US2081091A - Burner control system - Google Patents

Description

May 18, 1937. l.. L. KUEMPEL BURNER CONTROL SYSTEM Filed Sept. a, 1934 gwuento@ Leon L.Kue1pel duoumv rotary type.

Patented May 18, 1937 PATENT QFFICE 2,081,091 BURNER CONTROL SYSTEM Leon L. Kucmpel, Minneapolis, Minn., assigner to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application September 8, 1934, Serial No. 743,261

11 Claims.

The present invention relates to an improved burner control system by means of which the flow of uel to a burner is prevented or discontinued if the ignition means is not operating properly or if there is a failure to establish combustion.

One of the objects of the invention is the provision of a burner control system in which fuel is initially supplied to the burner only in the event the ignition means is operating properly and wherein the supply of fuel to the burner is maintained only in the event that combustion is established and properly continues.

It is a further object of the invention to provide a burner control system in which a single device or mechanism responds both to the condition of the ignition means and to the presence or absence of name at the burner to prevent the initial supplying of fuel to the burner if the ignition means is not operating properly and to prevent the continued supplying of fuel to the burner if the ignition means operates properly but com'- bustion is not successfully established or maintained. The single device preferably takes the form of a mechanism which utilizes the electrical conductivity of the ignition means and the burner flame, and the ignition means is preferably of the flame producing type.

Another object of the invention is the provision of an improved burner control system in which the burner motor. ignition means, and a fuel valve are all controlled in a new and novel sequence.

Other objects of the invention will become apparent from the detailed description, the appended claims, and the drawing.

For a more complete understanding oi the invention reference may be had to the following de scription and accompanying single drawing which is a diagrammatic illustration of one form of my novel burner control system.

Referring to the single figure in the drawing, the control system oi the present invention is shown applied to an oil burner il) of the horizontal Oil is supplied to the oil burner l0 by an oil supply pipe i l which is controlled by an electromagnetic oil Valve I2 of any of the wellknown constructions. The oil issuing from the oil burner ID is adapted to be ignited by a gas pilot. igniter I3 which is supplied with gas by a gas supply pipe I4 that is controlled by an electromagnetic gas valve l5. The pilot I3 may be ignited in any desired manner, and is herein shown as being ignited by always maintaining a small supn ply of gas thereto by means of a by-pass pipe I6 which by-passes the electromagnetic valve I5.

The control system is controlled by a main control switch that is preferably of the type which automatically responds to changes in some desired condition and is herein shown as a room thermostat comprising a bimetallic actuating element 2I which has one of its ends secured as at 22. The other end of bimetallic actuating element 2| controls a pair of contacts 23 and 24 which, upon a fall in room temperature, sequentially engage contacts and 26 in the order named. Upon a rise in the room temperature, the contact 24 first disengages contact 26 and thereafter, upon further room temperature rise, the contact 23 disengages contact 25.

The main control switch 20 controls a pair of relays generally indicated at 21 and 28, both' of these relays being operated by direct current as will hereinafter become apparent. The relay 21 includes a relay coil 29 and a cooperating armature 30. Upon energization of relay coil 29, armature 30 is attracted and in turn moves a pair of switch arms 3I and 32 into engagement with a pair of cooperating contacts 33 `and 34. The relay 28 includes a relay coil 35 and a cooperating armature 36 which is attracted upon energization of relay coil and moves switch arms 31 and 38 into engagement with respective contacts 39 and 40. Such movement of armature 36 also moves switch arms 31 and 38 from engagement with contacts 4I and 42 and further moves a switch arm 43 from engagement with a contact 44. The arrangement is such that switch arm 3l engages contact 39 before it disengages contact 4I upon energization of relay coil 35. Associatedwith relay 28 is a condenser 45, the utility of which will be hereinafter explained.

Magnetic gas valve I5 is directly controlled by a pair of thermal time switches generally indicated at 5U and 5I. The thermal time switch 50 includesa bimetallic actuating element 52 which is secured at one end as indicated at 53, the other end thereof normally being'disengaged from a Contact 54. An electrical heating element 55 is operatively associated with thermal element 52 for heating the same. The karrangement is such that energization of electric heating element 55 for a period of about thirty (30) seconds causes movement of the free end of thermal element 52 into engagement with contact 54. The thermal time switch 5I includes a member 56 which is pivoted as indicated at 51 and includes an extension 58 that 'cooperates with an actuator 59.

