U.S. patent number RE30,936 [Application Number 06/208,957] was granted by the patent office on 1982-05-18 for safety control for furnace burner.
This patent grant is currently assigned to Scotty Vent Dampers, Inc.. Invention is credited to George E. Joumas, Edward R. Kmetz.
United States Patent |
RE30,936 |
Kmetz , et al. |
May 18, 1982 |
Safety control for furnace burner
Abstract
A burner cut-out safety control for a combustion heating device
having an automatic exhaust flue damper. The safety controls act to
discontinue burner operation in the event the damper actuator
device or controls fail, or other flue blockage causes products of
combustion to be exhausted through the draft diverter inlet
opening. The control is integrated with an existing burner pilot
safety circuit and pilot valve to cause the pilot valve to be
closed in the event combustion gases begin to pass out of the flue
through the draft diverter inlet opening, this condition being
detected by a lineal temperature sensor extending about the draft
diverter inlet opening, which senses combustion gas spillage by the
resultant heating of any portion of the lineal temperature sensor.
The lineal temperature sensor is placed in series with the pilot
burner ignition temperature sensor to cause closing of the pilot
valve, located ahead of the main gas valve activated by the burner
controls during normal automatic operation of the burner. The fuel
supply is thus cut off even if the main gas valve fails. A second
temperature sensor is located in the plenum of the warm air ducting
as a secondary safety control feature also acting to cause the
pilot valve to close in the event of an excessive temperature being
sensed in the warm air plenum.
Inventors: |
Kmetz; Edward R. (Grosse Point
Park, MI), Joumas; George E. (St. Clair Shore, MI) |
Assignee: |
Scotty Vent Dampers, Inc.
(Hazel Park, MI)
|
Family
ID: |
26903688 |
Appl.
No.: |
06/208,957 |
Filed: |
November 21, 1980 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
875328 |
Feb 6, 1978 |
04204833 |
May 27, 1980 |
|
|
Current U.S.
Class: |
431/22; 431/20;
236/1G |
Current CPC
Class: |
F23N
5/245 (20130101); F23N 1/065 (20130101); F23N
2235/04 (20200101); F23N 5/10 (20130101); F23N
2227/22 (20200101); F23N 2225/08 (20200101); F23N
2229/00 (20200101); F23N 2225/10 (20200101) |
Current International
Class: |
F23N
1/06 (20060101); F23N 1/00 (20060101); F23N
5/24 (20060101); F23N 5/02 (20060101); F23N
5/10 (20060101); F23N 005/24 () |
Field of
Search: |
;431/16,20,21,22
;126/116A,116R,11R,312 ;236/1G,15BB,9R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Dority, Jr.; Carroll B.
Assistant Examiner: Barrett; Lee E.
Attorney, Agent or Firm: Benefiel; John R.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. In combination, a safety control arrangement and a combustion
heating device of the type having a burner ignition safety circuit
detecting ignition of the fuels burned within the combustion
chamber of the heating device, the combustion heating device
further having an exhaust vent means for exhausting the products of
combustion of said combustion chamber, said exhaust means including
a draft opening having an inlet to induct air into said exhaust
means, said safety control arrangement comprising:
a temperature sensor located in said draft opening inlet,
comprising a lineal sensor consisting of a sensor tube extending
about said inlet to sense spillage of combustion gases therethrough
at any point along the periphery of said inlet;
control means responsive to the sensing of an abnormal temperature
condition by said temperature sensor in the exhaust vent means
causing said burner ignition safety circuit of said heating device
to be activated;
whereby said burner ignition safety circuit also acts as a safety
shutdown of burner operation in the event an abnormal temperature
condition develops in said exhaust vent means.
2. The safety control arrangement according to claim 1 wherein said
burner ignition safety circuit arrangement comprises a thermocouple
heated by combustion of said fuel and wherein said burner ignition
safety circuit further includes a pilot burner adapted to ignite
said burner, wherein said thermocouple is positioned to be heated
by ignition of said pilot burner and wherein said voltage generated
by said thermocouple operates said burner ignition safety
circuit.
