Note: Descriptions are shown in the official language in which they were submitted.
CA 02580986 2007-03-05
S !
HEAT ACTIVATED AIR SHUTTER FOR FIREPLACE AND RELATED METHODS
s
FIELD OF THE INVENTION
The present invention relates generally to fireplaces and similar devices. In
particular, the present invention relates to an apparatus and methods by which
the airflow to
a burner of a fireplace or other heating/lighting unit may be regulated. More
particularly, with
lo respect to embodiments of the apparatus, the present invention includes an
air shutter
assembly that is generally automatically responsive to heat for controlling
primary airflow to a
main burner and/or a secondary burner to a gas fireplace or similar
heating/lighting unit.
BACKGROUND OF THE INVENTION
15 Fireplaces are desirable features in the home. However, devices that burn
non-solid
materials, such as gas, or that produce heat electrically have gradually
replaced traditional
wood or other solid fuel-burning fireplaces. Like, wood, the combustion of gas
does provide
real flames and heat, but requires a careful mixing of gas and air for optimal
performance
and a realistic flame. This aspect of the gas fireplace, and similar
appliances, typically
20 involves the delivery of air for combustion to an arrangement or device
where the air is mixed
with gaseous fuel, e.g., natural gas and propane ("gas"). Clearly, it is
advantageous that the
air and gas are mixed at a ratio for proper combustion. Then, the mixed air
and gas are
delivered to a burner, and ultimately provided to a combustion chamber of the
fireplace. In
some instances, the mixing of air and gas is accomplished in the actual burner
itself.
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r r
Multiple such arrangements have been created that are passive in nature, such
as
manifolds of a given size and shape with orifices designed to deliver a fixed
ratio of air and
gas for combustion. This ratio is typically optimized at a steady state,
heated operating
condition. It is well known that what is termed the "steady state" operation
of a gas fireplace
s is achieved after the unit has had an opportunity of burn for 30 minutes or
more. Some
manifolds, ducts, inlet passages, air passages and the like are routed through
the fireplace
to preheat the combustion air and increase the efficiency of the fireplace.
One example of
such a device is illustrated in U.S. Patent No. 6,295,981, which is
incorporated in its entirety
by reference.
io As a fireplace, or similar type of unit transitions from an initial or cold
start condition
to ultimately the "steady state" condition of combustion it has been observed
that the change
in efficiency of the combustion and an increase in the heat generated causes a
change in the
properties of the flames produced. Namely, the flames tend to be blue at the
onset of
combustion when the unit components and intake gases are generally at room
temperature
15 or, given that heating units may not be used only in interior locations,
other ambient
temperature. The flames gradually transition to a more desirable yellow color
as heat
increases and combustion becomes more complete. Since the air/gas ratio of the
known
unit is typically preset for correct burning at a heated, steady state
condition in conventional
gas fireplace units, a unit may operate under less than ideal combustion
conditions from the
20 initial cold start and for a long initial period of time thereafter. Very
little yellow flame is
observable during this period.
The generation of a blue flame is symptomatic of a "pre-steady state"
condition, also
termed "start-up" condition. Separate and apart from what is occurring inside
the heating
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unit, a predominantly blue flame is disadvantaged in a sales environment.
However,
consumers do not necessarily find a heating unit that is generating a blue
flame to be
desirable. Consumers wish to see a unit with a yellow flame since they can
more easily
envision how the unit will look in their htome when fully operated. Consumers
that ask to see
the operation of various heating units made by various manufacturers at the
point of
purchase may likely make their purchasing decision based on which one produces
the yellow
flame quicker.
Whereas many gas/air mixing schemes are simply designed and set for a steady
state condition, i.e., at operating temperature at equilibrium, some
fireplaces provide a
io mechanism for adjusting the air/gas mixture. However, if improperly
adjusted or
malfunctioning, these types of schemes can be unreliable, can produce improper
air/gas
mixtures, and can cause a buildup of soot or unburned carbon deposits or a
dangerous
condition.
There is a demand therefore, for a simple, reliable, and cost-effective way of
producing desirable combustion and aesthetic flame conditions of a fireplace
unit or the like
in a generally instantaneous manner that is, without the wait for the known
transition from an
initial cold start condition to the fully "steady state" condition. The
present invention satisfies
that demand.
