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Definition of a safety valve: A safety valve is an automatic valve that discharges a certain amount of fluid using the force of the fluid itself, without any external force, in order to prevent the pressure within the system from exceeding a predetermined safe level. Once the pressure returns to normal, the valve closes on its own to prevent further flow of the medium. Principle of safety valves: Safety valves are typically composed of components such as a valve seat, a valve disc, and a spring. When the pressure within the system is below the set pressure of the safety valve, the force of the spring presses the valve disc against the valve seat, keeping the valve closed. When the pressure in the system reaches or exceeds the set pressure, the force exerted by the medium on the valve disc overcomes the force of the spring, causing the valve disc to open and the medium to be discharged rapidly, thereby reducing the system pressure. As the system pressure decreases, the force of the spring once again presses the valve disc against the valve seat, closing the valve. A safety valve typically consists of the following main components: 1. Valve body: This is the main part of the safety valve, usually made from pressure-resistant materials, and it serves to house the other components as well as to connect to the pressure system. 2. Valve seat: Located inside the valve body, it is the contact surface when the valve disc is closed, ensuring tightness. 3. Valve disc: This is a key component of the safety valve; when the system pressure exceeds the set value, the valve disc is pushed away from the valve seat, thereby releasing pressure. 4. Guide element: Ensures the stability of the valve disc during opening and closing, preventing skewing or jamming. 5. Spring: Located above the valve disc, it provides the closing force; when the system pressure is below the set value, the spring pushes the valve disc back against the valve seat to restore sealing. 6. Adjustment screw: Used to adjust the degree of compression of the spring, thereby setting the opening pressure of the safety valve. 7. Lifting wrench: Used to manually lift the valve disc for testing or manual discharge when necessary. 8. Discharge port: After pressure is released, the medium is discharged through this point. 9. Valve cover: Covers the top of the valve body to protect the internal components; sometimes it also contains adjustment screws. 10. Sealing gasket: Ensures sealing between various parts of the valve body to prevent leaks. History of safety valves The development history of safety valves dates back to the early 19th century. With the progression of the Industrial Revolution, the widespread use of steam equipment gave rise to the demand for safety valves. In 1818, a brass casting factory was established in Hamburg, Germany, to begin producing products such as safety valves. Since then, safety valve technology has continued to develop, undergoing a evolution from simple to complex and from manual to automatic. Since the 1970s, safety valve technology has gradually matured, becoming an essential safety accessory in industrial production. Types of safety valves: Depending on their structure and function, safety valves are mainly classified into the following categories: 1. Spring-loaded safety valves: These use the force of a spring to regulate the opening pressure of the valve, and they are the most common type of safety valve. Widely used in small and medium-sized pressure vessels and piping systems in industries such as petroleum, chemicals, and power generation. 2. Weight-type safety valve: Uses the gravity of a weight to balance the pressure of the medium, and is commonly used in large boilers. It is mainly used in large boilers and steam power plants. 3. Pilot-operated safety valve: It consists of a main valve and a pilot valve; the pilot valve controls the opening and closing of the main valve, and it is suitable for high-pressure and high-flow applications. Suitable for high-pressure, high-flow, and high-precision pressure control systems. 4. Rupture disc safety valve: When the pressure reaches the set value, the rupture disc breaks, releasing the pressure. It is commonly used in applications where leakage is not allowed, such as compressed air storage tanks. Precautions for using safety valves: Before installation, it is necessary to check whether parameters such as the model, specifications, and set pressure of the safety valve meet the requirements, and to calibrate it. The safety valve should be installed vertically in the gas space of the equipment or pipeline, with its outlet facing in a safe direction. During installation, care should be taken to keep the safety valve clean, to prevent impurities from entering the valve and affecting its proper operation. The installation location should facilitate inspection and maintenance, while also being protected from high temperatures or corrosive substances. During use, the safety valve should be inspected and maintained regularly to ensure its proper performance. The set pressure of the safety valve must not be adjusted arbitrarily, so as to avoid compromising its protective function. When a safety valve is used to vent flammable liquids, its outlet should be connected to the accident storage tank. When the material being discharged is a high-temperature flammable substance, the receiving container must be equipped with appropriate protective facilities. General safety valves can be vented on-site; the vent opening should be at least 1 meter above the level of the operators, and it must not face any open flames, spark-producing areas, or high-temperature equipment within a radius of 15 meters. The vent openings for the safety valves of indoor equipment and containers should lead outside the roof, at a height of more than 2 meters above it. When there is a block valve at the inlet of the safety valve, the block valve must be kept in the open position and sealed with lead to prevent any errors. The spring-loaded safety valve with threaded connections must be connected to a short threaded pipe; this short pipe, in turn, must be welded to the shell and header. The safety valve discharge pipe must be secured to prevent excessive additional stress on the safety valve or vibrations. Safety valves installed outdoors must be equipped with reliable measures to prevent the water contained in the fluid inside the valve from freezing when the temperature drops below 0°C, thereby avoiding any impact on the valve’s ability to discharge. Safety valves must be equipped with mechanisms to prevent the weight from moving on its own, as well as guides to stop the lever from moving out of place. Spring-loaded safety valves should have lifting handles and devices to prevent the adjustment screws from being turned arbitrarily. The safety valve must undergo a regular inspection at least once a year. The inspection includes dynamic testing and disassembly testing. The steps of dynamic testing are divided into assembly, pressurization (to operating pressure), pressure holding (no leakage for 3–5 minutes), pressure increase action (action immediately at the opening pressure), depressurization and return to rest, and further pressure holding (remaining at operating pressure for 3 minutes with no leakage after returning to rest). During the use of safety valves, there are some common misconceptions that can affect their proper functioning and even lead to safety risks. Here are some common misconceptions that require special attention: 1. Failure to perform calibration and maintenance within the specified time frames: Safety valves should be calibrated and maintained regularly to ensure their sensitivity and reliability. Ignoring regular calibration can lead to a decline in the performance of the safety valve, or even its failure. 