US 3747586 A
A burner arrangement for sealed combustion type furnace systems of the gaseous fuel consuming type in which a constant burning pilot is used, wherein a check valve controlled connection between the furnace plenum chamber, from which heated air is circulated by a circulation blower for heating purposes, is provided to supply air to the pilot to avoid extinguishment of the pilot by backflow of products of combustion due to wind conditions acting on the furnace flue or negative pressure conditions applied to the burner, through leakage in the system, by the action of the circulation blower. The burner arrangement also includes a combination main and vernier shutter control arrangement for the burner blower, and a change over orifice arrangement in the gaseous fuel supply lines in the burner permitting ready switching of the burner between natural gas and propane gas.
Claims available in
Description (OCR text may contain errors)
United States Patent 1 Weiss BURNER ARRANGEMENT FOR SEALED COMBUSTION TYPE SYSTEMS  Inventor: Frank F. Weiss, Park Ridge, Ill. [7 3] Assignee: Mid-Continent Metal Products Co.,
 Filed: Feb. 2, 1972  Appl. No.: 222,825
 US. Cl 126/110 B, 126/116 R  Int. Cl. F24h 3/10  Field of Search ..126/110 B, 110 E,
 References Cited UNITED STATES PATENTS 3,124,120 3/1964 Best 126/110 B 3,680,541 8/1972 Honaker, Jr. 126/110 B 3,152,633 10/1964 Morrison 126/116 R 2,56l,l00 7/1951 Dahlstrom 126/116 R 3,448,736 6/1969 Shenberger 126/116 R 11 3,747,586 1 Jul 24,1973
Primary Examiner-William E. Wayner Assistant Examiner-William E. Tapolcai, Jr. Attorney-Robert C. Brown, Jr., John M. Mann et al.
A burner arrangement for sealed combustion type furnace systems of the gaseous fuel consuming type in which a constant burning pilot is used, wherein a check valve controlled connection between the furnace plenum chamber, from which heated air is circulated by a circulation blower for heating purposes, is provided to supply air to the pilot to avoid extinguishrnent of the pilot by backflow of products of combustion due to wind conditions acting on the furnace flue or negative pressure conditions applied to the burner, through leakage in the system, by the action of the circulation blower. The burner arrangement also includes a combination main and vernier shutter control arrangement for the burner blower, and a change over orifice arrangement in the gaseous fuel supply lines in the burner permitting ready switching of the burner between natural gas and propane gas.
ABSTRACT 9 Claims, 10 Drawing Figures PRODUCT OF COMBUSTION WARM AIR- AIR TO BURNER BURNER ARRANGEMENT FOR SEALED COMBUSTION TYPE SYSTEMS This invention relates to a burner arrangement for sealed combustion type systems, and more particularly, to gaseous fuel burning apparatus for use in combustion systems of the type in which the air for supporting combustion is taken from and discharged into the outside air, and the furnace heats air circulating within the structure to be heated, which inside air is circulated by a circulation blower.
One important application of heating systems of the type to which the invention relates is mobile homes, wherein the furnace is mounted within a closet structure in the mobile home and comprises a combustion chamber fired by a gaseous fuel consuming burner apparatus including a main burner and a constant burning pilot therefor, and a burner blower which brings outside air in and through the burner into the combustion chamber to support combustion, with the products of combustion being discharged through the furnace flue. A circulation blower is provided which blows inside air through the furnace plenum chamber and into and through the warm air ducts, thence into the space to be heated, for return through return air ducts to the circulation blower. In systems such as this, a room thermostat controls actuation of the burner blower, with the electrical system involved being such that the circulation blower starts a delayed interval after the burner blower is energized, and continues for a period of time after the burner blower is shut off.
A long standing problem that has been experienced with equipment of this type has been the tendency of the pilot to become extinguished after the burner blower is shut off, requiring relighting of the pilot, with the inconvenience and irritation that is attended with such situations.
My studies of the problem show that a frequent reason for pilot extinguishment in equipment of this type is that products of combustion in the combustion chamber at the time of burner shut off are either held within the combustion chamber or back flow into the burner, resulting in smothering of the pilot flame. This condition can be result of wind conditions causing back flow of the products of combustion in and from the flue, or leakage in the furnace in closeting and ducting structure that allows the suction side of the circulating blower to apply a negative pressure on the combustion chamber.
