US2959219A

US2959219A - Control apparatus

Info

Publication number: US2959219A
Application number: US649171A
Authority: US
Inventors: Charles E Hajny
Original assignee: Baso Inc
Current assignee: Baso Inc
Priority date: 1957-03-28
Filing date: 1957-03-28
Publication date: 1960-11-08
Anticipated expiration: 1977-11-08

Description

Nov. 8, 1960 c. E. HAJNY CONTROL APPARATUS 2 Sheets-Sheet 1 Filed March 28, 1957 INVEN 7:012. Char/es E. Ha ny Affys 2 Nov. 8, 1960 c. E. HAJNY 2,959,219

CONTROL APPARATUS Filed March 28. 1957 2 Sheets-Sheet 2 0 30 MV 49 b 65 INVENTOR.

Char/es E. Hajn y BY Y Affys United States Patent CONTROL APPARATUS Charles E. Hajny, Milwaukee, Wis., assiguor to Base Inc., Milwaukee, Wis., a corporation of Wisconsin Filed Mar. 28, 1957, Ser. No. 649,171

Claims. (Cl. 158-130) This invention relates in general to control apparatus and more particularly to a novel thermoelectrically powered safety shut-off apparatus for fluid fuel burning systerns.

Heretofore, in the thermoelectric safety shut-off control of the fuel flow to a plurality of ignition or other burners, it has been necessary to employ separate fuel flow-control means such as valves or switches individually responsive to the outage of the respective individual burners. There have been various unsuccessful attempts in the past to provide a single, practical thermoelectrically powered electromagnetic fuel flow-control device capable of integrating the responses from a plurality of separate thermoelectric generators associated with individual burners in order to afford safety shut-off control for each of the burners.

It is a general object of this invention to provide an apparatus for controlling fuel How to a plurality of burners through single magnetic control means which efliciently integrates response from two separate generators associated with two separate burner flames.

Another object of the present invention is to provide a control apparatus of the general type aforementioned permitting increased effective range of safe pilot burner operation, thereby reducing false field response.

Another object of the present invention is to provide an apparatus of the general type set forth wherein the safety shut-off control to a pair of burners is provided upon the faulty operation of one of the burners without substantially decreasing the versatility of application of said burners in fluid fuel burning systems.

Another object of the present invention is to provide an apparatus as above characterized including a novel electromagnet structure which effectively and efficiently utilizes the small amount of power available from a pair of thermoelectric generators associated respectively with a pair of ignition burners to provide safety shut-off control of the fuel flow to said burners.

A more specific object of the invention is to provide a novel electromagnetic device as aforementioned having a novel core structure and having a pair of fluxgenerating windings connected to the generators associated with said novel core structure in a manner to afford the improved safety shut-off control of the fuel to the burners.

The novel features that are characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation together with additional objects and advantages thereof will best be understood by the following description of the specific embodiment when read in connection with the accompanying drawings, in which:

Figure 1 is a fragmentary vertical sectional view of a novel control apparatus constructed in accordance with the inventive concept and embodied in a system controlling gaseous fuel burners, portions of said apparatus and system being shown semi-diagrammatically;

ice

Figure 2 is an enlarged fragmentary perspective view of a portion of the control apparatus shown in Figure 1;

Figure 2a is a perspective view similar to Figure 2 and showing an alternative magnet structure within the inventive concept; and

Figure 3 is a graph showing performance curves in terms of millivoltage produced by two separated pilot burner-thermoelectric generator assemblies in circuit therewith, of prior art safety shut-off devices and the improved safety shut-off device, and also showing an idealized performance curve.

While the fixed magnet and movable armature described in the following detailed description are embodied in a valve device for directly controlling the fuel flow to a pair of main and pilot burners, it is to be understood that it is with full awareness that controlling movement may be obtained by having both the armature or magnet movable with respect to each other, or the armature fixed and the magnet movable. It is to be further understood that the relative movement of the armature and magnet may be used to control a switch or other suitable or desired device, rather than to directly control a valve as shown.

