US2519889A - Cyclic burner safety control system - Google Patents

Description

Aug. 22, 1950 c. w. CRAWFORD 2,519,839

CYCLIC BURNER SAFETY CONTROL SYSTEM Filed Nov. 28, 1947 2 Sheets-Sheet 1 Fig. I.

0 a 6 912/549 21242730 33 36 a9 4.? 4548 5/ 54.5760 45 1 Q l 5/ l n 50 I: I 40 I III] 4 [2:11 l 1 49 l I I 1 J I I- spa/7r PER/00' +mw+ so: l [AGM/G I o lam-0w POM/7'8 *1 Clinton W Cr'avvfovd,

by 5 :2. 2k

His Attorney.

ug- 1950 c. w. CRAWFORD 2,519,889

CYCLIC BURNER smwy cou'mor. SYSTEM Filed Nov. 28, 1947 2 Sheets-Sheet 2 Pig. 3.

it 16' N i: 50 $1 26%] \f 70 l 49 47 25 T62 I 68 z}? l A i J Inventor: Clinton W. Crawfofd,

His Attorney Patented Aug. 22, 1950 UNITED STATES PATENT OFFICE CYCLIC BURNER SAFETY CONTROL SYSTEM Clinton W. Crawford, Oak Lawn, 111., assignor to General Electric Company, a corporation of New York Application November 28, 1947, Serial No. 788,455

14 Claims.

ordinated conditions for igniting the fuel to start combustion. Then the igniter is shut off and the burner flame is normally self-propagating during a continued burner running period under thermostatic safety control that automatically provides for flame failure and power failure recycling and scavenging protection as well as lock-out against further automatic operation of the burner in case any combustion starting trial should fail.

The Eaton Patent 2,278,252 assigned to the present assignee, relates to an improved automatic burner sequential control of the above type and the present invention provides further improvements that although not limited thereto, are particularly advantageous for relatively high oil rate commercial or other burners where special ignition failure protection, double lock-out and after run scavenging protection are desirable.

One object is to insure safe operation of the burner by providing an improved automatic sequential control for introducing a preliminary igniter trial period into the sequence and for preventing the supplying of fuel for the subsequent burner combustion starting trial period unless the igniter functions normally during the preliminary igniter trial period.

Another object is to provide an improved double lock-out sequential burner control system effective to automatically lock-out in case of failure of an automatically lighted gas pilot or other suitable igniter to function normally during the preliminary igniter trial period as well as to lockout automatically in case combustion is not subsequently established during the normal fuel combustion starting trial period prior to the continued burner running period.

Another object is to provide for the energization of a signal lamp upon the opening of the look-out switch to indicate that a lookout of the automatic control has occurred.

Another object is to provide an improved burner control system having a cycle timer provided with sequential control elements for oper- 2 ating the burner combustion air blower for a fixed period during the time cycle and for operating the igniter and fuel supply means during a trial period intermediate the blower operating period together with automatic combustion responsive means for stopping the timer to provide a continued burner running period intermediate the fixed blower operating period provided the igniter operation is normal and combustion is successfully established.

Another object is to enable the automatic burner sequential control to provide an "afterrun scavenging period during which the air supply is continued with the fuel shut oil? to insure combustion of any residual fuel in the burner as well as to purge the fuel supply nozzle. With an oil burner this materially reduces carbonizetion and servicing.

Further objects and advantages of the invention will appear in the following description of the accompanying drawing in which Fig. 1 is a schematic perspective view of the improved sequential control system for an oil burner having an automatically ignited gas pilot for igniting the oil; Fig. 2 is a sequence chart showing the starting sequence for the cam operated timer switches in the centre shown in Fig. 1; and Fig. 3 is a simplified circuit diagram of the high voltage burner and igniter control circuits and the low voltage sequential control circuits involved in the oil burner control system of Fig. 1.

As shown in Fig. 1 the oil burner I0 is ofa conventional type having an air tube l'l projecting through the furnace wall i2 with an inner oil atomizing nozzle I 3. The combustion air is supplied to the air tube II from the blower it through conduit I5 upon energization of a suitable blower driving motor l6 indicated schematically. nozzle l3 through the oil supply pipe l9 upon energization of the electromagnetically operated oil supply control valve 20.

