Fluidic control system including variable venturi

A variable structure which provides throughout an extended range the characteristics of a Venturi whose differential velocity-pressure output is proportional to the mass-volume of a fluid stream passing therethrough, said structure comprising:

• A a tubular casing into which the fluid stream is admitted;
• B a cylindrical spool supported within the casing for free axial movement therein, said spool having an interior flow passage, said spool defining an exterior flow passage in the annular space between the spool and the casing which exterior passage is always open in the course of said movement whereby the stream admitted into the casing is divided and flows through the interior and exterior passages, said spool having a Venturi-contoured surface lying in at least one of said passages, causing said stream to exert a hydrodynamic force on the spool which acts to displace the spool axially in the downstream direction;
• and
• C means imposing a countervailing force on the spool whereby the extent of spool displacement is the resultant of the hydrodynamic and countervailing forces, said displacement providing a differential velocity-pressure output proportional to the mass volume of the admitted fluid stream throughout an extended range.