Abstract: An apparatus for regulating fluid flow through a spray nozzle comprising a circular chamber (1) defined by spaced apart end walls, a peripheral side wall (3), a central axis, and a first inlet at or near the peripheral side wall (3) to allow a flow of fluid to enter said chamber (1) tangential to the peripheral side wall (3), and an outlet (4) exiting through one of the end walls. In use a flow of fluid entering through the first inlet has a primary lower layer (16) that follows a first circular flow path which forms a vortex commencing at the peripheral side wall (3) and increases in velocity and pressure towards the outlet and at least one secondary upper layer (17) that substantially follows a second flow path radially inwardly towards the central axis. The primary lower layer (16) and the secondary upper layer (17) interact and support each other over at least a portion of flow between the inlet and outlet (4).