US2403412A

US2403412A - Ignition and safety control system for fuel burners

Info

Publication number: US2403412A
Application number: US609626A
Authority: US
Inventors: Charles K Strobel; Samuel G Eskin
Original assignee: Robertshaw Thermostat Co
Current assignee: Robertshaw Thermostat Co
Priority date: 1945-08-08
Filing date: 1945-08-08
Publication date: 1946-07-02
Anticipated expiration: 1963-07-02

Description

July 2, 194

c. K. sT|oBEL EIAL 2,403,412 7 IGNITION AND SAFETY CONTROL SYSTEM FOR FUEL BURNERS Filed Aug. 8, 1945 %7r20 18"1a 1 9 v 15 I I N VEN T OR! Clza lemhiSfiofiel ana'Samael 4.5412512 Patented July 2, 1946 IGNITION AND SAFETY CONTROL SYSTEM FOR FUEL BURNERS Charles K. Strobel, Pittsburgh, Pa., and Samuel G. Eskin, Los Angeles, Calif., assignors to Robertshaw Thermostat Company, Youngwood, Pa, a corporation of Pennsylvania Application August 8,- 1945, Serial No. 609,626

This invention relates to ignition and safety control systems for fuel burners and, more'par-v ticularly, to; electrically operated systems therefor.

Systems of the type indicated may be arranged so that an electromagnetic safety valve may be opened when a main switch is closed and the fuel supply. turned on. The fuel is then ignited by an electric igniter controlled by the main switch and after the expiration of a startin period the .igniter is disconnected by operation of a timing device. The valve then either remains open or is closed by varying the current 6 Claims. (Cl. 158-4171) supply thereto according to variations in the re- I in conjunction with the timing device it is apparent that power consumption and operating noise would be'reduced if the power consuming element of the relay were disconnected after the starting period. It is, therefore, an object of this invention to render the system substantially noiseless during the running period.

Another object of the invention is to effect a saving in power consumption in the operation of safety and ignition systems.

Another object of the invention is to insure reliable operation of the system in performing its functions during the starting and. running periods when normally operated.

Another object of the invention is to render the system sufficiently flexible as to length of the starting period to provide a wide range of operation.

Another object of the invention is to place the 2 main fuel cock and switching means which may form part of a. thermostatic fuel control device of well-known form. The cock and switching means It is arranged for manual operation by a handle l5 carrying temperature indicia- It.

It will be apparent that the main fuel cock and switching means it could be arranged for separate operation if desired and that the thermostatic device could be dispensed with.

Interposed in the fuel supply pipe it between the main fuel cock l4 and the burner it is an electromagnetic fuel valve l6 of any known type which may be arranged, as in this instance, to be opened when current of sufllcient energizing value is supplied to the solenoid ill thereof and closed by gravity, spring. or other means upon a reduction of the current value thereto below holding value. A pilot burner it is provided for igniting the main burner ill and is supplied with fuel from a conduit 28 connected to the main fuel pipe it between the main burner it and the electrometlc valve it. .It will be observed, therefore that the electromagnetic valve 86 controls the flow of fuel to both the main burner til and the pilo burner 58. It will be apparent, however, that where the pilot burner it is not desired it could be. dispensed with without afiecting the operation of the system in its essential aspects.

The fuel issuing from the pilot burner it is adapted to he ignited by an electric resistance ignite: The heat of the flame of the burnin .fnei adapted to cause variation in resistance timing device in condition for another starting other objects and advantages will become apparent from the following description taken in connection with the accompanying drawing,

wherein:

Fig. 1 is a schematic view of part of'a safety control apparatus for a gaseous fuei tanner embodying this invention;

2 is a circuit diagram trical connections: and

Figs. 3 and e are detailed views of the main switching means in difierent positions of operation.

