US2282551A - Burner safety control - Google Patents

Description

May 12, 1942. R, E YATES. 2,282,551

BURNER SAFETY CONTROL Filed Dec.r 12, 195e 4 sheets-sheet 1 A F/t 2. f I y l 7 I 137 L j fil/f 131 7 HFBT 1417 i@ 2 1.38 16 j f3.9 165:* .170162 j! j .\141 132 Je.; .l f6, 59 l zderzfaf: 68 la?? .Pa/#XE l/a'es i 169 166 @M @da-4 @www May 12, 1942. R, E, YATES- l 2,282,551

BURNER SAFETY- ONTRQL Filed nec. 12.` lse Aswan-sneer 2 33' ',EL-- I3 )fa 156 156 ifm/ffgg 147 :1X a of, l a 55 0 z/e'rzfar.'

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R. E. YATES yBURNER sAFE'rYlcoNTRoL May 12, 1942.

Filed Dec. 12. 193e 4 sheets-sheet 3 4 Sheets-Sheet 4` W1 )Si s@ M BMJ R. E. YATES Filed Dec. 12, 1938 BURNER SAFETY CONTROL .J/// 77Al 0/1 /d V May 12, 1942.

Patented May l2, 1942 BURNER SAFETY CONTROL mum E. rates, chicago, nl.,

ing Systems, Inc., Chicago, lll.,

i of Illinois f assignor to Drya corporation .application December 12, 193s, serial No. 245,113

(c1. 15s-2s) 'l Claims. This invention relates to fuel burners Yor like heating devices, and particularly to-safety control mechanisms for a multiplel arrangement of such devices.

In many industrial drying, baking or heating systems the requisite heat is. supplied bya series of individual burner units from which either a fluid heated therein or the heated products of combustion therefrom are circulated through the several parts of the system, and in some instances both such a fluid and the productsl of combustions are so circulated. Such individual burner units must each be equipped with safety control means to detect the presence or'absen'ce of a flame in the individual burner units, and to cause automatic interruption ofthe fuel feed upon failure of a flame. So to do prevents the accumulation of unburned combustible fuel in the' comf bustion chamber and thereby circumvents the risk of explosion and like hazards.

Control means of the type described above has been heretofore proposed for single burner units. In order to avoid the duplication of parts which is necessary wheresuch control means are used in multiple burner installations, it has been proposed, as in the co-pending application of Ralph J. Pleinand Robert E. Yates, Serial No. 225,996, filed August 20, 1938, to provide a mechanical distributor arrangement whereby a single safety control means is brought 'under the iriuence of each of the individual burners in sequence. Such an installation, however, entailed the use of moving .parts whichwere subjected to wear and which, thereferdrequired replacement.

It is a iin'bary` object, ofl this invention to eliminate 4g parts, and the attendant wear and replacement, in a safety control'means for multiple burner-:installations and yet avoid any duplication'- of 'the more costly parts utilized in such control means.

Another object is to effect instantaneous shutdown of the fuel supply system upon failure of the flamezat any one of the individual burner units.

A further object is to effect a shutdown of the fuel feed shoulda defect arise in the safety control apparatus or in the event of tampering with, such apparatus, Y

It has been proposed heretofore to employ electron tubes in safety devices of the kind described above, but such prior devices have several disadvantages. Firstly, there is no provision to automatically close the fuel supply valves in the event that a llame-detecting means lassociated with any one of the individual burners is rendered inoperative due to -a ground-out or other type of short circuit; or, secondly, if there is a short circuit protective feature, it has been achieved only to give rise to another disadvantage, namely, the employment of electron tubes of the double triode type in which the filaments are in parallel, and, if a filament of one amedetecting triode should burn out, and the triode thereby goes dead, there would be no effect manifested, in so far as the rest of the system :ls concerned, to indicate thatI a fault has occurred.

It is therefore an additional object of this invention to shut oil the fuel supply in the event that either an unwanted ground or other type of short circuit develops in the flame-detecting system, or that a filament in any one of the electron tubes burns out.

A still further object is to attain the foregoing results in a novel and efficient manner, and one which will be commercially feasible.