SUMMARY OF THE INVENTION
The present invention has an objective of providing a desirable mixture of
combustion
air to a fireplace as the fireplace transitions from a cold start condition to
a steady state,
heated condition. One example of a fireplace that would be a suitable
candidate for the
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invention is a model "DV360" fireplace manufactured by CFM Corporation. It
will be
understood that the invention contemplates any suitable gas fireplace or like
device, More
specifically, the invention is directed to an automatic, heat activated air
shutter assembly for
moderating the amount of air entering a burner assembly of a fireplace. The
air shutter collar
assembly is opened and closed by one or more bi-metal coils attached to the
shutter in such
a fashion so that an increasing amount of air is permitted to enter the burner
assembly as the
heat acting on the coil(s) increases.
The fireplace may include a housing, which may take any suitable form as
needed or
desired and may be in the form of an enclosure or framework, sized and shaped
according to
a number of considerations. Examples of these considerations include budget,
space,
aesthetic, mechanical, safety, and other design and operating considerations.
Generally, the
housing is an enclosure or structure in which or to which mechanisms and
components are
enclosed or attached. The housing is also that which is attached at an
installation location.
The housing or box may be manufactured from a wide variety of materials,
including plastic
resin suitable for the application, sheet metal, burner tube material or any
other material
known to those skilled in the art.
One embodiment of the housing includes a top panel, a bottom panel, a back
panel
and opposing side panels. The two opposing side panels are further optional
depending on
the application. The housing of this embodiment is sized and shaped to
accommodate a fire
display box positioned therein. The fire display box is designed to present to
a viewer the
impression of a working, more traditional fireplace. The fire display box may
be open to the
front for viewing purposes and may optionally be provided with a fixed or
movable front panel
or panels, which may be at least in part transparent, translucent or opaque.
For purposes of
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this application, the front of the fireplace unit is that side of the unit
through which the interior
of the unit is at least partially viewable. It should be understood that the
exemplary unit used
to describe the invention herein will be similar to a conventional fireplace
with a single front
panel, through which the interior of the fireplace may be viewed. However, the
invention also
contemplates a"dual-front" or "see-through" unit or other suitable units in
which it is desirable
to automatically control the flame appearance.
A fire display box is positioned in the housing. For purposes of this
application, the
term "fire display box" will broadly signify the area similar to the portion
or area found in a
fuel-burning fireplace in which combustion takes place and from which the fire
that is
produced thereby may be viewed. Traditionally, this area is known as a
"firebox," "box," or
"fireplace."
Combustion takes place in or near the firebox by way of a burner, which is
supplied
with air and gas and preferably some form of pilot light or ignition device
with which to ignite
the air and gas mixture. A shutter is attached on or near the burner or in the
intake air
pathway to control the flow of intake air into the burner. The shutter
includes one or more bi-
metal coils attached thereto. When the burner is first lit, the burner
assembly, shutter and
coils are at ambient temperature and the shutter is in a closed condition.
This condition
permits a reduced amount of intake air to enter the burner housing. The
burner, shutter and
coils gradually warm to a heated condition and, in response, the coils
function to open the
shutter to provide an increased amount of intake air over the time the burner
transitions from
an initial ambient temperature to a steady state heated condition.
It has been found that the desired, yellow appearance of the flame may be
achieved
in an instantaneous fashion by use of the bi-metal coil and shutter assembly
according to
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embodiments of the invention. "Instantaneous" for purposes of this invention
is considered
about 1-5 minutes, which is a significant improvement over the prior art
systems which take
much longer to produce the desired yellow flame.
The invention provides, in one embodiment for example, a gas heating unit,
including
a combustion chamber. A burner housing assembly is positioned in the heating
unit to
provide combustion to the combustion chamber, wherein the burner housing
assembly
includes a burner housing and a gas and air mixing assembly in communication
with said
burner housing. The gas and air mixing assembly functions to mix gas and air
to provide a
yellow appearing flame instantaneously after initiation of combustion.
Another aspect of the invention provides a gas and air mixing assembly
automatically
responsive to changes in temperature to maintain said yellow appearing flame
over time. Yet
another embodiment of the invention provides a gas heating unit, including a
combustion
chamber and a burner housing assembly positioned to provide combustion to said
combustion chamber, wherein the burner housing assembly includes a burner
housing and a
gas and air mixing assembly in communication with the burner housing. The gas
and air
mixing assembly includes a mixing tube assembly. The mixing tube assembly
includes a
mixing tube having at least one air opening formed at an outer end thereof and
a shutter
collar assembly sized, shaped and positioned to seal with the at least one air
opening of the
mixing tube. The shutter collar assembly is attached to a bi-metal coil
spring. The bi-metal
coil spring is responsive to changes in temperature to withdraw the shutter
collar assembly
from the at least one air opening in response to an increase of temperature
from an ambient
temperature and permitting air to enter the at least one air opening.
