Патент USA US2411342код для вставки
Nov. 19, 1946. R. M. SHERMAN 2,411,342 ' HYDROCARBON ‘COMBUSTION TUBE BURNER 3 Sheet's-Sheet 1 Filed March 17, 1944 m\ww /7 9 \7 O a}a” OI./ k‘. ,. 3,67.0 \5 a as Z m.. ao\ Wa /s h . ,2 m\\ 9 \\\\\ \. ,9 W 1 nw?\ \ h .17/l w d.\\7. / ‘h a a “M n I , .. 4m? a.Wm a‘ , r Nqv. 19, 1946. 2,411,342 R. M. SHERMAN HYDROCARBON ‘COMBUSTION TUBE BURNER ~ Filed March 17, 1944 3 Sheets-Sheet 2 /7 5.9 I \\\\ ' Ivenioz'. Rallgi‘onlqsherfuan Egan,“i I !”Z e??'ys ‘ Nov. 19, 1946. R. M. SHERMAN 2,411,342 HYDROCARBON COMBUSTION [TUBE BURNER Filed‘ March 17, 1944 3 Sheets-Sheet 3 ‘97 77 83 97 a)?’ F913 Inveni‘or: Patented Nov. 19, 1946‘ - 2,411,342 Wires 3 e TENT ‘ OFFICE 2,411,342 HYDRUCARBON COMBUSTIOhl TUBE BURNER . Rallston M. Sherman, Glastonbury, Conn. Application March 1'1, 1944, Serial No. 526,884 12 Claims. (Cl. 158-.-86) ‘ 1 My invention relates to hydrocarbon combus 2 - , responding to Fig. 2, on an enlarged scale of two tion tube burners. Heretofore much difficulty has been expe further modi?ed burners; rienced in providing a combustion tube burner . showing a further modi?ed form of burner; Fig. 12 is a plan of a further modi?ed form of that will permit a wide range of fuel consump ‘ Fig. 11 is a; section, corresponding to Fig. 2, tion and operate satisfactorily and e?iciently throughout such range particularly at the lower end thereof. This is markedly true of combus tion tube burners designed to utilize low density gases such as those customarily supplied by city 10 gas mains. Further, heretofore much dif?culty has been experienced in securing a satisfactory‘ burner with parts in, section and parts broken uniform distribution of ?ame about the combus- \ In the embodiment of the invention shown by Figs. 1, 2 and 3 the burner is designed for burning light weight gaseous fuel, that is to say, fuel tion chamber when it is attempted to use such low density gases as fuel, the ?ame in burners as heretofore constructed, when supplied with such fuel, tending to be localized at various points away and with the combustion tube covers re moved; v12 Fig. 13 isa section on the'line |3-l3 of Fig. with parts broken away; and Fig. 14 is a fragmentary section on the line 14 M of Fig, 12, _ which has a speci?c gravity less than that of air. As illustrated, the perforated combustion tubes l' and 3, which are preferably formed of refractory sheet metal such as stainless steel, are chamber instead of being uniformly distributed 20 cylindrical and are carried in spaced relation to along it. form between them an annular combustion The present invention has among its objects chamber 5. The base supporting the combustion the elimination of the defects of prior burners in tubes is formed with a bottom wall ‘I having a ‘ the respects above mentioned, burners according central opening 9 for admitting air to the space to the invention being capable of a wide range of fuel consumption and operating satisfactorily 25 surrounded by the inner combustion tube I. As shown, the base has a peripheral upstanding wall and efficiently throughout such range, and when ' II, and an upstanding wall l3 surrounding the employing low density gases as fuel securing a opening 9, these walls forming between them a uniformly distributed ?ame. fuel groove and being of suf?cient height to pre The invention however-will be best understood 30 vent overflow of oil from the base in case it is de from the following description when read in the sired to convert the burner to one which burns ‘ light of several embodiments of the invention oil. submitted for illustrative purposes, while the As shown in Fig. 2, the two combustion tubes scope of the invention will be more particularly extend into the space between the upstanding pointed out in the appended claims. 35 walls H and i3, the outer combustion tube 3 In the drawings: ' contacting with the upstanding wall H so that Fig. 1 is a plan of a combustion tube burner said wall positions the tube. Carried by the up accordingto the invention with the combustion per edge of the upstanding wall i3 is an annular cover It, preferably formed of thin refractory chamber cover omitted; Fig. 2 is a section on the line 2—2 of Fig. 1 40 sheet metalv such as stainless steel, which cover with parts broken away; is secured at its inner edge by screws I‘! to said Fig. 3 is a fragmentary section on the line 3-3 wall, a, compressible gasket I9 of refractory ma of Fig. 1 on an enlarged scale illustrating the I terial such as asbestos being provided for render ?ame, and gas and air ?ow, under low fuel con~ ' ing gas-tight the joint between the cover and the wall. As shown, the cover is provided with a sumption conditions; peripheral ?ange fl which ?ts and is welded to Figs. 4 and 5 are fragmentary sections, cor the inner side of the inner