A principal object of the invention is to provide a burner arrangement for sealed combustion systems of the type indicated that makes provision for supplying fresh air to the pilot burner for the period immediately after the burner blower is shut off.
Another principal object of the invention is to arrange the burner mounting structure so that fresh air passing through the furnace plenum chamber under the action of the circulation blower has limited access to the burner pilot.
Yet another object of the invention is to provide a simplified fuel change over valve arrangement for gaseous fuel type burners permitting ready switching between natural gas and propane gas without requiring the special control device that is commonly used in burners adapted for this purpose.
Yet a further object of the invention is to provide an improved burner blower shutter arrangement making possible ready and accurate air flow control to the burner from the burner blower.
Still other objects of the invention are to provide a burner arrangement for sealed combustion type systems that is inexpensive of manufacture, convenient to install and use, and long lived in operation.
In accordance with this invention, the burner assembly makes provision for a check valve controlled connection between the furnace plenum chamber, through which return air from the space being heated is driven by the circulating blower, and the burner pilot, to supply the pilot with fresh air during the critical period just after the burner blower is shut off and products of combustion may remain in the combustion chamber. Continued supply of fresh air to the burner pilot will thus be assured after the burner blower ceases operation, even though wind conditions or negative pressure acting on the burner tend to retain the products of combustion temporarily in the combustion chamber. The burner is equipped with a simple dual orifice head change over valve arrangement in its fuel supply conduit between the burner manifold main control valve and the manifold tube for ready switching between natural gas and propane, and the air port between the burner blower and the burner plenum is controlled by a composite shutter arrangement providing for close adjustment control of air feed to the burner.
Other objects, uses and advantages will become obvious or be apparent from a consideration of the following detailed description and the application drawings.
In the drawings:
FIG. 1 is a diagrammatic view illustrating a typical sealed combustion heating system of the type to which the invention relates, as it might be applied to a mobile home, the figure being in the form of a vertical section with parts shown in elevation;
FIG. 2 is a fragmental view on an enlarged scale illustrating the burner arrangement itself, insofar as it is pertinent to the invention, with parts of the burner being shown diagrammatically only;
FIG. 3 is a perspective view of a check valve employed in the arrangement of FIGS. 1 and 2;
FIG. 4 is a fragmental view similar to that of FIG. 2
but illustrating a modified form of the invention;
FIG. 5 is a fragmental view, partially in elevation, illustrating a novel change over valve arrangement in accordance with this invention;
FIG. 6 is a fragmental view showing on an enlarged scale, and in section, the shutter arrangement shown in FIG. 2 that is employed to control the port between the burner blower and the burner plenum chamber;
FIG. 7 is a plan view of the main shutter member of the shutter control arrangement;
FIG. 8 is an end view of the member shown in FIG.
FIG. 9 is a plan view of the vernier shutter member of the shutter control arrangement; and
FIG. 10 is an end view of the member shown in FIG.
However, it is to be distinctly understood that the specific drawing illustrations provided are supplied primarily to comply with the requirements of the Patent Code, and that the invention is susceptible of other embodiments that will be obvious to those skilled in the art, and which are intended to be covered by the appended claims.
GENERAL DESCRIPTION Reference numeral generally indicates the furnace closet area of a mobile home or the like in which sealed combustion type furnace 12 is mounted for purposes of heating the mobile home or the like, which comprises a combustion chamber 14 suitably mounted within a furnace jacket 16 and fired by burner apparatus 18 that is suitably mounted in the jacket wall 20 in alignment with firing tube 22 that extends between the wall 24 of the combustion chamber and jacket wall 20. Burner apparatus 18 generally comprises a suitable blower 26 drawing fresh air from a suitable conduit 28 leading to the outside air (at a suitable grilled opening or the like), a main gas burner nozzle assembly 30 of any suitable type to which gaseous fuel is supplied for burning in combustion chamber 14 and which is suitably mounted in burner plenum chamber 31, a pilot burner 32 that may be of any suitable and conventional type for igniting the gaseous fuel emitting from nozzle assembly 30, a suitable pilot hood 33 in which pilot 32 is mounted, and a suitable flue 34 through which the products of combustion pass to the atmosphere in the usual and customary manner. The discharge end 35 of nozzle assembly 30, and pilot 32, are operablyassociated within burner blast tube 37 in the usual manner.
