Operate smart Fix stuff Thanks for your time, any questions e mail me at ... 2 to 4 times cost of starter Why? Moving water slower reduces friction . Why VFD's? Throttling Stinks . Head (feet) 1,800 RPM curve System curve Flow (gpm) 1,200 RPM curve 0 500 1,000 1,500 2,000 2,500. 250 200 150 100 50 0 90 hp 70 hp . throttling valve VFD: 36 hp 1,125 gpm 2,250 gpm System curve: throttled . Pump ...