I would say you can calc your system back to the gauge on the riser only when you have completed a flow test where the effective point of the test is the gauge on the riser. E.g., you have a backflow test connection that ties to the riser at or near the point of connection of the gauge.
Otherwise, I could have a riser with a gauge that reads 50 psi. I look down and follow the 4" pipe to the ground and it disappears. For all I know that 4" ties into a 75 year old 6" coast iron pipe that has deteriorated to the point that it is effectively a 2" diameter pipe. The flows available through that 6" pipe are miniscule compared to a new 6" with a c-factor of 140 or 150. Yet I still have a static pressure on the riser of 50 psi. The point being, as Craig said, we don't know anything about the water supply to that riser by simply reading the static pressure on that gauge. Mark A. Sornsin, P.E. | Karges-Faulconbridge, Inc. | Fire Protection Engineer | Fargo, ND | direct: 701.552.9905 | mobile: 701.371.5759 | http://www.kfiengineers.com -----Original Message----- From: Sprinklerforum [mailto:sprinklerforum-boun...@lists.firesprinkler.org] On Behalf Of Sean Lockyer Sent: Tuesday, October 20, 2015 5:24 PM To: sprinklerforum@lists.firesprinkler.org Subject: Is calcing back to the riser gauge acceptable ? Quick question for everyone here. When the situation prevents one from being able to provide a calculation back to the U.G. connection at the street when can you calculate the system back to the gauge on the riser ? For example, if you have, say, 50 psi city pressure (worst case) on a system at the riser gauge couldn't one calc it to the base of the riser, add in your hose allowance and call it a day as long as your system demand is less than the lowest "day pressure" in the system ? In addition, if there any mention on this in NFPA 13 ? Sean Lockyer Project Designer 4617 Parkbreeze Court Cell 386-279-1197 Orlando, Florida 32808 slock...@aitlifesafety.com Phone: 407-816-9101 www.AITLifeSafety.com Fax: 407-816-9104 _______________________________________________ Sprinklerforum mailing list Sprinklerforum@lists.firesprinkler.org http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please visit http://www.symanteccloud.com ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please visit http://www.symanteccloud.com ______________________________________________________________________ _______________________________________________ Sprinklerforum mailing list Sprinklerforum@lists.firesprinkler.org http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
