As per NFPA 20-2013: 4.7.7.1 The net pump shutoff (churn) pressure plus the maximum static suction pressure, adjusted for elevation, shall not exceed the pressure for which the system components are rated.
So yes it is only by 3 psi, but you are crossing that line in the sand. Since your only components that aren't rated for more than 175 psi are the sprinklers, why not use high pressure sprinklers instead. I know that both Viking (250 psi) and Reliable (300 psi) have those. Using sprinklers rated for 250 psi or 300 psi would be a lot more convenient for all parties than using pressure reducing valves. Larry Keeping, P.Eng. Professional Loss Control 3413 Wolfedale Road, Suite 6 Mississauga, Ontario L5C 1V8 Phone: 905-949-2755, ext. 204 Fax: 905-949-1752 E-mail: [email protected] -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Matsuda, Richard Sent: February-18-14 4:22 PM To: [email protected] Subject: RE: Static Pressure/Working Pressure Ron, 1. The engr firm is correct...anything over 175-psi requires a PRV and the maximum expected static pressure (churn pressure) is used to determine where the PRV's are required. 2. If you do not put the PRV and something starts to leak and cause water damage, then you will assume responsibility. 3. I agree with you 100%...that the churn pressure only exists during the pump tests and that a city water supply may vary as much as 10 to 15-psi during the day so most of the time it will actually be less than 175-psi. 4. I also feel that installing a PRV for the "excessive" 3-psi is a waste of time and money. The hydrant test was done with a gauge that was bouncing around between 4 to 6-psi, and what if it was only 176-psi instead of 178-psi. However, I am not the responsible party to address this issue from a liability perspective. rick -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Tuesday, February 18, 2014 1:50 PM To: [email protected] Subject: Static Pressure/Working Pressure 3.8.1.9.2 Static Pressure. The pressure that exists at a given point under normal distribution system conditions measured ... We have a project with an electric pump and when combined with the current water supply the churn pressure is 178 psi. A nationally known engineering firm wants us to install PRV's on the lowest level of the building because of the 3 psi. Our position is that the pressure only exists at churn and that is similar to an overnight pressure surge in a municipal water system. The over pressure will be compensated for by the pressure relief valves once the pump stops. Are we being overly loose with our interpretation of "normal" or is the engineering firm correct? Ron F _______________________________________________ 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
