A reliable pressure gauge is a guarantor of trouble-free operation of the system, regardless of whether it is a water supply system, a gas pipeline, a heating system or a closed cycle of any production. There are different types such devices, and in this article we will dwell on them in detail.

1. Atmospheric. This is when the atmosphere affects the surface of the earth, as well as everything on it. A healthy person does not feel it, since it is usually compensated by the internal pressure of the body.
2. The water in the tap may be overpressured. Hence the rule - it occurs in a confined space in various environments.
3. The absolute arises from the interaction of the first and second types pressure, that is, it is the sum of atmospheric and excess pressure.

A pressure gauge is a device that measures the second type of pressure (excess) in various systems.

Device selection

Today's industry uses different types of pressure gauges. To make the right purchase of a measuring device, which will be suitable in all respects for solving production processes, you need to know:

• Pressure gauge type.
• Operating pressure measurement range.
• Its accuracy class.
• Its installation environment.
• Case dimensions.
• Functional load of the device.
• Where it will be installed, as well as the thread size of the fitting.
• Operating conditions.

If you follow the above list, then you can choose optimal device, since all manufacturers of pressure gauges adhere to established standards. Therefore, devices from different companies are essentially interchangeable.

Types of pressure gauges

Modern instrument making offers several types of devices, which are pressure meters in different ranges:

To make the correct choice of device according to the permissible pressure range, you should know the working pressure values technological process , for which the purchase of a measuring device is made. Don't make a mistake with the plus and minus signs and add 30% to the work rate.

The measuring device is selected taking into account the operating conditions and environment. It will be special pressure gauge for working with air, water, steam, oxygen, ammonia, acetone or gas. The environment can be different, including aggressive, so the materials of the devices are designed for such operating conditions. The parameters of the housing, in particular, strength, diameter, are taken into account when choosing if it is to be operated in conditions of vibration or high humidity to prevent damage to the housing from corrosion or mechanical stress.

Functional load

The pressure measuring device is selected depending on the needs production process, it must be suitable for the functions and operating conditions. Pressure gauges are divided into the following types functional load:

The purpose is indicated by the type of device housing, it can be:

• Vibration resistant.
• explosion-proof.
• Corrosion resistant.

Pressure gauges are used in boiler systems, ship and railway equipment. There is a group of devices capable used in the food industry production. The body material of the measuring device allows it to meet the service conditions.

Pressure gauge installation

Before installation, be sure to know the cases when measuring instruments should not be used:

The device is installed in a visible place so that any employee can see its readings. The pressure gauge is mounted on the pipeline between shut-off valves and a vessel.

The body must have a diameter of at least 10 centimeters, at least 16 centimeters at a height of 2-3 meters. Pressure gauges that are used for measuring gas pressure, have different colors buildings. For example, if the body of the device is blue, then this means you have a device for measuring oxygen pressure, yellow indicates the purpose of working with ammonia, red is used for flammable gases, black is for non-flammable gases, white is intended for acetylene.

It is extremely important to install a mechanism in front of the pressure gauge that will turn it off and ventilate it, for example, it could be a three-way valve. Also installation of a siphon tube is required, its diameter should be at least one centimeter. After the device is installed, you need to put a red line on the pressure gauge scale; it will indicate the operating pressure.

So, the accuracy with which the device measures pressure depends on its the right choice and installation, as well as operating conditions. When to make a choice take into account the physical and chemical properties of the measured medium and the required measurement accuracy. It is rational to use membranes to measure viscous liquids, since tubular ones make it difficult to transmit pressure due to thin tubes. To measure gas media containing aggressive gases, such as sulfur dioxide, protected instruments are used. They are equipped with a special housing with a color characteristic of each gas, and also have markings on the device scale.

Devices for pressure measurements can be classified according to the following characteristics:

type of pressure being measured;

operating principle;

purpose;

accuracy class.

