Coefficient of velocity Cy 1.00 200" X 100" 0.95 0.90 0.85 4" X 2" 0.80 103 10 105 10 107 Vzd Reynolds number H Figure 9.25 Coefficient of velocity C, as a function of Reynolds number for venturi meters having a diameter ratio Did = 2. number at the throat (R, = pVd/u) in Fig. 9.25. These data indicate that Cy ranges from 0.97 to 0.99 over a wide range of sizes and Reynolds numbers. Experimental evidence at other diameter ratios indicates that Cy decreases with increasing diameter ratios.