A pressure gauge is a device used to measure the pressure of a liquid column, which is usually made of water or mercury, and the height of the column shows the amount of pressure. A pressure gauge is an industrial device located in a reservoir, piping system, reaction medium, and reservoir buried on land or under the sea. This barometer is basically like the hands of a clock in that the movement of its hands is based on the pressure applied to them. It should be noted that the report of this device is in the form of analog or digital data. This tool is made up of a sensor part and an indicator part, the changes of each of these parts cause our final pressure to show a number, and we must report these changes as pressure changes.
In other words, pressure gauges are tools designed to measure the pressure of fluids in a system. Measuring the pressure in your system is a critical quality step to ensure product compatibility and safety checks to be aware of leaks or building pressure in the system. Before determining a pressure gauge, it is important to understand the basic principles of pressure. The correct pressure gauge can then be determined based on selection criteria to measure the pressure inside the system correctly. Even the best measuring equipment creates a certain deviation from the actual value. It is important to know how this measurement accuracy is defined. Digital gauges are more accurate than analogs.
For example, if you hold a plastic tube in your hand that has high flexibility, when you blow into the tube, the tube becomes stiff and inflexible, which will bend at first if you reduce your pressure to blow, and Eventually it becomes a dormant sound. These are the basic principles for the design of pressure gauges, which were designed and invented in 1849.
The operation of the pressure gauge is somewhat similar to the pressure difference gauge, except that the pressure difference gauge shows the difference between the two points, while the pressure gauge or pressure gauge is used to measure the pressure of one point relative to the base and standard mode. To take. Due to the fact that the contraction and expansion of all fluids change with temperature, all the pressures obtained must be corrected by manometers for temperature deviation if necessary. The technology used in pressure gauges has been around for over a century, and the sphygmomanometer is one of the most common methods of measuring pressure today. Most pressure gauges have a Bourdon socket and gear drive with an indicator and dial to indicate process pressure .Pressure devices such as hydraulic and pneumatic, medical, pumps and compressors, refrigeration controls, water and electricity and gas control can be used to measure liquid pressure and gas pressure. In addition to visual pressure indicators, some barometers are tuned to provide electrical output and monitor other variables such as temperature .
History of pressure gauge
This device was registered in 1849 by Mr. Eugene Bourdon in France and is currently used to measure pressure due to its features such as its very high sensitivity, linear performance and accuracy. In 1852, in the United States, a man named Ashcroft bought the patent of Eugene Bourdon and became the largest manufacturer of barometers. Also in 1849, in a town called Magdeberg in Germany, he patented a diaphragm sphygmomanometer, which, in addition to Bourdon’s sphygmomanometers, created a revolutionary measure of pressure in industry. Finally, in 1875, after the end of Bourdon’s invention, Schaefer and Bodenbergenz produced Bourdon barometers.
Different types of pressure gauges
Pressure gauges can be divided into four categories, which in this section we will give a brief explanation in this regard:
Diaphragm Pressure Gauge
A diaphragm is a shell that is elastic and is pulled as soon as pressure is applied to it. A diaphragm is a sheet that forms a capsule if it is stretched and joined to two other diaphragms to allow this to happen. The sensitivity of the gauge increases with the addition of more capsules to the diaphragm. In such a way that when pressure is applied to the diaphragm, it causes it to bend and this movement is reached through the connection with the hand. The hand then moves and shows the amount of pressure on the diaphragm, and as long as this pressure is present, the diaphragm remains in its original position.
Cylindrical Pressure Gauge
The shape of the cylinder is similar to an accordion, which is made of metal. Increasing the pressure in the cylinder increases the elongation and length.
Bourdon Tube Pressure Gauge
Bourdon tube is made of alloys that are circular in shape. An attempt is made to keep the Bourdon tube in its original shape under any conditions before it bends during production and under pressure. Most pressure gauges use a Bourdon tube as an element meter. Pressure transmitters also use apertures as pressure gauges.
Digital Pressure Gauge
Digital pressure gauges measure the pressure inside the system in a special way. They convert pressure into an electronic signal. Digital pressure gauge shows the pressure using a digital display, in addition to the signal can be used to control equipment. Digital gauges are more accurate than analogs.
Principles of pressure measurement
Pressure is the amount of force applied perpendicular to a surface per unit area. In stagnant liquid or gas, this is the amount of force applied to the vessel wall at a specific point. The static pressure is uniform in every direction. However, a moving fluid exerts additional pressure in the flow direction while having little effect on the parallel surfaces of the flow direction (Figure below). This extra pressure is called dynamic pressure. The total pressure of a current (also called a stagnant pressure) is the sum of the static and dynamic pressures in that current. If the instrument is in the direction of flow, it measures the pressure of the total flow. The instruments discussed here are designed to measure static pressure in the system.
Pressure is often measured in three ways:
- Absolute pressure represents the total amount of force per unit area. A complete vacuum has an absolute pressure of zero, while the Earth’s atmosphere at sea level has an absolute pressure of 1 atmosphere.
