差別點在於TSV 通常是液體，而PSV通常是氣(汽)體(除了正位移高壓泵出口的PSV)。兩者都是洩壓的。

Thermal safety valves are used for protection in case of excessive temperature for liquid applications in long pipes/pipelines exposed to the environment (sunlight), closed vessels, water heater applications, cooling water return side of heat exchangers between isolation valves, and pumps that recirculate water where heat buildup can be a problem.

https://whatispiping.com/thermal-relief-valve/?utm_source=feedburner&utm_medium=email

這裡有不錯的解釋

http://www.eptq.com/qandaquestion.aspx?q=7a831c67-920c-4e9d-8daf-817cec2026cc

(通常放於冷凝器冷卻水回去的管路上)