Tandem pneumatic brake booster

Tandem pneumatic brake booster for a vehicle comprising a shell, a pneumatic piston sliding in the shell, two pairs of chambers, each pair comprising a front chamber and a rear chamber, the front chamber being situated closer to a brake master cylinder than the rear chamber, a fixed partition in the booster, separating a first front chamber from a second rear chamber, a first plate skirt, separating the first front chamber from the first rear chamber, and a second plate skirt, separating the second front chamber h from the second rear chamber, these plate skirts being movable, sealed and moving the pneumatic piston, a seal fixed to the fixed partition, the pneumatic piston sliding inside this seal in a sealed manner, this seal comprising a first lip pressed on the pneumatic piston in a sealed manner, and extending parallel to the axis of movement of the pneumatic piston, characterized in that the first lip is crenellated, and characterized in that the seal comprises a second lip extending in the first front chamber perpendicular to the axis of movement of the pneumatic piston, this second lip comprising protrusions on its wall opposite the first plate skirt, a space between two merlons is situated opposite a space between two protrusions.