- Gage pressure is what most gauge pressures show, ie ambient pressure relative to atmospheric pressure. This means that the gauge pressure is the absolute pressure minus the atmospheric pressure. If a pressure gauge is designed to measure pressures below atmospheric pressure (known as vacuum pressure), they may be labeled “pressure gauge” and negatively removed. To indicate that the pressure measurement is relative to atmospheric pressure, the letter “g” follows the unit pressure, for example 50 psi g
- The pressure difference gauge is simply given the pressure difference between the two points. Some gauges offer this measurement to eliminate the need to subtract two pressure readings in the system.
Pressure gauges are available in a variety of display units. Common units used in pressure gauges along with their equivalents in Pascals are listed below:
|PASCAL (PA OR N / M2)|
|104. 665 9.80 =||1at (kg / cm2 or kgf / cm2 or Technical Atmosphere)|
|760Torr =||105. 325 1.01 =||1atm (Standard Atmosphere)|
|102. 224 1.333 =||1Torr (mmHg or Millimeter of mercury)|
|10mmH2O =||98.0665 =||1cmH2O (cmWc or Centimeter of water)|
|665 9.80 =||1mmH2O (mmWc or Millimeter of water)|
|16ozf / in2 =||103.948 6.8 =||1lbf / in2 (Psi)|
|102.922 4.30 =||1oz / in2 (ozf / in2)|
|103.685 3.37 =||1inHg (inch of mercury)|
European standard EN 837 uses standard methods, design requirements, test and installation guidelines for common pressure gauges. EN 837-1 and EN 837-3 provide information on the design of concentric plates. Pressure gauges can work with a wide range of low pressure compression gauges, high pressure hydraulic pressure gauges. The unit of pressure pressure is the load and the pressure range is as follows:
Pressure range per unit load
Pressure range in millibars
Vacuum ranges per unit load
In a vacuum pressure gauge, the indicator rotates counterclockwise as the vacuum increases.
Vacuum range in mbar
Limited vacuum pressure gauge and pressure
|5.1-||3.1-||1.5… 1-||0.6… 1-|
|24. 1-||۱۵… ۱-||9.1-|
Page diameter size
Plate Size (NS) is a measure of the diameter of a pressure gauge plate. The screen sizes of the measurements in accordance with EN 837 are as follows:
40, 50, 63, 80, 100, 160 and 250 mm
Accuracy classes (KL) determine the maximum allowable margin of error for measuring the pressure gauge in terms of the percentage of maximum reading of the scale. For example, a pressure gauge with a maximum reading of 10 bar and an accuracy class of 4 may deviate from the actual pressure of 4% (0.4 bar).
Because pressure gauges use different elements in measuring pressure, it is very important to consider the chemical compatibility of the material when choosing the right pressure gauge.
Types of installation and connection
- Standard thread connection : This type of gauge is easily available in the new thread. Threads are sealed using a pressure seal for tapered threads and an O-ring for parallel threads.
- Pressure gauge : This type of pressure gauge installation is done by a female thread.
- Flange pressure gauge : This type of installation is provided for those who want to install a pressure gauge on the control cabinet.
Safety and service life
According to EN 837-2, for safety purposes, a pressure gauge shall be selected with an amplitude not exceeding 75% of the maximum scale value for constant pressure or 65% of the maximum scale value for rotational pressure.
When using hazardous pressure fluids such as oxygen, acetylene, combustibles and toxic substances, it is necessary to select a pressure gauge with additional safety measures such as a rear blower. These safety measures ensure that any leaks or bursts of the pressurized components do not injure the person in front of the scales. All pressure gauges that are prone to constant mechanical vibrations are often filled with oil or glycerin. At fast pulse pressures, such as the placement of gauges in reciprocating pumps, an orifice limit is usually used to level the pressure fluctuations and create a moderate reading. This increases the life of the gauge by eliminating unnecessary wear on the gears. It is good to know that wear and tear is normal over time.
Pressure measurement techniques
Many techniques have been developed to measure pressure in the system, based on which it has been used as the main mechanism in the numerous pressure gauges available today. Among these techniques, Android sensors, also known as mechanical sensors, have the most technology. Android gauges measure pressure using a metal pressure response element. This element takes many forms, but its main function is to be flexible under differential pressure. The deformation of this element can then be measured and converted to rotating a marker on a scale display. The three main aneurysm gauges are the Bourdon tube, the diaphragm, and the capsule element.
The Bourdon tube is a closed flat-walled end tube formed in a C or helix shape, as shown in the figure below. When liquid pressure enters the tube, the oval cross section of the tube becomes more circular and flattens the tube. As the fluid pressure disappears, the tube regains its shape. The change in the shape of the tube creates a movement pattern at the free end of the tube, which is converted into pointer rotation by links and gears. A Bourdon tube measures gauge pressure (relative to atmospheric pressure). Bourdon tube is the highest type of pressure gauge due to its sensitivity, linearity and accuracy.
Bourdon tube gauges come in a variety of designs and types to offer a wide variety of applications. The range of Bourdon tube pressure gauges varies from 0 to 0.6 bar to 0 to 1600 bar with accuracy class typically between 0.1 and 4.0 bar.
