CA1036692A - Positive automatic draft control - Google Patents
Positive automatic draft controlInfo
- Publication number
- CA1036692A CA1036692A CA220,539A CA220539A CA1036692A CA 1036692 A CA1036692 A CA 1036692A CA 220539 A CA220539 A CA 220539A CA 1036692 A CA1036692 A CA 1036692A
- Authority
- CA
- Canada
- Prior art keywords
- burner
- switch
- furnace
- valve
- damper
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
- F23L11/00—Arrangements of valves or dampers after the fire
- F23L11/005—Arrangements of valves or dampers after the fire for closing the flue during interruption of burner function
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
- F23L3/00—Arrangements of valves or dampers before the fire
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Regulation And Control Of Combustion (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A furnace control means is provided for reducing heat losses in the chimney stack to a minimum. The flow of air through the furnace and the flue pipe is controlled by a means to interrupt the flow of air during the period when the burner is not in operation. The control means closes the flue pipe damper or the air valve in the primary air duct to the combustion chamber and includes a variable "purging" delay to and the closing of the damper, or valve in the primary air duct from the stopping of the burner.
A furnace control means is provided for reducing heat losses in the chimney stack to a minimum. The flow of air through the furnace and the flue pipe is controlled by a means to interrupt the flow of air during the period when the burner is not in operation. The control means closes the flue pipe damper or the air valve in the primary air duct to the combustion chamber and includes a variable "purging" delay to and the closing of the damper, or valve in the primary air duct from the stopping of the burner.
Description
~Q3t;~9'~
This invention relates to furnace controls and in particular to the control of the flow of air through the furnace by closing a flue damper or air valve in the primary air duct to the burner thereby to reduce heat losses up the stack when the furnace burner is not operating.
Present oil burning furnaces are provided with a barometric stack control in the form of a draft regulator or damper on the flue pipe to ensure that vacuum or draft at the burner does not exceed a specified amount. This control is automatic and it admits ambient air from the furnace room into the stack when the draft is considered too great and reduces the amount of raw air into the stack as the draft or vacuum on the burner decreases.
Present gas furnaces are provided with secondary air inlets to the combustion chamber and an unrestricted opening in the flue pipe. These presently practiced draft controls are wasteful and unnecessary, since a large percentage of the oxygen `~
in the air that is admitted to the furnace system is not required for the combustion of the fuel. The amount of air to the furnace ¦
burner is preset to give proper combustion.
All heating installations are designed to provide ample heating capacity for maximum requirements to be encountered and the burner, therefore, is only in operation for a small percentage of time for a given period. With the amount of air to the furnace burner being manually preset, it will be appreciated that there is a large loss of heat through the furnace and up the stack when the burner is inoperative.
In order to reduce heat losses in the stack under the above conditions, the position of the flue damper or the primary air inlet valve must be controllable and in accordance with the present invention the opening and closing of the damper or the primary air inlet valve is operated by motor means which is actuated in response to room temperature through a thermostat.
... - 1 - ~ ' ' - -" 103~f~92 The position of the motor output shaft, that is directly related to the damper angle, controls the switch which actuates the furnace burner. Moreover, a delay in closing the damper -or the primary air intake valve after the burner shuts off is included in the control so that purging time is provided to rid the combustion chamber of the furnace and the flue pipe of combustion gases. This purging time can be varied in duration by means of adjustments to suit whatever conditions that are encountered in specific burner installations.
The general concept of furnace damper control is known, U.S. Patent 2,085,912 of July 6, 1936 to J.K. Lencke being one example. However, the Lencke patent discloses the use of a solenoid type of motor to activate the damper, a very abrupt and instantaneous method of operation. While such a method may be acceptable for starting a burner, it does not provide any purging time in closing.
In the present invention I provide an important improvement over the prior art by including means in the control to give a variable "purging" time between the shutdown of the burner and the stopping of the flow of air. The draft control consists basically of a thermostat to actuate an electrical mechanism to open and close the flue damper or primary air inlet valve and a switch responsive to damper positioning to activate the fuel burner. In one embodiment a three wire type thermostat energizes two circuits, the first being closed, with the second open, when calling for heat and the second circuit being closed, with the first open, when heat is not required.
