Does the plant realize that once all your air is gone that these prv's will be dribbling water every time the system warms up? Hopefully they have a good mop-up crew.
Air is the cushion in the system, systems will over pressurize once they have become water logged and there is no place for the water to expand. Take a look at some previous posts concerning thermal expansion of water in closed systems. There are basic thermodynamic principals at work here. Craig L. Prahl, CET Fire Protection Specialist Mechanical Department CH2MHILL Lockwood Greene 1500 International Drive PO Box 491, Spartanburg, SC 29304-0491 Direct - 864.599.4102 Fax - 864.599.8439 [email protected] http://www.ch2m.com -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Rodney Hamm Sent: Friday, March 20, 2009 11:42 AM To: [email protected] Subject: Excessive system pressure 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 syste m. 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) _______________________________________________ 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)
