Pressure relief device

Claim 1

A PRESSURE RELIEF DEVICE FOR AN ENCLOSURE HAVING AN APERTURE COMPRISING FLANGE MEANS HAVING A PORTION EXTENDING EXTERNALLY FROM SAID ENCLOSURE ABOUT SAID APERTURE, THERE BEING AN ANNULAR EXTERNAL GROOVE IN SAID FLANGE MEANS, O-RING GASKET MEANS IN SAID GROOVE, SAID GROOVE HAVING A WIDTH SUBSTANTIALLY GREATER THAN THE THICKNESS OF SAID O-RING, COVER MEANS EXTERNALLY COVERING SAID FLANGE MEANS AND HAVING A FLANGE TELESCOPICALLY ENGAGING OVER SAID PORTION OF SAID FLANGE MEANS AND ENGAGING SAID ORING TO PROVIDE A SEAL ABOUT SAID OPENING, SHAFT MEANS ATTACHED TO SAID COVER MEANS AND EXTENDING THROUGH SAID APERTURE INTO SAID ENCLOSURE, AND MEANS ON SAID SHAFT PROVIDING A FORCE RESTRAINING SAID SHAFT FROM MOVEMENT UNTIL A PREDETERMINED PRESSURE ON THE INSIDE OF SAID COVER HAS BEEN EXCEEDED, SAID LAST-MENTIONED MEANS BEING ARRANGED TO RAPIDLY DECREASE SAID RESTRAINING FORCE IMMEDIATELY UPON MOVEMENT OF SAID SHAFT RESPONSIVE TO A PRESSURE IN EXCESS OF SAID PREDETERMINED PRESSURE, THE COVER FLANGE BEING MOVABLE WITH SAID SHAFT AND CAUSING SAID O-RING TO ROLL IN SAID GROOVE TO MAINTAIN SAID SEAL UNTIL AFTER SAID RESTRAINING FORCE HAS BEEN DECREASED WHEREBY UPON THE ROLLING OF SAID O-RING IN SAID GROOVE RESISTANCE TO MOVEMENT OF THE COVER IS SUBSTANTIALLY ELIMINATED.