# Calculation Methods - Gas Regulator

FluidFlow includes two flow equations for modelling regulators in compressible flow systems. The methods which users can choose from are the Standardized Method (ISA-75.01.01 2007) and the Traditional Method (Universal Equation). Standardized Method - ISA-75.01.01 2007 Equation. Cv = w / N6 Y (x P1 ρ 1)0.5. where: w is the mass flow rate. ρ 1 is the specific gravity of the gas (ratio of density of flowing gas to density of air with both at STP conditions). N6 is the numerical constant used to convert units in the equation. The value of N6 is automatically determined by FluidFlow. Cv is the regulator flow coefficient as defined in the database. Y is the gas expansion factor. P1 is the regulator valve inlet absolute static pressure (kPa a). x is the ratio of the static pressure differential to the absolute static pressure (ΔP/p1) at the regulator inlet (kPa). Traditional Method - Universal Equation. Qlb/hr = 1.06 (d1 P1)0.5 Cg SIN (3417 / C1) (ΔP / P1)0.5 Deg. where: Qlb/hr is the gas flow rate (lb/hr). d1 is the gas density of the gas or vapor at the regulator inlet (lb/ft3). Cg is the gas sizing coefficient. ΔP is the static pressure loss across the valve (psi). P1 is the regulator valve inlet absolute static pressure (psi a). C1 is equal to Cg/Cv. Note, the above equation is also known as "the density form of the Universal Gas Sizing Equation". This equation is used to predict flow for perfect or non-perfect gas sizing applications, for any vapor including steam, at any service condition when fluid density is known. The Standardized Method is accepted worldwide for its level of accuracy.