By mind measured pressure devices are divided into the following:

pressure gauges;

vacuum gauges;

pressure and vacuum gauges;

pressure meters;

draft meters;

thrust gauges;

differential pressure gauges;

micromanometers;

barometers.

According to GOST 8.271-77 pressure gauge is a measuring device or measuring installation for measuring pressure or pressure difference.

To measure absolute pressure, i.e. Absolute pressure gauges are produced that are read from absolute zero; to measure excess - excess pressure gauges, and most often “by default” these types of devices are called pressure gauges.

Most manufactured pressure gauges are used to measure overpressure. Their distinctive feature is the “zero” reading of the device when the sensing element is exposed to atmospheric pressure.

The pressure of rarefied gas is measured using vacuum gauges. Accordingly, a vacuum gauge is a pressure gauge for measuring the pressure of a rarefied gas.

A pressure gauge that has the ability to measure rarefied gas pressure and excess pressure (the device has a single scale) is called a pressure-vacuum gauge.

Measurement of small values ​​(up to 40 kPa) of excess pressure is carried out by pressure meters, although such a name, as well as such a division according to the type of pressure measured (for small values), is absent abroad. Traction meters are used to measure low (up to -40 kPa) vacuum pressure. Devices that have part of the vacuum scale and part of the excess pressure within ±20 kPa are called draft pressure meters. European standards (EN837-1, EN837-2 and EN837-3) make this division according to the type of sensing element: tubular (Bourdon tube - Rohrfedern), membrane - membrane box - capsule (Diaphragm - Plattenfeder or Capsule - Kar-selfeder).

Devices designed to measure the pressure difference at two arbitrary points are called differential pressure gauges (differential pressure gauges). Moreover, this name is more applicable to indicating instruments. A device for measuring differential pressure with a unified output signal is called a differential pressure transducer.

A differential pressure gauge that functionally provides measurement of small values ​​of the difference between two pressures and has an upper measurement limit of no more than 40 kPa (4000 kgf/m) is called a micromanometer.

Atmospheric pressure is monitored and measured using barometers.

In the future, to simplify the presentation of the material in unimportant moments, pressure gauges, vacuum gauges, pressure and vacuum gauges, pressure gauges, draft gauges, draft pressure gauges are combined under the name pressure gauges or pressure gauge instruments.

By operating principle The main group of instruments for measuring pressure can be divided into the following:

liquid;

deformation (spring);

deadweight piston;

electrical, etc.

Liquid pressure gauges include pressure gauges whose operating principle is based on balancing the measured pressure or pressure difference with the pressure of a liquid column. These pressure gauges include U-shaped pressure gauges, which consist of communicating vessels in which the measured pressure is determined from one or more liquid levels.

In deformation pressure gauges, the degree of deformation of the sensing element or the force developed by it depends on the measured pressure. The deformation gauge includes a tubular-spring pressure gauge, in which the sensitive element is a tubular spring. Bellows operates on the basis of a bellows, membrane - on the basis of a membrane or membrane box.

A pressure gauge with a flaccid membrane, in which the measured pressure is perceived by a flaccid membrane and is converted into a force balanced by an additional device, also belongs to the deformation type.

In deadweight devices, which in most cases have liquid as a working fluid and are often called liquid ones, the measured pressure is balanced by the pressure created by the mass of the piston with the load receptor and the mass of the loads, taking into account the forces of liquid friction.

Electric pressure gauges operate on the principle that one of the electrical parameters of the sensitive element of the primary transducer depends on pressure.

According to their purpose, pressure gauges are divided into the following:

general industrial, also called general technical or working;

reference, including state primary, working and other standards.

General industrial pressure gauges are designed to measure pressure directly during production processes at operating points of industrial equipment.

Reference instruments are used to store and transmit the size of pressure units for the purpose of uniformity, reliability and high accuracy of its measurements.

In order to streamline domestic metrological terminology and bring it closer to the international one, in our country the term exemplary measuring instrument has been replaced by the term working standard. Working standards are divided into categories (1, 2, 3rd), as was customary for standard products.

