What is a pressure gauge? Pressure gauge for measuring pressure. Pressure gauge for measuring low pressure of a gas medium Digital pressure gauges measuring gas pressure value

When designing and operating heating systems, the most important indicator and parameter is the coolant pressure. At normal pressure, which is within the limits of the hydraulic schedule, the work process goes without disturbances, the coolant reaches the most distant points of the heating system. If the pressure exceeds the critical point, there is a risk of pipeline rupture. When the pressure drops below the permissible level, there is a threat of cavitation - the formation of air bubbles, leading to corrosion and destruction of pipelines. In order to keep the pressure indicators at the required level, you need to constantly monitor them. It is for this that manometers are used - devices that measure this very pressure.

The main classification of pressure gauges is based on the principle of pressure measurement. The use of any particular type of pressure gauge is determined by the peculiarities of the technological process, the scope of use, as well as the possibility of using it in certain conditions. There are five kinds of these devices:
— liquid pressure gauges;
— spring pressure gauges;
— diaphragm pressure gauges;
— ;
— differential pressure gauges.

Working Principle of Liquid U-Shape Gauge

Of all the above types of pressure measuring instruments, the simplest are liquid pressure gauges ... They represent U-shaped glass tube half filled with liquid and equipped with a scale, usually in millimeters and pascals. The liquid level in the tube must be opposite the zero mark on the scale. If one end of the tube is connected to the place where the gas pressure is measured, and the other end of the tube is left open, then the liquid in the first tube will go down, and in the second it will rise. The difference in levels of liquids relative to zero will be the value that determines the pressure in millimeters of the liquid column. Moreover, the cross-sectional area of ​​the tube will in no way affect the readings of the device. Liquid U-shaped gauges are used to measure low pressure with indication ranges 100, 160, 250, 400, 600 and 1000 mm column of liquid. When the tube is filled with water, the countdown is carried out in millimeters of water column ( mm h.st.), mercury - in millimeters of mercury ( mmHg.). When filling liquid U-shaped mercury pressure gauges, pour over the mercury into both tubes. 8-10 mm water or technical oil to avoid the ingress of mercury vapors into the room.

The most widely used instruments for measuring pressure are found spring pressure gauges ... Their advantages are that they are simple in design, reliable and suitable for measuring medium pressure in a wide range 0.01 to 400 MPa (0.1 to 4000 bar).

Spring pressure gauge design

The sensitive element of the spring pressure gauge is hollow curved tube of ellipsoidal or oval section which deforms under pressure. One end of the tube is sealed, and the other is connected to choke, through which it is connected to the medium in which the pressure is measured. The closed end of the tube is connected to transmission mechanism rack-mounted, which consists of leash, toothed sector, gearwheels with an axis and gauge arrows... To eliminate the backlash between the teeth of the sector and the gear, a spiral spring... The scale is graduated in pressure units (pascal or bar) and the arrow shows the direct value overpressure measured medium. The pressure gauge mechanism is housed in a housing. The measured pressure enters the inside of the tube, which, under the action of this pressure, tends to straighten, since the area of ​​the outer surface more area inner surface. The movement of the free end of the tube through the transmission mechanism is transmitted to the arrow, which rotates through a certain angle. There is a linear relationship between the measured pressure and the deformation of the tube, and the arrow, deviating relative to the pressure gauge scale, shows the value of the pressure.

Electrical contact pressure gauge

As a sensing element in diaphragm pressure gauges advocates corrugated metal diaphragm chamber which is sandwiched between two flanges. Under the influence of pressure, the diaphragm bends upward and, with the help of the transmission mechanism, turns the arrow. The amount of bending of the diaphragm and therefore the rotation of the arrow depends on the pressure. Diaphragm gauges are less sensitive and accurate than spring-loaded gauges.

They are used in automatic control, regulation and signaling systems. V two special arrows set to the minimum and maximum pressure within the scale, contacts are mounted electrical circuit... When the movable arrow of one of the contacts is reached, the circuit closes, which causes a signal to be given or the corresponding action of the system to which the pressure gauge is connected.

Differential Diaphragm Pressure Gauges are used to measure the pressure drop in gas filters or in the restriction devices of the flow meters.

To measure any pressure of the working medium in the process, a pressure gauge is used to measure the pressure. The working medium is liquids, gases, air and even steam. A variety of gauges are used, the design of which depends on the way the readings are taken. The devices are used in all branches of industry, construction and medicine.

Types of detected pressures

It is known from the school physics course that three types of pressures are used for calculations. Among them are the following:

• Atmospheric. It has been calculated for a long time and is constant for a certain point on the earth's surface. Atmospheric pressure affects all surrounding objects, including humans. But healthy person it is not felt because of the equilibration by internal pressure.
• Excessive. It is created by means of injection installations under the condition of a closed space. High blood pressure It is mainly used to drive power mechanisms from a weak engine.
• Reduced (vacuum). The use of vacuum pressure is due to technological conditions. The created vacuum helps to draw the working medium into a container.

When studying at the institute, an additional concept appears - absolute pressure. This is the sum of atmospheric and elevated pressures.

