We produce flow/pressure curves. Then we select a point on that curve. Once we’ve selected a design flow point, does the rest of the curve matter. I wouldn’t adjust the curve at all.
Best. Bruce > On Aug 8, 2018, at 15:47, Mark Sornsin [FAR] <[email protected]> wrote: > > It’s clear there are many ways to do it and thus it depends on who’s calling > for it. > > IMHO, if there is an engineer of record specifying this, then they should do > the work themselves. I.e.: > 1. evaluate the water supply (like conduct and/or observe the actual > test) > 2. Investigate the source – is it a pumped supply or gravity only, or > whatever > 3. Identify normal low pressures. E.g. many small towns up north > reduce their tower elevations in winter to reduce freeze potential. That > reduced static pressure should be used regardless of the result of a summer > flow test. > 4. Identify situations unique to that location – such as a nearby user > that has regular high demand flows that significantly reduce the water supply > available at your site. > > So you might have a summer test of 60psi static flowing 1,500 gpm at 40 psi. > But after investigating the above, you learn the static pressure drops 10 > psi every winter. So the adjusted flow test would be 50/1500/30. A line > parallel and below the summer test because that’s how the test would look if > conducted in the winter. The slope of the line is unique to the piping > arrangement up to the point of the flow test. This is why I don’t necessarily > agree with applying a 10% reduction that creates a non-parallel line – > because it effectively alters the characteristic curve of the water supply at > that location. On the other hand, it’s just a means of creating a safety > factor so who really cares. > > If the water supply utilizes multiple flowing pumps, then it gets more > complicated since you need to consider altering flow and pressure. > > If an engineer or AHJ wants some additional safety factor, then require a > cushion of a given pressure or percentage of the demand pressure and the > demand flow. But if you’ve done your homework and have identifies the a > reasonable ‘lowest pressure’, then you may not need to apply much safety > factor. > > It’s all personal preference of the engineer/AHJ, but given the opportunity, > I do it my way…. > > -Mark > > > <image9c32d3.JPG> Mark Sornsin > Sr. Fire Protection Engineer > Direct: 701-499-1391 > Cell: 701-526-8585 > From: Sprinklerforum [mailto:[email protected]] > On Behalf Of MFP Design, LLC > Sent: Wednesday, August 08, 2018 4:04 PM > To: [email protected] > Subject: Flow Test Reductions > > Lets assume a flow test of 100 static, 80 residual, 1500 gpm flow. You are > required to reduce it by 10%. Is the reduced flow test 90 / 70 / 1500 or > 90/72/1500? > > I’ve always done it the first way because that keeps parallel lines. > However, I’ve run into more than a few people doing it the 2nd way lately. > Doing that has differing slopes and the lines would intersect. The > theoretical reduction could actually have a higher pressure at a given flow > with #2 since it is a flatter curve. > > <image002.jpg> > Travis Mack, SET > MFP Design, LLC > 3356 E Vallejo Ct > Gilbert, AZ 85298 > 480-505-9271 > fax: 866-430-6107 > email:[email protected] > > http://www.mfpdesign.com > https://www.facebook.com/pages/MFP-Design-LLC/92218417692 > Send large files to us via: https://www.hightail.com/u/MFPDesign > LinkedIn: https://www.linkedin.com/in/travismack > > “The bitterness of poor quality remains long after the sweetness of low price > is forgotten.” > > > ______________________________________________________________________ > This email has been scanned by the Symantec Email Security.cloud service. > For more information please visit http://www.symanteccloud.com > ______________________________________________________________________ > _______________________________________________ > 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
