US2693913A - Ignition and fuel control means for liquid fuel burners - Google Patents

Description

AN Y 9i I1954 M. REsEK ETAL IONITION AND FUEL CONTROL MEANS FOR LIQUID. FUEL BURNERS original Filed June 16, v.1350

United States Patent IGNITION AND FUEL CNTROL MEANS FOR LIQUID FUEL BURNERS Marc Resek, Shaker Heights, Wilbur A. Schultz, Lakewood, and Lloyd V. Antl, Cleveland, Ohio, assignors to Perfection Stove Company, Cleveland, Ohio, a corporation of hio Original application June 16, 1950, Serial No. 168,524. Divided and this application August 14, 1951, Serial No. 241,866

7 Claims. (Cl. E36-m1) This application is a division of one tiled by us on June 16, 1950, Serial No. 168,524, and the invention that constitutes the subject matter of the-present case is an electrical ignition and controlmeans for liquid fuel burners, particularly of the vaporizingvclass, disclosed in the original application.

An object of the present invention is the provision of an electrical control system, desirably including a sheathed, embedded electrical igniter, for liquid fuel burners, especially of the type aforesaid, that renders the burner entirely automatic in operation and thoroughly reliable and safe.

Another object of the invention is to provide an electrical control system for liquid fuel burning apparatus that insures a safe condition of the apparatus in case of current failure.

Another object is to provide an electrical ignition and control means for liquid fuel burners having a. low rate of current consumption.

One advantage arising from the use of an electrical igniter of the kind above described and which permits the use of a high capacity resistance element is that the igniter may be supplied with current directly from the regular 110 volt house potential, thus eliminating the need of an ignition transformer, such as is employed with exposed hot wire or spark gap igniters.

The foregoing objects and advantages are realized in the embodiment of the invention illustrated in the accompanying drawing wherein the figure represents a sectional side elevation of liquid fuel burning apparatus equipped with the electrical ignition and control means of our invention, schematically illustrated.

Proceeding with a more detailed description of the invention wherein the parts disclosed in the drawing will be referred to by reference characters, 1 denotes, generally, ,a burner pot orA bowl, that is incorporated, in the liquid fuel burning apparatus. 2 designates generally, an air housing that surrounds the burner pot or bowl, and a casing 3, shown in broken lines, surmounts and is in operative relation to the pot or bowl andencloses a combustion space or chamber C.

The burner pot includes a perforated cylindrical peripheral wall 5, and a slightly dished circular bottom wall 6, the latter being shown as formed integralwith the peripheral wall. Attached. to the exteriorof thepot at about the junction of the walls 5 and 6 isa continuous` annular overow trough 8'which communicates with the interior of the pot through the lowest row of perforations, designated 10. The peripheral wall 5V is provided with a relatively large opening 12, and securedV to said wall about the opening, preferably by welding, is theI inner end of the cylindrical neck 15 'that terminates atits outer end in a ange 16.

Welded or otherwise secured to the outwardly dared upper end of the peripheral wall 5 of the burner pot 1 is a generally upwardly convergent annular top wall 1S, and shown as likewise secured to the edge portion of said top wall about the relatively large opening therein is the base hange of a perforated neck 20. This neck is shown as flared outwardly and thence upwardly toprovide a peripheral flange thatis secured to. anupstanding flange of a ring-like rnember`23. AToward its outer edge said member is stepped abruptly upwardlyv to provide a vertical cylindrical shoulder 24, outwardly beyond which the member is provided with` abroadlatj flange.25 that;

-subject to leakage,

2,693,913 ylcatented Nov. 9, 1954 ,2l isadapted-to'be engaged with lthe undersideof ariannu'-i larbottomfwall 28-of the casing\3,and to -be detach-ably' secured thereto by fastening. means or bolts E9. l,