combustion tube i, responding to' Fig. 2, of two modi?ed forms of along the horizontal extent of the combustion , burners; so as to form a gas-tight joint between them. In this way an endless fuel. chamber 23 is formed Fig. 6 is a section, corresponding to Mg. 2, of a 50 in the base, into which chamber the gaseous fuel modified form of burner; may be admitted through the opening 25 in the Fig. '7 is a fragmentary section, corresponding base, this opening communicating‘ with the gas to Fig. 6, on an enlarged scale showing a detail supply pipe El which it will be understood is pro of a modi?ed burner; ‘ vided with a valve (not shown) for regulating Fig. 8 is a section on the line 8—-8 of Fig. 7; Figs. 9 and 10 are fragmentary sections, cor- (1:1 Ul the amount or” gas supplied to the chamber. 2,411,842 As illustrated, at the bottomof the combustion chamber 5 is a sleeve 29 in spaced relation to each 4 omitted such space is too wide to permit the sup ply of fuel to be diminished very much, the gas of the combustion tubes l and 3, this sleeve be ‘under such conditions becoming so attenuated 1 ing positioned on the base by the three upstand that at localized points the mixture of it and the lng lugs 3|, the sleeve, like the combustion tubes, CI air passing through the perforations of the com being formed of perforated sheet metal prefer bustion tubes above the cover l5 becomes over ably stainless steel. lean and burns either ine?iciently or» not at all; A pilot burner in the form of a tube 3.3 is However, when the sleeve 29 is present the gas shown as positioned in the space between the entering the combustion chamber tends to be sleeve 29 and combustion tube l_ for initially lg 10 confined between the sleeve and the combustion niting the gaseous fuel, this pilot burner being tube I so that the upper portion of that space supplied with gas through a valve controlled pipe in effect forms a jet delivering the gas upward 35 leading from the source which supplies the _ly into the body of the combustion chamber pipe 21. ' where it burns in the form of a ?ame F (Fig. 3) In practice, the gaseous fuel supplied the 15 uniformly extending about the combustion chamber 23 passes from that chamber through chamber. Air entering the perforations of the . the perforations in the combustion tube I which outer combustion tube 3 slightly above the upper lie below the cover is into the adjacent portion edge of the upstanding wall H tends to ?ow of the combustion chamber 5. The cover iii, downwardly into the space between that ‘com when the screws i‘? are tightened, presses ‘the bustion tube and the sleeve 29, as indicated by the lower edge of the combustion tube i againstthe 20 arrows in Fig. 3, and passes through the perfora upper surface portion of the bottom wall of the tions in the sleeve to mix with the gas entering base with su?lcient tightness to insure that all the space between the latter and the combustion the gas will pass into the combustion chamber tube i so that a carbureted mixture discharges through the perforations 31 of the lower end por 25 from this last mentioned space, it having been tion of the combustion tube, or at least enough of found that where the sleeve .29 is imperforate the gas to insure that the gas distribution in the satisfactory results cannot be secured, the ?ame combustion chamber will be controlled by the size in such case burning with a so-called “dirty and number of the perforationsin said portion of ' the combustion tube and will not be adversely a?’ected by passage of an uncontrolled material amount of gas between the base and the lower edge of the combustion tube. It has been found that when gaseous fuel hav yellow" ?ame. Satisfactory results have been secured with the burner ‘described, when supplied with ordinary city gas having a. B. t. u. value of about 550 per cubic foot, in which the two combustion tubes and sleeve 29 are provided with perforations 31 about ing a density less than that of air, for example 35 0.07 inch in diameter‘ arranged in rows 1/; inch ordinary city gas, is employed in a combustion apart and spaced 1A inch apart in these rows. tube burner as heretofore constructed, the gas Thenumber of rows of perforations establish because of its pronounced tendency to escape up lug-communication between the chamber 23 and wardly tends to produce an extremely streaky the combustion chamber will vary with the sizev ?ame, this commonly resulting in an excess of 40 of the burner. For burners of the ordinary size ?ame at localized points about the horizontal ex suitable for domestic cooking ranges two or three tent of the combustion’ chamber with a. very rows will su?