Key equations for Process Engineers Process Control Process Design

Guidelines for control valve sizing calculation

Information required for sizing control valve is as follows

  • Inlet pressure all possible cases
  • Outlet pressure (or pressure drop) all possible cases
  • Inlet temperature all possible cases
  • Mass Flowrate all possible cases
  • Solids content and size
  • Critical temperature and critical pressure
  • Allowable shutoff differential pressure
  • For liquid service
    • Vapor pressure
    • Density
    • Viscosity
    • Surface tension
  • For gas service
    • Molecular weight
    • Compressibility factor at the inlet and outlet conditions
    • Cp/Cv ratio
    • Dew point temperature
  • Multiphase service
Gas Properties Liquid Properties
Molecular weight Vapor pressure
Compressibility factor at the inlet and outlet conditions Density
Cp/Cv ratio Viscosity
Dew point temperature Surface tension


  • Expected valve characteristics
  • Design pressure or pressure rating of connecting system
  • Deign Temperature
  • Body size (connecting flange rating)
  • Allowable noise level
  • Actuator/Air/gas fail status


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