Compressed air system of a trailer of a commercial vehicle

The compressed air system (1) has an emergency brake valve (19) which is applied with a pressure of a container (4) depending on the pressure at a terminal (141). The terminal is connected with a coupling head (2). A shuttle valve is provided with an input which is connected with another terminal (143) for the emergency brake pressure. Another input is connected with a coupling head brake (3). An output is connected with a control unit (72) which controls the operating brake pressure for the service brakes.