Standards
The flow behaviors of the most common obstruction meters, namely the orifice plate, venturi, and flow nozzle, have been studied to such an extent that these meters are used extensively without calibration. Values for the discharge coefficients, flow coefficients, and expansion factors are tabulated and available in standard U.S. and international flow handbooks along with standardized construction, installation, and operation techniques (1, 3, 4, 16). Equations 10.10 and 10.12 are very sensitive to pressure tap location. For steam or gas flows, pressure taps should be oriented on the top or side of the pipe; for liquids, pressure taps should be oriented on the side. We discuss the recommended standard tap locations with each meter (1,4). A nonstandard installation or design requires an in situ calibration.