Per Roland’s comment, I always tried to get new people to use ‘background’ or ‘normal consumption’ flow.
And to kill mythology that around 0700 or 1800-2000 being highest normal flows. Highest background flow, by far, was 0100-0300, May-September. Commercial landscape irrigation is biggest flows, at least in Puget Sound. Best. Bruce Verhei > On Jan 2, 2019, at 16:30, Roland Huggins <[email protected]> wrote: > > Occasionally one does get a much higher residual pressure in the flatlands > but that's due to additional pumps coming on line as flagged by Cecil. > > The methodology identified by NFPA is for a very simple system and has not > yet evolved to address the part of the world where simple does not apply. > > I believe the discharge Pv (as read by your pitot gauge) is the same as the > Pn as read at the other outlet minus losses imposed by squirting water > through an orifice. > > The Pn is acting on the walls of the pipe (as well as the orifice of the > sprinkler or hydrant) which is perpendicular to the flow of the water (so > that doesn’t belong in your definition of Pv). Think of Pv as the energy > tied up by the actual movement of the water. The energy tied in by the > direction of flow can not push water out through an orifice attached to the > wall of the pipe. > > One last thought, except for tanks feeding ONLY your system, static does not > mean ZERO flow. Your static reading is actual a residual reading that > reflects the OTHER demands on the system. Your residential reading is just > the additional demand YOU put on the system. > > Roland > > > Roland Huggins, PE - Senior VP Engineering > American Fire Sprinkler Assn. > Dallas, TX > http://www.firesprinkler.org > > Fire Sprinklers Saves Lives > > > > >> On Jan 2, 2019, at 11:19 AM, Skyler Bilbo <[email protected]> wrote: >> >> Steve, >> >> This was actually very helpful. I was thinking of it wrong. Our pitots >> measure velocity pressure. The gauge on the test hydrant is measuring >> normal pressure inside of the pipe, or hydrant. I think I have it sorted, >> but feel free to correct me. A better explanation is below. >> >> -The normal pressure is the pressure acting on the walls of the pipe, and is >> what is typically measured with our regular gauges. >> -The velocity pressure is the pressure acting on anything that is >> perpendicular to the direction of flow, like one of our pitot gauges (it >> would be the pressure you would feel pushing you if you tried to stand in >> front of a flowing hydrant) >> -The total pressure is both of these things combined. >> >> Velocity pressure goes up as you increase the velocity of the water, which >> can be accomplished by going from a large pipe to a small one (like going >> from an 8" water main to a 2-1/2" connection on a fire hydrant; 1,000 GPM in >> an 8" main travels at about 5.96 ft/sec, which equals a velocity pressure >> of 0.24 psi; 1000 GPM comes out of a 2-1/2" hydrant at about 65 ft/sec >> *that's why it shoots out so far* with a velocity pressure of about 28.8 >> psi, which is a pitot pressure of about 35.5 psi, if the opening coefficient >> is 0.9). This velocity pressure is dependent on the velocity of the water. >> >> I was wrong in my original thinking. Hopefully my explanation is useful to >> others. >> >> I don't think the pitot reading should/could ever be larger than the static >> pressure, however (assuming elevation is the same, no additional water >> supplies kick on, and no negative gauge pressure possible), due to >> conservation of energy. The static pressure is the total pressure when no >> water is flowing, and no matter how much water is flowing after that, no >> combination of velocity pressure or normal pressure could ever exceed this >> total pressure. >> >> >> Thanks guys, >> Skyler Bilbo >> >> >>> On Wed, Jan 2, 2019 at 11:33 AM Steve Leyton <[email protected]> >>> wrote: >>> Pitot measures velocity pressure, residual is atmospheric pressure. >>> There’s not a fixed correlation between the two values – I’m guessing that >>> the main supplying the test hydrants is a very large diameter one? >>> >>> >>> >>> Steve Leyton >>> >>> >>> >>> >>> >> _______________________________________________ >> 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
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