The actuator 59 is operated by the armature 30 of relay 21. This member 56 carries a contact 60 which is normally latched into engagement with a cooperating contact 6| by means of a bimetallic element 62 having one of its ends secured as indicated at 63. An electrical heating element 64 is operatively associated with the bimetallic element 62 for heating the same. When the electrical heating element 64 has been energized for a predetermined length of time, say sixty (60) seconds, the free end of bimetallic element 62 moves from engagement with member 56, thereby allowing contact 60 to move from engagement 'with Contact 6|, it being noted that the actuator 59 will be moved out of the path of the extended end 58 of member .56 by energization of relay 21 under these conditions, as will hereinafter appear. Upon subsequent cooling of the bimetallic element 62 by reason of deenergization of the electrical heating element 64, the contacts 60 and 6| will remain separated until such time as relay 21 is deenergized, whereupon actuator 59 will engage the extended end 58 of member 56, raising the same to the position shown in the drawing, whereupon the free endof bimetallic element 62 can move under the member 56, as shown in the drawing, to latch contacts 60 and 6| into engagement.

Operation of the complete system is dominated by a thermal time switch or safety switch 10 of well-known construction. This thermal safety Switch 10 comprises a pair of contacts 1| and 12 which are normally held latched in engagement by means of a bimetallic element 13 having one of its ends secured as indicated at 14. Associated with the bimetallic element 13 is an electric heating element 14, commonly known as a safety switch heater, which upon energization for a predetermined length of time, say .two minutes causes the free end of bimetallic element 13 to unlatch contacts 1| and 12, whereupon they separate. The contacts 1| and 12 thereupon remain separated until they are manually reclosed, whereupon they are thereafter maintained closed by the bimetallic element 13, provided the same has cooled suiiciently in the meantime.

The flow of current to safety switch heater 14 is controlled in part by a combustion responsive mechanism which includes a ame responsive device 15 and a thermionic tube 16, herein shown as comprising a grid glow tube. 'I'he flame responsive device 15 includes a suitable support 11 which supportsan electrode 18 that is adapted to be impinged by the expanded or enlarged pilot y ignition flame upon energization of the magnetic gas valve I 5 and by the oil burner flame upon the establishment of combustion. The grid glow tube 16 includes a grid 19, an anode 80, and a cathode 8|.

Power is supplied to the system by means ofl a combination step-up and step-down transformer 82 that includes a high voltage primary 83 which is connected to line wires 84 and 85 that are in turn connected to a suitable source of volt alternating current. The transformer 82 includes a high voltage secondary 88 which delivers approximately 440 volts and a center tap low voltage secondary which is in effect two secondaries 81 and 88, each of which delivers substantially 10 volts. Certain of the alternating current circuits are rectified by a copper oxide rectifier 89 of usual construction which is provided with Cul'- rent paths 90, 9|, 92, and 93.

Operation of the system With the parts in the position shown, the room temperature is at or above the desired value, and both relay coils 29 and 35 are deenergized. A small iiame (shown in full lines) is issuing from the pilot I3 by reason of the by-pass |6, but this small pilot ame does not implnge upon electrode 18. Now as the room temperature falls, contact 23 will rst engage contact 25, but no circuits are completed by such engagement. Upon a further fall in room temperature, contact 24 engages contact 26, whereupon an energizing circuit for relay coil 29 and safety switch heating element 14, in series, is established during one-half of each cycle of the alternating current as follows: secondary 88, secondary 81, wire 95, contact 25, contacts 23 and 24, contact 26, wire 96, switch arm 43, contact 44. wire 91, wire 98, safety switch contacts 1| and 12, wire 99, current path 90 of rectifier 89, wire |00, relay coil 29, wire |0|, current path 9| of rectifier 89, wire |02, switch'arm 31, contact 4|, wire |03, safety switch heater 14, and wire |04 to secondary 88. During the other half of each cycle of the alternating current supplied by secondaries 81 and 88, the series circuit for relay coil 29 and safety switch heater 14 is as follows: secondary 81, secondary 88, wire |04, safety switch heater 14, wire |03, contact 4|, switch arm 31, wire |02, current path 92 of rectifier 89, wire |00, relay coil 29, wire |0|, current path 93 of rectifier 89, wire 99, safety switch contacts 12 and 1|, wire 98, wire 91, contact 44. switch arm 43, wire 96, contact 26, contacts 24 and 23, contact 25, and wire 95 to the other side of secondary 81. In this manner, upon engagement of both contacts 23 and 24 with their respective contacts 25 and 26, the relay coil 29 is continuously energized by current flowing in only one direction through the medium of the rectifier 89, it being noted that these energizing circuits can be established only in the event the relay coil 35 is deenergized so that the various switches controlled thereby are in the position shown in the drawing.

