What is Pressure Safety Valve (PSV)?

What is Pressure Safety Valve (PSV)?

What is Pressure Safety Valve (PSV)?

Pressure Safety Valve is a means of protection in most cases is the last line of defence. It is important to ensure that the safety valve is capable of operating at all times and under all circumstances.

The Pressure Safety Valve is not a pressure regulator and should not be abused as such. It must operate for only one purpose: overpressure protection.

The purpose and function of the Pressure Safety Valve (PSV)

The main purpose of a PSV is to protect life, property and the environment. PSV are designed to open and relieve excess pressure from vessels or equipment and close again and prevent further release of fluid once normal conditions have been restored.

The reason for the excess pressure on the ship

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

  • Clogged debit
  • Exposure to external fire, often referred to as a “Fire Case”
  • Thermal expansion
  • Chemical reaction
  • Heat exchanger tube broke
  • Cooling system failure

Each of the events listed above may occur individually and separately from the others. They may also occur simultaneously.

Each cause of overpressure will also create a different mass or volume flow to discharge, e.g. small mass flow for thermal expansion and large mass flow in case of chemical reaction.

It is the user’s responsibility to determine the worst case scenario for the size and selection of the appropriate pressure relief device.

Pressure Safety Valve Type

There are two main types of Pressure Safety Valves (PSV).

  • Spring loaded safety valve
  • Safety Valve which is operated automatically or so-called pilot operated
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