Referring more particularly to the drawing, a gaseous fuel burner la is shown in Fig. l as being supplied with fuel by a main fuel pipe E2. The fuel supply is under control of a combmed showing the elecof a thermos resistance element 2%. The thermal resistance eie nent 2 5 is preferably in the form of soil wire of material having normally a reiatively low resistance and a positive temperature eoefdcient of resistance and is adapted to increase appreciably in resistance when heated by the Same. While this resistance element 2 is also heated by passage of current therethrough and other types of ballast resistors or flame sensitive elements could he substituted, it wili he tinderstocd to he primarily responsive to the heat of the The igniter 22 and thermal resistance element both located in proximity to the piiot banner where this burner is disensed these elements wonid be positioned in proximity to the main turner id.

a. second thermai resistance er -sent at is mburner and is adapted to vary its resistance only due to the passage of current therethrough. As will be apparent hereinafter, the thermal resistance characteristics of the element 26 could be dispensed with and a fixed or constant resistor employed if desired.

A cut-out 28 is provided for opening the circuit of the solenoid ill in the event of an open circuit occurring in the thermal resistance element 24. The cut-out 28 is preferably of the thermal type having time-lag operation. Such devices are constructed with predetermined time current char-.

36 to which the armature is hinged at one end.

A plurality of pairs of switch contacts, in this instance two, 36 and 4|], are adapted to be opened and closed by operation of the armature 34. In the arrangement shown both contact pairs 38 and 46 are closed and opened substantially simultaneously by appropriate movements of the armature, 34.

'Means are provided for latching the armature 34 in the closed position for a predetermined period during which the winding 32 may be deenergized. The latching means comprises a pivoted arm 42 adapted to engage and latch the armature 34 but being normally biased to free position by a spring 44. A thermal timer of any known type comprising a bimetal element 46 and heater coil 48 therefor is adapted to overcome the bias of the spring 44 to enable the arm 42 to move into latching engagement with the armature 34 when the bimetal element 46 is cold as shown in Fig. 2. The thermal timer preferably includes the so-called instantaneous reset device (not shown) generally consisting of a cold conducting surface for the bimetal element 4-8 which causes return of the latter to its cold position after warping therefrom.

The switching means of the main fuel cock l4 includes two

movable switch arms

50 and 66 and two spaced

terminals

52 and 68. The movable switch arm 50 is adapted for operative engagement with terminal 52 when the handle I5 is rotated to an intermediate position between off and on (Fig, 3). The switch arm 66 is of arcuate form and is adapted to maintain operative engagement with terminal 58 from the on position (Fig. 4) throughout a range of movement of the handle 55 so that various temperature settings may be selected at which the thermostat will operate. The arcuate switch arm 66 does not, however, engage the terminal 52 at any time.

The operation of the system is as follows: The main fuel cock i4 is shown in Fig. 2 in the off position and no fuel is being supplied to the main burner it) or the pilot burner It. When the main fuel cook it is turned toward the on posi tion engagement occurs in an intermediate on position between the movable switch arm 56 and the terminal 52 of the switching means as shown in Fig. 3. A circuit is then established for the winding 32 of the control relay 3!! which may be traced as follows: From a source of electrical 7 energy by line wires 54, primary of transformer 56, wire 58 connected to one terminal of the secondary of transformer 56, movable switch arm 50, terminal 52, wire 60, winding 32, wire 62 and wire 64 to the other terminal of the secondary of transformer 56.

The winding 32 being now energized from the source of current supply, the armature 34 will be operated to close the

contact pairs

38, 40, provided that the contacts are not already closed, as will'be hereinafter explained. As the heater coil 55 is notenergized at this time the bimetal element 45 is cold and occupies the full line position shown in Fig. 2 of the drawing. In this position the bias of the spring 44 is overcome and the arm 42 is enabled to latch the armature in its contact, closed position.

The normal rotation of the handle l5 of the main fuel cock l4 from off to on position will next cause disengagement of the switch arm 50 from the terminal 52 and positioning of the parts in full on position as shown in Fig. 4. It is apparent that the circuit for the winding 32 is opened but the

contact pairs

38 and 40 remain engaged due to the latching arrangement. In this full on position the fuel cock I4 is fully opened and the fuel may flow in the main fuel pipe [2 at least as far as the electromagnetic valve IB which is normally closed. The

terminal 68 of the main switching means of fuel cock l4 and establishes a starting circuit for the safety control and ignition apparatus.