The gas pilot burner 22 is shown extended through the furnace wall I2 to project a gas flame adjacent the outlet of the oil burner air supply tube H and the oil atomizing nozzle 13 so as to ignite the combustible mixture of air and oil projected into the furnace. Gas is supplied to the pilot burner 22 when the electromagnetic operated pilot burner gas control valve 23 is energized and is ignited by means of the spark elec- Oil is supplied under pressure to the trode 24 connected to the high voltage secondary of the ignition transformer 25, that is energized simultaneously with the gas supply control valve 23.

The improved automatic sequential control system indicated generally by the reference character 21 and embodying the improvements of the present invention starts the operation of gas pilot burner 22 and provided gas combustion is normally established then the oil valve 29 is opened to supply oil for ignition by the gas flame. The operation of the sequential control 21 is initiated by a suitable automatic starting device 28 that may be a conventional room temperature responsive thermostat or other master controller and the gas pilot burner combustion responsive switch 29 and the oil burner combustion responsive switch 39 together with relay 3| controlled thereby cooperate with the master controller 28 in controlling the sequential operation of the burners under both normal and abnormal combustion conditions.

The burner starting cycle timer 32 is operated by a self-starting synchronous motor 33 that drives, through suitable speed reducing gearings within the case 35, the cam shaft 34 to rotate a series of sequential switch operating cams 36. 31, 38, 39, 49, 4| as well as a relatively rotatable multi-fingered stop member 42 that is frictionally driven by spring washer 43 and serves to lock out the control upon failure of either the gas pilot burner combustion or the oil burner combustion becoming established at the proper time in the starting sequence. The rotatingcams 36 to 4| inclusive sequentially operate the corresponding switch members 46 to 5| inclusive and the lock out stop member 42 can be angularly positioned to arrest the movement of the lockout switch member 53 towards the cooperating lockout switch member 54 so as to open the starting-circuit controlled thereby. The pair of lockout switches 53 and 54 are normally in circuit closing engagement and are biased to bodily move together as a unit toward the rotatable stop member 42 which thus may have one of the fingers 44 thereof received into the opening 55 formed in member 53 depending upon the angular position of the stop member 42. When any one of the fingers 44 is received in opening 55 as shown in Fig. 1, the lock out switch members 53 and 54 are then free to move together as a unit to engage the insulating spacer 58 carried by member 54 with the movable contact 51 that in turn is biased into engagement with a fixed stop 58.

An electromagnetic power failure responsive relay 83 upon energization thereof, operates the armature 6| to carry contact 62 into engagement with movable contact member 51 and thereby exert force through the insulating spacer 58 to move the lock out contacts 53 and 54 as a unit away from the rotatable stop member 42 and in this way permit rotation .by the friction drive washer 43. The combustion responsive relay 3| having its winding 85 energized under the separate and joint control of the gas pilot combustion responsive switch 29 and the oil burner combustion responsive switch 39 positions the contacts 89 and 81 to cooperate with the timer 32 and relay 69 in controlling the sequential starting of the bumers. The relay 19 serves to control the energization of the blower driving motor l8.

Operation Electric power is supplied for energizing the blower motor l6, the oil control valve 29, and the 25 and relay 18 from conventional supply lines LI and L2 while low voltage power is supplied to energize the timer motor 33 and the relays 99 and 65 from the secondary of the transformer 1|. The improved sequential igniter and oil burner control 21 is started into operation upon closure of the contacts of the master control or room thermostat 28. This will establish an energizing circuit for the timer motor 33 extending from the secondary of the transformer through conductor 15, the contacts of master controller 28, conductor 16, the contact 11 of the thermostat l9 responsive to the temperature of the oil (in case an oil preheater is used), conductor 19, contact 66, conductor 98, the normally closed lock out contacts 54 and 53, conductor 8|, the energizing winding of the timer motor 33, and conductor 82 to the other terminal of the secondary of transformer H. In this way the timer motor 33 is energized to start rotation of the cam shaft 34 to operate cams 36 to 4| and thereby close the corresponding switches 48 to 5| in the timed sequence indicated in the diagram of Fig. 2. Thus cam 36 will close contact 48, 3 seconds after the energization of timer motor 33 thereby establishing a circuit through conductors 83 and 94 for maintaining the energization of the timer motor 33 independently of the master control 28 as more clearly indicated in Fig. 3. At the 6 second point cam 4| closes contact 5| to effectively shunt or bypass both the master controller 28 and the contact 11 of the oil preheat responsive thermostat 18 as indicated in Fig. 3. At the 9 second point cam 39 closes contact 49 to energize motor relay 10 through conductors 99, 9|, contact 49, conductor H6, 98 and 96 and thereby start operation of the blower motor l8. The energizing circuit for motor l6 likewise extends from supply line Ll through conductors 90, 9|, and 92 motor l6 conductor 93 contact 94 of relay 19 and conductors 95 and 98 to supply line L2. As a result air under pressure is supplied from the blower H to the burner tube H and into the combustion chamber of the furnace H to provide a preignition scavenging action.

