Rupture disc pressure relief device

A safety pressure relief assembly of the rupture disc type for mounting between inlet and outlet supporting members and adapted to block flow therepast within a predetermined pressure range having limits extending both above and below zero differential pressure, said assembly comprising:

• (a) a relief disc having a concave-convex portion,
• (b) a plurality of perforations extending through said relief disc concave-convex portion and permitting rapid flow therepast,
• (c) a sealing disc of greater flexibility than said relief disc and having a concave-convex portion with the convex side thereof nested into the concave side of said relief disc concave-convex portion, said sealing disc blocking said perforations to prevent flow past said relief disc only up to a predetermined first pressure applied to the concave side of said sealing disc,
• (d) a sealing disc support member having stay structure projecting into close proximity the concave side of said sealing disc concave-convex portion, and
• (e) a cutting member having a cutting blade edge positioned in axially spaced relation from the concave side of said sealing disc concave-convex portion and stay structure, said blade edge operably extending a substantial part of the transverse distance across said sealing disc concave-convex portion and being offset from said stay structure whereby said sealing disc concave-convex portion is exposed to said blade edge along a substantial extent thereof for cutting therethrough upon deflection of said sealing disc concave-convex portion thereagainst,
• (f) said stay structure having a resistance to deflection only sufficient to retain said sealing disc concave-convex portion out of cutting contact with said blade edge up to a predetermined second pressure applied to the convex side of said sealing disc through said relief disc perforations.