How is gas pressure measured in physics? What instruments are used to measure gas pressure

A pressure transducer is a measuring device designed for continuous measurement of the pressure of various media and subsequent conversion of the measured value into a unified output signal for current or voltage. Pressure transducers are often called pressure sensors. Pressure is defined as the unit of force produced per unit surface area. The SI unit of pressure is Pascal (Pa). One Pascal is equal to a force of one Newton applied over an area of one square meter (Pa = N/m²).

Depending on the type of pressure being measured, pressure transducers are divided into several types.

Exact sciences

The unit of measurement of pressure in physics and chemistry is the letter “P” (translated into Latin as “pressūra”). If there is equilibrium inside and outside the cylinder walls, the indicator is designated “P”. The international system uses Pascals. Using the formula for fluid pressure and force, we can come to the conclusion that 1 Pa = 1 N/ 1 sq. m. Since the unit is small, it is difficult to use in calculations.

From the table of standard converters in physics, the following notations are more often used:

Bars. 1 Bar=105 Pa.
Torrs or mmHg (1 torr equals 133 Pa).
mm water pillar

To determine pressure, force and area are used: P = mg / S. There is a dependence of the value on volume and mass. The indicator is characterized by the following property: the smaller the area, the greater the force exerted on the body. If the pressure does not change, but S increases, then the desired indicator decreases.

General information about pressure

The maintained gas pressure depends on the purpose of the pipeline

By definition, pressure is a physical quantity equal to the force that acts per unit area at 90° to the surface. Since blue fuel is transmitted through pipelines, the cross-sectional area of the pipe is the conventional surface, and the pressure determines the speed of movement of the substance.

The pressure in different sections of the gas pipeline from the field to the nozzle in the gas boiler is maintained at different levels.

Types of pressure

The pressure in the pipes is strictly standardized. If the value in the main pipe is too small, it will simply not be possible to move the gas to another station. If the pressure in the home network is too high, at the final point - the burner, the gas mixture will not be able to be mixed with oxygen in the required proportion to support combustion and not provoke an explosion.

Gas pipelines are classified according to the pressure. And since it is constantly maintained, the gas is “associated” with this value.

There are main and distribution gas pipelines.

Trunk

Distribution

Trunk - through such a pipeline the gas mixture is transmitted over long distances. Gas compressor stations are installed here at a certain frequency to maintain the required level. The final destination for the main line is the local distribution station. Based on the pressure level, there are 2 types:

1st class trunk networks – with operating pressure from 2.5 to 11.8 MPa inclusive;
Class 2 – maintained according to the standard 1.2–2.5 MPa.

Distribution - gas is delivered through pipelines from stations to the end consumer - in-house networks. There are:

Category 1 – household gas is transmitted under pressure from 0.6 to 1.2 MPa;
category 1a – more than 1.2 MPa;
Category 2 – 0.3–0.6 MPa.

Residential buildings are traditionally equipped with the lowest pressure networks. However, with the advent of gas boilers, the situation has changed somewhat. To satisfy the demand for gas, a gas pipeline with average performance is connected to residential multi-storey buildings.

Units

Pressure is measured in a variety of ways. But when it comes to a gas line, the following options are most often used:

1 mm. Hg st - this unit is very clear, especially when a liquid pressure gauge is used for measurement.
1 atm is a more traditional unit of measurement. The first quantity that could be compared with something was atmospheric pressure. The value calculated from absolute zero is called absolute. Hence, excess pressure is equal to the difference between the absolute and atmospheric values. When the vacuum changes, it is determined how much the level in a certain limited volume - a pipeline - is less than atmospheric. This value is called vacuum pressure. When repairing or inspecting intra-house networks, vacuum pressure is measured in the smoke removal system, and excess pressure is measured in the gas pipeline.
1 bar is a unit more common in Europe. 1 bar is equal to 100000 Pa.
1 Pa is the unit of measurement adopted in the SI system. It is inconvenient because it is too small - only 1 newton per 1 m². When inspecting gas pipelines, a large unit is used - 1 MPa, equal to 1,000,000 Pa (pascals).

