US2477216A - Control and ignition system for fuel burners - Google Patents

Description

July 26, 1949. c. K. STROBEL v 2,477,216

' CONTROL.AND IGNITION SYSTEM FOR FUEL BURNERS 7 Filed March 13, 1946 Thermal Switch closed when cold Main Fuel Cook Pilot Burner Volvo INVENTOR.

Charles K. Strobe! ATTORNEY.

N Main Burner Valve Patented July 26, 1949 CONTROL AND IGNITION SYSTEM FOR FUEL BURNERS Charles K. Strobe], Pittsburgh, Pa., asslgnor to Robertshaw-Fulton Controls Company, a corporation of Delaware Application March 13, 1946, Serial No. 654,202 '7 Claims. (Cl. 158-1171) This invention relates to control and ignition systems for fuel burners and, more particularly, to electrically operated systems therefor.

Space heating fuel burner systems may include an electrically operated safety control which is the main fuel and electric control devices are supplied with electrical energy from a thermoturned on. c pl or mopile during the normal running Another object of the invention is to incorpoperiod of the burner and which utilizes energy rate the required transformers for adjusting the from a source of commercial supply for resetting voltages to diiferent circuit elements while utiliz purposes. A system of this type may employ a ing certain characteristics thereof for dual pursingle control device such as a solenoid valve of poses where feasible. standard form for both safety and condition con- Other objects and advantages will become aptrol and this valve may be deenergized whenever parent from the following description taken in the room thermostat or the safety control reconnection with the accompanying drawing, quires a shutoff of the main burner. which is a, schematic view of acontrol and ignition Such systems may be of the completely resystem for a gaseous fuel burner embodying the cycling type or may utilize a normally constant invention. burning pilot burner. In the completely recycling Referring more particularly to the drawing. a type the fuel flow to both the main and pilot burnmain burner I 0 is supplied with fuel by a main ers is shut oil. whenever the room thermostat is fuel pipe l2 in which a main fuel shutofl' cock l4 satisfied and a complete ignition cycle is peris provided. The flow of fuel in the pipe I! is formed each time the thermostat calls for heat. also under the control of an'electromagnetic valve On the other hand, the normally constant burnit which is biased to closed position. interposed ing pilot burner arrangement does not undergo between the main fuel cock It and the electrosuch a complete recycling and the system is ordi- 2 magnetic valve I6 is a T connection I8 having narily required to perform the ignition cycle only a reducing outlet to accommodate a conduit 20 at the beginning of the heating season, it being for supplying fuel to a pilot burner 22 located understood, however, that this system also readjacent the main burner ill. The flow of fuel quires an ignition cycle should the safety control in the conduit 20 is under control of a, pilot burner operate due to extinguishment of the pilot burner. valve 23 which may also be 01 the electromagnetic In either type of installation it is of great contype. venience if the householder or other user can stop The main burner valve I6 is preferably of and start the heating system by merely operating standard commercial form having an operating the room thermostat in a normal manner. Thus, coil 24 and armature 25 which are shown sepathe householder need not visit the burner inrated therefrom in the drawing for purposes of stallation at all to relight or extinguish the pilot clarity in illustration. The armature 25 is pivburner. Hence, a primary object of this invenoted at one end and is adapted to engage a relation is to permit convenient shutdown or relighttively fixed contact 2| at the other end when ing of the pilot burner at any time that the user attracted by the coil 24. As will be apparent heredesires. inafter, the main burner valve ll may be provided Another object of the invention is to make the with a manual setting device for opening the system either completely recycling orof the. convalve in the event of a power failure and an autostant burning pilot burner type by a simple altermatic resetting device for superseding the manual ation in the wiring connections. control when the power supply is resumed. As Another object of this invention is to utilize such types of manual set, automatic reset devices a single electromagnetic valve for condition or are well known to those skilled in the art, illussafety control in conjunction with a gaseous fuel tration of the details thereof has been omitted burner without requiring alteration or modificaand further description is deemed unnecessary. tion in standard forms of valves to adapt them for As this description proceeds, it will be apparent such uses. 60 that the coil 24 of the main burner valve l6 and Another object of the invention is to employ the corresponding coil of the pilot burner valve thermoelectric energy independent of any out- 23 are assumed to be either energized or deeperside source for operating the safety control durgized for the purpose of preventing flow of fuel ing the burner running period while utilizing ent to the main burner II and the pilot burner 22,

respectively, and such energization is suflicient ergy from a commercial source of supply in con- 2 nectlon with this control during the starting period only.

