A de-aeration system for a fuel system, the fuel system having a housing for containing a fuel filter element, a fuel inlet and a fuel outlet is disclosed. The de-aeration system includes a de-aeration valve having a valve inlet in a lower face of the valve for connection to the housing for purging the air trapped in the housing. The de-aeration valve also includes a valve outlet in an upper face of the valve and a ball. The ball is configured to lift between the lower face and the upper face in response to an air pressure differential acting on the ball. This opens the valve to purge air trapped in the housing. The ball is further configured to close the valve by sealing against the valve outlet in the upper face in response to a pressure differential across the ball created by unfiltered fuel entering the valve.