Now that I understand the intent of the topic ... Ironically, this underscores something that's somewhat controversial and is a current topic in the NFPA 14 revision cycle, i.e. currency of flow tests and the use of flow models in lieu of open port flow testing. If you're dealing with a water agency that has their system(s) modeled, or uses a third party to run flow models, it can be determined with a very high level of accuracy just how much flow (and at what velocity) a particular leg or main will produce. Craig's point about a single 8" not likely producing 4,000 gpm may be true, but two or three 8" legs of a municipal grid certainly can and that's where extrapolation of flow test results or the use of a model can help a fire official determine whether a particular water supply is capable of delivering the require fire flow to particular parcel.
BTW Mark Sornsin, I've already heard about this from others so if you want to make fun of me anymore the line forms over there. SL -----Original Message----- From: Sprinklerforum [mailto:[email protected]] On Behalf Of [email protected] Sent: Wednesday, May 14, 2014 7:41 AM To: [email protected]; [email protected] Subject: RE: Can a hydrant flow from the pumper connection be used for the hydraulic calculations ? I understand the purpose of the 20 psi value. I have seen 20 psi values that in no way would flow. 4000 gpm+ though an 8" water main, or a flow value not achievable by the municipal water supply. My point is there is a danger in posting non-verified values in a flow report. If you want to know what's available at 20 psi then flow the system until it bottoms out at 20 psi then you have factual data. Otherwise when it's needed most that fictional 4000 gpm may only actually be half or less. In the midst of a fire fight, is not the time to find out reality and extrapolation are not the same. Now I realize that most project do not require large flow rates, so it's typically not a big deal. In the industrial world, it's a big deal. We had a large project, water department did a flow test on a single hydrant butt with less than 1000 gpm flowing, extrapolated the curve out and modeled the water supply to the site which indicated we would have sufficient flow and pressures for our system. When the final pump test was performed the flow rate was not there, not even close, the water department had assured the owner of a "robust" water supply. In actuality, they had "a lot of water" but their modeling was flawed and their test inconclusive due to extrapolation and not actual verification. The owner had to add an above ground suction tank which delayed occupancy of the facility. Facts are facts and extrapolations are nothing but a good guess in many cases. Craig L. Prahl, CET Fire Protection Group Lead CH2MHILL Lockwood Greene 1500 International Drive Spartanburg, SC 29303 Direct - 864.599.4102 Fax - 864.599.8439 CH2MHILL Extension 74102 [email protected] _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