The-air housing ifincludesy a cylindrical peripheralgwall 30fandfa=circularrbottom wall 31, formed to-fit a suitable distance within thel lower end of lthe peripheral wall. These walls aresuitably secured together, by weldingor-other means, and attachedto the upperend of thefp'eriph'eral'wall 3l) is a top member-32, shown as extending' inwardly'andthenceupwardly and as fitted to the shoulder 24' of the previously'described ring-like member' 23', the parts being fastened together, preferablyby welding. Opposite the neck 15 ofy the burnerpot, the 7wall 30"-is provided with a vlarge opening 35` and welded orl otherwise secured to said wall-about the opening 35 isthe inner end* of a` sleeve 36. A suitable distance from* its outer end, the sleeve 36 is provided with an internal liangeStl formed, in `thepresent instance, of an annular member. that is4 L-shaped in cross section -andy al cylindrical portion'of which is welded or otherwise secured tothe sleeve. IAttached by suitable fastening meanslltl, suchas screws, to the flange 16 of thel neck` 15, are the peripheral portions of circular plates 42'and 44, witha gasket 45' of packing material interposed betweenl the latter' plate and the ange'16. By reason oftheir function, these plates willv be referred to, respectively, las the` nozzle plate, andthe igniter plate. These plates are provided. with relatively largeregistering openings, `and shown as fitted within the opening of the'nozzleplate .42 isv the outer: end of a cup-like shell Sil, which we shall refer to as the'outer shell, said shell and plate being -secured together, desirablyby welding. 52'denotes a nozzle guide. 1t consists of acylindrical body that is reduced in 'diameter adjacent its lower end, and said endr occupies a circular aperturein the lower side of the shell 5l), the parts being welded orA otherwise rigidly connected together. 55 denotes an inner shellv that is nested within andspaced from theV outer shell and is provided with-an aperture on its under side wherein is lfitted the bottom portion of thev larger end 4of the nozzle guide 52. AThe inner shell is also welded or otherwise iirmly secured to the nozzle guide and is supported solely thereby. It may be explained that the nozzle guide has an axial passage that-is enlarged at its upper end and is made convergent at its lower end, as will be seen by reference to the original application above identified. The discharge end` of a nozzle 62 is located within' and centrally of the nozzle guide. At its upper end the nozzle lisprovided with a lateral extension that is communicatively connected, by a conventional coupling 63, to the adjacent endl of a fuel supply pipe 65.

7l) denotes a sheathed electrical igniter, which may be described, briefly, element or wire that is embedded in refractory insulating material of high heat conductivity encased in a tube of heat resisting metal, from which said element or wire is electrically insulated by said refractory material. The inner end portion of the igniter istshown as in the form of acoil, and the terminal portions thereof extend through aligned holes in the plates 42 and 44, and are welded or otherwise secured to the plate 44 which has heretofore been referred to as the igniter plate. Forwardly of the plate 42, the terminal portionsof the igniter.` are provided with binding posts, one being shown and designated inthe drawing. A baie 8l) is suitably attached to the igniter and includes a bottom wall 81 thatextends beneath the coil of the igniter, and a relativelysteep inclined wall portion 83 that is disposed insubstantially vertical alignment with the nozzle 62tso that fuel descending by gravity from the nozzle will impinge. against said 1 inclined wall portion.

Liquid fuel is supplied to the burner pot through a so-called constant level control valve, shown in a conventional manner in the drawing and designated 90. :It' consists of a receptacle to which fuel is conveyed from a suitable source (not shown) by a pipev 92;,under the control of a valve 93 that is closed by a float 94, where. with it has the usual operative connections, when fuel rises within the receptacle a given distance. While these floatcontrolled valves are reasonably reliable, they are and for that reason, as will presently as consisting of a currentV carryingy appear, we do not rely upon this float controlled valve to positively shut o the ilow of fuel to the burner. Also incorporated in this unit that is now under consideration is a metering valve 98 that reciprocates within a hollow boss that rises from the bottom of the receptacle and through which communicative connection is established between the interior of the receptacle and the previously mentioned fuel supply pipe that leads to the nozzle 62. Included in this pipe is a so-called fuel release valve 100 of the well known solenoid operated type, the solenoid and valve being shown in a conventional manner in dotted lines. The valve is biased toward closed position and accordingly shuts olf the ow of fuel when the solenoid is deenergized. Reversely, so long as current ilows through the coil of the solenoid, the valve will be held open. 102 denotes a similar inlet valve in the pipe 92 which functions when the current is cut off to positively arrest iiow of fuel to the constant level control valve 90. As an emergency measure, so that the burner will operate on low re in case of a general power failure, a by-pass 103 is provided in each of the pipes 65 and 92 about the respective valves 100 and 102 therein, each by-pass, in turn, being equipped with a manual valve 104.

