Abstract: The invention relates to a pneumatic brake-booster comprising a casing (10) inside which is a piston formed by a hub (20) and by a skirt (14) and which, with the aid of an unrolling membrane (12), defines a front chamber (16) permanently connected to a partial vacuum source and a back chamber (18) connected selectively to the front chamber (16) when a first valve passage (56, 58) is opened or to the atmosphere when a second valve passage (76, 78) is opened, the first and second valve passages (56, 58; 76, 78) being formed by first valve means (58, 78) co-operating with second valve means (56, 76), and being actuated by a control rod (35) capable of bearing, through the intermediary of a plunger (32), against one of the faces of a reaction disk (42) securely attached to a push rod (44).According to the invention, the first valve means (58, 78) are formed on the hub (20) of the piston.

Abstract: The invention relates to a brake-booster comprising a casing (10) within which is found a piston structure which, with the help of an unrolling membrane (12), defines a front chamber (16) permanently connected to a partial vacuum source by a valve (17) and a back chamber (16) selectively connected to the front chamber (16) or to the atmosphere via a valve means (34) when a control rod (30) is actuated, and a device (36) for fastening the booster on a wall (38) adjacent to a first face of the casing (10). According to the invention, apertures (50, 60) are made in the piston structure (14) and in a second face of the casing (10) and are aligned in the axial direction of the booster so as to permit the actuation of the fastening device (36) through the aperture (60) made in the second face of the casing (10).