Coupling head for the pneumatic connection of the brakes of a towing vehicle and a trailer with lip valve

The invention relates to a coupling head (1) for the pneumatic connection of the brakes of a towing vehicle and a trailer, with a filter means for filtering between two terminals (4, 6) of flowing compressed air which integrated in said housing (2) of the coupling head (1) filter insert (8) and a valve means (22, 24) which at a a predetermined level of contamination exceeding contamination of the filter insert (8) a bypass connection between the two terminals (4, 6) produces, bypassing the filter insert (8). The invention provides that the valve means (22, 24) at least one with a valve seat (30, 32) co-operating elastic valve flap (26, 28) includes, occurring in to integrated filter insert (8) against the valve seat (30, 32) seals, and which exceeds at a said predetermined amount of impurity contamination of the filter cartridge due to elastic deformation caused by lifting off from the valve seat (30, 32) releases a flow cross-section for the pressurized air.