US2411642A - Safety control apparatus for fuel burners - Google Patents

Description

NOV. 26, c STRQBEL 2,411,642

SAFETY CONTROL APPARATUS FOR FUEL BURNERS Filed March 23, 1945 Cambizzea'i'ael Value a'adMaL'n Swz'eob IN VENTOR. Cbarlerki Szfrabel.

.HYSATTURNEK the normal running period is initiated and the Patented Nov. 2c, 1946 um'rso s ssrs'rvcou'mos APPARATUSFOR Business iLharles K. Strobei, Pittsburgh, Pa., assignor to Robertshaw Thermostat Company, Youngwoou, Pa, a corporation of Pennsylvania Application March 23, 1945, Serial No. 584,218

This invention relates to safety'control systems for fuel burner and,mcre particularly, to electrically operated controls'thereior.

Safety control systems of the electrically operated type may be arranged to include a starting period during which the circuit conditions are such that sufiicieht current is supplied to the fuel controlling means to actuate it to a position in which fuel is supplied to the burner. Thereafter,

iii circuit conditions automatically reduce the current supplied to the iuel controlling means to holding value. The fuel controlling means does not move from the fuel supply position providing the burner is producing a flame. However, subsequent extinguishiment of the burner will result in a prompt response of the circuit ele ments to further reduce the current to the fuel controlling means below the H value. This causes the fuel contra me to assume a position in which ely the burner is prevented.

The means for cleteiuii controlling means remains i ting position may taise the i sistance element locatecl' burner flame and arranged aul-181:. r

WEE t controlling means is couuectec, presence or abse scribed and claimed my copeum Serial No, 436,032, filed February Patent No. 2,379,114; granted protective device is therefore seem event that the thermal r sistance comes open-circuiteai. prior L cutout was employed to internist the 5 Claims. (Cl. 158-1171) Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawing, wherein is shown a. schematic view of a safety control apparatus for a gaseous fuel burner embodying the invention.

Referring more particularly to'the drawing, a, main fuel burner is is supplied with gaseous fuel by a main fuel pipe The fuel supply in the pipe 52 is controlled by a main valve is which, in thi instance, is adapted; for manual operation but which may be'arrariged for thermostatic op- 'eration if desired. interposed in the fuel supply pipe l 52 between the main valve ii.- and the burner is is an electromagnetic or solenoid gas valve ill of any known type which may" be arranged, as in this instance, to be opeuesi when current of sumcient energizingvalue s cplied to the solenoid and closed by gravity more. a reduction of the current value thereto below holding value.

A pilot burner it is provided for main burner iii and is supplied wit a conduit 2s connected to the ma under control or the main valve be understood, however, that could be dispensed v/i' v the essential principles of ih relation and eluded for the purpose of at the main burner at" various elements of the system in their relative positions of 1186,

Electric current for the o" ratus is supplied by the to the primary of a trau able in such apparatus current cease when to terminate the sushi, main switch for the elect transformer 23 may he i valve l l with suitable closure of the main 3 i is actuated to open The main switch of connected by a wire to secondary of thetrausio minal of the main sv by a Wire it to one t of a control relay the coil 32 is connectecl by the ocerat e other terl wire s to o -.e

tion A of a parallel mesh which is connected the other terminal of secondary of the trans former 2:3 by a wire The main switch of valve is and the operating coil arethus in series circuit with the secondary of transformer One branch of the narallel mesh consists of a thermal resistor 38 having a preselected temperature coeificient of resistance and located in proximity of the flame from the pilot burner I8.

The thermal resistor 38 is preferably in the form ments or so-called ballast resistors could be substituted for the thermally responsive resistor disclosed herein. The branch consisting of the thermal resistor 38 is connected at one end by a wire 40 to the junction A and at the other end by a wire 42 to the opposite junction B of the parallel mesh.

The other branch of the parallel mesh consists of an operating coil 44 for the electromagnetic valve 16, a first constant resistor 48 and a cutout 48. These elements are connected in series circuit in the other branch by a wire 50 connecting one terminal of the coil 44 to wire 38 at junction A, a wire 52 connecting the opposite terminal of coil 44 to one end of the resistor 48, a wire 54 connecting the opposite end of the resistor 48 to one terminal of the cutout 48, and a wire 58 connecting the opposite terminal of the cutout 48 to wire 42 at junction B of the parallel mesh.

