The pressure drop term represents the driving force for flow through the orifice, normalized by the gas specific gravity. This accounts for the fact that lighter gases will flow faster for the same pressure drop.

\begin{equation}\label{eq:flow-calculations-pressure-drop} \Delta P_{norm} = \sqrt{\frac{\Delta P_{orifice}}{SG}}\end{equation}

Symbols

\(\Delta P_{norm}\)	Normalized pressure drop \([\unit{ \inchWaterColumn}]\)
\(\Delta P_{orifice}\)	Orifice pressure drop \([\unit{ \inchWaterColumn}]\)
\(SG\)	Gas specific gravity (relative to air) \([\unit{ \unitless}]\)