US2380125A - Safety control for fuel burners - Google Patents

Description

y 10, 1945. c. K. STROBEL 2,380,125

SAFETY QONTROL FOR FUEL BURNERS Filed Oct. 1, 1942 77/75 DELH)" I Cl/FOl/T fi/VD JW/TCH 98 H z 4a 7a INVENTOR.

CHARLES K.6TR0BL. BY M ATTORNEK sequence oi manipulations tagesl will' f nes i a circuit,

l atent'ed July 10, v v

- j umrso STATE-S PATENT orrics sal ary conrnfifiii ronr. stillness Charles K. strobel, Plitlbillfll, P... 83811110! to llobel'tlha w Thermostat Company, Yonnlwood,

Pa.,'a corporation oi Pennsylvania Application October 1, 1942, Serial No. 460,456

:2 Claims. 7 (c1. ts-117.1)

This invention relates to safety controls for fuel burners and, more particularly, to electrically operated controls therefor.

Electrically operated fuel control apparatus has been arranged to permit supply of fuel to the.

mainburner if a flame sensitive portion of the apparatus has previously been heated by a pilotburner. The flame sensitive device may comprise an electrical resistance elementwhich changes its resistance when heated and thus changes the value or the energizing current supplied toa sole.- noid valve controlling the supply 01' fuel. The current values in the circuit are adjusted so that during the starting period (before theflame sens I sitive device has heated) the current to the solenoid valve is suillcient to cause actuation to open position; During the operating period (after the a be arranged, as in this instance, to be opened,

Referring more particularly to the drawing, a gaseous fuel burner It is shown in Fi 1 as being supplied with fuel by a main fuel pipe I2. The

fuel supply is controlled by a main valve H which, i

in this instance, is adapted for manual operation but which may be arranged for thermostatic operation if desired. Interp I fuel supply pipe 12 between the main valve l4 and the burner I (I is an electromagnetic or solenoid gas valve Ii of any known type which may ,by energization of the solenoid and" closed by connected'to the main valve N to receive fuel flame sensitive device is heated) the current.

through the solenoid valve is only sufllcient to,

, maintain it open. Hence, immediately upon coolingof the flame sensitive device due to extinguishment oi'the pilot burner, the current values in the circuit automatically change causing insufllcient' current to flow throush the solenoid valve tomai ntainit open, whereupon the fuel supply tothe main bumeris promptlycut ofl.

gravity upon deenergization thereof. A pilot burner I8 is provided for igniting the main burner I III and is supplied with fuel from a conduit from the pipe l2 when the main valve is open."

Electric current for the operation of the apparatus is supplied by the line wires 22 connected I 2Q to the primary of'a, transformer 24. It is desirable in such apparatus that the electric cur-. rent be shut of! when the main valve I4 is closed to shut 011 the supply of fuel to both the main and pilot burners. Accordingly. a main switch 25 for the electric current from the transformer 24 may be incorporated in the valve It with suitable in such systems the occurrence of an undesired open circuit, such-as from fracture of the whereacoil isused.

flame sensitive device in cases would eliminate the safety feature by permitting the solenoid valve to remain open even though .the pilot burner became .eirtinguished: The additionofa thermaltime-lag type of cut-out in circuit with the solenoidvalve and operable upon failure or the flame sensitive device has been roposed, Thi expedient introduces the disad-r vantage of undesired closing of the solenoid valve ii a number oron oiI-on cycles or the main contiiol device are performed in quick succession permi 's" 1 rse. s rtinc P riod current to, oncrate the cut-out I when the time-lag has expired An object of fuel burner embodyinsthislnv nflm. and

men connections.

dlasramshowins the eta-v as, mally closed switch 42 01' performed upon the apparent mm 'the tollowln's ml is a schematic view or a safety control apparatus "fora a'a'seous arrangement for causing closure of the main switch when the valve II is actuated to open posion v k i so The electrical circuit for the safety control and I 'transiprmer 24 and the 40 electrically connected, upon initial closure of this invention is to maintain com- 1 plete safety in pparatusflof the; Wi -described ignition system of this invention, as shown more particularly in Fig. 2, includes the main switch of valve II- which has one terminal connected by a wire 28 to one terminal or the secondary of the other terminal oiv the main switch connected by a wire 28 to a Junction 3l. The other terminal of the secondary of the transformer 24 is connected by a wire 32 to a in the Junction 34. It may be noted that the various I operated elements of the system are the main switch l4, in a bridge type 01' circuit.