With the foregoing in mind and proceeding to Figure l of the drawings, the reference numeral 13 indicates flowcontrol means in the form of an electroresponsive valve disposed in a supply conduit 12 to control the fuel flow to a pair of main burners conventionally illustrated at 10 and 11. A pair of ignition burners 14 and 15 are associated with the burners 11 and 10 respectively to ignite the latter as is well understood in the art. As shown, the pilot burners 14 and 15 may be supplied with fuel through separate conduits 16 and 17 leading from the valve 13.

The valve 13 comprises a valve body 9 having an inlet 19, a main outlet 20 and a partition 21 intermediate said inlet and outlet separating the interior of the valve body into an inlet chamber 22 and an outlet chamber 23. The partition 21 may be formed with an enlarged central portion having a bore 2111 at the ends of which are formed a pair of oppositely disposed valve seats 24 and 25. As shown, a pilot outlet 18 is formed in the bore 21a intermediate the valve seats 24 and 25 and has external connection to the pilot fuel supply conduits 16 and 17 as indicated. A pair of

valve discs

26 and 27 are operable to coact respectively with seats 25 and 24, disc 26 being referred to as a flow-interrupter disc and disc 27 being referred to as safety shut-off disc for reasons hereinafter appearing.

The position of safety shut-off valve disc 27 is controlled by an electromagnetic holding means 28 which may take the form of a generally tubular housing 33 enclosing a magnet 29 and a cooperable disc armature 32 movable to attracted and retracted positions with respect thereto. As shown, an armature stem 35 is fixed to the armature 32 at one end and extends through the housing 33 to carry the safety shut-off valve disc 27 at the other end. A coil spring 34 may surround the armature stem 35 with one end engaging the valve disc 27 and the other end engaging the housing 33 to bias the armature toward retracted position and valve disc 27 into engagement with seat 24. The magnet 29 is operable, under conditions to be explained, to retain the armature 32 attracted thereto and the valve disc 27 in open position against the bias of the spring 34. The electromagnet as generally indicated at 29 has separated though similar

energizing windings

30 and 31. The

windings

30 and 31 each have the same number of turns and are respectively connected for energization by a pair of thermoelectric generators 41 and 42, the latter being mounted so as to be heated by the pilot burners 14 and 15 respectively. The configura- 1 tion of the core of magnet-29 and the disposition of

windings

30 and 31 with respect thereto will be described in detail hereinafter.

It is to be noted that'the holding means 28 shown is of the resettable type in contradistinetion-tothe automatic type, and thereforethe'foroe of biasing spring ,34 on arinature32. is greater thanthe-- attraetive='force I of magnet 29 thereon whensaid armature is in the= retracted position shown in Figure l.- --Stated- =another'way,

. when magnet 29 is energized by both windings swan-i1 31,

- disc 27 toopen-position and the'reby to-reset the armature 32 to. attracted relationwith respect tothe pole faces of magnet129. 1 The illustrated reset'means isshown as comprising a reciprocatable stem "37ahaving a manually engageable external knobo'rbuttonBS at one end and an enlarged. tip '39 at itsinner-end. The stem 37a slidably carries the flow-interrupter disc- 26 which-is biased to- .ward the.tip:39 by a spring w. 'Tht stem- 37a is biased outwardlyby aspring (not shown)-which is stronger than the spring 40. Depression of the reset button 38 causes upward movement of the stem tip' 39, as viewed in Figure 1, into actuating engagement with valve member 27 formovement of the armature 32into--engagement with thepole faces of magnet Blas aforementioned and simultaneouslifting of safety shut-oif'valve 27 off seat 24, allowing fuel'flowinto bore 21a. During this movement of the reset stem, the flow-interrupter disc-moves therewith under the bias of spring 40 into seating engagement with valve seat 25 to prevent flow of fuelto the main burners 10 and: 11 during'the resetting operation. The slidable mounting of the disc 26 on reset stem37a permits, further inward movement ofthe stem 37aafter seating of the disc 26 :in order to accomplish thereafter resetting .of the armature 32 relativeto the pole faces of .magnet 29. It will thus be noted that fuel-may'fiow through the pilot outlet 18 to the pilot burners'14 and 15 for safe lighting thereof once valve"discii27- is lifted from seat 24 during a resetting operation.