Other objects and advantages will become apparent from the following description, taken in connection with the accompanying drawings, in which- Fig. l is a vertical sectional view of a gas-fired burner unit of the kind to which my invention is applicable;

Fig. 2 is a plan sectional view taken along the line 2-2 of Fig. 1; i

Fig. 3 is a sectional view taken along the line 1 3 of Fig. 1;

Fig. 4 is a vertical sectional view of an oilfired burner unit;

Fig. 5 is a front elevation of the multiple burner installation;

Fig. `6 is a 'diagrammatic view illustrating the electrical connections external to the safetyr con trol unit; and

Fig. 7 is a wiring diagram showing the internal parts of the control unit.

In the preferred closure herein a conventional multiple unit burner system i is employed, which, as illustrated in Fig. 5, comprises a battery of live similarly formed heater units 2, arranged side by side, and it will be obvious that additional or fewer units can be used if desired. The heater units 2 are equipped with individual fuel burners |20 which can be ofueither the gas-fired type Villustrated in' Fig. 1, or-the vlifiuil fuel type shown in Fig. 4. As will be explainedihereinafter, the differences in construction between these two types ofburners have been minimized by a feature of the prest5 ent lnventionso as to permit certain standard embodiment chosen for dis- `of Ralph J. Plein, Serial The burners I 20 are supplied from a common fuel source such as a main fuel supply line 3.

f Manually operable valves |22, Figs. 1 and 5, are

preferably included in thebranch pipes |23 lead ing from the supply line 3 to the various individual burners. A pilot fuel supply line 4 is utilized to furnish fuel to the pilot burners 1, line 4 being connected to the various pilot burners 1 through branch pipes |21 in which are included manually operable valves |26.

Considering nrst the burner unit shown in Fig. 1, each heater 2 has a combustion chamber |29 and a return flue or mixing chamber |30, (these being interconnected in a manner well understood in the art but not shown herein). The fuel burners |20 are positioned to discharge the fuel into the forward end of the combustion chamber |29. Each burner |26, as herein shown, is associated with a venturi |3| formed from refractory material and located within fa supporting sleeve |32, and the venturi is secured in an operative relation on the forward end of the combustion chamber by bolts |32' extended betweenthe sleeve |32 and the wall of the combustion chamber |29.

A hollow mounting casting |33 is secured to the outer end of the Venturi sleeve |32, this casting being in the general V form of a truncated cone and having bosses |34 at its larger end through which bolts |35 pass to secure the casting |33 to a flange |36 at the outer end of the Venturi sleeve |32. A plate |39 is fastened to the other or outer end of the'casting |33, this plate |39 having a central sleeve |31 which passes through an opening |39' at the outer end of the casting |39, and through which sleevea main fuel discharge nozzle |38 projects so as to discharge fuel longitudinally7 toward the ad7 jacent end of the venturi |31. The opening |31' in sleeve |61 is of larger diameter than nozzle |36 so as to provide for the entrance of an annular stream of air about the nozzle |38, such air supply being controlled by an adjustable baille plate |40. Additional air may enter the venturi through the annular slot Mi formed between the flange |36 and the bosses |34. Gas is supplied to the nozzle |36 by the pipe |23 leading from the common gas line 3. At its lower end the pipe |23 has an elbow |41' which through. a pipe |42 discharges the gas into a mixer |43. 'I'he mixer |43 has an upper air inlet governed by an adjustable valve plate |44, and a mixture of gas and air is discharged downwardly through tige connector |45 and an elbow |46 to the nozzle In the preferred form shown herein, each bumer unit |20 is equipped with means for igniting the fuel flowing from the main fuel nozzle |33, this means being shown herein as comprising an electrically ignited pilot burner its flame, as indicated at 6, diagonally upward and into the flame zone |41 of the main fuel nozzle. As herein shown the pilot burner 1 is mounted in a flanged sleeve |48 secured to an angularly positioned apertured pad |48 formed on the mounting casting |33.

The pilot burner 1 is preferably of the type shown and claimed in the co-pending application No. 223,657, filed August The fuel supply pipe |21, for the pilot burner 4 `1, is connected to a nozzle |5| which discharges longitudinally into the reduced outer end of the 75 I3 the gaseous fuel within the burner tube |49 may be ignited. 'I'he resulting combustion of the fuel is supported by air which enters through a plurality of small ports |53 formed in the tube |49.

