US2304200A - Safety control mechanism for fuel burners - Google Patents

Description

Dec. 8, 1942. R. J. PLEIN ETAL SAFETY CONTROL MECHANISM FOR FUEL BURNRS Filed Aug. 20, 1938 5 Sheets-Sheet l '/l/l//lf Dc 8, 1942 R. J. PLEIN ETAL SAFETY CGNTROL MECHANISM FOR FUEL BURNERS Filed Aug. 20, 1938 5 Sheets-Sheet 2 Dec. 8, 1942. R. J. PLEIN ETAL 2,304,200

SAFETYl CONTROL MECHANISM FOR FUEL BURNERS F'iled Aug. 20, 193.87l 5 Sheets-Sheet 3 De- 8, 1942 rR. J. PLEIN ETAL SAFETY CONTROL MECHANISM FOR FUEL BURNERS Filed Aug. 20, 1958 5 Sheets-Sheet 4 www "Dea 8, 1942. R. J. PLEIN ETAL SAFETY CONTROL MECHNISM FOR FUEL BURNERS Filed Aug. 20, 1938 5 Sheets-Sheet 5 j? Jef; for

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Patented Dec. 8, 1942 SAFETY coN'raoL MEcnAmsM Fon FUEL f BURNER Ralph J. Plein and Robert E. Yates, Chicago, Ill., asslgnors to Drying Systems, Inc., Chicago, Ill., a corporation of Illinois Application August 20, 1938, Serial No. 225,996

(Cl. 15S-23) 13 Claims.

This invention relates generally to fuel burners or heating devices, and more particularly it relates to safety control mechanism for multiple burner installations.

In many industrial drying, baking or heatingsystems the requisite heat is supplied by a series of individual burner units from which heated air or the heated products of combustion are circulated through the several parts of the system. Such individual burner units must each be equipped with safety control means to insure the desired sequence of operations in starting units and also to cause automatic interruption of the iuel leed upon llame failure in the individual burner unit.

in important object, therefore, of the'present invention is to enable a multiple burner installation having e. relatively large number or burner units to he controlled by a central control system which is responsive to llame failure in any one of the burner units to shut down the entire multiple burner system.

More speclncally, it is an oicject of the present invention to provide a central safety control system for `multiple burner installations which avoids duplication of the more expensive ele ments of the control apparatus.

A further object is to provide such a multiple burner control system wherein each burner unit -oi the system acts periodically to govern the fue] supply to the burners.

Another object is to provide a multiple burner system wherein a control impulse the continuity of which governs the operation of all of the burners is made up of a related series of short control impulses originating successively in the different burners oi' the system only during nor mal or safe operation of such individual burners.

Other objects and advantages will become sipparent from the following description, taken in connection with the accompanying drawings, in which:

Fig. 1 is a fragmental vertical sectional view taken through a fuel burner adapted to be controlled in accordance with the present invention, the view being taken along the line I--l of Fig. 6;

Fig. 2 isan enlarged sectional view of the progressive detector switch utilized in our new control system, the view being taken along the line 2 2 of Fig. 5;

Fig. 3 is a view showing the progressive detector switch and the ignition distributor of the present invention, the ignition distributor being shown in central section;

Fig. 4 is a sectional view of the ignition distributor taken along the line 4-6 of Fig, 3;

Fig. 5 isy a sectional view of the progressive detector switch taken along the line 5 5 of Fig. 3;

Fig; d is e. front elevational view showing a battery of eight heaters adapted to be controlled in accordance with the present invention;

Fig. 'l is a diagrammatic view illustrating the control of the multiple heater system of Fig. 6 in accordance with the present invention; and

Fig. 8 is a wiring diagram illustrating a part of the control system of Fig. 7.

In the form chosen for disclosure herein the invention is embodied in a multiple unit `lourner system lil, which, as illustrated in Fig. 6, oomprises a battery of eight similarly formed heater units l l, arranged side by side, and having indiu vidual fuel burners l2 constructed as shown in Fig. l. The burners i2 are supplied Jfrom a conimon fuel source such as a main gas supply line i3 and all the burners are controlled by a cornrnon control system such as that illustrated diagramlnatically in Fig. 7.

The heater units Il and their fuel burners i2 may be of any preferred type, such as the gasred type illustrated in detail in Fig. l. In this formI each heater il has its combustion chamber I5 merging at the rear end of the unit with a return llue or mixing chamber i6, the fuel burners l2 being positioned to discharge the fuel into the forward end of the combustion chamber l5. Each burner l2, as herein shown, is associated with a venturi il formed from refractory ruaterial within a supporting sleeve i8, and by means of bolts lil hetween the sleeve lli and the wall of the combustion chamber l5, the venturi isI secured in an operative relation on the lor- Ward end of the combustion chamber.