Connected to junction ignition means-comprising a coil 40 andgthe nor- ,a control relay having ti elayed operation, all of which form one arm of the-aforesaid bridge circuit. These elements are connected in series circuit which may be traced by a wire 36 from junction 1| to the re-;

so sistor 3I,,-wire 44 connecting the resistor II to the ll connecting the igni- 'iflnitlon'coil i0 and a wire tion coil u to the switch 42. The switch 42 is connected by a wire 48 to a Junction Ill and -a wire]! extending therefrom serves to connect the thyme terminal ortheelectromagnetic valve I! are-series resistor 38,

thereto, the other terminal of this valve being connected by a wire 54- to the junction 34. The electromagnetic valve l6 and the connections described form the second arm of the aforesaid bridge circuit.

Connected by a wire 56 to the junction 34 is a resistance element 58 which may be designated as a. control resistance for the electromagnetic valve II; for reasons which will appear hereinafter. Preferably, the resistance element 58 is in the form of a coil of wire of material having normally a relatively low resistance and a positive temperature coeflicient of resistance, commonly termed a ballast resistor and being thermally responsive to the passage of current therethrough. Primarily, however, this element is responsive to the heat of the pilot burner flame to which it is exposed as shown in Fig. 1 and will vary in resistance in response thereto. The opposite end of the resistance element 58 is connected by a wire 50 to the Junction 62 and forms the third arm of the aforesaid bridge circuit.

Connected by awire 64 to the junction 62 is a second resistance element 66 which is also formed from a coil of wire having normally a relatively low resistance and a positive temperature coefllcient of resistance. As indicated in Fig. 1, this second resistance element 66 is not however exposed to the flame from the pilot burner 18 and is adapted to vary its resistance only due to the passage of current therethrough. The opposite end of the resistance element 66 is connected by a wire 68 to the junction and forms the in arm of the aforesaid bridge circuit.

The detector arm of the bridge circuit comprises a cut-out 10 having one terminal thereof connected by a wire 12 to the junction 50 and the other terminal thereof connected by a wire 14 to the junction 62.. Preferably, the cut-out 10 is of the thermal type having time-lag operation for a purpose which will be apparent hereinafter. Such devices are constructed with predetermined time-current characteristics and usually contain a heater element in addition to and affecting a fusible member which opens the circuit by passage of overcurrent. I

The electrical circuit is completed by the provision of a second normally closed switch 18 of the control relay having time-delayed operation connected from one terminal by a wire I8 to the junction 50 and the other terminal thereof connected by a wire 80 to the junction 24. The switch 16 is therefore connected in shunt with the electromagnetic valve l8 which remains in closed position while the shunt is effective.

Means are provided to complete the circuit manually in order that the pilot burner l8 may be lighted with a match should the ignition coil fail and cause an open circuit. This means takes the form of a manually operated switch 82 which is normally held open by a spring 84 and is connectedin shunt with the igniter 40. The connections may be traced by way of a wire 88 connected atone end to the wire 44 and at the other end to one terminal of the switch 82 and by a wire 88 extending from the other terminal of,

the switch 82 to the wire 40.

A suitable electrical resistance element 90 may be included in the wire 88 in series with the switch 82 to compensate for the loss of the resistance of the ignition coil 40 when this coil becomes open circuited for any cause.

