How to select, repair and calibrate safety valves in coal chemical system - part two
Safety valve calibration
On-line calibration and checker calibration are the two most commonly used calibration methods. According to the equipment conditions of the coal chemical plant, the type of medium, the working pressure, etc., select the appropriate calibration method. The advantage of on-line calibration is that it is carried out while the equipment is running. The safety valve does not need to be removed from the equipment. The verification speed is faster, it is convenient for the verification of the welded safety valve, and the return pressure can be measured. The verification result is closer to the actual work. The disadvantage is that the calibration is dangerous and the leak test cannot be done. The calibration table calibration is to open the safety valve through medium such as nitrogen or water, and record the opening pressure. The advantage is to solve the safety valve setting and leak detection, for safety valves with normal temperature medium and working temperature below 250 °C, saving adjustment time of newly installed safety valve, reducing energy consumption and reducing work risk.he disadvantage is that there is an error between the operating temperature and the normal temperature (the spring becomes soft at high temperature), and only the opening pressure setting and the sealing test can be performed, and the return pressure cannot be verified. During calibration, it should be noted that for safety valves that cannot consider back pressure relief valves, high temperature or low temperature media, the calibration table calibration should be used. The high-pressure safety valve spring adjustment can only be fine-tuned, and the verified airflow and water flow must be filtered.
When checking the safety valve, pay attention to the adjustment of the return pressure. The return pressure refers to the static pressure at the inlet of the safety valve when the valve flap is in re-contact with the valve seat, the valve opening height is zero, and the medium stops continuously flowing out as the system pressure decreases. If the return pressure is too low, the medium outflow will be large, causing loss of medium and energy. If the return pressure is too high for the system medium to discharge, the valve will have a frequency jump. Therefore, as far as the emission can be achieved, the return pressure should be increased as much as possible to reduce the loss of medium and energy. The adjustment method is to adjust the gap by adjusting the ring. The smaller the gap is, the larger the resistance is. The greater the force that holds the spool is, the more difficult it is to return to the seat. The larger the gap, the easier the spool will fall back and the higher the return pressure. Since the normal temperature calibration table cannot test the opening height and the discharge amount, the adjustment ring should be kept in the factory state when the calibration table verifies the safety valve.
Conclusion
Let me make a brief description of the selection, maintenance and verification of safety valves for coal chemical systems. Before the equipment is put into operation, there should be enough purging to prevent the welding debris, iron pin and other debris in the pipeline from being carried out with the medium, and to prevent harder debris from eroding the sealing surface and causing damage to the sealing surface when the safety valve jumps. After purging according to the specifications, most safety valves can maintain a good seal after the jump, and some faults can be avoided, which is of great significance for ensuring the safe operation and energy saving of the equipment.
On-line calibration and checker calibration are the two most commonly used calibration methods. According to the equipment conditions of the coal chemical plant, the type of medium, the working pressure, etc., select the appropriate calibration method. The advantage of on-line calibration is that it is carried out while the equipment is running. The safety valve does not need to be removed from the equipment. The verification speed is faster, it is convenient for the verification of the welded safety valve, and the return pressure can be measured. The verification result is closer to the actual work. The disadvantage is that the calibration is dangerous and the leak test cannot be done. The calibration table calibration is to open the safety valve through medium such as nitrogen or water, and record the opening pressure. The advantage is to solve the safety valve setting and leak detection, for safety valves with normal temperature medium and working temperature below 250 °C, saving adjustment time of newly installed safety valve, reducing energy consumption and reducing work risk.he disadvantage is that there is an error between the operating temperature and the normal temperature (the spring becomes soft at high temperature), and only the opening pressure setting and the sealing test can be performed, and the return pressure cannot be verified. During calibration, it should be noted that for safety valves that cannot consider back pressure relief valves, high temperature or low temperature media, the calibration table calibration should be used. The high-pressure safety valve spring adjustment can only be fine-tuned, and the verified airflow and water flow must be filtered.
When checking the safety valve, pay attention to the adjustment of the return pressure. The return pressure refers to the static pressure at the inlet of the safety valve when the valve flap is in re-contact with the valve seat, the valve opening height is zero, and the medium stops continuously flowing out as the system pressure decreases. If the return pressure is too low, the medium outflow will be large, causing loss of medium and energy. If the return pressure is too high for the system medium to discharge, the valve will have a frequency jump. Therefore, as far as the emission can be achieved, the return pressure should be increased as much as possible to reduce the loss of medium and energy. The adjustment method is to adjust the gap by adjusting the ring. The smaller the gap is, the larger the resistance is. The greater the force that holds the spool is, the more difficult it is to return to the seat. The larger the gap, the easier the spool will fall back and the higher the return pressure. Since the normal temperature calibration table cannot test the opening height and the discharge amount, the adjustment ring should be kept in the factory state when the calibration table verifies the safety valve.
Conclusion
Let me make a brief description of the selection, maintenance and verification of safety valves for coal chemical systems. Before the equipment is put into operation, there should be enough purging to prevent the welding debris, iron pin and other debris in the pipeline from being carried out with the medium, and to prevent harder debris from eroding the sealing surface and causing damage to the sealing surface when the safety valve jumps. After purging according to the specifications, most safety valves can maintain a good seal after the jump, and some faults can be avoided, which is of great significance for ensuring the safe operation and energy saving of the equipment.
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