A cleaning system for an agricultural work vehicle comprising:
- a reciprocating sieve mounted within the cleaning system of the work vehicle, the sieve including a plurality of rows of fingers wherein confronting surfaces of adjacent rows define lateral grain passages therebetween, the fingers extending laterally along the rows in spaced apart side by side relation defining spaces therebetween,
- the sieve including a first sieve region of a limited extent having a predetermined first number of rows of fingers configured to define first spaces and a second sieve region beyond the first sieve region in a predetermined direction having a predetermined second number of rows of fingers configured to define second spaces, the first spaces being larger than the second spaces;
- the sieve disposed in relation to a threshing system to receive a downward flow of airborne crop material including grain and particles of material other than grain, including particles lighter than the grain, the flow of crop material including a first portion containing a significantly higher density of crop material compared to a second portion of the flow beyond the first flow, the first sieve region disposed to receive the first portion of the downward flow of airborne crop material, the second sieve region disposed for receiving the second portion of the flow of crop material;
- and
- a fan system disposed below the sieve and configured for directing an air flow stream through the sieve, the air flow stream including a first air flow portion, of a limited extent, directed through the first sieve region at a first air flow rate and a second air flow portion directed through the second sieve region at a second air flow rate, the first air flow rate being at least about one and one half times greater than the second air flow rate, such that the first air flow portion through the larger first spaces of the first sieve region will generate an air flow condition above the first sieve region which will interact with the downward flow of the first portion of the flow of crop material to separate and propel beyond the first sieve region substantially all of the particles of material lighter than the grain and to allow essentially only grain to fall onto the first sieve region to pass through the larger first sieve spaces.