US2430040A - Fuel pressure responsive burner control - Google Patents

Description

Nov. 4, 1947. F. a. AUBERT 2,430,040

FUEL PRESSURE RESPONSIVE BURNER CONTROL 1 Filed Jan. 15. 1944 21 J lg/1m I 69 p INVENTOR 3M 23. W BY J; ATTORNEY Patented Nov. 4, 1947 FUEL PRESSURE RESPONSIVE BURNER CONTROL Fred B. Aubert, Grosse Pointe, Mich.

Application January 15, 1944, Serial No. 518,931

This invention relates to new and useful improvements in control systems for fluid fuel burners and more particularly for a liquid fuel or oil burner.

An object of the invention is to provide a. system which is certain and positive in operation and which provides for scavenging of the combustion chamber.

Another object is to provide a control system in which. during the operating period, either ignition is on or flame is present at all times.

Another object is to provid electronic control means for instantaneous response to presence or absence of flame.

The foregoing and other objects will be noted in the following description.

The invention consists in the improved system or apparatus and the cooperative relation of the control devices comprising the same to be more fully described hereinafter and the novelty of which will be particularly pointed out and distinctly claimed. y

In the accompanying drawings, to be taken as a part of this specification, there are fully and clearly illustrated several preferred embodiments of the invention, in which drawings Figure l is a schematic view of a heating apparatus having a control system embodying the invention and showing the wiring diagram for the control devices, and

Fig. 2 is a detail view showing a portion of the diagram of Fig. 1 having added thereto a switch cut-out means for a, warp switch heater.

Referring to the drawings by characters of reference, l designates generally a heating apparatus such as. a boiler or furnace having a combustion chamber 2 and a water space or plenum chamber 9 for the medium to be heated. The

apparatus I has a fluid fuel burner 4, preferably an oil burner, having an air supply conduit 5 discharging into the combustion chamber 2 and supplied with air under pressure by a blower or other air impelling means 6 driven by an electric motor I. Liquid fuel or oil for mixture with the air is fed to the burner nozzle 9 which discharges into the chamber 2 concentric with the conduit 9. The nozzle 9 is connected to the feed line or supply conduit 9 which is supplied with oil under pressure by the pump ll) driven by gearing or other suitable means from the motor I.

- The pump l0 preferably forms part of a pressure regulating device or unit ll interposed between the pump discharge and the feed pipe 9. Intercalated in the pipe 9 between the pressure regulating device and the nozzle 9 there is a pres-- 11 Claims. (CL 158-28) sure responsive switch l2 having normally open contacts including a fixed contact I! and a pressure operated movable contact l4 engageable with the fixed contact. The fuel mixture discharged by the burner 4 may be ignited by ignition means II comprising a pair of spaced electrodes insulated from ground and connected by lead wires l6, H to the opposite ends of the secondary coil i9 of an ignition transformer I9 having one terminal of its primary coil 29 connected directly to one of the high voltage line or service wires 2i of the usual 110 v. A. C. supply and having its other terminal connected to a lead wire 22 connected to the other line Or service wire 29, as will be hereinafter described.