As previously indicated herein, the cutout 48 is of th simple renewable type and will operate to interrupt the 'flow of current to the coil 44 of the electromagnetic valve I8 upon the occurrence of an open circuit in'th'e thermal resistor 38. As will appear hereinafter, no time delay or other special construction is required in connection with the cutout 48 due to the circuit arrangements of this invention. The first constant resistor 48 serves to adjust the current value to the cutout'48 so that during the starting period it is less than the steady operating value of the current supplied thereto and is of suitable resistance value for this purpose. It is apparent that during the starting period of the burner if current of suflicient value to actuate the electromagnetic valve l8 to open position is supplied to the coil 44 thereof, then the cutout 48 which is in series circuit with the coil 44 would also receive sufiiciently large current to cause it to operate and open the circuit of the electromagnetic valve I8. Means are provided in this invention to prevent this undesired operation of the cutout 48 as will now be described.

The control relay 38 embodies switching means including a timing element 80 which is initially closed and has a specified time delay of eighteen seconds before opening. Any suitably type of timing element may be used and, in this instance, the mercury tube arrangement well known to those skilled in the art is preferred. One electrode of the timing element 88 is connected by a wire 82 and a common wire 84 of the relay to the wire 52. The other electrode of the timing element 88 is connected by a wire to one end of an electric resistance igniter 88 for th pilot burner. the opposite end of which is connected by a wire'12 to one end of a second constant resistor 88. The opposite end of the second resistor 88 is connected by a wire 14 to junction B of the parallel mesh. Thus, timing element 80, igniter 88 and resistor 88 are in series circuit and jointly stablish a parallel circuit with cuto t a a th first resistor 48 when the timing element is closed.

The second constant resistor serves to adjust the current value to the igniter 88. It is apparent, therefore, that in addition to opening and closing the parallel circuit for the cutout 48, the timing element 88 will simultaneously open and close the circuit of the igniter 88. Should the igniter 88 become. burntout or otherwise damaged that an open circuit occurs therein, then means provided herein may be operated manually to complete the circuit of the igniter. This means takes the form of a manually operated switch 18 which is normally held open by a spring 18 and is connected in parallel circuit with the igniter 88. The connection may be traced by way of a Wire 88 connected at one end to the wire 12 and at the other end to one terminal of the switch 18, and by a wire 82 extendingfrom the other terminal of the switch |8 to th wire 10. A suitable constant resistor 84 may be included in the wire 88 in series with the switch 18 to compensate for the loss of the resistance value of the igniter 88 should it become open-circuited.

The operating coil 44 of the electromagnetic valve I8 is arranged to be short circuited for a predetermined period of time during the initial or starting period in order to permit the igniter 88 to produce a flame at the pilot burner l8 before the main burner i8 is suppliedwith fuel. The short-circuit for the coil 44 is established by switching means in the form of a second timing element 88 in the control relay 30. As in the case of the timing element 88 the second timing element 88 may be of the mercury tube type and arranged to open from its initially closed position after a predetermined time delay following energization of the coil 32 but after a delay period of. only six seconds. Preferably, both the timing elements 80 and 88 close instantaneouly upon deenergization of the coil 32, it being noted,

' however, that it is not essential that the timing element have an instantaneous closing action as long as it assumes a closed position before reopening of the timing element 88. Thus, where such a short time delay as six seconds in established for the timing element 88, then the timing element 60 would almost necessarily have an instantaneous action also. one electrode of the timing element 88 to wire 48 and a wire 90 connects the other electrode to the common wire 84.

The circuit from junction B of the parallel mesh to the transformer secondary is completed by a wire 92 connecting one end of a variable resistor 94 to junction B and a wire 98 connecting the other'end of the resistor 94 to the wire 28. The variable resistor is similar to the thermal resistor 38 in having a positive temperature coefllcient of resistance and normal low resistance but ary thereof by the wire 38 to junction A of the parallel mesh and by the wire 28, main switch of valve I4, wire 28, wire 98, valve control resistor A wire 88 connected.

short-circuited for six seconds by the shorter time delay element 85 and no fuel is supplied to the main burner to during the starting period.

