Abstract: A valve device to control fluid through a passageway under a pressure head which may vary, has at least one vane which lies in the passageway to restrict the fluid flow. The vane is effectively flexible and resilient to deflect under fluid flow and so increase its restricting effect on increase in the pressure head and decrease its restricting effect on decrease in the pressure head so as to maintain a substantially constant flow output through the passageway.The valve device may be incorporated in a nozzle for insertion as one of a series along the length of an irrigation pipe, and the nozzle may be provided with a pointed head part and an outlet tube or cap.The device also has application in other forms of fluid control.