I would take a close look at the reports that your program is generating to make sure that everything looks reasonable. With a reputable program, the most common errors are input errors (one pipe can accidentally get set to an odd size) - although I sometimes see a device or pipe section 'turned off'.
It sounds like you are only talking about a 10% ish difference in flow, so that sounds pretty reasonable. One design could easily flow 10% more than another. Try this - look at the sections of pipe that are carrying the total flow. Then check the pressure loss per foot and see what the difference is. For example: if you are using 4" main it would take about 350' of main to account for this pressure change (1168 gpm in 4" = .367 psi/ft; 1027 = .289psi/ft). The difference is .08 psi/ft. over 350' - that adds up to 27psi. Smaller pipe will add up even faster. That is a pretty rough way to figure it, but it will let you know if you are in the right ballpark. [numbers above include generous rounding] Matt From: Sprinklerforum [mailto:[email protected]] On Behalf Of Brian Harris Sent: Tuesday, January 30, 2018 7:25 AM To: [email protected] Subject: Is this remotely possible ?? I have a calculation for a dry system that is currently -2.945 psi (-19.8%) over the curve. My most demanding head is one of (2) heads on a 1" arm-over, if I change the section of pipe (7'-6" long) that feeds this head to 1-1/4" my calc changes to +24.168 psi (136.8%) under the curve. Seems fishy to me, thoughts? Brian Harris, CET BVS Systems Inc. Design Manager bvssystemsinc.com<http://bvssystemsinc.com/> Phone: 704.896.9989 Fax: 704.896.1935
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