What is a pressure gauge and what is it used for? Manometer - a device for measuring pressure

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 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).

Low pressure gauge(USSR)

Types of pressure gauges

By purpose, pressure gauges can be divided into technical - general technical, electrical contact, special, recorder, 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 produced in blue cases with O2 (oxygen) symbol on the dial; 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 to test 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 a 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.

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 mm Hg. 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 the 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 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 usually 30 V, while the grid voltage under constant voltage is 180-210 volts, unless there is optional electronic bombardment, through grid heating, which may have high potential approximately 565 Volts. The most common ion gauge is the 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 can 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 pressure gauges to 10−8 mmHg. Art. and Bayard-Alpert to approximately 10−10 mmHg. Art. Additional wires at cathode potential in the sight line 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.

Cold cathode

There are two types of cold cathode pressure gauges: the Penning gauge (introduced by Max Penning), and the inverted magnetron. The main difference between them is the position of the anode relative to the cathode. None of them have a filament, and each requires up to 0.4 kV to function. Inverted magnetrons can measure pressures up to 10−12 mmHg. Art.

Such pressure gauges cannot operate if the ions generated by the cathode recombine before they reach the anode. If the mean free path of the gas is less than the dimensions of the pressure gauge, then the current at the electrode will disappear. The practical upper limit of the measured pressure of a Penning manometer is 10 −3 mm Hg. Art.

Similarly, cold cathode pressure gauges may not turn on at very low pressures, since almost complete absence gas interferes with the establishment of electrode current - especially in the Penning gauge, which uses an auxiliary symmetrical magnetic field to create ion trajectories on the order of meters. In the surrounding air, suitable ion pairs are formed through exposure to cosmic radiation; The Penning gauge takes measures to make it easier to set the discharge path. For example, the electrode in a Penning gauge is usually precisely tapered to facilitate field emission of electrons.

Service cycles for cold cathode pressure gauges are generally measured over years, depending on gas type and the pressure under which they work. Using a cold cathode gauge in gases with significant organic components, such as pump oil residues, can result in the growth of thin carbon films within the gauge, which eventually short out the gauge electrodes, or interfere with discharge path generation.

Application of pressure gauges

Pressure gauges are used in all cases where it is necessary to know, control and regulate pressure. Most often, pressure gauges are used in heat power engineering, chemical and petrochemical enterprises, and food industry enterprises.

Color coding

Quite often, the housings of pressure gauges used to measure gas pressure are painted in various colors. So pressure gauges with blue housings are designed to measure oxygen pressure. Yellow the housings have pressure gauges for ammonia, white for acetylene, dark green for hydrogen, grayish green for chlorine. Pressure gauges for propane and other flammable gases have a red body color. The black housing has pressure gauges designed to work with non-flammable gases.

see also

• Micromanometer

Notes

Links

This article or section needs revision.

A pressure gauge is a device that allows you to measure the pressure in a water system or environment. With the help of this simple device You can get accurate pressure readings at any point in the pipeline or pumping unit. Below we will study the design, operating principle and differences between different types of pressure gauges.

A pressure gauge for measuring water pressure in a water supply system has a very simple design. The device consists of a body and a scale on which the measured value is indicated. A tubular spring or a double-plate membrane can be located inside the housing. Also inside the device there is a holder, a tribco-sector mechanism and an elastic sensing element.

The principle of operation of the device is based on balancing pressure indicators through the deformation force of a membrane or spring. As a result of this process, the elastic sensing element is displaced, which activates the indicating arrow of the device.

Classification of pressure gauges according to operating principle

Nowadays, devices operating under pressure are used in almost all spheres of human activity. Consequently, pressure gauges are also used with them, providing accurate information about pressure indicators. In this case, measuring instruments may differ from each other in design and principle of operation. The devices available on the market are divided into the following types:

Modern pressure gauges are also divided into mechanical and electronic devices. A mechanical pressure gauge for a pump or water supply system has simple design, however, cannot measure pressure accurately enough. The design of the electronic device includes a contact unit that more accurately measures the pressure of the working medium.

According to the method of use, pressure gauges are divided into the following types:

• Stationary - such devices are mounted and used only on a specific unit without the possibility of dismantling measuring device. Often, the unit used also uses a water pressure regulator with a pressure gauge;
• Portable - these measuring instruments can be dismantled and used to work with different units and in various systems. The portable device has smaller dimensions.

Each of the listed types of devices has found its active use. Many of modern models are used in the heating system of a private house or apartment, others are used to service large industrial enterprises.

