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Data for Calculation of Flow The coefficient of flow Cv expresses the rate of flow in gallons per minute at 60°F water with a pressure drop of 1 psig across the valve.The Cv coefficients for the various types and sizes shown in the tables, have been determined from actual flow tests. Note: Kv is the metric equivalent of Cv. KV = CV x 0.85 For Liquids: Where QL = Flow in U.S. gallons per minute. Δ P = (P1–P2) Pressure drop in psi. GL = Specific gravity of liquid (water = 1 at 60°F). For Gases: Where Qg = Volumetric flow of gas (SCFH). Gg = Specific gravity of gas at standard conditions. (air at atmosphere and 60°F = 1) T = Absolute temperature of gas (°F + 460). Note: For gas, max. ΔP = 1⁄2 P1, and min. P2 = 1⁄2 P1, and P1, P2 are absolute pressures (psia) |