Steve.. Thanx for the detailed information.. You have helped me learn some new things for sure.
On Mon, Nov 3, 2008 at 8:40 PM, Steve Leyton <[EMAIL PROTECTED]>wrote: > 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]<[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]<[EMAIL PROTECTED]> > (Put the word unsubscribe in the subject field) > _______________________________________________ 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)