‘lce. The number of perforations in meager ?ame or no ?ame at all at other points. the sleeve 29 is not critical, and with the perfo By causing the gas to‘ enter the combustion rations spaced the distances mentioned ordi chamber through the perforations of the com narily three or four such rows will suffice. It bustion tube I a uniform distribution of the fuel has been found, however, that best results will be admitted to the combustion chamber is secured secured when the sleeve extends upwardly to‘ at " and the ?ame is uniformly distributed about the least the top of the portion of the cover i5 welded combustion chamber. - It also has been ‘found that with ‘combustion 50 tube'burners as heretofore constructed it is im possible to secure satisfactory and ef?cent oper ation when the burner is “turned down” to any material extent, the diminished supply ~of gas under such conditions causing the ?ame to ?ick er, and to wander about the horizontal extent of the combustion chamber. This commonly causes the ?ame to be extinguished, and aside from that does not result in satisfactory or e?‘icient opera tion of the burner. In the present burner, how ever, the presence of the perforated sleeve, 29 avoids these defects and permits the burner to operate satisfactorily and e?‘iciently when the supply of gas is much‘dirfiinished. For example, it has been found that when the sleeve 29 is pres ent the minimum e?icient fuel consumption may be about one-eighth the maximum e?icient fuel _ ' _ consumption, whereas with the sleeve omitted it can be only about one-third. to the combustion tube I. ' ' It will be understood that the combustion tube 3 need not be positioned interiorly of the up standing wall Ii, but may be supported at its ex- > terior as shown'in Fig. 4. Similarly, the combus tion tube I need not extend to the extreme bot tom of the chamber 23, as, for example, the tube, which being welded to‘ the cover I5 is supported thereby, may adjacent its lower end fit an up standing circumferential ?ange 39 projecting up wardly from the bottom wall 1 of the base as shown in Fig. 5, so that as in the construction shown by Fig.v 2 the lower end portion of the tube and the base have cooperating portions prevent ing substantial communication ‘between the chamber 23 and combustion chamber other than by way of the perforations in the tube. If desired, for admitting‘ additional air to the space between the sleeve 29 and combustion tube 3, the upstanding wall ll of the base may be ‘formed-on its interior with an annular groove 4| In the above connections it will be observed 70 (Fig; 9) opening on the upper edge of said wall, that the space between the two combustion tubes so that air will be admitted into said groove and must be great enoughv to afford a combustion .. pass therefrom into said space through the ad chamber of sumcient transverse width properly to take care of the higher fuel consumption, and it has been found that when the sleeve 28 is .iacent perforations'in the combustion. tube. Simi larly, the cover is need not be ?at, but may take the form of the cover I! (Fig. 9), the peripheral 2,411,842 portion 45 of which is frusto-conical and extends non than u omitted. It has been found, i'or ex’ downwardly so as to expose sumclent perforations ample, that in an ‘oil burner, in which emcient of the inner combustion tube l to admit an in operation can be secured with no less than about creased amount of air into the space between that Vs the maximum eiiicient' fuel consumption, by‘ tube and the sleeve 29 for admixture with the 5 use of the sleeve e?icient fuel consumption can gas in such space. be" secured with about $41 the maximum e?lcient The burner according to Figs. 6 to 8 is de fuel consumption. , signed for burning either gaseous‘or liquid fuel In the modi?cation shown by Fig. 11 the an selectively. The burner shown by these ?gures is nular fuel chamber 6! is positioned at the outer in general identical with that shown by Figs. 1 10 side of the outer combustion tube 3, the space and 2 except that an'annular wick't'l is provided between the upstanding wail II and said tube in the space between the sleeve 29 and outer com being closed by the annular cover 63.. As shown, bustion tube 3, the wick being spaced from the ' the cover is secured to the upper edge of the sleeve to provide an air space 49 between the two wall Ii by screws 65, the cover having an inner so that air may pass through the perforations of 15 peripheral ?ange 61 welded to the tube 3. Also, the sleeve into the space between the latter and as shown, the inner combustion tube I is posi the inner combustion tube I for the reasons here tioned against the inner upstanding wall i3 of inbefore described. The wick may be spaced from the base, and the inner peripheral portion of the the sleeve byproviding a su?icient number of lugs cover 63_ is depressed at 69 to secure the same iii. More conveniently, however, a number of effect as the depressed portion 