In the liquid fuel burner shown in section in Fig. 4, the casting |33 is identical to that similarly numbered in Fig. 1. The plate |39 and the sleeve |31 shown in Fig. 1, however, are in this instance replaced by a plate |54 having a shelf |55 on which a fuel nozzle |56 is supported in a manner now to be described. Nozzle |56 is in communication wilth a hollow cylindrical casting |56. A slot |55' in shelf |55 accommodates a short continuously-threaded pipe |51, which is screwed into the cylinder |56', pipe |51 serving to supply liquid fuel to the nozzle |56 via the cylinder |56'. Pipe |51 is clamped to shelf |55 by c An opening |58 is provided in plate |54 to permit the admission of the liquid fuel, in spray form, into the interior of thehollow casting |33,

. and also to allow air to enter therein.

In association with either of the burners illustrated in Figs.v 1 or 4, there is provided, according to the present invention, safety means whereby proper operation of the burners is detected and the operation of the burners is automatically suspended upon failure of combustion. Of the many different types of detecting means which may be employed for this purpose, I have shown herein'a flame detecting device |59, Figs. 2 and 3. Such a safety detecting device |59, Fig. 2, comprises a hollow mounting member |66 secured on a pad |62 on-the mounting casting |33 so that an insulated rod or electrode Ii carried by the member projects through an opening |65 in casting |33 and into the zone of the pilot name 9.

Preferably the electrode li is replaceably mounted in an insulating structure |63 clamped permanently to a shelf |19 within the mounting member |60. That portion of the rod il which is enclosed in the insulating structure |63 is continuously threaded to accomodate a nut |64 which bears on the inner end of the insulating structure |63. Another nut |55 bears on the opposits, or outer, end of the insulating structure |63, to thereby firmly clamp the rod il in position so that it is well insulated from the sur 1 which projects ber |60. The shelf |10 has openings |1| there-v in so that air will iiow in through the Ventilating ports |69 and along the exposed portion of the rod which is preferably of a highly heat-resistant conductive material. When it is defsired to remove the 'rod for purpose of replacement, the entire flame detecting assembly |59 is unfastened from the casting |33. Cover |66 is removed from member |66, and nuts |65 and |66 are unscrewed so that the threaded end of the rod may pass through the insulators |63 as rod is withdrawn from the opposite end of the insulating structure. A new rod which has been previously equipped with a nut |64, is then substituted and clamped in place by the nut |65. Terminal |61 may then be clamped by nut |66, cover |69 replaced, and

th; assembly |59 secured baci: on the castingl but, as has been included in the subject matter claimed in my present invention.

An advantage which arises from the particular construction of the hollow mounting casting |33 may now be brought out with reference to Figs. 1 and 4. It has heretofore been the practice to place the flame-detecting assembly |59 at the top of the casting |33, thereby causing an electrode such as that indicated at to depend therefrom in such a manner that it is exposed both to the main name |41 and the pilot flame 8. While this would be suitablein a gas burner, it is not a satisfactory procedure in the case of liquid fuel burners, for the reason that the atomized fuel has a tendency to collect on the electrode and drip off the lower end thereof. In the present construction the electrode comes in from the side of casting |33 and'passes rearwardly and downwardly to pilot flame 8, as is shown in Figs..2 and 3. on which the pilot burner 1 and the flame detecting device |53 are respectively mounted are spaced from each the casting |33 a distance substantially equal to one-fourth of the periphery thereof.

In the liquid fuel burner shown in Fig. 4, that portion of electrode which lies within the pilot flame 8 will be substantially at the fringe of the main flame |41, and yet no portion of electrode lies within thev flame |41. In the gas burner of Fig. 1,-the fuel nozzle |38 is of relatively large diameter and since the gas flame tends to spread soon after leaving the nozzle,more so than does an cil flame, the main ame |41 will in all probability envelop a portion of the electrode indicated hereinabove, this does not interfere with the successful-operation of a gas type burner. The position which is occupied by that portion of electrode which lies within the interior hollow portion of casting |33 relative to pilot burner 1, is shown best'in Fig. 3. y

Another advantage derived from such novel construction of the casting |33 is that this same casting may be used on both gas-.med and liquid fuel types of burnerunits. This practice effects a substantial reduction in manufacturing costs since it reduces the number of different parts required to be made and carried in stock.