Any liquid fuel that overflows, under abnormal conditions, from the burner pot 1 into the trough 8 is conveyed through a pipe 105 to a closed vessel 106 from which a tube 107 rises through the bottom of the receptacle of the constant level control valve 90 and terminates therein above maximum liquid level. A oat operates within the vessel 106 and a rod 111 rises from said oat through the tube 107 and is maintained by the latter with its upper end in vertical alignment with a finger 112 on the float 94. Accordingly, when overllow fuel rises to a sufficient height within the vessel 106 to acomplish such end, the float 110 ascends and lifts the rod 111 so as to engage its upper end with the finger 112 and prevent the float 94 from dropping and lifting the valve 93 from its seat. By this means normal feed of fuel to the burner is prevented until the vessel 106 is drained by the opening of a valve 114 adjacent the bottom of the latter.

designates an air impeller or centrifugal blower that supplies combustion air to the burner. The outlet of the casing of the air impeller or blower 120 fits within the sleeve 122 that is carried by and extends through an opening in a disc or plate 125, and to which said sleeve is rigidly secured, as by welding. The disc or plate 12S is anged about its edge and fits within the outer end of the sleeve 36 against the previously mentioned flange 38 to which it is secured by a plurality of fastening means 126. The plate 125 is provided with an aperture for the accommodation of thefuel supply pipe 65. A damper 127, of common and well known type, is desirably located in the outlet of the casing of the air impeller or blower and by means of which the quantity of combustion air supplied to the apparatus may be regulated.

The electrical system of our present invention by means of which the operation of the above described liquid fuel burning apparatus is automatically controlled includes, besides the solenoids of the valve 100 and 102, the following parts: a transformer 130, the primary and secondary windings of which are designated 131 and 132, respectively; a room thermostat 135 that is shown conventionally as comprising a thermosensitive element of the bimetal variety 136 through which, and a leaf 137 that is carried thereby, a current is adapted to be conducted to the low tire contact 138, and the high tire" contact 139; a so-called Micro switch 140, the movable element 141 of which is biased in a direction to engage a contact 142, and which is movable into engagement with a con# tact 143 through the intervention of a push rod 144. Said push rod has operative connection at its lower end with a leaf spring 145, as by ,bearing thereon, and under tion, thereby to pass sufficient fuel to maintain high tire operation of the burner. Associated with the previously mentioned leaf spring 145 is a thermostatic or thermosensitive current carrying element in the form of a bimetal strip, designated 165. When this element or strip is cold it contacts the free end of the leaf spring 145 and holds the latter under tension in a position to maintain, through the intervention of the push rod 144, the movable element 141 of the Micro switch in engagement with the Contact 143 thereof. When heat is imparted to the element or strip by an electrical resistance heater 167, said element or strip will warp in a direction to relax the leaf spring 145 and thereafter withdraw from said spring and engage a contact 168, the latter occurring after a suitable interval of time. Relaxing of the spring 145 permits the movable element 141 of the Micro switch 140 to snap over into engagement with the contact 142.

designates a so-called top limit switch, a safety feature usually employed in domestic furnaces and other similar apparatus, to open the control circuit in case the apparatus becomes overheated, such switch, obviously, being disposed in intimate heat exchange relation to a suitable part of the apparatus.

