The vertical prepress flaps in the filling opening the pressclose simultaneously, resulting in a closed press channel. Because of this, optimal-weight homogeneous bales are produced without cutting being necessary. These flaps have been built in such a way that any impacting forces are effectively absorbed. The front flap is small in view of the distribution of forces, and is equipped with a toothing, so that material between the flaps can be cut. The rear flap is equipped with a fallback mechanism and an anti-blockage switch, which minimizes interventions.