Combined cylindrical service brake and spring brake cylinder, with a) a central axis, b) a movable diaphragm, which is located in a housing of the service brake cylinder, bounds a service brake chamber capable of being ventilated and vented, is held at the housing of the service brake cylinder by its mounting edge and acts on a diaphragm plate joined to a service brake piston rod, and with c) a spring brake piston with a spring brake piston rod, which spring brake piston is located in a housing of the spring brake cylinder, is actuable by at least one accumulator spring and bounds a spring brake chamber capable of being ventilated and vented, wherein d) the spring brake piston rod extends through a central piston rod bore of a partition between the service brake cylinder and the spring brake cylinder in such a way that is acts on the diaphragm plate, wherein e) the partition has a first edge flange, f) the housing of the spring brake cylinder is made of a deformable material and has a second edge flange, g) wherein at least one annular seal element sealing the spring brake chamber against the environment is located between the first edge flange and the second edge flange, wherein h) the second edge flange of the housing of the spring brake cylinder is formed plastically from the outside around the seal element on the one hand and around the first edge flange of the partition on the other hand in such a way that on the one hand the housing of the spring brake cylinder is joined to the partition and on the other hand the seal element is positively held between the first edge flange of the partition and the second edge flange of the housing of the spring brake cylinder, characterised in that i) the cross-section of the seal element has at least one radially inner recess, with which at least one radially outer projection of the first edge flange engages positively, and in that j) the cross-section of the seal element tapers from the recess towards the spring brake cylinder as viewed in the direction of the central axis. a) a central axis, b) a movable diaphragm, which is located in a housing of the service brake cylinder, bounds a service brake chamber capable of being ventilated and vented, is held at the housing of the service brake cylinder by its mounting edge and acts on a diaphragm plate joined to a service brake piston rod, and with c) a spring brake piston with a spring brake piston rod, which spring brake piston is located in a housing of the spring brake cylinder, is actuable by at least one accumulator spring and bounds a spring brake chamber capable of being ventilated and vented, wherein d) the spring brake piston rod extends through a central piston rod bore of a partition between the service brake cylinder and the spring brake cylinder in such a way that is acts on the diaphragm plate, wherein e) the partition has a first edge flange, f) the housing of the spring brake cylinder is made of a deformable material and has a second edge flange, g) wherein at least one annular seal element sealing the spring brake chamber against the environment is located between the first edge flange and the second edge flange, wherein h) the second edge flange of the housing of the spring brake cylinder is formed plastically from the outside around the seal element on the one hand and around the first edge flange of the partition on the other hand in such a way that on the one hand the housing of the spring brake cylinder is joined to the partition and on the other hand the seal element is positively held between the first edge flange of the partition and the second edge flange of the housing of the spring brake cylinder, characterised in that i) the cross-section of the seal element has at least one radially inner recess, with which at least one radially outer projection of the first edge flange engages positively, and in that j) the cross-section of the seal element tapers from the recess towards the spring brake cylinder as viewed in the direction of the central axis.