company news about Why Pressure Gauge Filled With Liquid? And Solutions To Common Problems of Pressure Gauges

Why Pressure Gauge Filled With Liquid? And Solutions To Common Problems of Pressure Gauges

 

Is there any difference between some gauges that have oil in them and others that don't? The difference is there, but it's not a big difference, it's just the difference in the use of the two. What does the "oil" in the pressure gauge do?

 

In fact, the resistance increases after filling with oil, so the pointer is relatively stable, which can prevent the vibration of the pointer. Or the pressure fluctuates greatly in the system (such as a plunger pump) to make the pressure gauge read accurately and prolong the service life. Is this "oil" free to choose? The answer is definitely NO! This "oil" is mainly two kinds of glycerin and silicone oil. The functions of the two oils are also different. Glycerin mainly plays an anti-shock effect; silicone oil can also play a role in anti-shock, but silicone oil is more resistant to low temperature than glycerin. If the outdoor temperature reaches minus 20 ℃, the glycerin will crystallize. , but the silicone oil can also make the meter work properly. Therefore, both glycerin and silicone oil can be used, but at least two points must be considered when making a specific choice:

1. Thermal expansion coefficient, the smaller the coefficient, the better, which is mainly affected by temperature;

2. Application occasions , Neither of these two oils can be used in the food industry. In case the diaphragm is damaged, the oil will contaminate the food. It is also not recommended in places where strong oxidants are measured, otherwise it will cause an explosion.

Pressure gauge selection experience
Pressure measuring instruments are widely used. Today, Wesen will share with you the experience of pressure gauge selection: users should correctly select the pressure gauge range and pressure gauge specification model according to the measured medium and the use environment. In general industrial production, grades 1.5 and 2.5 are used. For precise pressure measurement, precision pressure gauges or digital pressure gauges can be used.

 

1. Selection of pressure gauge range

When measuring relatively stable pressure, the maximum range should be 1.5 times the measured value; when measuring fluctuating pressure, the maximum range should be 2 times the measured value. The range of the pressure gauge should be selected properly, which can prolong the service life of the instrument.

 

2. Different pressure gauges should be used to measure different media and use environments

 

(1) For general media, such as air, water, steam, oil, etc., Y-type ordinary pressure gauge can be used, and its shell is black. Usually there are several common types of axial pressure gauge, radial pressure gauge, axial band edge and radial band edge;

 

(2) Special pressure gauges are required for certain media, such as YA type ammonia pressure gauges for ammonia, whose shell is yellow; YO oxygen pressure gauges for oxygen, whose shells are sky blue; oxygen pressure gauges, acetylene pressure gauges Oil should be strictly prohibited. If the watch is contaminated with oil, a syringe can be used to inject carbon tetrachloride into the spring tube; it can be used after cleaning.

 

(3) For the pressure measurement of strong corrosive medium and corrosive gas environment, such as dilute hydrochloric acid, hydrochloric acid gas, etc., in addition to the isolation method, the YB series all-stainless steel pressure gauge can also be selected, but the all-stainless steel pressure gauge is not suitable for There are corrosive media outside, such as chlorine, nitric acid and other environments. YM series diaphragm pressure gauges can also be used. The diaphragm materials include OCr7Nil2Mo2 (316), Monel alloy (Cu30Ni70), Hastelloy (H276C), tantalum (Ta) and fluoroplastics (F4). Make a selection and fill its body with an appropriate working fluid, such as glycerin or silicone oil, according to the requirements of the tested medium. This kind of instrument is widely used in petrochemical industry. It adopts indirect measurement structure and is suitable for measuring the pressure of liquid, gas or medium with solid floating substance with high viscosity, easy crystallization, high corrosiveness and high temperature. Isolation diaphragms are available in a variety of materials to suit a variety of different measurement media.

 

(4) YTZ series resistance remote transmission pressure gauge can be selected when remote transmission is required. This type of instrument is suitable for measuring liquids, gases and vapors that are not explosive, non-crystalline, non-solidifying and non-corrosive to copper and copper alloys. The pressure of the medium can be transmitted through the synchronous resistance transmitter set inside the instrument to transmit the measured pressure to the secondary instrument far away from the measuring point in the form of electric quantity, so as to realize centralized detection and long-distance control.

