US Patent 7451689 Combined service brake and spring brake cylinder assembly

A combined service brake and spring brake cylinder for the braking system of a motor vehicle, in particular for utility vehicles, includes service and spring brake pistons guided inside a casing which is common for the two brake cylinders. The spring brake piston is loaded by at least one storage spring and has an external diameter greater than that of the service brake piston. The spring brake piston is in the form of an annular piston, and at least a part of the rod thereof is constructed in the form of a piston tube, which surrounds the service brake piston and forms an external radial running and sealing surface therefor.