Pressure gauge refers to the elastic element as the sensitive element, measuring and indicating higher than the ambient pressure of the instrument, the application is extremely common, it is almost all over the industrial process and scientific research field.They can be found everywhere in the fields of heat networks, oil and gas transmission, water and gas supply systems, vehicle repair and maintenance workshops and so on.Especially in the industrial process control and technical measurement process, due to the mechanical pressure gauge of the elastic sensitive element has a high mechanical strength as well as production convenience and other characteristics, so that the mechanical pressure gauge has been more and more widely used.
Working Principle
Pressure gauges display pressure through the elastic deformation of the sensitive components (bourdon tube, membrane box, bellows) inside the gauge, and then the conversion mechanism of the movement inside the gauge conducts the pressure deformation to the pointer, causing the pointer to rotate.
Fabric
Overflow hole: In case of an emergency situation where the bourdon tube bursts, the internal pressure will be released to the outside world through the overflow hole to prevent the glass panel from bursting.Note: In order to maintain the normal performance of the overflow hole, it is necessary to leave a space of at least 10mm behind the meter, and the overflow hole should not be modified or plugged.
Pointer: In addition to the standard pointer, other pointers are also optional.
Glass panel: In addition to the standard glass, other special materials such as reinforced glass and non-reflective glass are also available.
Performance classification: General type (standard), general type for steam (M), heat-resistant type (H), vibration-resistant type (V), vibration-resistant type for steam (MV) heat-resistant vibration-resistant type (HV).
Treatment: No oil/water treatment Water or oil residue in the liquid-access portion is removed at the time of manufacture.
Exterior designation: Case color is to be specified in addition to the standard color.
Throttle (optional): To minimize pulsating pressure, the throttle is installed at the pressure inlet.
Notes on use
1, the instrument must be vertical: the installation should be tightened using a 17mm wrench, should not be twisted case; transportation should be to avoid collision;
2, the instrument should be used in the surrounding ambient temperature of -25 ~ 55 ℃;
3, the use of the working environment, vibration frequency <25HZ, amplitude is not greater than 1mm;
4, due to the use of the ambient temperature is too high, the instrument does not return to the zero position of the indicator or the value of the display value of the super-differential, the case can be sealed rubberPlug cut, so that the instrument cavity and the atmosphere can be communicated;
5, the instrument should be used in the upper limit of the range of 1 / 3 ~ 2 / 3;
6, in the measurement of corrosive media, may be crystallization of the medium, the viscosity of the medium should be added to the isolation device;
7, the instrument should be regularly calibrated (at least once every three months), such as faults should be repaired in a timely manner;
8, instrumentation from the factory date, within six months if the use of the normal storage conditions found under poor manufacturing quality failure.8, instrumentation from the date of shipment, within six months under normal storage and use conditions, if found due to poor manufacturing quality failure or damage, the company is responsible for repair or replacement;
9, need to measure corrosive media instrumentation, in the order should indicate the requirements of the conditions.
Principles of Selection
Pressure gauge selection should be based on the use of technology production requirements, for specific situations to do specific analysis.Under the premise of meeting the process requirements, should be in line with the principle of saving a comprehensive and integrated consideration, generally should consider the following aspects of the problem:
1. Selection of type
Instrumentation type selection must meet the requirements of the production process.For example, whether the need for remote transmission, automatic recording or alarm; the nature of the measured medium (such as the measured medium temperature, viscosity, size, corrosivity, degree of dirt, whether flammable and explosive, etc.) whether the instrument puts forward special requirements, the site environmental conditions (such as humidity, temperature, magnetic field strength, vibration, etc.) on the type of instrumentation requirements.Therefore, according to the process requirements to correctly select the type of instrumentation is to ensure the normal operation of the instrument and the important premise of safe production.
2. Determination of the measuring range
In order to ensure that the elastic element can work reliably within the safety range of elastic deformation, when selecting the range of the pressure gauge, it must be based on the size of the measured pressure and the speed of the pressure change, leaving enough room for error, so the upper limit of the pressure gauge should be higher than the maximum possible pressure value in the production process.According to the "chemical automatic control design technical regulations", in the measurement of stable pressure, the maximum working pressure should not exceed 2/3 of the upper limit of measurement; measurement of pulsating pressure, the maximum working pressure should not exceed 1/2 of the upper limit of measurement; measurement of high-pressure, the maximum working pressure should not exceed 3/5 of the upper limit of measurement.The minimum value of the measured pressure should not be lower than 1/3 of the upper limit value of the instrument, so as to ensure the linear relationship between the output quantity and the input quantity of the instrument.