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Yet another embodiment of the invention provides a method of controlling the
color of
a flame in a heating unit, including the steps of supplying a burner housing
of the heating unit
with a flow of gaseous fuel, sensing an initial start up condition of the
heating unit, limiting the
amount of air flow into the burner housing of the heating unit in response to
the sensing of
the initial start up condition to generate an instantaneous yellow appearing
flame upon
combustion, sensing an increase of temperature relative to the initial start
up condition, and
increasing air flow into the burner housing in response to the sensing an
increase in
temperature to maintain the color of the flame.
These and other advantages, as well as the invention itself, will become
apparent in
the details of construction and operation as more fully described and claimed
below.
Moreover, it should be appreciated that several aspects of the invention can
be used in other
applications where aesthetically pleasing flames would be desirable.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 shows an embodiment of a gas fireplace suitable for use with the burner
assembly of the invention;
Fig. 2 shows a perspective view of an assembled burner housing assembly made
in
accordance with one embodiment of the present invention;
Fig. 3 shows an expanded perspective view of the burner housing assembly of
Fig. 2;
Fig. 4 shows an exploded view of a dual spring assembly, shutter collar
assembly and
mixing tube assembly according to an embodiment of the invention;
Fig. 5 shows a perspective view of the assembly of Fig. 4 assembled;
Fig. 6 shows a partial top view of the assembly of Fig. 5;
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Fig. 7 shows an end view of the assembly of Fig. 4;
Fig. 8 shows a side view of the mixing tube assembly in an assembled
condition;
Fig. 9 shows a perspective view of a mixing tube assembly in an expanded
condition;
Fig. 10 shows a perspective view of a mixing tube;
Fig. 11 shows an end view of mixing tube;
Fig. 12 shows a first side view of a mixing tube;
Fig. 13 shows a second side view of a mixing tube rotated 90 degrees;
Fig. 14 shows an end view of a spring plate;
Fig. 15 shows a perspective view of a spring plate;
Fig. 16 shows a side view of a spring plate;
Fig. 17 shows a side view of a tube cap;
Fig. 18 shows the tube cap of Fig. 17 in an end view;
Fig. 19 shows an expanded perspective view of another embodiment of a mixing
tube
assembly and bimetal coil spring assembly;
Fig. 20 shows a side view of a spring bar;
Fig. 21 shows an end view of a spring bar;
Fig. 22 shows a perspective view of a spring bar;
Fig. 23 shows a top view of bimetal coil spring;
Fig. 24 shows a side view of the bimetal coil spring of Fig. 23; and
Fig. 25 shows an expanded view of the shutter collar assembly.
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DETAILED DESCRIPTION OF A PRESENTLY PREFERRED EMBODIMENT
The present invention will now be described in detail with reference to
certain
embodiments thereof as illustrated in the accompanying drawings. In the
following
description, numerous specific details are set forth in order to provide a
thorough
understanding of the present invention and how it may be applied to a gas
fireplace. It will be
apparent, however, to one skilled in the art, that the present invention may
be practiced
without some or all of these specific details. In other instances, well-known
process steps
and/or structures have not been described in detail to prevent unnecessarily
obscuring the
present invention.
Fig. 1 illustrates a gas-fueled heating unit, which in a preferred embodiment
is a
fireplace in accordance with one embodiment of the present invention.
Referring to Fig. 1, a
gas heating unit 60 includes a combustion chamber 61 with sidewalls (not
shown), a rear wall
66 and top and bottom walls 63 and 65. Simulated logs, e.g., ceramic gas logs
68 are
arranged in a conventional manner over a burner housing assembly 100 according
to an
embodiment of the invention. A glass front door (not shown) closes the
combustion chamber
61 and provides visual access thereto. While the invention will be described
by reference to
a unit having a single glass front door, the unit may also be what is termed a
"dual-front" or
"see-through" unit.
Surrounding the combustion chamber 61 is a unit housing or fireplace housing
67.
Air circulation pathways are formed within the fireplace housing 67 in a
conventional manner.
One such pathway allows room air to be brought in from the bottom front of the
fireplace
housing and beneath the combustion chamber 61 (arrows 72). The room air is
then directed
along the rear of the combustion chamber 61 (arrows 73). Finally, the room air
is directed
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along the top of the combustion chamber 61 (arrows 74) and back into the room.
