Abstract: A vortex valve flow control includes a housing defining a vortex chamber having an inlet for introducing a liquid into the vortex chamber in a manner to promote swirl and an outlet in one axial end of the vortex chamber. The peripheral wall of the of the vortex chamber, which is situated between the two end walls and surrounds the longitudinal axis of the vortex chamber, has a cylindrical cross-section. The distance between the end walls of the vortex chamber is no more larger than the diameter of the vortex chamber. A mounting device mounts a vortex valve flow control in a drainage gully whereby the outlet of the vortex valve communicates with the outlet from the gully. The mounting device includes a first element being securable to an end wall about the outlet opening and a second element mountable in or adjacent the outlet opening of the gully.