Concept and selection skills of the hottest safety

The concept and selection skills of safety valve

Abstract: starting from the concept, this paper introduces the differences and selection of safety valve and relief valve in detail. The main safety valve series in China are analyzed, and the general rules for selecting safety valves are listed

concept:

1. Safety valve is an important safety accessory on boilers, pressure vessels and other pressure equipment. Its action reliability and performance are directly related to the safety of equipment and personnel, and are closely related to energy conservation and environmental protection. Some users and design departments always choose the wrong model when selecting the model. Therefore, this paper analyzes the selection of safety valve

2. Definition of safety valve: broadly speaking, the so-called safety valve includes relief valve. From the perspective of management rules, it is directly installed on steam boilers or a class of pressure vessels. The necessary condition is that the valve must be approved by the technical supervision department. In a narrow sense, it is called safety valve, and others are generally called relief valve. The safety valve and relief valve are very similar in structure and performance. Both of them automatically discharge the internal medium when the opening pressure is exceeded, so as to ensure the safety of the production device. Because of this essential similarity, people often confuse the two when using them. In addition, some production devices also stipulate which one can be selected in the rules. Therefore, the differences between the two are often ignored. Thus, many problems have arisen

if we want to make a clear definition of safety valve and relief valve, we can understand it according to the definition set forth in the first chapter of ASME boiler, boiler, blast furnace and Pressure Vessel Code:

(L) safety valve is an automatic pressure relief device driven by the static pressure of the medium in front of the valve. It is characterized by full opening action of sudden opening. Used for gas or steam occasions

(2) relief valve, also known as overflow valve, is an automatic pressure relief device driven by the static pressure of the medium in front of the valve. It opens proportionally as the pressure exceeds the opening force. It is mainly used in fluid occasions. How to choose and operate the plastic tension machine and what are the precautions?

(3) safety relief valve, also known as safety relief valve, is an automatic pressure relief device driven by medium pressure. It can be used as both safety valve and relief valve according to different applications. Taking Japan as an example, there are few clear definitions of safety valves and relief valves. Generally, the safety devices used for large energy storage pressure vessels such as boilers are called safety valves that give full play to the advantages of human resources and tackling key problems, and those installed on pipelines or other facilities are called relief valves. However, according to the provisions of the "technical standard for thermal power generation" of the Ministry of foreign trade and industry of Japan, safety valves, such as boilers, superheaters, reheaters, etc., are designated as important parts of safety assurance on equipment. Where the lower side of the pressure reducing valve needs to be connected with the boiler and turbine, a relief valve or safety valve needs to be installed. In this way, the safety valve is required to be more reliable than the relief valve. In addition, from the recognition and provisions of safety emissions in the high-pressure gas management rules of the Ministry of labor of Japan, the rules of the Ministry of transport and ship associations at all levels, we call the valve that ensures emissions as a safety valve, while the valve that does not guarantee emissions as a relief valve. In China, whether full lift or micro lift is collectively referred to as safety valve

II. Classification

at present, the safety valves produced in large quantities include spring type and rod type. In addition, there are impulse safety valves, pilot safety valves, safety switching valves, safety decompression valves, dead weight safety valves, etc

1). Spring type safety valves mainly rely on the force of spring. There are closed and unclosed spring type safety valves. Generally, flammable, explosive or toxic media should be closed, steam or inert gas can be unclosed, and spring type safety valves also have wrenches and wrenches. The wrench is mainly used to check the flexibility of the valve disc, and sometimes it can also be used for manual emergency pressure relief

2). The lever type safety valve mainly depends on the force of the lever hammer, but the large volume of the lever type safety valve often limits the scope of selection. When the temperature is high, choose the safety valve with radiator

2. The main parameter of the safety valve is the displacement, which depends on the diameter of the valve seat and the opening height of the valve disc. According to the different opening height, it can be divided into micro open type and full open type. Micro opening type means that the opening height of the valve disc is 1/40 ~ 1/20 of the throat diameter of the valve seat. Full open type means that the opening height of the valve disc is 1/4 of the throat diameter of the valve seat

III. selection skills of safety valve:

the nominal pressure of the safety valve is determined by the operating pressure, the service temperature range of the safety valve is determined by the operating temperature, the constant pressure range of the spring or lever is determined by the calculated constant pressure value of the safety valve, the material and structural type of the safety valve are determined according to the medium used, and the throat diameter of the safety valve is calculated according to the discharge capacity of the safety valve

1. General rules for the selection of safety valves:

(L) generally, open safety valves with wrenches are used for hot water boilers

(2) steam boilers or steam pipelines generally use non closed full open safety valves with wrenches

(3) water and other liquid incompressible media generally use closed micro open safety valves or safety relief valves

(4) closed full open safety valves are generally used for high-pressure feedwater, such as high-pressure feedwater heaters, heat exchangers, etc

(5) gas and other compressible media generally use closed full open safety valves, such as gas tanks, gas pipelines, etc

(6) class E steam boilers generally use dead weight safety valves

(7) pulse safety valves are generally used in large-diameter, large displacement and high-pressure systems, such as temperature and pressure reduction devices, utility boilers, etc