People unfamiliar with measuring instruments often cannot distinguish a water pressure gauge in a water supply system from a device that is used to measure air and gas pressure. Externally, both of these devices are practically no different from each other. However, there is still a difference between them.


The difference between a pressure gauge for water and air lies in the design and principle of their operation. In water devices, the role of a sensitive element is played by a membrane and a vessel with liquid. In air pressure gauges, the sensing element is a tubular spring, which during operation is filled with gas or air.

You can find out the water pressure in the pipeline without using a pressure gauge. All that is required is to use homemade device from a transparent 2-meter hose, which is very easy to make with your own hands.

Basically, the hose is used to obtain measurements of water pressure at the outlet of the tap. To find out the required indicators, one end of the hose is inserted into the tap, and the other is sealed with a stopper. After this, you need to let some water into the hose.

Before starting the “experiment”, you will need to fulfill 2 conditions:

• Place the hose in a vertical position;
• Move the lower end of the hose as indicated in the diagram.

• P – pressure in the system, measured in atmospheres;
• Patm is the pressure that is present inside the hose until the tap is opened;
• H0 is the height of the air column inside the hose until the tap opens;
• H1 – height of the air column after filling the hose with water.

It should be noted that the assembled device, according to the principle of operation, completely replicates an ordinary liquid pressure gauge.

Checking pressure based on water flow

The second way to determine pressure is to perform calculations using data on the amount of water flowing from the tap. In addition to this data, you will also need:

• Find out the configuration of the pipeline and determine what material it is made of;
• Calculate the pipe diameter;
• Determine the intensity of liquid leakage;
• Determine the degree of opening of the tap.

It is possible to determine the approximate pressure after the operation, but the results obtained will be very inaccurate. Indeed, in any case, the jar will be completely filled in less than 10 seconds, which is why the resulting pressure value will be significantly less than according to the regulations. However, you should always start from the fact that a 3-liter container will be completely filled with water in 7 seconds or less. In this case, the pressure inside the pipeline will be closest to the regulated one.

A pressure gauge is professional device, which was created to allow precise measurement gas and liquid pressure. there are the most various types, in particular, they come in low and high pressure. Usually this device is placed in a small case to make it convenient to use. Science has moved forward, and now there are complex pressure gauges that also include temperature scale– thermometers, vacuum gauges – have vacuum pressure gauges. Which are designed to measure the pressure of those gases that are discharged. The most this device is equipped with is pressure sensors, they help measure it.

Such devices are needed in a variety of scientific and technical fields. They are used to study physical processes that are observed in nature, or to measure technological processes that are created by man. It is worth keeping in mind that these devices differ in accuracy class. So, for example, there is an accuracy class of 0.2, 0.6, 1.0, 2.5, 4.0. Moreover, the lower the number, the less accurate the device is.

It is important to note that the pressure gauge finds its application in thermal power engineering, as well as in chemical organizations, and those related to petrochemicals. It is interesting that it is also used in the food industry, because it is here that it is very important to know the pressure and regulate its condition.

Of course, such a common and required device divided by different types. So, there are pressure gauges:

• technical;
• special;
• electrical contact;
• general technical.

Devices are also divided based on their purpose. There are pressure gauges:

• special;
• ship;
• self-writing;
• vibration-resistant;
• electrical contact and others.

So, consider each one separately in order to understand in more detail which pressure gauge, where it is more convenient and better to use. The first type is general technical. Such devices can measure different areas, even excess and vacuum. Such devices are used in particular to measure pressure during the production process in industrial equipment directly at their work points. Such pressure gauges are resistant to vibrations. They are used in gas supply, in mechanisms and machines, in heat supply, and in technological systems.

For example, electric contact pressure gauges can regulate the medium being measured, and they do this due to the presence of an electric contact organism. They can measure the pressure of liquid, steam, gas and more. Another type is special pressure gauges - for measuring various gases, such as ammonia, oxygen, hydrogen, acetylene. It is important to know that each gas has its own pressure gauge, this is indicated by the special color on the device’s body.

Reference pressure gauges are designed for testing, pressure calibration and to accurately measure excess gas and liquid pressure. But ship pressure gauges are used in the river and sea fleets.

By type, pressure gauges also differ into several types. For example, liquid devices used in laboratory conditions. Pressure here is measured by balancing the weight of the liquid in its column, and the measure of pressure here is measuring the amount of liquid in communicating vessels. There are also piston pressure gauges, deformation gauges, spring gauges, tubular gauges, diaphragm gauges, and bellows gauges. They all differ in how they are used. Here you can find various pressure gauges that will help you measure and control water and gas pressure.