The ignitei' til is energized through the circuit from transformer secondary, wire as, main switch of valve l5, wire 96, valve control resistor 94;

wire M, junction B, wire '14, second resistor 68 wire 12, igniter 55, wire tirning element 60, wires so and 9 3, timing element 86, wire88,

junction A, and wire 85 back to the transformer 24. During this starting period, the fuel flow ing from the "pilot burner i3 is ignited by the igniter 65 but this period is too short for the thermal resistor 38 to become appreciably heated by the pilot burner flame and increase its relativelylovv resistance. At the end of the shorter time delay period the timing element lit opens and removes the short-circuit from the operating coil lid of the electromagnetic valve l6 and this valve is actuated to open position. it will be observed that the coil Q4 thus receives current of sufllcient value to cause opening of the electromagnetic valve l5 although the parallel circuit established by the thermal resistor 38 across junctions A and B of the parallel mesh still exists. Such forced pick-up of the electromagnetic valve 16 is due to the combined resistance values of the valve control resistor 9t, second resistor 68 and igniter lid being low enough for such pick--up to occur. Consequently, fuel then flows through the fuel pipe l2 to the main burner it! where it is ignited by the pilot burner l8.

Upon the expiration of the longer time delay period of the timing element 60 which, as stated, may be eighteen seconds, the circuit of the igniter 66 is discontinued causing deenergization thereof. In addition, the parallel circuit is removed from the cutout E8 and first resistor 46 by this opening operation of the timing element 60. The total circuit resistance is thus increased sufllciently to reduce the value of the current to the operating coil 4d of the electromagnetic valve i6 and cause this valve to close, unless the thermal resistor 38 is heated by the flame from the pilot burner i8 and its resistance increased suificiently to compensate for this increase in total circuit resistance. if at any time during the operation of the apparatus the flame of the pilot burner l 8 becomes extinguished, then the thermal resistor 38 will cool and its resistance be decreased sumciently to render the value of the current to the valve coil-44 insumcient to maintain the electromagnetic valve it in open position, whereupon this valve will close to terminate the supply of fuel to the main burner to.

It is apparent that the temperature condition of the thermal resistor does not influence the actuation of the electromagnetic valve l8 to open position, but does control the holding and release of the valve. Should this thermal resistor 38 become open-circulted and. discontinue its branch of the parallel mesh, then the provision of the cutout which would consequently receivecurrent of operating value, serves to open the circuit of the operating coil 3-5 in the other branch of the mesh. Hence, this safety feature tin provided by the cutout 18 is required only during the running period oi the burner, that is, while the thermal resistor 38 is controlling the electromagnetic valve i6, and the parallel cir-v cuit or shunt provided for the cutout 48 during the starting period does not interfere with its essential function.

The circuit arrangement described and shownherein permits considerable variation in the value of the respective resistances without detracting from the desired operating characteristics. Moreover, while the preferred arrangement of parts has been illustrated and described it will be apparent that the apparatus is not limited to this particular embodiment but various changes may be made within the scope of the appended claims.

I claim:

1. A safety control system for fuel burners having a source of electrical energy, comprising electrically operable means movable between positions for controlling the supply of fuel to a fuel burner, a thermal resistor having a preselected temperature coefficient of resistance located in proximity of the burner so as to be heated by the flame produced by the burner and connected in parallel circuit with said controlling means for varying the energy value supplied thereto upon variations in the resistance of said thermal resistor due to the presence or absence of said flame, current responsive means in said circuit and operative for causing movement of said concontrolling means to a position in which said fuel supply is prevented upon the occurrence of an open circuit in said thermal resistor, and

means electrically connected to said current reelement operable upon expiration of said period for rendering said last means ineffective.

2. A safety control system for fuel burners having a source of electrical energy, comprising electrically operable means for controlling the supply of fuel to a burner and being actuable to a fuel supplying position when energy of sufficient value is supplied thereto and being movable to a position for preventing said fuel supply when energy of insufilcient value is supplied thereto, a thermal resistor having a preselected temperature coeificient of resistance located in proximity of the burner so as to be heated by the flame produced by the burner and connected in a parallel circuit with said controlling means for varying the energy value supplied thereto upon variations in the resistance of said thermal resistor due to the presence or absence of said flame, current responsive means in said circuit and operative for causing movement of said controlling means from fuel supplying to fuel supply preventing position upon the occurrence of an open circuit in said thermal resistor, and means electrically connected to said current responsive means and effective for preventing operation thereof for a predetermined period during which said thermal resistor has time to become heated, said last means including a timing element operable upon expiration of said period for rendering said last means inefiective and increasing the total circuit resistance to cause energy of said insufiicient value to be supplied to said controlling means unless said thermal resistor has varied due to the presence of the burner flame.

