Safety valve Tutorial
LESER Safety valves

Purpose and function of safety valves

The primary purpose of a safety valve is the protection of life, property and environment. A safety valve is designed to open and relieve excess pressure from vessels or equipment and to reclose and prevent the further release of fluid after normal conditions have been restored. 

A safety valve is a safety device and in many cases the last line of defence. It is important to ensure that the safety valve is capable to operate at all times and under all circumstances. A safety valve is not a process valve or pressure regulator and should not be misused as such. It should have to operate for one purpose only: overpressure protection.

Reasons for excess pressure in a vessel

There is a number of reasons why the pressure in a vessel or system can exceed a predetermined limit. API Standard 521/ISO 23251 Sect. 4 provides a detailed guideline about causes of overpressure. The most common are:

  • Blocked discharge
  • Exposure to external fire, often referred to as “Fire Case”
  • Thermal expansion
  • Chemical reaction
  • Heat exchanger tube rupture
  • Cooling system failure

Each of the above listed events may occur individually and separately from the other. They may also take place simultaneously. Each cause of overpressure also will create a different mass or volume flow to be discharged, e.g. small mass flow for thermal expansion and large mass flow in case of a chemical reaction. It is the user’s responsibility to determine a worst case scenario for the sizing and selection of a suitable pressure relief device.

Main types of safety valves and their function

There are two main types of safety valves. Spring loaded safety valves and pilot operated safety valves.

弹簧阀 安全阀

弹簧力Fs通过销轴传递到板子上,与板子一起关闭过程,确保密封。只要弹簧力大于力F,这个条件就能保持。p在阀门入口处产生的压力。
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先导操作的安全阀

先导操作的安全阀通过打开主阀来补偿超压,从而限制系统中的压力。但是,由于表面尺寸不同,在关闭方向上的作用力较大。

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