Metered combustion air supply system

Claim 1

IN COMBINATION: A SINGLE BURNER HAVING A FIXED INLET THROAT OPENING; A FORCED AIR DRAFT SOURCE FOR SUPPLYING AIR TO SAID BURNER THROUGH SAID THROAT OPENING; A WING BOX CONNECTING SAID SOURCE TO SAID BURNER; PRIMARY AIR CONTROL MEANS IN AN OPEN INLET SIDE OF SAID WIND BOX BETWEEN SAID SOURCE AND BURNER AND BEING IN SERIES COMBINATION WITH SAID THROAT OPENING; SAID PRIMARY AIR CONTROL MEANS COMPRISING AT LEAST ONE ADJUSTABLE VANE MOVABLE FROM A SUBSTANTIALLY FULLY OPEN POSITION TO A NEARLY CLOSED POSITION TO CONTROL THE RATE OF AIR FLOW FROM THE AIR SOURCE TO THE BURNER IN RELATION TO THE OPERATING LOAD DEMAND OF SAID BURNER; THE CROSS SECTIONAL AREA OPENING OF THE PRIMARY DAMPER WHEN IN SUBSTANTIALLY OPEN POSITION BEING SUBSTANTIALLY LARGER THAN THE FIXED CROSS SECTIONAL AREA OF THE THROAT OPENING, AND THE CROSS SECTIONAL AREA OPENING OF THE PRIMARY DAMPER WHEN THE VANES ARE IN NEARLY CLOSED POSITION BEING SUBSTANTIALLY SMALLER THAN THE CROSS SECTIONAL AREA OF THE THROAT OPENING, WHEREBY THE AIR PRESSURE DROP ACROSS THE PRIMARY AIR CONTROL MEANS WHEN THE LATTER IS IN NEARLY CLOSED POSITION IS SUBSTANTIALLY GREATER THAN THE PRESSURE DROP ACROSS THE THROAT OPENING, AND WHEREBY THE PRESSURE DROP ACROSS THE THROAT OPENING IS SUBSTANTIALLY GREATER THAN THE PRESSURE DROP ACROSS THE PRIMARY AIR CONTROL MEANS WHEN THE LATTER IS IN SUBSTANTIALLY OPEN POSITION; SECONDARY ADJUSTABLE AIR CONTROL MEANS LOCATED TO THE UPSTREAM SIDE OF SAID PRIMARY AIR CONTROL MEANS OPERABLE TO CONTROL THE RATE OF AIR FLOW FROM THE SOURCE TO THE BURNER; PRESSURE SENSING MEANS FOR SENSING PRESSURE DIFFERENTIAL ACROSS THE SERIES COMBINATION CONSTITUTED BY SAID PRIMARY DAMPER AND SAID THROAT OPENING; AND MEANS OPERATIVELY CONNECTED TO AND RESPONSIVE TO SAID PRESSURE SENSING MEANS FOR ADJUSTING SAID SECONDARY AIR CONTROL MEANS TO MAINTAIN A SUBSTANTIALLY CONSTANT PREDETERMINED PRESSURE DIFFERENTIAL ACROSS THE SERIES COMBINATION.