Effects of upstream bends and valves on oriffice plate pressure distributions and discharge coefficients

An extensive series of tests has been carried out to determine the effect of upstream fittings (bends, valves, bend-bend and bend-valve combinations) on the discharge coefficients of orifice plates. The pressure data acquired during these tests have been studied in detail and a number of general recommendations for reducing the errors associated with using orifice plates in disturbed flow conditions are presented in this paper. It is noteworthy that other tapping combinations in place of the standard D and D/2, flange and corner combinations were less sensitive to disturbances in the flow so that their use could result in smaller errors. Of more direct practical use, as the internationally standardized tapping arrangements are unlikely to be changed, it was established that the use of a further pressure measurement would allow the change in the discharge coefficient for corner and flange taps to be estimated with reasonable accuracy for most adverse flow conditions