Abstract: A vortex flow control device is manufactured by forming a template unit having end walls of which the wall has an outlet opening, and a partial outer wall. The partial outer wall has an opening. A plate is subsequently secured to the template unit to partially close the opening, to leave an inlet. The size of the plate is selected so as to result in an inlet 30 sized to achieve required flow characteristics for the finished device. The plate his inclined to a planar portion on the opposite side of the inlet at an angle in the range 85° to 95°, so as to induce turbulence in the region of the inlet.