Safety device against overpressures

An overpressure relief device comprising fluid flow means providing a tubular passageway having an input end for connection to an enclosure with fluid under pressure and an output end for exhausting said fluid to the atmosphere, an imperforate, flexible membrane blocking said passageway and connected at its edge in fluid-tight relation to said means so as to prevent the flow of fluid from said input end to said output end, said membrane having insufficient strength by itself to prevent rupturing deformation thereof when the pressure at said output end exceeds the pressure at said input end by a predetermined amount, a perforate membrane holder mounted in said passageway between said membrane and said input end for engaging said membrane when it moves toward said input end, said holder having sufficient strength to prevent rupturing deformation of said membrane when the pressure at said output end exceeds the pressure at said input end by said predetermined amount, membrane perforating means mounted on said fluid flow means adjacent said membrane at the side thereof opposite from the side thereof at which said membrane holder is disposed for puncturing said membrane when it moves toward said output end under fluid pressure and by a predetermined distance away from said holder and detector means for indicating fluid pressure in said passageway less than the pressure required to cause said membrane to engage said membrane perforating means, said detector means having control means mounted in the path of movement of said membrane and engageable by said membrane prior to the time that said membrane engages said membrane perforating means.