45 of the cover spaced clips 5i may be secured at their lower ends according to Fig. 9. Further, as shown; the in by welding to the combustion tube 3 for holding ner upstanding wall i3 is provided with an arr the wick in such spaced relation. nular groove ‘ll corresponding to the groove 41 As shown in Fig. 6, the gas supply pipe 2'! com of Fig. 9‘for securing the same effect :as the municates with an opening 53 in the upstanding latter. It will also be understood that in the boss 56 formed integrally with the bottom wall 1 construction shown by Fig. 11 the outer oom of the base so as to prevent ?ooding of the pipe bustion tube 3 may terminate above the base in during the ‘starting period of the burner by the the same way as the inner combustion tube i of oil admitted to the chamber through the open Fig. 10 for securing the ‘same effect as the latter. ing 57 of the base, with which latter opening com 30 In the modi?cation shown by Figs. 12 and 13 municates the oil supply pipe 59, this latter pipe, like the pipe 2?, being controlled by a valve (not shown) for regulating the amount of ‘oil supplied the burner. ' two annular combustion chambers 13 are pro vided, respectively positioned between the pairs of combustion tubes i and 3. As shown, the base is provided with‘ a bottom wall 15 provided with pairs of upstanding walls ‘l1, 19, the pairs of combustion tubes being positioned between the walls of these pairs and being arranged with n; will be understood that the lowermost per- ; forations 31 of the inner combustion tube | and sleeve 29 of the burner according to Figs. 6 to 8 will be positionedclose enough to the base to per relation to said walls as hereinbefore described. mit sufficient oil to reach the wick for the start ‘As illustrated, the spaces between the upstand ingqof the burner. After the burner has started ing walls 19 and combustion tubes 3 are closed the oil will be vaporized in the chamber 23, the by covers 8!! welded to said tubes and resting on , cover it of which is highly heated by heat re ?ected against it from the combustion tube l and compressible gaskets 82 positioned on the upper edges of'said walls. As shown, the ‘covers are by heat conducted to it by said tube with which it makes intimate contact. Also, the time con sumed in starting the burner when using oil as clamped to the upper edges of said walls by clips 83. connected by clamping screws 85 to lower clips 81, all these clips bridging the spacebe . fuel is much reduced by reason ofthe inner com tween said walls 19. The walls 19 being in bustion tube l extending into the ‘oil space, the spaced relation permit air to enter the space lower portion of the tube being highly heated by between the combustion tubes 3, while air enters heat conducted to it from the cover i5 and from 50 the- interior of thefinnner combustion tube I the portions of the tube above that cover, at through the opening 89 in the base. ‘ which portions the ?ame exists. ‘ As shown, the burner according to Figs. 12, It will be understood that, although the sleeve 13 and 14 is arranged for burning either gas or 2% may with advantage be ‘used when burning oil selectively, gas being admitted through the oil, the vapors of which are heavier than air, 55 valve controlled pipe ill and oil through the valve the distribution of the fuel tended to be eifected controlled pipe 93 for supplying regulated by the perforations of the combustion tube I be amounts of gas or oil thereto. At spaced points low the cover it is then of no importance, for such , heavy vapors or gases tend to ?ow like water and distribute themselves, that is t5 say, like water would if admitted through the pipes 59 or 21, they tend to lie at the bottom of the chamber 23. When using such heavier fuels, therefore, it is the fuel chambers 95 below thecovers 8| are connected by spoke-like parts 91 integral with the upstanding walls 19, which parts are jperfoe rated as shown at 99 for admitting the oil va pors 'or gas from the inner fuel chamber 95 to the outer fuel chamber 95. As shown, a wick 47 is provided at the bottom of the inner com not necessary to have the lower end of the inner combustion tube i in close proximity to the bot 65 bustion chamber which serves to start the burner tom wall 7 of the base, but it may be spaced therefrom say about 0.1 inch as shown in Fig. 1.0 so that the oil vapors or the heavier gases will flow beneath i'he lower end of the tube into the space between that tube and the sleeve 29. With these oil vapors or heavier gases the effect of the sleeve 29 is not so pronounced as when burning the lighter gases. However, with such vapors and heavier gases the sleeve secures a useful effect in that it permits a greater range of fuel consump ' when oil is supplied as the fuel. It will be understood that, within the