Gas pressure in the gas pipeline at home

A gas pipeline is the movement of gas through pipes from its storage location to the user. Gas pipelines can be above-ground, underground, surface or underwater. The gas pipeline is divided into different categories, which are determined by the gas pressure. To supply villages and cities, the pressure can be low up to 0.05 kgf/cm2, medium – up to 3 kgf/cm2 or high – up to 6 kgf/cm2. A very high indicator is considered to be up to 12 kgf/cm2. The pressure level depends on the purpose of a given section of the gas pipeline; the highest pressure is in the main line, and the lowest is inside the living room. There is a special GOST for the gas pipeline that must be met. Areas with high pressure are intended for industrial enterprises or gas supply between cities. Low or average pressure is intended for the average user; for a residential building, 0.05 kgf/cm2 is usually supplied.

Pressure measurement methods

The widespread use of pressure, its differential and vacuum in technological processes necessitates the use of a variety of methods and means of measuring and monitoring pressure.

Pressure measurement methods are based on comparing the forces of the measured pressure with the forces:

pressure of a column of liquid (mercury, water) of the corresponding height;
developed during deformation of elastic elements (springs, membranes, pressure boxes, bellows and pressure tubes);
elastic forces that arise during deformation of some materials and cause electrical effects.

Classification of pressure measuring instruments

Classification by principle of action

In accordance with these methods, pressure measuring devices can be divided, according to the principle of operation, into:

Deformation measuring instruments are most widely used in industry. The rest, for the most part, have found application in laboratory conditions as exemplary or research ones.

Classification depending on the measured value

Depending on the measured value, pressure measuring instruments are divided into:

pressure gauges – for measuring excess pressure (pressure above atmospheric);
micromanometers (pressure meters) – for measuring small excess pressures (up to 40 kPa);
barometers - for measuring atmospheric pressure;
microvacuum gauges (draft meters) – for measuring small vacuums (up to -40 kPa);
vacuum gauges – for measuring vacuum pressure;
pressure and vacuum gauges – for measuring excess and vacuum pressure;
pressure gauges – for measuring excess (up to 40 kPa) and vacuum pressure (up to -40 kPa);
absolute pressure gauges – for measuring pressure measured from absolute zero;

Study of the purpose, design, principle of operation and calibration of pressure measuring devices (absolute, manometric, vacuum).

Pressure measuring instruments

Devices for measuring pressure are classified according to various criteria. Based on the nature of the measured pressure, devices are divided into the following classes:

barometers – instruments for measuring atmospheric pressure:
pressure gauges – devices for measuring excess pressure;
vacuum gauges – instruments for measuring vacuum;
pressure and vacuum gauges – devices for measuring both excess pressure and vacuum;
absolute pressure gauges – devices for measuring absolute (total) pressure;
differential pressure gauges – devices for measuring pressure differences.

According to the principle of operation, the devices are distinguished:

The simplest device for measuring excess pressure is a piezometer (Fig. 1, a). It is a vertically installed transparent glass or PVC tube with an open top end

Measurements using a piezometer are carried out in units of length, so sometimes pressures are expressed in units of the height of a column of a certain liquid. Piezometer height 1.5. 2m allows you to measure pressure up to 0.15. 0.20 atm.

The main advantage of a piezometer is its simplicity of design and measurement accuracy. The main disadvantage of a piezometer is the small range of measured pressures. At high pressures the piezometer becomes too bulky. The disadvantages of a piezometer also include fragility.

Excess pressure in liquids or gases is measured by pressure gauges. This is a very extensive set of measuring instruments of various designs and designs.

Figure 1,b shows the operation diagram of a piston pressure gauge. When the pressure in the vessel increases, the liquid or gas, according to Pascal's law, transfers this pressure to the lower surface of the piston, thereby causing it to rise or fall. The piston is connected through a system of levers with an indicator arrow.

Fig.1 Instruments for measuring excess pressure

a) piezometer, b) piston pressure gauge, c) liquid pressure gauge, d) membrane pressure gauge, e) bellows pressure gauge

Another type of pressure gauge is an open (liquid) pressure gauge (Fig. 1, c). It consists of a U-shaped tube filled with mercury or other liquid. The work is based on the law of communicating vessels and on balancing the measured gas pressure with the pressure of a liquid column (mercury, water, etc.). Pressure is applied to one end of the tube. The liquid in the other tube rises until the measured pressure is exactly equal to the pressure caused by the difference in liquid levels in the two legs of the tube. Knowing this height difference, the pressure can be calculated.

