Pressure gauges UAM

The use of an electric contact pressure gauge

islamovbogdan — Thu, 14 Sep 2023 17:51:00 +0000

Electric contact pressure gauge (signalling) for water supply systems. Principle of operation, application, design, marking and types.

Ensuring pressure control in water supply systems and systems of a similar type is a necessary component for the normal operation of water supply systems. There are equipment options that solve this problem by providing control of the system components, including the pump. For this purpose, a pressure switch or an electrocontact pressure gauge is used. In this article, you can learn about the nuances of the pressure switch and proximity switch, the advantages and disadvantages of each.

Advantages and disadvantages of the electrocontact pressure gauge in relation to the pressure switch.

The advantage of the electrocontact pressure gauge is that it is assembled in a single housing for the switching contacts and the control pressure gauge. This is convenient because this design does not require additional tees for assembly. Although you can find a version of the pressure switch that has a built-in pressure gauge. Perhaps one of the main advantages of the pressure gauge is the ease of setting up the device and accurate visualisation of the triggering limits by pressure readings. The design of this type of pressure gauge allows you to set the lower and upper limits at which the mechanism will be triggered. This is achieved without the use of special keys, only with the help of contact arrows. In this case, we get a visual setting of the pressure gauge. Relays do not have this capability.

The disadvantages of the electrocontact pressure gauge are low switching currents, on average 0.3-0.5 A. This does not allow you to connect powerful devices without additional equipment. For this purpose, powerful relays are used, which, in turn, require an additional power supply.

This feature is the reason why the electrocontact pressure gauge is called a signalling gauge. When changes occur, it signals about them, and a power relay serves as the actuating device.

The second disadvantage of this pressure gauge is its high cost relative to pressure switches. On average, the price can differ by 2-3 times not in favour of the pressure gauge.

The field of application of the signalling pressure gauge is heat supply, water supply, ventilation systems, mechanical engineering, etc.

In particular, they are widely used to switch on pumping stations that supply water.

General information about the electrocontact (signalling) pressure gauge.

The electrocontact pressure gauge is used to determine the overpressure of the working medium. The measured medium must be non-aggressive, non-crystallising (liquid, steam, gas, including oxygen). These are devices with an electrical contact group.
When a certain upper and lower pressure limit is reached, the pressure gauge mechanism triggers the contact group. Using additional arrows on the scale of the device, you can set the pressure ranges – minimum and maximum – that correspond to the closing points of the electrical circuit. These switching modes are used to control electrical circuits. When the medium pressure crosses the limit arrows, the contacts of the electrical circuit open or close.
Different contact groups can be used depending on the type of pressure gauge.
Information about the contact groups is given below.

Connecting an electrical contact (signalling) pressure gauge.

Depending on the scope of application, conditions and purpose, different types of ECM pressure gauges are used, which have different modifications of electrical circuits:

Type 1 – single-contact closing type;
Type 2 – single-contact open circuit;
Type 3 – two-contact open-open switch;
Type 4 – two-contact closing-opening;
Type 5 – two-contact contact for opening and closing;
Type 6 – two-contact open-close switch.

(For clarity, the following is a diagram of the possible switching groups in the wiring diagram for pressure gauges types 3 to 6)

The signalling device can be of different versions:

III – both contacts are open. The left pointer (min) is blue, the right pointer (max) is
red.

IV – both contacts are closed. Left indicator (min) red, right indicator (max)
blue.

V – one contact is open (min), the other is closed (max). Both indicators are blue

VI – one contact is closed (min), the other is open (max). Both indicators are red.

Note: When the pressure arrow reaches the setpoint of the left or right pointer, the contact is opened (closed).

There are accepted standards for colour coding of signalling devices.
The standards for colour marking of the switching wires of electrocontact pressure gauges during manufacture and also during connection are as follows:

blue – minimum
red – maximum;
yellow – common.
The principle of operation of an electrocontact (signalling) pressure gauge.