Referring now to the details of themagnet-assembly as best shown in the perspective drawing comprising 'Fig ure 2, .it is seen that the core-of magnet 29 maycomprise .a pair of spaced inverted U-sha-ped'core portions .or members 29a and 29ban'd -spaced connecting pole v piece portions ormembersi29c and-29d. The connecting .members29d and 29c have coplanar surfaces-facing the armature 32 which are adapted to function as the pole faces of the magnet'29 for coaction with said armature.

As shown, winding 36, which-is connected forenergization-to thermoelectric generator 41, is wound on one leg .of the .U-shaped portion 29a, whereas the windingSl,

which is. connected for energization by thermoeouple42, is woundon one leg of'the U-shaped'portion 2%. This configuration of magnet core and position of the windings thereonaiford, when generators 41 and 42 are energized in a particular manner to be explained, flow of "flux along parallel paths which are setup in thecore portions and armaturesubstantially as shown by the solid line arrows in Figure2.

More particularly, the flux produced by winding 31 tends to flow throughout the extent of the U-shaped portion 29b, across the first armature-magnet pole face air gap adjacent the connecting member 2% into-the armature 32, through the second armature-pole face air gap adjacent the connecting member 290 and return to said winding. The lines of flux created by winding 30 tend to flow similarly throughout the extent of U-shaped portion 29a, across the first .air gap into the armature 32, through armature 32 and returning through the second .in' the-core itself, i.e., in the sense that the windings are not seriallyarranged on 'the'magnet core structure in a manner to cause the flux to flow serially through the corepo'rtions within'said windings. Thus, very little flux flows in the pole pieceextents orconnecting

members

29d and 29c when both

windings

30 and 31 are energized by substantially the same amount of electrical energy. However, when one winding, for example winding 31, isenergized and the other winding, for example winding 30, is completelydeenergized', the connecting

portions

29d and 29c 'together"witl1"the'core'portion bearing the deenergized winding, i.e., core portion 29a, provide a closed path magnetic circuit between the ends of the other core portion, i.e.,' portion 29b, toafford ashu'nting: elfect which diverts a subs'tantialportion of the 'fiux'from' winding 31 away from'the 'armature32, i'the divertedfportion of the flux-traveling in"'the= aforementioned closed path magneticcircuit. I The major reason whyfluxis 'diverted'fromthe former path through the 'air' gaps jand'totheaforementiOned closed magnetic path is the 'absenceof an'opposing fiux normally created" by energization' offtheother winding and preventing flux fromthe'one winding from entering this low reluctance path. For example,"a'ssuming winding 31 is energized and windingj30 is deen'er'gized, a por tion of'the flux created by' winding 31" will continueto flow through the core portion 29b'and' thearm'ature'in the path shown by the solid'line' arrows, but adiverted ture-magnet air gap as related to the otherffac'tors. All

of these factors are "calculatable by] men skilled in the electromagnetic art, so that the specific structurefarrived at can best suit the requirements of the precise field application desired. v

Between-one extreme wherein both of the windings 3t and 31 are producing "exactly the same'amount of'flux to afford the aforedescribed paralleling of fluxpaths to produce the optimum attractive force relationship at the magnet-armature air gap; and another extreme wherein the situation of one winding being completely deenergized and the other energized obtains to'cause a substantial amount of diversion of flux through the remainder of the core as also aforedescribed; are third situations wherein generators 41 and 42 are producing or generating uneven amounts of thermoelectric

power putting windings

30 and 31 in imbalance. When this third or imbalanced situation occurs, there'is a paralleling of'fiux through the armature and magnet air gaps'in amount roughly proportional to the output of the weaker of the two generators, the excess of flux created by the stronger generator being used partially for armature-magnet pole face attraction and part for travelling throughthe closed path afforded by the magnet core.