As shown in the figure below, a diaphragm pressure gauge uses a flexible membrane deflection that separates the two media. Absolute pressure can be measured. The diaphragm is often metal or ceramic that can be closed or welded between two flanges. By applying pressure, it flexes the diaphragm, which can be turned into a plate measurement using gears and fittings.
Diaphragm pressure gauges are suitable for corrosive gases, liquids or highly viscous environments. This type of gauge is widely used in chemical / petrochemical industries, power plants, mines, overseas and overseas industries and environmental technologies. The measuring range of this type of gauges is between 0… 2.5 mbar and 0… 25 bar with an accuracy class between 0.6 to 2.5.
Pressure Gauge Capsule elements are produced to measure air and dry gases at low pressure. As shown in the figure below, this device consists of two circular membranes located along their outer edges. Expansion or contraction of the chamber due to the pressure differential between the external and internal environment makes it possible to measure the pressure.
These pressure gauges are used almost exclusively for accurate pressure measurements in gaseous environments. They are most common among low pressure pneumatic systems, breathing valves, overpressure monitoring, filter monitoring and vacuum pumps. The measuring range of these meters is usually from 0.1 ar 1 mbar to 0… 600 mbar with an accuracy class between 0.1 and 2.5. While pressure gauges usually require very little maintenance, this can happen.
Application of pressure gauge
Pressure gauges have many applications in various industries, the most important of which are:
Chemical, petrochemical, rubber, automotive, drilling, food, sanitary, air conditioning, power generation, power plants, laboratory equipment, pneumatic and hydraulic equipment, leak detection and
Important points in choosing a pressure gauge
Several factors must be considered when choosing a sphygmomanometer for an application.
The first points to consider are the required engineering and system design, including cost and safety factors, as well as the degree of accuracy required. Pressure gauges are available with different accuracy ranges from 0.25, 5.5, 1.5%, 1.5% and 2 to 2.5%. There are different scale options for many single and double scale ranges. The level of accuracy required for newly designed systems may differ from the replacement components. Engineering requirements are also used for precision pressure gauges. Higher accuracy indicates larger dial measurements to show an increase in small, legible pressure scale, so space may be of interest. In addition, the ability of the user or operator to read the scale remotely may be a factor depending on the physical condition of the system or application. Selecting the range of the barometer should also allow the desired readable scale from the required visual scale.
To select the correct pressure range for the gauge, where there is dynamic pressure with pulse and potential, select a full pressure pressure that occurs at an operating pressure in the middle (50 to 75%) of the scale to apply pressure. Fluctuations are due to the pulse rate and pressure in the system.
Other engineering considerations include excessive pressure conditions and loss of measurement accuracy. Process fluids generally flow through a relatively high pressure piping system, and most pressure gauges are pressurized to monitor the workflow. When the pumps are turned on or off, or the valves are opened or closed, it can occur and fluid can pass through the pipe, causing spikes in the sphygmomanometer, which can damage the pressure gauge. To prevent this, a pressure gauge must be used to absorb the pressure and shock in the system. Over-pressure protectors such as snipers or valves can be used to protect against situations where shock is likely to occur.
The accuracy meter can also be affected by temperature changes. In general, for each change of 18 degrees Fahrenheit (10 degrees Celsius) at the temperature from which the caliper is calibrated, the user can experience an additional error of 0.4 ٪ error. It is caused by a change in the elasticity or spring value of the Bourdon tube element with temperature. While it is difficult to bypass the effect of workplace temperature, the effect of process temperature can be addressed. In steam service, the usual method is to install coil siphons or colorful siphons to dissipate process heat. Another common method is to install a capillary diaphragm seal to separate the gauge from the heat source. There are many options with liquid filling in the sealing system and temperature resistance up to 600 degrees Fahrenheit. In very cold environments, many users choose to heat tracking instruments by electric or steam tracking. Process and ambient temperature are important considerations when selecting and using barometers. To address temperature extremes, installation options may be considered depending on the operating temperature range. Diaphragm seals, capillaries, cooling elements, and pigment vapor siphons can be used to dissipate heat and protect the tool.
Another possible cause of gauge failure is corrosion. Bourdon tubes can be attenuated by the use of corrosive chemicals in the environment or the environment. This may occur as a hole leak or premature failure due to stress cessation. Therefore, it is important to be aware of the chemical compatibility of media with gauges and building materials. Diaphragm seals can also be used to protect the gauge from the media.
Vibration can have a significant effect on the performance of the meter. Vibration due to pumps, motors and other rotating equipment can cause excessive wear and possible premature failure of the internal components of a barometer, including the Bourdon tube and the drive or gear mechanism. Vibration also causes problems in accurate meter reading due to indicator fluctuations. One of the most common causes of sphygmomanometer failure is constant vibration exposure. The most common solution is to use a liquid pressure gauge. The liquid of choice is glycerin or silicone. Liquid gauges not only show pointer oscillations but also help protect and lubricate the internal gear.
Pressure devices are available in a variety of process connections, case sizes and installation styles. The appropriate process connection should be specified depending on the system and application requirements.
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