On the outer end of the Venturi sleeve I8 the various parts of the burner assembly are mount-- ed by means of a hollow mounting casting 2i this casting being in the general form of a. truncated cone and having a flange 2l at its larger end through Vwhich bolts 22 pass to secure the casting 2U to a flange 23 at the outer end of the Venturi sleeve I8. At its other or outer end the casting 20 has a central sleeve 24 through which a main fuel discharge nozzle 25 projects so as to discharge fuel longitudinally toward the adjacent end of the venturi Il. The sleeve 24 is carried by a spider 2B so as to provide for the entrance of an annular stream of air about the nozzle 25, such air supply being controlled by an adjustable baille plate 21. Additional air may enter the venturi through an annular slot 28 formed between the flanges 2l and 23 by placing spacer collars 29 on the bolts 22 between said flanges. Gas is supplied to the nozzle by a pipe 30 leading from the common gas line I3, a valve 3l preferably being included in the pipe 30. At its lower end the pipe 8U has an angle 32 which through a pipe 33 discharges the gas into a mixer 34. The mixer 34 has an upper air inlet governed by an adjustable valve plate 35, and the mixture of gas and air is discharged downwardly through the tapered connector 38 and an elbow 31 to the nozzle 25.

In the preferred form shownl herein, each burner unit I2 is equipped with means for igniting the fuel flowing from the main fuel nozzles 25, this means being shown herein as comprising an electrically ignited pilot burner 40 which projects it flame, as indicated at 4I, laterallyinto the flame zone 42 of the main fuel nozzle. Asherein shown the pilot burner 40 is mounted in an angularly-related sleeve 43 formed on the mounting casting 20, the burner 4I comprising a burner tube 44 having a flange 45 intermediate its ends whereby the tube 44 is secured to the anged outer end of the mounting sleeve 43.

In the present burner installation, fuel gas is supplied to each pilot 4U from a common pilot fuel supply line 46 through individual branch pipes 4l, each of which includes a manual valve 48 as shown in Fig. 6.

The pipe 4l is connected to a nozzle 49 which discharges longitudinally into the reduced outer end of the burner sleeve 42. On the sleeve 42 an internally threaded hub 50 is formed outwardly of the flange 45 to receive a spark plug 5I by means of which the gaseous fuel within the burner sleeve 42' may be ignited. rlhe resulting combustion of the fuel is supported by air which enters through a plurality of small ports 52 formed in the sleeve 42. A

In association with each of the burners I2 of the present illustrative installation, safety means is provided 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, we have shown herein a dame detecting device 55. 'I'his particular safety detecting device 55 comprises a hollow mounting member 56 secured by means of a threaded nipple 56 on an angular sleeve 51 on the mounting casting 2I so that an insulated electrode 58 carried by the member 56 projects through the sleeve 5l and into the common zone of the main flame 42 and the pilot flame 4l. Preferably the electrode 58 is replaceably mounted in an insulating structure 5S clamped permanently within the mounting member 58. With this construction either flame may serve as an electrical conductor to complete a circuit to ground through the insulated electrode 58, and this circuit may therefore be utilized as a means to detect the presence or absence of the desired flame in the combustion chamber I5.

In carrying out the objectives of the present invention, the main burner fuel line I3 and the pilot fuel line 4G are both fed from a common source I3' (Fig. l) and each is provided with normally closed valve means whereby to shut olf the fuel flow to all of the pilot burners or main burners under the governing action of our novel control system. As indicated in Fig. '7, the main fuel line I3 has a normally closed valve 60 therein adapted to be opened only during energization has a similar valve 32 similarly operated by a solenoid 38.

When a battery of two or more heaters I2 is to be employed, it has heretofore been necessary to duplicate, for each heater, the various ignition and control elements ordinarily used with such individual heaters, while in accordance with the present invention such duplication is avoided except as to the detecting means of the control system and the spark plugs or equivalent means of the ignition system.

Furthermore, the present system is such that opening of the main fuel valve 60 lis dependent upon the existence of a pilot flame in each burner I2 of the system, and hence it is impossible for an operator to flood any of the heaters with the large quantities of unignited fuel which would otherwise be supplied to a combustion chamber having a faulty pilot.

To this end the present invention provides for operative interconnection of the various manually operable control elements whereby any particular operation in the burner-starting sequence is rendered dependent upon the actuation of the manual control elements in the proper sequence and is also rendered dependent upon proper functioning of several elements of the apparatus. Thus the electrical power for the various elements herein shown, in Fig. '7, is taken from leads L1 and In which are connected in series through the such other operative elements, such as relays and control switches, as are to be used in association with the heating system, so that power reaches a main switch only when the preceding electrical eleof its actuating solenoid 6I, while the pilot line 75 ments are properly energized.

Under such conditions. closure of the main switch 65 energizes wires Le and L4, which may include fuses 66; and between the wires L3 and L4 an indicator light 6l is preferably connected to indicate visually the presence of power in these leads.

