Variable orifice using an iris shutter

A variable orifice forming mechanism for controlling flow of medium therethrough comprising:

• a mounting ring defining a central orifice and consisting of an inner section, an intermediate section, and an outer section, a plurality of curved members pivotally mounted on said mounting ring, said inner section of said mounting ring having a plurality of spaced holes therein, said curved members each having an extending pivot pin located at one end thereof positioned in one of said holes, said intermediate section of said mounting ring having a thickness greater than said inner section and having a countersink therein, and said outer section of said mounting ring having a thickness greater than said intermediate section and being provided with means by which said mechanism is adapted to be secured to an associated system through which medium to be controlled flows, a drive ring having a plurality of grooves therein, said drive ring being positioned on said inner section of said mounting ring, said curved members having pins extending therefrom and movably secured in said grooves of said drive ring, and drive means mounted in said countersink of said intermediate section of said mounting ring for moving said drive ring with respect to said mounting ring thereby moving said curved members such that said orifice in said mounting ring is effectively changed in diameter.