Hydraulic parking brake and method of using said brake on a slope

The system has a hydraulic actuator (57) connected to a hydraulic line (10) via a valve (50). The valve is selectively opened or closed so as to transmit or not to transmit a control pressure to the actuator. The actuator actuates a push rod (66) and a lever (70) for locking a piston up to an active position in response to the control pressure. A steering rack (77) and a lock (80) lock the rod and the lever in the active position.