According to the maximum and minimum values of the measured parameters to calculate the upper and lower limits of the instrument, can not use this value directly as the measuring range of the instrument.When we choose the upper limit of the scale of the instrument, we should select the standard series in the national regulations.China's standard series of pressure gauge measuring range are: -0.1-0.06,0.15;0-1,1.6,2.5,4,6,10X10" MPa (where n is a natural integer .(Can be positive and negative values).
3. Selection of accuracy level
According to the maximum absolute error permitted by the production process and the selected instrumentation range, the maximum quoted error permitted by the instrumentation is calculated, and the precision of the instrumentation is determined in the precision level specified by the state.Generally speaking, the more precise the selected instrument is, the more accurate and reliable the measurement results.But can not be considered to choose the higher the accuracy of the instrument the better, because the more precise instrumentation is generally more expensive, operation and maintenance of the more laborious.
Selected examples:
1, used to measure viscous or acidic and alkaline and other special media, should be selected diaphragm pressure gauge, stainless steel spring tube, stainless steel movement, stainless steel shell or gum wood shell.
According to the different media measured, there should be a prescribed color code on the pressure gauge, and indicate the name of the special media, oxygen table must be marked with red "no oil" words, hydrogen with dark green under the horizontal line of the color code, ammonia with yellow under the horizontal line of the color code and so on.
2. When installed against the wall, the pressure gauge with edge should be used; when installed directly on the pipeline, the pressure gauge without edge should be used; when used for direct measurement of gases, the pressure gauge with safety holes at the back of the case should be used.For the consideration of pressure measurement position and easy observation and management, the size of case diameter should be selected.
Major category
There are many kinds of pressure gauges, it is not only general (ordinary) pointer indication type, there are digital type; not only conventional type, there are special type; not only contact type, there are remote transmission type; not only vibration-resistant type, there are seismic type; not only diaphragm type, there are corrosion-resistant type and so on.Pressure gauge series is complete.It is not only the conventional series, there are digital series; not only ordinary media application series, there are special media application series; not only switching signal series, there are remote signal series, etc., which are derived from the practical needs, has constituted a complete series.The specifications and models of pressure gauges are complete, and the structure type is perfect.In terms of nominal diameter, there are Φ40mm, Φ50mm, Φ60mm, Φ75mm, Φ100mm, Φ150mm, Φ200mm, Φ250mm and so on.From the point of view of installation structure type, there are direct mounting type, embedded type and convex mounting type, in which embedded type is divided into radial embedded type and axial embedded type, and convex mounting type is also divided into radial convex mounting type and axial convex mounting type.Direct mounting type, which is divided into radial direct mounting type and axial direct mounting type.Radial direct mounting is the basic installation type, generally not specified in the installation structure type, are referred to as radial direct mounting.Axial direct mounting type considering the stability of its own support, generally only in the nominal diameter of less than 150mm pressure gauge on the choice.The so-called embedded and convex mounted pressure gauge, is what we often say with the edge (mounting ring) pressure gauge.Axial embedded both axial front with edge, radial embedded means radial front with edge, radial convex mounted (also called wall mounted) means radial back with edge pressure gauge.From the range and range segments, in the positive pressure range is divided into micro-pressure range segments, low-pressure range segments, medium-pressure range segments, high-pressure range segments, ultra-high-pressure range segments, each range segment is subdivided into a number of types of measurement ranges (instrumentation ranges); in the negative-pressure range (vacuum) and there are three types of negative pressure (vacuum gauge); positive pressure and negative pressure range pressure gauge is a cross-domain pressure gauge.Its standardized name for the pressure vacuum gauge, also called vacuum pressure gauge.It can measure not only positive pressure but also negative pressure.The accuracy classifications of pressure gauges are very clear.Common accuracy levels are 4, 2.5, 1.6, 1, 0.4, 0.25, 0.16, 0.1 and so on.The accuracy level should be marked on the dial, and there are corresponding regulations for its marking, such as "①" indicates that its accuracy level is 1.For some of the accuracy level is very low pressure gauge, such as 4 under the level, and some do not need to measure the exact pressure value, only need to indicate the pressure range, such as fire extinguishers on the pressure gauge, you can not identify the accuracy level.
