I. Overview Safety valves are important safety accessories on boilers, pressure vessels and other pressurized equipment. The reliability and performance of its movement is directly related to the safety of equipment and people, and with energy conservation and environmental protection are closely related. And some users and design department in the selection, always choose the wrong model. To this end the selection of safety valve to be analyzed. Second, the definition of the so-called safety valve in the broad sense, including the relief valve, from the management point of view, directly installed in a steam boiler or a class of pressure vessels, the necessary conditions must be approved by the technical supervision of the valve, narrowly referred to as Safety valve, other commonly known as the relief valve. Safety valve and relief valve in the structure and performance are very similar, both in the opening pressure automatically discharge the internal media, in order to ensure the safety of the production plant. The existence of such an inherent similarity, often when people use the two are often mixed, in addition, some production facilities in the rules also provide for the choice of what can be. Therefore, the differences between the two are often overlooked. Thus there are many problems. If you want to make a clear definition of both, you can follow the "ASME Boiler and Pressure Vessel Code," the first part of the definition set out to understand: (l) safety valve (Valve) Driven automatic pressure relief device. It is characterized by having an open full opening action. For gas or steam occasions. (2) relief valve (Relief Valve), also known as a relief valve by the media before the static pressure drive automatic pressure relief device. It opens proportionally as pressure increases beyond the opening force. Mainly used for fluid applications. (3) Safet relief valve (Safet Relief Valve), also known as safety relief valve A pressure-driven by the media automatic pressure relief device. Depending on the use of the occasion not only for the safety valve is also suitable as a relief valve. In Japan, for example, safety valves and relief valves are clearly defined, and safety devices commonly used for large storage pressure vessels such as boilers are referred to as safety valves and are installed on pipelines or other facilities The relief valve. However, if the Ministry of MITI's "Technical Standard for Thermal Power Generation" is concerned, safety valves, such as boilers, superheaters, reheaters, etc., are to be specified as an important part of the safeguards on equipment. In the lower side of the pressure reducing valve needs to be connected with the boiler and turbine occasions, need to install the relief valve or safety valve. So, safety valve requirements than the relief valve more reliable. In addition, judging from the rules and regulations of high-pressure gas regulations of Japan's Ministry of Labor and Ministry of Transport and shipping associations at all levels, we regard the guarantee of emissions as a safety valve without any guarantee The valve of discharge is called the relief valve. Whether in the country Kai-type or micro-Kai collectively referred to as safety valve. Third, the selection 1. Classification Currently mass-produced safety valve spring and rod two categories. There are also impulse-type safety valve, pilot-operated safety valve, safety switch valve, safety relief valve, static heavy-duty safety valve. Spring-loaded safety valve depends mainly on the force of the spring to work, spring-loaded safety valve has closed and not closed, the general flammable, explosive or toxic media should be used closed, steam or inert gas can choose not closed Type, in the spring-loaded safety valve with wrench and without wrench. The role of the wrench is to check the valve flap flexibility, and sometimes can also be used as a manual emergency pressure relief. Lever safety valve rely mainly on the leverage of the hammer and work, but because of the large size of the lever safety valve often limits the scope of selection. When the temperature is high, select the safety valve with a radiator. The main parameters of the safety valve displacement, the displacement of the valve seat depends on the caliber and the valve opening height, the opening height is different, is divided into two kinds of micro-Kai and full Kai. Micro-Kai refers to the valve opening height of the valve seat throat diameter 1/40 ~ l / 20. Throttle refers to the valve opening height of the valve seat throat diameter 1/4. 2. The selection of safety valve is determined by the operating pressure of the nominal pressure of the safety valve, the operating temperature of the safety valve to determine the temperature range, the calculated value of the safety valve determines the fixed pressure spring or lever range, and then use the media to determine the safety Valve material and structure type, and then calculated according to safety valve relief valve throat diameter. The following general rules for the selection of safety valve. (L) General use of hot water boilers are not closed with micro-valve wrench safety valve. (2) steam boiler or steam pipe is generally not closed with a wrench full safety valve. (3) water and other liquid incompressible media commonly used closed micro-valve, or safety relief valve. (4) high-pressure water supply Generally closed full Kai-type safety valve, such as high-pressure water heaters, heat exchangers. (5) compressible gas and other gases generally use closed-type safety valve, such as gas tanks, gas pipelines. (6) E-class steam boilers generally use heavy-duty safety valve. (7) large-caliber, large displacement and high pressure systems generally use pulse safety valve, such as temperature and pressure reduction devices, power station boilers. (8) General purpose built-in safety valves for tank trucks, tank trucks and storage tanks for transporting liquefied gas. (9) The top of the tank with hydraulic safety valve, need to be used in conjunction with the breathing valve. (10) Downhole drainage or natural gas pipeline generally with pilot-operated safety valve. (11) liquefied petroleum gas station tank pump outlet liquid return pipe commonly used safety valve. (12) Negative pressure or negative pressure may occur during operation of the system is generally used vacuum negative pressure safety valve. (13) Bellows relief valves are generally used for container or piping systems with large back pressure fluctuations and toxic flammability. (14) medium freezing point lower system generally use insulation jacket safety valve. 3. Comparison of the major domestic manufacturers and the choice of connection size Domestic manufacturers of safety valves are more connected 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. The nominal diameter of this standard is 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 & rd
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