This was a new thing I saw at Ag-Quip 2010.  It is an air dump for the distributor head on top of your primary air hose, instead of having individual air dumps above each sowing row.  It has a butterfly in it to regulate air pressure to the tyne, reducing the amount of seed bounce out of the trench, but keeping enough pressure to push seed through.  For more info call James on 0428 514 126.