The operation of the gas pilot igniter 22 is started at the 12 second point upon closure of the switch 41 by the cam 31 to complete a circuit for jointly energizing the gas valve 23 and the gas pilot ignition transformer 25 with the circuit extending from supply line L| through conductor 99, the primary of the transformer 25 and the operating winding of valve 23 in parallel, conductor 91. switch 41, conductors 98 and 93 to supply line L2. The resulting opening of gas valve 23 to supply gas to burner 22 and the operation of ignition transformer 25 to ignite the gas should normally produce combustion of the gas pilot burner 22. When gas combustion is established, the resultant response of the gas combustion responsive switch 29 to close its contacts energizes relay 3|. The energizing circuit for relay 3| extends from supply line L| through conductors 99, 9|, and Hill, the closed contacts of the gas combustion responsive device 29, conductor IN, the operating winding 85 of relay 3| and the conductor I92 to the supply line L2.

Thus upon successful establishment of the gas pilot combustion, relay 3| is energized by closure of the gas combustion responsive switch 29 to open relay contact 68 and close relay contacts 81 and 68. The opening of contact 88 interrupts the starting circuit through which the timer motor 33 was initially energized and the closing gas control valve 23 and gas ignition transformer 75 o contact 61 completes a holding circuit for relay 88 that will only become eflective however upon energization of the relay. This holding circuit extends from conductor 82 through conductor I03 the winding ofrelay 88, conductors I84 and I05, the holding current limiting resistor I05 that serves to maintain the current in the holding circuit below the value required to attract the relay armature 8| against the opening bias of spring 83, conductor III! the normally closed conductor I08 of the manual reset switch III8, conductor IIII, contact 51 of relay 3| in its closed position and then by conductor I3, master control 28, and conductor I5 to the other side of the secondary of transformer II. Due to the current limiting action of resistor I06 relay 68 remains ineil'ectively energized even though the holding circuit is completed.

The operation of the blower I4 by motor I6 to provide a pre-combustion scavenging period continues until the 21 second point is reached. Thereupon as indicated in Fig. 2 cam 40 temporarily closes contact 50 in order to effect full and effective energization of relay 60 with the circuit extending from conductor 82 through conductor I83, the energizing winding of relay 50, conductors I84 and II I, switch 50 and then through conductor 8I, switch 48 and conductors 84, 83 and I5 to the other side of the transformer secondary. The resulting effective energization of relay 58 attracts the armature 8| to a position in which the limited current through the previously traced holding circuit becomes effective to maintain the relay energized under the control of the combustion responsive relay 3 I.

When armature GI is attracted relay contact 82 is carried into engagement with contact 51 and thereby completes a circuit for energizing the oil valve 28 with the oil valve energization circuit extending from supply line LI through conductor 88, conductor II3, the operating winding of the oil valve 28, conductor I I4, contact 68 of relay 65, conductor II5, contacts 62 and 51 of relay 58, conductors H5, and 88 and 98 to supply line L2. Thus the oil valve 20 is jointly controlled by the automatic combustion responsive device including relay 3!! and the gas burner flame responsive switch 28 and the voltage failure responsive relay 58 upon energization of relay 60 while the relay 3| is responsive to establishment of combustion of the pilot gas burner.

