Definition and difference between safety valve and relief valve

Safety relief valve, also known as safety overflow valve, is an automatic pressure relief device driven by medium pressure. It can be used as both a safety valve and a relief valve depending on the application.

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Take Japan as an example, there are relatively few clear definitions of safety valves and relief valves. Generally, safety devices used for large energy storage pressure vessels such as boilers are called safety valves, and those installed on pipelines or other facilities are called relief valves. However, according to the provisions of the "Technical Standards for Thermal Power Generation" of the Ministry of International Trade and Industry of Japan, safety valves are specified for important parts of equipment safety assurance, such as boilers, superheaters, reheaters, etc. In situations where the lower side of the pressure reducing valve needs to be connected to the boiler and turbine, a relief valve or safety valve needs to be installed. In this way, the safety valve requires more reliability than the relief valve.

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In addition, from 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, the identification and regulations of safe discharge volume, we call the valve that guarantees the discharge volume a safety valve, and the valve that does not guarantee the discharge volume a relief valve. In China, whether full-open or micro-open, they are collectively referred to as safety valves.

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I. Overview

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Safety valves are important safety accessories for boilers, pressure vessels and other pressure-bearing equipment. The reliability of their operation and the quality of their performance are directly related to the safety of equipment and personnel, and are closely related to energy conservation and environmental protection. However, some users and design departments always choose the wrong model when selecting. For this reason, this article analyzes the selection of safety valves.

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II. Definition

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The so-called safety valves broadly include relief valves. From the management rules, valves that are directly installed on steam boilers or a type of pressure vessels must be approved by the technical supervision department. In a narrow sense, they are called safety valves, and others are generally called relief valves. Safety valves and relief valves are very similar in structure and performance. Both of them automatically discharge the internal medium when the opening pressure is exceeded to ensure the safety of the production equipment. Due to this essential similarity, people often confuse the two when using them. In addition, some production equipment also stipulates that either type can be selected in the rules. Therefore, the differences between the two are often overlooked. As a result, many problems arise. If we want to give a clearer definition of the two, we can understand them according to the definition in the first part of the "ASME Boiler and Pressure Vessel Code":

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(1) Safety Valve, an automatic pressure relief device driven by the static pressure of the medium in front of the valve. It is characterized by a sudden full opening action. It is used in gas or steam applications.

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(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 in proportion to the increase in pressure exceeding the opening force. It is mainly used in fluid applications.