Two 32-inch pumps from the figure shown below are to be used in series at 1170 rpm to lift water through 500 ft of vertical cast-iron pipe. What should the pipe diameter be for most efficient operation? Neglect minor losses. For water at 20C, take p = 1.94 slug/ft and = 2.09E-5 slug/fts. For cast iron, & 0.00085 ft. Take = 22/7. Total head, ft n = 1170 r/min 800 700 36-in dia. 600 500 32-in dia. 400 28-in dia. 300 65% 72% 78% 82% NPSH 85%. 87% 88% 87% 1500 bhp 200 0 4 8 12 16 20 3500 bhp 3000 bhp 2500 bhp 2000 bhp 24 24 28 U.S. gallons per minute x 1000 50 40 30 20 NPSH, ft From the given figure, read H* 385 ft at Q* 20,000 gal/min. Equate: H = 2 H* = Hsyst Az+f = L V2 d 2g Iterate, guessing f 0.02 to get d, then get Red and /d and repeat. The final result is: f0.0185; V 45.8 ft/s; Red = 4.72E6