Connected across the service line wires 2i, 2! is the primary coil 24 of a transformer 29 having a plurality of secondary coils 29, 21 and 28, preferably of say 24 v., 6 v. and 142 v., respectlvely'. The secondary coil 28 is connected to one terminal of a main control switch 29, such as a room thermostat, by a lead wire 39 having therein a normally closed pressure or temperature operated limit switch 9| responsive to the pressure or temperature of the medium in the boiler or furnace space I. The switch 29, preferably positioned in the space or room of. which the temperature is to be controlled and which is heated by the apparatus i, has a compensating heater 92 which is energized when the switch 29 is closed by the bimetal actuator 23, as is well understood in the art. The fixed contact of the switch 29 is connected by a lead wire 34 to one terminal of the coil 25 of a main relay switch 99. The heater 92 has one terminal connected to the lead wire 94 and has its other terminal connected by a lead former l9, and the electric resistance heating ele- I ment 44 of a burner motor controlling warp switch 49 comprising a safety timing m ans. The fixed contact 46 of the switch 99' is connected by a lead wire 41 to a switch arm 49 of an electron tube operated relay switch 49. The arm 48 forms part of a double throw switch having a contact it normally closed or engaged by the cooperating contact of'arm 48 and operable to control 3 the circuits of the burner motor, the ignition transformer, and the warp switch resistance coil. The switch 56 also has a contact 52 normally open or spaced from the contact of its cooperating arm 46 and operable to control the circuit of the burner motor. The relay switch 46 also includes a switch 53 having a movable contact carrying arm 54 cooperable with a fixed contact 55, the arm 54 being movable in unison with the arm 46, these arms preferably being mechanically connected together for simultaneous movement. The fixed contact 55 is connected by a lead wire 56 to the free or other end terminal of the main relay coil 35. The switch arm 54 is connected by lead wire 51 to the lead wire 3'! and thence to the transformer secondary coil 26 so that the switch 66 controls the circuit of the main relay coil 35. The relay switch 46 has a fixed contact 56 and has its arm 43 connected by a lead wire 56 to the lead wire 56, the contact 59 being connected by a lead wire 66 to the lead wire 51 so that the switches 46 and 53 are in parallel with each other. The fixed contact 5I of the double throw switch 66 is connected by a lead wire 6I to one terminal of the resistance heater coil 44, which has its other terminal connected by a lead wire 62 to the service line wire 2I. The ignition transformer primary lead wire 22 is connected to the lead wire 6| bec tween the coil 44 and the switch contact 5| so that heater coil 44 and the transformer primary coil 26 are in shunt circuit. The lead wire 6I is connected by a lead wire 63 to a contact carrying switch arm 64 of a burner motor controlling switch 65 forming part of a motor safety relay switch 66. The switch 65 has its normally closed fixed contact 61 connected by a lead wire 66 to one terminal of the pump and blower motor I which has its other terminal connected by a lead wire 69 to the return line wire 2|. The motor switch fixed contact 52 of tube relay 49 is connected by a lead wire I6 to the motor lead wire 66. 'The switch 36 of the main relay switch 36 has its fixed contact II connected by a lead wire 12 to the transformer secondary coil 26 at its connection to the room thermostat lead wire 36. The relay switch arm 4I cooperable with contact II is connected by a lead wire 13 to one terminal of the relay coil 14 of the motor safety relay switch 66, which has its other terminal connected by a lead wire I5 to the movable contact I4 of the pressure switch I2, from the fixed contact I3 of which a leadwire I6 is connected to the lead wire 51 and thence through lead wire 31 to the transformer secondary coil 26, so that the main relay switch 36 controls the relay coil 14. The motor safety relay switch 66 has aholding switch 11 with a fixed contact 18 connected by a lead wire I9 to the relay coil lead wire I5. The contact carrying switch arm 66 of switch I1 is movable in unison with the switch arm 64 and is preferably mechanically connected thereto so that arms 64 and 86 are simultaneously movable. The switch arm 86 of the normally open switch 11 is connected by a lead wire 6| to the lead wire '16 which is connected to the transformer secondary coil 26. The warp switch 45 is in parallel circuit with the holding switch 11 and has its fixed contact 82 connected by a lead wire 63 to the lead wire 8i. The heat responsive or bimetal element 84 of the switch 45 carries a contact cooperable with contact 82 and is connected by a lead wire 85 to the pressure switch lead wire I5, so that each of the switches I1 and 45 is also in parallel circuit with the pressure switch I2, 50 that upon closure of any one of these parallel 4 connected switches. switches 26 and 66 having first been closed, the relay switch coil 14 will be energized.

