Pressure gauge refers to a gauge that uses elastic elements as sensitive elements to measure and indicate pressures higher than the ambient pressure. It is widely used. It covers almost all industrial processes and scientific research fields. It can be seen everywhere in the fields of heating pipe network, oil and gas transmission, water and gas supply system, vehicle repair and maintenance factories and stores. Especially in the process of industrial process control and technical measurement, because the elastic sensitive element of the mechanical pressure gauge has the characteristics of high mechanical strength and convenient production, the mechanical pressure gauge has been more and more widely used.
Main structure
Overflow hole: In the event of an emergency such as a Bourdon tube burst, the internal pressure will be released to the outside through the overflow hole to prevent the glass panel from bursting. Note: In order to maintain the normal performance of the overflow hole, a space of at least 10mm must be left behind the table, and the overflow hole cannot be modified or plugged.
Pointer: In addition to standard pointers, other pointers are also optional.
Glass panel: In addition to standard glass, other special material glass, suc as tempered glass , and non-reflective glass are also optional.
Performance classification: ordinary type (standard), ordinary type for steam (M), heat resistant type (H), vibration resistant type (V), vibration resistant type for steam (MV) heat resistant and vibration resistant type (HV).
Treatment method: Oil-free/water-free treatment removes the water or oil remaining in the wetted part during manufacturing.
Exterior designation: The shell color must be specified in addition to the standard color.
Throttle valve (optional): In order to reduce the pulsating pressure, the throttle valve is installed at the pressure inlet.
Use attention
1. The meter must be vertical: a 17mm wrench should be used for tightening during installation, and the case should not be forcibly twisted; collisions should be avoided during transportation;
2. The temperature of the surrounding environment should be -25~55℃;
3. The vibration frequency of the working environment is less than 25HZ, and the amplitude is not more than 1mm;
4. During use, due to the high ambient temperature, the indicating value of the instrument does not return to zero or the indicating value is out of tolerance, you can cut the sealing rubber plug on the upper part of the case to make the inner cavity of the instrument communicate with the atmosphere;
5. The use range of the instrument should be between 1/3 and 2/3 of the upper limit;
6. Isolation devices should be added when measuring corrosive media, media that may crystallize, and media with high viscosity ;
7. The meter should be checked frequently (at least once every three months), and if any malfunction is found, it should be repaired in time;
8. If the instrument is found to be invalid or damaged due to poor manufacturing quality under normal storage and use conditions within half a year from the date of leaving the factory, the company will be responsible for repair or replacement;
9. An instrument for measuring corrosive media is required, and the required conditions should be indicated when ordering.
Selection principle
Pressure selection table to be used in accordance with the requirements of production process, to make analysis of the specific situation. On the premise of meeting the technological requirements, comprehensive consideration should be given to the principle of economy. Generally, the following aspects should be considered:
1. Selection of type
The selection of instrument type must meet the requirements of process production. For example, whether remote transmission, automatic recording or alarm is required; whether the nature of the measured medium (such as the temperature of the measured medium, viscosity, corrosiveness, degree of contamination, flammable and explosive, etc.) puts forward special requirements for the instrument, on-site Environmental conditions (such as humidity, temperature, magnetic field strength, vibration, etc.) require the type of instrument, etc. Therefore, the correct selection of the instrument type according to the process requirements is an important prerequisite to ensure the normal operation and safe production of the instrument.
For example , the spring tube of the ordinary pressure gauge is mostly made of copper alloy (alloy steel is used for high pressure), while the material of the spring tube of the pressure gauge for ammonia is all carbon steel (or stainless steel), and copper alloy is not allowed. Because ammonia reacts with copper and will explode, ordinary pressure gauges cannot be used for ammonia pressure measurement.
The oxygen pressure gauge and the ordinary pressure gauge can be exactly the same in terms of structure and material, but the oxygen pressure gauge must be oil-free. Because oil enters the oxygen system and can easily cause an explosion. When calibrating the oxygen pressure gauge used, oil cannot be used as the working medium like ordinary pressure gauges, and the oxygen pressure gauge should be stored strictly to avoid contact with oil. If it is necessary to use the existing oily pressure gauge to measure the oxygen pressure, it must be repeatedly cleaned with carbon tetrachloride before use , and carefully checked until there is no oil.