scope of the appended ‘claims, wide deviations may -be made from the forms of the invention de scribed without departing from the spirit thereof. I claim: ' ‘ 1. A. gas burner for gas having a density less than air having, in combination, a base carrying a pair of perforated combustion tubes one of which surrounds the other in'spaced relation , 2,411,342 7 . ' thereto to form a combustion chamber between > them, said base having an opening for supply ing'air to the side of one of said tubes opposite said ‘combustion chamber, means cooperating with said base and one of said combustion tubes to form a gaseous fuel chamber positioned later ally of that tube adjacentv its lower end coex _ 8 I .5. A burner according to claim 3 having, a , perforated sleeve within the combustion cham ber at its bottom in relatively widely spaced re lation to each of the combustion/tubes for divid ing the bottom portion of said chamber into _ two relatively wide open top chambers,‘ the fuel chamber, communicatingwith the chamber be~ tensive with the peripheral extent of said tube, tween said sleeve and the combustion tube‘adja which latter forms one of the walls of said fuel cent the fuel chamber. chamber‘ whereby the two chambers are placed said' tube, the end portion of the latter and said 6. A burner according to claim 3 having a perforated sleeve within the combustion cham ber at its bottom in relatively widely spaced re base having 7 cooperating portions preventing other substantial‘ communication between said lation to each of the combustion tubes for divid ing the bottom of‘ said chamber into two rela -in' communication solely by the‘ perforations of chambers. 2. A burner according to claim 1 having a perforated sleeve within the combustion cham her at its bottom in relatively widely spaced rela ‘. tion to each of the combustion tubes for divid ing the bottom portion of said chamber into two relatively wide open top chambers, the fuel chamber communicating with the chamber be tween said sleeve and the combustion tube ad jacent. the fuel chamber. 3. A gas gurner for gas having a density less _ than air having, in combination, a base having ‘ a central-air opening, and, surrounding said » opening, spaced upstanding walls extending from . v tively wide open top chambers, the fuel cham ber communicating with the-chamber between that sleeve and the combustion tube adjacent the fuel chamber, and a wick in the space at theopposite side of said sleeve surrounding the latter in spaced relation thereto‘. . 7. A burner according to claim 4 having a wick in the chamber at the side of said sleeve opposite the fuel chamber, said wick surround- _ ing the sleeve in spaced relation thereto. 8. A burner of the character‘ described having, in combination,‘ a base having a central air opening, and, surrounding said ‘opening, spaced upstanding walls extending from a bottom ‘wall a bottom wall of the base to form an endless of the ‘base to form an endless fuel groove, .a pair gaseous fuel groove, a pair of perforated com 30 of perforated combustionv tubes one of which bustion tubes one of which surrounds the other _ surrounds the other in spaced relation thereto in spaced relation thereto to form a combustion to form a. combustion chamber between them, chamber between them, which tubes are carried which tubes are carried ‘by said base with the by said base with the end portion of one of said ' end portion of one of said tubes contacting one tubes contactingone of said upstanding walls 35 of said upstanding walls and the other tube» and the other tube extending into said groove in extending into said groove in- spaced relation spaced relation to the other of said upstanding to the other of said upstanding walls, a cover walls, a cover member above the bottom of said member above the bottom of said groove extend-' groove ‘extending'from the last mentioned up ing from the last mentioned upstanding wall to standing wall to the combustion tube spaced 40 the combustion tube spaced therefrom so as to therefrom so as to form an endless gaseous fuel chamber communicating with the combustion chamber solely through the perforations of the last mentioned tube, the end portion of the .latter and said base having cooperating portions preventing other substantial communication be tween said chambers' - ‘ I 4, A burner of the character described having form. an endless fuel chamber communicating with the combustion chamber solely through the perforations of the last mentioned tube, the end portion of the latter and said base having co operating ‘portions preventing other substantial communication between said chambers, a perfo rated sleeve within the combustion chamber at its bottom in relatively widely spacedirelation to in combination, a base having a central 'air said combustion tubes for dividing