Stack damper control safety interlock with lockout prevention

In a heating system including a furnace having a fuel fired burner apparatus, fuel supply means including pilot valve means operable when energized to supply fuel to a pilot outlet for ignition, and main valve means operable when energized to supply fuel to said burner apparatus for ignition by the pilot flame, a vent stack for conducting combustion products away from said burner apparatus, and stack damper means including a stack damper plate pivotally mounted within said vent stack, said damper plate being normally maintained in a first position to close said vent stack and being rotatable to a second position to open said vent stack, and a drive motor operatively coupled to said damper plate for driving said damper plate between said first and second positions, a control arrangement comprising switching means, first limit switch means connected in an energizing path for said switching means and said drive motor to permit energization of said switching means and said drive motor over said energizing path whenever said damper plate is at said first position, activate means responsive to a request for heat to effect the energization of said switching means and said drive motor over said energizing path, including said first limit switch means, when said damper is at said first position to permit said damper plate to be driven towards said second position, said switching means being operable when energized to prepare an energizing path for said fuel supply means, and to provide a holding path for said switching means, said first limit switch means being operable when said damper plate has been driven to said second position to interrupt said energizing path for said switching means and said motor drive and to complete said energizing path for said fuel supply means, said pilot valve means being connected to said energizing path for said fuel supply means for operation whenever said energizing path for said fuel supply means is completed, said fuel supply means including flame sensing means having a

• first switching device operable when energized to interrupt the energizing path for said fuel supply means, said fuel supply means including a second switching device connected to said energizing path for said fuel supply means and normally operable prior to operation of said first switching device to provide a holding path for said pilot valve means, said first switching device being operable to connect said main valve means to said holding path for operation, said activate means being operable when the heating demand has been met to deenergize said fuel supply means and said switching means, permitting said drive motor to be reenergized over a return drive path to drive said damper plate to said first position, and second limit switch means operable when said damper plate has been driven to said first position to interrupt said return drive path to effect the deenergization of said drive motor.

In a heating system including a furnace having a fuel-fired burner apparatus, fuel supply means operable when energized to supply fuel to said burner apparatus for combustion to provide heat, a vent stack for conducting combustion products away from said burner apparatus, and stack damper means including a drive motor, and a damper plate pivotally mounted within said vent stack, said damper plate being normally maintained at a first position to close said vent stack and being rotatable to a second position to open said vent stack, said drive motor being operatively coupled to said damper plate for driving said damper plate between said first and second positions, a control arrangement comprising switching means first limit switch means having first contacts for controlling the energization of said drive motor and second contacts for controlling the energization of said fuel supply means, said first limit switch means being coupled to said stack damper means and operated thereby to close said first contacts to complete an energizing path for said drive motor and to open said second contacts to prevent energization of said fuel supply means whenever said damper plate is at said first position, and second limit switch means having third contacts for controlling the energization of said switching means and fourth contacts connected in a return drive path for said drive motor, said second limit switch means being coupled to said stack damper means and operated thereby to close said third contacts to connect said switching means to said energizing path for said drive motor, providing an energizing path for said switching means over said first and second limit switch means, and to open said fourth contacts to interrupt said return drive path when said damper plate is at said first position, activate means for connecting power to said energizing paths to effect energization of said switching means and said drive motor in response to a request for heat, said switching means being operable when energized to complete an energizing path for said duel supply means and to provide a holding path for said switching means, said drive motor being operable when energized to drive said damper plate from said first position to said second position, said stack damper

• means operating said second limit switch means to close said fourth contacts and to open said third contacts to interrupt said energizing path for said switching means when said damper plate is driven away from said first position, whereby said switching means is maintained energized over said holding path, and said stack damper means operating said first limit switch means when said damper plate has been driven to said second position to open said first contacts to interrupt said energizing path for said drive motor to deenergize said drive motor and to close said second contacts to connect power to said energizing path for said fuel supply means to effect energization of said fuel supply means, said fuel supply means and said switching means being deenergized when the heating demand has been met, permitting said drive motor to be reenergized over said return drive path including said fourth contacts of said second limit switch means to cause said damper plate to be driven to said first position, said stack damper means operating said second limit switch means to open said fourth contacts to interrupt said return drive path when said damper plate has been driven to said first position to deenergize said drive motor.

