US2733759A

US2733759A - mccammant

Info

Publication number: US2733759A
Authority: US
Publication date: 1956-02-07
Anticipated expiration: 1973-02-07

Description

Feb. 7, 1956 L. H. MCCAMMANT BURNER CONTROL AND ELECTRIC IGNITION SYSTEM FOR STOVES I5 Sheets-Sheet 1 Filed July 18, 1951 z n n f 1 g 0 Q J 1 w r W B y 5 W Q w? W l W 3 I /i 7 if m H h; w V wk a K 5 I| J V 3 1 70 M #0 1 Feb. 7, 1956 1.. H. M CAMMANT 2,733,759

BURNER CONTROL AND ELECTRIC IGNITION SYSTEM FOR STOVE-S Filed July 18, 1951 3 Sheets-Sheet 2 g fiudww, A M

fl omeya 1956 L. H. MOCAMMANT 2,733,759

BURNER CONTROL AND ELECTRIC IGNITION SYSTEM FOR STOVES Filed July 18, 1951 3 SheetsSheet 3 United States Patent BURNER CONTROL AND ELECTRIC IGNITION SYSTEM FOR STOVES.

LeonardH'. McCammant, Rockford, Ill., assignor to Geo. D. Roper Corporation,Rockford,.lll.,,a corporation of Illinois Application July 18, 1951, Serial No. 237,412

7- Claims. (Cl. 158-124).

This invention relates: to a burner control and ignition system. for gas appliances, and in particular to such asystem for: igniting to top burners on a gas stove.

Itis an' object of thisinvention to provide an ignition system including a pilot burner for igniting a main gas burner andmeans for insuring that the pilot burnershall be'lighted' whenever gas is supplied to the main burner.

A further object of'this invention is to ignite an igni-' Still another object of this invention is to electrically" ignite an ignition pilot burner in response to the opening of av manually operated main shut-off valve for the top burner of a gas stove and to maintain the pilot burner lighted for a time interval after closing the main shut-oil valve.

Another object or" this invention is to provide a top burner ignition system for a gas stove which eliminates thenecessity for a constantly burning pilot burner'at the top of the-stove and which is safe and dependable in its.

operation.

Another object of this invention is to provide for auto-- matic re-ignition of the top pilot burner on a gas stove in the event that a draft of air should blow out the pilot burner flame while a top burner of the stove is on.

Another object of this invention is to provide an ignition system including an ignition pilot burner and a thermal' switch controlling the energization of an igniter for. lighting the pilot burner, wherein the construction of the thermal switch insures a quick response thereof to the pilot burner and'insures that the operation of the thermal.

switch is not ailected by the ambient temperature..

Other and further objects and advantages ofthe inven-- tion will, be apparent from the following description of preferred embodiments thereof.

In the drawings:

Figure. 1 is a top view illustratinga stove incorporatingone form of the present invention.

Fig. 2v is a; schematic view showing the circuit" diagram of this system.

Fig: 3 is a framentary view, partly in section, illustrating the. pilot burner, thermal switch associated therewith, the. igniter for the pilot burner, and the flash tubes leadingto thetop burners of the stove.

Fig. 4 is a section along the line 4-4 of Fig. 3'.

Fig. 5 is a sectional view' of the solenoid valve which controlsthe gas supply to the pilot burner.

Fig 6 is a. perspective viewof the pilot burner-and the igniter therefor in the first form of the invention.

Fig. 7 is a top view of a stove incorporating a second form of the present invention.

