A.4.7.7 A pressure relief valve is not an acceptable method of reducing system pressure under normal operating conditions. Prior to the 2003 edition, NFPA 20 did not strictly prohibit the use of pressure relief valves for management of excessive pressure at churn or low water flow conditions and only recognized it as a poor design practice as part of the 1999 edition. Existing installations designed under previous editions of NFPA 20 and containing pressure relief valves designed for such purposes might still be in service.
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. When selecting the fire pump, the maximum pump discharge pressure should not subject any system component to a pressure that exceeds the component pressure rating. The maximum discharge pressure normally occurs at zero flow (churn) and is calculated by adding the suction pressure to the net pump pressure. The maximum reasonably anticipated suction pressure should be used for this calculation. All listed fire protection components have a pressure rating of 175 psi (12.1 bar) or higher. If the system components have been properly selected, some fire protection systems may be rated for 300 psi (20.7 bar). Pressures in excess of the component rating can damage system components. The maximum pressure permitted in a standpipe system per NFPA 14, Standard for the Installation of Standpipe and Hose Systems, currently is 350 psi (24.1 bar), although NFPA 14 does not restrict the pressure in express risers in standpipe systems. See Exhibit II.4.2 for a check valve rated for 300 psi (20.7 bar). View Large EXHIBIT II.4.2. Print Check Valve Listed for 300 psi (20.7 bar). (Courtesy of Aon Fire Protection Engineering) 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. The use of pressure relief valves is limited in this standard to the following situations: ■ Diesel engine drivers where pressures developed may exceed the pressure rating of system components if an overspeed condition occurs ■ Variable speed drivers where pressures developed may exceed the pressure rating of system components if a failure causes the driver to revert to rated speed A pump should never be deliberately oversized so that a pressure reducing valve is needed. Pressure reducing valves and pressure relief valves are maintenance intensive and should be incorporated into the design of a fire pump system only when necessary and allowed by this standard. Pressure reducing valves are not permitted to be installed in the fire pump system piping. Where pump discharge pressures exceed 175 psi (12.1 bar), flanged cast-iron valves and fittings between the fire pump discharge flange and the discharge isolation valve must be extra heavy pattern. It is not the intent of Section 4.7.7.2 to limit the use of pressure reducing valves or pressure regulating valves downstream of the discharge isolation valve. The use of pressure regulating valves downstream of the discharge isolation valve is covered in other standards. In many cases, high-pressure output is needed to meet the design requirements of systems installed in high-rise buildings and in standpipe systems in particular. 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. Thank you, Sean Roberts 4456 Campbell RD, Houston, TX 77041 713-896-9941 Fax 713-896-9945 Cell 713-206-8837 [email protected] -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Morey, Mike Sent: Monday, June 03, 2013 12:05 PM To: [email protected] Subject: RE: Fire Pump - Pressue Relief Valve I believe the correct answer is NFPA 20 does not allow this, but NFPA 20 only governs the fire pump itself, so anything downstream of the discharge is governed by 13/14/etc and the PRV would be the correct, while maybe not preferable, solution. Mike Morey, SET, CFPS Sprinkler Designer BMW Constructors, Inc. O: 317.651.0596 | C: 317.586.8111 www.bmwc.com <http://www.bmwc.com/> ________________________________ From: [email protected] on behalf of Joe Powell Sent: Mon 6/3/2013 1:00 PM To: [email protected] Subject: Fire Pump - Pressue Relief Valve Does the 2010 NFPA 20 allow PRV's to be used to limit pressure on a fire pump system? The insurance inspector wants the existing pressure reducing valve to be replaced with a pressure relief valve. The pressure reducing valve is downstream of the fire pump and limits pressure on a supply to an older part of the facility. Joe C. Powell Pruett Ford & Associates, Inc. Consulting Engineers 1201 Broad Street, Suite 3A Augusta, GA 30901 Ph: 706-722-3959 Fax: 706-724-5127 Email: [email protected] _______________________________________________ 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