When the indicator light 5l shows the presenceA of power in leads Le and L4, a manual control element such as push button 68 is depressed to start the pilot burners 40 of the several burners I2. This starting operation includes the 'opening of the pilot fuel valve 62, which opening is attained through energization of the solenoid 63 thereof. Hence, the actuation of the push button 68 operates to close a normally open switch 69 to connect the lead L4 to a circuit to one terminal 63 of the solenoid 63, the other terminal 63" of the solenoid 63 being connected by a wire 70 to the lead L3. As herein shown, this circuit from the switch 59 comprises wires 'II and I2 to a stationary contact an ignition transformer 80, since one end of the primary winding of the transformer is connected by a wire 8| to lead La, while the other end of the primary is connected to the wire 1I by a wire 82. In the system herein shown a single transformer 80 of relatively small size is utilized to energize the spark plugs 5I of all of the burners I2, this end being accomplished by applying the output potential of the single transformer 35, successively, to the several spark plugs in the general manner and by means of apparatus substantially like that shown and claimed in co-pending application Serial No. 223,658, tiled August 8, 1938, now Patent No. 2,212,352, patented August 20, i940. This apparatus is shown in detail in Figs. 3 and 4 of the drawings, and takes the form of a distributor device 85 mounted on and driven by an electric motor 88. Preferably the distributor device 85 has a mounting plate 81 having an axial sleeve shaft 88 rotatably mounted therein. The sleeve 88 is connected at 80 to the motor shaft 88. About the lower end of the shaft 88 a housing 8| surrounds the connection 80, the housing 8| being secured to the motor housing by screws 82 and the mounting plate being secured to the housing by screws 83. n the other or upper end oi' the shaft 88 a radial distributor-arm 94 of insulating material is mounted and keyed for rotation with the shaft, the arm 84 having a sleeve portion acting as an external support about the projecting end of the sleeve 88.

A distributor cap 85 which houses the arm 94 is ilxed to the mounting plate 8'I by screws 98, and in the cap 85 a plurality of insulated contacts 98 are mounted at circumferentially spaced points so as to be successively engaged by a wiper contact 99 mounted on the end of the distributor arm 8l. On the upper face of the arm 84 is a spring contact |00 which is located on the axis of the shaft 89 so as to engage a stationary contact IM on the inner face of the cap 05, and by means of a wire |02 this contact mi is connected to one side of the secondary coil of the transformer 80. The other end of the transformer secondary is grounded at 03.

Thus when each contact 98 of the distributor t5 1 is connected to one of the spark plugs 5|, as inn dicated by wires i104 in liig. '7, rotation of the distributor arm Se by its motor B6 acts tri-energize the spark plugs 5| in rapid succession, and each plug is energized once for each 'revolution of the shaft 89. With the distributor arm 94 rotating at motor speed, a rapid succession of igniting sparks is created at each plug without placing excessive load on the transformer.

As hereinbefore described, the depression of the push button 68 opens the pilot gas valve 62 and energizes the ignition transformer 80; and, in addition, the motor 86 is started so as to cause the spark plugs 5I to be energized in rapid succession and thereby light the pilot burners 40. in Fig. 7, the motor-starting circuit comprises a wire |05 leading from the wire 16 to one of the terminals of the motor 86, and a wire |06 from the other rnotor terminal to the lead La.

When all the pilot burners 40 have been lighted I control of the motor 86 with the result that unless I the vmotor and all of the pilot burners are operating properly, the main fuel supply to the main burners cannot be turned on. Thus the primary safety control contactor 14 serves as conditioning means for a secondary magnetic contactor I0 which serves as the control means goveming the opening and closing of the main gas valve 60. Such actuation of the contactor I4 opens the circuit 13-15 so that there can be no feed of current to the primary of the transformer As shown 80 after the push button 88 has been released, with `the result that the ignition means does not operate after such release of the push button. The contacter III has normal open stationary switch contacts and ||2 adapted to be closed by a bridge contact ||2 carried by the armature I I4.

They contact I|| is connected by wires Il! and I8 to one terminal o'f the main valve solenoid 6|, while wires ||1 and ||8, in series, connect the other terminal to the line In, so that when the contacts III and ||2 are bridged and the contact ||2 is connected to line L4, the main fuel valve will be opened. Thus the initial opening of the main fuel valve, as well as the maintenance of this valve in its open position is rendered dependent upon energization of the contact ||2 from the line L4. When the contact ||2 is thus energized,A as wiil presently be explained, the coil ||9 of the contactor H0 may be energized by momentary ciosure of a normally open push button switch |20. The switch |20, which forms a shunt circuit around the switch ii|| i2, has one contact iti connected by wires 622, |23 and I 2 to the contact I I2, while its other contact U25 is connected at the junction of wires ||5 and H6. From this junction wires |21 and |28 carry the circuit to one end of the coil I I8, the other end being connected by a wire |28 to the Wire |I8. Hence by closure of the push button switch |20 the contactor ||0 is energized to close'the contacts iii-H2 and this closure of contacts III- it ,establishes a holding circuit which maintains the circuit to the main vat/'e solenoid @i so long as the contact ii 2 remains energized. The closure of the contacts Iii-itil is preferably indicated visually by an indicator iight it@ connected across the wires Iii-mi2?.

