How do you size a control valve using Cv?

Cv (valve coefficient) relates flow to pressure drop: for liquids, Q = Cv*sqrt(dP/SG). Valve sizing: calculate required Cv at normal, minimum, and maximum flows; select valve with rated Cv allowing adequate travel range (typically 10-90% opening). Check for choked flow (vaporization limiting flow), cavitation, noise, and velocity limits. The installed Cv may differ from rated due to fittings (reducers, piping geometry). Undersized valves cannot achieve required flow; oversized valves give poor control resolution.