Steve was a tad softer on this issue which is an old point of contention for me. The older editions of NFPA 20 simply said where the pressure exceeds the rating of the system, a relief valve shall be installed. So some (we'll many) folks well golly gee willickers, we can overs die that baby, reduce some pipe size, and take care of the problem with a relief valve. That ignores every churn test you dump thousands of gallons of water to ground. Gee nice skating rink in the parking lot. Bad practice is the nicer terms for such poor designs.
That was finally fixed by NFPA 20 a couple of cycles ago. The 2013 ed says: 4.7.7* Maximum Pressure for Centrifugal Pumps. 4.7.7.1 The net pump shutoff (churn) pressure plus the maxi- mum static suction pressure, adjusted for elevation, shall not ex- ceed 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. It also tells us when a relief valve shall be used (ONLY for diesel drivers where at 121% of rating (run away pump) + inlet pressure exceeds the rating of system and diesel pressure limiting drivers. The problem is that statement about not using pressure regulating devices. That is why they are located after the last component required by NFPA 20 (the discharge control valve) so done so under the control of other NFPA system standards. The relief valve is not located after the control valve so that approach won't fly. This is a good example of where one committee totally ignores the reality of the world and choice design purity instead of listening to input from the NFPA 14 committee. Roland Roland Huggins, PE - VP Engineering American Fire Sprinkler Assn. --- Fire Sprinklers Saves Lives Dallas, TX http://www.firesprinkler.org On Jun 3, 2013, at 8:36 PM, "Steve Leyton" <[email protected]> wrote: > To arbitrarily oversize a pump (as specifying engineers are sometimes wont to > do) and then slap a reducing (or worse, relief) valve into the discharge main > is a bad practice. So if you have a pump that's oversized for the > application, that arguably should be addressed in a more meaningful remedial > way. _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