In the diagrammatic view, Fig. 6, the main fuel supply line 3 is fragmentarily represented. A normally closed valve means 5 controls the flow of the fuel through line 3 to the various branch pipes |23 leading'to the individual burners |20,

and a valve actuator 3,. which in'this instance is electrically operated, regulatesthe opening or closing of valve 5. Similarly, a valve means 6 and valve actuator are provided on the pilot fuel supply line 4. The pilot line 4 is grounded as indicated at i2.

In carrying out the objectives of my present invention, each electrode is connected by a conductor |4 to a terminal as ,E1 to E1n inclusive, on the terminal strip I5 of the multiple safety unit generally designated by I5. Each conductor I4 is shielded by means of a shield I1, only a portion of which is shown. AThe various shields |1 are connected to a common termi- The pads |48 and |62- other around the periphery of 1 are shown in Fis. the apparatus disclosed herein can accommodate 'a greater, or if desired, a lesser, number of burnerunits.

Incommencing operation of the multiple burner installation a switch |8 is closed to thereby connect conductors I9 and 28 with the line wires 2| and 22 respectively. The closingof switch 'I8 is indicated by a lamp 23. Thereupon potential is applied to terminals 24 and 25 on the terminal strip I5 through conductors 26 Vand 21. A conductor 28 connects conductor 26 to and 38. As shown in Fig. 1, terminals 29 and 3| are normally in electrical connection with each other through the medium of contacts 32 and. 33 of the relay generally indicated by 34.

To operate the valve actuator I0, the pushbutton 42 is pushed'inwardly to thereby establishelectrical connection between conductor 43 leading from terminal 29 and conductor 44 which connects to terminal 31. A conductor 45 connects terminal 31 to one terminal of the pilot valve actuator i0, the other terminal of the pilot valve actuator i8 being connected to line wire 20 by a conductor 45. An indicating lamp 41 then lights.

When the button 42 is pressed inwardly connection is also established between conductor 48 leading from terminal 3| and conductor 49 which is connected to one terminal of the primary winding 50 of the ignition transformer 5|, and also to one terminal of the motor 53. Circuit is completed through the primary 50 back to line wire 28 bymeans of a conductor 54. The motor 53 is likewise connected to line wire 20 by a conductor 55.

The secondary grounded at 55, the other end of this winding being connected by a conductor 51 to the rotating arm 53 of a spark distributor 59. A shaft 58' of the motor 53 is connected to arm 58. A wiping contact 80 on arm 58 establishes circuit from the secondary 52 to each of the stationary contacts as 5| in succession as the shaft 53' is rotated by the motor 53. A conductor as 5| connects the insulated electrode of leach` spark plug tive to supply potential to spark plugs I3 even nal-S on the terminal strip I5 of the multiple as I3, Figs. 1,4 and 6,;to one of the contacts 3|.

Ground for the spark plugs |3 is provided through the pilot burners 1, pilot line '4, and the ground connection at l2, Fig. 6. Thus, the spark plugs I3 are rendered operative in sequence as the wiping contact 3|) touches each of the stationary contacts 5| in turn, and this serves to ignite the various pilot flames 8..

After all the pilot burners 1 have. been lighted, a control relay 34, Fig. 1, will become energized, ina manner to be described, to thereby close contacts 32 and .38, and 40 and 4|, and open' contacts 32 and 33, and 33' and 4Q. This serves to break circuit to the primary 50 of transformer 5| and also to the motor 53 so that the spark distributor assembly 59 will no Ilonger be effecthough the push-button 42 is still held inwardly. If the button 42 is released at this time circuit will be maintained to the pilot valve actuator I0 because of the fact that terminals 30 and 31 are -now connected through contacts 40 and 4|, Fig.

'7. Hence, lamp 41 will stay lit after button 42 is released, indicating that the apparatus is in such condition that the main fuel supply valve 5 may i now be opened.