Fig. 8 is acircuit diagram of the form of the invention shown in Fig; 7

In the form of the invention shown in Figs. 1'-6, the ignition system is shown. in association with a conventional gas stove having aplurality of top burners 1, 2' and 3 supplied with gas through

valves

4, 5 and 6 and

conduits

7, 8 and 9 from a gas main 10. The main shut-oil valves 4, Sand 6 -are controlled manually by knobs 11, 1-2 and 13in theusualmanner. The stems'1'4, I5 and 16, whose: angular positionis controlled bythe manually actuated knobs, carry mercury switches 17', 1'8 and 19 0f conventional design. As. best seen in Fig. 2 each of these switches comprises a pair of spaeed electrodes' 20, 21 and mercurypool- 22. When one oftheknobs is rotated angularl y to open the respective main shut-off valve the mercury switch carried onthe corresponding stem is tilted" so that the mercury pool ZZbridges-the gap between the

electrodes

20, 21 to form a conductive electrical path therebetween.

A pilot burner 23 is located at the top of the stove centrally between the several top burners and is adapted toignite the same through horizontal fi'ash tubes 24,- 25 and 26. To supply gas to the pilot burner a conduit 21 is. connected to the gas main 10*and'is supplied with gas independently of the: main shut-off valves for the main top burnersr A solenoid valve 28 located at the bacle of the stove: controls the g-as supply to-the pilot' burner.

As. best seen in Fig. 5, the solenoid valve includes aninlet 29 and an outlet 30leadingto the pilot burner; An aperture 3 1 effecting" communication between the inlet and outletv of the valve is normally closed by a closure member 32, preferably of rubber. A plunger 33 controls the. position of valve closure member 32'. Under the actionv of gravity, and: of a coil spring 34 interposed between. valveumember'32 and the top 35 of'the' valve casing, valvemember 32- is normally'biased to a position where it: closes aperture 31 and shuts 01f the gas flow to the pilot burner 23. A solenoid coil- 36 surrounds the.- upper: end of a tube 33a provided with alost-motion connectionto plunger 33 by meansof a transverse pin 33b engaging in an elongated slot 330 in plunger 33. Energization of. the solenoid coil pulls tube 33a upwardly, and thuspullsplunger 33 upwardly to lift closuremember 32' ofi its. seat; Thus, energization of the" solenoid" coil opens. the valve 28 to permit gas to how to the pilot burner;

At: its lower end plunger 33 is suitably joined to a plate 37 which is united to a flexible'rubber diaphragm 38" extending across the valve housing. Plate 37 carries a tube 39: which communicates between thechambers'above and below diaphragm 38. A pin 40 extends through tube 39 to limit the size of the aperture effecting communication between the valve chambers above and below diaphragm. 39. This diaphragm assembly forms a time delay opposing immediate return ofv valve member 32 to its closed position after de-energization of coil 36,, as will appear hereinafter.

Asv best seen in Fig, 2, thesolenoid coil 36 is. adapted to be energized when. any of the.-

mercury switches

17, 18 or 19 is closed. The mercury switches are in" parallel with. each. other, the parallel combination being connected in series. with coil 36 across the 24 volt secondary of" transformer 41. The primary of the transformer is connected to conventional volt house current through plug 42'. A suitable ground connection 43 is provided for the secondary circuit which includes the transformer secondary, mercury switches 17-19, and solenoid coil 36. With this arrangement it will be seen. that when any of. the knobs 11-13 is turned angularly, to: open. the re;- spective main shut-off valve and supply gas to a top burner, the corresponding mercury switch is closed to complete the circuit to solenoid coil 36. Energization of coil 36 causes the solenoid valve 28 to open and permit the flow of gas to pilot burner 23.

As best seen in Figs. 3 and 6, pilot burner 23 includes a horizontal outlet port 44 and a vertical outlet port 45. A tube 46 extends above outlet port 45 in register therewith and is formed with a top ignition port 47 at its top. A vertical slot 48 extends from top port 47 to the horizontal outlet port 44 to form a flame path for ignition of top port 47 from port 44.

A pair of

spark ignition electrodes

49 and 50 are disposed adjacent port 44 and are adapted to pass an ignition spark transversely across the gas jet issuing from port 44, which then ignites top ignition port 47. For controlling the generation of this spark there is provided an electrical circuit including a transformer 51 whose primary is connected in the secondary circuit of transformer 41 in series with the parallel combination of mercury switches 1720.

