Remember, all of our formulas are approximations. They can be more accurate in some situations and less in others. The velocity restrictions of years back were originally to compensate for the inaccuracies in the formula when velocity exceeded a certain amount.
Todd G Williams, PE Fire Protection Design/Consulting Stonington, CT www.fpdc.com 860-535-2080 (ofc) > On Jun 25, 2014, at 8:31 PM, Brad Casterline <[email protected]> wrote: > > I tried that Ron and it blew up in my face! Q=500, C=120, d=8. > If the section you referenced is the H-W friction loss formula, the Pf/ft > difference with Q^2 instead of Q^1.85 might blow your mind. Then I made C^2, > and it was closer, but only it came out about half the 'as is' result. > I would not change it. I think Hazen and Williams stirred a dash of theory > into a ton of water flow measurements using different pipe types, picked a > nice 'room temperature' for viscosity, factored gravity out, used gallons and > minutes instead of feet and seconds and decided on a nice range of turbulent > (sprinkler) flows that matched the curves close enough for sprinkler work. > Friction Head IS proportional to the velocity squared (turbulent flow, to the > velocity for laminar, and to velocity cubed for speeds past the speed of > sound). > I just took a quick and dirty look though so I might get different results at > the office tomorrow, and I hope Rae gets a lot of replys. > > BC > >> On Jun 25, 2014, at 5:57 PM, <[email protected]> wrote: >> >> In the friction loss formula found in 13-23.4.2.1.1 (13 Ed) I would use Q >> squared rather than Q to 1.85. >> Ron F >> >> -----Original Message----- >> From: Sprinklerforum [mailto:[email protected]] >> On Behalf Of Rahe Loftin - 7PMC >> Sent: Wednesday, June 25, 2014 3:50 PM >> To: SprinklerFORUM >> Subject: Underground Piping >> >> In the Hydraulics chapter of the 3rd edition of the SFPE Handbook, the >> following verbiage occurs “It has been noted, however, that in rough pipes >> head loss varies with flow (and velocity) to the power of 2 rather than the >> power of 1.85 characteristic of smooth pipes.” >> >> >> The question is, shouldn't we use a water supply testing graph based on an >> exponent of 2 instead of 1.85 since we do not know the condition of the >> underground pipe? >> >> Rahe Loftin >> _______________________________________________ >> 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 _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