The usual house circuit, furnishing electrical energy at a potential of say 110 volts, is represented by a conductor that leads to the primary winding 131 of the transformer 130, and a conductor 176 that leads from said winding. The circuits of higher potential or voltages are shown lin heavy lines, and those of comparatively low voltage, in light lines. The motor 180 of the air impeller or blower 120, and the igniter 70, which may have a capacity of say 750 watts, are in high voltage circuits, as will presently appear. Current is carried from the conductor 17S, through a conductor designated 182, to the movable element 141 of the Micro switch 140. The contact 143 of said switch is placed in electrical connection with one side of the motor 180 through a conductor 183.

certain conditions that will hereinafter appear this leaf spring serves as an electrical conductor, wherefore, in certain of the claims, it is termed a current carrying resilient member. 150 designates, generally, a switch including blades 151 and 152 that are mechanically connected by an extension 153 of the core of a solenoid 155. A bimetal strip 158 has operative connection with the previously mentioned metering valve 98 and serves, when cold, to retain the valve open suliiciently to pass enough fuel to maintain low tire burner operation. Associated with said bimetal strip is an electric resistance heater 160, and when this heater is energized and its temperature accordingly raised, it causes the bimetal strip to warp a direction to lift the metering valve to wide open posi- The other contact 142 of said switch has electrical connection with the terminal 75 of the igniter 70 through a conductor 184. Current returns from the motor and igniter to the other side of the high voltage circuit through a conductor and its respective branches 186 and 187. The low voltage circuits, say of 24 volts, that have as their source of current the secondary winding 132 of the transformer 130, will be described in connection with the operation of the apparatus.

As illustrated in the drawing, the apparatus is inactive excepting for the operation of the air impeller or blower, it being assumed that the temperature of the space to which the room thermostat 135 is subjected is above that requiring immediate low re operation. Upon decline of said temperature to the upper limit of a temperature range for which the thermostat is set, and which may be referred to as the comfort range, the element 136 thereof will swing in a direction and only far enough to engage the leaf 137 with the contact 138. This will close a circuit (starting with the secondary winding 132 of the transformer) through a conductor 190, the winding of the solenoid of inlet Valve 102, conductor 191, the beforementioned parts of the roorn thermostat, and a conductor 192, including the limit switch 170 back to the source. This will result in the opening of the valvc 102, insuring ample fuel supply to the constant level control valve 90. Current will also flow from the conductor through a conductor 195, the blade 152 of the switch 150 and a conductor 197 to the electrical resistance heater 167 and thence, through a conductor 198, to the previously mentioned conductor 191 and back to the source. Very shortly, say about ten seconds, after the energization of the heater 167 the element or strip 165 will warp enough to relax the spring 145 and permit the movable element 141 of the Micro switch 140 to snap into engagement with the contact 142, whereupon current will ow through the conductor 184 to the igniter 70, returning through the conductors 187 and 185 to the negative side of the main circuit. Withdrawal of the element 141 from the contact 143 will, of course, cut off the supply of current to the motor 180 of the air impeller or blower, thus interrupting the air supply to the burner during the ignition phase and accordingly accelerating the preheating of the igniter and adjacent parts of the burner due to the absence of the cooling effect ot' the air. While the element or strip 165 is warping suiciently to engage contact 168, the igniter 70 will continue to build up heat in itself and in the adjacent parts of the burner pot. Afterl an vintervalof time, .say vone and one-half minutes, said element -or strip 165l will engage the contact kv168Uandclose a circuitv including, be sides said elementiand contact, yconductorsr200 and `201, the winding of the solenoid Y155,;and a conductor 202 that leads back to the previously mentioned conductor 191. Upon energization of the solenoid ;155,-.the,blades 1,51 and 152 of the switch 150 will be swung into, engagement with the respective `contactsf205 and l206, the latter blade 152 withdrawingfrom a. Contact 207 that controls the previously described circuitincluding the electrical heater 167, thereby kopening said heater circuit. By engagement .of the blade .152 with the contact 206, a circuit is established from .the beforementioned conductor 195, through theblade. .152, contact 206 and a conductor 208 thatjoins the,previously...mentioned conductor 201, thereby to insure continued ,flow of current to the solenoid .155 after the element or strip 165 cools and withdraws from contact A168. .During the interval of time that represents the cooling off period of the element or strip 1.65, approximately .one and one-half minutes, which is measured fromthe time .said strip withdraws from Contact 168 until it engages and deects the spring 145, the igniter 70 will remainenergized. There is, however, an appreciable fraction of .this time, .say ten seconds, when electrical Contact is made. between the element or strip 165 and said spring 145 before the latter yields enough to effect operation of the Micro switch. During this dwell current will flow through the conductor 210, the switch blade .151, contact 205, a conductor 212, the winding of the solenoid ofthefuel release valve 100, and a .conductor 213 to the previously mentioned conductor 202 and thence to the source, thus opening said valve to permit oil to flow,.under the control of the metering valve 98,. from the fuel supply of. the. constant level control valve 90 to the burner.

