Pneumatic distributor of granular and/or powdery materials, in particular for sowing machines

1. A pneumatic distributor of at least one of granular and/or powdery materials, comprising:

a main distribution duct having a first end in the region of an air-flow which is injected into the duct under pressure, and a second end, the main duct having respective adjacent converging-diverging portions, with reference to the direction of the air-flow, defining a Venturi duct,

dosing means for delivering a metered quantity of material into the main duct in the region of the narrow cross-section portion of the Venturi duct, for the mixing of the material into the air-flow and the entrainment of the mixture obtained towards the second end, and

at least one auxiliary air-flow duct, bypassing the Venturi duct in order to connect a section of the main duct disposed upstream of the Venturi duct to a section of the main duct disposed downstream of the Venturi duct, a portion of the air-flow injected into the distribution duct being tapped off by said auxiliary duct in the region of the section disposed upstream of the Venturi duct and being introduced, at a section downstream of the Venturi duct, into the air and material mixture produced in the main duct.

2. The distributor according to claim 1 , comprising at least two auxiliary ducts bypassing the Venturi duct.

3. The distributor according to claim 2 in which both of the auxiliary ducts are connected to the main duct in the same sections of the main duct, upstream and downstream of the Venturi duct, respectively.

4. The distributor according to claim 1 , wherein the Venturi duct comprises a diverging portion and the auxiliary air-flow bypass duct is in flow communication with the main duct downstream of the Venturi duct at the output of the diverging portion of the Venturi duct, with reference to the direction of the air-flow.

5. The distributor according to claim 4 , comprising at least two auxiliary ducts bypassing the Venturi duct.