The principle of operation of electrocontact pressure gauges is based on the fact that when the pressure level reaches a certain set point, the built-in contact group is opened or closed by a movable contact, which is an arrow, and the built-in contact group is triggered. The closing or opening of the electrical circuit depends on the type of device. Such a wide range of capabilities of electrocontact pressure gauges allows them to be widely used in various industrial areas.
All types of electrocontact (signalling) pressure gauges are marked with the technical parameters of the device.

An example of decoding a device marking.
Electro contact pressure gauge DM 2005-U2 (1.0, MPa, ac. 1.5, M20x1.5, IR40, bottom, V)

1.0 – measuring range (from 0 to 1.0 MPa);
MPa – units of measurement
accuracy class 1.5 – accuracy class
M20x1.5 – thread of the connecting fitting
IP40 – degree of protection
Bottom – location of the connector (radial)

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Useful information about pressure gauges

islamovbogdan — Thu, 14 Sep 2023 17:40:00 +0000

The term “pressure gauge” is used throughout the text, and the name pressure gauge is generic. This term also includes vacuum gauges and manovacuum gauges. This material is not related to digital instruments.
Pressure gauges are devices that are widely used in industry and housing and communal services. In the production process, enterprises need to control the pressure of liquids, steam and gas. Depending on the specialisation of the enterprise, there is a need to measure different media. For this purpose, pressure gauges for various purposes have been developed. The difference between the devices is determined by the medium to be measured and the conditions under which the measurement is performed. Pressure gauges differ in design, size, connection thread, units of measurement and possible measuring range, accuracy class, and material of manufacture, which determines the possibility of using the device in aggressive environments. The choice of a device that does not meet the tasks to be performed may result in failure of the device earlier than the expected service life, measurement errors, or overpayment for functions of the device that are not used.

Classification of pressure gauges according to criteria
Depending on the area of application.

Technical pressure gauges of standard design – used to determine the overpressure and vacuum of non-corrosive, non-crystallising media: liquids, steam and gas.

Technical special pressure gauges – this type of gauge is used to measure specific media (e.g. corrosive) or in special conditions (high vibration or temperature, etc.).

Special devices:

ammonia pressure gauges;
Corrosion-resistant pressure gauges for aggressive environments;
Vibration-resistant pressure gauges – copper metal;
Vibration-resistant pressure gauges – stainless steel;
precision measurement pressure gauges;
railway gauges.

Ammonia pressure gauges, as well as corrosion-resistant pressure gauges, have stainless steel and alloy parts and mechanisms that are resistant to aggressive media, which makes this type of device suitable for use in applications where interaction with aggressive media is required.

Vibration-resistant pressure gauges can be used in conditions of vibration frequency exceeding 4-5 times the permissible vibration frequency for a conventional pressure gauge.
The main distinguishing feature of vibration-resistant pressure gauges is the presence of a special damping device located in front of the pressure gauge. This device helps to reduce pressure pulsation.
Some types of vibration-resistant pressure gauges can be filled with a damping liquid. Resistance to vibration is achieved by a vibration-absorbing substance, which is glycerin.

Precision pressure gauges are used in the areas of state mercological control, heat supply, water supply, energy, mechanical engineering, etc. In addition, they are used as a reference for verification and calibration of pressure measuring devices in compliance with the requirements for compliance with the accuracy classes of the device used as a reference and the device to be verified.

Railway pressure gauges are used to measure the overpressure of media that are not aggressive to copper alloys in systems and installations of rolling stock and to measure the pressure of refrigerants in refrigeration machines in refrigerated wagons.
Depending on the application, the pressure gauge bodies are painted in the appropriate colours. Ammonia pressure gauges are yellow, hydrogen pressure gauges are dark green, red for flammable gases, blue for oxygen, and black for non-flammable gases.

Electric contact pressure gauges. The peculiarity of electrocontact pressure gauges is that they are devices with an electrocontact group. They are designed to measure the pressure of non-corrosive, non-crystallising media (steam, gas, including oxygen), as well as to close and open electrical circuits when a certain pressure limit is reached. The electrocontact mechanism allows for adjustment of the medium.