Forexample, assume a fixed system as described and that the millivoltage output of the generators 41 and 42-may be translated directly into attractive forces at :the armature and magnet pole faces when the armature is in attracted .position'. Assume further that the generator 41 is producing ninety millivolts and generator 42 is producing fifty millivolts. Under these conditions the attractive force produced at the air gaps is roughly equivalent to the amount produced by two balanced generators producing fifty millivolts each plus an increment of attractive force for the excess millivoltage of the stronger generator, i.e., forty millivolts. This force, however, is not the force generated by a single generator producing 40 millivolts, but rather, is that increment measured on the magnetization force curve and defined by the difference between the force generated by a single generator producing fifty millivolts and that generated by the same generator producing ninety millivolts with the other generator deenergized. A further example would be generator 41 producing sixty millivolts and generator 42 producing sixty-five millivolts. The attractive force produced in the armature-magnet air gap will be equivalent to that produced by two balanced generators generating sixty millivolts each, plus the increment of attractive force produced by a single generator measured on the force curve between the sixty and sixty-five millivolt levels with the other generator deenergized.

The advantages of the disclosed electromagnetic arrangement are perhaps most clearly portrayed when contrasted with an ordinary horseshoe or U-shaped core wherein windings similar to 30 and 31 are wound in series or aiding relationship on the legs thereof, everything else being identical with the structure thus far described. Let us assume, for illustration, the following values of a normal safety shut-01f system. A pilot flame at 14 or 15 producing thirty millivolts at generators 41 and 42 is safe, i.e., will ignite the main burners 11 and 10, and a pilot flame producing 29 millivolts is unsafe, i.e., will not ignite the main burners. Thus, in order to effect shut off of fuel flow to the burners whenever there is an unsafe pilot flame, the system must be designed such that whenever one of the two generators falls below 30 millivolts, the spring 34 overcomes the attractive force between the magnet 29 and armature 32 and releases said armature to effect closure of the valve disc 27 for shut off of all fuel flow.

Since it is impossible to provide a practical pilot burner and generator that will produce a single safe millivoltage such a thirty millivolts without causing a lot of shutdowns or drop-outs in normal field use, a practical pilot burner and generator arrangement must be employed, which avoids such shut-downs by allowing for variations in fuel supply pressure, environment, composition of fuel, restrictions in the fuel orifices, distortions of parts. occasioned by subjection to elevated temperature and changes in atmospheric humidity and pressure. In fact, in various commercial single thermoelectric generator and pilot burner arrangements in present use, it is generally accepted rule of thumb that the drop-out valve of a valve or switch in terms of millivoltage be at thirty percent of the optimum millivoltage that the pilot burner and generator can produce. For example, if burner and associated generator can produce, under optimum conditions, one hundred millivolts, then the drop-out value should be designed to be thirty millivolts. As another example, if a thermoelectric generator and associated pilot burner can produce thirty-three millivolts at optimum, the drop-out value should be nearly ten millivolts. So-called normal output of pilot burner-generator assemblies having an optimum output of one hundred millivolts is in the neighborhood of sixty to eighty millivolts, whereas the normal output of those having an optimum output of thirty-three millivolts is in the neighborhood of twenty to twenty-six millivolts.