Electrodes

49, 50 are connected across the 5000 volt secondary of transformer 51. Thus, closing of one of the mercury switches is a prerequisite to the generation of an ignition spark. The primary circuit of transformer 51 is completed through a normally closed thermal, switch 52 to the ground connection 53. Thus, an ignition spark at

electrodes

49, 50 can be generated only if switch 52 is closed.

Switch 52 is thermally responsive to heat from pilot burner 23 so as to open after ignition of the pilot burner and to close again when the pilot burner goes out. As best seen in Figs. 3 and 4, the switch includes a fixed contact 54 connected to the primary of transformer 51 and a grounded movable contact 55. The movable contact 55 is carried on a depending arm 56 which is mounted on a shaft 57 to be angularly movable therewith. At its other end shaft 57 is connected to a bimetal helix 58. The other end of the bimetal helix is connected to a transverse collar 59 which is mounted on a tube 60 rotatably mounted on shaft 57. One face of collar 59 abuts against a wall 61 which is part of the bracket assembly supporting the thermal switch. At its other end tube 60 is threaded to hold a nut 62. An annular collar 63 abuts against the other face of bracket wall 61 and rotatably receives tube 60. A coil spring 64 is under compression between nut 62 and collar 63.

The bimetal helix 58 consists of two different interconnected segments 65 and 66. The segment 65 is exposed to the flame issuing at port 44 and rotates shaft 56 angularly in response to said flame. The segment 66 of the bimetal helix 58 is shielded by bracket wall 67 from the flame at port 44. Segment 66 is of reverse formation from that of segment 65--one having the high expansion metal on the outside and the other having the high expansion metal on the inside. By this arrangement, when variations in ambient temperature occur the respective helical segments 65, 66 tend to rotate in opposite directions, resulting in no regular movement of shaft 57 due to ambient temperature changes. However, the helical segment 65 does respond directly to a flame at port 44 without opposition from the shielded segment 66, so that the shaft 56 is readily moved angularly in response to the condition of the flame at port 44.

With the described thermal switch, when gas issuing from port 44 is ignited by a spark at

electrodes

49 and 50 the flame at port 44 heats the exposed segment 65 of the bimetal helix and to cause angular movement of shaft 57. .This angular movement of shaft 57 moves the movable switch contact 55 away from fixed contact 54 to break the circuit to the igniter 49, An adjustable stop 68 limits this circuit-breaking movement of contact 55 and thus prevents continued angular movement of shaft 56 in the same direction in response to the con tinuing flame at port 44. The continuing rotation of the bimetal helix 58 is then imparted to collar 59 which rotates sleeve 60 and nut 62. Thus collar 59 rides frictionally over bracket wall 61 after the movable contact 55 has moved to this extreme of movement.

Then when the flame at port 44 goes out shaft 57 is immediately moved angularly in response to the rotation of bimetal helix segment in the opposite direction. Movable contact 55 is immediately moved the short distance from engagement with stop 68 into engagement with the fixed contact 54. After this engagement takes place further rotation of shaft 57 is prevented and any continuing rotation of helix 58 as it cools is taken up by the described slip friction clutch arrangement. In this manner, the clutch takes up the override of the bimetal helix and insures that only a very small movement of the movable switch contact 55 is required to control the circuit for the igniter in response to the condition of the flame at port 44.

An upstanding annular fitting 69 is disposed above the pilot burner tube 46 and receives the inner ends of the

flash tubes

24, 25, 26. This assembly is disposed irnmediately above top port 47 of the ignition pilot burner, so that a flame at that port is adapted to ignite gas in the flash tubes issuing from the respective top burners.

A bracket assembly 70 of any convenient form, and including the walls 61 and 67, is attached to fitting 69 by means of a screw 71 for supporting the pilot burner, ignition electrodes and thermal switch.