The disadvantage of such a pressure gauge is that the pressure value depends on the acceleration of gravity at a given location. Such a pressure gauge is not always calibrated in pascals; it is often convenient to measure pressure in units of the height of a column of a given liquid - in millimeters of mercury, water column (1 mm water column - 9.8 Pa; 1 mm Hg = 133.3 Pa)

One of the simple instruments for measuring increased and high pressures is a tubular pressure gauge or Bourdon pressure gauge. Its main component is a brass pipe 1 of oval cross-section bent in an arc (Fig. 2).

Liquid or gas is supplied to fitting 3, connected to tube 1. The tube, straightening, sets in motion a system of gears and levers 2, which turn arrow 4; the greater the pressure, the greater the angle the needle will rotate. The angle of rotation of the arrow is proportional to the measured pressure. The scale printed on the dial is graduated in pressure units. Typically the pressure gauge is calibrated in MPa. Such pressure gauges are used to measure the pressure of air, steam, gases and liquids. Pressure gauges for measuring car tire pressure are often of the Bourdon type.

So it is a strain gauge.

Deformation gauges also include membrane and bellows pressure gauges (Fig. 1, d, e)

The main part of the diaphragm pressure gauge is a flexible round flat plate capable of deflection under pressure.

A bellows pressure gauge (bellows) is a thin-walled cylindrical shell with transverse corrugations, capable of significant movement under pressure. To increase rigidity, a spring is often placed inside the bellows. Bellows are made of bronze, carbon steel, aluminum alloys. Seamless and welded bellows with a diameter from 8-10 to 80-100 mm are mass-produced. Bellows are more sensitive than diaphragm pressure gauges and have a larger measuring range.

The main advantages of the devices are a wide range of measured pressures, simplicity of design and use, portability and versatility.

The main disadvantage of the devices is the variability of their readings, due to gradual changes in the elastic properties of the spring element, the occurrence of residual deformation, and wear of the transmission mechanism. Therefore, such devices must be checked periodically.

Pressure gauges allow you to determine pressure only with a certain accuracy; the accuracy class of pressure gauges is determined by the value k, which expresses the maximum permissible error of the value corresponding to the maximum reading of the instrument scale

Nominal range of classes, accuracy of pressure gauges: 0.005; 0.02; 0.05; 0.1; 0.2; 0.35; 1; 2; 2.5; 4.0; 6.0.

Pressure gauges and vacuum gauges, standard spring gauges, are used to control general-purpose pressure gauges and to carry out particularly precise measurements. To control standard pressure gauges, deadweight piston pressure gauges are used.

Pressure gauges of class 0.05 are intended for testing standard spring and other precision pressure gauges, pressure gauges of class 0.2 are for testing technical general-purpose pressure gauges.

Gauge pressure converters

Figure 1 — General industrial pressure sensor PTE5000
These converters measure the pressure created by any medium relative to atmospheric pressure. This type of pressure transducers is the most common and is used in almost all industries: housing and communal services, energy, water treatment, water purification, heating, air conditioning and ventilation systems, food industry, chemistry, etc.

To measure excess pressure of water, steam, neutral liquids and gases, KIP-Service LLC offers a pressure sensor for general industrial use PTE5000. These sensors are widely used by Russian enterprises to measure water pressure in boiler automation systems, water supply and sewerage systems, housing and communal services and other systems where the low cost of equipment is in the foreground.

Classification by type of pressure measured

Instruments used to obtain data on gas pressure parameters in gas tanks, transport lines, gas cylinders and other reservoirs are classified according to several criteria. They differ in their structure and principle of operation.

Devices used to measure pressure are divided into classes according to:

type of pressure being measured;
purpose;
operating principle;
accuracy class.

Based on the type of pressure being measured, instruments designed to determine accurate indicators are divided into pressure gauges, vacuum gauges, draft gauges, pressure gauges, barometers and others.

Depending on the degree of protection from the influence of the external environment, the following devices are produced:

standard;
protected from dust;
waterproof;
protected from aggressive environments;
explosion-proof.

One product can combine several types of protection.

The diagram shows the division of measuring devices according to operating principle, type of pressure, application and display. Liquid and deadweight instruments are rarely used to obtain data on gas pressure

A pressure gauge is a small device that is used to measure pressure or pressure difference. The operating principle of this instrument depends on its internal structure. Within one class, they are further divided into groups depending on the accuracy class.

To measure absolute pressure, measured from absolute zero (vacuum), absolute pressure gauges are used. Excess pressure is determined using an excess pressure gauge. In general, all varieties of such devices are called in one word: “pressure gauge”.

