Note: Descriptions are shown in the official language in which they were submitted.
CA 02458190 2006-09-20
Docket No.: WHIC-0007CIP2
FUEL-FIRED HEATING APPLIANCE WITH TEMPERATURE-BASED
FUEL SHUTOFF SYSTEM
10
BACKGROUND OF THE INVENTION
The present invention generally relates to fuel-fired heating appliances and,
in
a preferred embodiment thereof, more particularly provides a gas-fired water
heater
having incorporated therein a specially designed combustion air shutoff
system.
Gas-fired residential and commercial water heaters are generally formed to
inciude a vertical cylindrical water storage tank with a gas burner disposed
in a
combustion chamber below the tank. The burner is supplied with a fuel gas
through a gas supply line, and combustion air through an air inlet flow path
providing communication between the exterior of the water heater and the
interior
of the combustion chamber.
Water heaters of this general type are extremely safe and quite reliabie in
operation. However, under certain operational conditions the temperature and
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CA 02458190 2004-02-20
Fx
carbon monoxide levels within the combustion chamber may begin to rise toward
undesirable magnitudes. Accordingly, it would be desirable, from an improved
overall control standpoint, to incorporate in this type of fuel-fired water
heater a
system for sensing these operational conditions and responsively terminating
the
firing of the water heater. It is to this goal that the present invention is
directed.
SUMMARY OF THE lNVENTION
In carrying out principles of the present invention, in accordance with a
preferred embodiment thereof, fue!-fired heating apparatus is provided which
is
representatively in the form of a gas-fired water heater and includes a
combustion
chamber thermally communicatable with a fluid to be heated, and combustion
apparatus operative to burn a fuel-air mixture within the combustion chamber.
The
combustion apparatus representatively includes a fuel burner structure
disposed
within the combustion chamber, a fuel valve for supplying fuel to the burner
structure, and a flow path through which combustion air may be flowed into the
combustion chamber.
Illustratively, the fuel valve is connected in an eiectrical circuit in series
with
a thermocouple portion of the burner structure. When the circuit is opened,
the
valve is precluded from supplying fuel to the burner structure.
In accordance with a key aspect. of the present invention, a combustion
shutoff system is provided which is operative to sense a temperature in the
combustion chamber and responsively terminate further combustion therein in
response to the temperature reaching a level correlated to and indicative of a
predetermined, undesirably high concentration of carbon monoxide present in
the
combustion chamber. Representatively, but not by way of limitation, this level
of
carbon monoxide present within the combustion chamber is in the range of from
about 200 ppm to about 400 ppm by volume.
In a first version of the combustion shutoff system, the combustion air
temperature is directly sensed by a spring-loaded temperature sensing
structure
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portion of the combustion shutoff system that projects into the interior of
the
combustion chamber. The temperature sensing structure, when exposed to the
predetermined temperature level within the combustion chamber, responsively
causes a damper external to the combustion chamber to.close off the combustion
air flow path and thereby terminate further combustion within the combustion
chamber.
The temperature sensing structure,. in various illustrative forms thereof, may
include a eutectic element which is meltable to permit the damper to be spring-
driven to its closed position, or a hollow, frangible, heat shatterable
member, such
as a glass bulb, containing a fluid such as mineral oil, peanut oil or an
assembly
lubricant.
In a second illustrative' version of .the combustion shutoff system, the
temperature within the combustion chamber is also directly sensed using a
spring- .
loaded temperature sensing structure, incorporating either a meltable eutectic
member, or a frangible,. heat shatterable fluid-containing member, projecting
into the
interior of the combustion chamber. In this version of the combustion shutoff
system, the spring-loaded temperature sensing structure is mechanically
coupled to
a normally closed switch structure connected in the fuel valve electrical
circuit.
When the spring-loaded temperature sensing structure is heat-triggered by the
predetermined temperature within the combustion chamber, the temperature
sensing structure responsively opens the switch, thereby opening the valve
circuit
and terminating further fuel flow to the burner structure. . This, in turn,
terminates
further combustion within the combustion chamber.
In a third illustrative version of the combustion shutoff system, the
temperature within the combustion chamber is indirectly sensed by a normally
closed thermally actuated switch externally positioned on an outer wall
portion of
the combustion chamber, such oUter wall,portion representatively being an
access
door portion of the combustion charnber. The thermal switch is operatively
connected in the fuel valve electrical circuit. When the predetermined
combustion
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temperature level in the combustion chamber is reached, the heat generated
thereby opens the thermal switch, thereby opening the fuel valve electrical
circuit,
terminating further fuel flow to the burner structure, and thus terminating
further
combustion within the combustion chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified partial cross-sectional view through a bottom portion
of
a representative gas-fired water heater having incorporated therein a
specially
designed combustion ' air shutoff system embodying principles of the present
invention;
FIG. 2 is an enlargement of the dashed area "2" in FIG. 1 and illustrates the
operation of a control damper portion of the combustion air shutoff system;
FIG. 3 is a simplified, reduced scale top plan view of an arrestor plate
portion
of the water heater that forms the bottom wa!l of its combustion chamber;
FIG. 4 is an enlarged scale cross-sectional view, taken along line 4-4 of FIG.
1, through a specially designed eutectic temperature sensing structure
incorporated
in the combustion air shutoff system and projecting into the combustion
chamber
of the water heater;
FIG. 4A is a cross-sectional view through a first alternate embodiment of the
eutectic temperature sensing structure shown in FIG. 4;
FIG. 5 is a perspective view of a specially designed bottom jacket pan which
may be utilized in the water heater;
FIG. 6 is a side elevational view of the bottom jacket pan;
FIG. 7 is a cross-sectional view through the bottom jacket pan taken along
line 7-7 of FIG. 6;
FIG. 8 is an enlargement of the circled area "8" in FIG. 7 and illustrates a
portion of an annular, jacket edge-receiving support groove extending around
the
open top end of the bottom jacket pan;
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CA 02458190 2004-02-20
FIG. 9 is a simplified partial cross-sectional view through a bottom end
portion of a first alternate embodiment of the FIG. 1 water heater
incorporating
therein the bottom jacket pan shown in FIGS. 5-8;
FIG. 10 is a cross-sectional view through an upper end portion of a second
alternate embodiment of the eutectic temperature sensing structure shown in
FIG.
4;
FIG. 11 is a cross-sectional view through an upper end portion of a third
alternate embodiment of the eutectic temperature sensing structure shown in
FIG.
4;
FIG. 12 is a cross-sectional view through an upper end portion of a fourth
alternate embodiment of the eutectic temperature sensing structure shown in
FIG.