The furnace closet area 10 is defined by a suitable wall structure 36 which is provided with a suitable access door 38. The furnace 12 includes a suitable housing structure 40 in which is mounted a suitable circulating blower 42 which draws return air from the space being heated through return duct 44, grilled opening 47 and interior opening 48 of the housing 40, for blowing into the furnace plenum chamber 46 and thence into warm air duct 49 for conveyance to the space being heated.
Housing 40 includes suitable furnace vestibule door 51 providing access to blower apparatus 18.
The furnace 12 and its burner apparatus 18 are conventionally arranged so that under the control of a room thermostat in the space being heated, when heat is desirable, burner blower 26 is turned on and the fuel control valving of the burner apparatus 18 supplies fuel to nozzle assembly 30, which is ignited by pilot 32. The burner blower 26 draws fresh outside air through duct 28 and directs same through firing tube 22 into combustion chamber 14, with the products of combustion emerging into the outside air through flue or chimney 34.
Circulating blower 42 is actuated at the same time as, or perhaps somewhat later than, the actuation of burner blower 26, to draw air from the space being heated through return duct 44 and into and through the furnace plenum chamber 46 for supply to warm air duct 49 that conveys same to the space being heated. When the temperature in the space being heated reaches the temperature set by the room thermostat in that space, the electrical system is such that burner blower 26 shuts off, and fuel supply to the burner apparatus is discontinued, but circulation blower 42 continues to operate for a predetermined time thereafter to continue to supply warm air to the space being heated from the residual heat in the furnace.
Pilot burner 32 is of the constant burning type, and as conventional, it is intended to burn continuously to be available to light the burner nozzle assembly 30 on actuation of the burner apparatus 18 to supply heat to the room space to be heated.
As discussed hereinbefore, heating apparatus of the type indicated, and especially that adapted for use in connection with mobile homes, has experienced continued difficulty in the extinguishment of the pilot burner flame after the operation of the blower apparatus 18 has been discontinued under control of the room thermostat. My studies of the problem have revealed that this has been caused by products of combustion smothering the pilot flame in the first few secomds after burner blower shut off, and this can be caused by several reasons. For instance, wind conditions may cause back flow of the products of combustion in flue 34 so that when the fresh air flow provided by the burner blower 26 is discontinued, the products of combustion tend to press in on the pilot burner 32, isolating it from its source of oxygen and then extinguishing its flame.
Also, the continued operation of the circulation blower 42 tends to create a negative pressure in the closet space 10A adjacent the furnace vestibule door, and any leakage through this door 51 or the paneling adjacent same subjects the space 50 in which the burner apparatus 18 is mounted to negative pressure conditions, whereby the products of combustion tend to back flow through burner apparatus 18, thereby extinguishing pilot burner 32.
In accordance with this invention, burner apparatus 18 is provided with a check valve controlled connection between the furnace plenum chamber 46 and the pilot hood 33 whereby fresh air under the pressure supplied by circulating blower 42 is made available to the pilot burner to maintain its flame in spite of conditions that might otherwise cause stagnation of the products of combustion within the combustion chamber or back flow into the burner apparatus. In the form shown, this connection is generally indicated at 52 in FIG. 2 and comprises an external air box structure 54 in communication with the plenum chamber 46 through passageway 56 and supplied with a check valve 58 for closing the passage 56 on operation of the blower apparatus 18. Air box structure 54 is in communication with internal air box structure 60 which overlies opening 62 formed in the burner blast tube 37 in alignment with passage 64 of the pilot hood 33 that already exists in conventional pilot hoods.
In the embodiment of FIG. 4, a modified check valve arrangement is provided in which the check valve 58A is .mounted within the internal air box structure 60.