Pressure gauge according to its measurement accuracy: can be divided into precision pressure gauge, general pressure gauge.Precision pressure gauge measurement accuracy level were 0.1, 0.16, 0.25, 0.4 0.05 level; general pressure gauge measurement accuracy level were 1.0, 1.6, 2.5, 4. 0 level.
Pressure gauge according to its measurement benchmark: pressure gauge according to its indication of the pressure of different benchmarks, divided into general pressure gauge, absolute pressure gauge stainless steel pressure gauge, differential pressure gauge.General pressure gauge to atmospheric pressure as a reference; absolute pressure gauge to absolute pressure zero as a reference; differential pressure gauge to measure the difference between the two measured pressure.
Pressure gauges are divided into vacuum gauges, pressure vacuum gauges, micro-pressure gauges, low-pressure gauges, medium-pressure gauges and high-pressure gauges according to their measuring range.Vacuum gauges are used to measure pressure values less than atmospheric pressure; pressure vacuum gauges are used to measure pressure values less than and greater than atmospheric pressure; micro-pressure gauges are used to measure pressure values less than 60,000 Pa; low-pressure gauges are used to measure pressure values from 0 to 6 MPa; medium-pressure gauges are used to measure pressure values from 10 to 60 MPa;
Pressure gauge according to its display: divided into pointer pressure gauge, digital pressure gauge.
Pressure gauge according to its use function: pressure gauge according to its use function can be divided into on-site indication type pressure gauge and with electrical signal control type pressure gauge.
General pressure gauges, vacuum pressure gauges, shock-resistant pressure gauges, stainless steel pressure gauges, etc. belong to the in situ indication type pressure gauges, in addition to the indication of pressure without other control functions.
With electrical signal control type pressure gauge output signals are:
1, switching signals (such as electric contact pressure gauge)
2, resistance signals (such as resistance remote pressure gauge)
3, current signals (such as inductive pressure transmitter, remote pressure gauge, pressure transmitter, etc.)
Pressure gauges can be categorized according to the characteristics of the measuring medium:
1, general type pressure gauge: general type pressure gauge for measuring non-explosive, non-crystallization, non-condensation of copper and copper alloy corrosion-free liquids, gases or steam pressure;
2, corrosion-resistant pressure gauge: corrosion-resistant pressure gauge for measuring the pressure of corrosive media, commonly used stainless steel pressure gauge, diaphragm-type pressure gauges, etc.;
3, explosion-proof pressure gauge: explosion-proof pressure gauge for use in the environment of explosive mixture, hazardous places, such as explosion-proof electric contact pressure gauge, explosion-proof transmitters, etc.Explosion-proof pressure gauge: explosion-proof pressure gauge used in the environment of explosive mixtures in hazardous places, such as explosion-proof electric contact pressure gauge, explosion-proof transmitter and so on.
4、Specialized pressure gauge.
According to the use of pressure gauge: can be divided into ordinary pressure gauge, ammonia pressure gauge, oxygen pressure gauge, electric contact pressure gauge, remote pressure gauge, vibration-resistant pressure gauge, with inspection pointer pressure gauge, double needle double tube or double needle single tube pressure gauge, digital pressure gauge, digital pressure gauge, digital precision pressure gauge and so on.
Basic term
1、Positive pressure and negative pressure
2、Relative pressure and absolute pressure
3、Vacuum degree
4、Pressure expression method
There are two ways to express pressure: one is to absolute vacuum as the reference pressure, called the absolute pressure; the other is to atmospheric pressure as the reference pressure, called the relative pressure.As most of the pressure measuring instruments measured pressure is the relative pressure, so the relative pressure is also known as the gauge pressure.When the absolute pressure is less than the atmospheric pressure, the absolute pressure in the container can be less than the value of one atmosphere to indicate.It is called "vacuum degree".Their relationship is as follows:
Absolute Pressure = Atmospheric Pressure + Relative Pressure
Vacuum = Atmospheric Pressure - Absolute Pressure
The legal unit of pressure in China is Pa (N/m2), which is called Pascal, or Pa for short.Since this unit is too small, it is often used 10^6 times its unit MPa (megapascals).