4;
FIG. 13 is a simplified perspective view of a bottom end portion of a second
embodiment of the FIG. 1 water heater;
FIG. 14 is an enlarged scale outer side perspective view of a molded plasfiic
snap-in combustion air pre-filter structure incorporated in the. FIG. 13 water
heater;
FIG. 15 is an inner side perspective view of the molded plastic pre-filter
structure;
FIG. 16 is an inner side elevational view of the molded plastic pre-filter
structure operatively installed in the FIG. 13 water heater;
FIG. 17 is an enlarged cross-sectional view through the molded plastic pre-
filter structure taken along line 17-17 of FIG. 16;
FIG. 18 is an enlarged cross-sectional view through the molded plastic pre-
filter structure taken along line 18-1~8 of FIG. 16;
FIG. 19 is a view similar to that in FIG. 2 but illustrating a heat-frangible
temperature sensing structure in place of the eutectic-based temperature
sensing
structure shown in FIG. 2;
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FIG. 20 is an enlargement of the dashed area "A" in FIG. 19 and illustrates
an upper portion of the heat-frangible temperature sensing structure in. a pre-
activation orientation;
FIG. 20A is a view similar to that in FIG. 20, but with the heat-frangible
temperature structure in a post-activation orientation;
FIG. 21 is an enlarged scale perspective view of a fluid-filled glass bulb
portion of the heat-frangible temperature sensing structure;
FIG. 22 is an enlarged scale perspective view of a support frame portion of
the heat-frangible temperature sensing structure;
FIG. 23. is an enlarged scale perspective view of a spring portion of the heat-
frangible temperature sensing structure;
FIG. 24 is an enlarged scale partially exploded perspective view of an upper
end portion of the heat-frangible temperature sensing structure illustrating
its
installation on the combustion chamber arrestor plate of a gas-fired water
heater;
FIG. 25 is a side elevational view of a portion of the heat-frangible
temperature sensing structure taken along line 25-25 of FIG. 24;
FIG. 26 is a schematic cross-sectional view through the combustion chamber
portion of a gas-fired water heater similar to that shown in FIG. 1 but having
incorporated therein _ a eutectic-based fuel valve shutoff system instead of a
combustion air shutoff system, a eutectic thermal trigger structure portion of
the
system being shown in its untriggered position;
FIG. 26A is a schematic detail view of the dashed circle area ."A" in FIG. 26
and illustrates the thermal trigger in its triggered orientation;
FIG. 27 is a view similar to that in FIG. 26A but illustrating a frangible
element-based thermal trigger structure, shown in its untriggered orientation,
used
in place of the eutectic-based thermal trigger shown in FIGS. 26 and 26A; and
FIG. 28 is a schematic, partly elevational cross-sectional view through a
combustion chamber portion of a gas-fired water heater similar *to that shown
in
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FIG. 26 but incorporating therein an alternate, thermally actuated switch-
based fuel
valve shutoff system.
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CA 02458190 2004-02-20
DETAILED DESCRIPTION
As illustrated in simplified, somewhat schematic form in FIGS. 1 and 2, in a
representative embodiment thereof this invention provides a gas-fired water
heater
having a vertically oriented cylindrical metal tank 12 adapted to hold a
quantity
5 of water 14 to be heated and delivered on demand to one or more hot water-
using
fixtures, such as sinks, bathtubs, showers, dishwashers and the like. An
upwardly
domed bottom head structure 16 having an open lower side portion 17 forms a
lower end wall of the tank 12 and further .defines the top wall of a
combustion
chamber 18 at the lower end of the tank 12. An annular metal skirt 20 extends
10 downwardly from the periphery of the bottom head 16 to the lower end 22 of
the
water heater 10 and forms an annular outer side waii portion of the combustion
chamber 18. An open upper end portion of the skirt 20 is press-fitted into the
lower side portion 17 of the bottom head structure 16, and the closed lower
end
27 of the skirt structure 20 downwardly extends to the bottom end 22 of the
water heater 10.
The bottom wall of the combustion chamber 18 is defined by a specially
designed circular arrestor plate 24 having a peripheral edge portion received
and
captively retained in an annular roll-formed crimp area 26 of the skirt
upwardly
spaced apart from its lower end 27. As best illustrated in FIG. 3, the
circular
arrestor plate 24 has a centrally disposed square perforated area 28 having
formed
therethrough a spaced series of flame arrestor or flame "quenching" openings
30
which are configured and arranged to permit combustion air and extraneous
flammable vapors to. flow upwardly into the combustion chamber 18, as later
- described herein, but substantially preclude the downward travel of
combustion
chamber flames therethrough. These arrestor plate openings 30 function
similarly
to the arrestor plate openings illustrated and described in U.S. Patent
6,035,812 to
Harrigill et al which is hereby incorporated herein by reference.
Illustratively, the
metal arrestor plate 24 is 1/16" thick, the arrestor plate openings 30 are
1/16"
circular openings, and the center=to-center spacing of the openings 30 is
1/8".
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CA 02458190 2004-02-20
A gas burner 32 is centrally disposed on a bottom interior side portion of the
combustion chamber 18. Burner 32 is supplied with gas via a main gas supply
pipe
34 (see FIG. 1) that extends into the interior of the combustion chamber 18
through a suitable access door 36 secured over an opening 38 formed in a
subsequently described outer sidewall portion of the water heater .10. A
conventional pilot burner 40 and associated piezo igniter structure 42 are
suitably
supported in the interior of the combustion chamber 18, with the pilot burner
40
being supplied with gas via a pilot supply pipe 44 extending inwardly through
access door 36. Pilot burner and thermocouple electrical wires 46,48 extend
1o inwardly through a pass-through tube 50 into the combustion chamber
interior and
are respectively connected to the pilot burner 40 and piezo igniter structure
42.
Burner 32 is operative to create within the combustion chamber 18 a
generally upwardly directed flame 52 (as indicated in solid line form in FIG.
2) and
resulting hot combustion products. During firing of the water heater 10, the
hot
combustion products flow upwardly through a flue structure 54 (see FIG. 1)
that is
connected at its lower end to the bottom head structure 16, communicates with
the interior of the combustion chamber 18, and extends upwardly through a
central
portion of the tank 12. Heat from the upwardly traveling combustion products
is
transferred to the water 14 to heat it.
Extending beneath and parallel to the arrestor plate 24 is a horizontal damper
pan 56 having a circular top side peripheral flange 58 and a bottom side wall
60
having an air inlet opening 62 disposed therein. Bottom side wall 60 is spaced
upwardly apart from the bottom end 22 of the water heater 10, and the
peripheral
flange 58 is captively retained in the roll-crimped area 26 of the skirt 20
beneath
the peripheral portion of the arrestor plate 24. The interior of the damper
pan 56
defines with the arrestor plate 24 an air inlet plenum 64 that communicates
with
the combustion chamber 18 via the openings 30 in the arrestor plate 24.
Disposed
beneath the bottom pan wall 60 is another plenum 66 horizontally circumscribed
by
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CA 02458190 2004-02-20
a lower end portion of the skirt 20 having a circumferentialty spaced series
of
openings 68 therein.