In industry, there are control pressure gauges that are used to monitor the correct readings of technical pressure gauges at their installation sites. The term “control” is specific to industrial conditions and has no place in current legal metrology, but was widely used in the past. Instead, the term “high precision pressure gauges” is now used.

According to their protection from environmental influences, devices, according to GOST 12997-84, are divided into the following versions: ordinary; protected from the penetration of solid bodies (dust) into the product; protected from water getting inside the product; protected from aggressive environments; explosion-proof; protected from other external influences. Several types of protection can be combined in one product.

Manufactured devices must be resistant and (or) durable to the effects of ambient temperature and humidity in the parameter ranges specified in table.

The devices must be resistant and (or) durable to the effects of high-frequency sinusoidal vibrations with parameters selected by design group from the table.

General technical pressure gauges are designed to be resistant to vibrations with a frequency of 10-55 Hz and a displacement amplitude of up to 0.15 mm.

The codification system for protecting devices from the ingress of solids (dust) into the product, as well as water, is established by GOST 14254-96. For such codification the designation “IP” is used.

We bring to your attention following types pressure gauges:

• Ship's pressure gauges
• Railway pressure gauges
• Digital pressure gauges

Pressure gauges are special devices, used to measure pressure in gas, steam and liquid media. Since there are many types of such equipment, before deciding on the device you need, clearly define your criteria. To make your task easier and speed up the process of purchasing a pressure gauge in St. Petersburg, contact our representative and get a free consultation. Our specialists will help you choose the device that is ideal in all respects to ensure the safe operation of your system.

Classification of pressure gauges

To quickly understand this group of products, you need to understand how one model differs from another. There are several signs by which types of pressure gauges are distinguished:

• Type of pressure measured;
• Operating principle;
• Purpose;
• Accuracy class.

Types of pressure gauges by type of measured pressure

1. Pressure meters - used to measure small excess pressure up to 40 kPa.
2. Pressure gauges - used to determine excess pressure in the range of 0.06-1000 MPa.
3. Vacuum gauges - the main purpose of these devices is to measure the volume of pressure discharge.
4. Traction meters - suitable for measuring pressure discharge with a limit value of up to -40 kPa.
5. Pressure and vacuum gauges - suitable for measuring vacuum and excess pressure in the range of 60-240,000 kPa.

Types of pressure gauges by operating principle

1. Liquid. Standard version of pressure gauges.
2. Deadweight piston. Models of this type differ high accuracy data.
3. Spring pressure gauges. They have several modifications, depending on the type of spring - box, plate, pipe. This group also includes differential devices.

Types of pressure gauges by accuracy class

The accuracy class has a digital value - from 0.15 to 4.0. The quality of measurement accuracy is determined in reverse order - the most low rate marking indicates that the device has maximum accuracy, the highest indicates that errors are allowed within the designated limits.

Types of pressure gauges by purpose

To simplify the selection process suitable device, manufacturers immediately label pressure gauges according to their recommended purpose. There are both devices for general technical use and special ones. The complete list includes the following groups of pressure gauges:

1. General technical.
2. Electric contact.
3. Oxygen.
4. Reference.
5. Railway.
6. Ship's.
7. Self-recording.

Additionally, separate groups of pressure gauges can be distinguished according to the degree of their resistance to specific adverse effects, for example, corrosion-resistant, vibration-resistant.

Operating principle

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 in a holder, and the other is connected through a rod to a tribic-sector mechanism that converts the linear movement of the elastic sensing element into a circular movement of the indicating arrow.

Varieties

The group of instruments measuring excess pressure includes:

Pressure gauges - instruments with measurements from 0.06 to 1000 MPa (Measure excess pressure - the positive difference between absolute and barometric pressure)

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

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

Pressure meters - pressure gauges for small excess pressures up to 40 kPa

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

Thrust pressure and vacuum gauges with extreme limits not exceeding ±20 kPa

Data are given in accordance with GOST 2405-88

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

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

A device that measures atmospheric pressure is called a barometer.