At this
point, the room air has been heated due to the placement of the pathway air
proximate to the
heated combustion chamber 61.
In another pathway, combustion air (i.e., air entering the combustion chamber
61) is
brought in from the exterior of the building through a concentric flue pipe
assembly common
to this type of fireplace. As will be described below, the combustion air can
enter from one
of two available ports. Once within the fireplace housing 67, the combustion
air travels a
pathway immediately outboard of the room air pathways. That is, the inboard
side of the
combustion air pathway includes the wall structure forming the outboard side
of the room air
pathway. This placement also aids in the heating of the room air contained
within the room air
pathways. Combustion air travels downward through the rear of the heating unit
60 (arrows
75), then into the combustion chamber 61 (arrow 76) through combustion chamber
air inlets
78 formed in a bottom portion of the rear wall 66. The fireplace housing 67
has exterior
sidewalls (not shown), top wall 82, a bottom wall 83 and a rear wall 84.
Disposed within the combustion chamber 61 is a burner housing assembly 100
according to an embodiment of the invention. The burner housing assembly 100
includes a
heat-activated mechanism 102 according to an embodiment of the invention. The
heat-
activated mechanism 102 regulates the mixing of gas and air entering the
burner housing
assembly 100 in response to changes in temperature by changing the mixture of
gas and air
in a manner that will be described in greater detail below.
Ignition of the gas and air mixed by the heat-activated mechanism 102 produces
a
yellow flame or flames 200 in an instantaneous fashion (which again for
purposes of this
application means in about 1-5 minutes after initial ignition) and not in the
30 or more minutes
CA 02580986 2007-03-05
that the prior art takes to produce a yellow flame. The mechanism 102
maintains the
appearance of the flames 200 generally from a start up condition of the unit
through a steady
state condition.
Described herein is a fireplace assembly with a heat-activated mechanism,
which
provides for a predetermined ratio of air and gas at a cold start up condition
and transitions
to a heated and steady state condition in response to changes in temperature,
experienced
by the mechanism. While the above-described assembly is intended to be used
with a
fireplace, it is to be realized that the described arrangement according to
the embodiments
of the invention could be incorporated in other types of units, such as for
example, direct
vent, natural vent and vent-less fireplace systems and even gas operated units
which are not
fireplaces.
Figure 2 shows an assembled burner housing assembly 100 according to an
embodiment of the invention that includes a burner housing 101 and an
assembled gas and
air mixing assembly 102. The burner housing assembly 100 includes a number of
associated or attached components, the details of which are provided in Fig. 3
and the
following drawings. Generally, the burner housing assembly 100 includes a
burner housing
101, which has a rectangular shape, within which gaseous fuel and air are
mixed at least in
part through the functioning of the gas and air mixing assembly 102. The
burner housing
101 may be fastened together by welding, for example. Other suitable shapes of
the
housing are contemplated.
Turning to Fig. 3, the burner housing 101 is provided with a port loading
channel
104, which fits atop the burner housing and closes the burner housing.
Preferably, the port
loading channel 104 is provided with a sealant, (not shown) to effect a seal
with burner
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housing 101. Port loading channel 104 includes a plurality of port loading
channel openings
106 formed therethrough for gas and air to leave the burner housing in a
pattern which may
be designed and intended to produce desired flame patterns.
A port loading channel gasket 108 is positioned atop port loading channel 104.
One
or more ceramic tile 110 is positioned adjacent or atop the port loading
channel gasket 108
at least in part to protect the burner housing assembly 100 from direct
exposure to heat
from flames. The one or more ceramic tile 110 is flanked by one or more burner
tile gasket
112. The one or more ceramic tile 110 is held in place by first and second
ceramic tile
mounting angles 114, which fasten to the burner housing 101 by conventional
fasteners 116,
such as screws. A securing bracket 118 attaches to the burner housing 101 and
includes a
pair of log spacer brackets 120, which log spacer brackets overlay ceramic
tiles 110 when
fastened to the securing bracket.
The burner housing assembly 100 may include other devices for supporting an
artificial log set (not shown) above the burner housing assembly. For example,
a front log
support bracket 122 may be mounted to the burner housing 101 over the ceramic
tile
mounting angles 114.
The burner housing 101 includes a burner housing opening 126. The gas and air
mixing assembly 102 is disposed in the burner housing opening 126. A spring
plate gasket
128 is interposed between the burner housing 101 and gas and air mixing
assembly 102 to
create a seal with the burner housing opening 126. Details of each of the
above assemblies
and elements of the burner housing assembly 100 are provided hereinbelow.