The tube relay 46 has a relay coil 66 which forms part of an electrical network including an electron tube 61 controlling energization of the coil 66. The tube 61 has its anode 66 connected by a lead wire 69 to one terminal of the coil 66, which has its other terminal connected by a lead wire 66 to one terminal of the transformer secondary supply coil 26. From the other terminal of coil 26 which is connected to the coil 21 there extends, as from a coil intermediate tap, a lead wire 6| connected to the cathode 62 and connected to ground, as at 93. The cathode 62 is heated or energized by a filament 64 having one terminal connected by a lead wire 65 to the lead wire 6| and having its other terminal connected by a lead wire 66 to the free end of the transformer secondary coil 21. A screen grid 61 of tube 61 is connected through a resistor 66 and lead wire 66 to the cathode lead wire II, the resistor 66 determining the negative bias on the grid 61. The tube control grid I66 is connected by a lead wire I6I to the cathode of a photo-electric cell or tube I62 responsive to burner fiame and having its anode connected to ground as by a lead wire I63. The tube I62 is supported within and shielded from extraneous light by a box or casing I64 such that it responds only to the light rays of the burner flame in the combustion chamber 2. A tubular shield or light conducting member I66 opens at one end into the interior of the casing I64 in line with the tube I62 and has its other end extending into the combustion chamber 2 and sighted on the flame position. The negative bias on the control grid I66 is controlled in part by a pair of balancing condensers I66, I61, the condenser I66 having one side connected to a cathode lead wire Si by a lead wire I66, and the other condenser having one side connected to the filament lead wire 66 by a lead wire I66. The condensers I66 and I6! have their other sides connected together and to the photo-cell lead wire Ilil by a lead wire H6. Inserted in the photocell lead wire l6l between the grid I66 and the condenser lead wire H6, there is a resistor III which, together with the condensers I66 and I61, determines the negative bias on the control grid I66. The extent of negative drain at the photocell I62 necessary for the tube 61 to become sufficiently conducting to energize the relay coil 66 is therefore controlled by the negative bias on the screen grid 61 and on the control grid I66.

