Abstract: A vacuum brake power booster, in particular for motor vehicles, which includes a poppet valve (12) sealing two valve seats (18, 19) and which is axially deformable within the area of a rolling fold (15) also includes an annular part which is either mounted on the outside of the rolling fold (15) in a form-fit manner or arranged inside the elastic material (24) of the poppet valve (12). This annular part prevents the rolling fold (15) from being blown up outwardly due to the pressure differential prevailing between its two sides so that it will be possible to reduce the return force and thus also the response force.

Abstract: A metal cup accommodating a reaction disc and the end of a push rod is fixed with respect to a control valve housing of a vacuum brake power booster. The manner of fixation is of simple design, allowing the parts to be manufactured at low cost and offering ease of mounting. According to the invention a metal cup is supported in axial direction at the front side of the control valve housing and is retained by a retaining clip in a positive locking fit with the control valve housing.

Abstract: Working pistons, in particular those of brake boosters, have to tolerate a considerable number of changes in stress and great forces acting on the piston. Simultaneously, it is an object to construct the pistons as light-weight as possible. Due to the considerable forces in the axial direction, it is imperative for the piston to be well secured on the guiding axis. On the other hand, the central guide's projection securing the piston in the axial direction can cause local stresses on the piston and, thus, fatigue in the material which implies a premature failure of the piston. It is an object of this invention to improve the central circumference of the piston no longer is rigidly clamped into the central guide, but rather in that the inner end and the support are designed so as to enable a swivelling motion of the piston plate without local bending stress, thereby the life of the piston being considerably prolonged.