Energization of relay coil 29 attracts armature 30 to move switch arms 3| and 32 into engagement with contacts 33 and 34 and also moves actuator 59 out of the path of movement of extension 58 of member 56. Engagement of switch arm 3| with contact 33 establishes holding circuits for the relay coil 29 and safety switch heater 14 which are independent of the contact 24 and contact 26 of the room thermostat 20, it being noted that wires |05 and |06, switch arm 3|, contact 33, and bimetallic element 2| parallel or shunt the wire 96, contact 26, contact 24, switch arm 43, contact 44, and wire 91.

Movement of switch arm 32 into engagement with contact 34 energizes burner motor l0, the electrical heating element 64 of thermal time switch 5|; and the electrical heating element 55 of thermal time switch 50. The energizing circuit for burner motor |0 is as follows: line wire 84, wire |08, contact 34, switch arm 32, wire |09, wire ||0, wire burner motor |0, wire ,||2, and wire ||3 to line wire 85. The energizing circuit for electric heating element 64 is as follows: line wire 84, wire |08, contact 34, switch arm 32, wire |09, wire ||0, wire ||1, contact 6|, contact 60, wire ||9, wire |22, heating element 64, wire |23, wire |24, and wire ||3 to line wire 85. The energizing circuit for electric heating element 55 is as follows: line wire 84, wire |08, contact 34, switch arm 32, wire |09, wire ||4, switch arm 38, contact 42, wire ||5, heatingelement 55, and wire ||6 to line wire 85. After approximately thirty (30) seconds the free end of bimetallic element 52 moves into engagement with contact 54, whereupon magnetic gas valve |5 is energized as follows: line wire 84, wire |08, contact 34,`

switch arm 32, wire |09, wire I 0, wire I1, contact 6|, contact 68, Wire IIB, wire ||9, bimetallic element 52, contact 54, wire |20, magnetic gas valve I5, and wire |2| to line wire 85. magnetic gas valve I5 causes the same to open, whereupon the pilot flame expands, as indicated in dotted lines, and impinges against electrodes 18. While the ignition means has herein been shown as comprising an expanding pilot wherein the large flow of gas is ignited by the small constant ow, it will4 be appreciated that other ignition means as well as other means of igniting the gas pilot igniter shown could also be utilized.

Impingement of the expanded pilot flame upon the electrode 18 connects the grid 19 of grid glow tube 16 to ground as follows: grid 19, wire |25, electrode 18, the expanded ignition ame, pilot pipe I3, and wire |26 to ground |21. Such grounding of grid 19 allows the charge thereon to be dissipated, whereupon current is permitted to iiow from the anode 80 to the cathode 8| of the grid glow tube 16 in a well-known manner. Relay coil 35 is thereupon energized as follows: high voltage secondary 86, wire |30, anode 80, cathode 8|, wire |3|, wire |32, relay coil 35, wire |33, and wire |34 to the other side of secondary 86. It will be noted that the condenser 45 is connected across or in parallel with the relay coil 35 by means of wires |36 and |31. This condenser serves to smooth out the pulsating direct current which results from the elimination of one-half of each cycle of alternating current delivered by the secondary 86 to the grid glow tube 16. l

