Adjustable duct for a combine harvester cleaning fan

1. A cleaning system for a combine harvester comprising:

a fan;

at least one duct having an interior passageway that is positioned to receive an air stream from the fan; and

a resiliently deformable surface defined within the interior passageway of the at least one duct that is resiliently deformable to a position that restricts a volume and increases a pressure of the flow of air passing through the at least one duct;

moving means for resiliently deforming the resiliently deformable surface in order to alter the volume of the flow of air passing through the at least one duct,

wherein the resiliently deformable surface is configured to (i) elastically move from an initial state to a deformed state in response to a pressure applied onto the resiliently deformable surface by the moving means and (ii) elastically return to the initial state in the absence of the pressure.

2. The cleaning system of claim 1 , wherein the fan is positioned within a fan housing and the at least one duct either forms part of the fan housing or is fluidly connected to the fan housing.

3. The cleaning system of claim 2 , wherein a second duct is fluidly connected to the fan housing for receiving the air stream from the fan.

4. The cleaning system of claim 3 further comprising a second resiliently deformable surface defined within an interior passageway of the second duct that is configured to restrict a volume and increase a pressure of the flow of air passing through the second duct.

5. The cleaning system of claim 1 , wherein the resiliently deformable surface has an hour-glass shape as viewed in cross-section.

6. The cleaning system of claim 1 , wherein the resiliently deformable surface is positioned on one side of the duct, and a second surface is positioned on an opposite side of the duct facing said surface, wherein a profile of said surface differs from a profile of said second surface.

7. The cleaning system of claim 1 , wherein the moving means comprises a rotatable cam positioned adjacent said resiliently deformable surface.

8. The cleaning system of claim 1 , wherein the moving means comprises an actuator for moving the resiliently deformable surface.

9. The cleaning system of claim 1 , wherein the resiliently deformable surface comprises a balloon, or a balloon is positioned adjacent said resiliently deformable surface, and the moving means comprises a pump for inflating or deflating the balloon.

10. The cleaning system of claim 1 further comprising one or more grain sieves positioned downstream of the at least of duct.

11. The cleaning system of claim 1 further comprising:

a first grain sieve positioned downstream of the at least one duct;

a second duct fluidly connected to the fan housing for receiving the air stream from the fan; and

a second grain sieve positioned downstream of the second duct.

12. The cleaning system of claim 1 , wherein the resiliently deformable surface comprises a first wall and a second wall, the first wall being positioned above the second wall in an overlapping fashion.

13. The cleaning system of claim 12 said moving means positioned adjacent the second wall for causing the first and second walls to deform.

14. The cleaning system of claim 13 wherein the first wall is biased to resist movement of the moving means.

15. The cleaning system of claim 12 , wherein each wall includes a first end that is fixed and stationary relative to the duct and a second end that is configured to move relative to the duct.

16. The cleaning system of claim 1 wherein the resiliently deformable surface comprises a wall including a first end that is fixed and stationary relative to the duct and a second end that is configured to move relative to the duct.

17. The cleaning system of claim 16 further comprising a bracket that is fixed and stationary relative to the duct and defines a channel in which the second end of the wall is slidably positioned.

18. A combine harvester comprising the cleaning system of claim 1 .