The control relay of which the switches 42 and 18 form part may be provided with a single actuating coil 92 (see Fig. 1) having one terminal thereof connected by a wire 84 to the wire 32 and the other terminal thereof connected by a wire 88 to the wire 68. As previously indicated, the switches 42 and 16 are similar in that both open after a specified time-delay, but the switch 42 'has a longer time delay period following closing of the main switch of valve I4. These switches are preferably of the, mercury tube type such as disclosed in patents, Nos. 1,778,439 and 2,224,873 among others and to which patents reference may be had for a fuller description. In the present.

embodiment of this invention the switch 42 may have a time-delay of eighteen seconds before opening following the closing of the main switch l4 and is adapted for instantaneous closing upon opening of the main switch valve l4 or otherwise deenergizing the actuating coil 92. The switch I6 may have a time-delay of five seconds before opening following the closing of the main switch 14 and also have instantaneous closing. It is not essential, however, that the switch 42 having the longer time-delay period also have an instantaneous closing upon operation of the main switch of valve l4 to open position or other deenergizing of coil 92 it being only necessary that it. assume a closed position before the switch 16 is again actuated to open position. In this embodiment,

where such a short time-delay as five secondsis established for opening of theswitch 16, it is exposed to the flame of the pilot burner I8 and the latter is arranged in proximity to the main burner ill to serve its intended purpose of igniting fuel flowing therefrom."

The operation of the device is as follows:

Manual or thermostatic closing of the main switchof valve I4 is effective upon opening of this valve as described and permits fuel to ilow to the pilot burner I 8 and also in the main fuel pipe l2 as far as the electromagnetic valve I! which is normally closed. The current from the transformer 20 is conveyed by the. wires 26 and 32 to the junctions 30 and 34 of the bridge circuit. As the elements comprising the bridge circuit are at this time unheated and the electromagnetic valve 1 is shunted by the time-delay switch 16, the bridge network is considerably unbalanced. Therefore, the current through wires 12 and 14 to cut-out I! is large. Within a few seconds the circuit elements heat up and the bridge balance is improved resulting in a decrease in current through the cut-out 10. There is a further decrease in the current to cut-out 10 to considerably below normal operating value after opening of the switch 16 having the shorter time delay period and this serves to remove the shunt from electromagnetic valve. l8 further improving the balance of the bridge. Due to the time-lag of the cut-out II the large inrush current upon initial closing of the main switch of valve I4 is ineflective to cause operation of the cut-out 10 at this time. Upon expiration of the specified five seconds time-delay period upon opening of the switch 16 and removal of the shunt from the electromagnetic valve ll,

the ignition coil 40 has reached igniting temperature, Thus, upon opening of the electromagnetic valve IS the fuel flowing from the main burner I0 is ignited by the flame from the pilot burner I! which is ignited by the ignition coil 4..

The resistance elements 58 and 66 have now become heated,'the formerdue to the flame from through, and the latter due to the passage of current therethrough only. Consequently,- the bridge balance is improved to such an extent that the pilot burner and the passage of current therethe current through the cut-out 10 is reduced to a value insuflicient to cause'operation thereof regardless of whether the main switch is manipulated in on-off-on cycles. At the expiration of the 18 seconds time-delay, if such is chosen for Operation of the long time-delay switch 42 to.

open position is entirely automatic and occurs regardless of whether the resistance element 58 i heated by the pilotburner, flame or even whether the pilot burner I8 has become ignited. Thus, when the switch 42 opens, unless the ballast resistor 58-has become heated and its resistance increased sufficiently to raise the resistance of the shunt established thereby around the valve l6 and cut-out l and to compensate for the increase in total circuit resistance then the current through the electromagnetic valve IE will decrease below holding value and the valve It; will close. If at any time during operation of'the apparatus the flame of the pilot burner l8 ceases then the resistance element 58 will cool and its resistance be lowered in consequence so that the current through the electromagnetic valve I6 is rendered insuflicient to retain this valve in open position, whereupon closure thereof will occur.

