The valve closure element (7) is guided axially through an opening (15) in the seating (16) concentric with the base (20) of a trough-shaped perforated plate (21) of very hard material with a traction resistance exceeding 80 N/sq.mm. The plate is built into the valve so that the first surface (19) to be struck by the stamping die is positioned downstream from the second surface (44). The holes (25) are splayed and the flow of material is in the opposite direction to the stamping. <IMAGE>