2. Inaccurate pressure setting: Newly purchased safety valves should be adjusted according to the specific operating conditions of the user to ensure that the opening pressure meets the required standards. Using the pressure set at the factory directly may not be suitable for specific working conditions, thereby affecting the protective function of the safety valve. 3. Incorrect selection of the safety valve: The safety valve must be used within its specified spring pressure range. Choosing the wrong type or pressure rating for a safety valve can result in it not functioning properly. 4. Improper handling of safety valve leaks: Any leakage from the safety valve under operating pressure must be addressed promptly to prevent wear of the sealing surfaces and further increase in leakage. Adjusting the spring compression of the safety valve by oneself or using improper methods to secure it may cause the safety valve to fail. 5. Incorrect installation of the safety valve: The safety valve should be installed vertically to ensure it can operate properly and in a timely manner. Improper installation may affect the proper functioning of the safety valve and increase the failure rate. 6. Discharge capacity and working medium not considered: The selection of safety valves should take into account the discharge capacity and the properties of the working medium. Improperly using fully-open safety valves in applications requiring slightly-open operation, or using safety valves that cannot withstand high temperatures in high-temperature environments, can both lead to safety hazards. 7. Incorrect use of the stop valve: Installing a stop valve between the equipment and the safety valve helps with the cleaning and calibration of the safety valve. If the stop valve is not fully open or remains closed for an extended period, it may affect the performance of the safety valve. Correct installation steps for safety valves: 1. Select an appropriate installation location: The safety valve should be installed at the highest point of the medium pipeline or at the maximum liquid level, to ensure that it can release excess pressure in a timely and effective manner. At the same time, it should be installed on the same pipeline along with pressure gauges, pressure switches, etc. 2. Determine the appropriate valve model and specifications: Select the suitable valve model and specifications based on parameters such as the medium’s pressure, temperature, and flow rate. Ensure that the selected safety valve meets the relevant standards and the operating conditions of the equipment. 3. Perform pre-treatment on the valves: Before installation, the valves should be cleaned and inspected to ensure that there are no impurities, deposits, or damage inside them. Adjust and calibrate the valves according to requirements. 4. Fix the safety valve: Select an appropriate fixing device for installation, based on the model and specifications of the safety valve. When fixing, attention should be paid to the position of the valve to ensure it is firmly connected to the relevant equipment and pipelines. 5. Perform connection and sealing: Select the appropriate connection method based on the type of interface of the safety valve, to ensure a tight and secure connection. For threaded connections, care should be taken to use appropriate sealing materials. Common faults and problems of safety valves: Safety valves may encounter various faults and problems during use, and these issues not only affect the proper operation of the equipment but can also pose safety risks. Here are some common faults along with their causes and solutions: 1. The safety valve fails to open automatically. Causes: Excessively high pressure set by the spring, contamination or rust on the sealing surfaces, too small a gap between the valve stem and the bushing, or permanent deformation of the spring. 2. Solution: Readjust the spring, clean the sealing surfaces, increase the clearance between the valve stem and the bushing, and replace it with a new spring. 2. Frequent activation of the safety valve 1. Causes: Excessively high discharge capacity that is not suitable for the container equipment, excessive resistance in the discharge pipe, and improper positioning of the adjustment ring. 2. Solution: Re-select an appropriate safety valve, replace or adjust the inlet pipeline of the safety valve, and readjust the adjusting ring to the proper position. 3. Safety valve leakage. 1. Causes: Excessive operating pressure, foreign substances on the sealing surface, improper assembly or pipeline load issues, relaxed spring. 2. Solution: Adjust the set pressure, remove foreign objects, reassemble or eliminate pipe loads, replace the spring. 4. Damaged sealing surface. 1. Causes: Particle impurities falling on the sealing surface, scale accumulation, corrosive substances and residues, improper assembly or inappropriate part dimensions and materials, calibration errors of the safety valve. 2. Solution: Grind off the indentations, repair the sealing surface, check and adjust the clearance, replace the sealing material, and adjust the opening pressure strictly in accordance with the specified values. 5. Frequent tripping of the safety valve 1. Causes: Excessively high spring stiffness, too small diameter of the inlet pipe or excessive resistance, high resistance in the discharge pipe. 2. Solution: Use springs with lower stiffness, increase the diameter of the inlet pipe or reduce resistance, and lower the resistance in the discharge pipe. 6. Leakage at the joint surface of the valve body 1. Cause: Leakage at the joint between the upper and lower valve bodies. 2. Solution: Check and repair the sealing of the joint surface. 7. Safety valve flutter 1. Cause: The shaking phenomenon that occurs in the safety valve during discharge. 2. Solution: Adjust the design of the safety valve or use vibration-damping devices. Standards related to safety valves include GB/T 12241-2005 \"General requirements for safety valves\", GB/T 12243-2005 \"Safety valves with direct spring loading\" and other such standards