What is a Temperature, Pressure relief valve?
Primarily used in cylinders - Tprv's or temperature pressure relief valves are a safety mechanism that monitors the pressure and temperature within the appliance. If either the temperature or pressure within the cylinder begin reaching an unsafe point it will discharge water to alleviate.
What is a Pressure relief & Safety Valve?
PRV's are similar to the above TPRV's but they only deal with pressure, not temperature.