3. A safety control system for fuel burners hav- ,inga source of electrical energy, comprising elecfuel supplying position when energy of sufficient value is supplied thereto and being movable to a position for preventing said fuel supply when energy of insufficient value is supplied thereto, a thermal resistor having a preselected temperature coefficient of resistance located in proximity of the burner so as to be heated by the flame produced by the burner and connected in a parallel circuit with said controlling means for varying the energy value supplied thereto upon variations in the resistance of said thermal resistor due to the presence or absence of said flame, current responsive means in series circuit with said controlling means and operable for causing movement thereof from fuel supplying to fuel supply preventing position upon the occurrence of an open circuit in said thermal resistor, and means electrically connected to said current responsive means for short-circuiting the same for a predetermined period during which said thermal resistor has time to become heated, said last means including a timing element operable upon expiration of said period for discontinuing the said short-circuit and increasing the total circuit resistance to cause energy of said insufiicient value to be supplied to said controlling means unless said thermal resistor has varied due to the presence of the burner flame.

4. A safety control and ignition system for fuel burners having a source of electrical energy, comprising electrically operable means for controlling the supply of fuel to a burner and being actuable to a fuel supplying position when energy of sufficient value is supplied thereto and bein movable to a position for preventing said fuel supply when energy of insufficient value is supplied thereto, an electric igniter adapted when energized to ignite the fuel and cause the same to produce a flame at the burner, means establishing a first circuit for supplying energy of said sufficient value from the source to said controlling means and including said controlling means, said igniter, and a control device having a timing element operable after a predetermined period for electrically disconnecting said igniter from said circuit, a thermal resistor having a preselected temperature coefiicient of resistance located in proximity of the burner so as to be heated by the flame produced by the burner and electrically connected in parallel with said first circuit for varying the energy value supplied to said controlling means upon variations in the resistance of said resistor due to'the presence or absence of said flame, current responsive means in series circuit with said controlling means for causing movement thereof from fuel supplying to fuel supply preventing position upon the occurrence of an open circuit in said thermal resistor, said current responsive means being short-circuited by said timing element and igniter for said predetermined period, and means cooperable with said current responsive means for establishing a second circuit for said controlling means upon operation of said timing element to discontinue said short-circuit and increase the total circuit resistance to cause energy of said insufllcient value to be supplied to said controlling means unless said thermal resistor has varied due to the presence of the burner flame.

5. A safety control and ignition system for fuel burners having a source of electrical energy, comprising a parallel mesh circuit connected to said source, a thermal resistor in one branch of said mesh having a preselected temperature coefiicient of resistance and located in proximity of a burner flame for varying in resistance due to the pres ence or absence of said flame, electrically operable means in another branch of said mesh for controlling the burner fuel supply and being actuable to a fuel supplying position when energy of sumcient value is supplied to said controlling means and being movable to a position for preventing said fuel supply when energy of insufllcient value is supplied thereto, a cutout operative to open saidother branch and cause movement of said controlling means from fuel supply to fuel supply preventing position upon the occurrence of an open circuit in said one branch, a first resistor in said other branch for adjusting 'the energy value to said cutout, an electric igniter adapted when energized to ignite the fuel and cause the same to produce a, flame at the burner, a second resistor for adjusting the energy value to said igniter, and a control device having a timing element for connecting said igniter and second resistor in parallel circuit with said cutout and first resistor for a predetermined period in which said thermal resistor has time to become heated and cause the supply of energy to said other branch to decrease to a value insufiicient to operate said cutout, said timing element bein I operable upon expiration of said period for elec-- tically discounting said igniter and said second resistor and thereby increasing the total circuit resistance to causeenergy of said insufilcient value to be supplied to said controlling means unless said thermal resistor has increased in resistance due to the presence of said burner flame.

CHARLES K. STROBEL.

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