3. The safety control arrangement according to claim 2 wherein said
burner ignition safety circuit further includes a pilot control
valve and further including a pilot valve hold-in coil and wherein
said safety control includes means for impressing said thermocouple
voltage on said hold-in coil, said pilot valve being manually
operable to be held open while said burner is ignited and said
thermocouple voltage serves to hold said pilot burner, and wherein
said safety control arrangement includes means interposing said
temperature sensor in series in said thermocouple circuit so as to
interrupt said thermocouple hold-in coil circuit upon sensing of
said abnormal temperature condition.
4. The safety control arrangement according to claim 1 wherein said
combustion heating device further includes a damper mounted in said
exhaust vent means, said damper including a damper disc movable
between an open and closed position, and further including a damper
actuator and control means associated with said combustion heating
device causing said damper disc to be opened whenever said burner
is in operation and said damper actuator to be closed whenever said
burner is not in operation, whereby said safety control arrangement
precludes burner operation with said damper disc closed.
5. The safety control arrangement according to claim 1 wherein said
combustion heating device further includes a main valve and a
burner control circuit causing automatic operation of said main
valve to control said burner operation, and further including a
pilot burner position to cause ignition of said burner and also a
pilot valve located upstream of said main valve and wherein said
burner ignition safety circuit includes means for closing said
pilot valve in the event said pilot burner is not ignited, and
wherein said control means includes means responsive to sensing of
an abnormal temperature condition by said temperature sensor to
cause said pilot control valve to be closed.
6. The safety control arrangement according to claim 5 wherein said
burner ignition safety circuit further includes a thermocouple
located with respect to said pilot burner to be heated thereby and
wherein said means for causing pilot valves to be closed includes
an electrical circuit comprised of said thermocouple and a hold-in
coil operatively associated with said pilot valve to hold said
pilot valve in the open position whenever said thermocouple is
heated by said pilot burner, and wherein said safety control
arrangement includes means interposing said temperature sensor in
said circuit connecting said thermocouple and said pilot burner
hold-in coil so as to cause said circuit to be interrupted upon
sensing of said abnormal temperature conditions.
7. The safety control arrangement according to claim 1 wherein said
combustion heating device comprises a warm air furnace, said
furnace including heat exchanger means adapted to be heated by said
burner operation, said furnace further including means for
circulating air over said heat exchanger to be heated thereby and
also including a warm air plenum chamber receiving said air after
being circulated over said heat exchanger means, the safety control
arrangement further including a plenum temperature sensor located
in said warm air plenum and means responsive to the development of
an abnormally high temperature condition sensed by said temperature
sensor in said plenum chamber to cause said burner ignition safety
circuit of said furnace to be activated, whereby said burner
ignition safety circuit further acts as a safety to shut down
burner operation upon development of an abnormally high temperature
condition in said warm air plenum.
8. A safety control arrangement for a combustion heating device of
the type having a combustion chamber, a burner disposed therein,
fuel feed means supplying fuel to said burner and an exhaust vent
means venting said combustion chamber, said exhaust vent means
including a draft opening having an inlet for inducting air into
said exhaust vent opening, said arrangement comprising:
a lineal temperature sensor located in said exhaust vent means
consisting of a sensor tube extending about said draft opening
inlet sensing gas spillage at any point along said inlet;
means responsive to the sensing of an abnormal temperature
condition by said temperature sensor at said draft opening to cause
said fuel feed means to shut off fuel flow to said burner;
whereby said burner acts as producing a shutdown of burner
operation in the event an abnormal temperature condition develops
in said exhaust vent means. .Iadd. 9. A safety control arrangement
for a combustion heating device of the type having a combustion
chamber, a burner disposed therein, fuel feed means controllably
supplying fuel to said burner, an exhaust vent means venting said
combustion chamber to the atmosphere, and said device including an
inlet opening for inducting ambient air, said inlet in fluid
communication with said exhaust vent means so as to be subject to
outflow of the products of combustion from interruption of flow
through said exhaust vent means, said arrangement comprising:
lineal temperature sensor means located to sense outflow of
combustion products through said air inlet opening, said means
including a sensor tube extending about said inlet opening so as to
sense outflow of said combustion products at any point through said
inlet opening, said sensor tube including means responsive to being
heated to a predetermined elevated temperature corresponding to
contact with said outflow of products of combustion at any location
along its length to generate a control signal;
control means responsive to said sensing of an abnormal temperature
condition by said sensor tube at said inlet opening and generation
of said control signal causing said fuel feed means to shut off
fuel flow to said burner;
whereby said control means acts to produce shutdown of burner
operation in the event of any blockage of said exhaust vent means
causing outflow of combustion products through said inlet opening.