The outer side periphery of the water heater 10 is defined by an annular
metal jacket 70 which is spaced outwardly from the vertical side wall of the
tank
12 and defines therewith an annular cavity 72 (see FIG. 1) which is filled
with a
suitable insulation material 74 down to a point 80. somewhat above the lower
side
of the bottom head 16. Beneath this point the cavity 72 has an empty portion
76
that extends outwardly around the skirt 20. A pre-fi.lter screen area 78,
having a
series of air pre-filtering inlet openings 79 therein, is positioned in a
lower end
portion of the jacket 70, beneath the bottom end 80 of the insulation 74, and
communicates the exterior. of the water heater 10 with the empty cavity
portion
76. Representatively, the screen area 78 is a structure separate from the
jacket 70
and is removably secured in a corresponding opening therein. Illustratively,
the pre-
filter screen area 78 may be of an expanded metal mesh type formed of 3/16"
carbon steel in a #22F diamond opening pattern having approximately 55% open
area, or could be a metal panel structure having perforations separately
formed
therein. Alternatively, the openings 79 may be formed directly in the jacket
70.
As illustrated in FIGS. 1 and 2, a lower end portion 82 of the jacket 70 is
received
within a shallow metal bottom pan structure 84 that defines, with its bottom
side,
the bottom end 22 of the water heater 10.
Water heater 10 incorporates therein a specially designed combustion air
shutoff system 86 which, under certain circumstances later described herein,
automatically functions to terminate combustion air supply to the . combustion
chamber 18 via a flow path extending inwardly from the jacket openings 79 to
the
arrestor plate openings 30. The combustion air shutoff system 86 includes a
circular damper plate member 88 that is disposed in the plenum 66 beneath the
bottom pan wall opening 62 and has a raised central portion 90. A coiled.
spring
member 92 is disposed within the interior of the raised central portion 90 and
is
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compressed betweeri its upper end and the bottom end 94 of a bracket 96 (see
FIG. 2) secured at its top end to the underside of the bottom pan wall 60.
The lower end of a solid cylindrical metal rod portion 98 of a fusible link
temperature sensing structure 100 extends downwardly into the raised portion
90,
through a suitable opening in its upper end. An annular loWer end ledge 102
(see
FIG. 2) on the rod 98 prevents the balance of the rod 98 from moving
downwardly
into the interior of the raised damper member portion 90. Just above the ledge
102 (see FIG. 2) are diametrically opposite, radially outwardly extending
projections
104 formed on the rod 98. During normal operation of the water heater 10, the
damper plate member 88 is held in its solid line position by the rod 98, as
shown in
FIG. 2, in which the damper plate 88 is downwardly offset from and uncovers
the
bottom pan wall opening 62, with the spring 92 resiliently biasing the damper
plate
member 88 upwardly toward the bottom pan wall opening 62. When the fusible
link temperature sensing structure 100 is thermally tripped, as later
described
herein, it permits the spring 92 to upwardly drive the damper plate member 88
to
its dotted line closed position (see FIG. 2), as indicated by the arrows 106
in FIG.
2, in which the damper plate member 88 engages the bottom pan wall 60 and
closes off the opening 62 therein, thereby terminating further air flow into
the
combustion chamber 18 as later described herein.
Turning now to FIGS. 2 and 4, it can be seen that the temperature sensing
structure 100 projects upwardly into the combustion chamber 18 through the
perforated square central area 28 of the.arrestor plate 24. An upper end
portion of
the rod 98 is slidably received in a crimped tubular collar member 108 that
longitudinally extends upwardly through an opening 110 in the central square
perforated portion 28 of the arrestor plate 24 into the interior of the
combustion
chamber 18, preferably horizontally adjacent a peripheral portion of the gas
burner
32. The lower end of the tubular collar 108 is outwardly flared, as at 112, to
keep
the collar - 108 from moving from its FIG. 2 position into the interior of the
combustion chamber 1 8 . Above its flared lower end portion 1 12 the collarhas
two
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CA 02458190 2004-02-20
radially inwardly projecting annular crimps formed therein - an upper crimp
114
adjacent the open upper end of the collar, and a lower crimp 1 16 adjacent the
open
lower end of the collar. These crimps serve to guide the rod 98 within the
collar
108 to keep the rod from binding therein when it is spring-driven upwardly
through
the. collar 108 as later described herein.
A thin metal disc member 1 18, having a diameter somewhat greater than the
outer diameter of the rod and greater than the inner diameter of the upper
annular
crimp 114, is slidably received within the open upper end of the collar 108,
just
above the upper crimp 114, and underlies a meltable disc 120, formed from a
suitable eutectic material, which is received in the open upper end of the
collar 108
and fused to its interior side surface. The force of the damper spring 92 (see
FIG.
2) . causes the upper end of the rod 98 to forcibly bear upwardly against the
underside of the disc 118, with the unmelted eutectic disc 120 preventing
upward
movement of the disc 118 away from its FIG. 4 position within the collar 108.
. When the eutectic disc 120 is melted, as later described herein, the upper
end of.
the rod 98, and the disc 118, are driven, by the spring 92 upwardly through
the
upper end of the collar 108 (as indicated by the dotted line position of the
rod 98
shown in FIG. 2) as the damper plate 88 is also spring-driven upwardly to its
dotted line closed position shown in FIG.. 2.
A first alternate embodiment 100a of the eutectic temperature sensing
structure 100 partially illustrated in FIG. 4 is shown in FIG. 4A. For ease in
comparison between the temperature sensing structures 100,100a components in
the temperature sensing structure 1OOa similar to those in the temperature
sensing
structure 100 have been given identical reference numerals with the subscript
'a".
The eutectic temperature sensing structure 100a is substantially identical in
operation to the temperature sensing structure 100, but is structurally
different in
that in the temperature sensing structure 100a the solid metal rod 98 is
replaced
with a hollow tubular metal rod 122, and the separate metal disc 118 is
replaced
with. a lateraliy enlarged, integral crimped circular upper end portion 124 of
the
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hollow rod 122 that underlies and forcibly bears upwardly against the
underside of
the eutectic disc 1 20a.
During firing of the water heater 10, ambient combustion air 126 (see FIG.
2) is sequentially drawn inwardly through the openings 79 in the jacket-
disposed
pre-filter screen area 78 into the empty cavity portion 76, into the plenum 66
via
the skirt openings 68, upwardly through the bottom pan wall opening 62 into
the
plenum 64, and into the combustion chamber 18 via the arrestor plate openings
30
to serve as combustion air for the burner 32.
In the water heater 10, the combustion air shutoff system 86 serves two
functions during firing of the water heater. First, in the event that
extraneous
flammable vapors are drawn into the combustion chamber 18 and begin to burn on
the top side of the arrestor plate 24, the temperature in the combustion
chamber
18 will rise to a level at which the combustion chamber heat melts the
eutectic
disc 120 (or the eutectic disc 120a as the case may be), thereby permitting
the
compressed spring 92 to upwardly drive the rod 98 (or the rod 122 as the case
may be) through the associated collar 108 or 108a until the damper plate
member
88 reaches its dashed line closed position shown in FIG. 2 in which the damper
plate member 88 closes the bottom pan wall opening 62 and terminates further
combustion air delivery to the burner 32 via the combustion air flow path
extending
from the pre-filter openings 79 to the arrestor plate openings 30. Such
termination
of combustion air delivery to the combustion chamber shuts down the main and
pilot gas burners 32 and 40. As the rod 98 is spring-driven upwardly after the
eutectic disc 120 melts (see the dotted line position of the rod 98 in FIG.
