Brad, In response to your question "why". Yes, the relief valves were first required on only the gridded systems due to the lack of trapped air in the systems. As an insurance inspector in the summertime here in Texas around the mid-1980's, we started to find existing gridded systems that were leaking. Several systems were noted with riser gauge pressure exceeding 200-psi which appeared to be causing the leaks. At first we thought that possibly this was from water hammer created by water trucks filling up from nearby hydrants and maybe closing the hydrant too quickly...so we had 24-hour pressure recorders installed at the risers. The recorders indicated that the pressure rise corresponded with the rise in temperature during the hot summer days, and all these systems were located in unconditioned warehouses with exposed metal deck roof systems. We did not notice the pressure rise on gridded systems in air conditioned buildings. Sometime in the 1980's, the Texas State Board of Insurance published it's rules to require a small pressure relief valve on all gridded wet-pipe systems because they did not want to limit it to only unconditioned warehouses...and later this was submitted as a proposal to NFPA-13. I'm not a thermal engineer so I don't know why or how the air and the gridded systems were affected by the heat, but these are my recollections of why this was done. rick On Wednesday, January 7, 2015 3:35 PM, Brad Casterline <[email protected]> wrote:
Interesting to those whom question "why" about everything- I did not wonder 'why grids but not trees' until a few years ago. I was getting nowhere on my own brain power so I asked and was told that grids have a trapped secondary main with aux drain and that helps get the air out so you do not have the air cushion like you do in a tree. Was the change made because of the increase in concern for getting the air out of both configurations these days? Brad -----Original Message----- From: Sprinklerforum [mailto:[email protected]] On Behalf Of Steve Leyton Sent: Wednesday, January 07, 2015 2:13 PM To: [email protected] Subject: RE: Pressure Relief Valve on Wet Pipe System Change to mandatory relief valve was in 2010. SL -----Original Message----- From: Sprinklerforum [mailto:[email protected]] On Behalf Of Aaron Peck Sent: Wednesday, January 07, 2015 3:46 AM To: [email protected] Subject: Pressure Relief Valve on Wet Pipe System I wonder if I've been doing it wrong all along since 2010, but NFPA 13, 2013 Ed. 7.1.2.1 require a pressure relief valve on ALL wet pipe sprinkler systems? I can't tell you how many times in the past none have been installed. Granted they might not have been all designed according to 2010+, but just surprised this hasn't jumped out at me before. Looking back the 2007 code mentions only in "gridded wet pipe systems" then 2010 eliminates the word "gridded" as well as the 2013 code reads the same as 2010. What's strange is my 2010 Hand book doesn't denote that as a changed section, actually none show up. Does the Hand book remove those that are there in the standard version? Well I learned something knew. _______________________________________________ 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