The electrical mechanism such as a small motor to operate the stack damper, or primary air inlet valve is actuated by the thermostat. When the thermostat calls for heat, the motor is energized to open the stack damper or inlet valve and when the second circuit is energized at the time when heat is no longer ;
required, the mechanism closes the stack damper or inlet valve.
This invention relates to furnace controls and in particular to the control of the flow of air through the furnace by closing a flue damper or air valve in the primary air duct to the burner thereby to reduce heat losses up the stack when the furnace burner is not operating.
Present oil burning furnaces are provided with a barometric stack control in the form of a draft regulator or damper on the flue pipe to ensure that vacuum or draft at the burner does not exceed a specified amount. This control is automatic and it admits ambient air from the furnace room into the stack when the draft is considered too great and reduces the amount of raw air into the stack as the draft or vacuum on the burner decreases.
Present gas furnaces are provided with secondary air inlets to the combustion chamber and an unrestricted opening in the flue pipe. These presently practiced draft controls are wasteful and unnecessary, since a large percentage of the oxygen `~
in the air that is admitted to the furnace system is not required for the combustion of the fuel. The amount of air to the furnace ¦
burner is preset to give proper combustion.
All heating installations are designed to provide ample heating capacity for maximum requirements to be encountered and the burner, therefore, is only in operation for a small percentage of time for a given period. With the amount of air to the furnace burner being manually preset, it will be appreciated that there is a large loss of heat through the furnace and up the stack when the burner is inoperative.
In order to reduce heat losses in the stack under the above conditions, the position of the flue damper or the primary air inlet valve must be controllable and in accordance with the present invention the opening and closing of the damper or the primary air inlet valve is operated by motor means which is actuated in response to room temperature through a thermostat.
... - 1 - ~ ' ' - -" 103~f~92 The position of the motor output shaft, that is directly related to the damper angle, controls the switch which actuates the furnace burner. Moreover, a delay in closing the damper -or the primary air intake valve after the burner shuts off is included in the control so that purging time is provided to rid the combustion chamber of the furnace and the flue pipe of combustion gases. This purging time can be varied in duration by means of adjustments to suit whatever conditions that are encountered in specific burner installations.
The general concept of furnace damper control is known, U.S. Patent 2,085,912 of July 6, 1936 to J.K. Lencke being one example. However, the Lencke patent discloses the use of a solenoid type of motor to activate the damper, a very abrupt and instantaneous method of operation. While such a method may be acceptable for starting a burner, it does not provide any purging time in closing.
In the present invention I provide an important improvement over the prior art by including means in the control to give a variable "purging" time between the shutdown of the burner and the stopping of the flow of air. The draft control consists basically of a thermostat to actuate an electrical mechanism to open and close the flue damper or primary air inlet valve and a switch responsive to damper positioning to activate the fuel burner. In one embodiment a three wire type thermostat energizes two circuits, the first being closed, with the second open, when calling for heat and the second circuit being closed, with the first open, when heat is not required.
The electrical mechanism such as a small motor to operate the stack damper, or primary air inlet valve is actuated by the thermostat. When the thermostat calls for heat, the motor is energized to open the stack damper or inlet valve and when the second circuit is energized at the time when heat is no longer ;
required, the mechanism closes the stack damper or inlet valve.
- 2 -,:
6~2 The limit switch on the motor output axis closes the circuit to the burner when the damper or air inlet valve is moving to an open position and, conversely, opens the circuit to the burner when the damper or inlet valve is moving to a closed position.
It is important that the flue pipe have a minimum of openings, and no secondary air inlets to the combustion chamber.
The only openings that would be acceptable in the flue pipe are those resulting from the fit of standard galvanized smoke pipe.
In accordance with a broad aspect, the present invention relates to an automatic draft control for furnaces having a burner and a damper in the exhaust stack between the furnace and the chimney or a primary air duct valve to the burner. The draft control effectively interrupts the flow of air through the exhaust stack when the burner is not in operation and it comprises motor means operatively connected to the damper or ~ -primary air duct valve to the combustion chamber for opening and closing the same; a temperature responsive switch to actuate the motor means; switch means responsive to the position of the -damper or the primary air duct valve for actuating the burner; and ~
20 means for providing a delay to a) the actuation of the burner -from the beginning of the opening of the damper or air duct valve and b) the closing of the damper or air duct valve from the stopping of the burner.