Types of pressure gauges

Depending on the design and sensitivity of the element, there are liquid, deadweight, and deformation pressure gauges (with a tubular spring or membrane). Pressure gauges are divided into accuracy classes: 0.15; 0.25; 0.4; 0.6; 1.0; 1.5; 2.5; 4.0 (the lower the number, the more accurate the device).

Types of pressure gauges

By purpose, pressure gauges can be divided into technical - general technical, electrical contact, special, self-recording, railway, vibration-resistant (glycerin-filled), ship and reference (model).

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

Electric contact: have the ability to adjust the measured medium, due to the presence of an electric contact mechanism. A particularly popular device in this group can be called EKM 1U, although it has long been discontinued.

Special: oxygen - must be degreased, since sometimes even slight contamination of the mechanism in contact with pure oxygen can lead to an explosion. Often available in cases blue color with the designation on the dial O2 (oxygen); acetylene - copper alloys are not allowed in the manufacture of the measuring mechanism, since upon 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 devices are used for checking other pressure gauges. In most cases, such devices are installed on deadweight piston pressure gauges or some other installations capable of developing the required pressure.

Ship pressure gauges are intended for use in river and marine fleets.

Railway: intended for use in railway transport.

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

Thermal conductivity

Thermal conductivity gauges are based on the decrease in thermal conductivity of a gas with pressure. These pressure gauges have a built-in filament that heats up when current is passed through it. A thermocouple or resistive temperature sensor (DOTS) can be used to measure the temperature of the filament. This temperature depends on the rate at which the filament transfers heat to the surrounding gas and thus on thermal conductivity. A Pirani gauge is often used, which uses a single platinum filament at the same time as heating element and like DOTS. These pressure 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 pressure being measured. 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. The resistance of a wire 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 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 pressure gauges are the most sensitive measuring instruments for very low pressures. They measure pressure indirectly by measuring the ions produced when a gas is bombarded with electrons. The lower the gas density, the fewer ions will be formed. Calibration of an ion pressure gauge is unstable and depends on the nature of the measured gases, which is not always known. They can be calibrated by comparison with the McLeod pressure gauge readings, which are much more stable and independent of chemistry.

Thermionic electrons collide with gas atoms and generate ions. The ions are attracted to the electrode at a suitable voltage, known as a collector. The collector current is proportional to the ionization rate, which is a function of system pressure. Thus, measuring the collector current allows one to determine the gas pressure. There are several subtypes of ionization pressure gauges.

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

Most ion gauges come in two types: hot cathode and cold cathode. The third type, a pressure gauge with a rotating rotor, 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 pressure gauge and ionize the gas molecules around them. The resulting ions collect on the negatively charged electrode. The current depends on the number of ions, which in turn depends on the gas pressure. Hot cathode pressure gauges accurately measure pressure in the range of 10−3 mmHg. Art. up to 10−10 mm Hg. Art. The principle of a cold cathode pressure gauge is the same, except that electrons are produced in a discharge created by a high-voltage electrical discharge. Cold cathode pressure gauges accurately measure pressure in the range of 10−2 mmHg. Art. up to 10−9 mm Hg. Art. Calibration of ionization pressure gauges is very sensitive to structural geometry, chemical composition of the measured gases, corrosion and surface deposits. Their calibration may become unusable when turned on at atmospheric and very low pressure. The composition of vacuum at low pressures is usually unpredictable, so a mass spectrometer must be used in conjunction with an ionization pressure gauge for accurate measurements.