Now, with the igniterand adjacent parts of the burner, including the baffle 80,l highly heated, the liquid fuel that drops from the nozzle 62fwill impinge against the inclined wall portion 83 of the battle 80 and practically instantaneously flash into vapor and be ignited, such fuel as remains liquid .rapidly vaporizing as it ows over the bottom wall of the bale, in contact with the igniter, or, if not before reaching this point, from the bottom of the burner pot, suicient air being supplied through the perforations of the peripheral wall of the pot to support such combustion as now occurs.

By .this time the continued movement of the element or strip 165 will have fully deectedthe leaf spring 145 and, through the medium of .the rod 144, operated the Micro switch 140, causing the element 141 thereof to withdraw from the contact 142 and resume engagement with the contact 143. This will 4cut off supply of current to the igniter and reestablish the circuit through which current is delivered to the motor 180 of the air impeller or blower 120. Air will now be supplied to the burner, desirably under the control of the damper 127, and which may be set to provide the proper amount of air to the burner to produce the best results. It will be observed that the discharge opening of the impeller or blower casing is so related to the shells 50 and S5 as .to insure air circulating through the space between the shells and about the nozzle, The constant flow of air will keep said shells and nozzle and nozzle guides relatively cool, notwithstanding their proximity to the intense heat within the burner pot. Some of the air entering the shell 55.Will pass through the nozzle guide about the nozzle and into -the burner pot and provide primary air in the vicinity of the igniter.

. Under the now` prevailing conditions fuel will continue to ow to the burner in proper amount to maintain low re. In the event the .temperature of the space to which the room thermostatv is. subjected risesas a result of the low fire condition to a value above 'the upper limit of the comfort range for which the room thermostat is set, the element 36 will swing towardtthe position shown in Fig. l, withdrawing the leaf 137 from the contact 138, thus opening all circuits and allowing. the burner to resume the condition assumed at .the beginning of the description of operation. On the other hand, should the temperature of said space, notwithstanding low tire operation, drop below the comfort range, the element 136 of the room thermostatI wilhswing still, further in its former direction,Arnaintainingengagement of the leaf 137with .the contact` 136 and,A at ,the `same. timee1 igag from second to rst position,

'6 ing itsterminalportionwith thecontact 139, thereby to close the circuitthat branches olffrom the previously described circuit represented .inapart bythe ,conductor 212 and through which current is supplied `to. th esolenoid of the fuel release valve .100. 'l`he..present. circuit includes a conductor225.thatleadsfrom the conductor 212 to the electrical.resistance.,heaten that is associated with the .thermosensitive element orA bimetal strip 158. Continuingon from .this heater,.the `current returns to the source; through aconductor 226, contact 139,

the element 136 .of .the room thermostat, 4and the conductor 192 which, as..previously mentioned contains the limit switch 1 70.

