Safety device for trailers

The device has a valve arrangement including mechanically-coupled ball valves (5, 7) that are actuated by clamping a traction member (21) from one switching position into another switching position. The switching positions correspond to a switching condition. One of the valves controls a connection between a supply input (P) and a brake output (V), and the other valve controls the connection between the brake output and a hydro pneumatic accumulator (4). The latter valve is provided with a return valve (25) that is pressure operatable for fluid flow from the brake output to the accumulator.