Pneumatic brake booster with tubular intake and balancing valves

The servomotor has a control rod (38) whose movements determine the opening and closure of a axial inlet valve (52) located between a pressure source and its rear chamber (18), and an axial re-balancing valve (50) between a forward chamber (16) and the rear chamber (18) to actuate a moving partition between the two chambers. It has a tubular component (76) with axially offset transverse faces carry the primary seal elements (82, 84) for the inlet and re-balancing valves, and the control rod operates through two concentric springs (40) with different degrees of stiffness.