Flap valve

摘要

The valve (1) has a cover flap (2) tiltable around a rotational axis (3) such that a contact surface (4) of the flap is cooperated with a valve seat (5), where the seat and the surface have a plastic coating. The surface aligned to the seat runs in a curved plane. One side (7) of the surface directed in an opening direction has larger distance around the axis than another side (8) directed in a closing direction when the seat is turned away from the axis. The former side has smaller distance than the latter side when the seat is turned towards the axis.