0. Foreword Pressure gauges, as the name suggests, are widely known as instruments for measuring pressure. Instruments that measure the pressure are widely used in industrial process control and technical measurement. In some containers such as boilers, pressure, etc., the pressure gauge can be said to be the most important accessory, which determines the quality level of the instrument. The production of pressure gauges and inspections are not as simple as the imaginary class. Therefore, when the pressure gauge is sent for inspection, the verification personnel are required to improve the efficiency and simplify the operation.
1. Pressure gauges and their selection and use Pressure gauges have a variety of pressure gauges in the market due to their simple structure and relatively easy operation and low cost. Although the pressure gauge has a simple manufacturing process, it is an instrument that intuitively and accurately measures other instruments, and requires high specifications and high standards for its production requirements. And should always maintain, reduce the error caused by the aging of the instrument. The full scale of the pressure gauge is 1.5 to 3 times the maximum working pressure of the container or container system, preferably 2 times. There is also a requirement for the pressure dial, which requires that the diameter of the dial should be greater than or equal to 100mm, and the red cordon is best engraved on the dial.
2. Installation of the pressure gauge First, the pressure gauge should be installed in a more obvious place to facilitate observation and cleaning. It should be kept away from the refrigerator and the boiler as far away as possible from the hot and cold places. In case these factors interfere with the gauge.
The installation position of the pressure gauge is preferably vertical and should be installed vertically. If the installation position is high, it can be slightly tilted to help observe. However, it must be noted that the angle of inclination should not exceed 30 degrees; under normal circumstances, the buffer tube will be installed in front of the pressure gauge to ease the direct injection of compressed air into the spring bend, and it is also possible to store condensate; between the pressure gauge and the buffer bend A three-way cock or needle valve can be installed to assist in changing and checking the pressure gauge.
3. Check the operating instructions of the pressure gauge Before installing the pressure gauge, first the pressure gauge must be inspected by the relevant state-recognized department prior to installation and a certificate of conformity issued. The pressure gauge shall be calibrated by a nationally recognized measurement department and an annual inspection shall be conducted every six months.
According to JJG52-1999 regulations, test personnel should carry out tests according to regulations. First, according to the range of the inspected table, select the same range standard table and checker larger than its range to check whether the validity period of the standard table label expires. At the same time, in order to ensure accuracy, the degree of clearance of the measurement technology must be strictly required, and the requirements of the errors within the limits, the accuracy of the calibration, and the precision measurement technical requirements must be met. The absolute value of the basic error of the selected precision pressure gauge should not exceed the detected instrument. Or a quarter of the absolute value of the basic error being measured. Only in this way can the actual value be accurately measured.
Observe and check the room temperature and humidity table to see whether the temperature and humidity meet the requirements of the verification regulations. That is, the temperature does not fluctuate up to 5 degrees at 20 degrees, and the wet toxicity does not exceed 85%. If it is not possible to meet this requirement, you can use external tools such as air conditioners to meet inspection requirements and record test values.
Visual inspection and zero inspection Some items can be visually measured directly, such as appearance, mark, reading part, dial content, etc. When observing the zero position, it is necessary to treat them differently with or without stop. See if the test procedure is correct. The requirements were recorded and the test results were recorded on the ""Pressure Gauge Verification Record"".
The pressure indications are sorted in numerical or ascending or descending order. The inspection should check the step-up or step-down, and when the standard table pointer indicates the corresponding index line, read the indicated value. You can then tap on the gauge reading 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 condition of the pressure gauge and record it. When the indication reaches the upper limit of measurement, the pressure gauge on the check table is closed. After the pressure is cut off, the result of three minutes of pressure resistance is recorded. Then check again in the reverse order.
If the pressure gauge being inspected belongs to a pressure vacuum gauge, we also need to test the vacuum part. If the gauge being inspected is a special material gauge, we need to analyze the specific problem. However, it must still be detected and recorded in accordance with the rules and regulations.
If there is a large error in the detection process, it is stated that the readout of the pressure gauge should be read in accordance with one-fifth of the scaled value. The pressure gauge that meets the standard is to take the line reading and the test table is the estimated reading. . Comparing these two methods, it is found that the line reading is more accurate than the estimated reading. The width of the end of the standard table pointer, the interval between the reticle and the background of the mirror on the dial, etc., are more conducive to accurate estimation reading than the examined table, and usually one tenth of the division value can be estimated. After recording, various types of test results are comprehensively evaluated. After the test, the data is determined to be correct. Ensure accurate and reliable data.
The qualified pressure gauge must first meet the basic national standards. After passing the inspection, the label indicating the qualified inspection shall be affixed to the inner side of the dial of the inspection table. After the work is completed, the seal will be sealed. If the inspection result shows that the standard does not meet the standard The pressure gauge to be inspected shall also be re-adjusted, repaired and tested until it meets the standards, and then re-evaluated; if it is seriously damaged and cannot be repaired, the ""report of scrapped measuring instruments" shall be completed." The person in charge of the measurement room shall be given retirement after examination and approval, and the inspected form shall have a “disabled†label. In order to avoid unnecessary trouble.
4. Common pressure failures during verification
(1) When the pressure increases, the pressure gauge pointer does not change. The reason for this may be that the cock has not been opened, or that the plug, gauge link, or trap has become clogged; the pointer has become loose with the center shaft or the pointer has become stuck.
(2) Due to the hand shake, the cause is the damage of the hairspring; the plug or the trap passage is partially blocked; the central axis is bent at both ends and the center of the shaft is offset at both ends. The third reason is that the pointer cannot be returned to zero after the verification is completed. The reason for this is that the elasticity of the spring is weakened or even inelastic, the pointer and the central axis are loosened, or the pointer is stuck; the channel of the cock, pressure gauge, or trap Blocked.
5. Adjustment method for pressure indication value overshoot The spring tube pressure gauge is very common in industrial applications. In the verification process, the problem of over-indicating values ​​is relatively 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 other than zero and calibrate the indication.
(2) The difference is a linear error. When the error is gradually increased, the indicating screw is moved outward to increase the arm length; otherwise, it is moved inwards to reduce the arm length.
(3) The value of the error is faster and slower. Rotate the movement counterclockwise to increase the angle between the lever and the sector gear; if it is the opposite, turn the movement clockwise to reduce the angle. After adjustment, the error is a linear error, and then the indication adjustment screw can be moved.
(4) The value of the indicator is more than half of the pressure. After raising the pressure, you can re-install the pointer in the middle position. If you still cannot eliminate the error, you can choose to adjust the angle between the lever and the sector gear for comprehensive integration.
(5) If there is only one or two points out of tolerance. Check the fit of the movement near this point. If it is a positive difference, there may be dirt and burrs on the gear mesh. If it is a negative difference, the teeth will wear out and be injured and should be repaired or replaced.
After the adjustment is completed, the components of the instrument are assembled and the test is repeated according to the verification procedures.
By monitoring personnel's high standards and strict testing pressure gauges, it not only improves work efficiency but also retains potential customers. During the inspection process, problems should be continuously solved and the standardization management of pressure gauges should be standardized to provide guarantees for safe production and management.
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