The appropriate instrument type must be selected for taking readings.

Types of measuring instruments

Manometers are compact instruments designed to measure the excess pressure of the working medium. With their help, visual control of the technological process is carried out. Technological equipment may collapse when the maximum value is increased.

For many, the problem arises, what are the pressure gauges and for what. Depending on the type of medium, the method of taking readings and the installation site, the following types are distinguished:

A spring-loaded device is designed to measure indicators of an increased load of a liquid or gas. The measurement technology is based on the ability to deform under load. A pointer arrow is attached to the spring. In front of the arrow there is a panel with a drawn scale.

In another version of such a device, a Bourdon tube acts. It has the shape of a hemisphere and, on the one hand, is deaf. The supplied load unbends the tube, and the single-coil spring with an indicator arrow rotates around the axis by the angle of expansion.

Diaphragm meters differ from spring meters in the principle of measurement. They work by means of pneumatic compensation. The deflection of the membrane depends on the applied load.

There are many options for measuring mechanisms:

• flat corrugated membrane;
• bellows diaphragm.

Among the many meters, the most popular are devices with a Bourdon spring. The measuring range is available in the range from 0.6 kgf / cm2 to 1600 kgf / cm2.

Liquid pressure gauges work in the manner of communicating vessels. In them, two columns of liquid are balanced. We can say that in this way the hydrostatic pressure is measured. There is a scale on one of the tubes. The devices have a small measuring range of 10-100 Pa and are therefore used in laboratories.

Electrical contact meters are used to determine the vacuum (vacuum) values. These include vacuum gauges and manovacuum meters. They work with neutral liquids and gases, because they are made of steel and brass.

By outward appearance electrical contact pressure gauges resemble spring-loaded, but have a much larger body. This is where the contact group is located. The main purpose of such devices is considered to be an alarm.

Exemplary manometers, in essence, are the standards with which the serviceability of working manometers is checked. They have high precision thanks to gear train transmission mechanism.

Special pressure gauges are named so because they are designed to measure the pressure of gases of the same type. For example, acetylene, ammonia, oxygen and others. The purpose is indicated on the front of the device, and its body is painted in a specific color:

• black - carbon dioxide;
• blue - oxygen;
• red - propane;
• yellow - ammonia.

Vibration resistant instruments are designed to monitor high pressure surges or environments that generate strong vibrations.

The recorders take measurements and immediately record the results in the form of a diagram.

Marine manometers measure water and steam in boilers, oil and diesel fuel for the power plant. When working under conditions high humidity they must be resistant to moisture and vibration.

Railway, as the name implies, are used in locomotives and rolling stock railway transport... Their feature is the conversion of the results obtained into electronic and other forms.

Differential instruments are categorized complex equipment... The work of the meter is based on the deformation of several blocks included in the tracking mechanism. The readings are determined after the blocks have been balanced, when the arrow stops moving.

Each device has a measurement error and manometers are no exception. They are divided into several precision classes:

1. 0,15;
2. 0,25;

Device device

Among the many devices, the device and the principle of operation should be considered on the most common model. The device of a pressure gauge for measuring pressure is as follows:

The body of the pressure gauge is made of steel, and its image resembles a cylinder, which is plugged on one side. A lever-spring mechanism with a Bourdon tube is fixed in it. A scale is set to display the readings. And the indicator hand, which is rigidly attached to the mechanism, shows the applied force. Glass protects against external influences.

Installation on the water supply is carried out through a hollow fitting. The liquid, passing through the fitting, enters the tube, which it tries to unbend.

Application area

Almost all industries use pressure gauges in their mechanisms. The most common are:

• mechanical engineering;
• automotive industry (compressors);
• Agriculture;
• gas equipment;
• housing and maintenance facilities (boiler equipment, water supply);
• household (heating boiler, autoclave);
• metallurgy.

Gas pressure gauge

Gas pressure gauges are marked KM. Designed for use in dry environments such as air, oxygen and others. To install a low pressure manometer on the pipeline, a M12x1.5 thread is used.

Before purchasing, you need to know what the gas pressure is measured in. The most common measurement systems in everyday life are atmosphere and Bar. The industry uses kgf / cm2 and MPa.

Selection rules

Different industries use different measuring instruments... To choose the right pressure gauge, you need to know the following requirements:

It is possible to measure with guaranteed accuracy after calibrating and testing the device. If necessary, it is configured.

Principle of operation

The principle of operation of the pressure gauge is based on balancing the measured pressure by the force of elastic deformation of a tubular spring or a more sensitive two-plate membrane, one end of which is sealed into the holder, and the other through a rod is connected to a tribo-sector mechanism that converts the linear movement of the elastic sensitive element into a circular movement of the indicating arrow.

Varieties

The group of devices for measuring overpressure includes:

Manometers - instruments with a measurement from 0.06 to 1000 MPa (Measure overpressure - the positive difference between absolute and barometric pressure)

Vacuum meters are devices that measure vacuum (pressure below atmospheric) (up to minus 100 kPa).