UNITS OF PRESSURE MEASUREMENT. GRADUATION OF PRESSURE GAUGE SCALES.

Pressure gauge scales are graduated in one of the following units: kgf/cm2, bar, kPa, MPa, provided that the device has a single scale. For pressure gauges with a dual scale, the first scale is graduated in the above units, and the second scale is graduated in psi – pounds per square inch. Psi is an off-system unit used in the United States.
Table 1 shows the ratio of measurement units to each other.

Table 1. Ratio of pressure units.

	Pа	кPа	МPа	kgs/сm2	bar
Pа	1	10-3	10-6	10,197*10-6	10-5
кPа	103	1	10-3	10,197*10-3	10-2
МPа	106	103	1	10,1972	10
kgs/сm2	98066,5	98,0665	0,980665	1	0,980665
bar	105	100	0,1	1,0197	1
psi	6894,76	6,8948	6,8948*10−3	70,3069*10−3	68,9476*10−3

Pressure gauges with a scale in kPa units are devices designed to measure low pressures of substances in a gaseous state. In their design, a diaphragm box serves as a sensing element. In contrast, high-pressure gauges have a curved or spiral tube as a sensing element.

RANGE OF MEASURED PRESSURES.

The following types of pressure are distinguished: absolute, barometric, overpressure, and vacuum.
Absolute pressure is the value of pressure measured relative to an absolute vacuum. The value may be negative.
Barometric is the atmospheric pressure. It is affected by altitude, humidity, and air temperature. At the zero mark of altitude above sea level, the barometric pressure is assumed to be 760 mm Hg.
For technical pressure gauges, this value is assumed to be zero. This means that the measurement results depend on the barometric pressure.
Overpressure is a value that shows the difference between absolute and barometric pressure. This is relevant when the absolute pressure exceeds the barometric pressure.
Vacuum is a quantity that shows the difference between absolute and barometric pressure in conditions when barometric pressure exceeds absolute pressure. Consequently, the vacuum pressure cannot be higher than the barometric pressure.
Based on the above, it becomes obvious that vacuum gauges measure discharge. Manovacuum gauges overlap the vacuum and overpressure regions.
The function of manometers is to determine overpressure.
As a result of the standardisation of the ranges of measured pressures, it is accepted that they correspond to a certain range of values (Table 2).

Table 2. Standard range of scale graduation values.

Тип прилада	Діапазони вимірюваних тисків, кгс/см2
Вакуумметри	-1…0
Мановакуумметри	-1…0,6; 1,5; 3; 5; 9; 15; 24
Манометри	0…0,6; 1; 1,6; 2,5; 4; 6; 10; 16; 25; 40; 60; 100; 160; 250; 400; 600; 1000; 1600
Манометри надвисоких тиску	0…2500; 4000; 6000; 10000

ACCURACY CLASS OF PRESSURE GAUGES.

The accuracy class of the device refers to the permissible error, which is expressed as a percentage of the maximum value of the pressure gauge scale. The higher the accuracy of the device, the lower the error. The accuracy class is indicated on the scale of the device. Pressure gauges of the same type may have different accuracy classes.

DIAMETER OF THE PRESSURE GAUGE BODY.

The most common diameters of pressure gauge bodies are 40, 50, 60, 63, 100, 150, 160, 250 mm. But there are devices with other body sizes. For example, vibration-resistant pressure gauges manufactured by UAM, type D8008-V-U2 – an analogue of DA8008-VUF manufactured by Fiztekh, have a diameter of 110 mm.

DESIGN OF PRESSURE GAUGES.

