure gauges, fuel pressure gauges, differential pressure gauges, and vacuum pressure gauges. While some uses are more obvious, each type serves a specific purpose.
Gauges Classified by the Substance They Measure
Water Pressure Gauges: These gauges monitor the pressure in any water-based system. They are commonly attached to tanks to keep track of the water pressure within.
Gas Pressure Gauges: These gauges measure and display gas pressure, frequently used in factories and manufacturing facilities to monitor the flow rate of natural gas and propane-based systems.
Fuel pressure gauges: Specifically used in automobiles, these gauges measure and display the fuel supply or the amount of gas left in a vehicle tank.
Air Pressure Gauges: These gauges measure pneumatic pressure in air-operated equipment.
Oil Pressure Gauges: These gauges measure the pressure of oil circulating within a lubricating system.
- Vacuum Pressure Gauges: These gauges measure and display the pressure within vessels or systems operating in a sub-atmospheric or vacuum environment, often used to achieve very low temperatures.
High pressure gauges are essential for manufacturing and industrial applications involving high-pressure hydraulic technologies, such as hydrodemolition, hydroblasting pumps, and water cutting machines.
Classification by Different Standards of Pressure
Gauge Pressure Gauges: These gauges measure pressure relative to the surrounding atmospheric pressure.
Gauges Classified by Types of Applications
Another method of classifying gauges is based on their specific applications. For instance, magnehelic gauges are specialized pressure test gauges that use a diaphragm to measure static pressure in the HVAC industry. Additionally, many gauges are tailored for particular products or uses. For example, dial gauges and weighted gauges are commonly employed with pressure canners.
Yet another way to approach gauge classification is focusing on the specific application a gauge is used for. To provide just one example, magnehelic gauges are a special type of pressure test gauge that uses a diaphragm and measures static pressure within the HVAC industry. Many gauges are designed for use with a specific type of product. A single example is the use of dial gauges or weighted gauges for use with pressure canners.
Accessories
More so than other industrial devices, pressure gauges are frequently used in conjunction with complementary instruments, like pressure sensors, pressure transmitters, pressure transducers, and switches. With the addition of these devices, gauges increase in accuracy and precision, displaying more specific readings with smaller margins of error. They may also be equipped with electric contacts that sound alarms, turn on signal lights, or control a valve or pump. Two specific examples of accessories used to increase the functionality of gauges are test point adapters and gauge isolators. Test point adapters fit to gauges and allow them to screw onto various points within the system, enabling a wide range of test pressure measurements without the purchase of multiple, separate gauges. Gauge isolators turn a pressure gauge into an “on/off” mechanism by mounting between a gauge and its circuit; unless a button is activated, the gauge will not be exposed to and will not read fluid pressure.
Many accessories for gauges have protective purposes. As sophisticated industrial instruments, gauges face a variety of threats such as pipe vibration, water condensation, etc. The aforementioned gauge isolator also serves a safety function by protecting a gauge’s internal mechanism from sudden pressure spikes. Snubbers provide a similar function by damping intense fluctuations in pressure. A variety of case protectors can be purchased to protect the exterior of a gauge from hard shocks, while chemical seals are available to protect gauges from being corroded or plugged up. While pressure gauges generally do not require a high level of maintenance, investing in protective accessories is one of the best things gauge users can do to protect and extend the life of a gauge.
Considerations
When choosing a pressure gauge for a specific application, several factors should be taken into account. Some of the major considerations include the size of the dial, the size of the connection or port the gauge will be using, units of measurement that the gauge is capable of (e.g. PSI, mmHg, PA, etc.), compatibility of gauge material with the operating conditions (including temperature, corrosiveness, etc.). and whether the gauge should be dry or liquid filled (the latter tends to have longer life due to shock absorption).
One of the most important factors to consider is the pressure range of the gauge. Generally speaking, you should use a gauge that is able to read at least twice the amount of the expected working pressure. This provides a reasonable margin of safety for using the gauge. As a rule of thumb, operating pressure should never go above three-quarters of a gauge’s reading range.
A corollary of the rules of thumb involving pressure is the importance of choosing application-specific pressure gauges. Hydraulic systems, for example, should only utilize hydraulic gauges designed for operating under normal conditions in hydraulic environments.
It is important to note that the different types of chambers utilized by pressure gauges correspond to different ideals concerning pressure conditions. Bourdon type gauges are especially useful for medium to high pressure environments. However, they do not work well for low pressure scenarios. Gauges which utilize bellows and diaphragm chambers, on the other hand, are well suited to sensing low amounts of pressure and incremental changes within them.
For even greater accuracy – as well as greater speed, reliability, and durability – digital pressure gauges should be used in place of analog devices (despite their greater expense). Keep in mind, however, that the limitations of analog devices can often be overcome with the variety of accessories available for pressure gauges. (For example, some analog gauges possess temperature compensation equipment and multiple dial sizes to enhance the accuracy of their readings.)
Since so many factors constitute proper pressure gauge selection, investing in a quality pressure gauge provider is one of the best choices that pressure gauge consumers can make. You should focus on finding a reputable provider that offers a broad array of gauge products and/or services (e.g. recalibration services.) Working with a quality supplier will ensure that you are able to maximize the usefulness and effectiveness of your pressure gauges for your particular application.
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