The accuracy of differential pressure flowmeters can be strongly affected by gas flow rates obtained from a pulsating source. This work discusses the error sources present when air flows through an orifice flowmeter which is installed downstream of a positive displacement rotary compressor in a gas-processing plant. Air velocity profiles were used successfully to identify the error sources, which indicate pulsation interference in a specific frequency band. This came in addition to an acoustic resonance caused by an installed pressure regulator in the flow system.

In order to improve the system the installation of the following devices were suggested:

  • a diffuser downstream of the orifice plate

  • an inline silencer to control valve noise

  • a pulsation damper to damp pulsation wavelengths of 7.83 and 7.33 m (23.86-23.34 ft) corresponding to frequencies of 38.67 and 41.33 Hz respectively.

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