Common Types
Bourdon tube pressure gauge: The sensitive element of the Bourdon tube is an elastic C-shaped tube bent into a round shape with an elliptical cross-sectional area.The pressure of the measuring medium acts on the inside of the fluctuating tube, so that the elliptical cross-section of the Borden tube tends to a circular cross-section.Due to the small deformation of the Borden tube, a certain ring stress is formed.This ring stress causes the Borden tube to extend outwards.Since the head of the elastic bourdon tube is not fixed, a small deformation occurs, the size of which depends on the pressure of the measuring medium.The deformation of the bourdon tube is indirectly indicated by the pointer through the movement to the pressure of the measuring medium.
Diaphragm Gauge: The sensitive element of the diaphragm consists of two diaphragms connected together in a circular wave pattern.The pressure of the measuring medium is applied to the inner side of the diaphragm chamber and the resulting deformation can be used to indirectly measure the pressure of the medium.The magnitude of the pressure value is indicated by a pointer.Membrane cartridge pressure gauges are generally used to measure the pressure of gases and are capable of measuring micro-pressures, overpressure protection to a certain extent.When several membrane box sensitive elements are stacked together will produce a large transfer force to measure the very small pressure.
Explosion-proof pressure gauge: explosion-proof pressure gauge is suitable for use in flammable and explosive occasions, it is different from the ordinary pressure gauge, explosion-proof pressure gauge is more demanding, first of all, the safety factor is high or not, there are many types of explosion-proof pressure gauges, how to choose the right pressure gauge for their own, it is necessary to consider the whole picture.Explosion-proof pressure gauge according to the explosion-proof coefficient: intrinsically safe explosion-proof pressure gauge and explosion-proof pressure gauge.Explosion-proof pressure gauge by explosion-proof coefficient: intrinsically safe explosion-proof pressure gauge and explosion-proof pressure gauge; explosion-proof pressure gauge with electric contact, pointer explosion-proof pressure gauge and digital display.
Explosion-proof electric contact pressure gauge: explosion-proof electric contact pressure gauge explosion-proof shell has a good performance of explosion-proof, so explosion-proof electric contact pressure gauge in the normal course of work due to the impact of sparks or arcs, in addition to withstand the explosive gas mixture inside the shell in the event of an explosion caused by the explosion of the pressure generated, and can effectively prevent the resulting heat to the outside of the smooth propagation of the shell can only be along the explosion-proof internaljoints along the explosion-proof surface of the tiny gaps in the slow diffusion to the outside.At this time, the instantaneous temperature transmitted to the outside of the shell has been reduced to below the ignition temperature of explosive gas mixtures, so it will not lead to the transmission of explosion.Explosion-proof digital (pointer) display pressure gauge: high precision, high stability, error ≤ 1%, internal power supply, micro-power consumption, stainless steel shell, strong protection, beautiful and delicate.Explosion-proof digital display pressure gauge is widely used in petroleum, chemical industry, metallurgy, power stations and other industrial sectors or mechanical and electrical equipment supporting the measurement of the explosion risk of various fluid media pressure.
Vacuum Pressure Gauge: Vacuum Pressure Gauge is used to measure the pressure or negative pressure of non-crystallizing, non-condensing liquid, gas or steam medium without corrosion on steel, copper and copper alloy, and without the danger of explosion.Shock-resistant vacuum pressure gauge table for vibration and pressure fluctuations, measurement of non-corrosive, non-crystallization of the negative pressure of the medium.Electric contact pressure vacuum gauge and electric contact vacuum gauge for copper and copper alloy corrosion-free, non-explosive risk of non-crystallization, non-condensable liquids, gases and other media (pressure) and negative pressure measurement, when the pressure reaches a predetermined value, with the help of contact device, can be connected or disconnected from the control circuit, and at the same time, send out an electrical signal.
Classification of vacuum pressure gauges:
Vacuum pressure gauges are instruments used to measure pressures greater than and less than atmospheric pressure with reference to atmospheric pressure.
Shock-resistant vacuum pressure gauge as a classification of shock-resistant pressure gauge, used for vibration and pressure has fluctuations, measurement of non-corrosive, non-crystallization of the negative pressure of the medium.
Electric contact vacuum pressure gauge and electric contact vacuum gauge copper and copper alloy non-corrosive, non-explosive risk of non-crystalline non-condensable liquids, gases and other media (pressure) and negative pressure.
