Rodney, Last week when I posted on the incompressibility of pure water (14.7 psi to reduce volume 1 part in 5x10^7) illustrated through a hypothetical temperature swing from 40F to 80F, I thought my statement of BIG PRESSURE was self explanatory on the massive pressure increase water can impart on piping. Let me now exchange "BIG PRESSURE" for two-million four-hundred seventy-two thousand three-hundred sixty-nine psi (2,472,369).
So in a worst case situation of pure water filling 100% of a fixed volume rigid system, the temperature does not need to rise much at all to get a 100, 200, or 300 psi increase in system pressure. Now let's take a 100% air filled dry pipe system. With an air regulator set at 50 psi and a temperature swing from -20F to 120F (244K - 322K), pressure will increase to 50 * 322 / 244 = 66 psi. Barely past the PRV's setting. I suspect the prv's on the dry pipe system are more about water delivery time then over pressurization protection. In short, the gridded systems experiencing over pressurization only need a prv not air-bleed valves. Don't confuse thermal expansion and compressibility. These are two different properties and it is the incompressibility property of liquid water that makes big problems out of a tiny amount of thermal expansion. Trevor Spain Fire Pro Corporation 404 N Cedar Shelbyville, IL 62565 Rodney Hamm wrote: > Wow what a week..I was at another plant yesterday which has the same exact > problem. This facility has 14 wet systems fed by a fire pump so the static > pressure is maintained by a jockey pump at 170 psi. Several systems had > system pressures >175 psi. One of the gridded systems had a system pressure > downstream of the alarm check valve of 205 psi just before lunch. At 4:00 > PM, the system pressure downstream of the alarm check valve was well above > 300 psi (the system gauge was pegged so I do not really know the actual > pressure). Riser nipple arrangement on the near main and the far main. The > ITC for the system was attached to the bottom of the far main (in other > words, essentially the same as for the facility I visited on Tuesday). This > system was also installed prior to the NFPA requirement of a 175 psi PRV for > all gridded systems. I have recommended the provision of a 175 psi PRV, > installing air bleed off valves and removing a significant amount of the > trapped air from the system. BTW, my client specifically requested that we > install a 175 psi PRV on the remaining 13 systems as a precautionary > measure; this approach might be considered unnecessary, but the PRV's will > not cause any detrimental effects and we will ensure the system pressures > for all 14 systems do not exceed 175 psi. > > > > Response to questions posted by Chris Cahill: Removal of the air would > resolve the excessive pressure problems; however, I still recommend the > provision of a 175 psi PRV (regardless of the "grandfather rule") because it > is required by NFPA and I believe it is in the best interest of my client. > As long as we provide the 175 psi PRV, any future high pressure incidents > will be immediately and automatically resolved. If the system is drained and > reinstated in the future (by plant employees or some other company which > does not bleed off the trapped air pockets), the system will more than > likely experience the same or similar high pressure problems due to the > trapped air pockets, so in my opinion the PRV is justified as a long term > and more permanent resolution of the problem. > > > > Rodney K. Hamm, P.E. > President/Owner > Falcon Fire Protection > Office (478) 953-1677 > > Cell (478) 396-6988 > > > > Date: Wed, 18 Mar 2009 21:22:44 -0400 > > From: "Rodney Hamm" <[email protected]> > > Subject: Excessive system pressure > > To: <[email protected]> > > Message-ID: <[email protected]> > > Content-Type: text/plain; charset="us-ascii" > > > > On a more serious note, I was at another plant yesterday which has the same > > exact problem. This is really why I am writing this email. Warehouse with 1 > > gridded system and 7 tree fed systems. The problem only exists for the > > gridded system; the remaining 7 systems had nominal pressure differences > > (0-10 psi difference) between the top & bottom gauges. On the gridded > > system, the public pressure upstream of the alarm check valve was fairly > > steady all afternoon at ~60 psi. At 1:50 PM, the system pressure downstream > > of the alarm check valve was 190 psi. I described the problem to the plant > > engineer and he wanted me to explain the problem to the plant manager. The > > three of us returned to the riser at 2:10 PM and the system pressure > > downstream of the alarm check valve was already up to 205 psi. We have not > > even entered our really hot days of summer yet! Riser nipples on the near > > main and the far main and the ITC for the system was attached to the bottom > > of the far main (in other words, the auxiliary or low point drain was > > converted into an ITC by installing the base of a sprinkler head at the end > > of the pipe and then someone placed an ITC sign on the valve). This system > > was installed prior to the NFPA requirement of a 175 psi PRV for all gridded > > systems. I have recommended the provision of a 175 psi PRV, installing air > > bleed off valves and removing a significant amount of the trapped air from > > the system. > > _______________________________________________ > 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) > ------------------------------------------------------------------------ > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 8.0.238 / Virus Database: 270.11.21/2014 - Release Date: 03/20/09 > 06:59:00 > > _______________________________________________ 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)