Another object of the invention is to render the system self-starting and recycling as long as tion.

The main burner valve i6 is under safety control of an electromagnetic device designated generally by the reference numeral 28. This device comprises a horseshoe magnet 28 having an armature 30 movable between attracted and released positions relative to the pole faces thereof. A stem 32 has lost motion connection with the armature 30 and is reciprocable relative to the horseshoe magnet 28 for moving the armature to released position under bias of a coil spring 34. The stem 32 is provided with an onlarged head 36 which is adapted to engage the armature 30 and to move it toward the pole faces of the horseshoe magnet 28 against the bias of the spring 34. When the armature 30 is engaged with the pole faces of the horseshoe magnet 28, that is, in its attracted position, then a contact bar 31 carried by the stem 32 is positioned thereby so that first and second switch contact pairs 38 and 40 at opposite ends of the bar, respectively, are closed. It will be understood that these contact pairs both comprise the usual fixed and movable contacts.

The resetting movement of the armature 30 to attracted position is under control of an electromagnetic resetting device designated generally by the reference numeral 42. The resetting means comprises a magnet plunger 44 having a swivel connection 46 depending therefrom.

A transformer 43 cooperates with the plunger 44 to form the electromagnetic portion of the resetting device 42 and, to this end, the primary coil 45 of the transformer forms the operating coil for the magnet plunger 44. It will be understood that it is not essential that a transformer be employed for this purpose but is merely illustrative of the preferred form of this invention. The swivel connection 46 carries a coil spring 48 which serves to support one end of a pivoted lever 50 loosely on the connection 46. The opposite end of the lever 58 carries a movable contact forming one of a third pair of switch contacts 52 associated with the electromagnetic device 26. It will be observed that the lever 50 is spaced from the enlarged head 36 of the stem 32 when all the contact pairs 38, 40 and 52 are engaged. The arrangement is such that upon upward movement of the magnet plunger 44 as will occur upon attraction thereof by means to be described, the lever '50 will be rotated on its pivotal mounting causing the end carrying the movable contact pair 52 to engage the enlarged head 3'8 and reset the armature 30 to attracted position relative to the pole faces of the horseshoe magnet.

The electromagnetic safety device 26 is adapted to be energized by thermoelectric means for maintaining the armature 30 in attracted position after it has been reset to such position by the resetting means 42. As shown, the thermoelectric means comprises a thermocouple 54 exposed to the heat of a flame at the pilot burner 22 and connected by wires 56 and 58 to a winding 80 fo r the horseshoe magnet 28. It will he understood that the electromagnetic device 26 does not receive sufiicient energy from the thermocouple 54 to attract the armature 30 into engagement with the pole faces of the horseshoe magnet 28 but that the resetting means 42 is relied upon for such operation. However, after the armature 30 has been thus reset the thermocouple 54 will generate sufficient energy to retain the armature 30 in attracted position provided that the pilot burner inafter appear.

22 is producing a flame. It is apparent that the resetting means, being no longer required, can then be deenergized as will hereinafter be explained. I l

The electromagnetic valve 15 is also under the control of a device responsive to changes in a condition to be controlled. As disclosed in this embodiment, this condition responsive device is designated generally by the reference numeral 62 and takes the form of a. room thermostat comprising a bimetallic spiral 64 carrying an arm 66 provided with a pair of spaced contacts 68 and 10. The contact 68 is cooperable with a fixed contact I2 and the contact I0 is cooperable with the fixed contact 14. A heater coil I6 is provided for accelerating operation of the bimetallic spiral 64 and is connected thereto at one end and to the contact 2| at the opposite end.

The condition responsive arrangement is such that upon a drop in temperature of the space in which the thermostat i2 is located the bimetallic spiral 64 moves in a clockwise direction to engage contacts 10 and 14 and thereafter contacts: 68 and 12; the contact arrangement being such that upon initial engagement of contacts 10 and 14 there still remains a gap between contacts 68 and 12. When the thermostat is satisfied the bimetallic spiral 64 will move in a counter-clockwise direction to disengage contacts 68 and 12 and thereafter to disengage contacts 1'0 and 14. The device thus provides a definite temperature difierential for energizing and deenergizing the coil 24 of the main burner valve I6 as will here- Moreover, neither of the pairs of contacts 68,12, or 10, I4 is required to make or break the full load of the main burner valve lli'thus reducing arcing and wear of the contacts. It will be understood that other commercially available forms of thermostatic devices could be substituted and that it is not essential that two contacts be employed for closing a single circuit for the main burner valve l5.

