IEC 60534-2-1:2011 includes equations for predicting the flow of compressible and incompressible fluids through control valves. The equations for incompressible flow are based on standard hydrodynamic equations for Newtonian incompressible fluids. They are not intended for use when non-Newtonian fluids, fluid mixtures, slurries or liquid-solid conveyance systems are encountered. The equations for incompressible flow may be used with caution for non-vaporizing multi-component liquid mixtures. This second edition cancels and replaces the first edition published in 1998. This edition constitutes a technical revision. It includes the following significant technical changes with respect to the previous edition: - the same fundamental flow model, but changes the equation framework to simplify the use of the standard by introducing the notion of Δpsizing; - changes to the non-turbulent flow corrections and means of computing results; - multi-stage sizing as an Annex.