Abstract: A servo valve comprising: a fluid transfer valve assembly includes a valve body having a supply port and a control port (C). The valve body cincludes first and second nozzles and a drive member therebetween, arranged to regulate flow of fluid from the supply port to the control port in response to a control signal. The drive member comprises an elongate member arranged to rotate in response to the control signal, and a cylindrical disk mounted on, and arranged to rotate with, the elongate member, between the first and second nozzles, the cylindrical disk having a cam profile such as to vary the spacing (A, B) between the disk and at least one of the nozzles as the cylindrical disk rotates relative to the first and second nozzles.