Abstract: A valve for controlling the fluid flow between two generally coannular ducts. The valve is provided with a pair of back-to-back, mutually facing flow mixers of the daisy variety, each associated with a section of the coannular ducts. Each mixer transists the two coannular duct passages into a plurality of circumferentially separated chute passages communicating alternatively with the inner and outer ducts, the mixers being indexed with respect to each other by half a chute width. A stage of radially extending, pivotable vanes cooperates with the chutes of both mixers and allows both the inner and outer upstream duct flows to be directed to either the inner or outer downstream duct, depending upon the orientation of the vanes. Alternatively, either or both of the fluid streams can be blocked off entirely. Complete flexibility for flow inversion is obtained without turning or indexing the flow through the vanes by more than half a chute width, thereby maintaining high efficiency.