The invention provides a device for extracting energy from a fluid flow. The device has an air compression chamber and an array of valves, operable to open and close to regulate flow of the fluid through associated valve apertures. The valves are operable to close progressively as the fluid flow is incident thereon, thereby focusing flow of the liquid towards the air compression chamber and compressing air therein. The valves also open on a return flow of liquid from the compression chamber.