The required energization ci' the contact i' i2 is, during normal opera-tion of the system, controlled bythe contacter ifi, while the contacter it is, dur ing such norrnai burner operation, controlled jointly by all of the detectors 55 and the operation oi the motor 86. The initial closure or energica' tion of the contacter it must, however, talee place under the controi and during the depression of the control button To this end, the contactor coil iii has one of its ends connected by a wire |32 to the wire |06 which connects with lead La. while its other end is connected by wires |33, 34, |23 and |35 to a stationary contact |36. A bridge Contact or switch member iti associated with the push button 60 acts to complete a circuit between the contact |36 and a second stationary Contact |38 which is connected by a Wire H39 to a Wire 640. As will be hereinafter explained, this wire is energized from the line Le during proper operation of the motor il@ and all oi the pilot burners 40, so that under such proper operating conditions, the continued closure of switch it? energizes the coil I3I of contacter 14 and moves its armature I 4| upwardly, as viewed in Fig. '1.

When the contactor I4 is thus energized, a

holding circuit from the wire |40 to lead La isl established. This is accomplished through a contact |42, carried by the armature |4i-in insulated relation to the contact l5, and connected to one end of the wire |40. The contact |42, when the'armafure |4| is actuated, engages a stationary Contact |43 which is connected b v a wire |44 to the juncture of Wires |33 and |34, thus establishing the desired holding circuit through the wire |33 through the coil |3I and wires |32 and |06 to line L3.

Closure or energization of the contactor I4 also establishes a running circuit to the motor 86 and pilot solenoid 63 by engagement of the contact 15 with a contact |45, this contact being connected by a wire |46 to the wire |36. Preferably the arrangement is `such that the contact 15 engages the contact |46 substantially simultaneously with orprior to being disengaged from the contact 13, thus insuring that there is no undue interruption in the supply of fuel to the pilot burners or current to the motor 66. This is common practice in the art and may be accomplished, for example, by the use of make-beforebreak contacts cr other equivalent expedients,

As hereinbefore described, each electrode 66 of the detecting devices 55 cooperates with a main flame 42 or a pilot flame 4| to form an electrical control circuit, and in accordance with the present invention the several detecting devices 55 are arranged to cooperate with a central or common control means, such as that which has been described, so that all of the burners i2 cooperate in the exercise oi' a governing iniluence on the central control means. To this end, the invention provides means whereby each electrode or detector circuit operates periodically as the ultimate governing control of the burner system', and the several electrode circuits operate in .succession to produce a continuous governing action upon the central control means. In the preferred form this cooperative governing action of the detecting means of the several burners is attained through the use of a progressive or cyclic detector switch i930 which places each detector 55 periodically in sole governing control of the central control means. Hence, if any detector circuit during its period of sole governing control indicates the absence of a flame in the associated burner i2, the central control means acts to shut down all of the burners oi the system.

rI'hus as shown diagrammatically in Fig. 7, the progressive detector switch l50 has a rotatable shaft |59 carrying a' wiper arm |52 which establishes Contact successively with a plurality of insulated contacts 263. Each contact |53 is connected by a wire to the electrode 56 of one of the detector devices 55 so that when the wiper arm |52 is in engagement with a particular contact i555, a darne from the associated pilot burner 60 (or main burner 25) will establish an electrical circuit from the wiper arm to the connected gas supply lines i3 and 46, these gas lines |3 and 46 being grounded in the control circuit.

The circuit thus established is utilized, in the present instance, to govern the energization of the lead wire i150 and thus control the contactors 10 and ii0, and such governing action is attained through a self-restoring relay mechanism indicated at i60. This relay mechanism |60 is preferably constructed as shown in Fig. 8, and in order to attain sensitivity of control this relay mechanism employs a grid-controlled therrnionic amplifier tube 200 which operates to control vthe supply of energizing current to a magnetic relay 20|.

With this particular relay, a wire |6| from the wiper arm i52 is connected to terminal |63, while a ground wire |64 from the relay cabinet is connected to the gas supply pipe 46, and these connections act in conjunction with the wiper arm |52 and any one of' the detectors 55 with which it is connectedy to supply control or grid potential to a grid-controlled thermionic amplifier tube 200.

As shown in Fig. 7, terminals |61 and |66 of the relay cabinet are connected by wires |66 and |10 to the leads La and L4, and the wire |10 has a branch lead |1| to the terminal |66. Thus the terminal |66 is connected to lead L4 and the contactors 14 and ||0 may be energized when a circuit is completed from the wire to the terminal |66,

To this end the relay switch 20| has its one stationary contact 202 connected by a wire 206 to the terminal |66, while its other contact 204 is connected by a wire 205 to a terminal |65, and means is provided forming a circuit connection from the terminal |65 to the wire |40. Preferably this circuit connection includes a normally open centrifugal switch |15 operated by the motor 86. 'I'he switch |15 has one contact |16 to which the wire |40 is connected, and a second contact |11 connected by a wire |16 to the terminal |65, and a centrifugally actuated bridging element |16 which operates to connect the contacts |16 and |11 when the motor 66 attains its running speed.

