An apparatus (1) for continuous gravimetric metering of pourable material comprises a housing (2) comprising a first and a second spaced wall (5,6), a charging port (7) through the first wall (5), and a discharging port (8) through the first wall (5) displaced from the charging port (7) and a primary air port (10) with a primary outlet opening (9) through the second wall (6) opposite to the discharging port (8). In the second wall (6) a secondary air port (12) is provided with a secondary outlet opening (11) having a substantially smaller outlet area than the primary outlet opening (9) and being displaced from the primary outlet opening in opposite direction to the rotational direction of the rotor (3) and being arranged opposite to the discharging port (8), and where the primary and secondary air ports (10,12) are connected to a compressed air supply.