scope:

This section of Part 2 covers equations suitable for use in sizing industrial-process control valves when the flowing media are compressible fluids. At very low ratios of pressure differential to absolute inlet pressure (Δ p/p₁), compressible fluids behave similarly to incompressible fluids. Under such conditions the sizing equations presented in this section can be traced to the basic Bernoulli equation for Newtonian incompressible fluids. However, increasing values of Δ p/p₁ result in compressibility effects which require that the basic equations be modified by appropriate correction factors. The equations presented are for use with gas or vapour and are not intended for use with multiphase streams as gas-liquid, vapour-liquid or gas-solid mixtures.