As herein shown, the progressive detector switch is driven from the motor 86, and it is for this reason that the running circuit for the motor is provided through contacter 14. Hence, during closure of the contacter 14 the detector switch |50 is constantly rotated to place the several detector circuits successively in sole controlling relation to the relay |60. Since the absence of a flame in any particular one of the burners i2 acts to break the detector circuit of that burner, the detector switch in its periodic association with this particular burner will fail, during such association, to transmit energizing potential of the required polarity to the grid terminal |63 ol' the relay |60. When this takes place the circuit is such that no plate current will be fed to the associated relay 20| so that this relay will open and break the circuit between terminals i65 and |66. Thus the holding circuit |18|15|40|62|43|44|33 through the coil i3| of the contactor 14 is broken so that the contactor 14 is released and moves to its open position. This breaks the circuit to contact ||2, and hence the holding circuit to the contactor I i0 is broken. Hence, the solenoid 6| of the main gas valve is deenergized so as to shut off the flow of the main fuel through the line I3.

This desired functioning of the apparatus is attained through thecircuit shown in Fig. 8, which will for present purposes be-considered as having its electrode terminal |63 connected through the progressive detector switch |50 to one of electrodes 50. The control tube 200 is herein shown in such a circuit that grounding or improper connection of the electrode 58, or of other sensitive elements of the circuit, will act to cause the relay switch 20| to open, and thereby insure proper shut down of the burner system not only upon flame failure but also upon failure of the safety detector system` The illustrated tube-circuit of Fig. 8 embodies a transformer 205, the primary 205 of which is connected by wires |61' and |68 across power supply terminals |61 and |68, while three similarly positioned secondary windings 206, 201 and 206 of substantially the output indicated are provided from which the tube 200 is powered. The tube 200 is of the type having two triodes within a single envelope (such as the commercial type 6N1), one triode being used as a primary control or amplifiergoverning the output of the other triode which energizes the actuating coil 2|0 of the relay 20|. Both triodes of this tube are of the zero bias type wherein current flows in the plate circuit while there is a zero bias on the grid or a positive bias on the grid, and plate current is cut oi only when the grid has a. negative bias. Since the tube is herein powered by alternating current, we will describe the operation during the operative cycle of the triodes, that is, during that portion of the current alternation when the plate is positive and the cathode negative.

Broadly considered, the safety circuit of Fig.` 8 is such that its elements are normally biased so as to prevent flow of alternating current to the relay 20|, and actuating current for the relay is supplied only when an abnormal biasing of the tube elements is caused by the presenceof a ame. Thus the electrode terminal |63 is connected by wires 2|| and 2| to the first grid Gi so that a circuit formed to the electrode 58 by a ilame may serve to complete an energizing circuit to the grid G1. To this end a circuit from ground, as at 2|2, is provided through a wire 2|3, a resistor 2| 4 of the order indicated in Fig. 8, a wire 2|5 to one end oi the coil 2|0, and a wire 2|6 to the upper end oi. the secondary 208, the lower end of which is connected by wires 2|8 and 2|9 to the common cathode C of the tube. This cathode C has a conventional heater circuit not herein shown. The plate P1 of the first triode is connected by wire 22| to the upper end of the secondary 206, the lower end being connected by wires 222 and 222 and a resistor 223 of the order indicated to the wire 2|0, thus providing the plate-cathode circuit for the iirst triode of the tube.

Bearing in mind the similar positioning and winding of the several transformer secondaries, and the fact that for present purposes the description is limited to that portion of the alternating cycle when a positive potential is applied to the plate and a negative potential is applied to the cathode, it will be evident that the bias as between plate P1 and C will be such as to normally cause current flow in the plate circuit of the first triode. In this connection it will be noted that the shielding terminal |62 is connected to a wire 2|1 to the cathode circuit at the juncture of wires 2|8 and 2|S, and that the wires 2|1 and 2|| are connected by a resistance 2 i1 and a parallel capacitance 2|1", these being of the order indicated in Fig. 8. IIfhus the grid G1 normally has no power or biasing connection so that current normally flows as above described in the plate circuit of plate Pi. This plate current of the circuit from plate P1 does not, however, actuate the coil relay 20|, the circuit being around the coil 2|0 as follows: plate P1, wire 22|, secondary 206, wires 222 and 222', resistance 223, wire 2|6, secondary 208 and wires 2|8 and 2|9 to the common cathode C. In this circuit the secondary 2 06 supplies a voltage of approximately 185 volts, while secondary 200 supplies a voltage oi' approximately 70 volts.

The plate current thus flowing in the plate circuit of plate Pi provides a negative biasing potential for the second triode of the tube 200, this potential being applied to grid G2 by a wire 22| tapped into the iirst plate circuit at the juncture of wires 222 and 222'.

When this negative bias on the grid G2 is removed, the circuit from plate P2 is such as to pass plate current to the relay coil 2 i 0 to actuate the relay, this circuit from plate Pz being provided by a wire 225 to the upper end of the 200 volt secondary 201, and a wire 22B from the lower end oi' secondary 201 to the upper end of the plate P1.

relay coil 2|0. The lower end of coil 2|0 has a circuit to the common cathode C through wire 2|6, secondary 208 and wires 2|8 and IIS.

