A thermal relief valve, also known as a temperature relief valve or a pressure-temperature relief valve, is a safety device used to protect equipment or systems from overpressure and overtemperature conditions. These valves are commonly employed in various applications, including pressure vessels, pipelines, and systems where changes in temperature can affect pressure.

Key features and functions of thermal relief valves include:

1. Overpressure Protection: The primary function of a thermal relief valve is to protect a system from overpressure conditions. When the pressure exceeds a predetermined setpoint, the valve opens to release excess pressure.

2. Temperature Protection: In addition to pressure, thermal relief valves are designed to respond to elevated temperatures. This is particularly important in systems where temperature increases can lead to a rise in pressure.

3. Automatic Operation: Thermal relief valves operate automatically. When the set pressure or temperature is reached, the valve opens to release pressure, preventing potential damage to the system.

4. Spring-Loaded Mechanism: Many thermal relief valves use a spring-loaded mechanism. The spring holds the valve closed until the pressure or temperature surpasses the setpoint, at which point the valve opens to relieve excess pressure.

5. Connection to Low-Pressure Area: The valve typically connects to a low-pressure area, such as the atmosphere or a designated relief header, allowing the excess pressure or temperature to be safely vented.

6. Application in Liquid or Gas Systems: Thermal relief valves are used in both liquid and gas systems. They are commonly found in pipelines, pressure vessels, heat exchangers, and other equipment.

7. Code Compliance: These valves often need to comply with industry standards and codes to ensure the safety and reliability of the systems they protect. Compliance with codes such as ASME (American Society of Mechanical Engineers) may be required in certain applications.

It’s important to note that the specific design, setpoint, and application of thermal relief valves can vary. Manufacturers provide guidelines and specifications for the correct selection, installation, and maintenance of these safety devices. Always refer to the manufacturer’s documentation and relevant codes and standards for accurate information on a particular thermal relief valve