.Iaddend.
Description
BACKGROUND DISCUSSION
With the recent dramatic increases in the cost of heating fuels,
particularly oil and gas, there has been increasing use of devices
and design arrangements for increasing the efficiency of combustion
heating devices such as oil and gas-fired furnaces or boilers.
Such combustion heating devices include an arrangement for
exhausting the products of combustion to the exterior of the
building by way of an exhaust or stack flue duct in communication
with the combustion chamber within which the burners are located.
In order to improve the draft of such exhaust ducts, there is
normally incorporated a diverter hood which serves to mix room air
with the exhaust gases to produce sufficient volume to get proper
flow through the exhaust flue ducting. The exhaust flue thus allows
the loss of warm air whenever the burner is not in operation by
virtue of the rapid cooling of the combustion chamber and the heat
exchanger structure, such that the stored heat is lost to the
outside. In addition, without the exhaust gases flowing into the
exhaust ducting, backdrafts into the building through the draft
diverter inlet may occur, as well as a loss of relatively warm room
air through the draft diverter opening.
Accordingly, automatic damper devices have been devised and
utilized which serve to automatically close the exhaust flue
ducting when the burner is not in operation. Such devices are
activated with the burner control such as to insure that the burner
is only operated when the damper device is opened. Reference is
made to U.S. Pat. No. 4,039,123 as typical of these devices.
The incorporation of such an automatic flue damper device presents
a safety hazard since in the event of a failure in the system
resulting in continuing burner operation with the damper actuator
in the closed position, the products of combustion tend to spill
into the confined space within the building via the draft diverter
opening, presenting a hazard to the occupants of the building. The
actuator controls are designed to be fail-safe in that the
thermostat signal first causes the actuator device to be moved to
the open position and then, upon movement of the damper to the open
position, an end switch or other similar device is closed to enable
burner operation. This enablement is by activating the main valve
typically associated with the combustion device burner allowing the
oil or gas to be delivered to the burner. In the event of a
component failure, such as the main valve being stuck in the open
position or other failure, operation of the burner may continue
even though the controls call for the burner to be shut off.
Thus, such devices sometimes include a thermostatically operated
safety switch in the exhaust stack or draft diverter to sense the
resultant high temperature condition existing in the exhaust
ducting.
The arrangement described in U.S. Pat. No. 4,039,123 includes a
thermostatic switch to interrupt the energization of the automatic
flue damper motor which allows a spring to open the damper.
However, this still allows continued operation of the burner, and
the stuck main gas valve or other failure would not promptly come
to the attention of those operating or observing operation of the
furnace.
In addition, the opening of the damper cools the switch upon
allowing reenergization of the damper motor such that a cycling of
the actuator could take place all while the failure of the main gas
valve goes undetected.
Temperature sensors associated with the exhaust flue ducting and
hence the draft diverter inlet opening present difficulties even
though the diverter opening is theoretically a good location to
sense blockage of the flue damper and abnormally high temperatures
inasmuch as the spillage of combustion gases provides a rapidly
developed high temperature condition.