With the foregoing millivoltages in terms of a pilot burner operation in mind, it will become apparent hereinafter that a safety shut-off apparatus utilizing a horseshoe type magnet having two series or aiding windings thereon separately connected to two separate pilot burners has a very limited range of so-called safe operating millivoltages. This obtains because in a series winding system, in order to have drop-out when any one of the two pilot burners becomes unsafe (i.e., causes generation of below 30 millivolts in the illustrative system), it is necessary that the minimum drop-out value of the dual system be the additive amounts of millivoltage of one burner at maximum unsafe value (at 29+) plus the maximum millivoltage'possible at the other burner operating at optimum or a total of 129+ millivolts. Since in a series system as described the millivoltage of the separate generators are additive in terms of flux generated, any combination of dual pilot operation which produces a total of 129+ millivolts or less causes dropout of the armature and shut off of the fuel flow to the burners. To illustrate how limited the range of such a system is, assume the situation wherein both pilot burners and their associated generators are operating at well above the safe minimum, for example, at sixty-four millivolts. Even though the burners are operating in a safe range, the total of 128 millivolts generated is below the drop-out value, and therefore the attractive force produced at armature-magnet air gap is insufficient to retain the armature against the bias of spring 34. Fuel shut off thus results, even though the burners are operating safely.

The electromagnetic core and winding structure shown in Figures 2 and 2a affords a much greater range of dual pilot burner operation than a series system of the type described. For example, the magnet and windings of the improved structure may be designed so that two generators such as 40 and 41 producing 36 millivolts each will provide the same attractive force in the armaturemagnet air gap as one of said generators operating at 100 millivolts and the other generator operating at 30 millivolts.

This relationship will be more readily apparent upon considering the performance curves shown on the graph of Figure 3 wherein the millivoltage output of one pilot burner-generator assembly, for example, the pilot burner 15 and generator 40, provides the ordinate or vertical axis, and the millivoltage output of a second pilot burnergenerator assembly, for example, the pilot burner 14 and generator 41, provides the abscissa or horizontal axis. As shown, the optimum output of each of the generators represented is one hundred millivolts.

On the graph, the line 57 represents the drop-out line of a dual type safety shut-off device utilizing a conven tional horseshoe magnet core with the windings energized by generators 40 and 41 disposed in series-aiding relation. The line 58 represents the drop-out line of a dual type safety shut-off control constructed in accordance with the present invention, and the line 59 represents the dropout line of an idealized dual type safety shut-off control.

In Figure 3 the L-shaped area represented by the capital letter A indicates a range of unsafe operation by one or both of the two pilot burner-generator assemblies. Thus, any point within the area A, at least one of the pilot burner-generator assemblies is producing less than the 30 millivolts arbitrarily assumed to be the minimum safe millivoltage for either pilot burner-generator assembly. For example, point 55 in area A represents condition in which generator 41 is producing approximately 28 millivolts and generator 40 is producing approximately 65 millivolts. This is unsafe in the sense that pilot burner 14 associated with generator 41 will not safely ignite the main burner 11 under these conditions.

The combination of areas represented by the capital letters B, C, and D represents the safe operating range for pilot burners 14 and 15, i.e., each of the assemblies is producing at least thirty millivolts and therefore any combination of pilot burner operations producing millivoltages falling within the areas B, C, and D afford safe ignition of the burners 10 and 11. For example, point 56 in area C represents generator 40 producing 65 millivolts and generator 41 producing 60 millivolts both of which are produced by safe pilot flames.

As aforementioned, line 57, which divides the area D before." Any point 'al ong line -7 is'representative of an "additive total of just below 130 millivolts produced by the two pilot burner-generatorassemblies. The area in the graph indicated by'fthe' capital letter'D represents the range of s afe pilotburner operation ina series type device, the extremes of said 'range'being those situations wherein one pilot -burne'r-gener-ator assembly is operating at maximum, i.e.,i100 millivolts, and the other is operating at the safe minimum of 30 millivolts. Thus, the areas B and C which also represent p ar t'of the safe operating "range of the pilot burners are lost to the dual pilot'burner systems using a horseshoe magnet and series-aiding Wind- 'lngs.

