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 semi-conductor and other industries. When filling customer tanks without a sonic choke, gas feed rates vary constantly as ΔP 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.
Rocket Engines, Chemical Lasers, and Super-Conductors
Fox Sonic Chokes have been used in these three applications for decades. Aerospace – Chokes are typically used to control hydrogen and oxygen, the fuel and oxidizer, in test-stand rocket engine firings as well as flight hardware. Pressure ratings are frequently 4000 psig or higher. Chemical Lasers similarly require precise flow control of very high pressure gasses. Superconductivity research often requires controlling helium or hydrogen gas flow rates at below -300° F, which is quite simple for chokes.
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.