When the. heater 160 is. energized, theelement or-strip 158 will warp in a direction to move: the metering vvalve 98 to wide open,.position,-..under .which ...cireumstances fuel in sufficient/quantity is delivered tothe burner to maintain high tire. When, under these.:circumstances, the temperature to which the roointhermostat is exposed rises to somewhere within the,.comfort..range, .under which conditions low fire .operation is suicient, the element 136 will withdrawfrom contact 139, and open the circuit including. the heater. 160, after which the element or strip 158. will cool and resume its former condition to return the metering valve. to thepositionshown in the drawing. c

The valves 101 .and .102, whenfthe solenoids thereof are deenergized, servetoy positively -shutv ohc the flow of fuel to the burner thereby.insuring against fuel drip when the room-thermostat` is not callingfor heat. However, When said thermostat isv in either of its effective positions, said valves 101 and .102 are open,.under which circumstances the fuel supply to the burner is regulated bythe constant level controlvalveY 90, which includes the metering valve 98 Having thus described ourinvention, what we claim is:

l. In combination, av liquidl fuel4 burner, means for conducting fuelthereto, a'normally closed fuel release valve in said conducting .means,la solenoid for operating said fuel release valve, an velectrical igniter for the burner,v a transformer, a. relativelyhigh. voltage circuit having a branch including` the primaryv winding of the transformer and a second branch. including the igniter, a switch in the latter branch .which is movable to a first position to close said branchen to a second position to open the same, a vthermosensitive.current carrying element, spaced. contacts associated with said element for alternate .engagement thereby, voperative connections between said element andithevaforesaid switch causing movementofl the. latter to firstV position when said element is heated and to. secondposition when said element is cool, aresistance Yheater for heating said thermosensitive element, ay two-blade f solenoid switch including in association withthe blades lthereof a single contact for .engagementby one blade, anda-first contact anda second contactfor.alternate-engagement bythe other blade, a relatively low voltage circuit `having as `its source .the secondary winding. of the transformer, a` room thermosta'tic` switchy characterizedby a movable current carrying elementandby acontact ar ranged to be engaged by said element as the element responds to a fall iny temperature, the.. element ywithdrawing from said contact as .saidelement subsequentiy responds to a rise in temperature, a irst..branch of said low voltage circuit including said othery blade of the solenoid switch and said first. contactk associated therewith, said resistance heater, the contact of `the room thermostatic switch andthe .movable .element of the latter; a second branch of the low voltage lcircuit including. said thermosensitivecurrent .carrying element and one of said contacts associatedtherewith, .the solenoid of said two-bladeswitch, and the contact and movable element ofthe room thermostatic switch, said second branch beingk closed upon response of said thermosensitive current carrying elementto the heat generated by said resistance heater and the resultant .engagement of said element with the contact associated with it, the last mentioned element, when heated, warping and there` hy permitting movement of the rst mentioned switch said t solenoid, upon .being energized, moving both blades of theaforesaid .two-blade switch so ast-to. open said. first-,branchvof the lowi volt age Circuit through the. resistance. heater; .a thirdbranch of the low voltage. circuit. including said. other .blade ofthe .two-blade. switchand. said ,second contact associessere ated therewith, the solenoid of the two-blade switchand the contact and movable element of the room thermostatic switch; and a fourth branch of said low voltage circuit including said thermosensitive current carrying element and the other contact associated therewith, the said single contact and the corresponding blade of the two-blade switch, the solenoid of the fuel release valve and the contact and movable element of the room thermostatic switch, the aforesaid thermosensitive current carrying element functioning with delayed action to open said second branch of the low voltage circuit and thereafter to close the fourth branch, the final movement of the thermosensitive current carrying element, upon becoming cool, causing movement of the first mentioned switch from first to second position, the room thermostatic switch opening all branches of the low voltage circuit when its movable element withdraws from the contact thereof.