Means are provided for adjusting the thermostat 62 and are shown as comprising a lever arm 18 which is secured to the bimetallic spiral 64. The bimetallic spiral B4 is pivotally mounted at so that upon movement of the lever arm 18 the bimetallic spiral 64 is rotated about the pivot point 80 thereby varying the temperature at which the engagement of the pairs of contacts 68, 12 and 10, I4 is effected. The lever arm I8 cooperates with a scale 82 carrying suitable indicia to indicate the temperature setting of the thermostat.

Secured to the arm 65 and insulated therefrom is a third contact 84 which is adapted to cooperate with a fixed contact 85 when the arm 66 moves to engage the contact pairs 58, I2 and Ill, 14. In addition, a toggle switch 88 may be located adjacent to the thermostat i2 and is adapted to be normally engaged with a'fixed contact 90. The toggle switch 88 isadapted to be opened by engagement with the arm 56 when the lever arm 18 is moved to the extreme left of the scale 82 which is the lowest temperature setting. In the so-called completely recycling type of system the toggle switch may be dispensed with inasmuch as the opening of contacts l4, 86 serves to deenergize the coil of the pilot burner valve 23.

Igniting means 92 for the pilot burner 22 are provided and may comprise a coil of high resistance wire adapted to become incandescent upon passage of electrical energy therethrough. The igniting means 92 is under control of a thermal switch designated generally by the reference numeral 94 and having fixed andmovable contacts 9'6 and 98, respectively. The thermal switch 94 is preferably of the bimetallic snap switch type and includes a bimetallic element I which serves to operate the movable contact 98 with snap action when heat is applied to the element causing it to warp. Such heat may be supplied by a heatin coil I02 wrapped around or otherwise disposed in proximity to the element I00. It will be observed that the thermal switch 94 is adapted to be closed when the bimetallic element IO0Jis unheated and the contacts 96 and 98 are at such times engaged.

Electrical energy from'a commercial source of supply is controlled by a double-pole main switch I04 connected to the line wires I08, Preferably, a transformer I08 is connected in the line to supply low voltage power for operation of the system. If desired, the usual fan and associated control IIO may be connected in the primary circuit of the transformer I08.

In the operation of the completely recycling type of control described the system is turned on by opening the main fuel cock I4 and closing the main switch I04, it being apparent that these devices could be interconnected for simultaneous operation if desired. As the description proceeds,

it will become apparent that during the burner starting period the commercial energy is utilized for resetting the safety control and then dispensed with in this connection when the selfcontained energy of the thermocouple becomes available during the running period. The commercial source is, however, still reliedupon during the burner running period in connection with the condition control and serves to energize both the main and pilot burner valves and the heating coil I02. The various elements of the system are shown in the position which they occupy when the thermostat 62 is calling for heat. Fuel is being supplied to the pilot burner 22 through the conduit 20 connected to the main fuel pipe I2 and, likewise, fuel is being supplied to the main burner I0 through the pipe I2. As previously pointed out, a feature of this invention is that the system may be completely shut down at the end of the heating season by merely manipulating the room thermostat and if the main fuel cock I4 and main switch I04 are left in open and closed positions, respectively, then the system may again be placed in operation at the onset of cold weather by merely setting the room thermostat at the desired temperature.

Assuming that the pilot burner has been extinguished and that the temperature falls below the setting of the thermostat so as to cause initial engagement of the contact 84 withthe fixed contact 86, then the following circuit is established: from the lower terminal of the secondary of transformer I08 to conductor II2, conductor II4, contact 86, contact 84, conductor II6, conductor II8, toggle switch 88, contact 90, conductor I20, conductor I22, primary coil 45 of transformer 43, conductor I24, contacts 98 and 96, conductor I26 and conductor I28 to the upper terminal of the secondary of transformer I08. As the primary coil 45 of transformer 43 is energized through the foregoing circuit due to the contacts 96, 98 of the thermal switch 94 being closed, then the secondary of this transformer is also energized. The igniting means 92 is connected in series circuit with the secondary of transformer 43 by conductors I30 and I32 and is thereby caused-to 'be heated so as to be in condition to ignite the pilot burner 22 upon opening of the pilot burner valve 23.