The operation of this control system is as follows: When the switch 23 is closed, as for example by a call for heat, and assuming that the line wires H and 23 are connected to a source of current supply, so that the transformer primary coil 24 is energized, current will fiow from the transformer secondary coil 26 through lead wire 36 and the closed limit switch 3| to the bimetal blade 33 and through the closed switch 29 and lead wire 34 to the relay coil 35, from which current will flow through lead wire 56, the closed tube relay switch 53, lead wire 51 and lead wire 31 back to the transformer secondary coil 26. Energization of coil 35 will close the switch 38 preparatory to energizing the safety relay switch coil I4, will close the high voltage switch 36 to place in operation the timing means 45 and to energize the burner motor and ignition transformer and will close its holding witch 46. Accordingly current will flow from lead wire 56 through lead wire 56 to switch 46 and thence via lead wire 88 to lead wire 81, so that the coil 88 will remain energized, even though switch 88 is opened. Closure of high voltage switch 88 will complete a circuit from line wire 28 to lead wire 41 which is connected to the double throw tube relay switch arm 48, thence through switch contact 8| and lead wire 8| to the warp switch heater coil 44 and thence via lead wire 82 to the line wire 2|; The energized heater coil 44, upon the lapse of a predetermined time period, say two minutes, will have imparted sufllcient heat to the warp switch blade or element 84 to close circuit between the blade con-' flow through lead wire 88 to the switch arm 84 oi the closed cut out switch 88 and thence via lead wire 88 to the motor 1 and back to the line wire 2| through lead wire 88. Ignition is therefore on, simultaneously with energization oi the burner motor I preparatory tothe supply of a combustible mixture to the combustion chamber 2. Operation of motor I drives the fan 8 and the fuel pump l8, building up under the control of the pressure regulator ii the desired spraying pressure at the nozzle 8. If for any reason the oil pressure in the conduit 8 does not build up to the desired spraying pressure suflicient to close the oil pressure responsive switch l2 prior to the lapse of the predetermined time period which will close the warp switch 48, then upon closure of switch 48 a circuit will be completed from the transformer secondary coil 28 through lead wire 12 to the now closed switch 88 and thence via lead wire 18 to the relay coil 14 and lead wires 18, 88 tothe closed switch 48- and thence via lead wires 83, 8|, I8, 81 and 81 back to the transformer secondary coil 28. Energization of relay coil 14 will break the motor circuit at switch 88 and will close its holding switch H. The control system will thus be locked out and be maintained ineflective until the control switch or room thermostat 28 is opened and circuit is thus broken through the main relay coil 88 to permit switch 88 to open. After opening of the room thermostat switch 28 which deenergizes the heater coil 44, a period for scavenging of the combustion chamber 2 must elapse, which is predetermined by the time required for cooling of the bimetal element 84 sufllcient to open the warp switch 48. Until the switch 48 opens at the end or the scavenging period, closure of the room thermostat 29 will energize the coil I4, thereby opening the motor switch 85 so that a, recycling of the burner cannot be had. Assuming that the desired spraying pressure does build up in the conduit 8 so as to close switch l2 prior to closure oi the timing means switch 48, then the relay coil 14 will be energized by current flow from the transformer secondary coil 28 through lead wire 12, closed relay switch 38, lead wire 78 to the relay coil 14, thence through lead wire 18 to and through the closed pressure switch contacts I4, l3 and lead wires 18, 51 and 31 back to the transformer secondary coil 28. At or upon the occurrence of the spraying pressure which will close switch contacts l3, I4, a combustible 6 mixture of air and oil should be discharging into the combustion chamber 2 to be instantly ignited by the ignition sparks. The occurrence of flame will render the photocell I82 conducting and cause, the control grid I88 to become sufllciently positive for current flow through the electron tube 81, thereby energizing the tube relay coil 86. Accordingly, substantially simultaneously with the operation oi the motor cut out relay switch 88 to deenergize the burner motor I, the tube'relay switch 48 will be energized, thereby remaking the motor circuit at the motor switch 88, so that the burner motor I will continue in operation. Although the lag between the opening of the motor switch 88 and the closure of the tube relay motor switch 88 is almost imperceptible in normal desired operation, it will be apparent that the inertia oi the motor I will maintain oil pressure on the nozzle 8 sufllcient to maintain the pressure switch l2 closed for an appreciable interval oi say one or two seconds during which, it not instantly with flame, the switch 88 is closed to reenergize the burner motor I. It may be noted that simultaneously with the opening of the motor cut out switch 85, the holding switch ll was closed, so that coil 14 will be maintained energized to prevent restarting of the burner once the pressure switch I2 is closed, even though the pressure switch l2 might open for any reason prior to a loss or flame which would deenergize the tube relay coil 88. Upon closure by coil 88 or thetube relay double throw switch 88 at contact 82 to close the motorrunning circuit, the switch arm breaks contact at 8|, thereby deenergizing the warp switch heater coil 44 and the ignition transformer primary coil 28. 'The operation of the tube relay 48 also breaks the starting circuit for the coil 88 of the main relay 38 at the relay switch 88 so that ii, for any reason the tube relay coil 88 is improperly energized as by a" short circuit iri'the photocell circuit, or by the photocell I82 giving a false indication of flame,

' or it for any reason the switch arm 48 should remain in closed circuit running position with contact 82, the system could not be placed in operation.