2), the
lower end projections 104 on the rod 98 prevent it from being shot upwardly
through and out of the collar 108 into the combustion chamber 18. Similar
projections formed on the alternate hollow rod 122 perform this same function.
The specially designed combustion air shutoff system 86 also serves to
terminate burner operation when the eutectic disc 120 (or 1 20a) is exposed to
and
melted by an elevated combustion chamber temperature indicative of the
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CA 02458190 2004-02-20
generation within the combustion chamber 18 of an undesirably high
concentration
of carbon monoxide created by clogging of the pre-filter screen structure 78
and/or
the arrestor plate openings 30. Preferably, the collar portion 108 of the
temperature sensing structure 100 is positioned horizontally adjacent a
peripheral
portion of the main burner 32 (see FIG. 2) so that the burner flame "droop"
(see
the dotted line position of the main burner flame 52) created by such clogging
more
quickly melts the eutectic disc 120 (or the eutectic disc 120a as the case may
be).
An upper end portion of a second alternate embodiment 100b of the
previously described eutectic temperature sensing structure 100 (see FIG. 4)
is
cross-sectionally illustrated in FIG. 10. For ease in comparison between the
temperature sensing structures 100,100b components in the temperature sensing
structure 100b similar to those in the temperature sensing structure 100 have
been
given identical reference numerals with the subscript "b". The eutectic
temperature sensing structure 100b is substantially identical in operation to
the
temperature sensing structure 100, but is structurally different in that in
the
temperature sensing structure 100b the metal rod 98b has an annular groove 144
formed in its upper end and receiving an inner edge portion of an annular
eutectic
alloy member 146.
As illustrated in FIG. 10, an outer annular peripheral edge portion of the
eutectic member 146 projects outwardly bey.ond the side of the rod 98b and
underlies an annular crimp 148 formed on the upper end of the tubular collar
member 108b. Crimp 148 overlies and upwardly blocks the outwardly projecting
annular edge portion of the eutectic member146, thereby precluding the rod 98b
from being spring-driven upwardly past its FIG. 10 position relative to the
collar
member 108b. However, when the eutectic member 146 is melted it no longer
precludes such upward movement of the rod 98b, and the rod 98b is spring-
driven
upwardly relative to the collar 1086 as illustrated by the arrow
An upper end portion of a third alternate embodiment 100c of the previously
described eutectic temperature sensing structure 100 (see FIG. 4) is cross-
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sectionally illustrated in FIG. 11. For ease in comparison between the
temperature
sensing structures 100,100c components in the temperature sensing structure
100c similar to those in the temperature sensing structure 100 have been given
identical reference numerals ,with the subscript "c". The eutectic temperature
sensing structure. 100c is substantially identical in operation to the
temperature
sensing structure 100, but is structurally different in that -in the
temperature
sensing structure 100c an annular eutectic alloy member 152 is captively
retained
between the upper end of the rod 98c and the enlarged head portion 154 of a
threaded retaining member 156 extended downwardly through the center of the
eutectic member 152 and threaded into a suitable opening 158 formed in the
upper
end of the rod 98c.
As illustrated in FIG. 11, an annularly crimped upper end portion 160 of the
tubular collar 1 08c upwardly overlies and blocks an annular outer peripheral
portion
of the eutectic member 152, thereby precluding upward movement of -the rod 98c
and the fastener 156 upwardly beyond their FIG. 11 positions relative to the
collar
108c. However, when the eutectic member 152 is melted the rod 98c and
fastener 156 are free to be spring-driven upwardly relative to the collar
.108c as
indicated by the arrow 162 in FIG. 11.
An upper end portion of a fourth alternate embodiment 100d of the
previously described eutectic temperature sensing structure 100 (see FIG. 4)
is
cross-sectionally illustrated in FIG. 12. For ease in comparison between the
temperature sensing structures 100,100d components in the temperature sensing
structure lOOdc similar to those in the temperature sensing structure 100 have
been given identical reference numerals with the subscript "d". The eutectic
temperature sensing structure 100dc is substantially identical in operation to
the
temperature sensing structure 100, but is structurally different in that a
trahsverse
circular bore 164 is formed through the rod 98d adjacent its upper end, the
bore
164 complementarily receiving a cylindrical eutectic alloy member 166.
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A pair of metal balls 168, each sized to move through the interior of the bore
164, partially extend into the opposite ends of the bore 164 and are received
in
partially spherical indentations 170 formed in the opposite ends of the
eutectic
member 166. An annular crimped upper end portion 172 of the collar 108d
upwardly overlies and blocks the portions of the balls 168 that project
outwardly
beyond the side of the rod 98a, thereby precluding upward movement of the rod
98d from its FIG. 12 position relative to the collar 108d. However, when the
eutectic member 166 is melted, the upward spring force on the rod 98d causes
the
crimped area 172 to force the balls 168 toward one another through the bore
164,
as indicated by the arrows 174 in FIG. 12,. thereby permitting the rod 98d to
be
upwardly driven from its FIG. 12 position relative to the collar 108d as
illustrated
by the arrow 176 in. FIG. 12.
According to another feature of the present invention, (1.) the opening area-
to-total area ratios of the pre-filter screen structure 78 and the arrestor
plate 24,
.(2) the ratio of the total open area in the pre-filter screen structure 78 to
the total
open area in the arrestor plate 24, and (3) the melting point of the eutectic
material
120 (or 1 20a, 146,152- or 166 as the case may be) are correlated in a manner
such
that the rising combustion temperature in the combustion chamber 18 caused by
a
progressively greater clogging of the pre-filter openings 79 and the arrestor
plate
openings 30 (by, for example, airborne material such as lint) melts the
eutectic
material 120 and trips the temperature sensing structure 100 and corresponding
air
shutoff damper closure before a predetermined maximum carbon morioxide
concentration level (representatively about 200-400 ppm by volume) is reached
within the combustion chamber 18 due to a reduced flow of combustion air into
the combustion chamber. The pre-filter area 78 and the array of arrestor plate
openings 30 are also sized so that some particulate matter is 'allowed to pass
through the pre=filter area and come to rest on the arrestor plate. This
relative
sizing assures that combustion air will normally flow inwardly through the pre-
filter
.
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area as .opposed to being blocked by particulate rnatter trapped only by the
pre-
filter area.
In developing the present invention it has been found that a. preferred
"matching" of the pre-filter structure to the perforated arrestor plate area,
which
facilitates the burner shutoff before an undesirable concentration of CO is
generated within the combustion chamber 18 during firing of the. burner 32, is
achieved when (1) the ratio of the open area-to-total area percentage of the
pre-
filter structure 78 to the open area-to-total area percentage of the arrestor
plate 24
is within the range of from about 1.2 to about 2:5, and (2) the ratio of the
total
open area of the pre-filter structure 78 to the total open area of the
arrestor plate
24 is within the range of from about 2.5 to about 5.3. The melting point of
the
eutectic portion of the temperature sensing structure 100 may, of course, be
appropriately correlated to the determinable relationship in a given water
heater
among the operational combustion chamber temperature, the quantity of
combustion air being flowed into the combustion chamber, and the ppm
concentration level of carbon monoxide being generated within the combustion
chamber during firing of the burner 32.