The energizing of the primary coil 45 of the transformer 43 also causes the magnet plunger 44 of the resetting device 42 to be picked up. The

lever 50 is thereby rotated on its pivotal mounting and causes the third contact pair 52 to be opened. The lever 50 also engages the enlarged head 36 of the stem 32 of the electromagnetic device 26 and overcomes the bias of the coil spring 34 to reset the armature 30 in engagement with the pole faces of the horseshoe magnet .28. The contact arm 31 attached to the stem 32 simultaneous'ly causes the first and second contact pairs 38 and 40, respectively, to be closed.

The closing of the second contact pair 40 causes energization of. the coil of the pilot burner valve 23 through the following circuit: From the upper terminal of the secondary of transformer I08, conductor I28, contact pair 40, conductor I34, coil of pilot burner valve 23, conductor I36, conductor I20. contacts 90 and 88, conductor II8,

conductor I I6, contacts 84 and 86 and conductors H4 and H2 to the lower terminal of the secon- I40, conductor I20, contact 90 and toggle switch 88, conductor II8, conductor II6, contacts 84 and 86 and conductors H4 and H2 to the lower terminal of the secondary of transformer I08. The 41 heat the bimetallic element I00 and causes the latter. to warp sufliciently to open the switch contacts 96 and 98; Thus, the circuit which includes the primary coil of the transformer 43 is opened and the magnet plunger 44 is no longer attracted. Since the secondary coil of this transformer 43 is also deenergized, the igniting means 92 which is in circuit therewith is likewise .deenergized for the duration of the running period of the burner.

The pivotal movement of the lever resulting from dropping of the magnet plunger 44 causes the third contact pair 52 to again be closed. However, if during this starting period the fuel 55 from the pilot burner 22 is ignited by the igniting means 92, then the thermocouple 54 has been sufliciently heated by the pilot burner flame to energize the winding 60. The armature 30 will then remain in its attracted position relative to no the pole faces of the horseshoe magnet 28 although the energy from the line wires I06 is no longer available due to opening of the thermal switch contacts 96, 98. The attracted position of the armature causes the first and second con- 05 tact pairs 38 and 40 to remain closed. As the third contact pair 52 is also closed, then a circuit from the coil 24 of the main burner valve I6 is established as soon as the thermostat 62 has operated to close the contacts 68-14. This circuit 70 may be traced as follows: from the lower terminal of secondary of transformer I08, conductor II2, conductor I42, contact pair 52, conductor I 44, contact pair 38, conductor I46, contacts I4. I0, arm 66, contacts 66, I2, conductor I48, valve coil 24 and conductor I50 to the upper terminal energization of the heating coil I02 causes it to of the secondary of transformer I08. The valve coil 24 being energized through this circuit, the armature 25 is attracted and will engage contact 2i. Heater coil 16 remains short-circuited as long as the contacts I2, 68 are engaged. The main burner valve l8 will then be operated to open position and fuel will be supplied to the main burner 10 where it is ignited by the flame from the pilot burner 22. It should be noted that the second contact pair 40 being closed causes the heater coil I 02 to remain energized and maintain the thermal switch 94 in its open position.

The system will remain in operation under control of the thermostat 62 and the safety device 26 as long as the pilot burner 22 continues to produce a flame and there are no power interruptions. Whenever the thermostat is satisfied the contacts 88, I2 thereof are first disengaged but the circuit for the coil 24 of the main burner valve I6 is maintained as long as the contacts I0, 14 remain engaged. The opening of contacts i0, i4 is accelerated by the provision of the heater coil IS which is energized upon opening of contacts 68, I2 to supply heat for the bimetallic spiral 64. The coil 24 is then deenergized to release the armature 25 and cause the main burner valve I 8 to close.

When the contacts 84, 88 of the thermostat 62 are opened then the coil of the pilot burner valve 23 is deenergized so that both the pilot valve 23 and the main burner valve iii are closed to shut off the fuel supply to both the main burner I and the pilot burner 22. The heater coil I02 of the thermal switch 04 begins to cool immediately before the contact pair 40 is opened by release of the armature 30 due to cooling of the thermocouple 54. However, eventually the thermocouple 54 will cool sumciently and cause contact pairs 38 and 40 to be opened and contact pair 52 to be closed.