Most types of pressure gauges are designed to measure excess pressure values. Their peculiarity is that they show pressure, representing the difference between absolute and atmospheric.

Vacuum gauges are devices that indicate the pressure value of a rarefied gas. Using pressure and vacuum gauges, excess pressure and rarefied gas pressure are measured. Information is displayed on a single scale.

Using pressure meters, excess pressure parameters are determined with values up to 40 kPa. Traction meters, on the contrary, make it possible to measure rarefaction down to – 40 kPa. Thrust pressure meters measure rarefaction and excess pressure in the range from – 20 to + 20 kPa.

Pressure gauges are used in a wide variety of industries. Working with gas involves a high risk, so it is important to monitor all system indicators. Pressure information gives users information about the current state of the object being measured

Differential pressure gauges can be used to determine the pressure difference at two arbitrary points to be studied. A micromanometer is a differential pressure gauge that allows you to measure pressure differences within 40 kPa.

Where to buy air flow pressure meters

You can leave a request or buy differential pressure gauges from our managers by calling, filling out a form on the website or writing by email. We can provide advice on equipment maintenance or select an analogue that meets your requirements. In addition, we provide product warranty service. The SOYUZ-PRIBOR company is the official distributor and dealer of a number of brands and has been operating for more than 25 years! Delivery is carried out throughout Russia.

Reference devices for pressure measurement

This type of pressure gauge is designed to test, calibrate and adjust other instruments to ensure the highest possible measurement accuracy. Such devices are distinguished by a higher accuracy class in comparison with general technical ones. Working standards are divided into three categories.

Control pressure gauges, used to monitor the reliability of the readings of measuring instruments at the installation site, are also called high-precision pressure gauges. The operating measurement range is from 0-0.6 to 0-1600 bar for gaseous media.

Pressure gauges for conventional and composite gas cylinders must undergo a verification procedure at least once a year, unless other periods are specified in the documents for the device. Verification is carried out by accredited metrological organizations that have the status of legal entities. After verification, a certificate is issued and a stamp is placed.

The device must be removed from the cylinder and taken to the metrological service. There, verifiers and calibrators, using a set of standards and auxiliary instruments, will carry out verification for about 10 days

The transmission mechanisms in the reference pressure gauges are machined at a higher gearing frequency. They are characterized by minimal friction in the pointer mechanism, as well as high sensitivity of the internal elements.

Standard pressure gauges with an accuracy class of 0.4 have a scale of 250 units, with an accuracy class of 0.15 or 0.25 they have a scale of 400 units with a division value of 1 unit. Operation of the device is possible at different temperatures depending on the housing filler. The ideal operating temperature is 20 °C.

The following article will introduce you to the specifics of refilling gas cylinders. All owners of country property not connected to a centralized gas supply should read it.

About pressure gauges

Externally, the devices resemble a small cylinder consisting of a metal body and a glass lid. As a rule, the diameter of pressure gauges is 50 mm. The scale, visible through the transparent glass, displays the pressure value in Pa or Bar. These devices are used in various systems, such as gas and water pipelines, heating boilers, autoclaves, compressors, cylinders, etc. Pressure gauges are connected to the systems through a tube that comes out of their housing. The tube has an external thread, due to which it is screwed into the desired place. The pressure gauge allows you to measure vacuum or atmospheric pressure, excess pressure or pressure difference.

Device structure

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

Device body.
Bourdon tube.
Indicator arrow.
Connection fitting.
Transmitting lever-spring mechanism.
Scale.
Protective glass.

The pressure gauge body 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 installed to display the readings. And the indicator arrow, which is rigidly attached to the mechanism, shows the applied force. Glass protects from external influences.

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

Pressure gauge with single-turn tubular spring

1 - scale; 2 - arrow; 3 - axis; 4 - gear; 5 - sector; 6 - tube; 7 - traction; 8 - spring hair; 9 - fitting

Recording pressure gauge with a multi-turn spring (figure below). The spring is made in the form of a flattened circle with a diameter of 30 mm with six turns. Due to the large length of the spring, its free end can move by 15 mm (for single-turn pressure gauges - only by 5-7 mm), the angle of unwinding of the spring reaches 50-60°. This design allows the use of simple lever transmission mechanisms and automatic recording of readings with remote transmission. When the pressure gauge is connected to the medium being measured, the free end of the lever spring will rotate the axis, and the movement of the levers and rods will be transmitted to the axis. A bridge is attached to the axis, which is connected to the arrow. The change in pressure and the movement of the spring are transmitted through the lever mechanism to a pointer, at the end of which a pen is installed to record the measured pressure value. The diagram rotates using a clock mechanism.