In a heating system including a furnace having a fuel fired burner apparatus, fuel supply means operable when energized to supply fuel to said burner apparatus for combustion to provide heat, a vent stack for conducting combustion products away from said burner apparatus, and stack damper means including a stack damper plate pivotally mounted within said vent stack, said damper plate being normally maintained in a first position to close said vent stack and being rotatable to a second position to open said vent stack, and a drive motor operatively coupled to said damper plate for driving said damper plate between said first and second positions, a control arrangement comprising activate means responsive to a request for heat to energize said drive motor to permit said damper plate to be driven to said second position, switching means including a heat sensor switch energized by said activate means to prepare an energizing path for said fuel supply means, limit switch means operable when said damper plate has been driven to said second position to deenergize said motor and to complete said energizing path for said fuel supply means, said heat sensor switch being responsive to heat from said burner apparatus to maintain said energizing path until the heating demand has been met, said limit switch means being operable in response to said drive motor driving said damper plate to said second position to deenergize said heat sensor switch to permit said heat sensor switch to interrupt said energizing path after a predetermined time interval in the absence of heat from said burner apparatus within said predetermined time interval, said activate means being operable when the heating demand has been met to deenergize said fuel supply means, and to effect the reenergization of said drive motor, permitting said damper plate to be returned to said first position.

In a heating system including a furnace having a fuel fired burner apparatus, fuel supply means operable when energized to supply fuel to said burner apparatus for combustion to provide heat, a vent stack for conducting combustion products away from said burner apparatus, and stack damper means including a drive motor, and a stack damper plate pivotally mounted within said vent stack, said damper plate being normally maintained in a first position to close said vent stack and being rotatable to a second position to open said vent stack, said drive motor being operatively coupled to said damper plate for driving said damper plate between said first and second positions, a control arrangement comprising switching means, first limit switch means coupled to said stack damper means and operated thereby to complete an energizing path for said drive motor to permit energization of said drive motor whenever said damper plate is at said first position, and second limit switch means coupled to said stack damper means and operated thereby to connect said switching means to said energizing path for said drive motor, providing an energizing path for said switching means over said first and second limit switch means when said damper plate is at said first position, activate means responsive to a request for heat for connecting power to said energizing paths to effect the energization of said switching means and said drive motor, said switching means being operable when energized to complete an energizing path for said fuel supply means and to provide a holding path for said switching means, said drive motor being operable when energized to drive said damper plate from said first position towards said second position, said stack damper means operating said second limit switch means to interrupt said energizing path for said switching means when said damper plate is driven away from said first position, whereby said switching means is maintained energized over said holding path, and said stack damper means operating said first limit switch means when said damper plate has been driven to said second position to interrupt said energizing path for said drive motor to deenergize said drive motor and to connect power to said energizing path for said fuel supply means to effect energization of said fuel supply means, said activate means being operable when the heating demand has been met to deenergize said fuel supply means and said switching means, permitting said drive motor to be reenergized over a return drive path to drive said damper plate to said first position, and said stack damper means operating said second limit switch means when said damper plate has been driven to said first position to interrupt said return drive path to effect the deenergization of said drive motor.

In a heating system including a furnace having a fuel-fired burner apparatus, fuel supply means operable when energized to supply fuel to said burner apparatus for combustion to provide heat, a vent stack for conducting combustion products away from said burner apparatus, and stack damper means, including a damper plate pivotally mounted within said vent stack, said damper plate being normally maintained at a first position to close said vent stack and being rotatable to a second position to open said vent stack, and a drive motor operatively coupled to said damper plate for driving said damper plate between said first and second positions, a control arrangement comprising switching means operable when energized to prepare an energizing path for said fuel supply means and a holding path for said switching means, stack damper control means including first limit switch means having first contacts connected in an energizing path for said drive motor, and second contacts connected in an energizing path for said fuel supply means, and a first actuator means including a first cam member coupled to said drive motor and operable to permit said first contacts to be maintained closed and said second contacts to be maintained open, providing an energizing path for said drive motor when said damper plate is at said first position to permit said drive motor to be energized in response to a request for heat, second limit switch means having third contacts connected in series with said first contacts in an energizing path for said switching means, and fourth contacts connected in a return drive path for said drive motor, and a second actuator means including a second cam member coupled to said drive motor and operable to maintain said third contacts closed and said fourth contacts open when said damper plate is at said first position, permitting energization of said switching means over a path including said first and third contacts in response to a request for heat, said drive motor being operable when energized to drive said damper plate from said first position to said second position, said second limit switch means being operated to open said third contacts and close said fourth contacts when said damper plate is driven away from said first position to interrupt said energizing path for said switching means whereby said switching means is maintained energized over said holding path, and said first limit switch means being operated when said damper plate has been driven to said second position to open said first contacts and to close said second contacts to interrupt said energizing path for said drive motor to deenergize said drive motor and to complete said energizing path for said fuel supply means, said third and fourth contacts being operated by a common switch member whereby the energization of said switching means is prevented, thereby preventing the energization of said fuel supply means in the event of a malfunction of said second limit switch means which permits said third contacts to be open when said damper plate is at said first position, said fuel supply means and said switching means being deenergized when the heating demand has been met, permitting said drive motor to be reenergized over said return drive path, including said fourth contacts, to cause said damper plate to be driven to said first position, said second limit switch means being operated when said damper plate has been driven to said first position to open said fourth contacts to deenergize said drive motor.