Abstract: Disclosed are apparatuses for controlling the flow of fluids which comprise a plurality of identical nozzle means arranged in an axially symmetrical configuration on a stator means and defining a plurality of identical flow channels or passageways. Each nozzle means comprises a fixed-spacer member and an adjustable-segment member. The fixed-spacer members are sealably fixed to the stator and mandate that the fluid flows through the flow channels. The adjustable-segment members are slideably connected to the fixed-spacer members in an essentially sealing relationship. Adjustable-segment members are operable to move only in straight-line direction and are not permitted to move pivotally. Jar-free movement of the adjustable members is possible regardless of flow or pressure of fluid. An essentially constant angle of discharge is possible for all adjustable positions of the nozzle means thereby enabling a high operating efficiency of the apparatus over a wide range of operating conditions.