Railway brake system and braking method of a railway vehicle comprising such a system

The invention relates to a rail braking system comprising a service brake having a movable piston (8) delimiting with a body (2) of the system a service brake chamber (13) supplied by a first source, a piston rod (21) disposed in this chamber and fixed to a second side (32) of the piston facing this chamber, and a parking brake (7) disposed in said body and comprising a locking device (20) disposed in this chamber and movable to act on said rod, and a control device (23, 24) movable and delimiting with said body a parking brake pressure chamber (25) supplied by a second source; with said locking and control devices which are configured to immobilize/unlock said rod so as to lock/unlock said piston in a position.