2. In combination, a liquid fuel burner, means for conducting fuel thereto, a normally closed fuel release valve in said conducting means, a solenoid for operating said fuel release valve, an electrical igniter for the burner, an air impeller for supplying combustion air to the burner, an electric motor for operating said impeller, a transformer, a relatively high voltage multiple branch circuit including in one branch thereof the primary of the transformer, two other branches of said high voltage circuit including, respectively, the igniter and the motor, a switch controlling the latter branches of said circuit movable to a rst position to supply current to the igniter and to a second position to supply current to the motor, a current carrying resilient member provided with a contact, operative connections between said member and the aforesaid switch causing movement of the latter to rst position when said member is in relaxed condition and to second position when the member is placed under tension, a thermosensitive current carrying element occupying a position, when cold, to engage the contact of said resilient member and hold said member under tension, and movable to a second position when heated to withdraw from said contact and permit the member to relax, a second contact associated with said thermosensitive current carrying element and engaged thereby when the element is sufficiently heated, a resistance heater for heating said thermosensitive L element, a two-blade solenoid switch including in association with the blades thereof a single contact for engagement with one blade, and a rst contact and a second contact for alternate engagement by the other blade, a relatively low voltage circuit having as its source of electrical energy the secondary of the transformer, a room. thermostatic switch in series circuit with said secondary and characterized by a movable current carrying element and by a contact arranged to be engaged by said element as the element responds to a fall in temperature, the element withdrawing from said contact as said element subsequently responds to a rise in temperature, a first branch of said low voltage circuit including said other blade of the solenoid switch and said first contact associated therewith, said resistance heater, and the contact and movable current carrying element of the room thermostatic switch; a second branch of the low voltage circuit including said thermosensitive current carrying element, the current carrying resilient member, the solenoid of said two-blade switch, and the movable current carrying element and contact of the room thermostatic switch, the second branch circuit being closed upon response of said thermosensitive current carrying element to the heat generated by said resistance heater, the last mentioned element, when heated, withdrawing from the contact of said resilient member, thereby to permit relaxing of the latter and the resultant movement of the first mentioned switch from second to first position, said solenoid, upon being energized, acting to withdraw said other blade from said first contact associated therewith and open said iirst branch of the low voltage circuit, a third branch of the low voltage circuit which includes said other blade and said second contact associated therewith, the solenoid of the twoblade switch and the movable current carrying element and contact of the room thermostatic switch; a fourth branch of the W voltage circuit adapted to be closed by action of said two-blade switch when the solenoid thereof is energized to cause said single contact to be engaged by the corresponding blade, and which fourth branch circuit includes the thermosensitive current carrying element, the aforesaid resilient member, the said single contact and corresponding blade of the two-blade switch, the solenoid of the fuel release valve, and the movable current carrying element and contact of the room thermostatic switch, the aforesaid thermosensitive current carrying element functioning to open the second branch circuit (that is closed by said element when heated) and thereafter, with delayed action, engaging the contact of the resilient member; the final movement of the thermosensitive current carrying element, upon becoming cool, placing said resilient member under tension thereby to cause movement of the first mentioned switch from first to second position, all branch circuits being open when the movable element of the room thermostatic switch withdraws from the contact of the latter.

3. The combination and arrangement of parts defined by claim 2, and, in addition thereto, a constant level valve in said fuel conducting means, a metering valve that controls the outlet of fuel from said constant level valve and which normally occupies a position to pass sufficient fuel for low fire operation, and movable to a second position to increase the amount of fuel passed to produce high tire operation; a thermostatic element having operative connection with the metering valve and moving, when heated, in a direction to shift the metering valve to second position; an electrical resistance heater for heating said thermostatic element; a second contact incorporated in the room thermostatic switch that is engaged by the movable current carrying element of said switch after engagement thereby of the first contact, as the element responds to a further fall in temperature, the element withdrawing from said contacts in reverse order as said element responds to a rise in temperature, and a further branch of the low voltage circuit including said resistance heater and the second contact and the movable current carrying element of the room thermostatic switch.

4. The combination and arrangement of parts defined by claim 3, and, in addition thereto, a normally closed solenoid inlet valve for controlling the supply of fuel to the constant level valve, and a further branch of the low voltage circuit including the solenoid of said inlet valve and the first contact and the movable current carrying element of the room thermostatic switch.