The invention is illustrated by way of example in the accompanying drawings wherein:
Figure 1 is a diagrammatic sketch of one embodiment of the mechanism for operating the burner switch responsive to damper or air duct valve position;
Figures 2a and 2b illustrate another embodiment of the burner switch actuating means;
Figures 3a and 3b are schematic views of another means of actuating the burner operating switch;
Figure 4 is an elevation view of a preferred form of ... ,, . , , :. . . - .. . ,: ~ .: :
~1~3669Z
motor used for controlling the position of the damper or the primary air duct valve;
Figures 5a through 6b are side and end elevations respectively of two forms of mounting the burner actuating switch on the motor of Figure 4;
Figure 7 is a schematic wiring diagram of the control system;
Figure 8 is a schematic illustration of the present invention applied to a gas fired, intermittently operated .
furnace, and - Figures 9 and 10 are end and plan views respectively of Figure 9.
As shown in the schematic diagram of Figure 7, a typical home type furnace 1 is provided with a burner 2 and a -draft damper 3. The movement of the damper 3 is operated .~
through interconnection with an electric motor 4 of suitable -~
size and power. I have, for example, successfully used a Minneapolis Honeywell Electric Janitor motor, type M26A, lOJ4, 20 volts, 8 watts, but any equivalent motor will do. Motor 4 is connected to a three wire type thermostat 5 which, as usual, is positioned in the "living" area of the house. Switch means, shown here in the form of a mercury switch 6, is operatively connected to the damper 3 and is electrically connected to the burner 2.
Functionally, the thermostat 5 can energize the two illustrated circuits. The first circuit C-l is closed (with the second circuit C-2 open) when the thermostat 5 calls for heat; ;
and the circuit C-2 is closed lwith C-l open3 when heat is not required. Motor 4 which operates the damper 3 is operated by the thermostat 5 so that a) when the thermostat 5 calls for heat, motor 4 is energized to open the stack damper; b~ when the damper 3 is moving to its open position, the switch means 6 - actuates the burner 2; c) when the thermostat 5 energizes the ~03~i6~
second circuit, when the desired room temperature is reached, the motor burner 2 is shut off when motor 4 moves the stack damper
6~2 The limit switch on the motor output axis closes the circuit to the burner when the damper or air inlet valve is moving to an open position and, conversely, opens the circuit to the burner when the damper or inlet valve is moving to a closed position.
It is important that the flue pipe have a minimum of openings, and no secondary air inlets to the combustion chamber.
The only openings that would be acceptable in the flue pipe are those resulting from the fit of standard galvanized smoke pipe.
In accordance with a broad aspect, the present invention relates to an automatic draft control for furnaces having a burner and a damper in the exhaust stack between the furnace and the chimney or a primary air duct valve to the burner. The draft control effectively interrupts the flow of air through the exhaust stack when the burner is not in operation and it comprises motor means operatively connected to the damper or ~ -primary air duct valve to the combustion chamber for opening and closing the same; a temperature responsive switch to actuate the motor means; switch means responsive to the position of the -damper or the primary air duct valve for actuating the burner; and ~
20 means for providing a delay to a) the actuation of the burner -from the beginning of the opening of the damper or air duct valve and b) the closing of the damper or air duct valve from the stopping of the burner.
The invention is illustrated by way of example in the accompanying drawings wherein:
Figure 1 is a diagrammatic sketch of one embodiment of the mechanism for operating the burner switch responsive to damper or air duct valve position;
Figures 2a and 2b illustrate another embodiment of the burner switch actuating means;
Figures 3a and 3b are schematic views of another means of actuating the burner operating switch;
Figure 4 is an elevation view of a preferred form of ... ,, . , , :. . . - .. . ,: ~ .: :
~1~3669Z
motor used for controlling the position of the damper or the primary air duct valve;
Figures 5a through 6b are side and end elevations respectively of two forms of mounting the burner actuating switch on the motor of Figure 4;
Figure 7 is a schematic wiring diagram of the control system;
Figure 8 is a schematic illustration of the present invention applied to a gas fired, intermittently operated .
furnace, and - Figures 9 and 10 are end and plan views respectively of Figure 9.