In the event that the safety device' 28 operates due to the flame from the pilot burner 22 becoming extinguished, thenthe thermocouple 54 cools so as to deenergize the winding 80 causing release of the armature 30 of the pole faces of the horseshoe magnet 28. The contact pairs 38, 40 are then opened by movement of the stem 32 under bias of the spring 34. Thus, the circuit of the main burner valve I8 is opened by the first contact pair 38 and the main burner valve i6 moves to closed position to shut ofl the flow of fuel to the main burner i0. Moreover, the opening of the second contact pair 40 causes deenergization of the heater coil I02 of the thermal switch 94 and also the deenergization of the coil of the pilot burner valve 23. However, the contacts 98, 98 of the thermal switch 84 do not close until after a purge period, the length of which is determined by the time required by the bimetal I00 to cool.

The complete recycling character of the system is now apparent. After the bimetallic element I00 of the thermal switch 94 has caused the contacts 96, 98 of this switch to close, then the sequence of operation is the same as described when the system is first turned on. As the use of electrical energy from an outside source is depended upon for resetting the safety device only during the short starting period then it is apparent that the system is adapted for safety operation in the event that a power failure occurs during the normal running period. As previously described, the electromagnetic valve I6 is preferably of the commercially available manual-set.

automatic-reset type and therefore to be manually moved to open position in the event that a power failure occurs causing this valve to be closed. The system will then operate under control of the thermostatic device 62 and upon resumption of the current supply the electromagnetlc valve I8 is automatically reset from its manual-set position without interruption of the fuel flow if the room thermostat is still calling for heat. The current consumption is very low due to the brief nature of the starting period and the deenergizing of the igniter during the running period of the burner.

In some instances it may be desirable to utilize a normally constant burning pilot burner instead of a. completely recycling ype of control as previously mentioned herein. In this event the only change required in the system as previously shown and described is to connect a conductor across points A and B as shown in broken lines in the drawing. Such connection will serve to short-circuit the contacts 84, of the thermostat so that in its ordinary operation during the heating season the coil of the pilot burner valve 23 would never be deenergized. However, provision may be made so that at the end of the heating season the coil of the pilot burner valve 23 can be deenergized by adjusting the thermostat to a preselected temperature setting which may be the lowermost position on the scale 82. Such a normal manipulation of the thermostat would cause the arm 86 thereof to operate the toggle switch 88 and disengage contact 90 to open the switch. whereupon the coil of the pilot burner valve 23 would be deenergized. Inasmuch as the contacts 88|4 of the thermostat would also be opened in this thermostat position, then the coil 24 of the main burner valve l6 would also be deenergized and the system would be completely shut down. Upon the householder desiring to put the system into operation again, the lever arm 18 would be moved to the desiredtemperature setting and, as soon as the thermostat called for heat, the system would again be placed in operation.

Ordinarily, the main fuel cock l4 and main switch I 04 will be located in the basement near the furnace and may either be left in open and closed positions, respectively, all of the time or during the heating season only. If the former expedient is used, then the flow of fuel to the main burner I0, or to the pilot burner 22 also, will be shut off during the summer months by the electromagnetic valves alone and a small amount of power (no load value). will be consumed by the transformer continuously.

While the invention described herein provides a relatively simple system of condition and safety control and ignition for gaseous fuel burnerscit will be apparent that many changes can be made in the arrangement and combination of parts and in the details of construction herein disclosed within the scope of the appended claims without departing from the spirit of the invention.

I claim:

1. In a control system for fuel burners having main and pilot burners and a source of electrical energy, the combination of first electrically operable means connected to the source and being movable between positions for controlling the supply of fuel to the main burner, second electrically operable means connected to the source and being movable between positions for controlling the supply of fuel to the pilot burner, a first electromagnetic device having separate pairs of contacts operable for controlling the energization of said electrically operable means respectively, means responsive to a flame at the pilot burner for controlling the energization of said device, and a second electromagnetic device connected to said source and operatively associated with the first said device for resetting the same and causing operation of said contacts for energization of said second electrically operable mean while maintaining said first electrically operable means deenergized,

2. In a control system for fuel burners having main and pilot burners and a source of electrical energy, the combination of first electrically operable means connected to the source and being movable between positions for controlling the supply of fuel to the main burner, second electrically operable means connected to the source and being movable between positions for controlling the supply of fuel to the pilot burner, a first electromagnetic device havingseparate pairs of contacts operable for controlling the energization of said electrically operable means respectively, means responsive to a flame at the pilot burner for controlling the energization of said device, a second electromagnetic device connected to said source and operatively associated with the first said device for resetting the same and causing operation of said contacts for energization of said second electrically operable means while maintaining said first electrically operable means deenergized, and timing means responsive to said resetting operation for causing deenergization of said second device after a predetermined period during which said flame responsive means has time to become heated, said contacts thereby being operated for causing energization of said first electrically operable means while maintaining said second electrically operable means energized.