A fitting is used to connect the device to the system. There are two types of fittings: radial (bottom) and axial (rear). The location of the axial fitting can be central or offset from the centre. Many types of pressure gauges are designed with a radial connection only. For example, electrocontact pressure gauges.
The thread size of the fitting corresponds to the diameter of the body. Pressure gauges with diameters of 40, 50, 60, 63 mm have threads M10x1.0-6g, M12x1.5-8g, G1/8-B, R1/8, G1/4-B, R1/4. Pressure gauges with larger diameters are made with M20x1.5-8g or G1/2-B threads. European standards use, in addition to the above-mentioned thread types, tapered threads – 1/8 NPT, 1/4 NPT, 1/2 NPT. In industrial environments, specific connections are used depending on the tasks and types of measured media. For pressure gauges operating at high and ultra-high pressure levels, an internal tapered thread or a cylindrical thread variant is typical.
Depending on the type of equipment, specify the required thread type when ordering the device. This will help to avoid additional unforeseen costs, which will entail the replacement of the fitting.
The design of the pressure gauge body is also selected according to the installation method and location. For open pipelines, the design of the devices does not provide for additional fasteners. For devices installed in cabinets or control panels, a front and rear flange is required.

Depending on the design, there are the following types:

with bottom connection without flange;
with back socket with rear flange;
with bottom connection with front flange;
with back connection without flange.

The standard version of pressure gauges has an IP40 rating. Special pressure gauges are available in IP50, IP53, IP54 and IP65 degrees of protection depending on the conditions of use.
To prevent unauthorised opening of the pressure gauge, the device must be sealed. For this purpose, an eyelet is made on the body, equipped with a screw with a hole in the head for installing the seal.

Protection against high temperatures and pressure drops.
The measurement error of a pressure gauge depends on the influence of the ambient temperature and the temperature of the measured medium.
For most devices, the temperature range of measurement is no more than +60°C, maximum +80°C. Some manufacturers’ devices have the ability to measure pressure at high ambient temperatures of up to +150°C or even 300°C.
For standard pressure gauges, operation in such conditions is possible only if there is a siphon outlet (cooler) through which the pressure gauge is connected to the system.
This is a specially shaped tube with threaded ends for connection to the mains and connection of the pressure gauge. The siphon branch creates a branch in which the measured medium does not circulate. Due to this, the temperature at the point of connection of the device is much lower than in the main line.

In addition, the durability of the pressure gauge is affected by sudden changes in measured pressure and water hammer. To reduce the impact of these factors, damping devices are used. The damper is installed in front of the device as a separate device or mounted in the channel of the pressure gauge holder.
If you do not need to constantly monitor the pressure in the system, you can install the pressure gauge through a push-button valve. This allows the device to be connected to the mains only when the tap button is pressed. This protects the device without the need for a damper device.

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Operating instructions for pressure gauges

islamovbogdan — Thu, 14 Sep 2023 17:32:00 +0000

Installation and disassembly must only be carried out when the pipeline is depressurised. Mounting must be carried out using a spanner on the fitting.

The torque must not exceed 20 Nm.

Use O-rings (PTFE or copper) to seal the connection between the pressure gauge and the pressure source.

The use of winding materials for this purpose is not permitted!

The pressure is supplied through pipelines with an internal diameter of at least 3 mm.

The pressure must be applied smoothly and evenly. In the process of changing the pressure, its speed should not exceed 10% of the scale per second.

Do not mount or dismount the appliance by the housing. Do not apply force to the case!

The pressure gauge must be installed through a shut-off valve or valve

The final installation of the device must comply with the standards required for its functioning: the housing must be positioned vertically (permissible deviation not exceeding ±5° in any direction) or in accordance with the operating position mark on the dial.

When measuring the pressure of media with a temperature higher than the maximum permissible temperature, a cooler should be installed upstream of the instrument. In this case, the error of the device readings under the influence of temperature will be reduced as much as possible.

THE PRESSURE GAUGE SHALL NOT BE OPERATED IF:

the device does not work;
there is damage to the glass;
the movement of the arrow is abrupt or the arrow does not return to its original position (zero mark) after the measurement;
the readings exceed the permissible rate of error.

If there is no pressure, the arrow normally returns to the zero mark. Deviations from “0” are permissible according to the limit value of the accuracy class of the device. If the arrow deviates beyond this range, the device is defective.