During the time that the bimetallic element 13 has been heating up, the burner motor I has been operated by the previously described circuit and is operating at top speed by the time relay coil 35 is energized. Energization of relay coil 35 establishes maintaining circuits for relay coil 29 which are independent of the safety switch heater 14 and utilize only theA one low voltage secondary 81. During one-half of each cycle of the alternating current delivered by secondary 81, the maintaining circuit for relay coil 29 is as follows: secondary 81, wire 95, contact 25, conta-ct 23, bimetallic element 2|, wire |06, contact 33, switch arm 3|, wire |05, wire 98, safety switch contacts 1| and 12, wire 99, current path 90, wire |00, relay coil 28, wire |0I, current path 9|, wire |02, switch arm 31, contact 39, and wire |38 to the other side of secondary 81. During the other half of each cycle of the alternating current produced by secondary 81, this maintaining circuit for relay coil 29 is as follows: secondary 81, wire |38, contact 39, switch arm 31, wire |02, current path 92, wire |00, relay coil 29, wire |0I, current path 93, wire 99, safety switch contacts 12 and 1|, wire 98, Wire |05, switch arm 3|, contact 33, wire |06, bimetallic element 2|, contact 23, contact 25, and wire 95 to the other side of secondary 81. In this manner, if the ignition flame is properly produced so that it impinges upon electrode 18, the safety switch heater 14 is operatively deenergized tovprevent the system from being locked up. It is obvious that if the proper ignition flame were not established so that relay coil 35 remained deenergized, the safety switch contacts 1| and 12 would be Energization of opened after a time period so as to render the system inoperative until manual intervention.

Energization of relay coil 35 also moves switch arm 38 from engagement with contact 42 and in to engagement with contact 48. Movement of switch arm 38 from engagement with contact 42 interrupts the'energizing circuit for heating element 55. The rate of heat input vto the bimetallic element 52 and its mass is such, however, that it does not cool sufficiently to cause movement of the free end of bimetallic element 52 from the contact 54`for a considerable period which is greater than the operating time of thermal time switch Engagement of switch arm 38 with contact 40 completes an energizing circuit for magnetic oil valve as follows: line wire 84, wire |08, contact 34, switch arm 32, wire |09, wire I4, switch arm 38, contact 40, wire |40, magnetic oil valve I2, wire I4|, wire |24, and wire ||3 to line wire 85. Energization of magnetic oil valve I2 causes the same to open, whereupon fuel is delivered to the burner I0 and should be ignited by the ignition flame. Approximately 30 seconds after the energization of magnetic gas valve I5 or 60 seconds after energization of the electrical heating element 64, the free end of bimetallic element 62 moves from engagement with member 56 and allows the same to drop, whereupon contact 60 disengages contact 6| and interrupts the circuit to the magnetic gas valve I5 and to the electrical heating element 64. The ignition flame is therefore reduced to a size depending upon the amount of gas going through the bypass pipe I6 and no longer impinges upon electrode 18. If combustion wasr not successfully established during this trial ignition period, electrode 18 will no longer be connected to ground, whereupon a charge will build up on the grid 19 which in turn prevents the ow of current between the anode 80 and the cathode 8|, where upon relay coil 35 is deenergized and returns the various switches controlled thereby to the positions shown in the drawing. Such deenergization of relay coil 35 reenergizes safety switch heater 14 so that the safety switch contacts 1| and 12 will open after a time period and render the system inoperative until manual intervention. If, on the other hand, combustion is successfully established, the main burner llame will impinge upon electrode 18 so that the electrode 18 will continue to be connected to ground |21 by way of the main burner flame, the oil burner I0, and a wire |43. Under these conditions, the grid glow tube 16 continues to permit the passage of current through the relay coil 35 so that the system remains in operation. `After the contacts 60 and 6| have been separated, the bimetallic element 52 will have cooled sufficiently to move from lengagement with contact 54.

The system is now in normal operation, and if the burner continues to operate properly so as to maintain a flame issuing therefrom which impinges the electrode 18, the system will remain in operation until opening of the main switch or room thermostat 20. When the room temperature rises, contact 24 will first disengage contact 26, but this will not in any manner interrupt the operation of the system by reason ofr the maintaining circuit which traverses switch arm 3| and contact 33. Upon continued rise in room temperature resulting in separation of contact 23 from contact 25, all energizing circuits for both relay coils 35 and 29 are interrupted. Deenergization of relay coily 29 allows armature 30 to return to the position shown in the drawing wherein actuator 59 engages the extended end 58 of member 56 and returns the member 56 to the position shown in the drawing wherein contacts 6D and Gi are engaged. At this time, the free end of bimetallic element 62 can again move to the position shown whereby to latch the contacts 60 and 6| in engagement. The system cannot now again be operated until such time as the room temperature lowers sufficiently to cause both contacts 23 and 24 to engage their respective contacts 25 and 26.

