The invention relates to a method and apparatus for of controlling the flow of a fluid. The fluid comprises a liquid phase and a dissolved gas phase. The fluid passes through a valve, the valve comprising a fluid inlet and a movable body located in a flow path through the valve, the movable body being arranged to move freely relative to the opening of the inlet to vary the flow-through area through which the fluid flows by means of the Bernoulli effect. The dimensions of the valve are such that flow of the fluid past the movable body causes a drop in pressure to below the bubble point of the gas phase in the liquid phase, thereby increasing flow of the fluid through the valve.