Gas pilot flame failure In case the combustion of the gas pilot 22 should Gas pilot failure lock out When the gas pilot combustion fails and no oil is admitted to the oil burner as just described, the relay 60 remains energized temporarily only during the time that contact 50 is maintained closed by cam 40. This temporary energization of relay 50 serves to move contact 51 and spacer 58 to the right and thereby bodily moved both of the lock out contacts 53 and 54 to the right so as to disengage opening 55 from the finger 44 of lock out stop member 42. This enables the stop member 42 to be rotated by the friction driving member 43 during the relatively short time that the relay 85 is energized by contact 58. Consequentlyat the end of the temporary energization of relay 58 at the 24 second point, the one of the equally spaced stop fingers 44 of the stop number 42 previously received in the opening 55 will have been rotated sufliciently into the path of movement of contact 53 to prevent the return thereof to the left when relay 80 is de-energized at the 24 second point. Consequently lock out contact 54 will disengage contact 53. When the contact spring 53 thus engages the stop finger 44, a detent 53a mounted upon the spring 53 slightly below the lower edge of the slot 55 engages the finger 44, so that no further rotation of the stop member 42 is permitted until the relay 88 is again energized. Such opening of the lookout contacts 53, 54 prevents automatic restarting of the control system. Such lock out will effectively prevent re-energization of both the timer motor 33 and the relay 88, since the master control 28 is rendered ineffective to restart the timer motor until the lock out contacts 53 and 54 are reclosed.

Whenever contacts 53 and 54 are disengaged to lock out the control, the timer 32 will continue in operation until the end of the cycle is reached and the oil burner elements, including the oil valve 20 and the blower motor I5, are deenergized. During such continuance of motor operation, however, the stop member 42 is held by the detent 53a, as described above. At the end of'the cycle, cam switch 48 opens. If the room thermostat 28 is still calling for operation of the burner, its contact will be closed, thus establishing a circuit extending from the secondary of transformer 'II through conductor I5, room thermostat 28, conductor I5, contact TI, conductor I8, contact 55, and thence through the signal lamp I25, conductor I28, conductor 8|, timer motor energizing winding 33, and conductor 82 to the other side of the transformer secondary. As a result, the signal lamp I28 will be lighted to indicate that a lock out of the control has occurred. The resistance of the filament of signal lamp I28 is such that timer motor 82 is not effectively energized even though the circuit extends through winding 33.

Oil combustion failure locl c out When combustion of the gas pilot 22 is succesfully established prior to or-during the relatively short period that relay 601s energized by the temporary closure of the cam operated timer contact 50, then the combustion responsiv relay 3I will be energized by closure of switch 29 as previously described. As a result, when relay 88 is temporarily energized by timer contact 58, the holding circuit for maintaining relay 66 energized is completed and extends through the current limiting resistor I88 and the contact 67 of relay 3| as previously described. Thus, with the voltage failure relay 80 energized and the combustion responsive relay 3I energized respon sively to the successful establishment of the gas pilot combustion, an energizin circuit for operating the oil supply control valve 20 to S ply oil for combustion is established as previously described. If, however, for any reason combustion 01' the oil should not be established before the end of the igniter operating period at the 36 second point, the oil valve 20 will bedeenergized and the control then will lock out in the following manner. When the igniter operation is stopped at the 36 second point, switch 28 will respond to de-energize relay 3| and thereby open contact II to interrupt the oil valve energising circuit. At the same time contact ll .of relay 8| will interrupt the holding circuit for relay ll. Upon the resulting de-energisation of relay ll, bothof the lock out contacts I! and Manual reset Whenever lock out of the control occurs due either to failure of the gas pilot combustion or failure of the oil combustion as described above, restarting of automatic operation of the control is effected by operation of the manual reset switch 109, preferably after the difficulties causing the lock out have been corrected; The upper reset contact Ill serves to shunt or bypass the lock out contacts 51, M as more clearly indicated in Pig. 3, with this shunt or bypass circuit extending through conductors I", III, and 8| to contact II and conductor 8| to contact 84. Thus the starting circuit for timer motor 33 is again completed upon closure of the manual reset contact Ill, and the timer starts rotation of the cam shaft 34. The manual reset contact II! is maintained closed until the three second point is reached. whereupon cam it closes contact 46, to continue operation of the timer 3!. Thereupon the manual reset switch I" must be released in order to reclose contact I08 in the holding circuit of relay 0 so that the control may function normally.