In the operation of this system, when one of the manual knobs is actuated the corresponding main shut-off valve is opened to supply gas to its top burner. A portion of the gas issuing to the top burner fills the corresponding flash tube, to be ignited by the pilot burner 23 and flash back to the top burner and ignite the same.

As the knob is actuated, the corresponding mercury switch is tilted to close its contacts and energize solenoid coil 36. The solenoid 36, when energized, exerts suflicient attraction on the tube 33a to overcome the dash-pot effect of the diaphragm 38 so that the valve 28 opens immediately in response to this energization of the solenoid coil and supplies gas to the pilot burner 23. In this regard it is to be noted that the pressures on opposite sides of the diaphragm 38 equalize through the bleed 39, after the valve 32 is closed, so that the initial force which must be applied to the plunger 33 to open the valve 32 is relatively small. Gas at the pilot burner issues from port 44 and from top port 47.

Thermal switch 52 being in its normal closed condition, closing of the mercury switch also results in energization of the igniter so that a spark occurs between

electrodes

49 and 50 to ignite the gas issuing from port 44. The flame from port 44 rises up along the gas path formed by slot 48 and ignites the gas issuing at top port 47. The flame at top port 47 ignites the gas in the flash tube whose top burner is being supplied with gas, and the resulting flash back in the flash tube ignites that top burner.

The flame at port 44 heats the bimetal helix to open switch 52 and break the circuit to the

ignition electrodes

49, 50. This circuit remains broken as long as the pilot burner 23 is lighted.

When the manual knob is actuated to shut off the gas supply to its top burner and extinguish the same the corresponding mercury switch is returned to its open position to de-energize the solenoid coil 36. The closure member 32 of the solenoid valve is thus free to return to its normal closed position under the influence of gravity and spring 34. However, the air within the valve chamber below diaphragm 38 exerts a dashpot effect opposing the return of plate 37 and closure member 32 to the closed position of the latter. Air bleeds slowly from the chamber below diaphragm 38 into the chamber above the diaphragm through the aperture around pin 40. The size of this aperture determines the time delay for closing of the solenoid valve 28 after de-energization of solenoid coil 36 by the opening of the mercury switch. Preferably, the solenoid valve is adjusted to have a time delay of from 15 to 30 seconds after a maintop burner is shut oil; The pilot burner therefore remains lighted for this interval of time after extinguishment of. the top burners By this provision for a. time delay in shutting ofi pilot burner 23 after the top burner is shut off a safety feature is present in the system to cover the situation where the operator turns on the wrong top. burner and discovers his. mistake right after ignition of that top burner and opening of the thermal switch 52. The operator would immediately turn oil? the mistakenly actuated. burner knob and turn on the correct one. However in this very brief interval, between ignition of the pilot burner 23. in response to turning on the wrong top burner. knob and reclosing of the top burner valve, the thermal switch will not. have. been heated sufficiently by the pilot flame at. port 44 so. that it will cool and re-close within four seconds after turning oil the top burner knob which has been mistakenly actuated. The rapidity with which the thermal switch 52" closes depends upon its temperatureit will close much more rapidly if heated long enough. by the pilot flame at 44 to have a high temperature. Therefore, the thermal switch would not be in its normal closed condition, which is necessary to energize the

igniter

49, 50, when the correct top burner knob is turned on. If the gas supply to pilot burner 23 had been shut off immediately upon turning off the mistakenly actuated top burner knob then the igniter would not be energized to re-ignite the. pilot burner upon turning on the correct top burner, and thus there would be no provision for igniting that top burner within the standard time limit. With the present system, however, the pilot burner stays on for a time interval after turning off a top burner which is: more than sutfi'cient to insure the ignition or" another top" burner turned. on irnmediately. When the pilot burner does go out it will have been lighted long enough to have heated the thermal switch sufiiciently that the latter will close quite rapidly, to condition the igniter for igniting the pilot burnerwh'en a top burner is turned on.