As shown in the schematic diagram of Figure 7, a typical home type furnace 1 is provided with a burner 2 and a -draft damper 3. The movement of the damper 3 is operated .~
through interconnection with an electric motor 4 of suitable -~
size and power. I have, for example, successfully used a Minneapolis Honeywell Electric Janitor motor, type M26A, lOJ4, 20 volts, 8 watts, but any equivalent motor will do. Motor 4 is connected to a three wire type thermostat 5 which, as usual, is positioned in the "living" area of the house. Switch means, shown here in the form of a mercury switch 6, is operatively connected to the damper 3 and is electrically connected to the burner 2.
Functionally, the thermostat 5 can energize the two illustrated circuits. The first circuit C-l is closed (with the second circuit C-2 open) when the thermostat 5 calls for heat; ;
and the circuit C-2 is closed lwith C-l open3 when heat is not required. Motor 4 which operates the damper 3 is operated by the thermostat 5 so that a) when the thermostat 5 calls for heat, motor 4 is energized to open the stack damper; b~ when the damper 3 is moving to its open position, the switch means 6 - actuates the burner 2; c) when the thermostat 5 energizes the ~03~i6~
second circuit, when the desired room temperature is reached, the motor burner 2 is shut off when motor 4 moves the stack damper
3 towards its closed position. It is important to appreciate - that, following the shut-off of the burner 2, the action of the motor 4 provides a delay in closing the damper 3 so as to give ample time for purging of gases up the stack from the combustion chamber of the furnace 1.
Referring now to Figure 1 there is schematically shown one form of mounting and operating the burner switch 6 by means Of a single cam 7.
The mercury switch 6 is securely positioned in a frame 1~ which is pivotally mounted at 12. Frame 10 is oscillated by means of a pin 14 on its lower end being engaged by a yoke 16 on one end of a bell crank 18. The latter is pivotally mounted at 20 and, at its other end, is provided with a cam -~
follower 22. As shown, the follower end of the bell crank 18 may be held in contact with the cam 7 by means of a spring 24 1 connected at one end to the crank 18 and at the other end to a I
stationary point 26.
Cam 7 is attached, for example, to a flange 28 on the ; output shaft 30 of motor 4, not shown. By using a single cam 7 as illustrated, only one setting could be selected for purging purposes. By example, the line X-Y in Figure 1 represents the position of the output shaft 30 when the damper 3 is in a fully closed position. Cam 7 would permit an angular movement of the damper shaft equal to angle X 0 B before the follower 22 dropped into the cam profile to cause ignition of the burner.
Likewise, after the burner 2 is shut off, the cam 7 would permit an angular movement equal to C 0 Y of the damper for purging purposes before closing of the damper. The "shaded" --areas on the cam 7 represent portions which could be removed to alter the timing of the unit, i.e. to give angle X 0 A as the dwell before ignition of the burner from the closed position of ;~
.
~3~692 the damper 3 and the dwell for purging would be reduced to angle Y 0 D.
In Figures 2a and 2b a pair of symmetrical cam plates 32, 34 provide a variable type of profile. In Figure 2a the discs or plates are shown in a position to give the maximum amount of time that the burner 2 can be operated during the period when the damper is moving from a completely closed to a completely open position. Accordingly this would be equal to 150 of the angular movement of the damper 3 thereby leaving 15 for partial opening of the damper before the burner starts and 15 for the damper 3 to be partially open when the burner 2 shuts off, for purging purposes. In Figure 2b, the two plates 32, 34 have been moved relative to one another to give only 90 of the angular movement of the damper shaft for the burner 2 to be operating, leaving 45 on either end of the cycle for opening the damper for accepting products of combustion or for closing the damper for purging time. It will be appreciated that any position between the above extremes would be available simply by altering the relative positions of the discs 32, 34 which can be releasably secured together by various known means.
Figures 3a and 3b illustrate another embodiment of actuating the mercury switch 6. As shown in Figure 3b the motor
Referring now to Figure 1 there is schematically shown one form of mounting and operating the burner switch 6 by means Of a single cam 7.
The mercury switch 6 is securely positioned in a frame 1~ which is pivotally mounted at 12. Frame 10 is oscillated by means of a pin 14 on its lower end being engaged by a yoke 16 on one end of a bell crank 18. The latter is pivotally mounted at 20 and, at its other end, is provided with a cam -~
follower 22. As shown, the follower end of the bell crank 18 may be held in contact with the cam 7 by means of a spring 24 1 connected at one end to the crank 18 and at the other end to a I
stationary point 26.