However, the flow pattern through the diverter opening of such
combustion gases due to the relatively low volume of combustion
gases relative to the volume of inducted air is such that the flow
of exhaust gases will not be evenly distributed across the opening
of the draft diverter. That is to say, the high temperature
condition may be localized at some portion of the draft diverter
openings. Accordingly, a sensor which is discretely located at a
point within the opening must be located at the particular region
whereat the combustion gases tend to exit. This requires tedious
flow testing of the system at installation, requiring a skilled
service technician to carry it out.
Another condition which may occur due to power failure or other
malfunction is the operation of the burners without the air
circulation blower being in operation. This causes overheating of
the heat exchanger and excessive furnace temperatures. While
combustion chamber temperature conditions have been sensed in prior
art safety control arrangements, it is difficult to design sensor
components to reliably distinguish between normal and abnormal
temperature conditions.
While warm air plenum located sensors have been utilized in the
past to detect this condition in a more reliable manner, they have
relied on shutdown of the main gas valve to correct the situation.
In some cases, the main gas valve failure is the cause of the
problem and prevents correction of the condition.
It is therefore an object of the present invention to provide a
safety control arrangement for combustion heating devices which
insure that burner operation will be discontinued in the event of a
component failure or other occurrence which results in burner
operation with a blocked flue duct such as automatic flue dampers
being in the closed position during burner operation.
It is yet another object of the present invention to provide a
safety control incorporating a temperature sensor located in the
draft diverter inlet opening which does not require complicated
testing to determine the proper sensor location.
It is yet another object of the present invention to provide such a
safety control arrangement in which the controls may be readily
incorporated in the existing burner control circuits without major
modifications such that the costs and difficulty of adding the
control circuits to such designs is minimized.
It is a further object of the present invention to provide a safety
control arrangement for reliably detecting a combustion chamber
overheating condition and causing shutdown of burner operation.
SUMMARY OF THE INVENTION
These and other objects of the present invention, which will become
apparent upon a reading of the following specification and claims,
are accomplished by a safety control which is integrated into the
existing pilot safety control circuit such as to prevent fuel
delivery to the main control valve in the event an abnormally high
temperature is sensed in the draft diverter inlet opening. The
safety control arrangement includes a lineal temperature sensor
tube which extends entirely about the draft diverter inlet opening
with any portion of the tube heated to a predetermined temperature
corresponding to abnormal system operation of the burner with the
stack damper closed or the flue blocked. This causes interruption
of the pilot safety control circuit to close the pilot valve,
precluding further burner operation. The safety control may be
integrated into low voltage-thermocouple pilot safety circuits by
placing the lineal temperature sensor in series with the
thermocouple sensing pilot ignition, or alternatively the lineal
temperature sensor may be interposed into intermittently operated
pilot control circuits, to cause the pilot safety valve to be
closed upon detection of the abnormal temperature condition.
A warm air plenum temperature sensor is also incorporated into the
safety control as a further safety measure.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified diagrammatic representation of a typical
combustion device together with the exhaust flue damper actuator
and controls therefor and illustrating in diagrammatic form the
safety control system arrangement according to the present
invention.
FIG. 2 is a circuit diagram of the furnace controls associated with
the actuator device.
FIG. 3 is a diagrammatic representation of the safety controls
according to the present invention associated with the main gas
valve of a gas-fired combustion heating device.
FIG. 4 is a perspective view of the installation of a lineal
temperature sensor into the inlet opening of the draft diverter
section of exhaust flue ducting.
DETAILED DESCRIPTION
In the following detailed description, certain specific terminology
will be utilized for the sake of clarity and a particular
embodiment described in accordance with the requirements of 35 USC
112, but it is to be understood that the same is not intended to be
limiting and should not be so construed inasmuch as the invention
is capable of taking many forms and variations within the scope of
the appended claims.
In the following detailed description, the particular application
of the invention described will be of a gas-fired, forced-air
furnace and is a typical application of the present invention.
However, it is to be understood that other combustion heating
devices may also utilize the arrangement of the present invention,
such as oil-fired furnaces or boilers.