Manovacuum gauges - pressure gauges that measure both excess (from 60 to 240,000 kPa) and vacuum (up to minus 100 kPa) pressure.

Pressure gauges - small gauge pressure gauges up to 40 kPa

Traction meters - vacuum meters with a limit of up to minus 40 kPa

Draft pressure gauges - vacuum gauges with extreme limits not exceeding ± 20 kPa

Data are given according to GOST 2405-88

Most of the domestic and imported pressure gauges are manufactured in accordance with generally accepted standards; therefore, different brands of pressure gauges replace each other. When choosing a manometer, you need to know: the measurement limit, the diameter of the case, the accuracy class of the device. The location and thread of the fitting are also important. These data are the same for all devices manufactured in our country and Europe.

There are also pressure gauges that measure absolute pressure, that is, gauge pressure + atmospheric

A device that measures atmospheric pressure is called a barometer.

Types of pressure gauges

Depending on the design, the sensitivity of the element, there are liquid, deadweight, deformation pressure gauges (with a tubular spring or a membrane). Manometers are subdivided according to accuracy classes: 0.15; 0.25; 0.4; 0.6; 1.0; 1.5; 2.5; 4.0 (than less number, the more accurate the device).

Types of pressure gauges

According to their purpose, pressure gauges can be divided into technical - general technical, electrical contact, special, self-recording, railway, vibration-resistant (glycerine-filled), ship and reference (exemplary).

General technical: designed to measure liquids, gases and vapors that are not aggressive to copper alloys.

Electrocontact: they have the ability to adjust the measured medium, thanks to the presence of an electrocontact mechanism. EKM 1U can be called a particularly popular device of this group, although it has long been out of production.

Special: oxygen - must be degreased, since sometimes even a slight contamination of the mechanism in contact with pure oxygen can lead to an explosion. They are often produced in blue cases with O2 (oxygen) designation on the dial; acetylene - they are not allowed in the manufacture of the measuring mechanism of copper alloys, since in contact with acetylene there is a danger of the formation of explosive acetylene copper; ammonia-must be corrosion-resistant.

Reference: having a higher accuracy class (0.15; 0.25; 0.4), these instruments are used to verify other pressure gauges. Such devices are installed in most cases on deadweight testers or any other installations capable of developing the required pressure.

Marine pressure gauges are designed for use in river and sea fleets.

Railway: intended for operation on railway transport.

Self-recording: pressure gauges in a case, with a mechanism that allows you to reproduce the graph of the pressure gauge on chart paper.

Thermal conductivity

Thermal conduction pressure gauges are based on the decrease in the thermal conductivity of a gas with pressure. These gauges have a built-in filament that heats up when a current is passed through it. A thermocouple or resistance temperature sensing (DOTS) probe can be used to measure the temperature of the filament. This temperature depends on the speed at which the filament releases heat to the surrounding gas and thus on the thermal conductivity. A Pirani gauge is often used, which uses a single platinum filament at the same time as a heating element and like DOTS. These gauges give accurate readings between 10 and 10-3 mmHg. Art., but they are quite sensitive to chemical composition measured gases.

[edit] Two filaments

One wire coil is used as a heater, while the other is used to measure temperature through convection.

Pirani pressure gauge (one thread)

The Pirani pressure gauge consists of a metal wire exposed to the measured pressure. The wire is heated by the current flowing through it and cooled by the surrounding gas. As the gas pressure decreases, the cooling effect also decreases and the equilibrium temperature of the wire increases. Wire resistance is a function of temperature: by measuring the voltage across the wire and the current flowing through it, the resistance (and thus the gas pressure) can be determined. This type of pressure gauge was first designed by Marcello Pirani.

Thermocouple and thermistor gauges work in a similar way. The difference is that a thermocouple and a thermistor are used to measure the temperature of the filament.

Measuring range: 10-3 - 10 mmHg Art. (roughly 10-1 - 1000 Pa)

Ionization pressure gauge

Ionization gauges are the most sensitive measuring instruments for very low pressures. They measure pressure indirectly by measuring the ions produced when electrons bombard the gas. The lower the density of the gas, the fewer ions will be formed. Ion gauge calibration is unstable and depends on the nature of the gases being measured, which is not always known. They can be calibrated by comparison with McLeod gauge readings, which are significantly more stable and independent of chemistry.

Thermoelectrons collide with gas atoms and generate ions. Ions are attracted to an electrode under a suitable voltage, known as a collector. The collector current is proportional to the ionization rate, which is a function of the system pressure. Thus, measuring the collector current allows the gas pressure to be determined. There are several subtypes of ionization pressure gauges.