In the event the burner flame should fail for any reason while the system is operating normally, the ground connection for electrode 1B will be removed, whereupon relay coil 35 will be deenergized resulting in reenergization of safety switch heater 14 so that the system will be rendered inoperative the same as though combustion had never been established. In the event of a failure of electrical power during normal operation of the system, both relay coils 29 and 35 will be deenergized and the parts will return to the position shown in the drawing provided the power failure did not occur too soon after deenergization of the heating element 64. In such case, if the power returns before the bimetallic element 62 has cooled sufciently to relatch contacts 6!! and 6l in engagement with one another, the ignition valve l cannot be energized, and the system will go to its safety shut-down condition. This possibility is rather remote, however, and in most cases the contacts 60 and Si will be properly relatched by the bimetallic element 62 so that the system will cornpletely recycle upon the return of electrical power in an effort to re-establish` combustion, and if this is not successful the system will lock up as previously explained.

It will be evident that many changes and rearrangements may be made in the system of the present invention without departing from the spirit thereof. For example, the particular means by which the operation of the ignition valve I5 is terminated is'not important, and any of the well-known ignition terminating arrangements could be utilized without affecting the general operation of the system. It will be evident that many other minor changes could be made in the system, and I therefore intend to be limited only by the scope of the appended claims.

I claim:

l. In a burner control system, the combination with a burner and a supply of fuel therefor, of electrical means in control of the supplying of said fuel to the burner, electrically controlled ignition means of the type which produces an igniting flame only so long as the same is energized, electrical timing means operative to energize said ignition means for a time period and then deenergize the same, means to energize said timing means upon a demand for heat, and means utilizing the conductivity of the igniting flame o-perative to energize said fuel supply controlling means, said last-named means also utilizing the conductivity of the burner flame to maintain the fuel supply controlling means energized after said ignition means is deenergized by said timing means.

2. In a fuel burning control system, the combination with a burner and a supply of fuel therefor, of electrical means in control of the supplying of fuel to the burner, an electrically controlled ignition llame producing means operative to produce an ignition flame only so long as the same is energized, means responsive to a demand for heat operative to energize said ignition means, means utilizing the conductivity of flame responsive to the production of an ignition ame operative to energize said fuel supply controlling means, said last-named means also utilizing the conductivity of the burner flame to maintain said fuel supply controlling means energized, and means to deenergize said ignition means a timed period after the energization of said fuel supply controlling means.

3. In a. burner and ignition control system, the combination with a supply of fuel, a burner, and an associated electrical burner motor for impelling the fuel, of a fuel valve in control of said supply of fuel, electrical ignition means to ignite the fuel, an electrical timer, a burner motor circuit, a timer circuit, a main control switch operative to complete said circuits, a timer switch closed by said timer after the same has been energized for a time period, a circuit forsaid ignition means controlled by said timer switch, timing means to deenergize said ignition means after a time period, and means to maintain said fuel valve closed for a period after energization of said burner motor whereby said burner motor will be operating at full speed before the fuel valve opens.

4. In a burner control system, the combination with a burner and a supply of fuel therefor, of electrical means in control of the supplying of fuel to the burner, electrically controlled ignition means operative to ignite the fuel supplied to the burner only so long as said ignition means is energized, a normally open power switch, means to close said switch upon a demand for heat, a normally open fuel supply controlling means switch, a time operated ignition switch, a circuit in control of said ignition means controlled by the power switch and time operated ignition switch, a circuit in control of the fuel supply controlling means controlled by the power switch and fuel supply controlling means switch in series, means independently responsive both to the proper operation of the ignition means and the establishment of combustion operative to close said fuel supply controlling means switch whereby said fuel controlling means can only be energized in the event the ignition means is operating properly, and means to open said time operated switch after closure of the fuel control means switch whereby the fuel control means can only be maintained energized if combustion is successfully established.

5. In a fuel burning system, the combination with a burner anda supply of fuel for the burner,

of electrical means in control of the flow of fuel to the burner, electrically controlled ignition means operative to ignite such fuel only so long as the same is energized. a normally closed switch, a normally open'switch, a circuit in control of the ignition means controlled by said two switches in series, a second normally open switch, a circuit in control of the fuel flow controlling means controlled by said two normally open switches in series, means operative to close said first normally open switch upon a demand for heat, means independently responsive both to the proper operation of the ignition means and the establishment of combustion open to close said second normally operative switch and open said normally closed switch, means to render the entire system inoperative after a time period rendered inoperative by said last-named means, and means to prevent reenergization of the ignition means upon a failure of flame during normal operation whereby the system is shut down without attempting to reestablish combustion, said means operating to maintain the ignition lmeans energized for a period after opening of said normally closed switch.