This starting circuit is in the form of an electrical bridge and may be traced from the source, line wires 54, primary and secondary of transformer 56, wire 58, switch arm 66, terminal 68, and wire 10 to junction 12 of the bridge. The first arm of the bridge may be traced from junction 12, wire I4,

contact pairs

38 and 40, wire I6, igniter 22 and wire 18 to junction 86 of the bridge. The second arm of the bridge may be traced from junction 80, wire 82, solenoid coil H and wire 84 connected to junction 86 of the bridge. The third arm of the bridge may be traced from junction 86, wire 88, thermal resistance element 24 and wire 90 connected to junction 32 of the bridge. The fourth arm of the bridge may be traced from junction 92, wire 94, second thermal resistance element 26 and wire 96 connected to junction 12.

The cut-out 28 is connected as the detector arm in the bridge circuit by a wire 3!! connecting one terminal thereof to junction 92, the opposite terminal of the cut-out 28 being connected directly to the junction 80. The circuit for the bridge is completed by a wire Hi6 connected at one end to the junction 86 and at the opposite end to wire 64 which is connected to the secondary of the transformer 56. If the cut-out 28 is considered of negligible impedance it is apparent that the bridge circuit is, in eiiect, two parallel meshes connected in series with the secondary of the transformer 58. The impedance of this circuit is relatively low and sumcient current flows to the solenoid ll of the electromagnetic valve it to open this valve regardless of whether or not the burning fuel. Moreover, it will be apparent that the cut-out 23 which is connected in the detector 'both burners will then cease.

to the various arms of the bridge being in substantial balance.

As the foregoing described bridge circuit causes energization of the igniter 22, the fuel which is admitted to both the main burner l and the pilot burner is is nited substantially simultaneously with the opening of the electromagnetic valve It.

The heat of the burning fuelwill cause the thermal 'of thethermal timer is also energized through a circuit which may be traced from the source, line wires l4, primary and secondary of transformer 56, wire 58, switch arm 88, terminal 68, wire 10, wire 14. contact pair 28, wire I02, heater coil 48,

v wire I04, wire 82 and wire 84 to the secondary of the transformer 58. The bimetal element 46 becomes heated by the heater coil 48 and warps to the broken line position shown in Fig. 2 of the drawing. Thus, the I bimetal element 46 is rendered incapable of overcoming the. bias ofthe spring 44 and the arm 42 istripped to cause opening of the contact pairs 38 and 40. The thermal timer may conveniently operate after an eighteensecond starting period which is sufficient to allow the thermal resistance element 24 to become heated bythe burning fuel. This period maybe varied as desired by adjustment of the timer as will be apparent. 4

This operation of the contact pairs Stand 40 terminates the starting period and marks the inception of the normal running period of the burner. The operation of contact pair 40 serves to open the first arm of the bridge circuit and deenergize the igniter 22. The bridge circuit is now converted to a circuit including the thermal resistor 24 in parallel with the solenoid i1 and cut-out 28 all in series with thermal resistor 26. The total circuit impedance'is thus increased and causes a'reduction in the value of the current through the solenoid H. The current value is not reduced below that required to hold the electromagnetic valve is in open position if the thermal resistance-element 24 has now become 'sufllciently heated by the burning fuel and has increased in resistance.. However, if at the end of the starting period or at anytime during operation of the system the flame of the pilot burner it should cease. then the "resistance of the thermal resistance element 24 will be reduced by cooling thereof and the current to the coil II will be rendered insumcient to maintain the electromag-,- netic valve iBin open position. Flow of fuel to This action is accelerated by making the resistance element 28 of the thermally responsive type.

It will be apparent that if the thermostatic control deyice previously mentioned is included as part of the main fuel cock and switching means N that the fuel supply to the main burner may be turned off and on thereby while the arcuate switch arm 86 which is in operative'engagement with the terminal 88 maintains closed circuit conditions at the temperature setting inwhich the handle I! is positioned. When the operation of the main burner i0 is no longer desired. then the handle ii of the main fuel cock 64 may be rotated v in reverse direction from "on" to "01! position.