2. Determination of the measurement range
In order to ensure that the elastic element can work reliably within the safe range of elastic deformation, when selecting the pressure gauge range, there must be enough room according to the size of the measured pressure and the speed of the pressure change. Therefore, the upper limit of the pressure gauge It should be higher than the maximum pressure value possible in process production. According to the "Technical Regulations for Chemical Automatic Control Design", when measuring stable pressure, the maximum working pressure should not exceed 2/3 of the upper limit of measurement; when measuring pulsating pressure, the maximum working pressure should not exceed 1/2 of the upper limit of measurement; When measuring high pressure, the maximum working pressure should not exceed 3/5 of the upper limit of the measurement. Generally, the minimum value of the measured pressure should not be less than 1/3 of the upper limit of the instrument measurement. So as to ensure the linear relationship between the output of the meter and the input
After calculating the upper and lower limits of the meter based on the maximum and minimum values of the measured parameters, this value cannot be directly used as the measuring range of the meter. When we select the upper limit of the scale of the instrument, it should be selected from the standard series prescribed by the country. The standard series of pressure gauge measurement ranges in China are: -0.1-0.06,0.15; 0-1,1.6,2.5,4,6,10X10" MPa (where n is a natural integer. It can be positive or negative).
3. Selection of accuracy level
According to the maximum absolute error allowed by the process and the maximum range of the selected instrument, the maximum quoted error allowed by the instrument is calculated, and the accuracy of the instrument is determined in the accuracy class specified by the country. Generally speaking, the more precise the instrument selected, the more accurate and reliable the measurement result will be. However, it cannot be considered that the higher the accuracy of the selected instrument, the better, because the more precise the instrument is generally more expensive, and the operation and maintenance are more laborious.
Selection example:
1. When used for measuring viscous or acid-base and other special media, diaphragm pressure gauge , stainless steel spring tube, stainless steel movement, stainless steel shell or bakelite shell should be used .
According to the measured medium, the pressure gauge should have the specified color code, and the name of the special medium should be indicated. The oxygen meter must be marked with the words "No Oil" in red, the dark green lower horizontal line color code for hydrogen, and the color code for ammonia Yellow underline color code and so on.
2. When installing against a wall, you should choose a pressure gauge with edges; when installing directly on a pipeline, you should choose a pressure gauge without edges; when you use it for direct gas measurement, you should choose a pressure gauge with a safety hole behind the case. For the consideration of the pressure measurement position and the convenience of observation and management, the size of the case diameter should be selected.
Main classification
There are many types of pressure gauges, not only the general (ordinary) pointer indication type, but also the digital type; not only the conventional type, but also the special type; not only the contact type, but also the remote transmission type; not only the vibration-resistant type, but also the anti-vibration type. Type; not only diaphragm type, but also corrosion-resistant type. The pressure gauge series are complete. It has not only the conventional series, but also the digital series; not only the ordinary medium application series, but also the special medium application series; not only the switch signal series, but also the remote signal series, etc., all of which are derived from practical needs and have formed The complete series. The specifications and models of the pressure gauge are complete, and the structure is perfect. In terms of nominal diameter, there are Φ40mm, Φ50mm, Φ60mm, Φ75mm, Φ100mm, Φ150mm, Φ200mm, Φ250mm, etc. From the perspective of the installation structure, there are direct installation, embedded installation and convex installation. The embedded installation is divided into radial embedded installation and axial embedded installation. The convex installation also has radial convex installation and axial installation. Convex-mounted points. Direct installation is divided into radial direct installation and axial direct installation. The radial direct installation type is the basic installation type. Generally, when the installation structure type is not specified, it refers to the radial direct installation type. The axial direct mounting type considers the stability of its own support, and is generally only used on pressure gauges with a nominal diameter of less than 150mm. The so-called built-in and convex-mounted pressure gauges are the pressure gauges with edge (mounting ring) we often say. Axial built-in type refers to both axial front with side, radial front-mounted type refers to the radial front side, and radial convex type (also called wall-mounted type) refers to the radial rear side pressure gauge. From the perspective of the measurement domain and the range section, the positive pressure measurement domain is divided into a micro pressure range section, a low pressure range section, a medium pressure range section, a high pressure range section, and an ultra high pressure range section. In each range section Several measurement ranges (instrument range) are subdivided; there are 3 kinds of negative pressure (vacuum gauge) in the negative pressure measurement domain (vacuum); the pressure gauge of the combined positive and negative pressure is a pressure across the measuring range surface. Its standard name is pressure vacuum gauge , also called vacuum pressure gauge. It can measure not only positive pressure, but also negative pressure. The accuracy level classification of the pressure gauge is very clear. Common accuracy levels are 4, 2.5, 1.6, 1, 0.4, 0.25, 0.16, 0.1, etc. The accuracy grade should generally be marked on the dial, and its marking has corresponding regulations. For example, "①" means its accuracy grade is level 1. For some pressure gauges with a very low accuracy level, such as those under level 4, some do not need to measure the exact pressure value, but only need to indicate the pressure range, such as the pressure gauge on a fire extinguisher, without marking the accuracy level. .
