A vehicle tank pressurization device has a valve seat establishing an opening for fuel vapors and/or air; such opening has a vertical axis coincident with the direction of application of an opening force, that is directed upwards and is produced, in use, by the pressure in an internal upper region of the tank; the device also has a movable shutter, placed on the valve seat, to open/close the valve seat, and having a weight set by design in such a way as to define the magnitude of a closing force directed downwards and with a center of gravity positioned eccentrically with respect to the vertical axis of the opening.