The operating pressure determines the nominal pressure of the safety valve, and the operating temperature determines the operating temperature range of the safety valve. The calculated constant pressure value of the safety valve determines the constant pressure range of the spring or the lever, and then determines the material of the safety valve according to the medium used. According to the structure type, the throat diameter of the safety valve is calculated according to the relief valve discharge amount. The following are general rules for the selection of safety valves.
(l) Hot water boilers generally use a non-closed wrench with a micro-opening safety valve.
(2) Steam boilers or steam pipes are generally closed with a full-opening safety valve with a wrench.
(3) Liquid incompressible medium such as water generally uses a closed micro-opening safety valve or a safety relief valve.
(4) High-pressure feed water generally uses closed full-open safety valves, such as high-pressure feed water heaters, heat exchangers, etc.
(5) Compressible media such as gas generally use closed full-open safety valves, such as gas storage tanks, gas pipes, and the like.
(6) Class E steam boilers generally use static weight safety valves.
(7) Large-diameter, large-displacement and high-pressure systems generally use pulse-type safety valves, such as temperature and pressure reducing devices, power station boilers, etc.
(8) Built-in safety valves for train tank cars, car tankers, storage tanks, etc. for transporting liquefied gas.
(9) The top of the tank is generally equipped with a hydraulic safety valve, which is used in conjunction with a breathing valve.
(10) Pilot-type safety valves are generally used for downhole drainage or natural gas pipelines.
(11) A safety return valve is generally used on the liquid phase return pipe at the outlet of the tank pump of the LPG station.
(12) Vacuum negative pressure relief valves are generally used in systems where negative pressure or negative pressure may occur during operation.
(13) Bellows safety valves are generally used for containers or piping systems where the back pressure fluctuates greatly and is toxic and flammable.
(14) The system with low solidification point of the medium generally adopts the insulation jacket type safety valve.
Comparison of major domestic manufacturers and selection of connection sizes There are many manufacturers of safety valves in China, and the connection sizes are mostly not uniform. Mainly divided into the following major categories:
(1) The general category based on JB/T2203-1999 "spring-type safety valve structure length". At present, most domestic safety valve manufacturers are designed and produced according to this standard. Such as Zhejiang Luofu Boiler Accessories Factory, Hangzhou Valve Factory, Jiangsu Wujiang Valve Tools Factory, Shanghai Valve Factory, Kaifeng High Pressure Valve Factory, Hai'an Valve Factory, etc. However, this standard is not perfect, the specifications are not complete, the micro-open safety valve Zui large nominal diameter is D NI 00, full-open safety valve zui large nominal diameter DN200, the lack of DN65, DN125 two specifications. At present, the nominal diameter of the micro-opening safety valve is DN250, and the nominal diameter of the full-open safety valve reaches DN400. According to my research, the connection sizes of various manufacturers are not uniform. For example, DN150 full-open safety valve, Zhejiang Luofu Boiler Accessories Factory, Shanghai Valve Factory and Jiangsu Wujiang Valve Tools Factory are different. In order to have a uniform standard, the user can exchange the same specifications during the selection and installation. It is recommended that the Hefei General Machinery Research Institute revise the JB/T2203-1999 "Spring-type Safety Valve Structure Length". It is recommended that the design institute and users select according to the standard, and the safety valve manufacturer designs and manufactures according to the standard.
(2) The American standard system based on API526 "Flanged Steel Safety Relief Valve". The safety valve connection size of domestic imported chemical equipment is generally in accordance with this standard, as shown in Figure 5. The nominal diameter of this standard is DN25~ DN200( l"~ 8"), the nominal pressure is 2~42MPa, and the throat diameter is from D-T (9.5~146mm). This standard is more scientific and standardized, and considers pressure, materials, temperature, and throat diameter. According to the throat diameter to determine the specifications, the same throat diameter can have several specifications, on the contrary, the same specification may have several throat diameters to choose from. For example, DN100~DN150 (4"~6") throat diameters are available in L, M, N and P. With the continuous advancement of international trade and the localization of imported equipment, the standard will be greatly promoted in China. The standard has not yet been converted into a national standard.
(3) Pilot Operated Pressure Relief Valves series based on the internationally influential Anderson Greenwood & Co.. Domestically referred to as a pilot-operated safety valve, as shown in Figure 6, the pilot-operated safety valve consists of a main valve and a pilot valve, and the pilot valve operates the main valve to open and close. The valve has a large displacement; it is not affected by the back pressure; it can be operated at a very close to the opening pressure; the opening and closing pressure difference is small. Generally applicable to natural gas pipelines, etc. At present, there is no pilot safety valve standard and connection size standard in China. And this type of valve has just been developed and has not been widely promoted. According to the experience of our factory and the information we have, most domestic manufacturers design and manufacture according to the company's data, such as Zhejiang Luofu Boiler Accessories Factory and Aerospace Eleven Institute. It is recommended that the Hefei General Machinery Research Institute draft and publish the pilot safety valve standard as soon as possible.
(4) The safety valve designed and developed by the 11th Research Institute of China Aerospace Industry Corporation is a self-contained system. The HT series safety valve developed by Aerospace Eleven has many varieties, including HTO ordinary safety valve (as shown in Figure 1), HTB balanced bellows type safety valve, HTR bleed valve, HTN special safety valve, HTGS high performance steam safety valve. . HTXY liquid pressure relief valve, HTXD pilot safety valve, etc., and good performance. However, except for the HTXD series pilot-operated safety valve and the connection size of Anderson Greenwood, the rest is different from the American standard and the national standard. Please be careful when choosing this.
(5) The A-type and TA-type closed full-opening spring-type safety valves designed and developed by Lanzhou Refinery are a system. The series diameter is DN25~DN150 (1â€~6'), the nominal pressure is 1.6~4.0MPa, and the throat diameter is D~R(9.5-115mm). The connection size of the system is different from the American standard and the national standard. Lanlian special.
(6) A series of impulse safety valves for boilers, power station equipment, and temperature and pressure reducing devices. Such as Harbin Boiler Factory, Dongfang Boiler Factory, Wuhan Boiler Factory, Qingdao Power Station Auxiliary Machine Factory and other special safety valves. These types of valve structures and connection sizes are generally different from manufacturer to manufacturer and may be partially identical. When choosing, be sure to pay attention to the difference between the throat diameter and the connection size.
4. Calculation of throat diameter The calculation of throat diameter is generally in accordance with the formula listed in Annex V of the “Safety Technical Specifications for Boiler and Pressure Vesselsâ€. Or follow the formula listed in "Partial Design for Recommended Practices for Design and Installation of APIRP520 Refinery Pressure Relief System." The calculation results of the above two formulas are basically the same or have little difference.
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