In addition, a particular type of pilot safety typical of
present-day gas furnace designs is described in combination with
the safety controls according to the present invention.
In this type of safety control, the pilot is lit and remains
continuously lit. In the event the pilot becomes extinguished or
fails to be lit, a thermocouple sensor is positioned with respect
to the pilot flame to sense pilot ignition which causes a pilot
safety valve to be closed in the event the pilot becomes
extinguished or fails to be lit.
In these designs, there is typically incorporated a low energy or
millivolt circuit in which a millivoltage generated by the
thermocouple is used to operate a pilot hold-in coil. In the
presence of the millivoltage impressed on the hold-in coil, a pilot
valving member is held in the open position to allow gas flow to
the main gas valve which is operated by the burner controls as
heating is required.
Alternatively, however, there are currently being adopted
intermittently operated gas pilot circuits which do not incorporate
such a millivoltage or low energy circuit in order to operate the
pilot safety valve, but rather are integrated and operated by the
normal low voltage (24 volt) control system used in the thermostat
circuit. It should be understood that the present safety control
system is applicable to such 24 volt pilot safety circuits and to
other safety controls associated with oil-fired combustion
devices.
Referring to FIG. 1, the application to a gas furnace 10 is
depicted in diagrammatic form. The gas furnace 10 includes a
combustion chamber 12 within which is disposed gas burner 14. The
burning within the combustion chamber 12 heats the combustion
chamber 12 and associated air heat exchanger firepot 13, around
which is circulated the air to be heated by a blower 16 which
passes about the combustion chamber 12 and into the warm air plenum
18 and thence is distributed through the warm air ducting system to
the areas to be heated.
The combustion chamber 12 is connected to the outside via exhaust
ducting means generally represented at 20 in communication with the
combustion chamber 12. The gas burner 14 is supplied with gas via a
pipe connection 22 which is supplied via a combination gas valve 24
which serves to supply gas to the burner 14. When open, the
combination gas valve 24 allows gas received from a supply pipe 26
to flow to the burner 14.
The pilot supply tube 28 is provided, which supplies a pilot burner
30 disposed opposite the jets of the burner 14 such as to cause
ignition of the gas supplied to the burner 14 whenever the pilot
nozzle is lit and gas supplied via combination gas valve 24.
The exhaust ducting means 20 includes a diverter section 32 which
has an inlet 34 which mixes room air into the products of
combustion flowing out through the exhaust ducting means 20. The
exhaust ducting means 20 further includes a stack section 36 within
which is disposed an automatically-operated damper assembly 38,
which is movable between the open and closed positions to either
open the exhaust ducting means 20 to a vent position, or to close
the damper disc 40 to seal off communication with the exhaust stack
and the outside, preventing backdrafts and the escape of room air
and the heated air present within the combustion chamber 12, after
the exhaust gases have passed out through the exhaust stack 36.
The damper disc 40 is operated by means of a damper actuator
mechanism 42 which in turn is controlled as is the combination gas
valve 24 by the operation of a burner control circuit 44. The
burner control circuit 44 operates to control the combination gas
valve 24 such that when a room thermostat 46 signals a demand for
heat, i.e., burner operation, a signal is generated which causes
actuation of the damper actuator mechanism 42 to rotate the motor
to the disc open position.
Upon achieving the open position, an end switch 47 associated with
the damper actuator mechanism 42 enables a control signal to be
transmitted to the combination gas valve 24 such as to permit gas
flow to the burner 14.
This operation occurs assuming that the pilot 30 is properly
ignited since there is provided a pilot ignition safety circuit in
the system including a thermocouple 48 which senses the high
temperature heated by the pilot flame. The pilot flame generates a
millivoltage which is impressed on a pilot valve hold-in coil
included within the combination gas valve 24 which permits gas flow
to pass through the pilot valve within the combination gas valve 24
to the main gas valve portion controlled by the burner control
circuit 44.