Advantages of working with pressure gauges

In fact, the advantages of working with pressure gauges are obvious. Firstly, this is a universal device that helps keep pressure levels under control. Secondly, this is the accuracy of measurement, including arrhythmias.

The third advantage is low cost. Anyone can afford such a device because it has a low price. And fourth, very important advantage the fact that this device is reliable, and its reliability does not deteriorate even with long-term operation. Another important property– this is the ability to operate in any conditions.

It is worth noting that without such devices, work at an enterprise that requires pressure measurements is significantly more difficult. After all, it is often this small device that keeps the entire manufacturing process. This is extra. equipment - indispensable assistant in many industries.

Of course, it is not at all easy to understand all the types of this device that exist. However, we are ready to help you with this and choose a pressure gauge that is suitable specifically for your purposes. The specialists of the electrical engineering online store of the Energopusk company are well versed in this matter and will help you make a choice and advise you on this issue. That is why you should contact us so as not to make a mistake in your choice.

In this article we will try to consider in detail all the issues related to pressure gauges, their selection and their operation. We will also consider vacuum gauges and pressure-vacuum gauges together with pressure gauges. 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 pressure-vacuum gauge?
2. What types of pressure gauges are there?
3. What parameters are important when choosing a pressure gauge?
4. Conversion of pressure gauge units.
5. How to install pressure gauges?
6. How to use pressure gauges?
7. How are pressure gauges checked?
8. Which pressure gauge is better to buy?
9. What is important to pay attention to when purchasing a pressure gauge?

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

Technical pressure gauge.

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

Technical vacuum gauge.

A vacuum gauge is a device designed to measure the vacuum of a working medium through the deformation of 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 measured is below atmospheric pressure.

Technical pressure and vacuum gauge.

A pressure vacuum gauge is a device designed to measure excess pressure and vacuum of the working medium through the deformation of a tubular spring.

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

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

Pressure gauge "from the inside".

2. What types of pressure gauges are there?

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

Technical pressure gauge TM610R.

Boiler pressure gauges are technical pressure gauges with a body diameter of 250 mm. These pressure gauges are used when installed at high altitudes or in hard to reach places, which allows you to take readings 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 widely used in pumping stations, compressors, cars, ships and trains.

Vibration-resistant pressure gauge TM-320R.

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

Corrosion-resistant pressure gauge TM621R.

Welding pressure gauges are devices designed to monitor pressure on oxygen and acetylene reducers, propane cylinders. Welding pressure gauges are oxygen (case color blue), acetylene (case color white or gray) and propane (case color red). On the dial of each device, the type of medium is indicated in a circle.

Precision pressure gauges (example pressure gauges) - devices with a low accuracy class of 0.6 or 0.4 are used for pressure testing of gas pipelines, checking technical pressure gauges, as well as for measuring the pressure of technological lines that require increased measurement accuracy.

Model pressure gauge.

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

Ammonia pressure and vacuum gauge.

Automotive pressure gauges are devices for measuring air pressure in tires. These devices can be purchased at automobile stores or service centers.

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

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

The fundamental difference These devices differ from the whole variety of pressure gauges due to the availability of the pressure gauge design parameter. To date, these devices are available in six versions.

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

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

The measuring range is the most important parameter.
Standard range of pressures for pressure 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 range of pressures for pressure and vacuum gauges:
-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 pressure gauges:
-1..0 kgf/cm2=bar=atm=0.1MPa=100kPa.

If you don’t know which scale to buy, then choosing a range is quite simple, the main thing is that the operating pressure falls in the range from 1/3 to 2/3 of the measurement scale. For example, your pipe usually has a water pressure of 5.5 atm. For stable operation, you need to choose a device with a scale of 0-10 atm, since a 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 operating pressure is less than 1/3 of the scale or more than 2/3 of the measurement scale? If the measured pressure is less than 1/3 of the scale, the pressure measurement error will increase sharply. 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 pressure gauge error yourself? Let’s say you have a 10 atm pressure gauge with accuracy class 1.5.
This means that the permissible error of the pressure gauge is 1.5% of the measurement scale, i.e. 0.15 atm. If the device error is greater, then the device must be changed. From our experience, it is unrealistic to understand whether a device is working or not without special equipment.
Only an organization that has a testing facility with a reference pressure gauge with an accuracy class four times less than the accuracy class of the problematic pressure gauge can make a decision about a discrepancy in the accuracy class. Two instruments are installed in line with the pressure and the two readings are compared.