Normal burner operation Assuming that both gas pilot combustion and oil combustion are successfully established before the end of the igniter operating period at the 36 second point, a normal burner extended operating period will be produced with relay maintained energized under the Joint control of the master controller 28 and the combustion rcsponsive relay 3| since the latter is maintained energized due to closure of the oil combustion responsive switch it. Thus contact ll of relay 3| and contact '2 of relay .0 will maintain the energizing circuit for oil valve III closed, the cam actuated contact ll will maintain the motor operating relay l0 energized, and the timer motor 33 will be maintained energized until the cam operated contact ll is opened at the 43 second point in the cycle. Thereupon operation of the timer is stopped in order to provide an extended burner running period under control of master controller 28 with both flame failure and power failure recycling protection.

Power and flame failure recycling with after-run scaveno'ia If during such extended burner running period a power failure should occur, the power failure relay to will respond to open the oil valve energizing circuit. Likewise in case a combustion failure occurs, relay ll will respond to open the oil valve energizing circuit. Under either condition, the control will recycle sequentially to restart the igniter 22 and the burner II in the manner previously described but only after a scaveng- 8. suit, timer motor a a "lame and operated to provide the scavenging period upon de-energization of relay ll through a special circuit Jointly controlled by cam operated contact ll and the relay contact I that is normally closed when relay I is de-energised. This timer scavenging period operating circuit may be traced from the secondary of transformer II through conductor II, conductor ",cam operated contact ll, conductor III, the normally closed relay contact I, conductor Ill, conductor II, the energizing winding 33 of the timer II, and con ductor I! to the other side of the transformer secondary. The resulting operation of the timer 3! will maintain the blower motor I energized until the 57 second point is reached, since the blower operating relay II is maintained energized by contact 40. This insures that the forced air supply to the burner is continued after the oil valve is closed to stop combustion, thereby providing an after-run" scavenging period to purge the burner combustion chamber and nozzle and insure combustion of any residual fuel in the burner. when the 60 second point is reached, if the master controller 28 is closed, the timer motor 33 is maintained energized through the initial starting circuit as previously traced. Thus, the after-run scavenging period inherently occurs whenever relay ll isde-energized during the extended burner running period, whether the relay de-energization is due to voltage failure, flame failure, or the opening of the master control contact 28. This inherent "after-run I scavenging period is obtained due to the fact that the operation of the timer 3! is stopped intermediate the fixed period in its time cycle during which the blower operating contact 48 is maintained closed by the timer cam 38. Hence. whenever the timer is automatically restarted by de-energization of relay It, the remainder of the blower operating period inherently produces the after-run" scavenging period.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a burner control system for sequentially operating 'an igniter and supplying fuel to be ignited thereby, the combination of 'fuel supply control means having an energizing circuit, a power failure responsive relay having a switch for opening said circuit to prevent the supply of fuel when said relay is deenergized, a device having a second switch connected in series circuit relation with said relay switch, means rendering said device separately responsive to normal operation of the igniter and combustion of the fuel to close said second switch thereby to complete said circuit to supply fuel during joint energization of said relay and response of said device, and means including a timer having circuit control elements for sequentially operating the igniter for a limited period and energizing said relay temporarily duringsaid period to start the supply of fuel upon response of said device to normal operation of the igniter during said temporary energization of said relay.

2. In a burner control system for sequentially 'operating an igniter and supplying fuel to be ignited thereby, the combinationof fuel supply control means having an energizing circuit, a power failure responsive relay having a swiwh for opening said circuit to prevent the supply.

of fuel when said relay is deenergized, a device having a second switch connected in series with in: period has occurred. To accomplish this re- 15 said relay switch,'means rendering said device separately responsive to normal operation of the igniter and combustion of the fuel to close said second switch thereby jointly to complete said circuit to supply fuel upon joint response of said device and energization of said relay, means including a timer having circuit control elements for sequentially operating the igniter for a limited period and energizing said relay temporarily during said period to start the supply of fuel upon response of said device to normal operation of the igniter during said temporary energization of said relay, and means including said device for maintaining said relay energized to continue the supply of fuel upon combustion of the fuel.

3. In a sequential control system for an igniter and a fuel burner ignited thereby, the combination of fuel supply means, a power failure responsive relay for preventing the supply of fuel upon power failure, control means including an electro-responsive device separately operable upon failure of the igniter and failure of combustion for separately preventing the supply of fuel independently of said relay, said control means being responsive separately and jointly to normal operation of the igniter and establishment of combustion for maintaining said relay energized to cont'nue the supply of fuel under the joint control of said relay and said device, and means including a timer having sequential control elements for operating the igniter for a limited period and energizing said relay for a temporary period intermediate said limited period to start the supply of fuel for combustion upon response of said device to normal operation of the igniter during said temporary period.