6. In a fuel burning system, the combination with a burner and a supply of fuel for the burner, of electrical means in control of the flow of fuel to the burner, electrically controlled ignition means operative to ignite such fuel only so long as the same is energized, a normally closed switch, a normally open switch, a circuit in control of the ignition means controlled by said two switches in series, a second normally open switch, a circuit in control of the fuel flow controlling means controlled by said two normally open switches in series, means responsive to a demand for heat to close said rst normally open switch, an electromagnetic coil operative to close said second normally open switch and open said normally closed switch when energized, means independently responsive both to the proper operation of the ignition means and the establishment of combustion in control of the energization of said electromagnetic coil whereby the same is initially energized upon proper operation of the ignition means and is thereafter maintained energized independently of the ignition means if combustion is established, means to render the entire system inoperative after a time period rendered inoperative upon energization of said electromagnetic coil, and means to maintain energization of the igni tion means for a period after opening of said normally closed switch and to prevent reenergization of the ignition means upon deenergization of said electromagnetic coil as a result of a failure of flame during normal operation whereby the system is shut down without attempting to reestablish combustion.

'7. In a fuel burning system, the combination with a burner and a supply of fuel for the burner, of electrical means in control of the flow of fuel to the burner, electrically controlled ignition means operative to ignite such fuel only so long as the same is energized, a normally closed switch, a normally open switch, a circuit in control of the ignition means controlled by said two switches in series, a second normally open switch, a circuit in control of the fuel flow controlling means controlled by said two normally open switches in series, an electromagnetic coil operative to close said first normally open switch when energized, a main switch in control of said electromagnetic coil, a second electromagnetic coil operative to close said second normally open switch and open said normally closed switch when energized, means independently responsive both to the proper operation of the ignition means and the establishment of combustion in control of the energization of said second electromagnetic coil whereby the same is initially energized upon proper operation of the ignition means and is thereafter maintained energized independently of the ignition means if combustion is established, means to render the entire system inoperative after a time period rendered inoperative upon energization of said second electromagnetic coil, and means to prevent reenergization of the ignition means upon deenergization of said second electromagnetic coil as a result of a failure of flame during normal operation whereby the system is shut down without attempting to reestablish combustion, and means to maintain said ignition means energized for a period after 'opening of said normally closed switch.

8. In a fuel burning control system, the combination with a burner, an electrical burner motor for impelling fuel and a supply of fuel associated therewith, of an electrical fuel valve in control of the supply of fuel, ignition means of the expanding pilot type for igniting said fuel and including an electrical device operative to cause expansion of said pilot only while energized, a normally open switch and a normally closed switch, a series circuit in control of said ignition means including said normally openswitch and said normally closed switch, a burner motor circuit controlled by said normally open switch, an electromagnetic coil in control of said normally open switch operative to close the same when energized, a thermal safety switch in control of the system and arranged to render the same inopera-` tive when opened, an electrical heating element associated' Awith the safety switch operative to open the same when energized for a time period, a main control switch operative to energize said heating element and said electromagnetic coil upon a demand for heat, a member arranged to be impinged by said pilot flame when expanded, circuit connections controlled by said member, a second electromagnetic coil in control of said normally closed switch for opening the same controlled by said circuit connections, and switching.

means controlled by said second electromagnetic coil when energized to operatively deenergize said electrical heating element and to lenergize said fuel valve, the flame thus produced impinging said member to maintain energization of said second electromagnetic coil after said pilot flame contracts, and means to maintain energization of said ignition means for a period after opening of said normally closed switch.

9. In a fuel burning control system, the combination with a burner, an electrical burner motor for impelling fuel and a supply of fuel associated therewith, of an electrical fuel valve in control of the supply of fuel, ignition means of thel expanding pilot type for igniting said fuel including an electrical device operative to cause expansion of said pilot only while energized, a thermal time switch in control of said ignition means, an elec' trical heating element arranged to heat said thermal time switch and cause closure thereof when energized for a time period, a normally open switch and a normally closed switch, a series circuit for said heatingelement including said normally open switch and said normally closed switch, a burner motor circuit controlled by said normally open switch, an electromagnetic coil in control of said normally open switch operative to close the same when energized, a thermal safety switch in control of the system and arranged to render the same inoperative when opened, an electrical heating element associated with the safety switch operative to open the same when energized for a time period, a main control switch operative to energize said last-named heating element and said electromagnetic coil upon a demand for heat, a second electromagnetic coil in control of said normally closed switch for opening the same, a circuit therefor controlled by means responsive to the presence of an expanded pilot flame, switching means controlled by said second electromagnetic coil when energized to operatively deenergize said last-named electrical heating element and to energize said fuel valve, said flame responsive means also responding to the flame thus produced whereby to maintain energization of said second electromagnetic coil after said pilot flame contracts, and means to maintain energization of said ignition means for a period after opening of said normally closed switch.