Cam 7 is attached, for example, to a flange 28 on the ; output shaft 30 of motor 4, not shown. By using a single cam 7 as illustrated, only one setting could be selected for purging purposes. By example, the line X-Y in Figure 1 represents the position of the output shaft 30 when the damper 3 is in a fully closed position. Cam 7 would permit an angular movement of the damper shaft equal to angle X 0 B before the follower 22 dropped into the cam profile to cause ignition of the burner.
Likewise, after the burner 2 is shut off, the cam 7 would permit an angular movement equal to C 0 Y of the damper for purging purposes before closing of the damper. The "shaded" --areas on the cam 7 represent portions which could be removed to alter the timing of the unit, i.e. to give angle X 0 A as the dwell before ignition of the burner from the closed position of ;~
.
~3~692 the damper 3 and the dwell for purging would be reduced to angle Y 0 D.
In Figures 2a and 2b a pair of symmetrical cam plates 32, 34 provide a variable type of profile. In Figure 2a the discs or plates are shown in a position to give the maximum amount of time that the burner 2 can be operated during the period when the damper is moving from a completely closed to a completely open position. Accordingly this would be equal to 150 of the angular movement of the damper 3 thereby leaving 15 for partial opening of the damper before the burner starts and 15 for the damper 3 to be partially open when the burner 2 shuts off, for purging purposes. In Figure 2b, the two plates 32, 34 have been moved relative to one another to give only 90 of the angular movement of the damper shaft for the burner 2 to be operating, leaving 45 on either end of the cycle for opening the damper for accepting products of combustion or for closing the damper for purging time. It will be appreciated that any position between the above extremes would be available simply by altering the relative positions of the discs 32, 34 which can be releasably secured together by various known means.
Figures 3a and 3b illustrate another embodiment of actuating the mercury switch 6. As shown in Figure 3b the motor
4 has extensions to either end of its output shaft 30. On one end, the mercury switch 6 is mounted in a T-shaped frame 36 which is pivotally mounted at 38, the free end of the frame being pivotally connected at 40 to one end of an adjustable length connecting rod 42 which has its other end pivotally connected at 43 to a crank 44 mounted on the output shaft 30. As seen in Figure 3a, the other end of shaft 30 is provided with a slotted crank 46 interconnected with the damper 3 through a rod 48 and slotted damper arm 50. It will be observed that the length of time that the burner 2 is in operation during the period that the damper 3 takes to move from a closed to an open position, .
can be altered to suit any conditions that may be encountered ¦-in practice merely by changing the length of the connecting -:
rod 42.
..
Another, preferred embodiment of the invention is ¦
shown in Figures 4 through 6b, where a reversing type motor is ¦
used which will rotate in opposite directions when energized ¦~
by the two separate circuits C-l or C-2 from the thermostat 5.
In Figure 4, the motor 52 has an output shaft which is connected at one of its ends 54 to the damper 3 by means of a crank arm ¦ ~ -~
10 and connecting rod similar to 46, 48 of Figure 3a. The mercury switch 6 is mounted on the other, auxiliary end 56 of the output ¦
shaft by way of a spring clip 58 which is attached to a collar -;~
60 that, in turn, is secured on the end 56 of the shaft by set screws 62 or the like. Another form of securing the switch 6 to the motor shaft is shown in Figures 6a and 6b wherein a pair of half collars 64, 66 are secured onto the shaft 56 by bolts 68 which also retain a pair of clips 72 securely holding the switch 6 therebetween.
In this embodiment, the stroke or angular movement 20 of the output shaft 54 would be about 90 and the time to move through this angle should be about 15 seconds. This will provide ample time for purging the combustion chamber and to place the damper 3 in a sufficiently open position when the burner is ignited. It will be noted from a comparison of Figure 3a and I `
Figure 5b that, when a reversing type motor is used, the , activating mechanism for the mercury switch controlling the operation of the burner 2 is substantially simplified.
The present invention is applicable also to gas fired intermittently operated furnaces wherein the control of the -~
30 invention is applied to the air supplied to the burner. By virtue of the fact that most gas fired furnaces require the use of a pilot flame instead of a high tension spark as in the case of an oil fired furnace, combustion gases are being created all of ~3~692 .
I the time that the furnace is in operation and therefore one cannot restrict the combustion gases through the flue pipe.