4. A sequential control system for an igniter and a fuel burner ignited thereby having in combination an automatic control device and means for effecting response thereof to normal operation of the igniter and to combustion of the fuel, a control relay having holding means rendered effective only upon response of said control device for maintaining said relay energized upon energization thereof, a timing device having sequential control elements for operating the igniter for a predetermined period and energizing said relay temporarily intermediate said period, and burner fuel control means jointly dependent upon response of said control device and energization of said relay for supplying fuel for combustion.

5. A sequential control system for an igniter and a fuel burner ignited thereby having in combination, an automatic starting control element, an automatic control device and means for effecting response thereof both to normal operation of the igniter and to combustion of the fuel, a control relay having h'oiding means rendered effective upon energization of said relay for control by said automatic starting control element jointly with said automatic control device upon response thereof for maintaining said relay energized, a timing device started into operation under joint control of said automatic starting control element and said control device and having sequential control elements for operating the igniter for a predetermined period and energizing said relay temporarily intermediatesaid period, and fuel supply control means jointly dependent upon response of said control device and energization of said relay for supplying fuel for combustion.

6. In a sequential control system for an igniter and a fuel burner ignited thereby, the combination of fuel supply means, a power failure responsive relay for stopping the supply of fuel upon power failure, control means including a device operable both upon failure of the igniter and failure of combustion to prevent the supply of fuel, said control means being responsive to operation of the igniter and establishment of combustion for maintaining said relay energized to continue the supply of fuel-under the joint control of said relay and said device, means including a timer having automatic starting means controlling the initiation of operation of said timer and having sequential control elements for operating the igniter for a predetermined period and energizing said relay temporarily intermediate said period to supply fuel for combustion upon response of said device to operation of the igniter, and lockout means under joint control of said timer and said relay for rendering said automatic starting means ineffective upon deenergization of said relay at the end of said temporary energization thereof and at the end of said predetermined period.

7. A sequential control system for an igniter and a burner ignited thereby having in combination an automatic control device and means for effecting response thereof both to normal operation of the igniter and to combustion of the burner, a control relay having holding means effective upon response of said control device for maintaining said relay energized upon energization there, automatic means including a timing device having sequential control elements for operating the igniter for a predetermined period and energizing said relay intermediate said period, fuel supply control means jointly dependent upon response of said automatic device and energization of said relay for supplying fuel for combustion, and lock-out means under joint control of said timing device and said relay for preventing automatic reenergization of said relay upon both deenergization thereof at the end of said temporary energization thereof and at the end of said predetermined period.

8. A sequential control system for an ignition burner and a main burner ignited thereby having in combination an electro-responsive device, separate combustion responsive means for energizing said device upon combustion at said main burner or said ignition burner, a relay having holding means including said electro-responsive device and effective upon energization of said device, means for maintaining said main burner in operation upon energization of both relay and said device, a combustion starting timing device having automatic starting means and sequential control elements for operating the ignition burner for a predetermined period and energizing said relay temporarily intermediate said period, said relay and said electro-responsive device jointly initiating operation of said main burner in response to combustion at said ignition burner and said main burner continuing in operation in response to combustion at said main burner, and lockout means under joint control of said timing device and said relay for rendering said automatic starting means ineffective upon both deenergization of said relay at the end of said temporary deenergization thereof and at the end of said predetermined period.

9. In a sequential control system for an igniter burner and a main burner ignited thereby, the combination of fuel supply control means for the main burner, means including a power failure responsive relay for controlling said fuel supply control means to prevent the supply of fuel 11 when said relay is deenergized, means including a holding circuit for said relay for deenergizing said relay responsively to failure of combustion of both the. igniter and main burners, said lastnamed means including a switch for separately controlling said ruel supply control means to prevent the supply of fuel to the main burner independently of said relay and to permit said fuel supply under control of said relay in response to combustion in either of said burners, and control means including a rotary cycle timer having rotating sequential control elements, one for operating the igniter burner for a limited pe riod and another for energizing said relay temporarily during said period to supply fuel to the main bumer only after response of said switch to combustion of the igniter burner and another for locking out said control means upon deenergization of said relay at the end of said temporary energizationthereof and at the end of said period.

