Dual Butterfly Control Valve and Method of Use

A valve for controlling flow to a exhaust gas recycling system of an engine, the valve comprising:

• a large butterfly valve element pivotally supported in plenum by at least one rod, the large butterfly valve element includes an opening for accommodating a small butterfly valve element;
• the small butterfly valve element being coupled to the rod by a shaft, the shaft includes a recess that accommodates the small butterfly valve element, the recess of the shaft being disposed between two opposing walls, each wall providing a clearance between the small butterfly valve element and the shaft to permit limited rotation of the shaft before the small butterfly valve element engages the walls of the recess of the shaft to thereby move the small butterfly valve element towards an open position;
• the large butterfly valve element being coupled to a spring for biasing the large butterfly valve element towards a closed position;
• the shaft element being coupled to an actuator for moving the small butterfly valve element between open and closed positions;
• wherein, after the small butterfly valve element engages one wall of the recess of the shaft, further rotation of the small butterfly valve element results in rotation of the large butterfly valve element towards an open position.

A method for controlling fluid flow through a plenum, the method comprising:

• installing a valve in the plenum, the valve including a large butterfly valve element pivotally supported in the plenum by at least one rod, the large butterfly valve element including an opening for accommodating a small butterfly valve element, the small butterfly valve element coupled to the rod by a shaft, the shaft includes a recess that accommodates the small butterfly valve element, the recess of the shaft being disposed between two opposing walls, each wall providing a clearance between the small butterfly valve element and the shaft to permit limited rotation of the shaft before the small butterfly valve element engages the walls of the recess of the shaft to thereby move the small butterfly valve element towards an open position, the small butterfly valve element coupled to an actuator for moving the small butterfly valve element between closed and open positions, the large butterfly valve element being coupled to a spring for biasing the large butterfly valve element towards a closed position;
• moving the shaft to engage at least one wall of the recess of the shaft with the small butterfly valve to provide limited flow through the plenum;
• continuing to rotate the small butterfly valve element resulting in rotation of the large butterfly valve element towards an open position to provide greater flow through the plenum.