By way of illustration and example only, the water heater 10 illustrated in
FIGS. 1 and 2 representatively has a tank capacity of 50 gallons of water; an
arrestor plate diameter of 20 inches; and a burner firing rate of between
40,000
and 45,000 BTUH. The total area of the square perforated arrestor plate
section
28 (see FIG. 3) is 118.4 square inches, and the actual flow area defined by
the
perforations 30 in the square area 28 is 26.8 square inches. The overall area
of
the jacket pre-filter structure 78 is 234 square inches, and the actual flow
area
defined by the openings in the structure 78 is 119.4 square inches. The ratio
of
the hydraulic diameter of the arrestor openings 30 to the thickness of the
arrestor
plate 24 is within the range of from about 0.75 to about 1.25, and is
preferably
about 1.0, and the melting point of the eutectic material in the temperature
sensing
-17-
CA 02458190 2004-02-20
structure 100 is within the range of from about 425 degrees F to about 465
degrees F, and is preferably about 430 degrees F.
Cross-sectionally illustrated in simplified form in FIG. 9, is a bottom side
portion of a first alternate embodiment 10a of the previously described gas-
fired
water heater 10. For ease in comparing the water heater embodiments 10 and
10a, components in the embodiment 10a similar to those in the embodiment 10
have been given the same reference numerals, but with the subscripts "a".
The water heater 10a is identical to the previously described water heater 10
with the exceptions that in the water heater 10a (1) the pre-filter screen
area 78
carried by the jacket 70 in the water heater 10 is eliminated and replaced by
a
subsequently described structure, (2) the lower end 82a of the jacket 70a is.
disposed just below the bottom end 80a of the insulation 74a instead of
extending
clear down to the bottom end 22a of the water heater 10a, and (3) the shallow
bottom pan 84 utilized in the water heater 10 is replaced in the water heater
10a
with a considerably deeper bottom jacket pan 128 which is illustrated in FIGS.
5-8.
Bottom jacket pan 128 is representatively of a one piece molded plastic
construction (but could be of a different material andlor construction if
desired) and
has an annular vertical sidewall portion 130, a solid circular bottom wall
132, and
an open upper end bordered by an upwardly opening annular groove 134 (see
FIGS.
8 and 9). Formed in the sidewall portion 130 are (1 ) a bottom drain fitting
136, (2)
a burner access opening 138 (which takes the place of the access opening 38 in
the water heater 10), (3) a series of pre-filter air inlet openings 140 (which
take the
place of the pre-fhlter openings 79 . in the. water heater 10), and (4) a
holder
structure 142 for a depressible button portion (not shown) of a piezo igniter
structure associated with the main burner portion of the water heater 10a.
As best illustrated in FIG. 9, the annular skirt 20a extends downwardly
through the interior of the pan 128, with the bottom skirt end 27a resting on
the
bottom pan wall 132, and the now much higher,annular lower end 82a of the
jacket 70a being closely received in the annular groove 134 extending around
the
-18-
CA 02458190 2004-02-20
top end of the pan structure 128. The use of this specially designed one piece
bottom jacket pan 128 desirably reduces the overall cost.of the water heater
10a
and simplifies its construction.
Perspectively illustrated in simplified form in FIG. 13 is a bottom end
portion
of a second alternate embodiment 10b of the previously described gas-fired
water
heater 10. For ease in comparing the water heater embodiments 10 and 1Ob,
components in the embodiment 10b similar to those in the embodiment 10 have
been given the same reference numerals, but with the subscripts "b".
The water heater 10b is identical to the previously described water heater 10
lo with the exception that in the water heater 10b the previously described
pre-filter
screen area 78 carried by the jacket 70 in the water heater 10 (see FIGS. 1
and 2)
is eliminated and replaced by a circumferentially spaced series of specially
designed, molded plastic perforated pre-filtering panels .178 which are
removably
snapped into corresponding openings in a lower end portion of the outer jacket
structure 70b of the water heater 10b.
With reference now to FIGS. 14-18, each of the molded plastic perforated
pre-filter panels 178 has a rectangular frame 180 that borders a rectangular,
horizontally curved perforated air pre-filtering plate 182. Each panel 178 may
be
removably snapped into a corresponding rectangular opening 184 (see FIGS. 16-
18) using resiliently deflectable retaining tabs 186 formed on the inner side
of the
frame 180 and adapter to inwardly overlie the jacket 70b at spaced locations
around the periphery of the jacket opening 184 as shown in FIGS. 16-18.
Formed on a bottom end portion of the inner side of each frame 180 is an
upstanding shield plate 188 which is inwardly spaced apart from the frame 180
and forms with a bottom side portion thereof a horizontally extending trough
190
(see FIGS. 16 and 18) having opposite open ends 192 (see FIGS 15 and 16). As
illustrated in FIGS. 15, 16 and 18, a horizontally spaced plurality of
reinforcing tabs
194 project outwardly from the inner side of the shield plate 188.
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CA 02458190 2004-02-20
As illustrated in FIG. 18, a top end portion of each installed pre-filter
panel
178 contacts an inwardly adjacent portion of the overall insulation structure
74b,
thereby bracing a portion of the jacket 70b against undesirable inward
deflection
adjacent the upper end of opening 184. At the bottom end of each installed pre-
filter panel 178, the arcuate outer side edges of the reinforcing tabs 194 are
normally spaced slightly outwardly from the skirt structure 20b. However, if a
bottom end portion of the panel 178 and an adjacent portion of the jacket 70b
are
deflected. inwardiy toward the skirt structure 20b, the tabs 194 (as shown in
FIG.
18) are brought to bear against the skirt structure 20b and serve to brace
and.
reinforce the adjacent portion of the jacket 70b against further inward
deflection
thereof.
The shield plate portion 188 of each pre-filter panel 178 uniquely functions
to prevent liquid splashed against a lower outer side portion of the installed
panel
178 from simply traveling through the plate perforations and coming into
contact
with the skirt 20b and the air inlet openings therein. Instead, such splashed
liquid
comes into contact with the outer side of the shield plate 188, drains
downwardly
therealong into the trough 190, and spills out of the open trough ends 192
without
coming into contact with the skirt 194.
Cross-sectionally illustrated in FIG. 19 is a bottom portion of the water
2o heater 10 in which the previously described eutectic-based temperature
sensing
structure 100 (see FIGS. 1 and 2) has been replaced with a specially designed
heat
frangible temperature sensing structure 200, further details of which are
shown in
FIGS, 20-25. As later described herein, the temperature sensing structure 200
includes a heat frangible element 202 which is positioned above the upper end
of
the rod 98 and serves to block its upward movement from its solid line
position in
FIG. 19 to its dotted line position, thereby blockingly retaining the shutoff
damper
88 in its solid line open position shown'in FIG. 19.
