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St. Francis Swimming Pool Main Drain Velocity <br />CSPHK 7.5 hp 325gpm @ 60' TDH <br />2 Hayward 12" x 12" main drains @ 78 sq. in. open area <br />Step 1 Calculate CFS <br />Step 2 <br />Gpm /7.48 gal/cu.ft. =cu. ft. / min 60sec/min =cfs <br />325 7.48 43.45 60 0.72 <br />Convert sq. in. to sq. ft. <br />Sq. In. /144 sq. in./sq.ft. =sq.ft. <br />156 144 1.08 <br />Calculate velocity in feet per second <br />Step 3 c s sq. ft. <br />0.72 1.08 <br />fps <br />0.67 <br />*standard grates 2' per second is maximum <br />"*antivortex 6' per second is maximum