The energization of relay 34 is. indicative of the fact that the safetyv control apparatus, Fig. 7,

is operative, which is to say, there is a pilot flame 6, vit will be manifest that` terminals 29- `winding 52 of transformer 5| isv .l ductors 'l5 and 18 to 8 at each of the electrodes If lamp 41 ree mains lighted after button 42 -is released, another pushbutton 52 is then pressed inwardly to thereby connect conductor 63, leading from terminal 29', with conductor 6d leading to the main valve actuator 9, circuit being then completed back to line wire 20 through a conductor 6E. The closure of this circuit and the resulting opening of main valve is indicated by the lamp 60. At the same time that button 62 establishes circuit between conductors 63 and 64 there will also be a circuit established to winding G1 ofv a relay 60, the other end of this winding being connected to line wire 20 through a conductor 10. This causes plunger t@ of relay 68 to establish a holding circuit to winding 01 and also to maintain the circuit to main valve actuator d so button t5. may now be released.

for any reason there is o. naine failure at one of the electrodes li, control relay lift, 7, will be deenerglscrl, as will explained cntly, thereby open contacts 32 and 38 and bresil: the connection between terminals d3 and serves to break the holding circuit to relay 68 whichv deenergizes and opens circuit to4 'the main valve actuator t. llt the same time cir-1 cuit will be broken to the pilot valve actuator i@ due to the opening of contacts 40 and 4| of relay 3d. The subsequent closing of contacts 39 and 0 will establish a connection between terminata 30 and 36 and an alarm 1| will become energized. Alarm 1| may be of either the audible or visual type. l

lt has been stated hereinabove that relay 34, Fig. '1, is energized when there is flame present at each of the electrodes il and is deenerglzed upon the failure of any one of the pilot flames 0. The manner in which thisresult is accomplished will now be described inconnection with the circuit shown in Fig. 7.

This arrangement embodies a transformer 13, the primary it of which is connected by conthe power supply terminals 2li and 25. Conductors 11 and 18 are also convnected across conductors and 18 and these.`

conductors supply the current to the filaments oi' the various electron tubes which are employed in the circuit. This filament supply circuit extends i'rom conductor 10 through a' resistor 19, which is, for the purpose of reducing the line voltage to the desired level, thence through a conductor 90 to the filament 8| of a control tube 82. A conductor 0I connects the other side of filament 8| to one side of the filament 04 of the first flame detector tube 55, and the ref spective filaments oi' the various flame detector tubes 85A, 85B, 85C, 05D, are connected in series with each other, provision being made for a. varying plurality oi such llame detector tubes by varying the value oi the resistance in resistor 19. If, for example, each or the tubes which are being employed has a rated filament voltage of 6.3 volts, andthe line voltage is 110 volts, then, assuming as in Fig. '1 that there are six tubes altogether, it will be necessary for the resistor 19 to have such a value of resistance that the filament current which is passing through it will produce a potential drop of 110 volts minus 6 times 6,3 volta'or '12.2 volts. The return line for this series circuit is established through con- ,7

ducto'r 11. It is manifest that a greater. or less number of tubes, having the same or different values of rated filament voltage, could beaccommodated in the mannerfindicated above. So to do eliminates the necessity of ,hevinla ,fila--A l tors ||0 and 85,.'secondary be energized.

o P" through conductors |04 ment winding on the transformer 1i, which filament winding would have to be specially made up for each customer. l

A secondary winding 06 is connected at one end to the plate P of thecontrol tube 82 by means of a conductor 91, the other end of secondary winding 0l being connected by a conductor 88 to conductors 99, and 9| which respectively lead to winding 35 of relay 94, a. capacitor 92 and a resistor 93. Conductors 94 and 95 serve to connect the other` sides ot the winding 35 and the capacitorA 82 to a conductor 98 which leads to the upper endol' secondary winding 91. Eesistor 93 is grounded -as indica-ted at 98 through a conductor 99.

The lower end of secondary winding 91 conneots to cathode C of control tube 82 through conductors |00 and lill. Qontrol tube l2 is preferably oi the pentode type in which a suppressor grid Gs joined 'to the cathode il. The screen grid G2 is connected directly plate P through a jumper |02.