In a gas fired furnace utilizing my invention, the flue pipe from the furnace to the chimney should be as airtight as possible and all secondary inlets to the combustion chamber should be eliminated. An opening to the combustion chamber should be provided to permit visual inspection of the flame and manual purging when required. This opening should be closed -, by means of a door seated against the outside frame of the furnace and hinged from the top.
In Figure 8, a gas fired, intermittently operated furnace 74 has a service door 76 and a primary air duct 78 -with a movable valve 80 therein, associated with a main gas pipe 82 feeding a nozzle 84.
It will be appreciàted that the air requirements for the pilot flame are extremely small and, as shown in Figure 8, ¦~
this air can be supplied via a duct 87 of small diameter through which the tube 86 supplying the fuel to the pilot is ` located and that discharges beneath and uniformly around the pilot light. This duct 87 is open at all times when the furnace is operating and, to insure this, the valve 88 controlling the duct 86 should be interlocked with the main electrical supply to the furnace. The primary duct 78 which supplies air to the main burner of the furnace is equipped with a valve 80 to be operated in the same manner as the flue damper control described with regard to Figures 4-6b.
Accordingly, a motor 90 is connected to the valve 80 by means of a slotted crank 92 mounted on one end 94 of the motor output shaft and an adjustable connecting rod 96. A mercury switch 98 is mounted on the other end of the motor output shaft .~. ~. .
in the same manner as figures 4 through 6b for operating the burner.
It will be appreciated that whether the invention is -- ,' . . , -.
lV3fj6~Z , ~
used on an oil fired or gas fired furnace, the principle of the invention is to control the amount of air going through ` the furnace when the burner is not operating. Therefore, the f terms and expressions that have been used in the abstract and .
disclosure have been used as descriptive terms and not terms of limitation and there is no intention in the use of such ~-~
terms or expressions to exclude any equivalents of the features shown and described or portions thereof but it is recognized :
that various modifications are possible within the scope of the invention claimed. :
!: ~
, - . . .. ..
-:
: -
can be altered to suit any conditions that may be encountered ¦-in practice merely by changing the length of the connecting -:
rod 42.
..
Another, preferred embodiment of the invention is ¦
shown in Figures 4 through 6b, where a reversing type motor is ¦
used which will rotate in opposite directions when energized ¦~
by the two separate circuits C-l or C-2 from the thermostat 5.
In Figure 4, the motor 52 has an output shaft which is connected at one of its ends 54 to the damper 3 by means of a crank arm ¦ ~ -~
10 and connecting rod similar to 46, 48 of Figure 3a. The mercury switch 6 is mounted on the other, auxiliary end 56 of the output ¦
shaft by way of a spring clip 58 which is attached to a collar -;~
60 that, in turn, is secured on the end 56 of the shaft by set screws 62 or the like. Another form of securing the switch 6 to the motor shaft is shown in Figures 6a and 6b wherein a pair of half collars 64, 66 are secured onto the shaft 56 by bolts 68 which also retain a pair of clips 72 securely holding the switch 6 therebetween.
In this embodiment, the stroke or angular movement 20 of the output shaft 54 would be about 90 and the time to move through this angle should be about 15 seconds. This will provide ample time for purging the combustion chamber and to place the damper 3 in a sufficiently open position when the burner is ignited. It will be noted from a comparison of Figure 3a and I `
Figure 5b that, when a reversing type motor is used, the , activating mechanism for the mercury switch controlling the operation of the burner 2 is substantially simplified.
The present invention is applicable also to gas fired intermittently operated furnaces wherein the control of the -~
30 invention is applied to the air supplied to the burner. By virtue of the fact that most gas fired furnaces require the use of a pilot flame instead of a high tension spark as in the case of an oil fired furnace, combustion gases are being created all of ~3~692 .
I the time that the furnace is in operation and therefore one cannot restrict the combustion gases through the flue pipe.
In a gas fired furnace utilizing my invention, the flue pipe from the furnace to the chimney should be as airtight as possible and all secondary inlets to the combustion chamber should be eliminated. An opening to the combustion chamber should be provided to permit visual inspection of the flame and manual purging when required. This opening should be closed -, by means of a door seated against the outside frame of the furnace and hinged from the top.
