Check valves

A duct comprising a check valve mounted therein and an inner wall, wherein the check valve comprises:

• a valve housing defining an opening;
• a plurality of flapper elements each having a proximal end and a distal end, the flapper elements being pivotally mounted to the valve housing at their proximal ends for pivotal movement between a closed position, in which the flapper elements block the flow of fluid through the opening and an open position in which the flapper elements permit the flow of fluid through the opening, wherein each flapper element is shaped as a sector or an annular sector such that the flapper elements together create a conical or frustoconical surface when the flapper elements are in the closed position;
• a resilient band extending around a circumference of the conical or frustoconical surface defined by the plurality of flapper elements in the closed position for biasing the flapper elements towards the closed position,
• wherein one or more of the flapper elements comprises a locator for locating the resilient band, the resilient band projects radially outward of the locator with the flapper elements in the open position and, with the flapper elements in the open position, the resilient band contacts the inner wall.