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

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

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

The inter-verification interval is the period when it is necessary to re-verify the device. All new devices come with an initial factory verification, which is confirmed by the presence of a verifier’s mark on the dial of the device and a corresponding mark in the passport. On this moment Primary verification can be 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 (heating station, boiler room, plant, etc.), then after the end of the initial verification period it is necessary to re-verify the pressure gauge at the Center for Standardization and Metrology (center for standardization and metrology) of your city or at 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 re-verification costs more or is comparable to the cost of a new device, and also submitting the device for verification costs money even if the device does not pass re-verification 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 already in a year lead to expenses of 200-300 rubles and unnecessary “running around”.
- before making a decision to re-verify devices, calculate the costs of re-verification - in most cases it is much more profitable to buy new devices. What you need to calculate is the cost of verification, several trips to the verifier. If the system has water hammer, pulsation of the medium (close proximity of pumps), vibration of the pipeline, then after 2 years of operation, usually 50% of the devices do not pass re-verification, and you have to pay for it, because calibration 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 you need to choose a specialized pressure gauge.

4. Conversion of pressure gauge units.

When purchasing a pressure gauge, there is often a need to measure pressure in non-standard units of measurement. Our work experience says that if we are talking about a small number of devices (less than 100 pieces), then the factories will not change anything on their scales and will have to convert the units of measurement themselves.

1kgf/cm2=10.000kgf/m2=1bar=1atm=0.1MPa=100kPa=100.000Pa=10.000mm.water column=750mm. rt. Art. = 1000 mbar

5. How to install pressure gauges?

To install a pressure gauge on a pipe, three-way taps and needle valves are used. Damper blocks, loop taps and diaphragm seals are used to protect 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 possible to install a two-way valve with the ability to manually relieve pressure from the pressure gauge when switched off. The use of standard ball valves is not recommended, because after closing the valve, the pressure gauge mechanism is under residual pressure of the medium, which can lead to its premature failure. Today this is the most common type for connecting pressure gauges at pressures up to 25 kgf/cm2. At high pressures, it is recommended to install needle valves. When purchasing a three-way valve, you need to make sure that the threads on the pressure gauge match the threads on the valve.

A needle valve is a control valve with the ability to smoothly supply a working medium, whose shut-off element is made in the form of a cone. Needle valves are widely used for connecting various instrumentation devices to equipment with high pressures. When purchasing needle valves, you must ensure that the threads on the pressure gauge match the threads on the valve.

The damper block is protective device, which is installed in front of the pressure gauge and is designed to dampen pulsations of the working environment. Under the pulsation in in this case This implies sudden and frequent changes in the pressure of the working environment. The main “organizers” of pulsations in the pipeline are powerful pumps without devices soft start and the widespread 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 pressure gauges. A decrease in the temperature of the medium entering the pressure gauge occurs due to the “stagnation” of the medium in the loop. It is recommended to install these devices at a working environment temperature of more than 80C. There are two types of selection devices: straight and angular. Direct sampling devices are installed on horizontal sections of pipelines, and angular ones are intended for installation on vertical pipelines. Before purchasing, you need to make sure that the threads on the tube match the threads on the three-way valve or pressure gauge.

Selective devices (straight and angular).

Membrane media separators are a protective device for a pressure gauge, designed to protect the device mechanism from aggressive, crystallizing and abrasive media entering it. When choosing a diaphragm seal, you must pay attention to the matching threads on the pressure gauge and the seal.

Membrane separator RM.

When installing pressure gauges, there are several requirements that must be met:
- installation work with a pressure gauge must be done when there is no pressure in the pipeline
- the pressure gauge is installed with vertical arrangement dial
- the pressure gauge is rotated by the fitting using a wrench
- it is prohibited to apply force to the pressure gauge body

6. How to use pressure gauges?

When using pressure gauges, it is necessary to follow the recommendations and physical parameters (medium temperature and permissible pressure), registered in the device passport. The most important requirement for operation is a smooth supply of pressure to the pressure gauge. If the device is selected correctly and is operated without violations, then there are usually no problems.
Let's consider cases in which the operation of a pressure gauge is not allowed:
- when pressure is applied to the device, the needle does not move
- the instrument glass is damaged or broken
- the instrument needle moves irregularly
- after releasing pressure from the device, the needle does not return to zero
- measurement error exceeds the permissible value

7. How are pressure gauges checked?

A pressure gauge is a means of measuring pressure and is subject to mandatory verification. Checking pressure gauges can be divided into two types:
- primary verification is a verification that is carried out by the manufacturer before selling the device and is confirmed by the presence of a verification mark on the glass or body of the pressure gauge, as well as a corresponding mark in the device passport. The initial verification is recognized by regulatory organizations without any problems and the device can be used until the end of this period.