With the oil burner placed in operation as above described, failure oi flame for any reason will render the photocell I82 non-conducting, thereby instantly blocking current'ilow through the electron tube 81 which will deenergize the relay coil 88 so that double throw switch 88 will move to its starting position, as shown, breaking circuit at contact 82 and making circuit at contact II. This will break the circuit of the burner motor I, since relay switch 88 is open and will close the circuits through the ignition transformer primary coil 28 and through the warp switch heater coil 44. However, it flame is picked up by reason of the reenergization of the spark electrodes l8 beiore switch 45 closes or pressure switch i2 opens, the tube relay '48 will be reenergized and the burner will continue in operation. If the flame failure caused the system to shut down, then in order to restart the burner motor I after such a complete flame failure, the room thermostat switch 28 must be opened to deenergize the main relay coil 38- in order to break the circuitoi the motor starting relay coil I4 to permit closure of switch 88.- If the timing means switch 48 has closed due to the time elapsed following closure of switch 8i then the main relay switch 39 must. be maintained open long enough for the bimetal element I4 to cool and break circuit at contact l2, for other- I wise closure of switch 2| will complete the circuit through the relay coil 14 via the switch I. 1

safe limit at which switch II is opened, thisopening of switch 3| will break the circuit through the main relay coil 25, thereby breaking the circuit to the burner motor at the main relay switch 39. Should the pressure or temperature drop sufficiently to close switch 3i while the switch 29 remains closed, then, switch 45 being open so that coil H is deenergized, the system will automatically again be placed in operation in the same manner as occurs upon closure of switch 28.

It may be noted that an electrode may be substituted for the photocell I02 and the light conducting tube I05, the electrode extending into proximity to the burner flame such that the electron tube 81 is controlled by capacitative impedance, such for example as is described in my co-pencling application Serial No. 408,139, filed August 25, 1941, entitled "Burner control means."

Referring to Fig. 2 there is shown a changed circuit arrangement which serves to break the.

circuit of the heater coil 44 while maintaining the motor starting relay coil H energized subsequent to stoppage of the burner motor I due, as above described, to loss of flame or blocking of the electron tube 81. This may be accomplished by employing another relay switch I having a motor switch I2! positioned in and controlling current flow through the wire 41 and having a contact carrying switch arm I22 cooperable with a fixed contact I23. The switch I20 also has a holding switch I24 having a contact carrying switch arm I25 cooperable with a fixed contact I28 in parallel circuit with the warp switch 45.

The switch arm I25 is connected by a lead wire I21 to the warp switch lead wire 85 and the switch contact I25 is connected by a lead wire I22 to the warp switch lead wire 83. I29 of switch I20 is inserted in the lead wire ll between its holding switch lead wire I28 and the lead wire 8|. The switch arms I22 and I25 are movable in unison and are preferably mechanically connected together so as to assure simultaneous movement to break circuit at switch HI and to make circuit at switch I24.

The operation of the circuit arrangement in Fig. 2 will, it is believed, be apparent from the foregoing and the description of Fig. 1 but it may be noted that upon flame failure which will deenergize relay coil 86 or in the event of initial failure of the electron tube 01 to become conducting, the heater coil 44 will cause the warp switch 45 to close, thereby completing a circuit through the relay coil I29 and also, if not theretofore completed, completing a circuit through the relay coil 14. Encrgization of coil I2! will attract or actuate the switch arm I22 to break circuit at switch I2i for the heater coil N, the motor and the ignition transformer I9 and will The relay coil actuate arm I2! to make a holding circuit for itself at switch I24 and therefore the call u and the bimetal element .4 will both. cool to open the warp switch ll preparatory to reatarting the burner operating cycle by the manual opening and closing of the circuit :of the main relay coil 35. It may be noted that the circuit of the relay coil H will remain completed as follows, from lead wire through lead wire I21, to closed switch I24, and thence via lead wire I28 through the relay coil I2! to the lead wire 8|, andaccordingly the motor switch '5 will be held open, thereby doubly preventing starting of the burner motor I. This feature of Fig. 2 not only eliminates consumption of current by the heater coil 44 during a lock out period but also eliminates the necessity of waiting for the coil 44 and element N to cool after the room thermostat switch 20 is opened, providing of course that the opening of the room thermostat switch 29 is had subsequent to the termination of the cooling period for element 84 initiated by opening of the switch I2I as above described.

