Thank you regarding the selection of safety valves!

This post was last edited by ali2277 on 2010-6-29 21:40. A safety valve is an automatic pressure release device used on pressurized equipment, containers, or pipelines. When the pressure within the protected system rises above the allowable level, the valve opens automatically to release some of the excess fluid, thereby preventing further increases in system pressure. When the system pressure drops to a specified level, the valve closes automatically again, ensuring the normal operation of the system. The main performance indicators of a safety valve are: 1) Safety. Upon leaving the factory, the valves undergo strength tests and sealing tests in accordance with **relevant standards, to ensure that their mechanical properties meet the requirements of those standards. 2) Sensitivity. The opening pressure and closing pressure of the valve are within the **standard ranges and those specified by the user; the opening pressure is accurate and rapid, while the closing pressure remains stable. 3) Sealing performance. After the valve returns to its seat, it exhibits excellent sealing performance with no leaks. 4) Safety valves with emission requirements: after the valve operates, its emission volume meets the mechanical specifications specified by the standards; moreover, the valve’s sealing performance and other characteristics remain stable and do not change. How to select a safety valve correctly is directly related to the economic efficiency of the using entity, as well as the safety of operators and equipment. The following outlines several key points for selecting a safety valve: 1. Determination of the operating pressure class (pressure rating). The operating pressure of a safety valve and the pressure rating of the spring have different meanings and should not be confused. Working pressure refers to the static pressure exerted on the valve before it during normal operation of the safety valve; it is the same as the working pressure of the system or equipment being protected. The operating pressure range of a spring refers to the range of working pressures for which that particular spring can be used; within this range, the opening pressure of the safety valve (i.e., the set pressure) can be adjusted by changing the degree of pre-compression of the spring. Safety valves with the same nominal pressure can be divided into various operating pressure classes depending on the requirements of their spring design. The specific classification is shown in the table below; the premise for this classification is that it ensures that both the upper and lower limits of the pressure for each operating pressure level meet the performance criteria specified by relevant standards. When selecting a safety valve, the operating pressure class of the valve should be determined based on the required opening pressure value. 2. Selection criteria: (1) Selection of nominal diameter – The nominal diameter of the safety valve should be determined based on the discharge volume required by the system to be protected. The rated discharge capacity of the safety valve used should be greater than and as close as possible to the required discharge capacity. The discharge volume necessary for the protected system refers to the amount of medium that must be removed in order to prevent excessive overpressure when the system experiences abnormal pressure buildup; it is determined by factors such as the operating conditions and capacity of the system or equipment, as well as the causes that may lead to overpressure. (2) Selection of material: The material for a safety valve should be chosen taking into account various factors such as the operating temperature and pressure of the medium, the properties of the medium, as well as the processability and cost-effectiveness of the material. Under normal circumstances, users can choose the appropriate safety valve based on the operating temperature, pressure range, and types of representative media for use, as specified in the sample safety valves provided by the manufacturing unit. If there are special requirements regarding the material, they can be discussed and resolved with the manufacturing unit at the time of ordering. (3) Selection of safety valves with special structures 1) Selection of safety valves with radiators. This type of safety valve is generally used in applications where the temperature of the medium is high, in order to reduce the temperature in the spring chamber. Generally, when the operating temperature of a closed-type safety valve exceeds 300°C and that of an open-type safety valve exceeds 350°C, a safety valve equipped with a radiator should be selected. 2) Bellows safety valve: This type of safety valve is suitable for those that are subjected to additional back pressure, and it should be used when the change in back pressure exceeds 10% of the set pressure. Furthermore, for safety valves used with corrosive media, in order to prevent the springs and guiding mechanisms from being corroded by the medium, diaphragm safety valves should also be selected. 3. Instructions for ordering regular safety valves When ordering regular safety valves, the following information must be specified: 1) The model of the safety valve, its nominal diameter, and nominal pressure. 2) The operating pressure class or opening pressure (set pressure) of the safety valve. 3) The material of the valve body and the material of the sealing surface. 4. Instructions for ordering special-specification safety valves When ordering special safety valves, in addition to specifying the model, nominal diameter, and opening pressure of the valve, the following information is also required: (1) The maximum discharge pressure of the safety valve and the minimum reseating pressure (or pressure difference for opening and closing) ； (2) Required flow rate of the protected system or equipment and the number of valves to be installed ； (3) Medium used and its specific gravity (for liquids) or molecular weight (for gases) ； (4) Temperature of the medium at the valve inlet ； (5) Type and value of the back pressure experienced by the valve ； (6) Other requirements. Source: (http://blog.sina.com.cn/s/blog_43e8d1fc0100bqkc.html) – Methods for Selecting Safety Valves _ Dushu Shi _ Sina Blog. Selection of safety valves; Classification of safety valves. Due to their different applications, safety valves come in various structural types, but they can generally be classified as follows: (1) By the medium used: Safety valves for steam (usually represented by the A48Y type); safety valves for air and other gases (usually represented by the A42Y type); safety valves for liquids (usually represented by the A41H type). (2) By nominal pressure: Low-pressure safety valves: those with a nominal pressure of PN ≤ 1.6 Mpa; Medium-pressure safety valves: those with a nominal pressure of PN 2.5–6.4 Mpa; High-pressure safety valves: those with a nominal pressure of PN 10.0–80.0 Mpa; Ultra-high-pressure safety valves: those with a nominal pressure of PN > 100 Mpa. (3) By applicable temperature: Ultra-low-temperature safety valves: those designed for temperatures of t ≤ –100°C; Low-temperature safety valves: those designed for temperatures of –100℃

You may refer to the \"Valve Selection Manual\" published by the Mechanical Industry Press

Reply to 2# ali2277: Is there no standard? I want to determine the model myself. Thank you

Reply to 2# ali2277: Regarding what you mentioned – 3. Instructions for ordering regular safety valves: When ordering regular safety valves, the following information must be specified: 1) The model of the safety valve, its nominal diameter, and nominal pressure. 2) The operating pressure level or opening pressure (set pressure) of the safety valve. 3) The material of the valve body and the material of the sealing surfaces. 4. Instructions for ordering safety valves with special specifications. Where can I find information on the model of the safety valve, as well as its nominal diameter? Thank you!

Reply to 5# *nchen: The method for determining model numbers has been found in JB/T308-2004, or in the valve selection manual. However, it’s not yet clear where to find information regarding the specific throat diameter. For example, for a valve with DN80 PN1.6, where can one find out what its throat diameter is? This information isn’t available in the valve selection manual. Thanks

HGT20570.2-95 Installation and Selection of Safety Valves or API520