3. In a. control system for fuel burners having main and pilot burners and source of electrical energy, the combination of a main burner fuel control valve, 9. pilot burner fuel control valve, separate electrically operable means for respectively controlling saidvalves, an electromagnetic device having first, second and third contact pairs, said first and third pairs being separately operable for controlling the energization of said main burner valve, said second pair being operable jointly with the first pair and being adapted for means responsive to a flame at the pilot burner and operable between a first position for causing energization of said electrically operable means for movement thereof to fiow permitting position and a second position for causing deenergization of said electrically operable means for movement thereof to fiow preventing position, meansfor resetting said thermomagnetic switch means in said first position including a second electrically operable means energized from the source, means responsive to movement of said thermomagnetic switch means to said first position for causing deenergization of said second electrically operable means, control switch means responsive to changes in a condition to be controlled for controlling the energization of the first said electrically operable means for movement thereof between flow preventing and permitting positions independently of said thermomagnetic switch means, and manual adjusting means for setting said control switch means to cause deenergization of said first electrically operable means irrespective of said controlled-condition.

5. A control system for fuel burners having main and pilot burners and a source of electrical energy, comprising in combination, electrically operable means connected to the source and being movable between positions for controlling the supply of fuel to the main burner, an electromagnetic device having contacts operable between open and closed positions for controlling energization of said electrically operable means for movement thereof between said positions, thermoelectric means responsive to a flame at the pilot burner for controlling the energization of said device, igniting means for said pilot burner, means for resetting said device to cause closure of said contacts and simultaneously causing energization of said igniting means including a second electromagnetic device energized from the source, timing means responsive to closure of said contacts for causing deenergization of said second device and said igniting means after a predetermined period during which said thermoelectric means has time to become heated by said fiame, means including a thermostat responsive to changes in temperature to be controlled for controlling the energization of said electrically opercontrolling the energization of said pilot burner valve, thermoelectric means responsive to a fiame at the pilot burner for controlling the energization of said device, means operable for resetting said device and causing operation of said contacts, said second pair being operated for energization of said pilot burner valve while said third pair is operated for maintaining said main burner valve deenergized, and timing means responsive to said resetting operation for rendering thelast said means inoperable after a predetermined period during which said thermoelectric means has time to become heated, said third contact pair being thereby operated to cooperate with ,said first pair for energization of said main burner valve while said second pair maintains said pilot burner valve energized;

4. A control system for fuel burners having main and pilot burners and a source of electrical energy, comprising in combination, electrically operable means connected to the source and being movable between fuel fiow preventing and per mitting positions for controlling the supply of fuel to the mainburner, thermomagnetic switch able means for movement thereof between said positions independently of the first electromagnetic device, and adjusting means for setting said thermostat at its lowest temperature to cause deenergization of said electrically operable means irrespective of said controlled temperature.

6. A control system for fuel burners having main and pilot burners and a source of electrical energy, comprising in combination, electrically operable means connected to the source and being movable between positions for controlling the supply of fuel to the main burner, electrically operable means connected to the source and being movable between positions for controlling the supply of fuel to the pilot burner, means responsive to changes in a condition to be controlled for controlling the operation of said electrically operable means for the main burner, means for adjusting the setting of 'said condition responsive means, and means including a control switch associated with said condition responsive means and operative upon said adjusting means being moved to a preselected setting for electrically disconnecting both said electrically operable means to shut oil the fuel supply to both the main and pilot burners.

7. A control system for fuel burners having said parallel circuit. means responsive to changes in a condition to be controlled for controlling the operation of said electrically operable means for the main burner. said condition responsive means including a pair oi contacts operative for opening the circuit of said electrically operable means for the main burner, means for adjusting the setting of said condition responsive means, and means including a control switch for opening the circuit of said electrically operable means for the pilot burner, said last means being cooperable with said pair of contacts upon said adiusting means being moved to a preselected setting for electrically disconnecting both said electrically operable means to shut oil the fuel supply to both the main and pilot burners.

, CHARIES K. STROBEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PA'I'ENTS Name Date Strobe] Sept. 3, 1946 Number

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