Such operation will serve to disengage the arcuate switch arm 68 from terminal 88 and cause deenergization of the coil ll of the electromagnetic valve i8 whereupon the valve willclose.

Further reverse rotationof the handle it toward I "01? position will cause the movable switch arm 50 to become engaged with terminal 52. The winding 32 of the control relay is thereupon energized and the contact pairs 38', 40 will be closed.

As the bimetal element 46 preferably is arranged to engage a cold conducting surface as described, when in the broken line position, it will return quickly to its initial position, shown in full lines, causing the arm 42 to be moved to latching position as soon as the contact pairs 28 and 40 are opened. Thus, when the off position shown in Fig. 2 of the drawing is finally reached and the winding 22 is again deenergized, the contact pairs 38 and 40 may be held in closed position by the latching means due to the operation of the thermal timer described.

The winding 32 forming the electromagnetic component of the control relay is thus energized momentarily and then deenergiaed by the normal operation of the main fuel cock during the starting operation. Thus, the circuit timing function is performed while the power consuming element is disconnected. The usual source of noise is thus not present during normal running of the burner and the current consumption is correspondingly reduced.

It will be understood that various changes can be made in the arrangement and combination of parts and in the form of the elements herein disclosed within the scope ofv the appended claims without departing from the spirit of the invention.

We claim:

1. An ignition and safety control system for fuel burners having a source of electrical energy, comprising electrically operable fuel controlling means movable between fuel. flow permitting and preventing positions, switching means for controlling energization of said fuel controlling means from the source and operative to cause said movement thereof, means responsive we condition caused by combustion of the fuel and electrically connected to said fuel controlling means for reducing the energy value supplied thereto sufliciently to cause movement thereof to flow reventing position in the absence of combustion, an electric resistance igniter for the. fuel, control means responsive to operation of said switching means for rendering said condition responsive means ineifective to cause said movement for a predetermined period during which said condition responsive means has time to become responsiVe. said control means comprising a winding and switch contacts adapted to be closed for establishing a circuit from the source including said fuel controlling means, said igniter and said condition responsive means of sufllcient enersizing value to cause said movement to fuel flow permitting position, said winding being connected ina separate circuit with the source and adapted to be deenergized by operation of said switching means to cause opening of'said switch contacts todisconnect said igniter and render said condition responsive means effective if combustion does not exist.

2. An ignition and safety control system for fuel burners having a source of electrical energy, comprisingelectrically operable fuel controlling means movable between fuel flow permitting and preventing positions, switching means for controlling energization of said fuel controlling means from the source and having a plurality of operative positionsjmeans responsive to a condition caused by combustion of the fuel and electrically connected to said fuel controlling means for re' ducing the energy value supplied thereto sumciently to cause movement thereof to flow preventing position in the absence of combustion, an electric resistance iguiter for the fuel, control means eflective in one said position of said switching means for rendering said condition responsive means ineffective to cause said movement for a predetermined period during which said condition responsive means has time to become responsive, said control means comprising a winding and switch contacts adapted to be closed for establishing a circuit from the source including said fuel controlling means, said igniter and said condition responsive means or suflicient energizing value to cause said movement to fuel flow permitting position, said winding being connected in a separate circuit with said source and adapted to be deenergized in said one position of said switching means and energized in another said position thereof, means responsive to closing of said switch contacts for holding the same closed when said switching means is operated from said other position to said one position thereof, and means for rendering said holding means inoperative upon expiration of said period to cause opening of said switch contacts to disconnect said lgriter and render said condition responsive means eilective if combustion does not exist.

3. An ignition and safety control system for fuel burners having main and pilot burners and a source of electrical energy. comprising electromagnetic valve meansimovable betweenclosed and open positions for controlling the fuel supply to the main burner, manually operable switching means for controlling energization of said electromagnetic valve means and having a plurality of operative positions, a thermal resistance element having a preselected temperature coment effective if the pilot burner does not produce a flame.