With reference now to FIGS. 19 and 20, the frangible element 202 is
disposed in the interior of the combustion chamber.18 and is carried in a
frame
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CA 02458190 2004-02-20
structure 204 which is secured as later described to the top side of arrestor
plate
24 adjacent the gas burner 32. The rod 98 slidably extends upwardly through a
hole (not shown) in the arrestor plate 24, with the upper end of the rod being
associated with the balance of the temperature sensing structure 200 as also
later
described herein.
Turning now to FIGS. 20-25, the frame structure 204 includes two primary
parts - a base portion, 206 and a support portion 208. The base portion 206
(see
FIG. 24) has an elongated rectangular base or bottom wall 210 with front and
rear.
side edges 212,214 and upturned left and right end tabs 216,218. A slot 220
lo horizontally extends forwardly through the rear edge of the left end tab
216 and
has a vertically enlarged front end portion 222, and a slot 224 horizontally
extends
rearwardly through the front edge of the right end tab 218 and has a
vertically
enlarged rear end portion 226. As shown in FIG. 24, the end tabs 216,218 are
in
a facing relationship with one another, and are spaced apart along an axis
228.
15. A pair of circular mounting holes 230 extend through the bottom wall 210,
with screws 232 or other suitable fastening members (see FIG. 20) extending
downwardly through holes 230 and anchoring the bottom wall 210 to the top side
of the arrestor plate 24. A somewhat larger diameter circular hole 234 extends
through the bottom wall 210 between the holes 230. As shown in phantom in
20 FIG. 24, the rod 98 extends Upwardly through the corresponding hole (not
visible)
in the arrestor plate.24, and hole 234 that overlies the arrestor plate hole.
In FIG.
24, the rod 98 is illustratively shown it its uppermost position
(corresponding to the
dotted line closed position of the damper 88 shown in FIG. 19) in which the
top
end of the rod 98 is positioned higher than the tab slots 220 and 224.
25 With reference now to FIGS. 20, 22, 24 and 25, the frame support portion
208 has an elongated rectangular horizontal bottom wall 236 with opposite
front
and rear side edges 238,240. A central front tab 242 having a rectangular slot
244 extending therethrough projects upwardly from the front side edge 238
across
from an elongated centrai rear tab 246 that rearwardly projects past the rear
side
-21-
CA 02458190 2004-02-20
edge 240 of the bottom wall 236 and has an upturned outer end 248. Just
inwardly of opposite left and right end portions 250,252 of the bottom wall
236
are horizontally spaced elongated rectangular bars 254,256 that longitudinally
extend upwardly from adjacent the rear side edge of the bottom wall 236, on
opposite sides of the rear tab 246, and are joined at their top ends by a
horizontal
top wall -258 having a circular hole 260 centrally disposed therein.
The opposite end portions 250,252 of the bottom wall 236 are spaced apart
along an axis 262. A central circular opening 264 (see FIG. 22) extends
downwardly through the bottom wall 236 and is bordered by a depending annular
collar 266 (see FIG. 25). The opening 264 and collar 266 are sized to slidably
receive the rod 98 as later described herein. The central opening 264 is
disposed
between two installation openings 268 extending downwardly through the bottom
wall 236.
With reference now to FIG. 21, the frangible element 202 has a hollow body
portion in the form of a generally tubular glass bulb 270 which is filled with
a fluid,
representatively peanut oil 272, which has a boiling point higher than the set
point
temperature of the temperature sensing strUcture 200 (representatively 'the
same
set point temperature of the previously described eutectic-based temperature
sensing structure 100) and a flash point temperature substantially. above the
predetermined set point temperature. Other suitable fluids include; by way of
example and not in a limiting manner, mineral oil or a suitable assembly
lubricant
such as Proeco 46 assembly lubricant as manufactured and sold by Cognis
Corporation, 8150 Holton Drive, Florence, Kentucky 41042.
The frangible element 202 is constructed in a manner causing it to shatter in
response to exposure to the set point temperature within the combustion
chamber
18. Illustratively, the peanut oil 272 is placed in the bulb 270 (before the
sealing
off of the bulb) in an assembly environment at_ a temperature slightly below
the set
point temperature of the temperature sensing structure 200. Bulb 270 is then
suitably sealed, and the frangible element 202 is permitted to come to room
-22-
CA 02458190 2004-02-20
temperature for subsequent incorporation in the temperature sensing structure
200.
Representatively, the bulb 270 has generally spherical upper and lower end
portions 274,276 and a substantially smaller diameter tubular portion 278
projecting axially downwardly from its lower end portion 276.
In addition to the previously described rod, frangible element and frame
portions 98, .202 and 204 of the temperature sensing structure 200, the
temperature sensing structure 200 further includes a small sheet metal spring
member 280 (see FIGS. 20 and 23-25). Spring member 280 has a generally
rectangular bottom wall 282 with a front end tab 284, and a downwardly curved
top wall 286 which is joined at area 288 to the rear edge of the bottom wall
282
and overlies the top side of the bottom wall 282. Top wall 286 has a central
circular hole 290 therein, and a front end edge portion 292 which is closely
adjacent a portion of the top side of the bottom wall 282 inwardly
adjacent.the tab
284.
With the rod 98 extending upwardly through its corresponding opening in the
arrestor plate 24 (see FIG. 24) and in its upper limit position, the balance
of the
temperature sensing system 200 is operatively installed as follows. The base
portion 206 of the frame structure 204 is lowered onto the top side of the
arrestor
plate 24 in a manner causing an upper end portion of the rod 98 to pass
upwardly
through the circular hole 234 in the bottom wall 210 of the base portion .206.
The-
base portion 206 is then 'anchored to the top side of the arrestor plate 24 by
operatively extending the fasteners 232 (see FIG. 20) downwardly through the
bottom wall openings 230 into the arrestor plate 24.
Spring'280 is placed atop a central portion of the bottom wal! 236 of the
frame support portion 208, between the tabs 242 and 248 (see FIGS. 24 and 25)
in a manner such.that the bottom spring wall 282 overlies the top side of the
bottom wall 236 and blocks the central opening 264 therein (see FIG. 22), and
the
spring tab 284 extends outwardly through the front tab slot '244. The heat-
frangible element 202 is then snapped into place between the top frame support
-23-
CA 02458190 2004-02-20
portion wall 258 and the top spring wall 286 (see FIGS. 24 and 25), thereby
resiliently pressing the heat-frangible element 202 between the frame and
spring
walls 258 and 286.
This installation of the heat-frangible element 202 is illustratively
accomplished by first downwardly inserting the bottom frangible element
projection
278 through the opening 290 in the top spring wall 286 (see FIG. 23),
depressing
the top spring wall 286, tilting the upper bulb end 274 of the element 202 to
position it under the top frame wall opening 260, and then releasing the
element
202. This causes the vertically oriented element 202 (see FIGS. 20, 24 and 25)
to
be resiliently pressed between the spring 280 and. the top frame wall 258,
with the
bottom bulb projection 278 captively retained within the top spring wall hole
290
(see FIG. 23),.and a sma.ll portion of the top bulb end portion 274 extending
into
the top frame wall opening 260.