What is claimed and is desired to be secured by Letters Patent of the United States is:

1. A heating apparatus comprising a fluid fuel burner, means to supply fuel under spraying pressure to said burner, starting and running circuits, electrically operable means controlling said fuel supply means and energized from said circuits, means to ignite the fuel supplied to said burner, means including a closed switch in said starting circuit and controlling current flow to said operable means, electrically heated thermostatic timing means operable to open said switch, means responsive to fuel pressure and operable at fuel spraying pressure to open said closed switch, means operable upon opening of said switch to maintain said switchv open, means responsive to occurrence of flame at said burner, means including a. switch in said running circuit and closed by said flame responsive means and controlling current flow to said electrically operable means, and main control means operable to control the supply of current to said switches and to said timing means.

2. A heating apparatus comprising a fluid fuel burner, a pump for supplying fuel to said burner, a motor starting circuit. a motor running circuit, a motor in said circuits and operable to drive said pump, means to ignite the fuel supplied to said burner, means including a switch in said motor starting circuit in series with said'motor and normally in and urged to closed position, timing means operable to open said switch, means responsive to occurrence of flame at said burner. means including a switch positioned in said motor running circuit in series with said motor andclosed by said responsive means, means including relay switch means having a holding circuit for itself and operable to control the supply of current to said switches and to said timing means, means including a switch controlling energization of said relay switch means and opened by said flame responsive means, said relay switch means upon energization closing said holding circuit, and means including a main control switch operable to deenergize said holding circuit.

3. A heating apparatus comprising a liquid fuel burner, a pump for supplying fuel to said burner, a motor for driving said pump, means instantly responsive to flame at said burner, means including a switch controlling said motor and closed by operation of said responsive means for energizing said motor upon occurrence of flame, circuit means in shunt with said controlling switch and including a closed switch for starting said motor, means operable upon the occurrence of a fuel spraying pressure to open said closed switch, and safety timing means operable to open said closed switch. i

4. A heating apparatus comprising a liquid fuel burner, a pumpfor supplying fuel to said burner, a motor for driving said pump, means instantly responsive to flame at said burner, means including a switch controlling said motor and closed by operation of said responsive means for energizing said motor upon occurrence of flame, circuit means in shunt with said controlling switch and including'a closed switch for starting said motor, means operable upon the occurrence of a fuel spraying pressure to open said closed switch, electrically operable safety timing means operable-to open said closed switch, and means operable by said flame responsive means to deenergize said timing means simultaneously with closure of said controlling switch.

5. A heating apparatus comprising a liquid fuel burner, a pump for supplying fuel to said burner, a motor for driving said pump, means instantly responsive to flame at said burner, means including a switch controlling said motor and closed by operation of said responsive means for energizing said motor upon occurrence of flame, circuit means in shunt with said controlling switch and including a. closed switch for starting said motor, means operable upon the occurrence of a fuel spraying pressure to open said closed switch, safety timing means operable to open said closed switch, and means operable by said flame responsive means to stop operation of said timing means.

6. A heating apparatus comprising a liquid fuel burner, a pump for supplying fuel to said burner, a motor for driving said pump, means instantly responsive to flame at said burner, means including a switch controlling said motor and closed by operation of said responsive means for energizing said motor upon occurrence of flame, circuit means in shunt with said controlling switch and including a closed switch for starting said motor, means operable upon the occurrence of a fuel spraying pressure to open said closed switch, safety timing means operable to open said closed switch, means including a main switch cooperable with said closed switch and operable upon closure to start said motor, ignition means energized by closure of said main switch, and means operable by said timing means to deenergize said ignition means simultaneously with closure of said controlling switch.