4. An ignition, and safety control system forfuel burners energizalole from a source oi current supply and comprising an electric igniter for the fuel connected in a first arm. of an electrical bridge circuit, an electrically operable fuel control device in a second arm of said bridge and operable to supply fuel when current of sumcient value is supplied thereto, a pair of resistors in third and fourth arms respectively of said bridge. one of said resistors being exposed to the heat of the burning fuel for varying in resistance and causing variation in said current value, control means for rendering said igniter inoperable and said current value ihsufiicient after a predeter mined period unless said one resistor is heated,

emcient of resistance located in proximity of, the

pilot burner and electrically connected to said electromagnetic valve means for reducing the energy value supplied thereto upon variations in the resistance of said element due to the absence of a flame at the pilot burner, an electric resistance igniter for the pilot burner; a control relay effec tive in one position of said switching means for men-- deringxsaid thermal resistance element ineffective to reduce said energy value sufliciently to cause closing." of said electromagnetic valve means for a predetermined period during which. said thermal resistance element has time to become heated, said control relay comprising a winding'and a plurality of switch contacts adapted to be closed i for establishing first and second circuits from the source in said one position of said switching means, said first circuit including said electromagnetic valve means, said thermal resistance element and said i'gniter and causing movement of said electromagnetic valve means to open posi 'tion, said winding being connected in a third circuit with the source and adapted to be enersized in another position of said switching means and immediately deenergized upon operation thereof to said one position, means responsive to closing of said switch contacts for holding the same closed when said switching means isoperated to said one position thereof, and a thermal t imcrhavinga heater coil in saidsecond circuit adaptedfor rendering said holding means inoperative upon expiration ofsaid period to cause.

opening of said switch contacts to disconnect said isnlter and render said thermal resistance elesaid, control means comprising switch contacts operative for opening and closing said first arm and a winding for operating said contacts, switching means for connecting the source across opposite junctions of said bridge with said first and second'arms and said third and fourth arm in series circuit resmctively and in multiple across said junctions, said winding being connected in a separate circuit with the source and adapted to be deenergized by operation of said switching means to cause operation of said switch contacts for opening said iirst arm.

5. An ignition and safety control system for fuel burners energizalole from a source or current supply and comprising an'electric igniter for the fuel connected in a first arm of an electrical bridge circuit, an electrically operable fuel control device in a second arm of said bridge and operable to supply fuel when current of sumcient value is supplied thereto, a pair of resistors in the third and fourth arms respectively of said bridge, one of said resistors being exposed to'the heat of the burning iuel for varying in resistance and causing variation in said current value, control means for rendering said igniter inoperable and said current value insumcient after a predetermined period unless said one resistor is heated, said control means comprising switch contacts operative for opening and closing said first arm and a winding for operating said contacts, switching means having a plurality of operative positions in one of which the sourceis connected across opposite Junctions of said bridge with said first and second arms and said third and fourth arms in series circuit respectively and in multiple across said junctions, said winding being connected in a separate circuit with the source and adapted to be deenergized in said one position of said switching means and energized in another of said position thereoi, means responsive to operation of said switch contacts to close said first armfor holding the same closed when said switching means is operated from said other position to said one position thereof, and means for rendering-said holding means inoperative upon expiration of said period to cause operation of said switch contacts to open said first arm. r

6. An ignition and safety control system for fuel burners energi'zable from a source of current supply and comprising an electric igniter device in a second arm of said bridge and operable to supply fuel when current of sufficient value is supplied thereto: pair of resistors in the third and fourth arms respectively of said bridge, one of said resistors being exposed to the heat oi the burning fuel for varying in resistance and causing variation in said current value, control means for rendering said igniter inoperable and said current value insuflicient after a predetermined period unless said one resistor is heated, said control means comprising a plurality 01' pairs of switch contacts, a winding and an armature,

one said contact pair being adapted for opening and closing said first arm, switching means havin: a plurality oi operative positions in one of which the source is connected to opposite junctions' oi 'said first and fourth arms and said sec- 0nd and third arms respectivel7,- said winding being connected in a separate circuit with the source and adapted to 'be deenergized in said one position of said switching means and I in another said position thereof, latching means tor said armature normally biased to free position and adapted to hold said first arm closed when said switching means is operated from said other position to said one position thereof, and I a thermal timer adapted to overcome the bias crmnms K. s'moBEL smear. a. serum.

energized