Sam: Both NFPA 13 and 14 offer prescriptive pressure limits for sprinkler and standpipe systems; 175 PSI (12 bar) has been the threshold for years but is excepted when components are rated higher. Obviously, there are many HP sprinklers and valves on the market and higher pressure fittings and heavier pipe schedules facilitate higher than 12 bar working pressures. NFPA 14 prescribes a 350 PSI (25 bar) pressure limit in any part of a standpipe system, so there isn't - to my knowledge - a higher pressure alternative to the 25 bar limit in high-rise buildings.
Pressure reducing valves require redundancy in standpipe systems when used to create separate zones or when otherwise arranged so that their failure would allow higher-than-approved pressure to more than two hose connections. Direct acting valves, such as PR sprinkler control and fire hose valves are allowed at any station where pressure reduction to the prescribed maximum (12 bar for Class I hose stations, for ex.) unless higher pressure is approved by the AHJ, so redundancy isn't required as the restrictor only impacts one hose connection. Your question draws two practices into question: 1) It's not a good practice to oversize a fire pump and then regulate it back down. NFPA 20 now states that pumps must be sized so that the designed demand falls between 90-140% of their rating. 2) If a pump does "over-supply" the downstream system (notwithstanding separate zones created by reducing valves), or if the measure of protection is to guard against diesel driver over-spin, then a RELIEF valve is the appropriate application, not a reducing valve. In my opinion, reducing valves should be treated like control valves - a necessary component that there can be too many of when they're redundant or applied for convenience, and a potential fail point at any point in a water supply or distribution system that requires regular inspection, testing and maintenance. Especially pilot-type reducing valves. I'm not sure I fully understand your last comment, "... like we consider 2 pumps with PRV stations each ..." but my experience has been that series pumps feeding multiple zones can in fact be arranged so that no in-line reducing valves are required. Please also be aware that both NFPA 14 and 20 are in cycle and that both technical committees have adopted proposals that will SIGNIFICANTLY change the prescriptive arrangement for high rise pumps if approved at the adoption hearings. The foregoing is my opinion only and does not necessarily represent the opinion or intent of the NFPA 14 Technical Committee on Standpipe and Hose Systems. Steve Leyton Protection Design & Consulting San Diego, CA -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of sam b Sent: Monday, November 03, 2008 12:36 AM To: [email protected] Subject: PRV Station : Hiii.. Everyone. Tis is sam again.. Have a small doubt,may b a simple one..but please help when designing fire protection systems for high rise buildings, we used to consider PRV stations if pressure required @ pump side is more than 12 bar. Is there any code requirment stating that.?? Also.. What about additional PRV stations.? suppose if the pressure required is 25 bar should we take two PRV stations.or is it like we consider 2 pumps with PRV stations each (high zone /lowzone)?? Is there any thumbrule or guidelines in this aspect..?? Please give your views. Thaanx in advance... Sam b _______________________________________________ Sprinklerforum mailing list http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [EMAIL PROTECTED] To Unsubscribe, send an email to:[EMAIL PROTECTED] (Put the word unsubscribe in the subject field) __________ Information from ESET NOD32 Antivirus, version of virus signature database 3578 (20081103) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com __________ Information from ESET NOD32 Antivirus, version of virus signature database 3578 (20081103) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com _______________________________________________ Sprinklerforum mailing list http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [EMAIL PROTECTED] To Unsubscribe, send an email to:[EMAIL PROTECTED] (Put the word unsubscribe in the subject field)