Upon the thermostat 46 contacts opening due to achievement of the
proper room temperature, the burner control circuit 44 causes the
damper actuator mechanism 42 to rotate damper disc 40 from the full
open position which causes opening of the end switch 47 and closes
the main gas valve portion of the combination gas valve 24 causing
the burner 14 to cease operation.
This portion of the burner control circuit is shown in FIG. 2 in
which the 24 volt control voltage generated by the transformer 50
is applied to the damper actuator motor 54 via the motor relay
which controls the movement of the damper actuator mechanism 42 to
either the open or closed position.
The movement of the damper actuator mechanism 42 to the open
position closes an end switch 47 which in turn allows the control
voltage to be applied to the combination gas valve 24 to thus
enable burner operation. Upon opening of the thermostat 46 contacts
to the actuator motor 54, it causes the damper actuator mechanism
42 to be rotated to the closed position which opens the end switch
47 and thus discontinues operation of the burner 14 by closing of
the combination valve.
Referring again to FIG. 1, the safety controls according to the
present invention include the provision of a lineal temperature
sensor 56 located within the draft diverter inlet 34. The lineal
temperature sensor 56 is placed in series with the pilot
thermocouple sensor 48 which in turn serves to control the pilot
valve as noted, contained within the combination gas valve 24. When
the circuit is interrupted by the lineal temperature sensor 56 upon
reaching a predetermined temperature, the generated voltage of the
thermocouple 48 can no longer act on the pilot valve hold-in coil
and causes this valve to shut down and discontinue further burner
operation, whether or not the main gas valve is opened or
closed.
In addition, a second discrete location temperature sensor such as
a snap disc temperature sensor 58 is located in the warm air plenum
18 and senses the abnormally high temperatures in the plenum (i.e.,
190.degree. F.) caused by overheating of the unit and the resultant
unsafe condition. This sensor 58 is also placed in series with the
pilot safety control millivolt circuit as shown in FIG. 1, to cause
closing of the pilot valve upon an abnormal temperature developing
in either the plenum 18 or at the diverter inlet 34.
Details of the safety control arrangement in relationship with the
combination gas valve 24 are indicated in FIG. 3.
A combination gas valve 24 of a commercially available
configuration is depicted in partial section in FIG. 3. Such a CGV
valve 24 has its inlet connected to the gas supply line 26 and its
outlet to the burner supply line 22. Such a combination gas valve
typically includes a pilot valve section 60 which is upstream from
the main gas valve 62, controlled by the burner control circuit
44.
The pilot valve 60 includes a valve disc 64 adapted to be seated
and unseated on a valve seat 66 to control gas flow therethrough.
The valve disc 64 position in turn is controlled by a valve lever
68 pivotally supported intermediate its length with its opposite
end to the end which supports the valve disc 64 engaged by a valve
opening spring 70 and a valve closing spring 72. The valve closing
spring 72 is adapted to be overcome by movement of a plunger 74
which acts to compress the closing spring 72 by a collar 76
movement to the compressed position being achieved manually when
the pilot is lit.
The holding of the plunger 74 in its compressing position is
carried out by a pilot valve hold-in coil 78 energized by the
voltage generated by the thermocouple 48. The coil windings pass
about a core 82 in order to magnetize the core 82, precluding the
force of the closing spring 72 from acting on the valve lever
68.
This allows the valve opening spring 70 to maintain the valve lever
68 in the open position.
As noted, to open the valve initially and overcome the pressure
acting on the seated valve disc 64, a pilot valve plunger 84 is
provided which has a stem 86 engaging the valve disc 64. When the
pilot is to be lit, the plunger handle 84 is depressed, overcoming
the pressure acting on the valve disc 64 and the pilot burner 30 is
lit while the plunger handle 84 is depressed.
The resulting voltage generated by the thermocouple magnetizes the
hold-in coil winding core 82 to maintain the open position of the
valve disc 64 allowing communication of the gas through the valve
seat 66.
