Abstract: A safety device for limiting the pressure of a fluid to a predetermined value comprises a preshaped diaphragm having a downstream convex face and an upstream convex face mounted as a closing or sealing device in a pipe. A first knife faces the convex face of the diaphragm at such a distance that a predetermined pressure exerted by the fluid on the concave face of the diaphragm brings the latter into contact with the knife which then causes a bursting of the diaphragm. A second knife is fitted to face the concave face of the diaphragm and a mechanism is provided for making the second knife strike against the diaphragm in order to bring about the tearing thereof when the concave face of the diaphragm is exposed by the fluid to a pressure below said predetermined pressure. The first knife has a passive operating mode, but the second knife has an active operating mode.

Abstract: Safety device for limiting the pressure of a fluid, having at least one hollow modular member, which is open at both ends, a diaphragm closing one end, and a knife mounted within the modular member facing the diaphragm at a regulatable distance from it. The device also has a piston for making the knife strike the diaphragm in order to bring about bursting before this would be done by deformation of the diaphragm under the effect of a given pressure. The knife may have a pointed central lip bordered by two leading lips so as to reliably bring about bursting of the diaphragm.