Introduction and selection of safety valves

In industrial production, the safety of boilers, pressure vessels and other pressurized equipment is of paramount importance. In order to ensure the safe operation of these equipments under high pressure environment, safety valves, as an important safety accessory, play an indispensable role. The performance and operational reliability of safety valves are not only directly related to the safety of equipment and operators, but also closely linked to energy saving and environmental protection. However, in the selection process, some users and design departments often encounter the problem of choosing the wrong model. Therefore, this paper will analyze the selection of safety valves in detail to help readers better understand this key component.
I. Definition and Classification
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 the ability to open quickly and completely when the set pressure is reached, thus releasing the internal medium and ensuring the safety of the production plant. Safety valves are mainly used in gas or steam applications.
Relief Valve:
Relief valve, also known as relief valve, is also a kind of automatic pressure relief device driven by the static pressure of the medium in front of the valve. However, unlike a safety valve, a relief valve opens proportionally as the pressure increases above the opening force. It is mainly used in fluid applications, capable of continuously discharging overpressurized media.
Safety relief valve:
Safety relief valve combines the characteristics of the safety valve and relief valve, can be used as both safety valve and relief valve. It has a wider range of applications and can be flexibly selected according to actual needs.
In Japan, the definitions of safety valves and relief valves are relatively vague. Generally, safety devices used in large energy storage pressure vessels such as boilers are called safety valves, while those installed on piping or other facilities are called relief valves. However, according to Japan’s Ministry of International Trade and Industry’s Technical Standards for Thermal Power Generation, safety valves must be specified for important parts of the facility where safety is ensured, such as boilers, superheaters, and reheaters. And where the lower side of the pressure reducing valve needs to be connected to the boiler and turbine, a relief valve or safety valve is required.
Second, the selection of safety valves
In the selection process, we need to consider a number of factors to ensure that the right safety valve is selected.
Classification:
The safety valves currently mass-produced on the market are mainly divided into two categories: spring-loaded and lever-loaded. In addition, there are impulse type safety valves, pilot operated safety valves, safety switching valves, safety relief valves and static weight safety valves.
Spring-loaded safety valve: mainly rely on the spring force to work. According to the different media, spring-loaded safety valves are also divided into closed and unclosed. Flammable, explosive or toxic media should be selected closed safety valve, while steam or inert gases, etc. can be selected not closed safety valve. In addition, spring-loaded safety valve with wrench and without wrench difference. The wrench is mainly used to check the degree of flexibility of the valve flap, and sometimes can also be used as a manual emergency pressure relief.
Lever-type safety valve: It mainly relies on the force of lever and weight to work. However, due to the large size of the lever-type safety valve, it often limits the scope of its selection. In high-temperature environments, safety valves with heat sinks should be selected.
Main parameters:
The main parameter of the safety valve is the displacement, which determines the caliber of the valve seat and the opening height of the valve flap. According to the different opening height, the safety valve is divided into micro-opening type and full-opening type. The opening height of the valve flap of the micro-opening safety valve is 1/40~1/20 of the seat throat diameter, while the opening height of the valve flap of the full-opening safety valve is 1/4 of the seat throat diameter.
Selection rules:
In the selection of safety valves, we need to follow the following general rules:
Hot water boilers generally use non-closed with wrench micro-opening safety valve.
Steam boilers or steam piping generally use non-closed with a wrench full-opening safety valve.
Water and other liquid incompressible media generally use closed micro-opening safety valve or safety relief valve.
High-pressure water supply generally use closed full-opening safety valve, such as high-pressure water supply heater, heat exchanger.
Gas and other compressible media generally use closed full-opening safety valves, such as gas storage tanks, gas piping.
E-class steam boilers generally use static weight safety valve.
Large diameter, large displacement and high-pressure systems generally use pulse-type safety valves, such as temperature and pressure reduction devices, power station boilers.
Train tankers, automobile tankers, storage tanks, etc. that transport liquefied gas generally use internal safety valves.
The top of the tank generally use hydraulic safety valve, need to be used in conjunction with the breathing valve.
Pilot operated safety valves are generally used for downhole drainage or natural gas pipelines.
Safety return valves are generally used on the liquid phase return piping at the outlet of the tank pump in LPG stations.
Negative pressure or the operation process may generate negative pressure system generally use vacuum negative pressure safety valve.
Back pressure fluctuations and toxic and flammable containers or piping systems generally use bellows safety valve.
The system with low solidification point of the medium generally use insulated jacketed safety valves.