An agricultural machine comprising a seed metering device to meter seeds for the distribution to the ground across which the agricultural machine moves. The seed metering device embraces a wall that is arranged to rotate. The seed metering device is furthermore arranged to communicate with a pressure actuating appliance for providing a wall pressure difference between a seed reception side, high-pressure side, of the wall and a side, low-pressure side, of the wall that is opposite the seed reception side. The wall is provided with a plurality of through retention openings for the reception on the seed reception side of the wall, by means of the wall pressure difference, of seeds at the retention openings. Then, the seeds are transported, by means of the rotation of the wall, through a wall transportation distance whereupon they are released from the wall. The pressure actuating appliance comprises a pneumatic device connected to an air line, which device provides a main air current through the air line toward the seed reception side of the wall. A return line is connected between the side of the wall that is opposite the seed reception side and the pneumatic device, in which return line a part of the main air current is arranged to be brought back to the air line and/or to an inlet side of the pneumatic device, while a part of the main air current is arranged to be directed down into the ground through a dump line.
