Single lap oven heating system

Claim 1

IN A BAKING CHAMBER ATMOSPHERE RECIRCULATING SYSTEM FOR AN OVEN PROVIDED WITH AN ENDLESS TRAVELING TRAY CONVEYOR FOR TRANSPORTING PRODUCTS TO BE BAKED THERETHROUGH IN AN UPPER AND A LOWER LONGITUDINALLY EXTENDING RUN, MEANS FORMING UPPER AND LOWER PLENUM CHAMBERS DISPOSED IN SPACED RELATION ABOVE AND BELOW A FORWARD PORTION OF SAID UPPER TRAY CONVEYOR RUN DEFINING AN UPPER FORWARD BAKING ZONE, MEANS FORMING UPPER AND LOWER PLENUM CHAMBERS DISPOSED IN SPACED RELATION ABOVE AND BELOW A REARWARD PORTION OF SAID UPPER TRAY CONVEYOR RUN DEFINING AN UPPER REARWARD BAKING ZONE, MEANS FORMING UPPER AND LOWER PLENUM CHAMBERS DISPOSED IN SPACED RELATION ABOVE AND BELOW A FORWARD PORTION OF SAID LOWER TRAY CONVEYOR RUN DEFINING A LOWER FORWARD BAKING ZONE, MEANS FORMING UPPER AND LOWER PLENUM CHAMBERS DISPOSED IN SPACED RELATION ABOVE AND BELOW A REARWARD PORTION OF SAID LOWER TRAY CONVEYOR RUN DEFINING A LOWER REARWARD BAKING ZONE, THE CONFRONTING FACES OF THE UPPER AND LOWER PLENUM CHAMBERS OF EACH OF SAID ZONES HAVING A MULTIPLICITY OF APERTURES DIRECTED TOWARD THEIR ASSOCIATED PORTION OF SAID TRAY CONVEYOR, FIRST AND SECOND FAN MEANS, A VALVE CONTROLLED BLOWING DUCT FOR SELECTIVELY PROVIDING COMMUNICATION BETWEEN THE DISCHARGE OF SAID FIRST FAN MEANS AND ONE OR THE OTHER OF SAID UPPER AND LOWER PLENUM CHAMBERS OF SAID UPPER FORWARD BAKING ZONE, A VALVE CONTROLLED RETURN DUCT FOR SELECTIVELY PROVIDING COMMUNICATION BETWEEN THE INTAKE OF SAID FIRST FAN MEANS AND ONE OR THE OTHER OF SAID UPPER AND LOWER PLENUM CHAMBERS OF SAID UPPER FORWARD BAKING ZONE, A VALVE CONTROLLED BLOWING DUCT FOR SELECTIVELY PROVIDING COMMUNICATION BETWEEN THE DISCHARGE OF SAID SECOND FAN MEANS AND ONE OR THE OTHER OF SAID UPPER AND LOWER PLENUM CHAMBERS OF SAID LOWER FORWARD BAKING ZONE, A VALVE CONTROLLED RETURN DUCT FOR SELECTIVELY PROVIDING COMMUNICATION BETWEEN THE INTAKE OF SAID SECOND FAN MEANS AND ONE OR THE OTHER OF SAID UPPER AND LOWER PLENUM CHAMBERS OF SAID LOWER FORWARD BAKING ZONE, THIRD FAN MEANS, BLOWING DUCT MEANS PROVIDING COMMUNICATION BETWEEN THE DISCHARGE OF SAID THIRD FAN MEANS AND THE LOWER PLENUM CHAMBER OF SAID UPPER REARWARD BAKING ZONE, RETURN DUCT MEANS PROVIDING COMMUNICATION BETWEEN THE INTAKE OF SAID THIRD FAN MEANS AND THE UPPER PLENUM CHAMBER OF SAID UPPER REARWARD BAKING ZONE, VALVE CONTROLLED BLOWING DUCT MEANS FOR SELECTIVELY PROVIDING COMMUNICATION BETWEEN THE DISCHARGE OF SAID THIRD FAN MEANS AND ONE OR THE OTHER OF SAID UPPER AND LOWER PLENUM CHAMBERS OF SAID LOWER REARWARD BAKING ZONE, AND VALVE CONTROLLED RETURN DUCT MEANS FOR SELECTIVELY PROVIDING COMMUNICATION BETWEEN THE INTAKE OF SAID THIRD FAN MEANS AND ONE OR THE OTHER OF SAID UPPER AND LOWER PLENUM CHAMBERS OF SAID LOWER REARWARD BAKING ZONE.