A plate circuit of control tube 02 is traceable from plate P through conductor 81 to secondary Sii, thence in parallel through winding 35 of relay 34 and capacitor 92 to secondary 81 and thence back to cathode C. The operation of control tube 82 is of course determined by the bias on the control'grid G1. If grid G1 has a substantial negative bias, plate current in the abovedescribed plate circuit of tube 82 will be cut oil and relay 34 will be deenergized. When the negative bias on grid G1 is removed, plate current will again ilowgand control relay 34 will Potential for the plate circuits of the various tubes included in the circuits shown in Fig. 'l is derived from the secondary windings 05, 91 and |03 and therefore an alternating current source. In view of the use of such an alternating current source, each of the various tubes is non-conduc-l tive during the lower\halves or negative portions of the alternating current cycles but is conductive during the upper half or positive cycles of the alternating current. Thus referring to the control tube d2, there will be a pulsating unidirectional current delivered to the control relay 34 when the negative bias is removed from the control grid G1 of this tube and this is sunlcient to maintain the relay 34 energized. The capacitor 92 serves to smooth out the pulsating current thus delivered to the relay 34.

A representative flame detector tube circuit will now be described. Considering the tube 05, plate P' to conductor |05 `which leads to the upper end of secondary winding |03 of transformer 13. Circuit to the grid G1 oi control tube I2 is provided through conductors |05 and |01. A conductor |00 leads from conductor |05 to a. resistor |09 which in turn is connected to the upper end of secondary 91 by conductors ||0 and 95. The plate circuit 'of the flame detector tub'e 95 is therefore traceable from plate P' through conductors |04 and |05 to secondary |03I thence through resistor |03 and secondary 91 and back .to cathode C' through conductors |00 and In this connection it is to be noted that the plate circuit of'` tube 85A is traceable from plate and |05, secondary |03,conductors |05 and |00, l 91, and conductors |00 andHl back to cathode C". Likewise, the plate circuit of every other ame detector tube, 4as 058.050, and so forth. is traceable through is connected through a conductor |04l resistor |09, conducthe secondary |03, resistor 108, 'and secondary 91, so that these last-named parts are common to the plate circuits of all the flame detector tubes 85, 85A, 85B, 85C and 85D. It is apparent that the heavier the plate cur rent flow in the plate circuit of a flame detector tube as 85, the greater will be the potential drop through the resistor |08 and, therefore, the greater will'be the tendency of this potential drop to bias the control grid G1 of control tube 82 negatively. Thus it can be seen that an inverse relation exists in the operationsof the control tube 82 and the various flame detector tubes 85, 85A, 85B, 85C and 85D, for if the plate current should increase in the plate circuit of any one of these ame detector tubes, the current in the plate circuit of the control tube 82 will be diminished, preferably to the point of cut-ofi of the tube 82 which would mean zero current in the circuit in which the winding of the relay 34 is included, and this` of course would result in release of relay 84. However, any diminishing of the current in the plate circuit of the control tube 82 below the current value required to maintain relay t! energized ,will result in release of this relay, and the point of cut-oil? of tube 82 is well below the current value required to maintain relay energized.

The grid G' of the :dame detector tube 85 is connected through conductors H2 and H3 to terminal E1 which, 'as has been explained hereinabove, 'is in communication with an electrode Il.

Likewise, grid Gf' of tube 88A is connected to terminal Er, and the grid of every other flame 85, will increase due to the electrodes ll,'the current in the plate circuit of the associated flame detector tube, say tube the removal of the negative bias from the grid as G'. This serves to so bias the tube 82 as to cut off the energizing current to the relay 8|,y effecting a shutdownjof the system, for example, closingvalves 5 and f8; Fig. 6, as has been previously explained.

Now assume that rather than a failure of the ame there has been a grounding of an electrode Il. This might occur, for example, if the eleotrode Il were jarred while hot and with such*l force that'it contacted the grounded pilot burner 1. Such an occurrence will effectively shortcircuit the flame resistance in the name-detecting circuit traceable through resistor IM and capacitor H5. This destroys the phase opposition relation of the negative bias on grid G' to the\voltage acting betweencathode C' and plate P', and will permit current to be reestablished in the plate circuit of the flame detector tube to thereby restore the negative bias on grid G' of control tubeBZ. Energizing current to the relay 34 will therefore be cut ofi.

detector tube will be connected to its corresponding E terminal. If tetrodes or pentodes are employed .instead of the triodes shown in Fig.. '1, the same general scheme oiconnections'will pre'- vail, the terminals Ei to Em inclusive, being connected to the control grids of their corresponding flame detector tubes.