10. In a fuel burning control system, the combination with a. burner. an electrical burner motor for impelling fuel and a supply of fuel associated therewith, of an electrical fuel valve in control of the supply of fuel, ignition means of the expanding pilot type for igniting said fuel and including an electrical device operative to cause expansion of said pilot only while energized, a thermal time switch in control of said ignition means, an electrical heating element arranged to heat said thermal time switch and cause closure thereof when energized for a time period, a normally open switch and` a. normally closed switch, a series circuit for said heating element including said normally open switch and said normally closed switch, a burner motor circuit controlled by said normally open switch, an electromagnetic coil in control of said normally open switch operative to'close the same when energized, a thermal safety;E switch in control ofthe system and arranged to render the same inoperative when opened, an electrical heating element associated with the safety switch operative to open the same when energized for a time period, a main control switch operative to energize said v last-named heating element and said electromagnetic coil upon a demand for heat, a space discharge tube including a cathode, an anode, and a control electrode, a member arranged to be impinged by said pilot flame when expanded, circuit connections between said member and control electrode whereby the bias on the control electrode depends upon the impingement or non-impingement of flame upon said member, a second electromagnetic coil in control of said normally closed switch for opening the same, a circuit therefor controlled by said anode and cathode and rendered operative when said member is impinged by flame, switching means controlled by said second electromagnetic coil when operatively energized to operatively deenergize said last-named electrical heating element and to energize said fuel valve, the flame thus produced being adapted to impinge said member to maintain operative energization of said second electromagnetic coil after said pilot flame contracts, and means to maintain said ignition means energized for a period after opening of said normally closed switch.

11. In a fuel burning control system, the combination with a burner, an electrical burner motor for impelling fuel and a supply of fuel associated therewith, of an electrical fuel valve in control of the supply of fuel, ignition means of the expanding pilot type for igniting said fuel and including an electrical device operative to cause expansion of said pilot only while energized, a thermal time switch in control of said ignition means, an electrical heating element arranged to heat said thermal time switch and cause closure thereof when energized for a time period, a normally open switch and a normally closed switch, a series circuit for said heating element including said normally open switch and said normally closed switch, a burner motor circuit controlled by said normally open switch, an electromagnetic coil in control of said normally open switch and operative to close the same when energized, a thermal safety switch in control of 'the system and arranged to render the same inoperative when opened, an electrical heating element associated with the safety switch operative to open the same when energized for a time period, a main control switch operative to energize said safety switch heating element and said electromagnetic coil upon a demand for heat, a grid-glow-tube including a cathode, an anode, and a control electrode, a member arranged to be impinged by said pilot flame when expanded, circuit connections between said member and control electrode whereby the bias on the control electrode depends upon the impingement or non-impingernent of flame upon said member, a second electromagnetic coil in control of said normally closed switch for opening the same, a circuit therefor controlled by said anode and cathode and rendered operative when said member is impinged by flame, -switching means controlled by said second electromagnetic coil when operatively energized to operatively deenergize said safety switch heating element and to energize said fuel valve, the flame thus produced being adapted to impinge said member to maintain operative energization of said second electromagnetic coil after said pilot ame contracts, means to maintain said ignition means energized for a period after opening of said normally closed switch, and means to prevent reenergization of said ignition means upon deenergization of said second electromagnetic coil by reason of a failure of ame during normal operation.

LEON L. KUEMPEL.

CERTIFICATE OF CORRECTION.

Patent No. 2,081,091. May 18, 1957.

LEON L. KUEMPEL.

It is hereby certified that error appears in the printed specification oi" the above numbered patent requiring correction as follows: Page 4, second column, line 70, claim 5, for the word "open" read operative; and line '71, same claim, for -|'operative" read open; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 21st day of September, A. D. 1937.

Henry Van Arsdale (Seal) Acting Commissioner of Patents.

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