Abstract: The housing of the filling device mounted on the tank wall defines a chamber wherein a spring-activated cut-off valve is mounted. This valve comprises a head cooperating with a valve seat at the end of a supply duct opening into the chamber and a piston-forming body separating the chamber into two volumes. The housing presents openings between the tank inner volume and the frontmost chamber volume, and a duct between the backmost chamber volume and the tank inner volume. A no-return valve, which only lets liquid to the tank inner volume, is mounted in this duct. At the end of this duct a valve controlled by the float in the tank is mounted.