As shown in Fig. 6, each electrode Il is connected to an E terminal, which is in turn 'connected to the grid oi a flame detector tube as 85, Fig. 7. Negative bias for the grid G' of tube 85 is provided because of the potential drop profl duced by a fiow of current through the parallel combination of resistor lll and the capacitor H5 which are connected between conductors H3 and Iii. This grid-biasing current flows through the grounded pilot burner l, pilot flame 8, and electrode Ii as wellvas through resistor IH and capacitor H5. The resistance of the flame is somewhat critical. With the circuit thus pro-n vided, the presence of a flame between the grounded pilot burner 1 and electrode il will cause the current flowing through resistor il@ and capacitor H5 to have such a phase relationship to the voltage acting between plate P' and cathode Cl that the bias on grid G.' will bearI a phase opposition relation to this voltage. Under such conditions, current in the circuit of the plate P will be substantially cut off and, if there is a .flame present at each of the other electrodes i I, the current in the plate circuit of each oi the other flame detector tubes 85A, 85B, 85C and 85D, will be likewise cut off.' It will therefore be seen that when a flame is properly'present at each electrode Il the plate current flowing through the resistor |09 will be of such a small value that it vwill be relatively ineffective in producing a voltage drop through resistor |88 to negatively bias the-control grid G1 of tube 82.

lIf. however. there is a flame failure at one of The terminal Sl which is connected to shielding I1 is connected inside ofthe multiple safety unit'to the cathode return wire |80 by means of a. conductor H6. If this shielding should become grounded, or if for any reason there is a short circuit between a grid as G' and a cathode as C', the resistor' III and capacitor H5. will be shorted out of circuit andthe negative bias removed from the vgrid as G. 'I'he apparatus then functions as though there had been a flame failure.

Provision is also made to insure a shutdown of the fuel supply in the event that one of the tubes goes dead.-` It will be noted that the filaments of the various tubes are all connected in series.

If one of the filaments should burn out, the curthe relay 38 would remain energized. t

Thus, while I have illustrated and described a selected embodiment of my invention it is to be understood that this is capable of variation and modification and I therefore do not wish to be limited to the precise details setyforth but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I claim: 1. In a safety control apparatus for a multifple fuel burner system having a plurality of pilot burners and associated main burners, the combination vof means for regulating the supply of fuel to said pilot burners and main burners, an electron `tube including a filament, a control grid and a plate, means embodied in a plate circuit oi said electron tube and controlling said regulating means to enable the supply of fuel to said burners only when said electron tube is conductive, a plurality of other electron tubes eachallocated to a respective one of said pilot burners and keach including a filament, a control grid and a plate, a nplurality of sensing devices each disposed to sense the presence orl absence of a plying fuel to all of said burners,

.a driving operation of said fuel by saidxnotor to energize said spark plugs flame in a respective pilot burner, circuit means connecting said sensing devices respectively to the grids ci said other electron tubes and, being so constituted and arranged that each tube is rendered nonconductive in the presence of a flame in its coresponding burner, other circuit means connecting the plates of said other eleotron tub-es in common to the grid of the firstnamed tube and being so constituted and arranged that said first tube is rendered conductive only when. all of said other tubes are nonconductive, and still other circuit means connecting the filaments oft" all of said tubes in series whereby failure of any oi' said filaments renders said first tube nonconductive and thereby prevents the sul)- ply of :Fuel to said pilot burners and said main burners.

2.1n a safety control apparatus for a fuel burner system having pilot burner and an associated. main burner, the combination ci' means for regulating the supply of fuel to said pilot burner and main burner, an electron tube including a filament. a control grid and a plate,

means embodied in a plate circuit of said elec- 'ron tube and controlling said regulating means to enable the supplyaof fuel to said burners only when said electrontube is conductive, another electron tube including a filament, a control grid and a platea sensing device disposed to sense the presence or absence of a flame in said pilot burner, circuit means connecting said sensing device to the grid of said other electron tube and being so constituted and arranged that said other tube is rendered nonconductive in the presence of a name in said pilot burner, other circuit means connecting the plate of said other electron tube to the grid of the first-named tube and being so constituted and arranged that said first tube is rendered conductive only when saldother tube is nonconductive, and still other circuit means connecting the filaments of both o f said tubes in series whereby filament failure in said other tube resulting in inability of said other tube to become conductive upon failureof combustion in said pilot burner renders said first tube nonconductive and thereby prevents the supply of fuel to said pilot burner and said main burner.

