An apparatus (1) for continuous gravimetric metering of pourable material, comprising:
- a housing (2) comprising a first and a second mutually spaced wall (5, 6), a charging port (7) through said first wall (5), a discharging port (8) through one of said walls displaced from said charging port (7) and at essentially same radius as said charging port (7) with respect to a predetermined vertical axis, a primary air port (10) through the other of said walls (6) and opposite to said discharging port (8), said primary air port (10) having a primary outlet opening (9) and being connected to a compressed air supply;
- a rotor (3) mounted in and sealed to said housing (2) for rotation about said predetermined vertical axis including a plurality of pockets (13) extending therethrough at spaced locations separated by a rotor partition wall (14) having a thickness (t), said pockets (13) having a pocket opening front edge (38) as seen in the rotational direction of the rotor (3) and said pockets (13) forming a first ring (32) of pockets along the same radius as said charging and discharging ports (7, 8), a circular measuring path (MP) being defined between the charging port (7) and the discharging port (8), the pockets (13) receiving material via the charging port (7) and material being emitted through said discharging port (8) during the rotation of the rotor (3);
- a drive motor (23) configured for rotating said rotor (3) in a rotational direction;
- a control unit configured for speed indication and controlling the rotational speed of said rotor (3);
- a load cell (22) configured for measuring the weight of the material travelling along the measuring path (MP);
- and
- a secondary air port (12) provided in the other of said walls (6), the secondary air port (12) having one or more secondary outlet openings including a first secondary outlet opening (11) and being connected to a compressed air supply, the secondary outlet opening(s) (11) of the secondary air port (12) having a secondary outlet opening front edge (36) and a total outlet area being substantially smaller than that of the primary outlet opening (9);
- wherein the improvement comprises:
- the first secondary outlet opening (11) being displaced from the primary outlet opening (9) of the primary air port (10) in opposite direction to the rotational direction of the rotor (3) and being arranged opposite to said discharging port (8);
- wherein on rotation of the rotor (3), when the pockets (13) pass the first secondary outlet opening (11), a smaller first portion of material in the pockets (13) is discharged into the discharging port (8) by a smaller first amount of compressed air emitted through the first secondary outlet opening (11);
- and
- wherein on rotation of the rotor (3), when the pockets (13) pass the primary outlet opening (9), a larger second amount of the material in said pockets (13) is discharged into the discharging port (8) by a larger second amount of compressed air emitted through the primary outlet opening (9).