Abstract: Disclosed is a nonreturn device for a pipe for carrying a fluid, including —a shut-off valve provided with actuating element including a device for accumulating/releasing potential energy, —a nonreturn valve designed to maintain a pressure difference ?P between its inlet and its outlet, and —a triggering piston, the internal volume of which is divided into two chambers by a mobile element which is equipped with an activation rod; the first and second chambers are in fluidic communication with the pipe, respectively upstream and downstream of the nonreturn valve; and the activation rod of the triggering piston is designed to be able to actuate the shut-off valve in order to move it from its inactive position into its active position if the pressure difference ?P drops below a predetermined threshold value, with the release of the potential energy accumulated in the device.