The assembled element, frame and spring portions 202,208,280 form a
thermal trigger subassembly 294 (see FIGS. 24 and 25) which is releasably
secured
to the in-place frame base portion 206 using a suitable tool 296 shown in
phantom
in FIG. 24. As depicted in FIG. 24, tool 296 has a horizontally oriented
cylindrical
handle portion 298 from which a longitudinally spaced pair of drive rods
300,302
transversely project in a downward direction parallel to a vertical axis 304.
Lower
end portions 300a,302a of the rods 300,302 (configured for receipt in the
bottom
wall openings 268) have laterally reduced cross-sections which create
downwardly
facing shoulders 300b,302b on the rods 300,302 at the tops of the lower end
portions 300a,302a.
To install the thermal trigger subassembly 294 on the in-place frame base
portion 206, the bottom wall 236.of the frame support portion 208 is
positioned
atop the rod 98 in a manner such that the upper end of the rod 98 passes
upwardly through the annular collar 266 (see FIG. 25) and bears against the
bottom side of the bottom spring wall 282, and the axis 262 is at an angle to
the
axis 228, with the bottom wall end portion 252 being positioned forwardly of
the
-24-
CA 02458190 2004-02-20
front side edge 212 of the bottom frame wall 210, and the bottom wall end
portion
250 being positioned rearwardly of the rear side edge 214. of the bottom frame
wall 219.
With an operator grasping the tool handle 298, the lower tool rod ends
300a,302a are then placed in the openings 268 of the bottom wall 236 of the
frame support portion 208 in a manner causing the rod shoulders 300b,302b to
bear against the top side of the bottom vvall 236. The tool 296 is then forced
downwardly to drive the thermal trigger subassembly 294 downwardly toward the
bottom wall 210 of the frame base portion 206, depressing the rod 98 against
the
resilient upward force of the damper spring 92 (see FIG. 19), until the bottom
wall
236 of the frame support portion 208 is vertically brought to the level of the
slots
220,224 in the vertical end tabs 216,218.
The tool 296 is then rotated in a counterclockwise direction (as viewed from
above) about the vertical axis 304, as indicated by the arrow 306 in FIG. 24,
to
cause the end portions 250,252 of the bottom wall 236 of the frame support
portion 208 to be respectively rotated into the end tab slots 220,224 and
underlie
the top side edges of their vertically enlarged portions 222,226. Tool 296 is
then
lifted out of engagement with the bottom wall 236 to thereby permit the damper
spring 92, via the rod 98) to drive the bottom wall end portions 250,252
upwardly
against the top side edges of the slot portions 222,226 and thereby captively
retain the end portions 250,252 within the slots 220,224 and bring the
temperature, sensing structure 200 to its fully assembled state depicted in
FIG. 20,
with the rod 98 upwardly bearing against the bottom wall 282 of the spring 280
(see FIG. 23), and the heat frangible element 202 blockingly preventing the
rod 98
from moving upwardly from its illustrated position in which the shutoff damper
88
is in its solid line open position shown in FIG. 19:
If the set point temperature within the combustion chamber 18 (for example,
430 degrees F) is reached, the bulb 270 shatters and unblocks the upper end of
the rod 98, permitting the damper spring 92 to upwardly drive the rod 98, as
-25-
CA 02458190 2004-02-20
indicated by the arrow 308 in FIG. 20A, to its upper limit position shown in
FIG.
20a. This causes the rod 98 to eject the spring 280 from the frame 204, and
the
shutoff damper 88 to be driven by spring 92 to its dotted line closed position
shown in FIG. 19.
To subsequently reset the combustion air shutoff system 86 after - this
occurs, the frame support portion 208 is simply removed from the underlying
frame
base portion 206, and another heat-frangible element 202 and spring 280 are
installed in the frame support portion 208 to form the previously described
thermal
trigger subassembly 294 which is then reinstalled on the underlying frame base
portion 206 as also previously described.
The, heat-frangible temperature sensing structure 200 provides several
advantages over the eutectic-based temperature sensing structures previously
described herein. For example, the glass bulb 270 is chemically inert and not
subject to thermal creep. Additionally, the temperature sensing structure 200,
due
to its assembly configuration, is easy to reset if the need arises to do so.
Moreover, due to the method.used to construct the heat-frangible. element 202
it is
easier to precisely manufacture-in a given trigger or set point temperature of
the
temperature sensing structure 200.
Schematically depicted in cross-section in FIG. 26 is a lower, combustion
chamber end portion of a further embodiment 10c of the previously described
water heater 10 shown in FIGS. 1 and 2. Representatively, water heater 10c is
identical to water heater 10 with the exception that the water heater 10c is
provided with a different combustion shutoff system.320. Unlike the previously
described combustion shutoff system 86 incorporated in water heater 10, the
combustion shutoff system 320 does not function to shut off further combustion
air flow into the combustion chamber 18 in response to the sensing of a
predetermined elevated temperature within the combustion chamber 18 during
firing of the water heater 10c. .
-26-
CA 02458190 2004-02-20
Instead, as will now be described, the combustion shutoff system 320
functions to shut off further fuel flow to the main/pilot burner striacture
32,40,
thereby terminating further combustion within the combustion chamber 18, in
response to a temperature within the combustion chamber 18 reaching a level
correlated to and indicative of a predetermined, undesirably high
concentration of
carbon monoxide in the combustion chamber 18. Illustratively, but not by way
of
limitation, this carbon monoxide concentration level is in the range of from
about
200 ppm to about 400 ppm by volume.
In addition to the main and pilot gas burners 32 and 40, the water heater
i0 10c also incorporates therein a thermostatic gas Valve 322 (which is also
present,
but not illustrated in the previously described water heater 10) and a
thermocouple
324 operatively associated with the pilot burner 40 in a conventional manner.
Gas
valve 322 is of a conventional, normally closed type,.is appropriately mounted
on
the exterior of the water heater 1 c, has an inlet coupled to a main gas
supply pipe
326, and has an outlet side coupled to the main and pilot burner gas supply
pipes
34 and 44. The normally closed gas valve 322 has a solenoid actuating portion
328 that includes a vertically movable metal rod 330 which is downwardly
biased,-
as indicated by the arrow 332, to a position in which it closes the valve 322
and
thereby terminates gas flow from the valve to the main and pilot burners
32,40.
The solenoid actuating portion 328 also includes an electrically conductive
wire
solenoid winding 334 that circumscribes the rod 330. When sufficient
electrical
current is passed through the winding 334 it creates on the rod 330 an
electromagnetic force which moves the rod 330 upwardly, as indicated by the
arrow 336, to thereby open the valve 322 and permit gas flow therethrough from
the main gas supply pipe 326.to the main and pilot burners 32 and 40.
The combustion shutoff system 320 includes an electrical wiring -circuit 338
in which the solenoid winding 334, the thermocouple 324 and a normally closed
switch structure 340 are connected in series as shown in FIG. 26, and a
-27-
CA 02458190 2004-02-20
temperature sensing structure 342 projecting upwardly through the arrestor
plate
24 into the interior of the combustion chamber 18 adjacent the main burner 32.
