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Title: Measurement Accuracy Of 1/4 (6.35 mm) Thick Orifice Plate Installed In An 8 (200 mm) Orifice Fitting Designed For 1/8 (3.175 mm) Thick Plate.
Author: Zaki D. Husain, John B. Roussel, Franklin D. Goodson
Source: 1999 International Symposium on Fluid Flow Measurement
Year Published: 1999
Abstract: In the current Standards 1, 2, the recommended orifice plate thickness for an 8 (200 mm) orifice flow meter is 1/8 inch (3.175 mm). A 1/8 thick orifice plate installed in an 8 fitting has a maximum allowable differential pressure limit of 150 inches of water column (37.3 kPa), which limits the maximum flow rate through the meter. The plate clearance, in a commercially available 8 orifice fitting designed for 1/8 thick plates, is adequate for installation of 1/4 (6.35 mm) thick plates with a special seal. Mechanical tolerances specified in the standard do allow installation of 1/4 thick orifice plates in an 8 orifice fitting designed for 1/8 thick plates, provided the beta ratio is less than 0.64. This experimental study was to evaluate the measurement accuracy of a 1/4 thick orifice plate installed in an 8 fitting designed for 1/8 thick orifice plates. Based on the data presented here, a 1/4 thick plate with beta ratios between 0.2 and 0.6 can be installed in an 8 fitting designed for a 1/8 thick plate and precise flow rate measurement is achieved without any modification to calculation method and/or secondary instrumentation. For the same beta ratio, a 1/4 thick orifice plate can be subjected to a higher differential pressure than a 1/8 thick plate. Hence increased flow rates through the meter can be achieved by using a 1/4 orifice plate in existing 8 orifice fittings designed for 1/8 thick plates.