Centrifugal fan

Claim 1

IN A CENTRIFUGAL FAN, A HOUSING OF SCROLL FORM HAVING SPACED SUBSTANTIALLY PARALLEL SIDES AND A SCROLL SHAPED WALL, INLET THROAT MEANS ATTACHED TO AND EXTENDING WITHIN SAID HOUSING, AN IMPELLER OF THE CENTRIFUGAL TYPE HAVING FLOW PASSAGES THEREIN AND HAVING SAID FLOW PASSAGES TERMINATING IN A PERIPHERAL AIR DISCHARGE SURFACE, MEANS ROTATABLY MOUNTING SAID IMPELLER IN SAID HOUSING FOR DRAWING AIR THROUGH THE INLET THROAT INTO SAID IMPELLER AND DISCHARGING THE SAME FROM THE FAN HOUSING, A SUBSTANTIALLY RECTANGULAR DISCHARGE OPENING IN SAID HOUSING, SAID OPENING BEING SPACED FROM AND IN A PLANE SUBSTANTIALLY PARALLEL WITH A PLANE TANGENT TO THE PERIPHERY OF SAID IMPELLER, TWO SIDES OF SAID DISCHARGE OPENING BEING SUBSTANTIALLY AT THE HOUSING SIDES, A THIRD SIDE OF SAID DISCHARGE OPENING BEING SUBSTANTIALLY AT THE SCROLL SHAPED WALL, A FOURTH SIDE OF SAID DISCHARGE OPENING EXTENDING BETWEEN AND BEING SUBSTANTIALLY NORMAL TO SAID SUBSTANTIALLY PARALLEL SIDES OF SAID HOUSING AND BEING LOCATED A PREDETERMINED DISTANCE FROM SAID THIRD SIDE OF SAID OPENING, AND A SLOPING SUBSTANTIALLY CONCICAL SHAPED CUT-OFF MEANS LOCATED IN SAID DISCHAGED OPENING ADJACENT SAID FOURTH SIDE TO REDUCE THE RECIRCULATION OF AIR AROUND SAID INLET THROAT AND TO PREVENT RECIRCULATION OF DISCHARGED AIR BACK THROUGH THE LOWER PORTION OF SAID DISCHARGE OPENING.