Safety Valve Technical Specifications

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1. Definition: A safety valve is a safety device used primarily to prevent pressure vessels, pipeline systems, or equipment from exploding or being damaged due to excessive pressure. Its main function is to open automatically when the system pressure exceeds the set safe level, thereby releasing pressure and protecting both the equipment and the people involved. 2. Working principle: When the system pressure reaches the set pressure of the safety valve, the valve disc is pushed by this pressure, causing the valve to open and allowing high-pressure fluid or gas to flow through it and be discharged, thereby reducing the system pressure. When the system pressure drops to the return pressure, the valve disc falls back, ensuring that no more pressure is lost from the system. 3. Classification 1) Based on the overall structure and the type of loading mechanism: safety valves can be divided into weight-lever type, spring type, and controlled (pilot valve type) safety valves. 2) Based on the ratio of the valve disc opening height to the valve flow diameter, safety valves can be divided into slightly open type and fully open type. 3) Based on the medium discharge method: safety valves can be classified into fully enclosed, semi-enclosed, and open types. 4) Based on the principle of operation: they can be divided into direct-acting and indirect-acting types (such as pilot-operated valves and safety valves with power assist devices). 4. Selection: When choosing a safety valve, various factors such as the properties of the medium, operating pressure and temperature, and discharge capacity need to be taken into consideration. Below is a comparison of several commonly used types of safety valves: Weight-lever type safety valve: This type of safety valve uses a weight and a lever to apply force to the valve disc; it is suitable for high-temperature applications, especially in boilers and high-temperature containers. Their advantages are simple structure and easy adjustment, but the disadvantages are a relatively bulky design and sensitivity to vibrations. The reset pressure of the weight-lever type safety valve is relatively low; it usually needs to be reduced to 70% of the normal operating pressure in order to maintain sealing. Spring-loaded safety valve: This type of safety valve is operated by a spring, with its set pressure controlled by the spring; it is suitable for applications where the pressure is not very high and the medium is non-corrosive, especially in mobile pressure vessels. The advantages of spring-loaded safety valves are their compact structure and high sensitivity, but they can be affected by back pressure, and the performance of the spring may decline in high-temperature environments. Controlled (pilot-operated/leading-type) safety valves: These safety valves are controlled by a pilot valve and are suitable for high-pressure, high-flow applications with back pressure. The advantage of pilot-operated safety valves is their stable operating performance, which is not affected by back pressure; however, their structure is more complex and their cost is higher. 5. Common parameters 1) Setting pressure: Also known as the opening pressure, it refers to the predetermined pressure at which the safety valve begins to open under operating conditions. This is the gauge pressure measured at the inlet of the valve; when this pressure is reached, the disc of the safety valve begins to rise and the fluid starts to be discharged continuously. The set pressure is usually not greater than the design pressure of the pressure vessel or pipeline; it is generally 1.10 times the normal operating pressure, with a minimum of 1.05 times. 2) Design pressure: It refers to the maximum pressure determined when designing pressure vessels or pipelines; the setting pressure of the safety valve should not exceed this design pressure. The design pressure is an important parameter to ensure the safe operation of equipment, and the selection and setting of safety valves should be based on this pressure value. 3) Reseat pressure: This is the pressure at which the valve disc of a safety valve closes again after it has opened to discharge, as the system pressure decreases. The return pressure is usually lower than the set pressure, ensuring that the safety valve can close automatically once the pressure drops to a certain level, thereby preventing continuous leakage of the medium. 6. 6) The safety valve used in 1) should be installed correctly in accordance with design requirements, usually vertically. 2) Valves should not be installed in front of or behind the safety valve; if such valves are installed, they must be sealed with lead seals and equipped with indicators showing whether they are in the open or closed position. 3) The diameter of the inlet pipe for the safety valve should not be smaller than the diameter of the valve’s inlet; if several safety valves share one inlet pipe, the cross-sectional area of that inlet pipe must be at least equal to the sum of the cross-sectional areas of the inlets of those safety valves. 7. Maintenance 1) Regular inspections: Safety valves should be visually inspected regularly to check for signs of wear, corrosion, or damage. Detailed records of maintenance activities, inspections, and tests should be kept to ensure traceability and to help identify trends or potential issues. 2) Calibration: The testing of safety valves must be carried out by a qualified testing institution, at least once a year. If a safety valve operates and triggers during use, it should be tested promptly; such testing should include at least the setting pressure and the return pressure. It is crucial to regularly calibrate safety valves to ensure they open accurately within the set pressure range. 3) Markings and seals: Safety valves shall have clear markings, including manufacturer information, model number, set pressure, etc. All external adjustment mechanisms shall be sealed with lead seals to prevent unauthorized adjustments. 4) Technical records: Technical records for safety valves should be maintained, including product quality certification documents provided by the manufacturer, installation and operation maintenance manuals, records and reports of regular inspections, as well as records of daily use and maintenance. 8. Recommended standards: GB/T 12241-2021 \"Safety valves – General requirements\", TSG ZF001-2022 \"Regulations for the safety technical inspection of safety valves\", TSG ZF001-2006 \"Regulations for the safety technical inspection of safety valves\", GB/T 12243-2005 \"Safety valves with direct spring loading\", GB/T 12243.1-2008 \"Safety valves with direct spring loading – Part 1: Design and calculation\", GB/T 12243.2-2008 \"Safety valves with direct spring loading – Part 2: Testing and inspection\", HG/T20570.2-95 \"Installation and selection of safety valves\"