Measuring range: 10-10 - 10-3 mmHg Art. (roughly 10-8 - 10-1 Pa)

Most ionic pressure gauges come in two flavors: hot cathode and cold cathode. The third type is a rotating rotor pressure gauge, which is more sensitive and expensive than the first two and is not discussed here. In the case of a hot cathode, an electrically heated filament creates an electron beam. The electrons pass through the gauge and ionize the gas molecules around them. The resulting ions are collected on a negatively charged electrode. The current depends on the number of ions, which in turn depends on the gas pressure. Hot cathode gauges accurately measure pressure in the 10-3 mmHg range. Art. up to 10-10 mm Hg. Art. The principle of the cold cathode pressure gauge is the same, except that electrons are generated in the discharge by the generated high voltage electrical discharge. Cold cathode pressure gauges accurately measure pressure in the 10-2 mmHg range. Art. up to 10-9 mm Hg. Art. The calibration of ionisation gauges is very sensitive to structural geometry, the chemical composition of the measured gases, corrosion and surface spraying. They may not be calibrated properly if turned on at atmospheric and very low pressures. The composition of a vacuum at low pressures is usually unpredictable, so a mass spectrometer must be used simultaneously with an ionization pressure gauge for accurate measurements.

Hot cathode

A Bayard-Alpert hot cathode ionization manometer usually consists of three electrodes operating in triode mode, where the filament is the cathode. The three electrodes are the collector, filament and grid. Collector current is measured in picoamperes with an electrometer. The potential difference between the filament and ground is usually 30 V, while the voltage of the grid at constant voltage is 180-210 volts, if there is no optional electronic bombardment, through the heating of the grid, which can have a high potential of approximately 565 volts. The most common ion pressure gauge is a Bayard-Alpert hot cathode with a small ion collector inside the grid. A glass casing with a hole to the vacuum can surround the electrodes, but it is usually not used and the pressure gauge is built directly into the vacuum device and the contacts are led out through a ceramic plate in the wall of the vacuum device. Hot cathode ionization gauges can be damaged or lose calibration if turned on at atmospheric pressure or even low vacuum. Hot cathode ionization gauge measurements are always logarithmic.

The electrons emitted by the filament move several times in a straight line and reverse direction around the net until they hit it. During these movements, some of the electrons collide with gas molecules and form electron-ion pairs (electron ionization). The number of such ions is proportional to the density of gas molecules multiplied by the thermionic current, and these ions fly to the collector, forming an ion current. Since the density of the gas molecules is proportional to the pressure, the pressure is estimated by measuring the ion current.

The low pressure sensitivity of hot cathode gauges is limited by the photoelectric effect. Electrons hitting the grid produce X-rays, which generate photoelectric noise in the ion collector. This limits the range of older hot cathode gauges to 10-8 mmHg. Art. and Bayard-Alpert to approximately 10-10 mm Hg. Art. Additional wires at cathode potential in the line of sight between the ion collector and the grid prevent this effect. In the extraction type, ions are attracted not by a wire, but by an open cone. Since the ions cannot decide which part of the cone to hit, they pass through the hole and form an ion beam. This ion beam can be transferred to the Faraday cup.

Very often in life, and especially in production, one has to deal with such a measuring device as a manometer.

A pressure gauge is an instrument for measuring gauge pressure. Due to the fact that this value can be different, devices also have varieties. There are many areas of application for these devices. They can be used in the metallurgical industry, in any mechanical transport, housing and communal services, agriculture, automotive and other industries.

Types and design of the device

Depending on the purpose for which the devices are used, they are divided into different types... The most common are spring pressure gauges. They have their own advantages:

• Measurement of a quantity in a wide range.
• Good technical characteristics.
• Reliability.
• Simplicity of the device.

In a spring-loaded pressure gauge, the sensing element is a hollow curved tube inside. It can have a cross-section in the form of an oval or an ellipsoid. This tube deforms under pressure... It is sealed on one side, and on the other there is a fitting, with which the value in the medium is measured. The end of the tube, which is sealed, is connected to the transmission mechanism.

The design of the device is as follows:

• Frame.
• Arrows of the device.
• Gears.
• Leash.
• Serrated sector.

A special spring is installed between the teeth of the sector and the gear, which is necessary in order to eliminate backlash.

The measuring scale is presented in Bars or Pascals. The arrow indicates overpressure the environment in which the measurement is carried out.

The principle of operation is very simple. The pressure from the measured medium flows into the tube. Under its influence, the tube tries to align itself, since the area of ​​the outer and inner surfaces has different sizes. The free end of the tube makes a movement, while the arrow turns through a certain angle due to the transmission mechanism. The measured value and the deformation of the tube are in a linear relationship. That is why the value shown by the arrow is the pressure of a certain environment.

Varieties of systems for measuring pressure

There are many different pressure gauges for measuring low and high pressure... But their technical characteristics are different. The main distinguishing parameter is the accuracy class. The pressure gauge will show more accurate if the value is less. The most accurate are digital devices.

According to their purpose, manometers are of the following types:

According to the principle of work, the following types are distinguished:

Liquid measurement systems

The value in these gauges is measured by balancing the weight of the liquid column. The measure of pressure is the level of fluid in communicating vessels. These devices can measure the value within the range of 10-105 Pa. They have found their application in the laboratory.

In essence, it is a U-shaped tube containing a liquid with a higher specific gravity compared to the liquid in which the hydrostatic pressure is directly measured. This liquid is most often mercury.

