Figure 77 Compressible Flow Equations


There are a number of different equations that can be used to calculate flow rate and pressure loss in a compressible gas system and the type of design and user preference often determines which equation is used to calculate the results.

The Pipe Flow Wizard software allows for the selection of a specific compressible isothermal flow equation from a list that includes:

  • General Fundamental Isothermal Flow Equation
  • Complete Isothermal Flow Equation
  • AGA Isothermal Flow Equation
  • Weymouth Isothermal Flow Equation
  • Panhandle A Isothermal Flow Equation
  • Panhandle B Isothermal Flow Equation
  • IGT Isothermal Flow Equation


The General Fundamental Isothermal Flow Equation (sometimes known as just the General Flow equation or the Fundamental Flow equation) provides perhaps the most universal method for calculating isothermal flow rates, however it relies on the inclusion of an accurate friction factor. The Pipe Flow Wizard software provides such a friction factor by calculating this using the Colebrook-White equation.

The preferred method of calculation can be selected from by tapping the Options button on the calculation panel.