Further in accordance with this invention, the change over valve device of FIG. 5 is employed in the fuel conduiting structure 72 that extends betweenthe main control valve 73 for the conventional manifold 74 that is conventionally incorporated in burner assembly 30. Change over valve device 70 comprises a pair of orifice forming heads 76 and 78 mounted in either end of orifice spring 80, which in the mounted position of the device, biases the heads 76 and 78 to the positions indicated. The head 76 defines an orifice 82 proportioned to supply natural gas to burner nozzle assembly 30, while orifice head 78 is formed with an orifice opening 84 proportioned to supply propane to assembly 30. Orifice heads 76 and 78 are received within orifice holder 86 that is provided with screw cap 88 sealed as at 90. To change over the burner apparatus from one fuel to another merely requires removal of cap 88 to reverse the positions of orifice heads 76 and 78.
Operably associated with burner blower 26 is shutter device 160 (see FIGS. 6 that controls the operative size of the port 102 between blower 26 and the burner plenum chamber 31. The shutter device 160 comprises a main shutter member 164 slidably mounted in a suitable trackway 1116 formed in the blower in alignment with port 102, with the main shutter member 104 telescopingly carrying a vernier shutter member 108. Port 102 can thus be controlled by spacing the main shutter member 164 across same to provide a rough port opening adjustment, and then adjusting the vernier shutter element 108 as desired to provide a fine adjustment of the effective opening of port 102.
SPECIFIC DESCRIPTION In practice, the specifics of the furnace 46 and its associated parts may be of any convenient type, the illustrations of FIGS. 1 and 2 being largely diagrammatic in nature. This also applies to the manner of mounting the furnace and associated parts where it is to be used and whether in a mobile home or other building structure in which equipment of this general type is used.
In the specific form illustrated, the burner apparatus 18 includes a mounting flange 110 suitably affixed to the furnace wall by bolts or the like, with a suitable gasket 112 being interposed between the flange 110 and the wall 20. The burner plenum 31 is part of the burner housing structure 114 in which the burner nozzle assembly is suitably mounted. The nozzle assembly 30 conventionally includes the aforereferred to manifold tube 74 suitably mounted within same in any suitable manner, which is in turn connected to the orifice holder 86, in accordance with the present invention.
The burner blower 26 may be made of any suitable type, the burner housing 114 being formed to define an opening 116 that is aligned with the opening 118 of the blower 26 to define a port 1112 through which air is supplied to the burner plenum 31 by blower 26. In the form shown, a suitable gasket 122 is interposed between the blower housing 119 and the burner housing 114, these parts being suitably secured together in any appropriate and convenient manner.
The firing tube 22 includes flange 124 that issuitably affixed to the furnace jacket wall 20.
The connection 52 of this invention comprises a check valve controlled passageway between the furnace plenum chamber 46 and the burner pilot 32 that is defined by hole or opening 125 formed in the firing tube flange 124, hole or opening 126 formed in the first jacket wall 20, hole or opening 128 formed in gasket 112, and hole or opening 130 formed in the burner mounting flange I10, together with the passageway segments 132 and 134 defined by the exterior and interior box structures 54 and 60, respectively, the opening 133 in the burner mounting flange 110 that connects passageway segments 132 and 134, the opening 162 that is formed in the burner blast tube, and the opening or hole 64 which is formed in the pilot hood 33.
The box structure 54 in the form shown comprises dished member 140 suitably secured, as by welding, to the burner mounting flange 110, with the joint between the member 140 and the mounting flange 110 being suitably sealed to avoid air leakage from the connection 56.
The internal box structure 60 comprises an appropriately shaped plate 142 fixed to the burner mounting flange and blast tube to close off the space about openings 62 and 133, so as to make the passageway segment 134 air tight.
