Safety device for pressure vessels

A safety device for a pressure vessel, said device comprising a reverse buckling disc including a concave-convex dome portion and an annular or substantially annular flange portion surrounding said dome portion, annular inlet and outlet support means defining an internal passageway for communication with said pressure vessel, the flange portion of the disc being clamped between said inlet and outlet support means with the convex side of the dome portion of the disc freely disposed in said passageway to be subjected to pressure within the vessel, the outlet support means including a substantially flat ring member having an inner, deformable, annular portion, the internal diameter of which is less than the internal diameter of the flange portion of the disc, said deformable portion being located to have a normal rest position in which it overlies, but is out of contact with the radially outer regions of the dome portion of the disc, and upon reversal of the dome portion of the disc, initially to be engaged by the reversing radially outer regions of the dome portion of said disc and thereafter itself to be displaced by the dome portion from the normal rest position to a deformed position whereby the movement of said radially outer regions of said dome portion is retarded.