The system demand is 2210.4 , From: Sprinklerforum [mailto:[email protected]] On Behalf Of Prahl, Craig/GVL Sent: April-06-17 4:52 PM To: [email protected] Subject: RE: NFPA 20 4.7.7.2
You can't use the PRV to relieve excess pressure under normal conditions due to an over designed pump. There can be unexpected times in a municipal supply where pressure spikes occur for various reasons. If your pump selection puts you close to the maximum system working pressure under normal conditions and a spike in the supply were to occur, with no means of relief, downstream system damage could occur. One other concern over this selection is that it is a 1500 gpm pump with only a 1583 gpm tested source flow rate. The pump may not be capable of reaching the 150 % mark unless you know if the municipal supply can actually provide more than 1583 gpm. Not knowing the actual system demands makes it difficult to address this issue any farther. Craig L. Prahl Fire Protection Group Lead/SME CH2M 200 Verdae Blvd. Greenville, SC 29607 Direct - 864.920.7540 Fax - 864.920.7129 CH2MHILL Extension 77540 [email protected]<mailto:[email protected]> From: Sprinklerforum [mailto:[email protected]] On Behalf Of Tom Duross Sent: Thursday, April 06, 2017 4:34 PM To: [email protected]<mailto:[email protected]> Subject: RE: NFPA 20 4.7.7.2 [EXTERNAL] Looks like you could be above 200 PSI churn or system pressure. The standard (2013 referenced) does not allow you to use the relief as a means of blowing off excess pressure above 175. Tom Is the 140 psi total pressure or pump rating? The pressure relief valve comes into play if the combination of supply pressure and pump pressure exceeds the allowable system pressure, which for most cases is 175 psi. So if you had fluctuating supply pressures, during a higher than normal pressure event, the system could relieve and not damage your downstream, 175 psi rated system. Is this a diesel or electric? How much pressure do you need at these heads? Craig L. Prahl Hi Forum , Could someone shed some light on the requirements for 4.7.7.2 . I have a project where the quoted fire pump comes with a Pressure relief valve and waste cone . City pressure is 58/56/1586 , we are using a 1500gpm pump at 140 psi to get the flow and pressure we need to supply a freezer using LP-46 heads . I find many references to the use of Pressure relief valves being Used but 4.7.7.2 is causing me to scratch my head . Colin
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