A flow control device for partitioning a fluid flow from a common supply stream into at least two delivery streams comprising: an elongate conduit comprising an outer wall and internal flow partitioning means defining internal flow zones (2; 3) for such delivery streams; one or more inlet flow control apertures disposed in the outer conduit wall to provide a flow inlet into each such internal flow zone (2,3) the internal flow partitioning means being so configured that flow inlet(s) to the respective internal flow zones (2,3) are spaced on the conduit wall; a common movable flow control damper (21,22) disposed about the outer conduit wall surface comprising at least one damper member movable about and over a portion of the conduit surface at which the inlet flow control aperture(s) defining a fluid supply to each of said internal flow zones (2,3) located in such manner as to selectively restrict flow through the inlet flow control aperture(s) of the respective internal flow zones (2,3) so as to effect relative flow modification between the said delivery streams; characterised in that the damper member is configured to partition flow between said internal flow zones (2; 3) in that a first internal flow zone is enabled to fluidly communicate with a fluid flow zone externally of the elongate conduit wall by provision of flow control aperture(s) at a first location on the wall and a second internal flow zone is enabled to fluidly communicate with a fluid flow zone externally of the elongate conduit wall by provision of flow control aperture(s) at a second location offset from the first location, and the damper member sits between the two locations to be movable so as to selectively occlude the respective flow control aperture(s) to a varying extent. an elongate conduit comprising an outer wall and internal flow partitioning means defining internal flow zones (2; 3) for such delivery streams; one or more inlet flow control apertures disposed in the outer conduit wall to provide a flow inlet into each such internal flow zone (2,3) the internal flow partitioning means being so configured that flow inlet(s) to the respective internal flow zones (2,3) are spaced on the conduit wall; a common movable flow control damper (21,22) disposed about the outer conduit wall surface comprising at least one damper member movable about and over a portion of the conduit surface at which the inlet flow control aperture(s) defining a fluid supply to each of said internal flow zones (2,3) located in such manner as to selectively restrict flow through the inlet flow control aperture(s) of the respective internal flow zones (2,3) so as to effect relative flow modification between the said delivery streams; characterised in that the damper member is configured to partition flow between said internal flow zones (2; 3) in that a first internal flow zone is enabled to fluidly communicate with a fluid flow zone externally of the elongate conduit wall by provision of flow control aperture(s) at a first location on the wall and a second internal flow zone is enabled to fluidly communicate with a fluid flow zone externally of the elongate conduit wall by provision of flow control aperture(s) at a second location offset from the first location, and the damper member sits between the two locations to be movable so as to selectively occlude the respective flow control aperture(s) to a varying extent.