# Calculation Methods - Thin Orifice

See ISO 5167 for detailed information. The total pressure loss is: ΔP = Pressure Loss at the corner tap points multiplied by [(1 - β 4)0.5 - C1 β 2] / [(1 - β 4)0.5 + C1 β 2]. where: β is the orifice diameter "beta" ratio (β = d/D where "d" is the orifice bore diameter and "D" is the internal pipe diameter). As a reference guide, a beta ratio of 0.45 indicates that the orifice bore diameter is 45% of the pipe inside diameter. Guidelines on design beta ratios are available in ISO 5167 & Perry's Chemical Engineering Handbook. Published literature makes reference to keeping the design beta ratio to within the range of 0.15 to 0.68 to develop the best performance from the orifice plate. If a thin orifice plate is solved in FluidFlow and the calculated beta ratio is outside of this range, a warning message is enunciated to prompt the designer into reviewing the design conditions. Beta ratios outside of this range are noted to introduce flow system errors and other potential flow problems. When sizing orifice plates, ensure the right pressure drop range, maximum flow and optimum beta ratio for best performance of the orifice plate. Note, beta ratio and pressure drop for an orifice plate are related and as such, altering one affects the other. C1 is the orifice plate discharge coefficient derived from equation 5.3.2.1 in ISO 5167.