Classification by mode of operation

According to the method of operation, devices can be water, electric or digital; in addition to these categories, there are other varieties.

Water devices operate on the principle of balancing a gaseous substance with pressure, forming a column of liquid. Thanks to them, it is possible to clarify the level of sparsity, difference, redundancy and atmospheric data. This group includes U-type regulators, the design of which resembles communicating vessels, and the pressure in them is determined taking into account the water level. Also included in the water category are compensation, cup, float, bell and ring gas meters; the working fluid inside them is similar to the sensitive element.

Resistive electric pressure gauge

This device for measuring household gas pressure converts it into electrical data. This category includes resistive and capacitive pressure gauges. The first ones change the readings of conductive resistance after deformation and measure values up to 60-10 Pa with minor errors. They are used in systems with fast processes. Capacitive gas meters affect a movable electrode in the form of a membrane, the deflection of which can be determined by an electrical circuit; they are suitable for systems with accelerated pressure drops.

Digital or electronic instruments are high precision devices and are most often used for installation in air or hydraulic environments. Among the advantages of such regulators are their convenience and compact size, the longest service life and the ability to calibrate at any time. They are mainly used to monitor the condition of vehicle components. In addition, digital gas meters are included in fuel lines.

In addition to regulators with standard characteristics and settings, other types of devices are used to obtain accurate data. This list includes deadweight gas meters, which are original samples for testing similar devices. Their main working part is the measuring column, the condition and accuracy of the readings of which changes the magnitude of the error. During operation, the cylinder is held inside the piston at the desired level, while on the one hand it is influenced by calibration weights, on the other only by pressure.

Types of measuring instruments

Instruments for measuring pressure are divided into the following types:

Thrust and pressure gauges are pressure and vacuum gauges that have extreme measurement limits of no higher than 40 kPa.
Traction gauges are a vacuum gauge that has a measurement limit of (-40) kPa.
A pressure gauge is a pressure gauge of low excess pressure (+40) kPa.
Pressure and vacuum gauges are devices that are capable of measuring both vacuum and excess pressure in the range of 60–240,000 kPa.
A vacuum gauge is a device that measures vacuum (pressure that is below atmospheric pressure).
A pressure gauge is a device that is capable of measuring excess pressure, that is, the difference between absolute pressure and barometric pressure. Its limits range from 0.06 to 1000 MPa.

Most 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 fitting is axial or radial.
The diameter of the fitting thread.
Instrument accuracy class.
Case diameter.
Limit of measured values.

Types of pressure measurement systems

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 accurately if the value is lower. The most accurate are digital devices.

According to their purpose, pressure gauges are of the following types:

Self-recording. They contain a mechanism that allows you to draw a graph of the device’s operation on paper.
Railway. Used in railway transport.
Ship's. Used on sea and river vessels.
Reference. They have a high accuracy class. That is why they are used for testing, adjusting and checking other pressure measuring instruments.
Special. Used to measure the value of various gases. Depending on what gas they are intended for, they have different body colors and marking letters: for measuring flammable gases - red, for non-flammable gases - black, yellow ammonia (A), white acetylene (Ac), blue oxygen (K).
Electric contact. They have an electrical alarm that allows you to regulate the measured environment. These devices are divided into two types: based on an electrical contact attachment and with microswitches.
General technical. Designed to measure pressure in various environments. They can measure excess and vacuum pressures.

Based on the principle of operation, the following types are distinguished:

Piezoelectric. Based on the piezoelectric effect. A charge appears in a quartz crystal under mechanical action.
Deformation. They are based on the deformation of the sensitive element (membrane, bellows, spring, etc.), which, when deformed, acts on the pointer.
Liquid. Their basis is a tube filled with liquid. They can be of two types: with one or two tubes. Devices with two tubes are used to compare pressure in different environments.
Piston. They consist of a cylinder with a piston inserted inside.

Gas production

In the depths of the earth, gas is found in microcracks under high pressure. The natural movement of methane occurs according to certain patterns. Gas lies in the earth's crust at a distance of 1-6 km from the surface, so geological exploration work is carried out first. Deep in the bowels of the planet there are very small pores and cracks that contain gas. The mechanism of natural gas movement is simple: methane is displaced from pores with high pressure to pores with lower pressure. Wells are installed evenly across the entire area of the field. Since the pressure underground is many times greater than atmospheric pressure, the gas itself comes out into the well.