In Figure 8, a gas fired, intermittently operated furnace 74 has a service door 76 and a primary air duct 78 -with a movable valve 80 therein, associated with a main gas pipe 82 feeding a nozzle 84.
It will be appreciàted that the air requirements for the pilot flame are extremely small and, as shown in Figure 8, ¦~
this air can be supplied via a duct 87 of small diameter through which the tube 86 supplying the fuel to the pilot is ` located and that discharges beneath and uniformly around the pilot light. This duct 87 is open at all times when the furnace is operating and, to insure this, the valve 88 controlling the duct 86 should be interlocked with the main electrical supply to the furnace. The primary duct 78 which supplies air to the main burner of the furnace is equipped with a valve 80 to be operated in the same manner as the flue damper control described with regard to Figures 4-6b.
Accordingly, a motor 90 is connected to the valve 80 by means of a slotted crank 92 mounted on one end 94 of the motor output shaft and an adjustable connecting rod 96. A mercury switch 98 is mounted on the other end of the motor output shaft .~. ~. .
in the same manner as figures 4 through 6b for operating the burner.
It will be appreciated that whether the invention is -- ,' . . , -.
lV3fj6~Z , ~
used on an oil fired or gas fired furnace, the principle of the invention is to control the amount of air going through ` the furnace when the burner is not operating. Therefore, the f terms and expressions that have been used in the abstract and .
disclosure have been used as descriptive terms and not terms of limitation and there is no intention in the use of such ~-~
terms or expressions to exclude any equivalents of the features shown and described or portions thereof but it is recognized :
that various modifications are possible within the scope of the invention claimed. :
!: ~
, - . . .. ..
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: -
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A positive automatic draft control for intermittently operated furnaces, comprising apparatus for interrupting the flow of air through to the exhaust stack when the burner is not in operation, said apparatus comprising motor means operatively connected to an air valve of the furnace for opening and closing the same; a temperature responsive switch to actuate said motor means; switch means, responsive to the position of the air valve, for actuating said burner; and means interconnecting the motor means with the burner actuating switch for providing a delay to the actuation of the burner from the beginning of the opening of the valve and to the closing of the valve from the stopping of the burner.
2. An automatic draft control according to claim 1 wherein said furnace is oil fired and the air valve comprises a damper in the exhaust stack between the furnace and the chimney.
3. An automatic draft control according to claim 1 wherein the furnace is gas fired and the air valve comprises a shutter in the primary air duct to the combustion chamber of the furnace.
4. A draft control according to claim 1, 2 or 3 wherein the temperature responsive switch is a thermostat and the switch means for actuating said burner is a mercury switch operatively connected to the air valve motor means whereby the burner is ignited after the valve has partially opened and is shut off prior to closure of the valve.
5. A draft control according to claims 1, 2 or 3 wherein the means interconnecting the motor means with the burner actuating switch includes a profiled cam on said motor means and a cam follower operatively connecting the cam with said burner actuating switch.
6. A draft control according to claims 1, 2 or 3 wherein the means interconnecting the motor means with the burner actuating switch comprises crank means mounted on the output shaft of said motor, and an adjustable length rod connecting said crank with the valve; the burner actuating switch being operable in response to predetermined movement of the motor output shaft.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA220,539A CA1036692A (en) | 1975-02-21 | 1975-02-21 | Positive automatic draft control |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA220,539A CA1036692A (en) | 1975-02-21 | 1975-02-21 | Positive automatic draft control |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1036692A true CA1036692A (en) | 1978-08-15 |
Family
ID=4102337
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA220,539A Expired CA1036692A (en) | 1975-02-21 | 1975-02-21 | Positive automatic draft control |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1036692A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4867106A (en) * | 1985-06-07 | 1989-09-19 | Bradford White Corporation | Direct power vented water heater |
| US5199385A (en) * | 1992-03-24 | 1993-04-06 | Bradford-White Corp. | Through the wall vented water heater |
-
1975
- 1975-02-21 CA CA220,539A patent/CA1036692A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4867106A (en) * | 1985-06-07 | 1989-09-19 | Bradford White Corporation | Direct power vented water heater |
| USRE34534E (en) * | 1985-06-07 | 1994-02-08 | Bradford-White Corporation | Direct power vented water heater |
| US5199385A (en) * | 1992-03-24 | 1993-04-06 | Bradford-White Corp. | Through the wall vented water heater |
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