Douglas, #1 and #2 are 94% legit. #3 is 90% legit. I never could 'see' the formula "twenty-nine point something times this to the that..." but I will never forget: ft/sec x ft x ft = ft x ft x ft/sec. This is Q=vA, or vA=Q. v is velocity. Q is easy; GPM/7.48/60=ft3/sec. A is the area of the orifice. The area of a circle is PI*r^2. Dividing the I.D. by 24 gives the radius in feet, squared, times PI is the area in ft2. Older editions of 13 show a coefficient of discharge for a nominal 1/2" head = .75. This is due ALMOST entirely to the fact that the I.D. is not 1/2". Even a "K=8.0 large orifice" head, at 17/32" is only 1/16 inch bigger than a so-called 1/2" head. The coefficient of discharge is the measured/theoretical. The most abstract part is getting the velocity from the PSI, but if you will pardon my craziness, Question-- Why does a big box of water and a small box of water fall side by side when dropped from the same height at the same time? Answer-- Because they both hit the ground going the same speed and direction, so they have to stay together. The speed depends only on the height they are dropped from, and the direction is toward the center of the Earth. It is this velocity we are looking for, and it is independent of the 'amount of water'. The formula is v=SQRT(2gh). g=32.2 ft/sec/sec. h=PSI/.433. I can relate to the foggy images you are dealing with. I guarantee if you take the time using feet and seconds and using gravity 'straight up' ;), the fog will lift for you too.
good luck, Brad ps-- I used coefficient of discharge of .97 for the 1.5", 2", and 2.25" nozzles, and assumed the pressures were pitot gage readings, so an overall legitimacy of 93% is really not too shabby! -----Original Message----- From: Douglas Hicks [mailto:[email protected]] Sent: Sunday, June 23, 2013 3:23 PM To: [email protected] Subject: Forward flow test results We a forward flow at a church last week. When we did the main drain flow test we got 30 PSI. We tested through a single snoot FDC, with the FDC check valve turned around, the clapper valve was not removed. #1 forward flow test with 1.5 nozzle. We got 24 PSI, 337 GPM #2 forward flow test with 2 nozzle, 16 PSI and 493 GPM # 3 forward flow test with 2.25 nozzle, 12 PSI and 536 GPM The above results were with a straight fixed nozzle The hydraulic name plate Design Density .10 GPM Area of operation 917 Sq Ft (the sprinkler protects the basement, which houses a day care, 2 bathrooms, janitor closet, mechanical room, elevator room, and a hallway. System demand at bottom of riser 242.8 GPM at 59.95 PSI Water supply flow test, 84 PSI static, 70 PSI residual flowing 981 GPM The water flow comes through the wall, 6 inches off the floor, makes a 90°, up through the backflow device, through the 2.5 inch alarm check valve, 3 more 90° to the single snoot FDC. Then through the wall and our flow tester. The water was clean after 1 minute. We did not do a comparison with a certified gauge, nor did we replace the gauges on the wet pipe. The chart is supplied with the flow tester. Do these results look legitimate? A larger nozzle = more GPM and less PSI? _______________________________________________ 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