This category includes working and general technical devices such as TV-510, TM-510. This category is the most in demand. They are used to measure the pressure of non-aggressive and non-crystallizing gases and vapors. Accuracy class of these devices: 1, 1.5, 2.5. They have found their application in industrial processes, in the transportation of liquids, in water supply systems and in boiler rooms.

Electrical contact devices

This category includes pressure gauges and vacuum gauges. They are intended for measuring the value of gases and liquids, which are neutral in relation to brass and steel. The design in them is the same as in the spring ones. The only difference is in large geometric dimensions... Due to the arrangement of contact groups, the body of the electrical contact device is large. This device can act on pressure in a controlled environment by opening / closing the contacts.

Thanks to the used electrical contact mechanism, this device can be used in an alarm system.

Exemplary meters

This device is intended for testing pressure gauges that measure the value in laboratory conditions. Their main purpose is to check the serviceability of these working pressure gauges. A distinctive feature is a very high accuracy class. It is achieved thanks to design features and a gearing in the transmission mechanism.

These devices are used in various industrial sectors to measure the pressure of gases such as acetylene, oxygen, hydrogen, ammonia and others. Basically, only one type of gas can be used to measure pressure with a special pressure gauge. Each device indicates the gas for which it is intended. The device is also painted in the color of the gas for which it can be used. Written and initial gas.

There are also vibration-resistant special pressure gauges that are capable of working with strong vibrations and high pulsating pressure. environment... If you use a conventional pressure gauge in such conditions, then it will quickly break down, as the transmission mechanism will fail. The main criterion for such devices is the corrosion-resistant steel of the body and the tightness.

Ammonia systems must be corrosion resistant. Copper alloys are not allowed in the manufacture of the acetylene measuring mechanism. This is due to the fact that upon contact with acetylene there is a risk of formation of acetylene explosive copper. Oxygen mechanisms must be fat free. This is due to the fact that in some cases even a slight contact of pure oxygen and a contaminated mechanism can cause an explosion.

Recorders

A distinctive feature of such devices is that they are able to record the measured pressure on a diagram, which will allow you to see changes in certain time... They have found their application in the industry with non-aggressive agents and energy.

Ship and rail

Marine pressure gauges are designed to measure the vacuum pressure of liquids (water, diesel fuel, oil), steam and gas. Their distinctive features are high moisture protection, resistance to vibrations and climatic influences. They are used in river and sea transport.

Railway, unlike conventional pressure gauges, do not show pressure, but convert it into a signal of another type (pneumatic, digital and others). Various methods are used for these purposes.

Such converters are actively used in automation systems, control technological processes... But despite their purpose, they are actively used in industries nuclear power, chemical and oil production.

Types of measuring instruments

Pressure measuring instruments are divided into the following types:

Most of the imported and domestic pressure gauges are manufactured according to all generally accepted standards. It is for this reason that it is possible to replace one brand with another.

When choosing a device, you must rely on the following indicators:

• The location of the choke is axial or radial.
• Connection thread diameter.
• Accuracy class of the device.
• Case diameter.
• Measured value limit.

Ionization pressure gauge

Ionization pressure gauges are the most sensitive measuring instruments for very low pressures. They measure indirectly by measuring those ions that are formed when electrons bombard gases. The lower the density of the gas, the less ions will be formed. The calibration of the ionization gauge is unstable. It depends on the nature of the gas being measured. And this nature is not always known. They can be calibrated by comparison with the values ​​of the McLeod gauge, which are independent of chemistry and more stable.

Thermoelectrodes with gas atoms strike and regenerate the ions. They are attracted to the electrode at a voltage that is suitable for them (this suitable voltage is called a collector). In the collector, the current is proportional to the ionization rate, which in the system is a function of pressure. This is how the gas pressure can be determined by measuring the collector current.

Most ionic pressure gauges are classified into three types:

Ion gauge calibration is very sensitive to the chemical composition of the measured gases, construction geometry, surface spraying and corrosion. They may become unsuitable for calibration when turned on in a very low or atmospheric pressure environment.

It is necessary to measure pressure in many industrial sectors, but different devices are used for this. But regardless of this, this value is not determined by anything other than a manometer.

In this article we will try to consider in detail all the issues related to pressure gauges, their choice and their operation. Also, together with manometers, we will consider vacuum gauges and manovacuum meters. All recommendations for these devices are the same, so in the text we will only mention pressure gauges.

1. What is a pressure gauge, vacuum gauge and manovacuum gauge?
2. What are the types of pressure gauges?
3. What parameters are important when choosing a pressure gauge?
4. Conversion of pressure units of manometers.
5. How to install pressure gauges?
6. How to use the pressure gauges?
7. How is the calibration of pressure gauges carried out?
8. What is the best pressure gauge to buy?
9. What is important to pay attention to when buying a pressure gauge?

1. What is a pressure gauge, vacuum gauge and manovacuum gauge?

Technical manometer.

A pressure gauge is a device designed to measure the excess pressure of a working medium by deforming a tubular spring (Bourdon tube).

Technical vacuum gauge.

A vacuum gauge is a device designed to measure the vacuum of a working medium by deforming a tubular spring. The standard scale for a vacuum gauge is from -1..0 atm. The scale on the vacuum gauge is always negative, since the pressure is measured below atmospheric.