 

(5) In the occasions requiring alarm and interlock, electric contact pressure gauge can be selected, and YXC or YNXC series products should be selected first. The damping device is installed inside the instrument, which significantly improves the performance of resisting medium pulsation and mechanical vibration, which not only enhances the reliability and vibration resistance of use, but also prolongs the service life of the product.

 

(6) The bellows pressure gauge can be used for micro pressure measurement, but the bellows pressure gauge is only suitable for measuring the tiny pressure of gas or liquid medium that is not corrosive to copper and copper alloys. In an environment with explosion-proof requirements, if an electric contact pressure gauge is required, an explosion-proof type should be selected. YN vibration-resistant pressure gauge or marine pressure gauge should be selected for occasions with large vibration.

 

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Details about the pressure gauge
As the name suggests, a pressure gauge is widely known as an instrument for measuring pressure. It is an instrument for measuring pressure and has been widely used in industrial process control and technical measurement. In some vessels such as boilers, pressure and other equipment, the pressure gauge can be said to be the most important accessory, which determines the quality level of the instrument. The production and inspection of pressure gauges are not as simple as imagined classes, so when the pressure gauges are submitted for inspection, the inspectors are required to improve efficiency and simplify operations.

 

1. Pressure gauge and its selection and use

 

Because of the simple structure, relatively easy operation and low cost of pressure gauges, various pressure gauges have appeared in the market. Although the manufacturing process of the pressure gauge is simple, it is an instrument for intuitive and accurate measurement of other instruments, and its production requirements require high specifications and high standards. And it should be maintained regularly to reduce the error caused by the aging of the instrument. The full scale of the pressure gauge is 1.5-3 times the maximum working pressure of the container or container system, preferably 2 times. There are also requirements for the pressure dial, which requires that the diameter of the dial should be greater than or equal to 100mm, and a red warning line should preferably be engraved on the dial.

 

2. Installation and setting of pressure gauge

 

First of all, the pressure gauge should be installed in a more obvious place, which is helpful for observation and cleaning, and try to stay away from high temperature and cold places to the refrigerator and boiler. In order to prevent these factors from interfering with the pressure gauge.

 

The installation position of the pressure gauge is preferably vertical, and it should be installed vertically. If the installation position is high, it can be slightly inclined to facilitate observation. But be sure to pay attention to the angle of inclination not to exceed 30 degrees; under normal circumstances, a buffer tube will be installed in front of the pressure gauge to relieve the compressed air from directly rushing into the spring elbow, and to store condensed water; in the middle of the pressure gauge and the buffer elbow A 3-way stopcock or needle valve can be installed to aid in changing and checking the pressure gauge.

 

3. Operating procedures for verifying pressure gauges

 

Before installing the pressure gauge, first of all, the pressure gauge must pass the inspection of the relevant departments recognized by the state, and issue a certificate of conformity at the same time. The pressure gauge should be calibrated by a nationally recognized metrology department, and an annual inspection should be carried out every six months.

 

According to the regulations of JJG52-1999, inspectors should conduct inspections in accordance with the regulations. First of all, according to the range of the test meter, select a standard meter of the same range and a calibrator larger than its range, and check whether the validity period of the standard meter label has expired. At the same time, in order to ensure the accuracy, it is necessary to strictly require the passing degree of the measurement technology, and the requirements of the error within the limit, the verification accuracy, and meet the technical requirements of precision measurement. The absolute value of the basic error of the precision pressure gauge should not exceed the instrument under test. Or a quarter of the absolute value of the basic error of the measurand during precise measurement. Only in this way can the actual value be accurately measured.

 

Observe and verify the room temperature and hygrometer to see if the temperature and humidity meet the requirements of the verification regulations, that is, the temperature does not fluctuate more than 5 degrees above and below 20 degrees, and the humidity does not exceed 85%. If this requirement cannot be met by itself, external tools such as air conditioners can be used to meet the inspection requirements, and the test values ​​shall be recorded.

 

Visual inspection and zero position inspection Some items can be directly visually inspected, such as shape, logo, reading part, dial content, etc. When observing the zero position, pay attention to distinguish between those with and without stop pins. Check whether they meet the verification regulations. requirements, and record the test results on "Pressure Gauge

Verification Record".

