Pitless air screen

Claim 1

A PITLESS STRUCTURE FOR MAINTAINING AN AIR SCREEN ADJACENT A DOORWAY OPENING WHICH CAN ACT AS A BARRIER AND SUBSTANTIALLY KEEP DRAFTS OF AIR FROM PASSING THROUGH SAID DOORWAY OPENING AND WHICH COMPRISES: (A) A VERTICALLY-DIRECTED AIR DUCT ADJACENT ONE SIDE OF SAID OPENING. (B) A SECOND VERTICALLY-DIRECTED AIR DUCT ADJACENT THE OPPOSITE SIDE OF SAID OPENING, (C) A PLENUM CHAMBER ADJACENT THE TOP OF SAID OPENING, (D) THE UPPER ENDS OF SAID AIR DUCTS EXTENDING TO AND COMMUNICATING WITH THE ENDS OF SAID PLENUM CHAMBER, (E) AN OPENING IN THE LOWER END OF THAT FACE OF THE FIRST SAID AIR DUCT WHICH CONFRONTS SAID SECOND AIR DUCT, (F) AN OPENING IN THE LOWER END OF THAT FACE OF SAID SECOND AIR DUCT WHICH CONFRONTS THE FIRST SAID AIR DUCT, (G) SAID OPENINGS BEING IMMEDIATELY ADJACENT THE BOTTOM OF SAID DOORWAY OPENING. (H) AIR-GUIDING ELEMENTS WITHIN THE DISCHARGE OPENING OF SAID PLENUM CHAMBER WHICH CAN GUIDE AIR PASSING OUTWARDLY THROUGH SAID DISCHARGE OPENING INTO THE FORM OF A BARRIER-LIKE AIR SCREEN MOVING DOWNWARDLY TOWARD THE BOTTOM OF SAID OPENING, AND (I) AN AIR MOVING DEVICE WHICH CAN CAUSE AIR TO ENTER SAID OPENINGS IN SAID FACES OF SAID AIR DUCTS, TO PASS UPWARDLY THROUGH SAID AIR DUCTS AND ENTER SAID PLENUM CHAMBER, AND TO PASS OUTWARDLY THROUGH SAID DISCHARGE OPENING AND PAST SAID AIR-GUIDING MEMBERS INTO SAID DOORWAY OPENING WITH SUFFICIENT VELOCITY TO FORM A BARRIER-LIKE AIR SCREEN THAT EXTENDS SUBSTANTIALLY FROM SIDE TO SIDE AND FROM THE TOP TO TO SUBSTANTIALLY THE BOTTOM OF SAID DOORWAY OPENING, (J) SOME OF SAID AIR BEING DRAWN BACK INTO SAID OPENINGS IN SAID CONFRONTING FACES OF SAID AIR DUCTS FOR RECIRCULATION ACROSS SAID DOORWAY OPENING AS PART OF SAID AIR SCREEN, AND (K) SAID BOTTOM OF SAID DOORWAY OPENING BEING SUBSTANTIALLY IMPERFORATE SO SAID DISCHARGE OPENING OF SAID PLENUM CHAMBER CONFRONTS A SUBSTANTIALLY IMPERFORATE SURFACE. (I) SAID DISCHARGE OPENING OF SAID PLENUM CHAMBER AND SAID AIR-GUIDING MEMBERS LIMITING THE DEPTH OF SAID AIR SCREEN, IN THE DIRECTION OF TRAFFIC PASSING THROUGH SAID DOORWAY OPENING, TO A VALUE SMALLER THAN THE DEPTH, IN THE DIRECTION OF TRAFFIC PASSING THROUGH SAID DOORWAY OPENING, OF SAID OPENINGS IN SAID FACES OF SAID AIR DUCTS, (M) WHEREBY SAID AIR SCREEN INCREASES IN DEPTH AS IT MOVES FROM SAID TOP OF SAID DOORWAY OPENING TO SAID BOTTOM OF SAID DOORWAY OPENING. (N) SAID PITLESS STRUCTURE RECIRCULATING ENOUGH AIR ACROSS SAID DOORWAY OPENING TO ENABLE SAID AIR SCREEN TO BE SUBSTANTIALLY CONTINUOUS, AND TO ACT AS A BARRIER, ACROSS SAID DOORWAY OPENING.