Technical manovacuum meter.

A pressure gauge is a device designed to measure excess pressure and discharge of a working medium by deforming a tubular spring.

The above is simple:
- if there is only positive pressure on the scale of the device, then this is a manometer.
- if there is only negative pressure on the scale of the device, then this is a vacuum gauge.
- if there is both negative and positive pressure on the scale of the device, then it is a manovacuum meter.

In industry and housing and communal services, the most common are pressure gauges with a Bourdon tubular spring. This is due to the simplicity of design and relatively low cost.

Manometer "from the inside".

2. What are the types of pressure gauges?

Technical manometers are the most common instruments for measuring the pressure of water, air, gases, which are widely used in the housing and utilities sector and industry. If you do not have any specific requirements for the device, then you should definitely consider technical pressure gauges.

Technical manometer TM610R.

Boiler manometers are technical manometers with a body diameter of 250mm. These gauges are used when installed at a high altitude or in hard-to-reach places, which allows you to take readings from the device from a long distance.

Boiler pressure gauge TM810R.

Vibration-resistant pressure gauges are devices for measuring pressure in conditions of increased vibration on a pipeline or installation. These devices are massively used in pumping stations, compressors, cars, ships and trains.

Vibration-resistant TM-320R manometer.

Corrosion-resistant pressure gauges - instruments made entirely of of stainless steel and designed to work with aggressive media.

Corrosion-resistant TM621R manometer.

Welding manometers - devices designed to control pressure on oxygen and acetylene reducers, propane cylinders Welding manometers are oxygen (body color blue), acetylene (body color white or gray) and propane (body color red). On the dial of each instrument, the type of medium is indicated in a circle.

Precise measurement manometers (exemplary manometers) - devices with a low accuracy class of 0.6 or 0.4 are used for pressure testing of gas pipelines, checking technical manometers, as well as for measuring pressure technological lines requiring increased measurement accuracy.

An exemplary pressure gauge.

Ammonia manometers are devices for measuring pressure in refrigeration systems. These instruments are manufactured on the basis of corrosion-resistant pressure gauges with a modified dial.

Ammonia manovacuum meter.

Automotive pressure gauges - devices for measuring the air pressure in tires. These devices can be purchased at auto shops or service centers.

Digital electronic pressure gauges are of two types: in a monoblock case and a set of pressure transducers and an electronic unit for indicating and regulating parameters. These devices are used for accurate pressure measurement and in process automation systems.

Electrical contact pressure gauges are technical pressure gauges with an electrical contact attachment intended for switching contacts in automation systems.

The fundamental difference between these devices from the whole variety of pressure gauges is the presence of the pressure gauge performance parameter. Today these devices are available in six versions.

3. What parameters are important when choosing a pressure gauge?

In this section, we will go over all the parameters that need to be considered when purchasing a pressure gauge. This is very helpful information for buyers who do not have an exact brand of the device or have a brand, but these devices cannot be bought and they need to correctly select analogs.

The measuring range is the most important parameter.
Standard pressure range for gauges:
0-1, 0-1.6, 0-2.5, 0-4, 0-6, 0-10, 0-16, 0-25, 0-40, 0-60, 0-100, 0-160, 0- 250, 0-400, 0-600, 0-1000 kgf / cm2 = bar = atm = 0.1MPa = 100kPa

Standard pressure range for manovacuum meters:
-1 .. + 0.6, -1 .. + 1.5, -1 .. + 3, -1 .. + 5, -1 .. + 9, -1 .. + 15, -1 .. + 24 kgf / cm2 = bar = atm = 0.1MPa = 100kPa

Standard range of vacuum gauge pressures:
-1..0 kgf / cm2 = bar = atm = 0.1MPa = 100kPa.

If you do not know which scale to buy, then the choice of the range is quite simple, the main thing is that the working pressure falls within the range from 1/3 to 2/3 of the measurement scale. For example, in your pipe there is usually a water pressure of 5.5 atm. For stable operation, you need to choose a device with a scale of 0-10 atm, because the pressure of 5.5 atm falls in the range from 1/3 to 2/3 of the scale of 3.3 atm and 6.6 atm, respectively. Many people ask the question - what happens if the working pressure is less than 1/3 of the scale or more than 2/3 of the scale of measurement? If the measured pressure is less than 1/3 of the scale, then the pressure measurement error will sharply increase. If the measured pressure is more than 2/3 of the scale, then the device mechanism will operate in overload mode and may fail before the warranty period.

Accuracy class is the permissible percentage of measurement error from the measurement scale.
Standard range of accuracy classes for pressure gauges: 4, 2.5, 1.5, 1, 0.6, 0.4, 0.25, 0.15.
How to calculate the manometer error yourself? Let's say you have a 10 atm pressure gauge with an accuracy class of 1.5.
This means that the permissible error of the manometer is 1.5% of the measurement scale, i.e. 0.15 atm. If the error of the device is greater, then the device must be changed. It is unrealistic to understand a working device without special equipment or not, according to our experience.
Only an organization that has a calibration facility with a reference pressure gauge with an accuracy class four times less than the accuracy class of the problem pressure gauge can make a decision on the discrepancy between the accuracy class. The two gauges are installed in line with the pressure and the two readings are compared.