'I'he invention is thus particularly directed toward the means to cause closing of the electromagnetic valve I6 in the event of failure ofthe resistance element 58 by fracture or other'destructive means. While the resistance element 58 remains intact, no interference with normal operation of the control by the cut-out will occur regardless of the manner of operation of the main switch l4.- It will be apparent that flame from the pilot burner l8 would have no responsive to energizing current in said circuit, said resistors being adapted to increase in resistance value when heated thereby, a cut-out connected across oppositejiirictions of said first and second arms and said third and fourth arms of said bridge and being inoperative during the initial unbalanced period, said cut-out being adapted to receive a reduced supply of current as said :bridge balance improves when said resistors increase in resistance value, and means for connecting oppositejunctions of said first and fourth arms and said second and third arms to said source of current supply.

2. A safety control and ignition system for fuel burners having main and pilot burners comprising an initially unbalanced electrical bridge circuit adapted to be energized from a source of current supply, one arm of said bridge including an electric resistance igniter for the pilot burner,

effect thereon-and the electromagnetic valve l6 would remain open. However, due to the provision of the cut-out lfl'the increase in current through the circuit of the solenoid yalve 16 upon fracture of the resistance element'58 will cause the cut-out to operate at any time subsequent to expiration of the time-lag thereof which renders it inoperable during the initial starting period when the inrush current may be large.

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 of the appended claims without departing from the spirit of the invention.

I claim:

1. A safety control and ignition system for fuel burners having main and pilot burners comprising an initially unbalanced electrical bridge circuit adapted to be energized from a source of current supply, one arm of said bridge including an electric resistance igniter for the pilot burner, a second arm comprising electrically operable means controllin supply of fuel to the main burner, a pair of resistors in the third and fourth arms one of which is exposed to the heat of the pilot burner flame and the other being thermally a second arm comprising electrically operable means controlling supply of fuel to the main burner, a pair of resistors in the third and fourth arms One of which is exposed to the heat of the pilot burner flame and the other being thermally responsive to energizing current in said circuit, said resistors being adapted to increase in resistance value when heated thereby, a cut-out having time delayed action for the initially unbal- 3. A safety control and ignition system for fuel burners having main and pilot burners comprising an initially unbalanced electrical bridge circuit adapted to be energized from a source of current supply, one arm of said bridge including an electric resistance igniter for the pilot burner and a switch for said igniter having time delayed action, a second arm comprising electrically operable means controlling fuel supply to the main burner, a pair of resistors in the third and fourth arms one being exposed to the heat of the pilot burner flame and the other being thermally responsive to energizing current in said circuit, said resistors being adapted to increasein resistance value when heated thereby, a cut-out having time delayed action for the initially unbalanced period and connected across opposite junctions of said first and second arms and said third and fourth arms of said bridge to receive a reduced supply of current as said bridge balance improves when said resistors increase in resistance value, said bridge being converted upon operation of said switch to a circuit containing said burner heated resistor in parallel with said electrically operable means and cut-out in series, and means for connecting opposite junctions of said first and fourth arms and said second and third arms to said source of current supply.

4. A safety control and ignition" system for fuel burners having main and pilot burners comprising an initially unbalanced electrical bridge circuit adapted to be' energized from a source of current supply, one arm of said bridge including an electric resistance igniter for the pilot burner and a switch having time delayed action to open position for deenergizing said igniter, a second arm comprising electrically operable means controlling fuel supply to themain burner, a pair of resistors in the third and fourth arms one being exposed to the heat of the pilot burner flame and the other being thermally responsive to energizing current in said circuit, said resistors being adapted to increase in resistance value when heated thereby, a, cut-out having time delayed and normal running periods in the absence of said pilot-heated element failure.