The temperature sensing structure 342, which directly senses a temperature
within the combustion chamber 18 near the main burner 32, is mechanically
associated with the switch structure 340 in a manner subsequently described
herein, and is similar in construction to the previously described temperature
. sensing structure 100 shown in FIGS. 1, 2 and 4. Specifically, the
temperature
sensing structure 342 includes the tubular collar member 108 projecting
upwardly
through a suitable opening in the arrestor. plate 24 and slidably receiving an
upper
end portion of the rod 98, the upper end of rod 98 being blocked by the
eutectic
disc member 120 captively retained in the open upper end of the collar 108.
Alternatively, this upper end portion of the eutectic-based temperature
sensing
structure 342 may have a configuration similar to that of one of the
previously
described eutectic-based temperature sensing structures 100a (FIG. 4A), 100b
(FIG. 10), 100c (FIG. 11), 100d (FIG. 12), or other suitable configuration.
Normally closed switch structure 340 includes schematically depicted,
spaced apart contact portions 344,346 fixedly secured in the wiring of the
circuit
338, and a central contact portion 348 anchored to a longitudinally
intermediate
portion of the rod 98 for vertical movement therewith and releasably
engageable
with the contacts 344,346 to close the switch 340. A lower end portion of the
rod 98 is slidingly received in an opening 350 extending through a
schematically
depicted fixed support structure 352. A coiled. compression spring 354
encircles
the rod 98, with the upper and lower ends of the spring 354 respectively
bearing
against the underside of the central contact 348 and the top side of the
support
structure 352. . Spring 354 , thus resiliently biases the rod 98 in an upward
direction.
With the temperature sensing structure 342 in its FIG. 26 position the
eutectic element 120 is intact and holds the rod 98 in its lower limit,
position in
which the central switch contact 344 is held against the contacts 344 and 346,
-28-
CA 02458190 2004-02-20
with the spring 354 being held in a vertically compressed state, thereby
closing the
circuit 338. Still referring to FIG. 26, during normal firing of the water
heater 10c,
impingement of the flame from the pilot burner 40 on the thermocouple 324
causes the thermocouple to thermoelectrically generate an electrical current,
through the closed circuit 338. This thermoelectrically generated electrical
current,
in turn, causes the solenoid winding 334 to create an electromagnetic force
that
upwardly shifts the metal valve rod 330 to thereby maintain the normally
closed
gas valve 32.2 in its open position to correspondingly maintain gas flow to
the
burners 32 and 40.
In the event that the temperature sensing structure 342 is exposed to an
elevated combustion temperature which is correiated to and indicative of a
predetermined, undesirably high concentration of carbon monoxide within the
combustion chamber 18, the eutectic element 120 melts, thereby permitting the
spring 354 to upwardly drive the rod 98, as indicated by the arrow 356, to its
FIG.
26A upper limit position in which the central switch contact 348 is lifted off
its
associated switch contacts 344 and 346, thereby opening the switch 340 and
thus
opening the circuit 338. The opening of the circuit 338, in turn, terminates
current
flow through the.solenoid winding 334 (se FIG. 26), thereby closing the gas
valve
322 and terminating further gas supply to the burners 32,30 and shutting down
combustion within the combustion chamber 18.
FIG. 27 schematically depicts an alternate embodiment 342a of the FIG. 26
temperature sensing structure 342. In the altered temperature sensing
structure
342a, the eutectic-based upper end portion 108,120 of the temperature sensing
structure 342 disposed within the combustion dhamber 18 is replaced with the
previously described frangible, fluid-containing bulb .202 and associated
frame
structure 204 shown in FIGS. 19-25. When the bulb 202 is heat shattered, by
exposure to a combustion chamber temperature indicative of and correlated to a
predetermined, undesirably high carbon monoxide concenfiration, within the
combustion chamber 18, the rod 98 is spring-driven upwardly away from its FIG.
-29- .
CA 02458190 2004-02-20
27 position, thereby opening the circuit 338 to thereby terminate, further gas
flow
to the burners 32 and 40.
Schematically depicted in FIG. 28 is a lower, combustion chamber end
portion of an alternate embodiment 10d of the previously described water
heater
10c shown in FIG. 26. Water heater 10d is identical to the previously
described
water heater 10c with the exception that it is provided with a modified
combustion
shutoff system 320a operative to shut off gas flow to the burner structure
32,40
in response ta an undesirably high concentration of carbon monoxide within the
combustion chamber 18.
1 o Combustion shutoff system 320a is identical to the previously described
combustion shutoff system 320 with the exception that the temperature sensing
structure 342 which projects upwardly into the interior of the combustion
chamber
18 to directly sense a combustion temperature therein; and the associated
switch
structure 340 mechanically linked . thereto, are replaced with a conventional,
normally closed thermally actuated switch 358 which is corinected in the
circuit
338 in series with the thermocouple 324 and the solenoid winding 334.
Representatively, but not by way of limitation, the switch 358 is a bimetallic
type
of thermally actuated switch.
The combustion chamber 18 has a metal vertical outer wail portion 360 that
includes an access door 362 illustratively positioned adjacent the main burner
32
and operative to provide selective access to the interior of the cornbustion
chamber
18. The switch 358 is mounted on the outer side of the metal access door 352,
in
thermal communication therewith, to thereby indirectly sense a combustion
temperature adjacent the inner side of the access door 362. ' Alternatively,
the
switch 358 could be mounted externally on another outer wall portion of the
combustion chamber 18.
The actuation temperature of the switch 358 (i.e., a temperature which will
open it) is selected in a manner such that when the combustion chamber
. temperature adjacent the inner side of the access door 362 reaches a level
-30-
CA 02458190 2004-02-20
correlated to and indicative of the presence of an undesirable carbon monoxide
level within the combustion chamber 18, the switch 358 will be subjected to
its
actuation temperature, thereby opening. This heat-actuated opening of the
switch
358 in turn opens the circuit 338 to thereby terminate gas flow to the burners
32,40 and shutoff further combustion in the combustion chamber 18.
While principles of the present invention have been illustrated and described
herein as being representatively incorporated in a gas-fired water heater, it
will
readily be appreciated by those skilled in this particular art that such
principles
could also be employed to advantage in other types of fuel-fired heating
appliances
such as, for example, furnaces, boilers and other types of fuel-fired water
heaters.
Additionally, while a particular type of combustion air inlet flow path has
been
representatively illustrated and described in conjunction with the water
heaters 10,
10a and 10b, it will also be readily appreciated by those skilled in this art
that
various other air inlet path and shutoff structure configurations could be
utilized, if
desired, to carry out the same general principles of the present invention.
Moreover, while several types of thermal trigger devices have been
representatively
utilized in the water heaters 10 -10d to shut off their associated gas valves,
or
further combustion air flow thereto, it will be readily appreciated by those
of skill in
this particular art that a variety of other types of thermal trigger devices
could be
alternatively utilized if desired.
The foregoing detailed description is to be clearly understood as being given
by way of illustration and example only, the spirit and scope of the present
invention being limited solely by the appended claims.
-31-
