Patent attributes
A valve for a plenum or pipe is disclosed. The valve includes a large butterfly valve element pivotally supported in the 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 is coupled to the rod by a shaft. The shaft includes a recess that accommodates the small butterfly valve element but which includes 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 at least one wall of the recess of the shaft. Thus, the combination of the shaft and the small butterfly valve element provide limited flow through the plenum. Further rotation of the shaft, however, results in rotation of the large butterfly valve element to provide greater flow through the plenum.
