What is thermal safety valve?
To complicate the issue you can also get combined temperature and pressure relief valves. These have two mechanisms 1. Normal spring to hold valve closed until set pressure is reached and valve opens. 2. Wax/oil filled probe, that as it gets to set temperature expands and opens valve. I have not yet seen these valves in the process industry, but there is one on my water heater at home. http://www.rmc.com.au/files/spec_sheets/HT501_1.
