Once you are past the final control valve required by NFPA 20, that standard is no longer applicable (regarding use of a PRV - still not ok to use a relief valve). As Pete already mentioned, it depends on what system the pump is feeding as to what arrangement is required for the PRV. If it is a standpipe, then the redundant set-up identified in NFPA 14 is required. NFPA 13 does not have a similar redundancy requirement so a single master PRV is allowed.
Roland Roland Huggins, PE - VP Engineering American Fire Sprinkler Assn. --- Fire Sprinklers Saves Lives Dallas, TX http://www.firesprinkler.org On May 20, 2014, at 9:24 AM, Travis Mack <[email protected]> wrote: > Doesn't it state in NFPA 20 that it is either bad design practice, or maybe > even prohibited to over size a pump and rely on a relief valve to take care > of the excess pressure. > > I can see if you have a situation where the city water was upgraded and now > an existing pump is in this situation. However, if new design, then > alternative options from the PRelV should be taken. > > 4.7.7* Maximum Pressure for Centrifugal Pumps. > 4.7.7.1 The net pump shutoff (churn) pressure plus the maximum static suction > pressure, adjusted for elevation, shall not exceed the pressure for which the > system components are rated. > 4.7.7.2* Pressure relief valves and pressure regulating devices in the fire > pump installation shall not be used as a means to meet the requirements of > 4.7.7.1. > > A.4.7.7 It is poor design practice to overdesign the fire pump and driver and > then count on the pressure relief valve to open and relieve the excess > pressure.Apressure relief valve is not an acceptable method of reducing > systempressure under normal operating conditions. > > A.4.7.7.2 It is not the intent of this subsection to restrict the use of > pressure reducing valves downstream of the discharge isolation valve for the > purpose of meeting the requirements of 4.7.7. > > I guess if you put it after the pump discharge control valve, then NFPA 20 no > longer applies and you go to NFPA 13 and/or 14 which may allow the device. > > Travis Mack, SET > MFP Design, LLC > 2508 E Lodgepole Drive > Gilbert, AZ 85298 > 480-505-9271 > fax: 866-430-6107 > email:[email protected] > > On 5/20/2014 9:12 AM, Steve Leyton wrote: >> Dewayne: >> >> Why a reducing valve instead of a relief valve? If the excess >> pressure is at churn only, then a relief valve would be the ticket as it >> only occurs in a no-flow condition. This would mitigate Pete's concerns >> about redundancy as prescribed in NFPA 14. >> >> SML >> >> >> >> >> >> -----Original Message----- >> From: Sprinklerforum >> [mailto:[email protected]] On Behalf Of >> Martinez, Dewayne >> Sent: Tuesday, May 20, 2014 5:20 AM >> To: [email protected] >> Subject: Pressure reducing valve on fire pump >> >> We have a situation where we have a pump that produces more than 175psi >> at churn. Can we put in a main pressure reducing valve after the pump >> discharge to bring it all down to 175psi or do we need one for each >> system? >> >> Thanks, >> >> Dewayne >> >> >> _______________________________________________ >> Sprinklerforum mailing list >> [email protected] >> http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler >> .org >> _______________________________________________ >> Sprinklerforum mailing list >> [email protected] >> http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org > > _______________________________________________ > Sprinklerforum mailing list > [email protected] > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