The gauge diameter is an important parameter for round case gauges. Standard range of diameters for pressure gauges: 40, 50, 63, 80, 100, 150, 160, 250 mm.

Location of the nozzle - there are two types: radial in which the nozzle comes out of the pressure gauge from below and end (rear, axial) in which the connecting neck is located at the rear of the device.

Connecting thread - the most widespread on manometers are two threads: metric and pipe. Standard range of manometer threads: M10x1, M12x1.5, M20x1.5, G1 / 8, G1 / 4, G1 / 2. Almost all imported pressure gauges use pipe thread... Metric thread is used mainly on domestic appliances.

Calibration interval is the period when it is necessary to recheck the device. All new devices come with initial factory verification, which is confirmed by the presence of the verifier's stamp on the dial of the device and the corresponding mark in the passport. On the this moment initial verification is for 1 year or 2 years. If the pressure gauge is used for personal purposes and verification is not critical, then choose any device. If the pressure gauge is installed at a departmental facility (heat point, boiler house, plant, etc.), then after the end of the initial verification period, it is necessary to recheck the pressure gauge at the CSM (center for standardization and metrology) of your city or in any organization that has a license for verification. and necessary equipment... For those who are constantly faced with the verification of pressure gauges, it is no secret that very often rechecking is more expensive or comparable to the cost of a new device, as well as putting the device into verification costs money even if the device does not pass the rechecking and repair of the device with subsequent verification may be added to the price ...
Based on this, we have two recommendations:
- buy devices with initial verification for 2 years, because saving 50-100 rubles on the purchase of a device with a verification period of 1 year can lead to expenses of 200-300 rubles in a year and to unnecessary "running around".
- before deciding to recheck devices, calculate the costs of rechecking - in most cases it is much more profitable to buy new devices. What you need to calculate is the cost of the verification, several trips to the verifier. If there is water hammer in the system, pulsation of the medium ( proximity pumps), the vibration of the pipeline, then after 2 years of operation, usually 50% of the devices do not pass the recheck, but you have to pay for it, since the verification work was carried out.

Operating conditions - if the device will operate in a viscous or aggressive environment, as well as when using the device in difficult conditions - vibration, pulsation, high (more than + 100C) and low temperatures (less than -40C), then it is necessary to choose a specialized pressure gauge.

4. Conversion of pressure units of manometers.

When buying a pressure gauge, it is often necessary to measure pressure in non-standard units. Our work experience says that if we are talking about a small number of devices (less than 100 pieces), then the factories will not alter anything on their scales and will have to translate the units of measurement on their own.

1kgf / cm2 = 10.000kgf / m2 = 1bar = 1atm = 0.1MPa = 100kPa = 100.000Pa = 10.000mm.WC = 750mm. rt. st. = 1000mBar

5. How to install pressure gauges?

Three-way taps and needle valves are used to install the pressure gauge on the pipe. Damping blocks, loop sampling devices and diaphragm seals are used to protect the pressure gauges.

A three-way valve for a pressure gauge is a three-way ball or plug valve designed to connect a pressure gauge to a pipeline or any other equipment. It is allowed to install a two-way valve with the ability to manually release pressure from the pressure gauge when it is turned off. The use of standard ball valves is not recommended, since after closing the valve, the pressure gauge mechanism is under residual pressure of the medium, which can lead to its premature exit from standing. Today it is the most common type for connecting pressure gauges at pressures up to 25 kgf / cm2. For high pressures, the installation of needle valves is recommended. When purchasing a three-way valve, make sure that the thread on the pressure gauge matches the thread on the valve.

The needle valve is a control valve with the ability to smoothly supply the working medium, in which the shut-off element is made in the form of a cone. Needle valves are widely used to connect various instrumentation and control devices to equipment with high pressures. When purchasing needle valves, make sure that the threads on the pressure gauge match the threads on the valve.

The damper block is a protective device that is installed in front of the pressure gauge and is designed to dampen the pulsations of the working medium. Under the ripple in in this case means a sharp and frequent change in the pressure of the working medium. The main "organizers" of pulsations in the pipeline are powerful pumps without devices smooth start and the ubiquitous installation of ball valves and butterfly valves, the rapid opening of which leads to water hammer.

Damper block.

Loop sampling devices (Perkins tube) are steel tubes that are designed to dampen the temperature in front of the pressure gauges. The decrease in the temperature of the medium entering the manometer occurs due to the "stagnation" of the medium in the loop. These devices are recommended to be installed at a working environment temperature of more than 80C. There are two types of selection devices: straight and angled. Straight sampling devices are installed on horizontal sections of pipelines, and corner ones are designed for installation on vertical pipelines. Please make sure the threads on the tube match the threads on the 3-way valve or pressure gauge before purchasing.

Selective devices (straight and angled).