Line'58 which divides areas B and C represents the "drop-out curve'of' the magnet structure shown in Figures 2

and2a whereinthe windings

30 and 31 are energized by generators 41 and 42. Thus, when the improved structure is used, a very substantially increased range of pilot burner operation represented by area C plus the area D is attained. The areaC, represents the range increase afforded by" the improved structure over the range D afforded by seriestypemagnet structure. It will'be observed that the performance curve 58 of the improved structure closely approaches the ideal represented by the curve 59, t v

The improved magnetic structure makes it possible to now provide a single control device affording safety shut-oft fuel control responsive to the operation of a pair of pilot burners, the system embodying said single control having, for all practical purposes, substantially the same operating characteristics as the much more eXpen sive present systems utilizing a separate safety shut-01f control for each pilot burner-generator assembly.

Figure 2a shows a slightly modified magnet structure as compared with that shown in Figure 2. The difference beingthat the area between the legs of the

U-shaped extents

29a and 29b is filled in, and the windings 31' and 3th are shifted to the closed end portions of said U-shaped extents. This structure operates substantially identically with the structure shown in Figure 2.

Although two specific embodiments have been shown and describediit is with full awareness that many modifications thereof are possible. The illustrated forms, of the invention have been selected forpurposes of disclosure only arid are not intended to limit the forms which the invention may take or to confine the invention to particular use, all of such other forms, modifications or changes being contemplated as may come within the scope of the invention as set forth in the appended claims.

I claim:

lfln a control device, a magnet'core comprising a pair of spaced U-shaped portions having the leg portions thereof magnetically connected by first and second pole pieces to form aclosed loW reluctance magnetic path, first and second windingmeans associated With said U- shaped portions and operable when energized to produce a flow of magnetic flux jtherethrough, first and second electric energy source means connected to said first and second Winding means respectively for energization of the latter, said first and said second winding means when either is energized singly being adapted to produce a flux flow in said closed path serially through both of said U-shaped portions and said pole pieces, and said first and said second Winding means when both are energized simultaneously being adapted toproduce flux flow through said U-shaped portions in direction to establish parallel flux paths each including one only of said U-shaped portions. I e a 2. In a control device, magnet means comprising a pair of spaced side members magnetically connected by firstand second, end pieces to .form atclosed low reluctance magnetic path, first and second winding means associatedwith said side members: and operablewhen' energized to produce a fiow of magnetic fiux-th'e'r'throilgh,

first and, second low'power'source means connected to said first and second'windi'ng means-respeetivelyrcsr energization of theflatter,'said first and said secondwinding means wherieither is energized singly "being adapted to produce a flux flown a portion ofwhich' news: in said closed path serially throu'glrbothof said side members and said end members, and said first l'and sa'idsecond Winding means When both are energizedsimultaneously, being adapted to produceflux flow through said "side members in direction toestablish parallel flux paths each including one'only'of said side members.

In a control device, electromagnetivmeans comprising core means includinga pair of spaced U-shaped members the leg portions of which'are magnetically connected by first and-second 'polepieces toform' acl'o'sed low reluctancemagnetic path, armature'me'ans"associated with said coremeans for'relative moverrr'ent"therewith, first and second winding meansassociated with said U-shaped members and 'operableWhen energized'to produce a flow-of magnetic flux therethrough; a first and second source-means connected to said'first and second winding means respectively for energization of theiatter, saidfirst and said second winding means when either is energized singly being adaptedto produce a flux'fiow a portionof-whichfiows insaid closed path serially through both-of said U-shaped membersand said'pole pi'eces,'and

-said first and said-secondWindingmeans when b'oth'are energized simultaneously being adapted to produce'fiux flow throughsaid- U-shaped'membersiand said armature means in a direction to establish parallel flux paths each including one only of said U-shapedmembers;