Stainless steel pressure vacuum gauge is used to measure the pressure and negative pressure of liquid, gas media without corrosive effect on stainless steel 316, 316L and 0Crl8Ni12MO2Ti, all stainless steel has stronger corrosion resistance to the environment.
Acid Resistant Pressure Vacuum Gauge is used to measure the pressure and negative pressure of nitric acid and alkali liquid medium; Acid Resistant Vacuum Gauge is used to measure the negative pressure of nitric acid and alkali liquid.
Installation
Pressure gauge national standard "General Pressure Gauge" GB/T1226-2001, No. 4.1.2 instrumentation according to the threaded joints and installation methods are divided into: direct installation of pressure gauges, embedded (disk mounted) pressure gauges, convex mounted (wall mounted) pressure gauges.
1, the installation position of the pressure gauge should be in line with the requirements of the installation status, the dial should not be placed horizontally, the height of the installation position should be easy for staff to observe.
2、The distance between the pressure gauge installation and the pressure measurement point should be as short as possible to ensure perfect sealing, no leakage phenomenon.
3, in the installation of the front end of the pressure gauge should be a buffer; in order to facilitate the inspection, below the instrument should be equipped with a shut-off valve; when the medium is dirty or impulse pressure, filters, buffers and stabilizer gas can be used.
Measurement limit
1, the size of the upper limit value of the pressure gauge measurement is based on the spring tube size, stiffness and non-linear conditions designed to measure the upper limit value of 1 × 10n, 1.6 × 10n, 2.5 × 10n, 4 × 10n, 6 × 10n five series, n is a positive integer, negative integer or zero.
2, digital pressure gauge pressure range: -100kPa ～ 2kPa ～ 260MPa.
3, the pressure gauge is lower than 1 / 3 range part of the accuracy is low, should not be used.Select the upper limit of measurement, in order to ensure the safe and reliable operation of the pressure gauge to maintain its service life, generally should be greater than 1/3 of the maximum operating pressure.
4, select the use of the range, according to the universality of the load condition, should be selected to use the full range of 1 / 3 ~ 2 / 3 is appropriate, because the use of this range of higher accuracy, and in the smooth, fluctuations in the two types of loads can be used.The maximum range of use should not exceed 3/4 of the full scale of the dial.
Quality requirements
1, the general pressure gauge spring tube is a certain cross-sectional shape (commonly used flat round and nearly oval two kinds), bent into a "C" shape, and can meet the requirements of a certain elasticity of the tubular spring.If the spring tube is too small, it will affect the accuracy level of the pressure gauge.
2, the display value of the pressure gauge exceeds the allowable error, it should be adjusted to repair the display value of the table adjusting screw, if the table does not display value adjusting screw, this table can only be judged as unqualified.
3, pressure gauge dial index numbers and symbols should be complete and clear.Dial index scale should be evenly distributed, the center angle of the package is generally 270 °, the pointer of the pressure gauge should be extended into all the index line, the width of the pointer indicator end should be no more than 1/5 of the minimum index interval. the distance between the pointer and the index plate plane should be in the range of 1 ~ 3mm case outside diameter of more than 200mm (including 200mm), the distance between the pointer and the index plate plane should be in the range of 2 ~ 4mm.The distance between the pointer and the plane of the indexing dial shall be within the range of 2-4mm.
4, with a stop pin pressure gauge, in the absence of pressure or vacuum when the pointer should be close to the stop pin, "shrinkage" shall not exceed the specified allowable error.
5, the pressure gauge case should be able to protect the internal components from contamination, the pressure gauge should be equipped with safety holes, safety holes need to have a dustproof device.
6, digital pressure gauge is to look at the overall structure of the rationality, the material selected, the aging process of electronic components, long-term stability.
Range Selection
1, in order to ensure that the pressure gauge elastic element can work reliably within the safety range of elastic deformation, the choice of pressure gauge range should not only be based on the size of the measured pressure, but also should take into account the speed of change of the measured pressure, and its range needs to leave enough room.When using the pressure gauge to measure the steady pressure, the maximum working pressure should not exceed 2/3 of the range;
2. When using the pressure gauge to measure the pulsating pressure, the maximum working pressure should not exceed 1/2 of the range;
3. When using the pressure gauge to measure the high pressure, the maximum working pressure should not exceed 3/5 of the range; in order to ensure the accuracy of the measurement, the minimum working pressure should not be less than 1/3 of the range; in accordance with this principle, the pressure gauge should be selected according to the maximum pressure under test.According to this principle, after calculating a value according to the maximum pressure to be measured, select a measurement range slightly larger than this value from the catalog of pressure gauges.
