Spring battery brake drum with a seal based on an expanding flow section

The cylinder (1) has a spring brake piston (8) actuatable by a loaded spring that is arranged in a spring chamber (14). The piston is adjustable in a releasing- or application position by aeration or deaeration of a spring brake chamber (12). An operating surface (76) of a side piece (64) of a sealing element (62) of a sealing arrangement is formed such that an intermediate space (77) between the operating surface and a contact surface (54) of a spring brake cylinder (4) has diverging cross-section in a flow direction from the spring chamber into the spring brake chamber.