Valve member 58 in the embodiment of FIG. 2 comprises a plate element 150 of generally T shaped configuration defining an enlarged head 152 and a stem 154. The stem is formed with a degree or right angle bend as at 156 so that by extending the stem 154 through opening 133 of the burner mounting flange, with the head 152 disposed in the space that is to define the passageway section 134, the major portion of the stem 154 projects downwardly under the action of gravity and overlies opening of the burner mounting flange. The valve 58 and burner mounting flange opening 133 should be proportioned so that in its normal operating position, the stem 154 of valve element 152 lies closely adjacent the burner mounting flange, and also overlies opening 136 formed in same; however, when the burner blower 26 discontinues operation while the circulating blower 42 continues operation, the pressure differentials involved will pivot valve element 152 counterclockwise of FIG. 2 toperrnit ready flow of air through connection 56. When the circulating blower 42 discontinues operation, the valve element 152 under the action of gravity has its stem 154 return to close adjacency to opening 130 to prohibit back flow of prod ucts of combustion through connection 56.
In the form of FIG. 4, valve member is omitted, and instead internal box structure 60 is formed with a support plate 161 that is perforated as at 163 for air flow therethrough on opening of valve 58A. Valve 58A is in the form of plate member 165 that rests under action of gravity on plate 161 in overlying relation to opening 163. When operation of the burner blower ceases, fresh air under the pressure generated by circulation blower 42 lifts valve member 165 to provide for flow of same through passage 62. Member 165 is formed with turned up edge portions 167 that limit upward movement of same relative to plate 161. The arrangement of FIG. 4 is otherwise the same as that of FIGS. 1 3, as indicated by corresponding reference numerals.
With regard to change over valve 70, the orifice holder 86 is suitably connected to the manifold main valve control by suitable coupling 72. The orifice holder 86 comprises tubular member 166 having its end 162 internally threaded as at 164 for connection to pipe seal 166 to which manifold tube 74 is conventionally affixed. The pipe seal 166 includes a threaded extension 168 that is received in the threaded opening, and defines a planar end portion 1'70 against which the orifice head 176 seats. The pipe seal and its extension 168, of course, defines a suitable bore that communi' cates between the head 76 and the manifold 74.
The orifice holder 86 defines bore or chamber 172 at which the orifice spring 80 and the orifice heads 76 and 78 are mounted. Holder 86 defines a port 174, and suitable affixed over the port 174, and to the holder 86 is threaded stud 176 that is adapted for connection to coupling 72 and defines bore 178 through which gas flow from the manifold main control valve 73 passes into the connector 86. Control valve 73 may be of any suitable conventional type.
The orifice holder 86 at its end 180, in the form shown, is internally threaded as at 182 to receive the threaded stem 184 of cap 88. Cap 88 defines an enlarged head portion 186, which is formed with a frusto conical recess 188 that receives the orifice head which contains the orifice opening that is not currently in use.
Interposed between the cap head 186 and the end 180 of holder 86 is a suitable seal element 190.
As already indicated, the orifice openings 82 and 84 of the respective orifice heads 76 and 78 are proportioned so that the necessary and desirable flow of each type of gaseous fuel to be employed (either natural gas or propane gas), with the smaller orifice opening being for propane gas. This is because natural gas provides heat on the order of 1,000 BTUs per cubic foot while propane gas provides heat on the order of 2,000 BTUs per cubic foot. Gas feed pressure through valve 70 may be in accordance with standard practices.
The orifice heads 76 and 78 may be suitably formed from brass while the orifice holder 86 and its fitting portion 176 may be formed from cold rolled steel. In the form shown, each orifice head includes head portion 194 formed with a planar annular surface 196 on one side thereof adapted for flush engagement with the flat end surface 170 of pipe seal extension 168, and a stem portion 198 extending from the other side thereof and proportioned to be received within the coils of the spring 80. Each orifice head defines a bore 200 having a narrow portion 202 in the stem portion 198 of same and a tapered enlarged portion 204 in the head portion 194 of same. The narrow portion 202 of the respective heads bores defines the nominal orifice size of the particular orifice head involved, and the bore wide portion 204 are diverging or tapered nature to insure smooth fluid flow of the gaseous fuel involved. As indicated, the narrow bore portion 202 of one orifice head should be suitable for natural gas, while the narrow portion 202 for the other orifice head should be suitable for propane gas.
The head portion 194 of each orifice head is formed with a frusto conical edge 205 that seats against cap surface 188 in centering relation thereto.