3n In a multiple heater system having a plurality of individual fuel burners. means for supindividual spark plugs for `ignltin'g the fuel delivered to said burnerameans for supplying high potential to said spark plugs and including a. distributor and motor therefor, said distributor operating when driven by said motor to energize said spark plugs in succession, control means for effecting concurrent operation of said fuel supply means and said motor, sensing devices for detecting vthe presence of flames in said burners, and governing means under the Joint control of said sensing devices and responding automatically when flames are established in all of said burners to disable said vvmotor and to regulate supply means independentlyof said control means. 4. In a multiple heater system having a plurality of individualfuel burners. means for sup'- plying fuel to all of said burners and including a fuel valve and electrically operated means for actuating said valve, individual spark plugs for igniting the fuel delivered to said burners, means for supplying high potential to said spark plugs and including a distributor'and a driving motor cession, manual control meansl for concurrently energizing said valve actuating means and said said sensing devices respectively to the grids of therefor, said distributor operating when driven in sucsaid tubes and being so constituted and arranged that each tube is rendered nonconductlve in the presence of a flame in its corresponding burner, and relay means jointly responsive to all of said tubes and controlling said valve actuating means and said high potential supply means, said relay means operating when all of said tubes are rendered nonconductlve to disable said motor and to maintain said fuel valve open independently of the condition of said manual control means.

5. In a multiple heaterv system having a plurality of pilot burners and associated main burners, means regulating the supply of fuel to said pilot burners, means regulating the supply of fuel to said main burners, ignition means for said pilot burners, a first manually operable ing means for controlling said main fuel supply means, said second manual means being effective when operated to enable the supply of fuel to said main burners in dependence upon the condition of said governing means whereby operation of said main burners ls initiated only when both said governing means and said second manual means are operated.

6. ln a multiple heater system having a plurality of pilot burners and associated main burners. means regulating the supply of fuel to said pilot burners, means regulating the supply of fuel to said main burners, ignition means for said pilot burners. a first manually operable means controlling said pilot fuel supply means and said ignition means and effective when operated to initiate operation of said pilot burners,

sensing devices for. detecting the presence of flames in' said pilot burners, a plurality of gridcontrolled thermionic tubes. means comprising a plurality of input circuits in which said sensing devices are respectively included and to which the grids of said tubes are respectively connected, said input circuit means being so constituted and arranged that a negative blocking potential is impressed on the grid included in each circuit so long as a flame is effective on the corresponding sensing device, another grid-controlled thermionic tube, means comprising a common output circuit for the first-named tubes and to which the grid of said other tube is connected, said' output circuit means being so constituted and arranged that a negative blocking potential is lmpressed on the grid of said other tube so long as there is a substantial current flow in said common output circuit, a relay, means comprising an output circuit for said other tube and in which a winding of said relay is embodied, the

stituted and arranged that said relay assumes an operative condition only when a substantial current flow exists in saidlast-named circuit, and a second manually operable means governed by said relay and in turn controlling said main fuel supply means, said second manual means being effective when operated to enable the supply of fuel to said main burners only when conditioned by the operation of said relay. l

7. In a multiple heater system having a plurality of pilot burners and associated main burners, means regulating the supply of fuel to said pilot burners, means regulating the supply of fuel to said main burners, individual spark plugs for ignitingr the fuel delivered to said pilot burners, means for supplying high potential to said spark plugs and including a distributor and a driving motor therefor, said distributor operating when driven by said motor to energize said spark plugs in succession, a first manually operincident to which vsaid motor is disabled andv the supply of fuel to said pilot burners is maintained independently of said first manual means, and a, second manually operable means governed by said governing means vfor controlling said main fuel supply means whereby operation of' l said main burners is initiated only when both said governing means and said second manual means are operated.l

^ ROBERT E. YATES.

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