A pressure safety valve (PSV), also known as a pressure relief valve (PRV) or safety valve, is a type of valve designed to automatically release excess pressure from a vessel, pipeline, or system to prevent it from exceeding its design limits. PSVs play a critical role in maintaining the safety and integrity of various industrial processes and equipment.

The main function of a pressure safety valve is to protect pressure vessels, pipelines, or systems from overpressure situations that could lead to catastrophic failure. When the pressure inside the protected equipment reaches a predetermined set point, the PSV opens and releases the excess pressure to the atmosphere or to a low-pressure area, restoring the pressure to a safe level.

Key features of pressure safety valves include:

1. Set Pressure: The set pressure is the pressure at which the PSV starts to open and relieve excess pressure.

2. Blowdown: Blowdown is the difference between the set pressure and the pressure at which the PSV closes. It ensures that the PSV remains open until the pressure decreases below a safe level.

3. Reseating Pressure: Reseating pressure is the pressure at which the PSV closes after the pressure is relieved. It ensures that the PSV remains closed at normal operating conditions.

Pressure safety valves are typically classified into two main types based on their operating principle:

1. Direct Spring-Loaded Pressure Safety Valve: This type of PSV uses a spring to keep the valve closed. When the pressure exceeds the set point, the spring is compressed, and the valve opens to release the excess pressure.

2. Pilot-Operated Pressure Safety Valve: Pilot-operated PSVs use a pilot valve and a control line to control the opening and closing of the main valve. The pilot senses the pressure and controls the flow of fluid to open or close the main valve based on the set pressure.

Pressure safety valves are widely used in various industries, including oil and gas, petrochemical, power generation, chemical, and process industries, to protect pressure vessels, storage tanks, pipelines, and other equipment from overpressure situations. Regular inspection, maintenance, and testing of PSVs are essential to ensure their proper functioning and reliability.

There are several types of pressure safety valves (PSVs), each designed for specific applications and requirements. The main types of pressure safety valves include:

1. Direct Spring-Loaded Pressure Safety Valve: This type of PSV operates solely based on the force of a spring. When the pressure inside the vessel or system exceeds the set pressure of the spring, the valve opens to relieve the excess pressure.

2. Pilot-Operated Pressure Safety Valve: Pilot-operated PSVs use a pilot valve to control the opening and closing of the main valve. The pilot senses the pressure and controls the flow of fluid to open or close the main valve based on the set pressure.

3. Balanced Bellows Pressure Safety Valve: This type of PSV uses a bellows element to sense the pressure and provide a balanced force on the valve’s disk. It offers high accuracy and is suitable for low and high-pressure applications.

4. Safety Relief Valve (SRV): Safety relief valves are a specific type of PSV that operates with a combination of a spring and a weight-loaded lever. They are commonly used for pressure relief in low-pressure systems.

5. Pilot-Operated Safety Relief Valve: Pilot-operated safety relief valves use a pilot system to control the main valve. They offer accurate and stable pressure relief and are often used for high-pressure applications.

6. Conventional Safety Valve: Conventional safety valves are spring-loaded valves designed for specific set pressure and blowdown requirements. They are widely used in various industrial applications.

7. Angle Type Safety Valve: Angle type safety valves have an angled body design, making them suitable for space-restricted installations.

8. Full-Lift Safety Valve: Full-lift safety valves open to their maximum capacity, allowing the entire cross-sectional area for pressure relief.

9. Low-Lift Safety Valve: Low-lift safety valves open to a partial lift position, allowing only part of the cross-sectional area for pressure relief.

10. High-Lift Safety Valve: High-lift safety valves open to a higher lift position than conventional valves, providing increased capacity for pressure relief.

11. Modulating Safety Valve: Modulating safety valves are designed to provide continuous and gradual pressure relief, suitable for applications where a gradual increase in pressure is expected.

The choice of pressure safety valve type depends on factors such as the application, pressure range, required capacity, set pressure, and specific industry requirements. Proper selection, sizing, and installation of pressure safety valves are crucial to ensure the safety and protection of equipment and personnel from overpressure situations.