Preparation and transportation

Gas is not immediately released through the pipeline; first it is prepared in a special way in boiler houses, thermal power plants and chemical plants. They are dried from water vapor and purified from impurities: hydrogen sulfide (causes corrosion of pipes), water vapor (causes condensation, interferes with the movement of gas). The pipeline is also prepared: an inert environment is created in it using nitrogen. Next, the gas moves through large pipes with a diameter of 1.5 m (under a pressure of 75 atmospheres). Since during transportation the potential energy of gas is spent on friction forces between particles of the gas itself and on friction between the pipe and methane, there are compressor stations that increase the pressure inside the pipe to 120 atmospheres. Underground gas pipelines are laid at a depth of 1.5 m to prevent the structure from freezing.

Requirements for pressure gauges

The color of the housing indicates the type of gas being measured: yellow - ammonia, blue - oxygen, black - non-flammable, red - flammable

The exact indicators according to which the device takes measurements directly depend on the correctness of its selection and installation in combination with operating conditions. When selecting, it is necessary to take into account the physical and chemical properties of the measuring medium and the expected pressure data. For example, for conditions with a high content of aggressive gases, it is better to purchase special devices made of durable materials. The diameter of the pressure gauge glass must be at least 10 or 16 cm if it is placed at a distance of 2 to 3 meters.

Devices used in gas environments have different body colors, for example, blue indicates work with oxygen, yellow with ammonia, red and black are suitable for flammable and non-flammable gases, respectively. According to safety rules, it is not recommended to use pressure gauges with an expired verification period, as well as in the absence of a seal or mark on this procedure. If the needle of the device does not return to zero after switching off, it is also considered inoperative.

Any damage, such as deformed housing or broken glass, indicates that the regulator needs to be replaced, as they directly affect the accuracy of the meter.

Instrument selection criteria

The best option is a regulator with a scale from 0 to 10 atm

When selecting a device, you need to take into account all the requirements for pressure gauges used in the gas industry. The main criterion is the measuring range; during the selection process, it must be remembered that the standard pressure should fall within the range from 1/3 to 2/3 on the measurement scale. The ideal option would be a regulator with a scale of up to 0-10 atm. In second place in terms of importance is the accuracy class indicator, which shows the normal error of measurement results during operation of the device.

If desired, this indicator can be calculated individually, for example, if the device is designed for 10 atm, and its class is 1.5, the error rate of such a gas meter is 1.5% of the total scale. Depending on the type of mounting of the fitting, pressure gauges can be radial or end, in addition, the regulators are supplemented with metric or pipe type threads. When choosing a device, you need to take into account its calibration interval; it would be better if it is two years.

Household appliances may not undergo a verification procedure, but it is mandatory for devices used in factories, gas pipelines, heating or combustion units, as well as similar facilities.

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

It is important to consider:

the pressure gauge must be new. Many instrument sellers understand by the word new that the pressure gauge has not been used. But the pressure gauge may be 15 years old, and they will tell you 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 purchasing an illiquid item.
there must be a mark on the initial verification on the pressure gauge or in the passport. There are sellers of illiquid goods who erase the verifier's mark so that they cannot be accused of selling old devices.
The pressure gauge must be verified for 2 years; if you buy a device with initial verification for 1 year, within 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 measurement range, scale diameter, type of fitting location, type of thread and design of the device - if you buy the wrong device, then replacing it may 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 about pressure gauges on the Internet, but most of them are custom-made and it is better to rely on the advice of people who have experience in actually operating the devices.
You should buy pressure gauges from an organization that inspires your trust, because the sale of illiquid goods from the USSR still exists and then it will be quite difficult to return old instruments or exchange them for normal instruments.

In this article we tried to consider the most popular questions about the whole 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 details, location, conditions and region of installation.

Sources

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https://morflot.su/kakimi-priborami-izmerjaetsja-davlenie-gaza/
https://sovet-ingenera.com/gaz/equip/manometry-dlya-izmereniya-davleniya-gaza.html
https://instrland.ru/c/manometry/
https://MetEkspert.ru/oborudovanie/kakimi-priborami-izmeryayut-davlenie-gaza.html
https://kangen.ru/osnastka/kak-zamerit-davlenie-gaza.html
https://msk.specarmatura.ru/articles/113950/