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Recommendations for choosing UAM devices

islamovbogdan — Thu, 14 Sep 2023 17:21:00 +0000

When choosing models and additional options of UAM devices, you should be guided by the requirements of
technical and design documentation, take into account the specific application conditions
of the devices:
• It is necessary to choose a device with such a measuring range that the operating
range of measured system pressures was in the range from 25% to 75% of the
scales;
• For work in open areas, it is necessary to choose devices with a higher degree of environmental protection. To work in difficult climatic conditions, it is necessary to choose UAM devices with the appropriate climatic version according to GOST15150-69;
• In areas of high vibration, it is recommended to choose devices with increased
vibration resistance;
• When measuring the pressure of aggressive media, it is necessary to use
corrosion-resistant versions.

Degree of protection of the UAM device case

The degree of protection of the UAM devices’ casing against environmental influences meets the requirements of DSTU EN 60529.
The degree of protection of the casing is indicated on the dial:

IP	The value of protected equipment
IP 40	Protected against dust with a diameter of more than 1 mm, not protected against moisture.
IP 53	Dust-proof, protected from harmful water in the form of sprinkling.
IP 54	Dustproof, protected from harmful water in the form of continuous spraying.
IP 63	Dustproof, protected from harmful water flow, protected from harmful effects.

Ratio of pressure units

	Pа	кPа	МPа	kgs/cm²	bar
Pа	1	10^-3	10^-6	1,0197х10^-5	10^-5
кPа	10³	1	10^-3	1,0197х10^-2	10^-2
MPа	10⁶	10³	1	10,1972	10
kgs/cm²	98066,5	98,0665	0,980665	1	0,980665
bar	10⁵	100	0,1	1,0197	1

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Order card

islamovbogdan — Thu, 14 Sep 2023 17:13:00 +0000

Ordering card for electric contact pressure gauges

Pressure gauge DM2005-U2 (1.0 MPa, ac. 1.5, M20x1.5, IP40, Bottom, V)

1 2 3 4 5 6 7 8

1 – type of device (vacuum gauge, manovacuum gauge, pressure gauge) 2 – model of the device 3 – pressure range limits with indication of measurement units 4 – accuracy class of the device 5 – connection thread 6 – degree of dust and water protection (IP) 7 – location of the connector 8 – version of the signalling device, contact group.

Order card for technical pressure gauges

Pressure gauge MP3-U2 (0.6 MPa, ac. 1.5, M20x1.5, IP40, Bottom)

1 2 3 4 5 6 7

Ordering card for thermometers

Bimetallic thermometer TB-U2 (0-120 C, ac. 1.0, L 50 mm, G 1/2, 100, IP54, Back)

1 2 3 4 5 6 7 8 9

1- type of device 2- model of the device 3- temperature range limits 4- accuracy class of the device 5- length of the device stem 6- connecting thread 7- diameter of the device body 8- degree of dust and water protection (IP) 9- location of the stem.

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Сontact group options

islamovbogdan — Thu, 14 Sep 2023 17:06:00 +0000

if the arrow is within the setpoint range, one contact is open, the other is closed
if the arrow goes beyond the red pointer, the contact opens (both contacts are open)
if the arrow goes beyond the blue pointer, the contact closes (both contacts are closed)

if the arrow is within the setpoint range, one contact is closed, the other is open
if the arrow goes beyond the red pointer, the contact opens (both contacts are open)
if the arrow goes beyond the blue pointer, the contact closes (both contacts are closed)

if the arrow is within the setpoint range, both contacts are open
if the arrow moves beyond the left blue pointer, the contact closes (one contact closed, the other open)
if the arrow moves beyond the right blue pointer, the contact closes (one contact is open, the other is closed)

if the arrow is within the setpoint range, both contacts are closed
if the arrow moves beyond the left red pointer, the contact opens (one contact is open, the other is closed)
if the arrow moves beyond the right red pointer, the contact opens (one contact is closed, the other is open)

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