The effects of upstream recesses on the discharge coefficient of flange tapped Senior? orifice fittings were investigated experimentally. The study was conducted in a 100 mm (4 inch) line and a 200mm (8inch) line using water as the working fluid. Calibrations were performed against a bi-directional volumetric ball prover. In the 100mm (4inch) line, the recess location was 200 mm (8 inches) upstream of the upstream face of the orifice plate and the depth and width of the recess was 9.2 mm (0.362 inches) and 4.77 mm (0.188 inches), respectively, that correspond in size and location to the recess formed by the union of a Ring Type Joint (RTJ) flanged Senior? orifice fitting with the upstream meter tube. Three plates with β ratios of 0.2, 0.4 and 0.67 were calibrated. In the 200 mm (8 inch) line the recess location was 232 mm (9.125 inches) upstream of the upstream face of the orifice plate, the depth of the recess was 18.5 mm (0.73 inches) and the recess widths were 4.37 mm (0.172 inches) and 6.17mm (0.243 inches) which correspond in size and location to the recess formed by the union of a RTJ flanged Senior? orifice fitting and the upstream meter tube. Within the precision of the calibration system, the test result indicated that the effect of the recess on the flow rate measurement was negligible for both the meter sizes and all the different beta ratio plates used in this experimental investigation.
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