Hot cathode

A Bayard-Alpert hot cathode ionization gauge typically consists of three electrodes operating in triode mode, with the filament being the cathode. The three electrodes are the collector, filament and grid. The collector current is measured in picoamps by an electrometer. The potential difference between the filament and ground is typically 30 volts, while the grid voltage under constant voltage is 180-210 volts unless there is optional electronic bombardment through grid heating, which can have a high potential of approximately 565 volts. The most common ion 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 usually it is not used and the pressure gauge is built directly into the vacuum device and the contacts are routed through a ceramic plate in the wall of the vacuum device. Hot cathode ionization gauges may be damaged or lose calibration if they are turned on when atmospheric pressure or even at low vacuum. The measurements of hot cathode ionization pressure gauges are always logarithmic.

The electrons emitted by the filament move several times in forward and reverse directions around the grid until they hit it. During these movements, some 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 gas molecules is proportional to pressure, pressure is estimated by measuring the ion current.

The low pressure sensitivity of hot cathode pressure gauges is limited by the photoelectric effect. Electrons striking the grid produce X-rays, which produce 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, the 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 transmitted to a Faraday cup.

When designing and operating heating systems, the most important indicator and the parameter is the coolant pressure. At normal pressure, which is within the hydraulic graph, the work process proceeds without disruption, the coolant reaches the most remote points of the heating system. If the pressure exceeds the critical point, there is a danger 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 pressure levels at the required level, you need to constantly monitor them. This is precisely what pressure gauges are used for - devices that measure this very pressure.

The main classification of pressure gauges is based on the principle of pressure measurement. The use of any specific type of pressure gauge is determined by the characteristics of the technological process, the scope of use, as well as the possibility of use in certain conditions. Total available five types device data:
— liquid pressure gauges;
— spring pressure gauges;
— membrane pressure gauges;
— ;
— differential pressure gauges.

Of all the above types of devices for measuring pressure, the simplest are liquid pressure gauges . They represent U-shaped glass tube , filled halfway with liquid and equipped with a scale, usually in millimeters and pascals. The liquid level in the tube must be opposite the zero mark of the scale. If one end of the tube is connected to the place where gas pressure is measured, and the second end of the tube is left open, then the liquid in the first tube will fall, and in the second it will rise. The difference in liquid levels 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 pressure gauges are used to measure low pressure with reading ranges 100, 160, 250, 400, 600 and 1000 millimeters column of liquid. When filling the tube with water, the count is in millimeters of water column ( mm in.st.), mercury – in millimeters mercury (mmHg). When filling liquid U-shaped mercury manometers, pour the mercury on top of both tubes. 8-10 mm water or technical oil to prevent mercury vapor from entering the room.

Most wide application among the instruments for measuring pressure found spring pressure gauges . Their advantages are that they are simple in design, reliable and suitable for measuring medium pressure over a wide range 0.01 to 400 MPa (0.1 to 4000 bar).

The sensitive element of the spring pressure gauge is hollow curved tube of ellipsoidal or oval cross-section, deformed under pressure. One end of the tube is sealed, and the other is connected to fitting, 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, mounted on a rack, which consists of driver, gear sector, gear with axle and pressure gauge needle. To eliminate 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 of the excess pressure of the measured medium. The pressure gauge mechanism is housed in the housing. The measured pressure enters the tube, which, under the influence of this pressure, tends to straighten, since the outer surface area is greater than the inner surface area. The movement of the free end of the tube is transmitted through a transmission mechanism to the arrow, which rotates at 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 pressure value.

As a sensing element in membrane pressure gauges stands wavy metal membrane chamber, which is sandwiched between two flanges. Under the influence of pressure, the membrane bends upward and turns the arrow using a transmission mechanism. The amount of bending of the membrane and, therefore, the rotation of the arrow depends on the pressure. Diaphragm pressure gauges are less sensitive and accurate than spring gauges.

Used in automatic control, regulation and alarm systems. IN two special arrows, set to minimum and maximum pressure within the scale, electrical circuit contacts are mounted. When the moving arrow reaches one of the contacts, the circuit closes, which causes a signal to be sent or a corresponding action of the system to which the pressure gauge is connected.

Differential diaphragm pressure gauges are used to measure pressure drop in gas filters or in restriction devices of flow meters.