The purpose of the temperature pressure relief valve is to release water, and in turn lower the pressure inside the tank, in the event that the temperature or pressure gets too high in your water heater.
WATTS® F156481 40L Automatic Reseating Valve, 3/4 in Nominal, Male NPTF x Female NPTF End Style, 93 psi Pressure, 210 deg F, 5 in L Probe, Bronze Body, Domestic
WATTS® F163803 LL40XL Automatic Reseating Valve, 3/4 in Nominal, Male NPTF x Female NPTF End Style, 112 psi Pressure, 210 deg F, 5 in L Probe, Bronze Body, Domestic
WATTS® F318825 N240 Automatic Reseating Valve, 1-1/4 in Nominal, Male NPTF x Female NPTF End Style, 112 psi Pressure, 210 deg F, 5 in L Probe, Bronze Body, Domestic