Rapidly closing vertical closure

Claim 1

IN AN ARRANGEMENT FOR RAPIDLY CLOSING SUBSTANTIALLY VERTICAL AIR SHAFTS AND EMERGENCY EXITS OF SHELTERS, PARTICULARLY UNDERGROUND SHELTERS, COMPRISING, IN COMBINATION, ANNULAR MEANS LINING THE UPPER END OF AN AIR SHAFT AND HAVING AN UPPER INNER SUBSTANTIALLY VERTICAL ANNULAR SURFACE PORTION; A HEAVY COVER PLATE HAVING A PERIPHERAL SURFACE SUBSTANTIALLY CONGRUENT WITH SAID UPPER INNER SURFACE PORTION, SAID COVER BEING MOVABLE BETWEEN AN OPEN POSITION UPWARDLY SPACED FROM SAID ANNULAR MEANS AND A CLOSED POSITION ARRANGED SUBSTANTIALLY WITHIN SAID ANNULAR MEANS WITH SAID PERIPHERAL SURFACE OF SAID COVER IN SUBSTANTIAL SEALING ENGAGEMENT WITH SAID UPPER INNER ANNULAR SURFACE PORTION; COMBINED LIFTING AND DAMPING MEANS ASSOCIATED WITH SAID COVER PLATE FOR DECLERATING MOVEMENT OF SAID COVER PLATE FROM SAID OPEN TO SAID CLOSED POSITION AND FOR LIFTING SAID COVER PLATE FROM SAID CLOSED TO SAID OPEN POSITION, SAID COMBINED LIFTING AND DAMPING MEANS INCLUDING AN ELONGATED SUBSTANTIALLY VERTICAL CYLINDER MEANS FIXEDLY MOUNTED IN THE AIR SHAFT AND PISTON MEANS INCLUDING A PISTON-TYPE GUIDE ROD FIXED AT THE UPPER END THEREOF TO SAID COVER PLATE AND EXTENDING IN SEALING ENGAGEMENT WITH A LEAST AN UPPER PORTION OF SAID CYLINDER MEANS INTO THE LATTER TO BE SLIDABLY GUIDED THEREIN, SAID GUIDE ROD FORMING THE ONLY SUPPORT OF SAID COVER PLATE IN THE OPEN POSITION O F THE LATTER; DISCHARGE PASSAGE MEANS COMMUNICATING WITH THE INTERIOR OF SAID CYLINDER MEANS FOR DISCHARGING AIR THEREFROM; VALVE MEANS FOR CONTROLLING SAID DISCHARGE PASSAGE MEANS AND MOVABLE BETWEEN AN OPEN AND A CLOSED POSITION; MEANS MOVING SAID VALVE MEANS INTO SAID CLOSED POSITION WHEN SAID COVER PLATE IS IN THE OPEN POSITION THEREOF; RELEASABLE BLOCKING MEANS COOPERATING WITH SAID GUIDE ROD FOR RELEASABLY LOCKING THE SAME IN A POSITION IN WHICH SAID COVER PLATE CONNECTED THERETO IS IN SAID OPEN POSITION; CONTROL MEANS RESPONSIVE TO ABRUPT CHANGES IN THE ATMOSPHERE AND COOPERATING WITH SAID LOCKING MEANS TO AUTOMATICALLY RELEASE THE SAME WHEN SUCH ABRUPT CHANGE OCCURS SO THAT SAID GUIDE ROD WILL MOVE UNDER THE WEIGHT OF SAID COVER PLATE RAPIDLY DOWNWARDLY IN SAID CYLINDER MEANS WHILE SAID VALVE MEANS IS CLOSED SO AS TO COMPRESS THE AIR THEREIN AND TO BRAKE THEREBY THE SUBSTANTIALLY FREE FALL OF SAID COVER PLATE SHORTLY BEFORE THE LATTER ENTERS SAID ANNULAR MEANS; AND VALVE OPENING MEANS ASSOCIATED WITH SAID COVER PLATE FOR OPENING SAID VALVE MEANS IN SUCH A MANNER AS TO PERMIT GRADUAL DISCHARGE OF COMPRESSED AIR FROM SAID CYLINDER MEANS WHILE SAID COVER PLATE ENTERS INTO SAID ANNULAR MEANS AT WHICH TIME SAID UPPER INNER SURFACE PORTION OF SAID ANNULAR MEANS COOPERATES WITH SAID PERIPHERAL SURFACE OF SAID COVER PLATE TO PRESEAL THE AIR SHAFT, SUCH OPENING OF SAID VALVE MEANS SLOWLY REDUCING THE BRAKING ACTION OF THE COMPRESSED AIR AND PERMITTING GRADUAL DESCENT OF SAID COVER PLATE INTO THE FINAL CLOSED POSITION OF THE LATTER.