The pilot plunger valve 84 may also act as a manual shutoff by
controlling a rotary valve member 88 disposed within a chamber 90
immediately downstream of the valve seat 66.
The gas passing through the valve seat 66 flows into a regulator
valve chamber 92 and past a regulating valve member 94, the
position of which may be adjustable by means of a pressure
regulator adjustment device 96 and thence into the main gas valve
chamber 98. The main gas valve 62 includes a valve member 100 which
cooperates with the valve seat 102. The valve member 100 is
electromagnetically operated by means of a magnetic actuator 104
which in turn is energized by the burner control circuit 44. The
supply pilot passage 106 is in communication with the regulator
chamber 92 while the valve chamber 108 downstream of the main gas
valve 102 is in communication with the burner supply line 22.
According to the concept of the present invention, the thermocouple
leads 110 are electrically connected to the hold-in coil windings
80 and are placed in series with the snap disc sensor 58 as well as
the lineal temperature sensor 56, such that both switches or
sensors must be closed indicating a normal temperature condition in
order for voltage to be applied across the hold-in coil windings
80.
Accordingly, if an abnormal temperature condition is sensed, the
hold-in coil 80 is deenergized allowing the closing spring 72 to
close the valve disc 64 preventing gas flow at a point downstream
of the system. Thus, even if the main gas valve 62 remains stuck
open, burner operation ceases.
The lineal temperature sensor is a device which is known, per se.
This device includes (FIG. 4) a length of copper tubing 112 which
has formed therein a very small capillary sized opening which
provides a fluid pressure communication on opposite sides of a
diaphragm switch 114. The diaphragm switch 114 controls the
electrical connection between a pair of terminals 116 which are
placed in series with the thermocouple connection and the burner
pilot safety controls as described. Upon any portion of the tube
112 being heated to a predetermined temperature which, for the
present application is on the order of 250.degree. F. to
260.degree. F., the small capillary passage becomes closed off due
to the expansion of the copper tubing which causes pressure
unbalance on the diaphragm 114 and breaking the electrical
connection with the contacts 116. Since such devices are known in
the art per se, a detailed description will not be included
here.
The installation, as can be seen in FIG. 4, includes a mounting of
a length of tubing 112 entirely about the diverter opening inlet
34, with a slight spacing from the walls of the diverter opening
inlet 34. This insures that if the gas spillage takes place at any
point about the periphery of the draft diverter inlet 34, the
lineal temperature sensor 56 causes interruption of the burner
pilot safety control circuit and shut down of the burner.
In similar fashion, the plenum snap disc sensor 58 is a temperature
sensing device well known in the art and comprises a bimetal spring
disc causing making and breaking of a circuit responsive to a
predetermined temperature being sensed by the snap disc sensor
58.
Similarly, this causes interruption of the burner pilot safety
circuit.
Accordingly, it can be seen that the safety control, according to
the present invention, when associated with an automatic vent
damper nearly completely eliminates hazards in such systems having
automatic flue dampers in a most reliable manner. The enhancement
of the safety characteristics of the heating device so equipped is
by a relatively simple and low cost component which is easily
installed by relatively unskilled persons, i.e., the need for
elaborate flow testing in order to properly locate the diverter
inlet temperature sensor is not required to insure proper
function.
The incidence of failure of the main gas valve which has
compromised the safety of the typical prior art systems have been
avoided.
Indeed, the safety controls, according to the present invention,
enhance the safety of the furnace over and above that of the
furnace controls on a furnace arrangement not having the automatic
flue damper actuator and indeed could be applied to furnaces and
other similar heating devices to improve safety even if not
equipped with the automatic flue damper. That is, the high
temperature condition sensed provides a safety measure against any
blockage of the exhaust stack tending to create a backup of the
combustion gases into the building spaces.
In addition, the condition in which burner operation continues
without blower operation is very reliably corrected by sensing of
the condition at the warm air plenum and shut down of the burner by
acting on the pilot valve.
* * * * *