According to its measurement accuracy , pressure gauges can be divided into precision pressure gauges and general pressure gauges . The measurement accuracy grades of precision pressure gauges are respectively 0.1, 0.16, 0.25, 0.4 grade and 0.05 grade; the measurement accuracy grades of general pressure gauges are 1.0, 1.6, 2.5, and 4.0 grades respectively.
The pressure gauge is divided into general pressure gauges, absolute pressure gauges, stainless steel pressure gauges, and differential pressure gauges. General pressure gauges are based on atmospheric pressure; absolute pressure gauges are based on absolute pressure zero; differential pressure gauges measure the difference between two measured pressures.
According to its measuring range , the pressure gauge is divided into vacuum gauge , pressure vacuum gauge , micro pressure gauge, low pressure gauge, medium pressure gauge and high pressure gauge. The vacuum gauge is used to measure the pressure value less than atmospheric pressure; the pressure vacuum gauge is used to measure the pressure value less than and greater than the atmospheric pressure; the micro pressure gauge is used to measure the pressure value less than 60000 Pa; the low pressure gauge is used to measure the pressure value of 0~6MPa ; The medium pressure gauge is used to measure the pressure value of 10~60MPa;
The pressure gauge is divided into pointer pressure gauge and digital pressure gauge according to its display mode .
Pressure gauges are classified according to their functions: pressure gauges can be divided into local indicating pressure gauges and charged signal control pressure gauges according to their different functions.
General pressure gauges , vacuum pressure gauges , shock-resistant pressure gauges , stainless steel pressure gauges , etc. are all in-situ indicating pressure gauges, which have no other control functions except for indicating pressure.
The output signals of the pressure gauge with electric signal control mainly include:
1. Switch signal (such as electric contact pressure gauge)
2. Resistance signal (such as resistance remote transmission pressure gauge)
3. Current signal (such as inductive pressure transmitter , remote pressure gauge , pressure transmitter, etc.)
Pressure gauges can be divided into different characteristics of the measured medium:
1. General pressure gauge: The general pressure gauge is used to measure the pressure of liquid, gas or steam that is non-explosive, non-crystalline, non-solidified and non-corrosive to copper and copper alloys;
2. Corrosion-resistant pressure gauges: Corrosion-resistant pressure gauges are used to measure the pressure of corrosive media, commonly used stainless steel pressure gauges, diaphragm pressure gauges, etc.;
3. Explosion-proof pressure gauges: Explosion-proof pressure gauges are used in dangerous places where the environment has explosive mixtures , such as explosion-proof electric contact pressure gauges , explosion-proof transmitters, etc.
4. Special pressure gauge.
According to the purpose of the pressure gauge: it can be divided into ordinary pressure gauge , ammonia pressure gauge, oxygen pressure gauge , electric contact pressure gauge , remote transmission pressure gauge , vibration-resistant pressure gauge , pressure gauge with inspection pointer, double needle double tube or double needle single Tube pressure gauge, digital display pressure gauge , digital precision pressure gauge, etc.