4.- In a control device,- a magnet core' comprising first and second spaced U-shaped portions the'leg' portions'of whichare magneticallyconnected by-first and second pole pieces toforma closed, loW reluctance 'magnetic path, first and second Winding means associated with said first and-second U-shaped portions respectively'and op erablewhen energized to produce a flow of magnetic flux therethrough, first and second thermoelectric source means connected to; said first and second winding'means respectively for energization'of the-latter, 'saidfirst winding means when energized singly 'being adapted to produce a flux flow a portion of which'flows in said closed path. serially i n a given'dire'ction' through both of said 1 U-shaped portions andtsaid-pole' pieces, said second "Wind- .ing means when energized 'sing'ly being adapted "to produce a flux flow a'portion 0fwhiclr'flows insaid closed path serially iin the opposite' direction-through both' bf s'aid U-shaped portions and said pole pieces, 5 and said first and said second winding means when bothare energized simultaneously-being adapted-to respectivelyproduce a flux flow through said first and second U shape'd' por- ,tionslin direction to establish first-and'sec'ond separate parallel fluxtpaths jthe first only ofsai'dfluxpathincluding said first U-shaped por-tionspa'nd the second only of said fluxpathiincluding said second U-sh'apedportions.

5. In a-control device,-electromagnetie-means including amagnettcore comprisinga pair ofsp'aced U-shaped members the 'legiportions ofwhich are-magnetically -con nected by first-andi-second pole-piecesto' forma' clo'sed magnetic path, a relatively movable armature associated with said core and providing an. air gap therewith; first and second Windingmeans'associatedwith said U-shaped members andoperabl'e when-energized to produce afiow of magnetic flux 1 .therethrough, 1 first-' and second source means connected to said first and-second Windingmeans respectively for energization of the latter, said'first and said second winding means'when either is energized singly being adapted to producer-a flux flow a portion of ,Whichis shunted to flow serially through the closedmagnetic path including both of saidU-shaped membersand .said pole pieces and another portion which 'fio'wsthrough said air gap and said armature, and said first and said Fewsecond winding means when both are energized simultaneously and equally being adapted to produce a flux flow through said air gap, said armature, and U-shaped members in a direction to establish parallel flux paths each including one only of said U-shaped members.

6. A control device for a pair of separated pilot burners comprising, a magnet and movable armature having a retracted position and resettable toward attracted position, biasing means biasing said armature with predetermined force toward retracted position, said magnet having spaced connected portions operable to form a closed magnetic path, first and second energizing winding means on said spaced portions of said magnet for creating in response to a safe condition an attractive force to retain said armature in attracted relation after movement thereto, a first thermoelectric generator associated with one of said pilot burners for energizing said first winding, and a second thermoelectric generator associated with the other of said pilot burners for energizing said second winding, said first and second thermoelectric generators each being operable to deliver an electromotive force to its winding corresponding to the flame condition at its respective pilot burner, when the generator for one winding is heated by a maximum safe pilot burner flame and the generator for the other Winding is heated by a pilot burner flame of a size just less than a minimum safe flame the energization of said windings thus aflorded creates an attractive force between said armature and magnet that is just less than the force of said biasing means, and when the generators for both windings are heated by pilot burner flames which are slightly larger than a minimum safe flame and therefore substantially smaller than a maximum safe flame, the energization of said windings thus afforded creates an attractive force between said armature and magnet that is greater than the opposing force of said biasing means and is therefore capable of retaining the armature in attracted position when moved thereto.

7. A control device for fuel burning apparatus having a pair of separated burners comprising, a magnet, movable armature having a retracted position and resettable toward attracted position with respect to said magnet, biasing means biasing with a predetermined force said armature toward retracted position, fuel flow-control means associated with said armature for movement therewith between flow-controlling positions, said magnet having spaced connected U-shaped portions, first and second energizing winding means on said spaced connected U- shaped portions of said magnet, a first flame responsive source of electrical energy associated with one of said burners for energizing said first winding and a second flame responsive source of electrical energy associated with the other of said burners for energizing said second winding, said first and second flame responsive sources of electrical energy each being operable to deliver an electromotive force to its winding corresponding to the flame condition at its respective burner, the configuration of said core and the arrangement of said winding thereon being such that when the flame responsive source for one of said windings senses a burner flame of a size just less than a minimum safe flame, attractive force created between said armature and magnet by the energization of said windings thus aiforded is just less than the force of said biasing means, and when the flame responsive sources for both windings sense burner flames which are only slightly larger than a minimum safe flame therefore substantially smaller than a maximum safe flame, the attractive force created between said armature and magnet by energization of said windings thus afforded is greater than the opposing force of said biasing means and is therefore capable of retaining the armature in attracted position and hence said flow-controlling means in one of its controlling positions when moved thereto.

