For gas measurements with an orifice plate, what additional factor must be considered?

• A. Expansion factor Y and appropriate coefficients
• B. Only temperature
• C. Viscosity is irrelevant
• D. No additional factors

Answer: (A)

Gas flow through an orifice plate changes with pressure because the gas expands as it passes the restriction. That expansibility means the simple pressure drop isn’t enough to determine the flow rate accurately. An expansion factor Y corrects the measured ΔP for this compressibility effect, bringing the differential pressure into a form that truly reflects the mass flow. In real practice you also use the appropriate coefficients, such as the discharge coefficient and geometry-related factors that account for non-ideal flow and installation conditions. Together, Y and these coefficients translate the pressure drop into an accurate flow rate. Temperature affects density and can influence these terms, but on its own it doesn’t provide a correct measure without the expansion correction and coefficients.