7. A heating apparatus comprising a fluid fuel burner, a burner starting circuit, a pump for supplying fuel to said burner, a motor for driving said pump, means instantly responsive to the occurrence of flame at said burner, a holding circuit, a relay having its coil in said holding circuit and having a switch in said starting circuit and Controlling current flow to said motor, said relay having a switch in and operable to close said holding circuit upon closure of said controlling switch, a closed safety switch in said starting circuit and opened by said flame re-' deenergization a time delay prior to stoppage of fuel supply to said burner, means instantlyresponsive to the occurrence of flame at said burner, a starting circuit and'a holding circuit including a relay having a switch controlling current flow-to said, energizable means,- said relay having a switch operable tofclose' said holding circuit upon closure of. said -controlling switch, means including a closed switch in' said starting circuit and opened by said flame responsive means upon occurrence of flame, means including a closed switch controlling current flow to said energizable means, means operableautomatically substantially coincident with supply'of fuel to said burner to open said last-named switch, and means including a switch for supplying current 'to said cnergizable means and closed by said flame responsive'means simultaneously with the opening of said closed starting circuit switch.

9. A heating apparatus comprising a liquid fuel burner, a pump for supplying fuel under pressure to said burner, a motor for driving said pump, means including a switch responsive to the pressure of the fuel supplied by said pump, electric ignition means, means including a safety warp switch having a heating coil, energizing and holding circuits including a main relay having a switch controlling current flow to said motor, to said ignition means and to said heating coil, means including an electron tube relay having a switch in series with said main relay switch, a network including an electron tube rendered conducting to energize said tube relay to open said tube relay switch upon occurrence of flame at said burner, means including a switch closed upon opening of said tube relay switch and establishing a circuit for said motor, means including a switch closed by said main relay to close said holding circuit, a relay having a closed switch in series circuit with said first-named tube relay switch and energized to open its closed switch upon closure of said pressure responsive switch, means including said warp switch controlling the circuit of said last-named relay, means including a switch controlled by said main relay and controlling said last-named relay, said last-named relay having a holding circuit and having a switch operable to close its holding circuit, and means including a main control switch controlling the operation of said main relay.

10. A heating apparatus comprising a liquid fuel burner, a pump for'supplying fuel under pressure to said burner, a circuit including a motor for driving said pump, a circuit including a switch responsive to the pressure of the fuel supplied by said pump, a circuit including electric ignition means, a circuit including a safety warp switch having a heating coil, a main relay having a switch controlling current flow to said circuits of said motor, said ignition means and said heating coil, an electron tube relay having a normally closed switch in series circuit with said main relay switch, a network having an electron tube rendered conducting to energize said tube relay to open said tube relay switch upon occurrence of flame at said burner, means including a switchclosed upon opening of said tube relay switch and establishing a circuit for said motor, an energizing circuit and a holding circuit for the coil of said main relay, a closed switch in said energizing circuit and opened by and upon energization of said first-named tube relay switch and having 11 its coil in said warp switch circuit and 'insaid parallel pressure switch circuit, saidlaat-named relay opening its closed switch lupon closure of said pressure responsive switch, .aaswitch controlled by said main relay and controlling the parallel circuits of the coil of said. last-named relay, a holding circuit for the coil. oi said .lastnamed relay andhavinga switch operahletoiclose its holding circuit, a main control switch controlling the operation of said 1118111 relay, and a 12- i'or energizing said motor upon occurrence of flame, circuit means in shunt with said controlling switch'and including a closed switch for starting saidmotor, means operable upon the occurrence or a fuel spraying pressure to open said closed switch, and safety timing means operable to break the circuit through said circuit'means.

FRED B. AUBERT.

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

UNITED STATES PATENTS Number Name Date 2,113,858 Ray Apr. 12, 1938 2,274,384 Scanlan Feb. 24, 1942 2,345,399 Jones Mar. 28, 1944 2,305,544 McGrath Dec. 15, 1942 2,335,655 Dickey Nov. 30, 1943

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