Circulation Relief Valve When is a pressure relief valve (PRV) required on a fire pump system? For a standard 175 PSI rated system, the simple answer is check and make sure that your expected churn pressure plus maximum static suction pressure will not exceed 144.6 PSI (or 206.6 PSI for a 250 PSI rated system). The sizing of the relief valve comes from NFPA 20 (2010 edition) table 5.25(a) which is summarized in our fire pump sizing app . For those of you that like to know the details read on. First let's clarify that we are taking about a main pressure relief valve and not a circulation relief valve. A circulation relief valve is generally 3/4-inch in size if less than 3,000 gpm and intended to provide a little fresh water into the pump casing for cooling purposes . Pressure Relief Valve When we say pressure relief valve in "fire pump" terminology, we are referencing a PRV that is only provided on diesel fire pumps to accommodate possible engine over
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