When the negative bias provided on the grid G2 is removed as will hereinafter be described, the plate Pz will, during half cycles of the alternating current, be positive, while the cathode C `is negative, and hence plate current will flow in the second plate circuit through the relay coil 2|0. The relay 20| will therefore be closed.' In this action a condenser 221, of the order indicated, connected across the coil 2|0 between wires 2|5 and 2|6, acts to smooth out the half cycle rectified current supplied to the coil 2|0.

With the circuit thus provided the presence of a name between the grounded fuel nozzle and the associated electrode 5B serves to apply a negative potential to the grid G1 so as to stop the iiow of plate current in the circuit from. plate P1. Such negative bias of the grid G1 is caused by the high resistance of the flame in the Gi-cath-` ode circuit, which in combination with the ca pacitance in the circuit causes the phase relationship in the circuit to grid Gi to approach a phase opposition relationship. As a result the negative cycle ci the alternating current is applied to the grid Gi at the time the plate P1 is positive, with the resultthat no current flows in the circuit of plate P1.

When a sensitive relay of this character is' employed the various wires such as wires |54 and |6| are shielded as indicated fragmentally at |62 and the shields are connected to terminal |62. This terminal |62 is connected internally of the relay housing |60 to the cathode element of the amplifier tube by means of a wire 230. A grounded shielding is also used on all high tension leads which are in close proximity to the detector circuits, such as the wires |04 and |02, and the lead |02 also has a conventional suppressor associated therewith to prevent undesired feedback currents.

Failure of the flame serves, of course, to remove the negative bias on grid Gi so that plate current flow is reestablished in the circuit of Such plate current ilow instantly applies a negative bias to grid G2 so as to stop the flow of the energizing current in the circuit of plate Pz through the relay coil 2 I0.

With this circuit the various short circuits or grounds which would tend to render thesystem unsafe act to stop the flow of plate current to the relay coil 2|0 so as to shut down the burner system. Thus a grounding of the electrode 58, or any part of the circuit between this electrode and the grid G1 serves to short out the flame resistance. Since this resistance is vital in producing the phase shifting required to negatively bias the grid G1, the tube will be so biased as t0 prevent ow of energizing current to the relay coil 2|0.

Similarly, a short between the shielding and the grid Gi, or between the grid G1 and the cathode, or any part of the circuits associated therewith, serves to short out the capacitance 2|1 and thereby disrupt the phase shifting in the circuit to G1. A similar action results from the grounding of the circuit of grid G1.

With the release of the main safety contactor 14, the running circuit to the motor 86 is broken, and the holding circuit through contacts 15|45 to the pilot gas solenoid 63 is broken. Hence, no

fuel can flow to either the pilot burners or the main burners of any of the heaters, and the burner system cannot be placed in operation again until the sequence of manual starting operations is properly performed by the operator.

To insure complete release of the several relays wheny there is a flame failure in any one of the burners I2, the progressive detector switch |50 is so constructed, and is rotated at such a speed, that each detector circuit remains in sole governing control for a time interval sufficient to permit the requisite releasing movement of the relays in the event that the absence of a flame is detected by the sensing element 55. To this end, the detector switch 50 is driven at a reduced speed from the motor 86 by a conventional speed reduction gearing |80 which has an output shaft |8| as shown in Fig. 5. A housing |82 is mounted in xed position surrounding the projecting end of the shaft |8|, and on the open end of the housing a base plate |83 is secured by screws |84. The drive shaft i| of the switch |50 is shown in Fig. 5 as being of a hollow form surrounding the shaft |8| and fixed thereto by a set screw |85. On the end of the shaft |5| which projects through an axial opening |85 in the plate |83 the wiper arm |52 is mounted by means of a sleeve |8`| and key |88, the arm being formed from an insulating material. At the endthereof the arm |52 has a, resilient metallic wiper contact |90 which in the rotation of the arm |52 successively engages the contacts |53. An insulating cover |9| is mounted on the plate- |83 by screws |92, and by means of metallic studs |93 projecting inwardly of the cover from individual connecter sockets |94, the arcuately faced metallic contacts |53 are supported for such engagement by the wiper contact |52.` The wires |54 are inserted into the connector sockets |94, which are constructed as shown in Fig. 3. A similar connector socket |95 receives the wire |6| to form an electrical path to a central internal contact |96 within the cover |9|, and a spring contact |91 connected to the wiper contact |90 engages the contact |96 to complete the circuit to the wiper contact |90.

While the speed of rotation of the detector switch |50 may be varied considerably, it has been found that with the number and type of burners herein shown, and with the contacts of the switch |50 constructed and related as herein shown, the present safety control system will operate to prevent unsafe conditions iri all of the burners when the switch |50 is operated at what might be termed a relatively slow speed. Thus the speed reducer |80 is so constructed and related to the motor 8B as to rotate the switch |50 at a speed of approximately ten revolutions per minute (10 R. P. MJ. This speed may be varied in accordance with the nature of the burners or the particular installation so that each individual burner is checked by the switch |50 at sufciently frequent intervals to prevent accumulation of dangerous quantities of unbumed fuel in the combustion chambers thereof.

