Precise safety device

Claim 1

A frangible disc relief device comprising a pair of mounting flanges each having seating faces and a central opening and means for securing the seating faces of said flanges together with a knife blade sub-assembly and a frangible disc sub-assembly clamped between said seating faces of the flanges, said knife blade sub-assembly comprising an annular body member carrying at least one V-shaped knife blade extending thereacross, said body member having a flanged end portion supported on one of the said seating faces and clamped between said seating faces of the mounting flanges, said end portion having an end face located in a plane perpendicular to the axis of said body member and said mounting flanges and proximate the apex of the V-shaped knife blade, said frangible disc sub-assembly comprising a thin, metallic disc having a central dome portion and an integral flat annular flange surrounding said dome portion with a circular transition therebetween, said dome portion being adapted to snap over center at a predetermined pressure and thereby to be impaled by said blade, first and second rings positioned on opposite sides of said annular flange on the disc and having flat faces engaging said flange and secured thereto, the inside diameter of the ring on the concave side of the disc being substantially equal to the diameter of said circular transition to support said transition with precise pre-alignment with respect to said transition, said ring on the concave side of the disc being seated against said end seating face of the said body member of the knife blade sub-assembly and with said rings and said annular flange of the disc and said end portion of the knife blade subassembly all clamped between said mounting flanges whereby the snap-over pressure of said disc is substantially independent of any eccentric misalignment of said transition with respect to said mounting flanges.