Domestic manufacturers more safety valve, the connection size are mostly not uniform. Mainly divided into the following categories: (1) to JB / T2203-1999 "spring-loaded safety valve structure length" based generic class. At present, most of the safety valve manufacturers are designed and manufactured according to this standard. Such as Zhejiang Luofu boiler annex plant, Hangzhou valve factory, valve plant in Jiangsu Wujiang, Shanghai Valve Factory, Kaifeng High Pressure Valve Factory, MSC valve factory. However, this standard is also not perfect, incomplete specifications, micro-Kai safety valve maximum nominal diameter of D NI 00, all-relief valve DN200 DN, the middle of the lack of DN65, DN125 two specifications. According to our factory production of safety valve specifications and grasp of the information, the current nominal diameter of the micro-Kai-type valve up to DN250, all-valve safety valve nominal diameter of DN400. After my research, the connection size of the manufacturers are not uniform, such as DN150 Kai-type safety valve, boiler accessories plant in Shanghai, Shanghai, Shanghai and Wujiang valve factory in Jiangsu valve factory are different. In order to have a uniform standard, the users can interchange the same specifications when choosing and installing, it is recommended that Hefei General Machinery Research Institute to amend the JB / T2203-1999 "spring-loaded safety valve structure length". Recommended design institutes and users according to the standard selection, safety valve manufacturer by standard design and manufacturing. (2) American Standard System based on API526 "Flanged Steel Safety Relief Valve". Domestic imports of chemical equipment and other safety valve with the connection size generally in accordance with this standard, as shown in Figure 5. This standard is the nominal diameter of DN25 ~ DN200 (l "~ 8"), the nominal pressure of 2 ~ 42MPa, throat diameter from D-T (9.5 ~ 146mm). This standard is more scientific and standardized on pressure, materials, temperature, throat diameter and other considerations. According to the throat diameter to determine the specifications, the same throat diameter can have several specifications, on the contrary the same specifications may have several throat diameter can choose. Such as DN100 ~ DN150 (4 "~ 6") throat diameter L, M, N, P four kinds of options. With the continuous promotion of international trade and the localization of imported equipment, the standard will be greatly promoted domestically. At present, the standard has not yet turned into a national standard. (3) Pilot Operated Pressure Relief Valves series based on Anderson Greenwood & Co., a globally influential company. Pilot generally known as the safety valve, as shown in Figure 6, the pilot-operated safety valve consists of the main valve and pilot valve, pilot valve operation of the main valve on and off. This valve displacement; from the impact of back pressure; can be very close to the opening pressure without leakage operation; opening and closing pressure differential advantages. Generally applicable to natural gas pipelines. At present, there is no pilot safety valve standard and connection dimensions. And this type of valve has just been developed, has not been widely promoted. According to my factory experience and information available, most domestic manufacturers in accordance with the company's data design and manufacturing, such as the attachment factory in Luoyang, Zhejiang, Aerospace Institute 11 and so on. It is suggested that Hefei General Machinery Research Institute drafts and issues the pilot safety valve standard as soon as possible. (4) The safety valve designed and developed by the Eleventh Institute of China Aerospace Industry Corporation has formed itself into a system. There are many kinds of HT series safety valves developed by Aerospace 11, including HTO common safety valve (as shown in Figure 1), HTB balanced bellows safety valve, HTR discharge valve, HTN special safety valve and HTGS high performance steam safety valve . HTXY liquid pressure relief valve, HTXD pilot safety valve, etc., and good performance. However, except HTXD series pilot safety valve and Anderson Greenwood company connecting the same size, the rest with the American Standard, GB are not the same. Please pay attention when choosing this point. (5) Designed and developed by Lanzhou Refinery A type, TA type fully open spring-loaded safety valve into a system. The series of diameter DN25 ~ DN150 (1 "~ 6 '), the nominal pressure l.6 ~ 4.0MPa, throat diameter D ~ R (9.5-115mm). The system connection size and the American Standard and GB are different, (6) For the boiler, power plant equipment, temperature and pressure relief device supporting the impulse safety valve series (shown in Figure 8), such as Harbin Boiler Factory, Dongfang Boiler Factory, Wuhan Boiler Factory, Qingdao Power Station Auxiliary Plant and other supporting safety valve.Such series of valve structure and connection dimensions of the manufacturers are generally not the same, there may be some of the same.Options must pay attention to the difference between the valve throat diameter and connection dimensions.