10. A sequential control system for an ignition burner and a main burner ignited thereby having in combination means responsive to the combustion of each burner, means including a relay for maintaining the main burner in operation after combustion thereof is started, relay holding means actuated by said combustion responsive means and eilective upon energization of said relay, a combustion starting timing device having automatic starting means and sequential control elements for operating the ignition bumer for a predetermined period and energizing said relay temporarily intermediate said period,

means jointly dependent upon response of said combustion responsive means to combustion of the ignition burner and temporary energization of said relay for starting operating of the main burner, and lock-out means having a movable control element operated by said relay and a plurality of interlocking elements operated successively by said timing device into the path of said control element for rendering said automatic starting means ineffective upon both deenergization of said relay at the end of said temporary energibation'thereof and at the end of said predetermined period.

11. A sequential control system for an ignition burner and a main burner ignited thereby having in combination a combustion responsiverelay and separate control elements for operating said relay responsively to the combustion of each burner, an electromagnetic relay having a holding circuit under control of said combustion responsive relay, means controlled jointly by said electromagnetic relay and said combustion rewonsive relay for maintaining the main burner separately in operation after combustion thereof is started, an electric motor operated timing device having automatic starting means and sequential rotary cam controlled elements for operating the ignition burner for a predetermined period and energizing said electromagnetic relay temporarily intermediate said period, means Jointly dependent upon response of said combustion responsive relay to combustion of the ignition burner and temporary energization of said electromagnetic relay for starting operation or the main burner, and lock-out means having a rotary stop member operated by said timing device and a cooperating switching element operated by said electromagnetic relay ior preventing automatic restarting of said timing device only upon deenergization at said electromagnetic relay at the end of 12 said temporary energization thereof and at the end of said predetermined period.

12. A sequential control system for an ignition burner and a main burner ignited thereby having in combination a combustion responsive relay and separate control elements for operating said relay responsively to the combustion of each burner, an electromagnetic relay having a holding circuit under control of said combustion responsive relay, means controlled Jointly by said electromagnetic relay and said combustion responsive relay for maintaining the main burner separately in operation aiter combustion thereof is started, an electrical timing device having automatic starting means and sequential control elements for operating the ignition burner for a predetermined period and energizing said electromagnetic relay temporarily intermediate said period. means jointly dependent upon response of said combustion responsive relay to combustion of the ignition burner and temporary energization of said electromagnetic relay for starting operation of the main burner, and lock-out means having an element operated by said timing device and a cooperating element operated by said electromagnetic relay having a. movable control element operated by said relay and a plurality of interlocking elements operated successively by said timing device into the path of said control element for preventing automatic restarting of said timing device only upon deenergization of said electromagnetic relay at the end of said temporar energization thereof and at the end of said predetermined period.

13. A burner control system having in combination an electrically operated cycle timer having a blower operating switch closed thereby during the major part of the cycle, means including a fuel supply control relay temporarily energized by said timer to provide a limited combustion trial period while said blower operating switch is closed, means including combustion responsive switching means for maintaining said relay energized to continue combustion after said trial period, and energizing circuit connections for said timer under the Joint control of said relay and said timer for stopping said timer to maintain said blower operating switch closed while said relay is maintained energized after said trial period and for restarting said timer to open said blower operating switch at the end of a scavenging interval after said'relay. is deenergized to sto combustion.

14. A burner control system having in combination an electrically operated cycle timer having a blower operating switch closed thereby during the major part of the cycle, a starting circuit for said timer including a master switch and combustion responsive switching means, means including a fuel supply control relay temporarily energized by said timer to provide a limited combustion trial period while said blower operating switch is closed and independently maintained energized under control of said master switch and said combustion responsive switching means upon response thereof to continue combustion after said trial period, and running circuit connections for said timer under the joint control of said relay and said timer for stopping said timer to maintain said blower operating switch closed while said relay is maintained energized after said trial period and for re-starting said timer to open said blower operating switch at the end of a scavenging interval l3 9 after said relay is deenergized to stop combustion. I CLINTON W. CRAWFORD.

' REFERENCES CITED The following references are of record in the file of this patent: I

UNITED STATESPATENTS Number Name Date 2,081,091 Kuempel May 13, 1937 Eaton Mar. 31, 1942 Number Number Switzerland Nov. 15, 1934

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