5. ln combination, a liquid fuel burner, means for conducting fuel thereto, liow control means in said fuel conducting means, an electrical actuator for said flow control means, an electrical igniter, a transformer, a relatively high voltage circuit having a branch including the primary winding of the transformer and a second branch including the igniter, a switch in said second branch movable to a first position to close said branch and to a second position to open the same, a time delay device incorporating a thermosensitive warp element, an electrical heater for supplying heat to said element, operative connections between said warp element and the aforesaid switch causing movement of the latter to first position when said element is heated and to second position when said element is cool, a second switch including a first contact and a second contact relatively movable into engagement with each other and a third contact and a fourth contact together with a fifth contact relatively movable alternately into engagement with the third and fourth conacts, a second elecrical actuator for operating the second switch to simultaneously effect engagement of the first and second contacts and the third and fifth contacts, and, alternately, to eifect engagement of the fourth and fifth contacts, a control circuit having as its source the secondary winding of the transformer, a third switch characterized by a thermosensitive element and by relatively movable contacts with at least one of which said element has operative connection and that are caused thereby to engage each other when the element responds to a drop in temperature and to separate when said element responds to a rise in temperature, a first branch of said control circuit including the third and fifth contacts of the second switch, said electrical heater, and the contacts of the third switch; two circuit closing means operatively associated with the aforesaid thermosensitive warp element and alternately rendered effective thereby to close circuits when said warp element is heated and is permitted to cool, respectively, a second branch of the control circuit including the first of said circuit closing means, the second electrical actuator and the contacts of the third switch, said second branch being closed upon response of said thermosensitive warp element to the heat generated by said electrical heater, the last mentioned element, when heated, warping and thereby permitting movement of the rst mentioned switch from second to rst position, the second electrical actuator, upon being energized, causing separation of the third and fifth contacts of the second switch thereby to open the first branch of the control circuit and establish contact between the first and second contacts and between the fourth and fth contacts of said second switch; a third branch of the control circuit including the fourth and fifth contacts of the second switch, the second electrical actuator, and the contacts of the third switch; and a fourth branch of the conrol circuit including the second circuit closing gneans associated with the thermosensitive warp element, the iirst and second contacts of the second switch, the first mentioned electrical actuator, and the contacts of the third switch, said thermosensitive warp element functioning with delayed action to open the second branch of the control circuit and thereafter to close the fourth branch, the final movement of the warp element, upon cooling, causing movement of the rst mentioned switch from first to second position, the contacts of the third switch separating, when the thermosensitive element of said third switch becomes suiciently heated to effect such action, thereby to open all branches of the control circuit.

6. The combination and arrangement of parts dened by claim 5, and, in addition thereto, an air impeller for supplying combustion air to the burner, an electric motor for operating said impeller, a third branch of the relatively high voltage circuit including said motor, and

contact means also included in said branch and operatively associated With the irst mentioned switch so as to be actuated thereby when said switch assumes second position to close the third branch of the high voltage circuit.

7. The combination and arrangement of parts -deined by claim 5, and, in addition thereto, a second set of relatively movable contacts incorporated in the third switch that are caused to engage, after engagement of the other contacts of said switch, by action of the thermosensitive element of said switch in its response to a further drop in temperature and that are caused to separate, before disengagement of said other contacts, by reverse action of said element, a constant level valve in said fuel conducting means, a metering valve that controls the outlet of fuel from said constant level valve and which normally occupies a position to pass sufficient fuel for low fire operation, and movable to a second position to increase the amount of fuel passed to produce high iire operation; a thermostatic element having operative connection with the metering valve and moving, when heated, in a direction to shift the metering valve to second position; an electrical resistance heater for heating said thermostatic element, and a further branch of the control circuit including said resistance heater and the second set of contacts of the third switch.

References Cited in the tile of this patent UNITED STATES PATENTS Cleveland Mar. 14, 1950

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