Turning now to the shutter device 100, the main shutter member 104 comprises shutter member 220 having handle member 222 suitably fixed to same so as to extend from one longitudinally extending side 224 of same, as by employing an appropriate rivet or eyelet where indicated at 226, and having the other longitudinally extending side 228 of same indented out of the plane of the member 220 as at 230, along the elongate opening 232 that is formed in same, to define a pocket 234 that receives the vernier shutter 108. The side edges 238 and 240 of the shutter member 220 are mounted between spaced apart plates 242 and 244 on either side of the port 102 to define guideways 106 along either edge portion 238 and 240 of the shutter member 104 along which the shutter device 100 may be moved to adjust the effective opening of portion 102.
The vernier shutter member 108 comprises shutter element 246 having a handle member 250 that is suitably secured thereto as by eyelet or rivet 252 to extend from one edge portion 254 thereof, with the opposing edge portion 256 serving to provide the fine adjustment of the effective size of the port 120. The vernier shutter member 246 is mounted in pocket 234 of shutter member 104 for sliding movement relative thereto.
The shutter members 104 and 108 may be moved as a whole, crosswise of port 102, by adjustable knob device 260, which in the form shown comprises a knob handle 262 that includes a threaded stem 264, threadedly received in element 266 suitably affixed to handle 250 and extending through hole 268 thereof. In the form shown, handle 222 is interposed between handle 250 and wall 263 of housing 119, knob stem 264 extending through elongate slot 267 formed in handle 222. The housing wall 263 of blower 26 is slotted as at 270 to receive stem 264 and accommodate the operation of knob device 260, the knob 262 clamping the handle members 222 and 250 to housing wall 263 on rotation of knob 262 in the appropriate direction relative to handle member 250, whereby handle 222 seals slot 270 and handle 250 seals slot 267. Coarse adjustment is obtained by loosening knob device 260 (by appropriately turning knob handle 262) and sliding shutter member 108 to the left of FIG. 6 until stem 264 engages end 271 of slot 267. Further movement of shutter member 108 to the left of FIG. 6 will move shutter member 104 to the desired position of coarse adjustment, after which movement of shutter member 108 is reversed for movement by itself to provide fine adjustment of the effective size of port 102. Knob device 260 is then tightened to make handles 222 and 250 fast to the housing 119 to fix shutter device 100 in the desired position of adjustment, while at the same time sealing slots 270 and 267. Increasing the size of the port 102 from a set position may be effected by moving shutter member 108 to the right of FIG. 6 until stem 264 contacts end 273 of slot 267, further movement to the right changing the position of shutter member 104 as desired, after which shutter member 108 is moved to the left of FIG. 6 for fine adjustment.
The side edges 238 and 240 of the main shutter member have a sufficient friction sliding fit between the plates 242 and 244 to permit shutter member 108 to be moved relative to shutter member 104 when knob device 260 is released. This may be done in any suitable manner, such as by pre-bending member 104 about its longitudinally extending axis for a jamb fit in its trackway 106.
It will therefore be seen that this invention provides a simple but effective solution to the problem of pilot smothering or extinguishment in sealed combustion type systems, by providing the fresh air connection between the furnace plenum chamber and the pilot that has been described herein. In addition, the change over valve device permits ready change over of the burner from one fuel to another without requiring the conventional separate pressure control device that is commonly provided on gas burners for change over purposes.
The shutter device permits close adjustment of the port between the burner blower and the burner plenum chamber that is desired to suit specific conditions.
The foregoing description and the drawings are given merely to explain and illustrate the invention and the invention is not to be limited thereto, except insofar as the appended claims are so limited, since those skilled in the art who have the disclosure before them will be able to make modifications and variations therein without departing from the scope of the invention.
1. In a hot air heating system of the sealed combustion type including a combustion chamber including a flue, a main burner firing the combustion chamber and including blower means for blowing air into the combustion chamber to support combustion and a constant burning pilot burner for igniting the main burner, and an air circulation system including a plenum chamber about and sealed from the combustion chamber, air flow conduit means extending between the space to be heated and the plenum chamber, and circulating blower means for effecting forced air flow through the air circulation system, the improvement comprising:
diverting conduit means communicating between said plenum chamber and said pilot burner for supplying air under pressure from said plenum chamber to said pilot burner on operation of the circulating blower means, and check valve means operating in said diverting conduit means for permitting air flow therethrough when air pressure in said plenum chamber exceeds that ambient to the pilot burner.