 

The pressure indication value is checked in ascending or descending order according to the graduation line marked with numbers. When checking whether the boost or buck should be checked, until the pointer of the standard meter points to the corresponding graduation line, read the value indicated by the test. You can then tap the pressure gauge to read and record the difference between before and after tapping. If the difference reaches the upper limit of error, close the valve, cut off the pressure source for three minutes, test the pressure resistance of the pressure gauge and record it. When the indicated value reaches the upper limit of the measurement, close the pressure supply valve of the meter to be tested, and then record the result of the pressure resistance for three minutes after cutting off the pressure. Check again in the reverse order from before.

 

If the pressure gauge to be checked is a pressure vacuum gauge, we also need to test the vacuum part. If the pressure gauge to be checked is a pressure gauge of special material, we need to analyze specific problems. However, it is still necessary to test and record in accordance with the rules and regulations.

 

If there is a large error in the testing process, it is stipulated that the reading value of the pressure gauge should be estimated according to one-fifth of the graduation value. . Comparing these two methods, it is found that the line reading is more accurate than the estimated reading. The end width of the pointer of the standard watch, the interval of the reticle and the background of the reflector on the dial are more conducive to accurate estimated reading compared with the tested watch, which can usually be estimated to one-tenth of the graduation value. After recording, the various test results are comprehensively evaluated, and after the test, the data is confirmed to be accurate. Make sure your data is accurate and reliable.

 

The qualified ones must first meet the national basic standards. After passing the inspection, stick the label indicating that the inspection is qualified on the inner side of the dial of the inspected watch. After completing these tasks, seal it with lead. The pressure gauge should also be adjusted, repaired and verified again until it meets the standard, and then re-verified; if the damage is serious and cannot be repaired, the ""Measuring Instrument Scrap Form"" should be filled in and approved by the measuring room. After approval by the person in charge, it will be scrapped, and the inspected form will be marked with a "disabled" label. to avoid unnecessary trouble.

 

4. Common pressure failures in the verification process

 

(1) When the pressure increases, the pointer of the pressure gauge does not change. The reason for this may be that the cock is not opened, or the cock, the pressure gauge connecting pipe or the water trap is blocked; the pointer is loose from the central shaft or the pointer is stuck.

 

(2) Due to the shaking of the pointer, the reason is that the hairspring is damaged; the cock or the water trap channel is partially blocked; the two ends of the central shaft are bent, and the center of the two ends of the shaft is offset. The third is that the pointer cannot return to zero after the verification is completed. The reason for this situation is that the elasticity of the spring is weakened or even inelastic, the pointer and the central axis are loose, or the pointer is stuck; the channel of the cock, the pressure gauge connecting pipe or the water trap blocked.

 

5. Adjustment method of pressure indication value out of tolerance

 

Spring tube pressure gauges are very common in industry. In the verification process, the problem of indicating value out of tolerance is common. The specific adjustment methods are as follows:

 

(1) Set the display difference of each verification point to be the same. After boosting, reinstall the pointer at the first verification point except the zero point to calibrate the display value.

 

(2) The difference is linear error. When the error gradually increases, move the indication adjustment screw outward to increase the arm length; otherwise, move it inward to reduce the arm length.

 

(3) The indication value is out of tolerance firstly fast and then slow. Turn the movement counterclockwise to increase the angle between the lever and the sector gear; if the opposite is true, turn the movement clockwise to decrease the angle. After adjustment, the error is linear error, and then move the indicator adjustment screw.

 

(4) The indication value is out of tolerance around half of the pressure. After increasing the pressure, you can reinstall the pointer in the middle position. If the error still cannot be eliminated, you can choose to adjust the angle of the pull rod and the sector gear for comprehensive integration.

 

(5) If only one or two points are out of tolerance. Check the fit of the movement near this point. When it is a positive difference, there may be dirt and burrs at the meshing of the gears; if it is a negative difference, the teeth are worn and damaged, and should be repaired or replaced.

 

After the adjustment is completed, assemble the components of the instrument and re-calibrate according to the calibration regulations.

 

Through the monitoring of pressure gauges with high standards and strict requirements of monitoring personnel, it not only improves work efficiency but also retains potential customers. In the process of testing, it is necessary to constantly find problems and solve problems, promote the standardized management of pressure gauge appraisal work, and provide guarantee for safe production and operation construction.