4, should be selected according to the working pressure of the boiler, the limit value of the range scale should be 1.5 to 3.0 times the working pressure, preferably 2 times.In industrial boilers, the actual situation is that the actual operation of the boiler working pressure is always lower than the rated pressure on the nameplate, industrial steam boilers and hot water heating boilers are so.For example, 4t / h of steam boilers, rated pressure of 1MPa, manufacturers such as 1.5 times to be equipped with pressure gauges, should be equipped with 1.6MPa range pressure gauge.If the user as a result of the production process needs, the actual operation of the 0.5MPa pressure that can meet the process requirements, then run the range, the pressure gauge pointer in the range of less than one-third of the position, the pointer turned over a small angle.That is, the selection of the pressure gauge range is too large.Hot water boiler is also the case, such as heating boiler rated pressure of 0.7MPa, equipped with a pressure gauge should be 1MPa or 1.6MPa, such as equipped with a 1MPa pressure gauge, for fear of overloading the pressure gauge in the hydrostatic test, so they are equipped with a range of 1.6MPa pressure gauge.Actual operation, as long as 0.2MPa can meet the heating requirements, the pressure gauge pointer in the range of one-eighth of the position, it is difficult to make people believe that the accuracy and sensitivity of the pressure gauge.
5, in order to solve the above problems, two pressure gauges should be used, that is, in the hydraulic test, the boiler factory is equipped with the pressure gauge according to the rated pressure;
6, in the daily operation of the actual working pressure of two times to be equipped with the pressure gauge.If the working pressure is 0.2MPa, that is, with 0.4MPa range of the pressure gauge.So that the pointer in the middle of the dial position, vertical up.The seating pressure of the safety valve is also adjusted according to the operating pressure, and the pressure gauge still has enough margin to cope with the overpressure indication.
Accuracy class
1, the accuracy level of the pressure gauge is to reflect the accuracy of the tested table and precision table for comparison, the indication value and the real value close to the degree of accuracy.It is equal to the percentage of the ratio between the absolute value of the maximum basic error and the upper limit of measurement, which is decided according to the size of the error generated in the calibration.
2, China's general industrial pressure gauge is divided into four accuracy levels, in line with JJG52-2013 "spring tube general pressure gauge, pressure vacuum gauge and vacuum gauge," the verification regulations on the pressure gauge proposed allowable error.The four accuracy levels are: level 1, level 1.6, level 2.5 and level 4.Allowable error (calculated as a percentage of the upper limit of measurement) is ±1%, ±1.6%, ±2.5%, ±4%.
3, China in 2005, the new digital pressure gauge calibration regulations published and implemented, in line with JJG875-2019 "Digital Pressure Gauge Calibration Regulations" [3].Provides for the pressure accuracy of ± 0.01%, ± 0.02%, ± 0.05%, ± 0.1%, ± 0.2%, ± 0.5%, ± 1.0%, ± 1.6%, respectively.
4, a reasonable choice of pressure gauge accuracy level method, should be based on the production process, economic practicality, testing methods and other requirements, according to the minimum value of the measured pressure required by the permissible error to select the accuracy level.
Maintenance(of equipment)
1, after a period of use and pressure, the pressure gauge movement will inevitably appear some deformation and wear, the pressure gauge will produce a variety of errors and failures.In order to ensure its original accuracy without distorting the transmission of the value, it should be replaced in time to ensure that the instructions are correct, safe and reliable.
2, the pressure gauge should be cleaned regularly.Because the internal pressure gauge is not clean, it will increase the wear and tear of the various components, thus affecting its normal work, and in serious cases, it will make the pressure gauge malfunction and be scrapped.
3, the pressure gauge installed in the pressure measurement part, according to the provisions of JJG52-2013, its calibration cycle is generally no more than half a year.Relating to production safety and environmental monitoring of the pressure gauge, the verification cycle must be in accordance with the verification procedures, only less than half a year; if the mining conditions are harsh, the verification cycle must be shorter.
4, the pressure part of the media fluctuations, frequent use, high accuracy requirements, as well as more stringent requirements for safety factors, according to the specific circumstances of the verification cycle will be appropriately shortened.