In order that the relays and other operating parts of the present system may be controlled by operating or control currents, applied in accordance with standard practice, thereby to permit the use of relays and other parts of a standard commercial construction, the progressive detector switch |50 is preferably so constructed that during normal operation thereof potential is continuously applied to the grid terminal |63. This end is attained by so constructing and relating the stationary contacts |53 and the wiper contact |90 that between the periods of sole governing control of the successive detector circuits. the two adjacent contacts |53 are simultaneously engaged by the wiper contact |98. The particular construction employed in this connection is best illustrated in Fig. 2 wherein the contacts |53 are shown as being of relatively great arcuate length so'as to leave but a slight space Y between adjacent contacts. With this construction the wiper contact |90 is provided with a contact portion |90' of sufficient length to bridge the slight space between adjacent contacts |59. Hence the wiper contact |90 as it approaches the end of one contact |59 makes circuit with the next contact |53, with the result that the control grid G1 of the relay mechanism |60 is continually biased in such a manner as to enable the fuel-supply to be maintained during the, existence of proper combustion conditions in all of the burners 2.

It is, of course, obvious that during those periods in which the wiper contact |90, Figs. 2 and 7, bridges two adjoining segments |59, the effective flame resistance in the flame detecting grid circuit of the tube 200, Fig. 8, may decrease due to the fact that two flame paths are electrically connected in parallel. The apparatus is so designed, however, that such reduction in the effective fiame resistance does not affect the bias on the grid Gi sufiiciently to cause any appreciable flow of current through the tube 200 from the'cathode C to the plate P1. Hence, under normal operating conditions, the fuel supply continues uninterruptedly irrespective of the position of the wiper arm |52, Fig. 2, and it is only when there is flame failure or an actual shortcircuit, or stoppage of the distributor motor Il, that the system automatically shuts` down as above described.

The control circuit herein shown is such that the burner system continues in operation so long as pilot flames exist in all of the combustion chambers, but it will be evident that in someinstances the pilot valve 53 might be shut off after the main burners have been started and that the detectors 55 and the progressive detecting switch |50 would continue to act as a safety means to stop the burner system upon failure of the main flame in any one of the burners.

From the foregoing description it will be apparent that the present invention provides a control system for multiple burner installations whereby expensive duplication of control equipment is avoided. Moreover, the present control system is such that completion of the starting operation is dependent upon proper operation of the pilot burners, and hence safety of operaation is insured.

While we have illustrated and described a selected embodiment of our invention it is to be understood that this is capable of variation and modication and we therefore do not Wish to be limited to the precise details set forth but desire to avail ourselves of such changes and alterations as fall within the purview of the following claims:

We claim:

1. In a multiple heater system having a plurality of pairs of burners each pair of which includes a main burner and a pilot burner, each pair of burners being associated with a combustion chamber, the combination of a common automatic governing means for starting all of said main burners and for stopping the operation of all of said main and pilot burners, and a sensing device associated with each of said combustion chambers and each operable to detect the presence or failure of a flame in the combustion erating with a series of arcuately arranged conchamber with which it is associated, individual detector circuits for each of said sensing devices, a progressive detector switch operable to make circuit witli 'said detector circuits in predetermined timed succession, a motor for actuating said detector switch, a normally open safety switch associated with said motor for closure during operation of said detector switch by said motor, and an energizing circuit through which said common governing means may be actuated to start said main burners, said energizing circuit including said safety switch and being jointly controlled by the progressive action of said detector circuits. v

2. I n a multiple burner control system for use with a burner system having a plurality of pairs of associated main and pilot burners, a plurality of detector elements adapted for operative individual association with the individual pilot burners of such a multiple burner system, a main control mechanism for starting all of the main burners of such a multiple burner system, an energizing circuit for operating said main control mechanism to start said main burners and including a common lead Wire, a normally open safety switch in said common lead, and a progressive detector switch, a motor for driving said progressive detector switch, said motor being operable to close said safety switch during operation of the motor, a plurality of stationary contacts forming part of said detector switch and each having a lead wire connected to one of said detector elements, anda movable contact forming part of said detector switch and connected to said common lead, said movable contact being driven by said motor and being operable in its movement to place said common lead wire successively in circuit with said stationary contacts.

3. In a heating system having a plurality of fuel burners, fuel supply means for said burners, sensing devices each associated with a respective burner for sensing the presence or absence of a name in such burner, automatic means governing said fuel supply means, sequencing means normally operating to place said automatic means sequentially under the control of said sensing devices, said automatic means responding to a flame failure detected by any of said sensing devices to disable said fuel supply means, and safety means controlling said burners and operatively related to said sequencing means for preventing the admission of fuel to said burners whenever' said sequencing means is not operating.

