Coupling head for pneumatic connection of braking systems on a traction vehicle and a trainer with lip valve

Coupling head (1) comprises a filter unit having a valve device (22) with a valve lip (26) interacting with a valve seat (30). The lip releases a flow cross-section for compressed air during contamination of the insert by the elastic deformation on lifting from the valve seat. Preferred Features: The valve seat is formed on a frame (10) of the filter insert. The valve device has at least two valves, in which one valve forms a bypass connection between one connection and a further connection.