Controlling Conveying Air Flow Rate in Dense Phase Pneumatic Transport Systems Fox sonic chokes have been incorporated into hundreds of dense phase pneumatic conveying systems. In these systems, it is essential that air flow rates are both controlled accurately and remain fixed and stable, even if downstream pressures due to changing product or flow rates (sugar, sand, coal, etc.) vary. The sonic choke must, therefore, maintain uniform air feed rates, and hence uniform, controlled transport velocities, that are unaffected by any changes in product rates or characteristics. Ultra-High Purity Gas Systems Traditional flow meters used by the industrial gas industry would contaminate the ultra high purity gasses needed by the semiconductor and other industries. When filling customer tanks without a sonic choke, gas feed rate vary constantly as P varies. With a sonic choke, which are easily provided in ultra-high purity configurations, flow rates are easily controlled and the lack of moving parts eliminates the chance of contamination.

Calibration Standard
Because sonic chokes are so simple, they have been preferred for years as a reference standard. One calibrated choke can be used as a reference to which other, less reliable flowmeters can be checked.

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