Figs. 4-7 show the air and gas mixing assembly 102 in detail. The air and gas
mixing
assembly 102 includes a mixing tube assembly 130, which is further detailed in
Figs. 8 and
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9. The mixing tube assembly 130 includes mixing tube 132, which is an
elongated cylinder
shape. Upper and lower air openings 134, 136 are formed at an outer end 138 of
the
mixing tube 132. An annular or washer shaped tube cap 140 is positioned at the
outer end
138 of the mixing tube 132,
A shutter collar assembly 142 positioned over the upper and lower air openings
134,
136 is sized and shaped to close over the upper and lower air openings 134,
136. At
ambient air temperatures, the shutter collar assembly 142 is held closely
against the mixing
tube 132 so as to close off the upper and lower air openings 134, 136. The
shutter collar
assembly 142 is held in the closed condition at ambient temperatures by
respective upper
and lower bi-metal coil springs 144, 146, which are configured to bias the
shutter collar
assembly 142 in the depicted position. The shutter collar assembly 142, which
is disposed
on the upper air opening 134, may be considered a first shutter collar
subassembly 142a
and the shutter collar assembly, which is disposed over the lower air opening
136, may be
considered a second shutter collar subassembly 142b.
Each of the upper and lower bi-metal coil springs 144, 146 are fastened to a
spring
bar 148, which in turn is fastened to a spring plate 150. Spring plate 150 has
an opening
152 which is sized and shaped to receive the mixing tube 132.
It can be seen, especially in Fig. 7, that the bi-metal springs on 144, 146
hold the
shutter collar assembly closely around the periphery of the mixing tube 132 at
the outer end
138 thereof (see Fig. 4). In this way, air is not drawn into the mixing tube
132 during
operation because the shutter collar assembly 142 closes over the upper air
are opening
134 and the lower air openings 136. The bi-metal coil springs 144, 146 are
constructed and
oriented in such a fashion to uncoil and pull the shutter collar assembly 142
away from the
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mixing tube 132 thus exposing the upper air opening 134 and the lower air
opening 136,
which permits air to enter interior of the mixing tube 132, mix with gaseous
fuel and enter the
burner housing 101 (see Fig. 3, for example). The embodiment of the gas and
air mixing
assembly 102 shown in Figs. 4-7 is intended for use with natural gas, but may
be adapted for
use with LP gas, as in known in the art and is also shown below with reference
to Fig. 19.
Figs. 8 and 9 show the mixing tube assembly 130. The mixing tube assembly 130
includes a cylindrical mixing tube 132. The mixing tube 132 is also shown in
Figs. 10-13.
Referring then to Figs. 8-13, at the outer end 138 of the mixing tube 132 are
formed a pair
of cutaway sections, which when tube cap 140 is attached to the outer end of
the mixing
tube cause the formation of openings 134, 136. The tube cap 140.has a washer
or annular
shape with a cap opening 141 centrally located therethrough. Spring plate 150
is generally
and L-shaped bracket having a plate opening 152, which is sized to receive the
mixing tube
132. A spring plate 150 is positioned close to the outer and 138 of the mixing
tube 132.
The mixing tube assembly 132 may be assembled by welding, for example.
Figs. 14-16 show spring plate 150 in detail. Spring plate 150 has a spring
plate tube
section 158 that includes plate opening 152. A spring plate bend 156 separates
the spring
plate tube section 158 from a spring plate spring section 160 at an angle of
about 90
degrees. The spring plate spring section 160 includes a pair of spaced spring
receiving tabs
154.
Figs. 17 and Fig. 18 show tube cap 140, which has a flat washer shape and a
centrally located cap opening 141. Tube cap 140 is attached to the outer end
138 of mixing
tube 132 (see Fig. 8, for example). The attachment may be accomplished in any
suitable
fashion, for example by welding.
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Fig. 19 shows an embodiment of a mixing tube assembly and a partial shutter
collar
assembly in detail and usable with LP gas (propane). The mixing tube assembly
230 includes
mixing tube 132, which is an elongated cylinder shape. Upper and lower air
openings 134,
136 are formed at an outer end 138 of the mixing tube 132. An annular or
washer shaped
s tube cap 240 is positioned at the outer end 138 of the mixing tube 132. A
manually
adjustable choke sleeve 162 is provided on the mixing tube 132 and has the
general shape
of a flattened ring with a pair of cutouts 164 corresponding in shape and size
to the upper
and lower air openings 134, 136. The choke sleeve 162 is slidably and
rotatably positioned
on the mixing tube 132 and over the upper and lower air openings 134, 136 and
when
rotated can be used to cover or uncover the upper and lower air openings and
thus adjust
how much of the openings are exposed. A set screw 166 is provided in a slot
168 of the
choke sleeve 162 to fix the choke sleeve in place, preferably after adjustment
for a desired
air/fuel ratio.