Re-verification of the pressure gauge is a verification of the device, which is carried out after the end of the period for the initial verification of the pressure gauge. Before re-checking the pressure gauge, you need to make sure that the device is working properly, because if the device malfunctions, you will receive a nice notification for money comparable to the cost of the device that the device is not working and needs to be repaired or thrown away. Re-verification of the pressure gauge is carried out at the Center for Standardization and Metrology (center for standardization and metrology) in your city or at any organization that has a license for verification and the necessary equipment.

8. Which pressure gauge is better to buy?

Today there are about 10 on the market Russian manufacturers devices, 2 Belarusian manufacturers and a myriad of foreign manufacturers of devices. Let's look at the features of each device.

Russian factories are the most optimal choice to buy pressure gauges. Many will ask - why? Everything is quite simple - Russian pressure gauges are significantly cheaper than imported ones with comparable quality, the initial verification period is 2 years, unlike Belarusian ones, a whole 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 double-checking.
- a simplified mechanism that does not work for a long time under heavy loads.
- plastic glass instead of instrument glass also adds complexity to the operation and reliability of the device.

Foreign pressure gauges - ours many years of experience trade in devices shows that the meaning of the purchase is similar to purchasing a Russian device, but only 2-3 times more expensive. All explanations from sellers of foreign devices about unique quality, super technologies, etc. are a common ploy to explain to the client why he overpays 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 tormented by doubts and you have the opportunity to disassemble two similar pressure gauges, Russian and imported, with a screwdriver, then you are unlikely to be lucky in finding several differences.

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

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

- 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.
- verification of the pressure gauge must last 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 keepsake.
- 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.
- pressure gauges should be bought from an organization that inspires your trust, because the sale of surplus 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.

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A metal pressure gauge (Fig. 140) consists of a curved metal tube, sealed at one end, the other end of the tube is connected to a reservoir in which the pressure is to be measured. Under the influence of gas or liquid entering the tube, the tube tends to unbend. The end of the tube is connected to an arrow that indicates the pressure on a scale. Instruments used to measure atmospheric pressure are called barometers.

Metal pressure gauges come in tubular and plate types. At atmospheric pressure, the pressure gauge needle shows 0 kg/cm2, which corresponds to a pressure of 1 eta.

Metal pressure gauges are simple in design and quite reliable in operation.

Metal pressure gauges are simple in design and quite reliable in operation. For periodic monitoring of the serviceability of pressure gauges, proven control pressure gauges are used. The pressure gauge in use on the device must have a seal with the date of inspection and testing.

Metal pressure gauges (Vourdon) are used in testing machines by direct connection to the working hydraulics.

Spring pressure gauge.

Metal pressure gauges are divided into membrane ones, in which the main working part is steel membranes, and spring ones, with a hollow spring tube.

Metal pressure gauges usually provide low measurement accuracy; they must be checked periodically and have a passport.

Schemes of throttle devices for chlorinators.| Schemes of gas flow meters operating on the principle of flow narrowing.| Mixer operating diagram.

Replacing liquid meters with metal pressure gauges significantly increased the accuracy of dosing and simplified the operation of the device. Mixing devices of chlorinators must ensure maximum gas absorption by water.

Figure 128 shows a metal pressure gauge. The main part of such a pressure gauge is a metal tube 1 bent into an arc (Fig. 129), one end of which is closed. The other end of the tube communicates through valve 4 with the vessel in which the pressure is measured. As the pressure increases, the tube unbends and the movement of its closed end, using lever 5 and gears 3, is transmitted to arrow 2, moving near the instrument scale. When the pressure decreases, the tube, due to its elasticity, returns to its previous position, and the arrow returns to the zero division of the scale.

For measuring high pressures A metal pressure gauge was used; for low temperatures, a mercury air pressure gauge closed on one side.

To measure high pressures, a metal pressure gauge is used (Fig. 59), consisting of a metal tube bent in the form of a curl. One end of the tube is fixedly attached to the pressure gauge box. This end is connected to the vessel in which the pressure is measured. The other, free end is closed, and an arrow is attached to it. Often the arrow is not connected directly, but with the help of levers and a rack and wheel.