8. In a control device, a magnet core comprising a pair of core portions magnetically connected by spaced first and second pole piece members to form a closed low reluctance flux path, and first and second winding means associated with said first and second core portions respectively intermediate the connections thereto of said pole piece members, either of said first and second winding means when energized alone producing a flux flow through the closed flux path serially through said core portions and pole piece members, and said first and second winding means, when energized simultaneously, producing flux flow through said core in a manner affording parallel flux paths each including one only of said core portions.

9. In a control device, a magnet core comprising a pair of core portions magnetically connected by spaced first and second pole piece members to form a closed low reluctance flux path, an armature having an attracted position with respect to said pole piece members, and first and second winding means associated with said first and second core portions respectively intermediate the connections thereto of said pole piece members, either of said first and second winding means when energized alone producing a flux flow through the closed flux path serially through said core portions and said pole piece members, and said first and second winding means, when energized simultaneously, producing flux flow through said core and armature in a manner affording parallel flux paths each including one only of said core portions.

10. Fuel flow control apparatus comprising a pair of burners, first and second thermoelectric generators respectively disposed in heating relation to said burners, and a fuel flow control device comprising electromagnet means having core means including a pair of U-shaped members magnetically connected by first and second pole pieces to form therewith a closed low reluctance magnetic path, an armature movable to attracted and retracted positions with respect to said pole pieces, means biasing said armature toward retracted position, a flow control member operatively associated with said armature and movable from one to another controlling position by movement of said armature from attracted to retracted position, first and second winding means on said U-shaped members connected for energization by said first and second generators respectively and operable when energized singly to produce a flow of magnetic flux a portion of which flows serially in both of said U-shaped members and in said pole pieces, said first and second winding means when both are energized simultaneously being operable to produce flux flow through said U-shaped members and said armature in a direction to establish parallel flux paths each including one only of said U-shaped members, linking of said armature by the flux in said parallel flux paths affording suflicient attractive force to retain said armature in attracted position and said flow control member in said one controlling position when moved thereto against said biasing means.

References Cited in the file of this patent UNITED STATES PATENTS 1,979,127 Warrick Oct. 30, 1934 2,183,855 Mansky Dec. 19, 1939 2,823,741 Thornbery Feb. 18, 1958 2,872,972 Matthews Feb. 10, 1959 FOREIGN PATENTS 708,491 France July 24, 1931 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,959,219 November 8, 1960 Charles E. Hajny It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent. should read as corrected below.

Column 3, line 28, strike out "the"; column 5, line 44,

for "a", first occurrence, read a's line 54, for "valve", first occurrence, read value column 7, line 2, for "cure" read curve column 8, line 22, strike out "a", second occurence; column 9, line 67, after "flame" insert and Signed and sealed this 14th day of November 1961.

(SEAL) Attest:

ERNEST W. 'SWIDER DAVID L. LADD Attcsting Officer I Commissioner of Patents USCOMM-DC- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,95%219 November 8; 1960 Charles E Hajny It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent. should read as corrected below.

Column 3, line 28, strike out "the"; column 5, line 44,

for "a", first occurrence, read as line 54, for "valve'fl first occurrence read value column 7 line 2 for "cure" read curve column 8, line 22 strike out "a", second occurence; column 9, line 67 after "flame" insert ERNEST W. SWIDER and -a Signed and sealed this 14th day of November 1961.,

(SEAL) Attest:

DAVID L. LADD Attesting Officer Commissioner of Patents USCOMM-DC