Abstract: Differential valve for a sub-sea flexible pipe having a valve body comprising an upper part communicating with the outside via at least one upper communication passage and a lower part communicating with at least one annulus of the flexible pipe via at least one communication duct, an internal chamber formed in the valve body and at a chamber pressure (Pc), a main clacker element mounted in the internal chamber and movable between a closed position and an open position, and urged toward the closed position by a first spring, a secondary clacker element mounted in the upper communication passage also movable between a closed position and an open position, the secondary clacker element being urged towards the closed position by a smaller preloaded spring, so that the pressure in the internal chamber is not below the exterior pressure (Pe) when the secondary clacker element is in the closed position.