(8) built in safety valves are generally used for train tankers, automobile tankers, storage tanks, etc. transporting liquefied gas

(9) the hydraulic safety valve is generally used on the top of the oil tank, which needs to be used in conjunction with the breather valve

(10) pilot operated safety valves are generally used for underground drainage or natural gas pipelines

(11) the safety return valve is generally used on the liquid phase return pipeline at the outlet of the tank pump in the liquefied petroleum gas station

(12) negative pressure or systems that may generate negative pressure during operation generally use vacuum negative pressure safety valves

(13) Bellows Safety valves are generally used for containers or piping systems with large back pressure fluctuations, toxicity and flammability

(14) the system with low freezing point of medium generally adopts insulation jacketed safety valve

2. Comparison of major domestic manufacturers and selection of connection size

there are many domestic manufacturers of safety valves, and most of the connection sizes are not unified. It is mainly divided into the following categories:

(1) general category mainly based on JB/t2203-1999 structural length of spring loaded safety valves. 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 tool factory, Shanghai Valve Factory, Kaifeng high pressure valve factory, Hai'an valve factory, etc. However, this standard is not perfect, and the specifications are incomplete. The maximum nominal diameter of the micro lift safety valve is DN200, and the maximum nominal diameter of the full lift safety valve is DN65 and DN125 are missing in the middle. According to the specifications of the safety valve produced by our factory and the information we have, the nominal diameter of the micro open safety valve is up to DN250 at present, and the nominal diameter of the full open safety valve is up to dn400. According to my research, the connection dimensions of various manufacturers are also different, such as DN150 full lift safety valve, Zhejiang Luofu boiler accessories factory, Shanghai Valve Factory and Jiangsu Wujiang valve tool factory. In order to have a unified standard, users can exchange the same specification when selecting and installing, Hefei General Machinery Research Institute is suggested to revise JB/t2203-1999 "structural length of spring safety valve". It is suggested that the design institute and users should select according to the standard, and the manufacturer of safety valve should design and manufacture according to the standard

(2) American Standard System Based on api526 flanged steel safety relief valve. The connection dimensions of safety valves equipped with domestic imported chemical equipment are 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 D-T (9.5~146mm). This standard is relatively scientific and standardized, and takes into account the pressure, material, temperature, throat diameter, etc. The specification is determined according to the throat diameter. There can be several specifications for the same throat diameter. On the contrary, there may be several throat diameters for the same specification. For example, the throat diameter of dn100~dn150 (4 "~6") can be selected from L, m, N and P. With the continuous promotion of international trade and the localization of imported equipment, the standard will be greatly promoted in China. At present, the standard has not been transformed into a national standard

(3) the series of piston operated pressure relief valves based on Anderson Greenwood & Co., which has great international influence. It is generally called pilot safety valve in China, as shown in Figure 6. The pilot safety valve is composed of a main valve and a pilot valve, which operates the opening and closing of the main valve. This valve has a large displacement; Not affected by back pressure; It can operate without leakage under very close opening pressure; Small opening and closing pressure difference, etc. It is generally applicable to natural gas pipelines, etc. At present, there is no standard for pilot operated safety valve and connection size in China. And this type of valve has just been developed and has not been widely promoted. According to our experience and information, most domestic manufacturers design and manufacture according to the company's data, such as Zhejiang Luofu boiler accessories factory, aerospace 11th Research Institute, etc. It is suggested that Hefei General Machinery Research Institute draft and issue the standard of pilot operated safety valve as soon as possible

(4) the safety valve designed and developed by the 11th Research Institute of China Aerospace Industry Corporation forms a system by itself. The HT series safety valves developed by the 11th Institute of aerospace industry have many varieties, including HTO ordinary safety valves (as shown in Figure 1), HTB Balanced Bellows Safety valves, HTR relief valves, HTN special safety valves, and HTGS high-performance steam safety valves. Htxy liquid relief valve, htxd pilot safety valve, etc., with good performance. However, except that the connection size of htxd series pilot safety valve is the same as that of Anderson Greenwood company, the rest are different from American standards and national standards. Please pay attention to this when selecting

(5) the A-type and Ta type closed full open spring safety valves designed and developed by Lanzhou Refinery form a system. The diameter of this series is dn25~dn150 (1 "~6"), the nominal pressure is 1.6~4.0mpa, and the throat diameter is d~r (9.5-115mm). The connection size of this system is different from American Standard and national standard, and it is specially used by LANLIAN

(6) impulse safety valve series for boilers, power station equipment and temperature and pressure reduction devices (as shown in Figure 8). Such as Harbin boiler plant, Dongfang Boiler Plant, Wuhan boiler plant, Qingdao power station auxiliary equipment plant and other supporting special safety valves. The structure and connection size of this series of valves are generally different from manufacturers, and some may be the same. Pay attention to the difference of valve throat diameter and connection size when selecting

3. calculation of throat diameter

throat diameter is generally calculated according to the formula listed in Annex V of the technical code for safety of boiler and pressure vessel. Or according to the formula listed in apirp520 recommended implementation method for design and installation of refinery pressure relief system Part I design. The calculation results of the above two formulas are basically the same or have little difference

IV. end