2. In a hot air heating system of the sealed combustion type including a combustion chamber including a flue, a main burner device firing the combustion chamber and including a main burner, means for supplying fuel in gaseous form to said burner, blower means for blowing air into the combustion chamber to support combustion and a constant burning pilot burner for igniting the main burner, and an air circulation system including a plenum chamber about and sealed from the combustion chamber, air flow conduit means extending between the space to be heated and the plenum chamber, and circulating blower means for effecting forced air flow through the air circulation system, with the main burner and pilot burner being mounted in a firing tube mounted in the combustion chamber, and the main burner device including a blast tube in which the main and pilot burners are mounted, and a plenum chamber communicating with the blast tube that is supplied with forced air flow by the burner blower means, the improvement comprising:
diverting conduit means communicating between the air circulation system plenum chamber and the pilot burner for supplying air from the air circulation system plenum and the pilot burner,
and check valve means operating in said diverting conduit means for permitting said air flow therethrough when air pressure in said air circulation system plenum chamber exceeds that ambient to the pilot burner.
3. The improvement set forth in claim 2 wherein:
said diverting conduit means includes an air box structure formed in said burner device and having a valve seat formed therein defining a valve opening therein,
and said valve means comprises a flap valve hinged in said air box structure to overlie said valve openmg,
said valve opening being aligned with an opening in said air circulating system plenum chamber. 4. The improvement set forth in claim 2 wherein: said diverting conduit means includes an air box formed on said blast tube and including an orifice plate extending thereacross that is oriented to be substantially horizontally disposed in the mounted position of said burner device,
said valve means comprising a valve plate overlyin said orifice plate and biased thereagainst by gravit 5. 'l he improvement set forth in claim 2 wherein:
the main burner device includes a 'port providing communication between the main burner device plenum chamber and blower means,
and means for adjusting the size of said port,
said port adjusting means comprising:
a main shutter member mounted for shifting movement across said port,
said main shutter member carrying a vernier shutter element shiftably mounted thereon for shifting movement across said port,
and means for moving said vernier element relative to said shutter member,
whereby, said main shutter member may be positioned across said port to provide rough adjustment of the opening defined thereby, and said vernier shutter element may be separately adjusted relative to said shutter member to provide a fine adjust ment of said port opening.
6. The improvement set forth in claim 5 including:
clamp means carried by said shutter element and including an operating handle positioned exteriorly of said blower means,
said shutter member being operatively associated with said clamp means for clamping both said shutter member and said vernier shutter element in desired positions of adjustment.
7. The improvement set forth in. claim 2 wherein:
the means for supplying fuel in gaseous form to the main burner includes change over valve means for permitting either natural gas or propane gas to be used in said system,
said change over valve means comprising:
a conduit through which the fuel in gaseous form is supplied to said burner,
said conduit being formed to define an annular seat in circumambient relation thereabout,
a dual orifice change over device mounted in said conduit and comprising resilient means carrying a pair of spaced apart orifice defining heads,
one of said heads being seated against said seat,
said conduit including a cap against which the other of said heads is seated,
and means for removably mounting said cap on said conduit against the action of said resilient means to bias said one head in sealing relation against said seat,
said resilient means being formed to accommodate flow of gaseous fuel to and through the orifice head that is seated against said seat,
said heads being respectively formed to provide alternate gaseous fuel flow rates there'through whereby flow rate of gaseous fuel through said conduit may be changed from one of said rates to the other by seating one or the other of said orifice heads against said seat.
8. The improvement set forth in claim 7 wherein:
said resilient means comprises a compression spring in helical form.
9. The improvement set forth in claim 6 wherein:
said port adjusting means is mounted within said burner blower means,
said clamp means operating handle extending exteriorly of said blower means through an operating slot therefor formed therein,
said clamp means clamping said shutter member and element in sealing relation with said slot.