Diaphragm seals are a protective device for a pressure gauge designed to protect the device mechanism from the ingress of aggressive, crystallizing and abrasive media into it. When choosing a diaphragm seal, pay attention to the coincidence of the threads on the pressure gauge and the seal.

Diaphragm separator RM.

When installing pressure gauges, there are several requirements that must be met:
- assembly work with a pressure gauge, it must be done when there is no pressure in the pipeline
- the pressure gauge is installed with vertical arrangement dial
- the rotation of the pressure gauge is carried out by the choke using wrench
- it is forbidden to apply force to the pressure gauge body

6. How to use the pressure gauges?

When operating pressure gauges, it is necessary to observe the recommendations and physical parameters (medium temperature and permissible pressure) prescribed in the instrument's passport. The most important requirement for operation is a smooth supply of pressure to the manometer. If the device is selected correctly and is operated without disturbances, then problems usually do not happen.
Consider the cases in which the operation of the pressure gauge is not allowed:
- when pressure is applied to the device, the arrow does not move
- the instrument glass is damaged or broken
- the arrow of the device moves in jumps
- after the pressure is released from the device, the arrow does not return to zero
- the measurement error exceeds the permissible value

7. How is the calibration of pressure gauges carried out?

The manometer is a pressure measuring instrument and is subject to mandatory verification. Calibration of pressure gauges can be roughly divided into two types:
- initial verification is a verification that is carried out by the manufacturer before the sale of the device and is confirmed by the presence of the verifier's mark on the glass or the case of the manometer, as well as by a corresponding mark in the device's passport. Initial verification without any problems is recognized by the regulatory organizations and the device can be operated until the end of this period.

Re-calibration of a pressure gauge is a verification of the device, which is carried out after the end of the initial verification of the pressure gauge. Before rechecking the pressure gauge, you need to make sure that the device is in good working order, because in the event of a device malfunction, you will receive a nice notification for money comparable to the cost of the device that the device is not working properly and needs to be repaired or discarded. The manometer is recalibrated at the Center for Standardization and Metrology in your city or in any organization that has a calibration license and the necessary equipment.

8. What is the best pressure gauge to buy?

To date, there are about 10 Russian manufacturers devices, 2 Belarusian manufacturers and a myriad of foreign instrument manufacturers. Consider the features of each device.

Russian factories are the most optimal choice for the purchase of pressure gauges. Many will ask - why? Everything is quite simple - Russian pressure gauges are significantly cheaper than imported ones with comparable quality, the initial calibration period is 2 years, unlike Belarusian ones, the entire line of instruments is produced, from technical to corrosion-resistant.

Belarusian factories are quite cheap devices, but they have 3 significant drawbacks:
- initial verification for 1 year, which turns their cheapness into a "myth" and "running around" with rechecking.
- a simplified mechanism that does not work for a long time under severe loads.
- plastic glass instead of instrument glass also introduces difficulties in the operation and reliability of the device.

Foreign pressure gauges - our many years of experience in trading devices shows that the point in buying is similar to purchasing a Russian device, but only 2-3 times more expensive. All the explanations of the sellers of foreign devices about the unique quality, super technologies, etc. are a common trick to explain to the client why he is overpaying so steeply. If the operating conditions are difficult, you just need to buy a specialized device instead of a technical one and it will work without problems. If you are plagued by doubts and you have the opportunity to disassemble two similar Russian and imported pressure gauges using a screwdriver, then you are unlikely to be lucky to find a few differences.

The exception is highly specialized devices with non-standard scales and parameters that are not produced in Russia.

9. What is important to pay attention to when buying a pressure gauge?

- the pressure gauge must be new. Many sellers of devices understand by the word new that the pressure gauge was not in operation. But the pressure gauge may be 15 years old, and you will be told that it is new. Check the year of manufacture of the device, or you may be in for an unpleasant surprise in the form of a purchase of illiquid assets.
- on the pressure gauge or in the passport there must be a mark on the initial verification. There are sellers of illiquid assets who wipe out the brand of the believer so that they cannot be accused of selling old devices.
- calibration on a pressure gauge should be 2 years, if you buy a device with an initial calibration for 1 year - after a year the savings will disappear and unnecessary complications will begin.
- the pressure gauge must have a passport and a valid certificate for measuring instruments.
- if the device is new and verified for 2 years, choose the cheapest option.
- pay attention to the measuring range, scale diameter, type of fitting location, type of thread and design of the device - if you buy the wrong device, then replacing it can be difficult, because if the device has non-standard parameters and is made for you, then most likely you will have to keep it as a souvenir.
- you can search for reviews of pressure gauges on the Internet, but most of of them are custom-made and it is better to rely on the advice of people who have experience in the actual operation of devices.
- it is worth buying pressure gauges from an organization that inspires your confidence, since the sale of illiquid assets from the times of the USSR still exists and then it will be quite difficult to return old devices or exchange them for normal devices.

In this article, we tried to consider the most popular questions about the entire variety of pressure gauges. If you want other questions to be considered or you do not agree with any answers - write to us and we will try to expand the article based on your experience. In the letter, do not forget to indicate your data, place, conditions and region of installation.

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