US 4,437,454 AGranted

Mechanical draft controller with vent damper

AssigneeJohnson Service Company

InventorThomas E. Hayes

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Abstract

A mechanical draft controller integrated in the draft hood of a furnace and coupled to a flue damper is responsive to the draft in the flue for controlling exhaust stack heat loss and eliminating heated room air loss via the draft hood under normal operating conditions. The pressure-sensitive controller is variably positioned as a face damper on a surface of the draft hood and is coupled to the flue damper by means of mechanical linkage. Increasing pressure in the draft hood caused by a reduction in the draft value due to partial flue blockage, large down draft, etc., displaces the pivoted controller resulting in a corresponding opening of the flue damper to re-establish the desired draft value. Similarly, excessive draft causes the displacement of the controller in an opposite direction resulting in flue damper displacement so as to reduce the draft value and exhaust stack heat loss. Between these two operating conditions the controller is variably positioned in the surface of the draft hood so as to block the escape of heated room air via the exhaust stack. A completely blocked flue resulting in an abnormal increase in pressure in the draft hood causes the controller to be further displaced resulting in the further displacement of the flue damper to a nearly completely open position to permit re-establishment of the desired draft value. Another safety feature provides for the breakage of the linkage coupling the draft controller with the flue damper in which case both dampers are automatically opened allowing the system to revert to normal draft hood operation. The draft hood control damper and the flue damper may be utilized in combination with a conventional bimetallic damper positioned downstream from the flue damper in reducing heat loss during burner OFF periods.

In a fuel burning heating appliance having a firebox and a flue for communicating combustion gases from said firebox to a chimney and including a housing having an aperture in a lateral surface thereof and coupling said firebox to said flue, a draft controller comprising:

control means positioned in and coupled to said aperture and movably responsive to variations in the draft in said housing over a first range of positions, said first range of positions defined by first upper and lower draft values representing the range of draft vlues under normal operating conditions, said control means including the combination of a moveable control damper and a plurality of tip shrouds attached to said housing, each of said tip shrouds having a curved surface cooperating with said moveable control damper, wherein said aperture is closed by said control damper over the first range of positions thereby preventing the introduction of ambient air into said flue and wherein said control damper is movably responsive over a second, larger range of positions defined by second upper and lower draft values corresponding to draft values in said housing outside of said normal range of operation wherein said aperture is open when said first upper or lower draft values are exceeded;
a second damper mounted in said flue downstream of said control means and variably positioned for controlling the draft therein, the position of said second damper continuously variable from a substantially closed position to a substantially open position and including a plurality of intermediate positions therebetween;
and mechanical coupling means connecting said first damper and said control damper for variably positioning said second damper in response to the displacement of said control damper in controlling the draft value over said first range of positions of said control damper and for substantially closing or opening said flue when said first range of positions of said control damper defined by said first upper and lowr draft values are respectively exceeded, wherein said control damper is moveably responsive to the difference in pressure between a first pressure within said housing disposed upstream of said second damper and a second ambient pressure.

Abstract

Claims16