Jerome, you're still mixing terms. Every water heater come equipment with a temperature/pressure safety valve, commonly referred to as a T/P valve. It will trip if the temperate or pressure reaches the danger points. Water heaters can and do explode, and I mean big time explode if this valve does not open. If your incoming water pressure is excessive, that's 80 psi or more, you need a pressure regulating valve, commonly called PRV. This will lower the pressure to a safe level. The PRV does have a slight downside. Most of them contain a back flow feature. I'll come back to that feature in a minute. We all know that heated water expands and it does not compress. This means when you water heater starts to heat, temperature builds up quite rapidly. If you do not have a PRV, the expansion can be absorbed by the city water main and you have no problem. However, with the PRV, the expansion has to find somewhere to go, and the back flow feature prevents it from get to the city main. It might find a weak toilet valve, but often it will trip the T/P safety valve. The cure for this is with a Thermal Expansion Tank that is installed in the incoming cold water line between the PRV and water heater. This tank provides a temporary escape route for the expansion. It is air charged to match the PRV setting. Hope this clears things a bit for you.