A closure device for a casing having at least one access opening wherein the closure device includes a cover member movably disposed within an interior chamber of the casing so as to be slidably displaceable along or in the direction of a casing central axis between an open and a closed position, the cover member being spaced at least partially axially from the access opening in the open position so as to permit access to the interior chamber and generally extending across and substantially obstructing the at least one access opening in the closed position.