the bottom opening, and, surroundlngsaid opening, spaced 50 portion ‘of said chamber into two relatively wide upstanding walls extending from a bottom wall open top chambers, means for admitting of the base to form an endless fuel groove, a pair ' vaporizable liquid fuel or gaseous fuel to said of perforated combustion tubes one of which fuel chamber, and a wick within the chamber surrounds the other in spaced relation thereto between said sleeve and the combustion tube to form a combustion chamber between them, 55 remote from said fuel chamber for initiating op which tubes are carried ~by said base withthe eration of the burner when said fuel chamber is ‘ end portion of one of said tubes contacting one supplied with liquid fuel. of said upstanding walls and the other tube ex 9. A burner of the character described having,v tending into said groove in, spaced relation to.‘ in combination, a base having a central air the other of' said upstanding walls, a cover mem 60 opening, and, surrounding said opening, spaced ber above the bottom of said groove extending upstanding walls extending from a bottom wall from the last mentioned upstanding wall to the I of the base to form ‘an endless fuel groove, a combustion tube spaced therefrom so as to form _ pair of perforated ' combustionv tubes one of an endless fuel chamber. the end of the last ‘which surrounds the other in spaced relation mentioned tube being supported in slightly 65 thereto to form a combustion chamber between ' spaced relation to the bottom of said groove to them, which tubes are carried by said base with establish communication between said- fuel the'_end portion of one of said- tubes contacting chamber and the combustion chamber, a perfo one of said upstanding walls and the vother tube rated sleeve within the combustion chamber at extending into said groove in spaced relation to its bottom in relatively widely spaced relation ‘to 70 the other of said upstanding'\:wal1s, a cover each of the combustion tubes ‘fol-‘dividing the bottom of said chamber into two relatively wide open top‘ chambers, the fuel chamber communi-_ eating with the chamber between said sleeve and member above ‘the, bottom of said groove ex tending from the last, mentioned upstanding wall to the combustion tube spaced therefrom so as to form an endless fuel chamber communi-‘ , the combustion‘ tube adjacent the fuel chamben', ‘lo catin! with the combustion chamber through‘ ' 2,41 1,842 the perforations of the last mentioned tube, the ' end portion of the latter and said base having cooperating. portions preventing other substan tial communication between said chambers, a 10 portion of said combustion chamber into two relatively wide open top non-liquid ?uid con ducting chambers communicating with the por tion of the combustion chamber above them; and means for supplying‘ non-liquid ?uid‘ fuel to one of said open top chambers for discharge into perforated sleeve within the combustion cham bar at its bottom in relatively widely spaced relation .to each of the combustion tubes for dividing the bottom portion of said chamber into the ‘portion of the combustion chamber above 10. A burner of the character described hav? established solely by the perforationsln the it through the open top oi.’ said open top cham ‘ her, which means comprises walls forming an an two relatively wide open top chambers, a pilot light device within the chamber between the 10 nular fuel chamber adjacent said lower portion of said combustion chamber, the last mentioned sleeve and the combustion tube adjacent the combustion tube constituting a portion of said fuel chamber, a wick in the space at the oppo walls and de?ning a side of said fuel chamber. site side 01 said sleeve surrounding the latter 11. A burner according to claim‘10 in which in spaced relation thereto, and means for admit ting‘vaporizableliquid fuel or gaseous fuel to 15 the'communication between‘the annular fuel chambem and one of the open top chambers is said fuel chamber. ' combustion tube de?ning a portion of the walls of said fuel chamber. _ extending perforated combustion tubes 0pera-‘ 12. A ‘burner according to claim 10 having tively carried at their lower ends by said base 20 an annular wick in the open top chamber at with their walls in laterally spaced relation to the side of the sleeve opposite the open top form between them an annular combustion chamber which communicates with the annular chamber: a vertically extending perforated fuel chamber, said wicl'r being in laterally spaced sleeve operatively carried by said base within the combustion chamber at its lower end por 25 relation to said sleeve. ing, in combination, a base; a pair of vertically - tion in relatively widely spaced relation to each - of the combustion tubes for dividing said lower RALISTQN M. SHERMAN.