6. A safety control and ignition system for fuel burners having main and pilot burners, comprisaction for the initially unbalanced period and connected across opposite junctions of said first and second arms and said third and fourth arms of said bridge to receive a reduced supply of current as said bridge balance improves when ing a source of current, a main switch, a bridge circuit controlled by said switch and having an unbalanced period upon initial operation of said switch, said bridge having arms arranged in a sequence including an electric igniter for the pilot burner and a control relay for said igniter in the first arm operative to deenergize said igniter said resistors increase in resistance value, a secelectrically operable means and cut-out in series,

and means for connecting opposite junctions of said first and fourth arms and said second and third arms to said source of current supply.

5. A safety control and ignition system for fuel burners having main and pilot burners, comprising electrically operable means having an open position when energized for supplying fuelto the main burner, an energizing circuit for said fuel supplying means, an electric igniter in said circuit and being thermally responsive to energizing current therein for igniting the pilot burner, a control relay having a timing element shunting said fuel supplying means until said igniting reaches igniter temperature, a second control relay having a timing element in series circuit with said igniter and operable to open the circuit thereof upon expiration of a predetermined period after after a time-delay period, an electromagnetic valve in the second arm actuable to a position permitting operation of the main burner, a resistance element in the third arm adjacent said sec- "ond arm and exposed to a flame from the pilot burner, and a second resistance element in the fourth arm being thermally responsive to current from said source, said resistance elements being adapted to vary in resistance when heated as aforesaid and improve the balance of said bridge before said igniter becomes deenergized, a second control relay short-circuiting said valve and operable after a time-delay period to permit actuationof said valve by removal of the shortcircuit, means for connecting the opposite Juncenergization of said igniter to open the circuitoperation of the first said control relay, said opening of the igniter circuit marking the end of the starting period and the inception of the normal running period of the burner, a plurality of resistance elements in said circuit one oi which is exposed to the heat of the flame of the pilot burner and another being thermally responsive to energizing current in said circuit, said elements being adapted to vary in resistance when heated as aforesaid during the starting period and per mit suificient energizing current to said fuel supplying means to maintain the open position during the running period, said elements during said starting period forming the third and fourth tions of said-first and fourth arms and said second and third arms to said energizing circuit, and a cut-out connected across the opposite junctions of said first and second arms, and of said third and fourth arms forming the detector arm of said bridge and having sufilcient time-delay in operation to remain inoperative during the initial unbalanced period when the current in the detector arm is suiflciently large for operation thereof, said cut-out being operable after deof said valve should an open circuit occur in the resistance element exposed to the pilot burner arms respectively of an electrical bridge, said arms being arranged in a sequence in which said 3 fuel supplying means formsthe second arm and said igniter and first control relay form the first arm thereof, means for connectingthe opposite junctions of said first and fourth arms and said 'second and third arms to said energizing circuit,

and a thermal protector for said fuei supplying means connected across the opposite junctions of said first and second arms and of saidthird and fourth arms as the detector arm of saidbrldge to receive a supply of current during the starting period which becomes reduced as said elementsbecome heated as aforesaid and by removal of said shunt from said fuel supplying means, said protector being operable to open the circuit of said fuel supplying means upon failure of said pilot heated resistance element but being inoperable for said purpose during the startingcontaining said'bumer heated resistor in parallel 7. A safety control and ignition system for fuel burners having main and pilot burners comprising an energizing circuit, a niain switch controlling said circuit, and an initially unbalanced electrical bridge in said circuit having arms resistance value when heated thereby, a fourth arm containing another resistor adapted to increase in resistance value when heated by passage of current therethrough, a thermal cutout connected across the opposite Junctions of said first and second arms and said third and fourth arms, said bridge being converted upon operation of said time delayed switch to a circuit with said electrically operable means and cut-out in series, said cut-out having time delayed action sufllcient to prevent operationthereof upon initial closure of said 'main switch, and means for connecting opposite junctions of said first and fourth arms and said second and third arms to said source of current supply.

CHARLES K. S'I'ROBEL.

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