4i. in a heating system having a plurality of fuel burners, electrically operated fuel supply means for said burners, sensing devices each associated with a respective burner for detecting the presence or absence of a name in such burner, automatic means governing said fuel supply means, sequencing means normally operating to place said automatic means sequentially under the control of said sensing devices, said automatic means operating in response to a flame failure detected by any of the sensing devices to interrupt the supply of fuel to said burners, and a centrifugal switch controlled by said sequencing means and effective to prevent said fuel supply means from supplying fuel to said burners when said sequencing means ceases operating.

5. In a multiple heater system having a plurality of fuel burners, sensing devices each associated with a respective burner for detecting lack of combustion of the fuel in such burner, a detector switch comprising a rotary wiper cooptacts, means for driving said wiper rotatively to successively engage said contacts, means affording a plurality of normally effective detector circuits, each of said circuits' including a particular one of said contacts and being controlled by a respective sensing device to become ineffective when such device detects lack of combustion in the associated burner, automatic means governed by said detector switch and responding when said wiper is engaged with .i contact included in an ineffective detector circuit to prevent operation of said burners, and a centrifugal safety device operated by the driving means for said distributor switch and effective to prevent operation of said burners when said wiper is rotating at less than a'predetermined Speed.

6, In a multiple heater system having a plurality of pilot Iburners and associated main burners, valve means regulating the admission of fuel to said pilot' burners, other valve means regulating the admission of fuel to said main burners, electrical ignition means for said pilot burners, a first manually operable means controlling said pilot valve means and said ignition means and' effective when operated to cause fuel to be admitted to said pilot burners substantially concurrently With the energization of said ignition means, governing means operatively associated with said pilot burners and effective in response to the establishment of flames in all of such burners to control said pilot valve means for maintaining the supply of fuel to said pilot burners independently of said first manually operable means, said ignition means remaining` under the control of said rst manually operable means, and a second manually operable means controlling said main valve means.

7. Anapparatus as set forth in claim 6, in which said governing means is adapted to prevent said second manually operable means from being effective to admit fuel to the main burners until all of the pilot burners are lighted.

8. In a heating system having a plurality of heaters each embodying a main burner and a pilot burner, a normally closed fuel valve for said pilot burners, a solenoid operating when energized to open said pilot valve, electrical ignition means for said pilot burners, manually controlled switch effective when operated to concurrently energize said pilot valve solenoid and said ignition means, a relay, governing means operatively associated with the pilot burners and responding to the presence of flames in all of such burners to operatesaid relay, means controlled by said relay and said governing means and effective when said relay is operated to maintain said pilot valve solenoid energized independently of said switch, said ignition means remaining under the control of said switch, and manual means controlled by said governing means and operable when all of said pilot burners are lighted to start the main burners.

9. In a multiple heater system having a plurality of fuel burners, means for supplying fuel to said burners, ignition means operable to light said burners, manually controlled means for concurrently initiating operation of said fuel supply means and said ignition means, and means operatively associated with said burners and respending to the presence of llames in all of the burners to maintain said fuel supply means in operation independently of said manual means, said ignition means remaining under the control of said manual means.

10. In a multiple heater system having a plurality of fuel burners, fuel supply means for said burners, control means effective when operated to maintain said fuel supply means in operation, individual spark ignition devices for said burners, distributor means operable to successively energize said ignition devices, driving means for said distributor means, and safety means governed by said driving means for preventing operation of said control means when said driving means is not in operation.

ll. An apparatus as set forth in claim 10, in which said safety means comprises a centrifugal device mechanically connected to said driving means.

12. In a multiple fuel burner system. means for supplying fuel to the burners in the system, manually controlled means for initiating operation of said fuel supply means, electrical means effective when energized to maintain said fuel supply means in operation independently of said manually controlled means, governing means effective when in one condition to establish a holding circuit for maintaining said electrical means energized and when in another condition to interrupt such holding circuit, said electrical means being arranged to remain deenergized following interruption of said holding circuit irrespective of the subsequent condition of said governing means, sensing devices each associated with a respective burner for detecting the presence or absence of a llame in such burner, and a rotary switch operating to place said governing means in controlled relation successively to said sensing devices, said governing means responding to the presence of flames in all of said burners to assume the first-named condition 'and assuming the second-named condition in response to the absence of a flame detected by a controlling sensing device. v

13. In a multiple fuel burner system, means for supplying fuel to the burners in the system. manually controlled means for initiating operation of said fuel supply means, electrical means effective when energized to maintain said fuel supply means in operation independently of said manually controlled means, governing means effective when in one condition to establish a holding circuit for maintaining said electrical means energized and when in another condition to interrupt such holding circuit. sensing devices each associated with a respective burner for detecting the presence or absence of a name in such burner. a rotary switch operating to place said governing means in controlled relation successively to said sensing devices, said governing means responding to the presence of flames in all of said burners to assume the first-named condition and assuming the second-named condition in vresponse to the absence of a flame detected by a controlling sensing device, and a centrifugal safety device operatively connected to the movable part of said rotary switch and enective in the event said switch ceases operating to deenergize said electrical means.

RALPH J. PLEIN. ROBERT E. YATES.

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