You took the words out of my mouth figuratively speaking. Design with a computer, measure with a laser, mark with a paint pen, cut with an axe.
If one is forced to take all their measurements at a single available hydrant, the result may not be 100% accurate, but then a two-hydrant test may not be either. And our industry's "best practices" arguably aren't the best at all. How many people, when requesting or performing a flow test or flow model, specify that the values be measured at peak seasonal and peak day demands? How much fluctuation does a given water system or zone experience in a day/week/month/year? How many of us review those fluctuations and factor them into a flow test once it's taken? We need the flow data as a benchmark for calculations that also have inherent susceptibility to variables we can't control; if you have doubts about the precision of a flow test, you can always reduce it by more than the widely applied 10% factor. How many people out there use a safety factor on a calculation that is based on a fire pump performance curve? If NFPA 20 and 25 both allow for a 5% degradation of a pump's performance, shouldn't we be taking 5-10% off of pumps too? The idea that we have to measure the water supply using exponential factors that have to be expressed in scientific notation is ... overkill. I'm not advocating sloppiness by any means, but if I had to choose between the results of a single hydrant flow test or a model that has been verified to represent peak seasonal and day demands and a two- or three-hydrant test that was taken at some time on some day that was convenient because the traffic was light, I'll go with the substantiated data every time, even if it isn't as "accurate" as more widely accepted good practice. SL -----Original Message----- From: Sprinklerforum [mailto:[email protected]] On Behalf Of Parsley Consulting Sent: Friday, June 20, 2014 8:20 AM To: [email protected] Subject: Re: to Pitot or not to Pitot? Roland, Excellent description of what the intent of -291 describes in section 4.9. As our mutual friend Joe Hankins used to say "Don't measure with a micrometer when you're going to cut with a chainsaw." *Ken Wagoner, SET *Parsley Consulting*** *350 West 9th Avenue, Suite 206 *Escondido, CA 92025-5053 *****Phone 760.745.6181* Visit our website <http://www.parsleyconsulting.com/> *** On 6/20/2014 8:04 AM, Roland Huggins wrote: > NFPA 291 says use a Pitot but IF a pitot is not available then a butt gauge will provide APPROXIMATELY the same results. Unless one broke the bloody thing, if one doesn't have a pitot I suspect they shouldn't be out there. Nonetheless, the velocity pressure in the discharge stream equals 100% of the pressure whereas the gauge pressure is just the normal pressure (that being total pressure minus velocity pressure) prior to the water outlet but it shouldn't be seeing the pressure loss associated with the water going through the outlet. Since the pitot reading is recommended to limit the velocity (not exceeding 30 psi on the pitot), it may not be a lot of difference. Combining this with the exacting precision associated with many pitot readings, it could be the TC felt it was close enough (like using hand grenades). > > Roland > > > Roland Huggins, PE - VP Engineering > American Fire Sprinkler Assn. --- Fire Sprinklers Saves Lives > Dallas, TX > http://www.firesprinkler.org > > > > > > On Jun 20, 2014, at 6:05 AM, Brad Casterline <[email protected]> wrote: > >> Yesterday's flow test thread, along with talk of "because that is the way we >> have always done it" reminded me of something I have been wanting to post >> since last Christmas-- I was 'calculating' flow tests and looking for any >> info that might help and I discovered something that surprised me, that >> being NFPA 13 (2007) A.23.2.1 (2). For the flowing hydrant we can either >> attach a second gage or use a pitot. I have always used a pitot because that >> is the way the person who taught me had always done it. >> >> No question here, just thought I'd throw this out there on a Friday morning. >> >> >> >> thanks, >> >> >> >> Brad Casterline, NICET IV >> >> Fire Protection Division >> >> >> >> FSC, Inc. >> >> P: 913-722-3473 >> >> [email protected] >> >> www.fsc-inc.com >> >> >> >> Engineering Solutions for the Built Environment >> >> >> >> _______________________________________________ >> 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