The following four 11 types of pressure gauges require mandatory calibration:
1, used for safety and protection of the pressure gauge is subject to mandatory certification.Including the following seven categories:
1) the measurement of the boiler main cylinder and feedwater pressure parts;
2) fixed air compressor air bin and the measurement of the pressure of the main pipe; 3) generators, gas turbine oil pressure and locomotive pressure measurement;
4) medical autoclave sterilizers, autoclave pressure measurement;
5) with the measurement of the pressure of the alarm device;
6) sealing pressurized container pressure measurement; Pressure gauges (Figure 18)
7) hazardous, toxic and corrosiveMeasurement of pressure of severe media.(e.g. spring tube pressure gauges, electric remote transmission and electric contact pressure gauges).
2, used for safety and protection of the wind pressure gauge needs to be mandatory calibration.That is: the measurement of wind pressure and wind speed in the tunnel in the mine.(Such as: mine wind pressure meter, mine anemometer).
3, used for safety and protection of oxygen meters need to be mandatory calibration.Including the following 2 categories:
1) in the process of filling oxygen cylinders oxygen monitoring pressure measurement; 2) in the process of explosive, affecting the safety of oxygen pressure measurement.
4、Oxygen meters used for medical and health care are subject to mandatory calibration.That is, the hospital oxygen delivery with buoy oxygen inhaler and oxygen supply device on the oxygen pressure measurement.
Common problems
Pressure gauge is composed of several main parts, including connector, spring tube and movement.The welding of the pressure gauge is mainly lead-zinc welding, silver welding, argon arc welding, special welding, etc. The normal work of the instrument's clarinet is 100,000 times.Its working principle is through the spring tube deformation, movement (fan-type teeth and the center gear work) to drive the pointer in the face plate scale shows the measured medium pressure.
Pressure gauge in the use of three common problems:
1, the pressure gauge fan gear work for some time will appear wear phenomenon;
2, the pressure gauge pressure measurement system by the measured medium instantaneous overpressure impact, so that the pointer can not return to the zero position or rushed to the restriction of the nail below;
3, the instrument pointer, in the system unpressurized does not return to the zero position.
Three ways to solve the common problems of pressure gauges:
1, increase the fan gear contact surface width, increase the contact surface (i.e., increase the modulus of the gear), in order to achieve anti-wear to increase the service life of the purpose;
2, in the instrument's movement on the installation of a limit block, the pressure measurement system in the instantaneous impact so that the movement of the cylindrical gears and fan gears are not easy to disengage, to solve the pressure gauge by the pressure of the impact of the needle does not go back to zero or the pointer is washed to theLimit nail behind the problem;
3, impact pressure measurement system to close the valve below the pressure gauge.
Anticorrosion measures
Corrosion protection of the housing:
1, the use of corrosive gases in the environment is recommended to use stainless steel shell or shell spraying PTFE, in order to extend the service life of the pressure gauge;
2, the use of high humidity in the environment is recommended to increase the level of protection of the shell in order to prevent the external moisture into the table, improve the service life of the pressure gauge.
Receiving liquid part of the corrosion:
1, for general corrosive media, if the stainless steel elastic components can withstand 1 to 2 years of corrosion, then you can use the general stainless steel pressure gauge, installation, the pressure guide pipe should be short, if necessary, buffer coils changed to buffer tanks, to prevent impurities clogging.
2, if the medium of stainless steel and copper have a purpose corrosion, the buffer tank can be changed to isolation tank, add corrosion-resistant isolation fluid.The type of isolation fluid can be selected according to the nature of the measured medium, but requires the use of more than half a year without deterioration is good.If the ordinary isolation fluid can not be applied, the available chlorofluorocarbon oil as an isolation fluid, but the price is very expensive, so the isolation tank should be made small, when disassembled to recover the fluorine oil for reuse.
3, diaphragm pressure gauge can be used, molybdenum-containing stainless steel, Hastelloy and tantalum sheet, diaphragm and ballistic tube with methyl silicone oil between the pressure transfer, the minimum range can be done to 0 ~ 100kPa, if the diaphragm material is not corrosion-resistant, it can be added to a layer of F46 (polypentafluoroethylene propylene) diaphragm, but the instrument sensitivity has been reduced.F46 can also be used directly as an isolation diaphragm, but pay attention to the permeability of the medium, high temperature and prohibit the use of oil media transfer fluid can be selected fluorine oil.