Each of the upper and lower bi-metal coil springs 144, 146 are fastened to a
spring
bar 148, which in turn is fastened to a spring plate 150. Spring plate 150 has
an opening
152 which is sized and shaped to receive the mixing tube 132. The free ends
180 of the bi-
metal coil springs 144, 146 occlude the upper and lower air openings 134, 136
when in an
initial start-up condition (i.e., ambient temperature). As the temperature
increases, the bi-
metal coil springs 144, 146 unwind and draw away from the upper and lower air-
openings
134, 136 to permit entry of an increased volume of air to enter the mixing
tube 132.
Figs. 20-22 show various views of spring bar 148. Spring bar 148 is an "L"
shaped
bracket having a spring bar hole 170 for fastening the spring bar to a spring
plate (see 150
in Fig. 19, for example).
CA 02580986 2007-03-05
Figs. 23 and 24 show a bi-metal coil spring 144 according to an embodiment of
the
invention. It should be noted that upper and lower bi-metal springs 144, 146
(See Fig. 4, for
example) are identical in material composition and geometric configuration in
this example.
For the fireplace used in the above example, it is desired to construct the bi-
metal coil
springs 144, 146 from a material that withstands 1000 degrees F maximum
temperature
and about 800 degrees nominal temperature. The spring type is an ASTM-TM-1,
available
from Atlanta Alloy Inc., and of a composite construction consisting of two or
more materials
with different thermal expansion coefficients, and which causes the spring to
unwind when
heated. Other bi-metal springs or the equivalent may be used. It should be
understood that
the amount of movement of the spring and, in some embodiments, the attached
shutter
assembly, will correspond to the bi-metal materials used, the construction of
the spring, and
the temperature range experienced by the spring. In other words, a spring used
in the
mechanism of the invention may be lighter in construction or more sensitive to
temperature
changes when a relatively lower range of temperature is experienced and a
heavier or less
sensitive spring will be used when relatively higher range of temperature
change is
experienced by the spring. In this manner, a properly controlled airflow and
mixing ratio is
maintained when applying the principles described herein to different unit
conditions.
The coil springs 144, 146 are provided in the coiled configuration, in part to
be
compact and usable in a small space, and in part to provide a large amount of
movement, or
deflection for the temperature changes experienced by the springs. Each of the
bi-metal coil
springs 144 include a mounting portion 178 for attaching to the spring
receiving tab 154 of
a spring plate 150 (see Fig. 15, for example) and spring bar 148. The
attachment method is
preferably welding to provide the correct positional relationship for proper
sealing of the
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shutter collar assembly 142 to a respective upper and lower air opening 134,
136 (Fig. 4,
for example). Other attachment methods may be employed, such as fasteners,
screws,
rivets and so on. At an end opposite the mounting portion 178 is an attachment
portion 180
for attaching the bi-metal coil spring 144 to a shutter collar assembly 142
(see Fig. 4, for
example and Fig. 25).
Fig. 25 shows an expanded view of one half of a shutter collar assembly 142.
The
assembly 142 shown includes a shutter collar 172, which is a curved metallic
semi-circular
member. Attached to an inside surface 174 of the shutter collar is a shutter
gasket 176.
The shutter gasket 176 is preferably a closed cell silicone sponge gasket of
medium density.
While endeavoring in the foregoing specification to draw attention to those
features of
the invention believed to be of particular importance it should be understood
that the
Applicants claim protection in respect of any patentable feature or
combination of features
hereinbefore referred to and/or shown in the drawings whether or not
particular emphasis
has been placed thereon. While the apparatus and method herein disclosed forms
a
preferred embodiment of this invention, this invention is not limited to that
specific apparatus
and method, and changes can be made therein without departing from the scope
of this
invention, which is defined in the appended claims.
Therefore, the foregoing is considered as illustrative only of the principles
of the
invention. Further, since numerous modifications and changes will readily
occur to those
skilled in the art, it is not desired to limit the invention to the exact
construction and operation
shown and described, and accordingly, all suitable modifications and
equivalents may be
resorted to, falling within the scope of the invention.
17