Also, if the pilot burner should be blown out by a draft of air through the kitchen while a top burner is on' the thermal switch will close promptly, provided the pilot burner has been on an appreciable length of time. The igniter will be energized upon such closing of the thermal switch, as long as one of the top burners is on, to reignite the pilot burner.

In the embodiment of the invention illustrated in. Figs. 7 and 8, the ignition system is designed for use with a stove having four or more top' burners and a pair of pilot burners, one for the top burners at each sideof the stove. As shown, four mercury switches 72-75 are provided, controlled by the manual knobs 76-79 which control the main shut-off valves Elk-83 for the respective top burners 84-37. A pair of pilot burner assemblies 823' and 89 are provided. Pilot burner 33 is located at the left side of the stove and is adapted to ignite

top burners

84 and 85 through the respective flash tubes 90' and 91. Pilot burner 89 is located at the right side of the stove and is adapted to ignite top. burners 86 and 87 through the

respective flash tubes

92 and 93. A single solenoid valve 28 controls. the" gas; supply to both

pilot burners

88 and 89.

The mercury switches 72-75 form a parallel combination in the secondary circuit of transformer 41. The sole noid coil 36 of solenoid valve 28 is connected in series with the parallel combination of mercury switches across the secondary of transformer 41. Transformer 41, solenoid valve 28 and solenoid coil 36 are preferably identical in construction with the corresponding, elements described in the system of Figs. 1-6.

Also in series with the mercury switches across the secondary of transformer 4th is a series combination consisting of. a pair of 12. volt ignition coils 94 and 95 in series and a pair of

thermal switches

96, 97 in parallel. These thermal switches are of the type described in corrnection with Figs. 1-6- and function in the same manner.

Ignition coil94 is positioned i'n'igniti'ng relation to pilot burner 88 and thermal switch 96 is positioned to beheated by that; plot burner in the same manner asthermal switch 52 is heatedby pilot burner 23 in the form. of the invention illustrated in Figs. 1-6. Likewise, ignition coil is positioned in igniting relation to pilot. burner 89 and thermal switch 97 is positioned to be responsive. to the heat from that pilot burner.

In the operation of this system, when any'ofthe knobs 72'-75 is actuated to supply gas to the corresponding top burner the correspondingmercury switch is also tilted to closed position. This completes the circuit for energiZaL- tion of solenoid coil 36 which opens valve 28 to supply gas to both

pilot burners

88, 89. In addition both. igniter' coils 94 and 95' are energized since both of the

thermal switches

96 and 97 are in their normal closed condition; r'loth pilot burners are ignited by'the ignition coils and heat the thermal switches to open the latter and thereby'deenergize the ignition coils. Thetop burner-which has been turned on is ignited through its flash tube from the corresponding pilot burner. Other top burners which may be turned on thereafter are ignited by one or theother of the lighted pilot burners. Both pilot burners remain lighted as long as any of the top burners is on.

The construction of solenoid valve 28 is such as to achieve the time delay described in connection with the form of the invention shown in Figs. 1-6, so that there is the safety feature that both pilot burners remain lighted for a time interval after the last top burner has been turned'ofi'l Also, if either or both pilots is blown out by a draft of air it will be promptly re-ignited when the adjacent thermal switch closes;

While there have been disclosed preferred embodiments of the present inventionit will be apparent that various changes and modifications from the describedsystems'may be resorted to without departing from the spirit and scope of the invention.

I claim:

1. A burner control system for a gas burning appli-- ance, said system comprising a main burner, a main shutoff valve controlling the supply' of gas to said main gas burner, a pilot burner in igniting relation to said main burner, a pilot burner valve controlling the supply of gas to the pilot burner and connected to receive a gas supply independent of the main shut-off valve, means responsive to the opening of said main shut-off valve for opening said pilot burner valve substantially simultaneous with the opening of said main shut-off valve to supply gas to the pilot burner, means responsive to said opening of said main shut-off valve for igniting the pilot burner, means for maintaining said pilot burner valve open, as long assaid main shut-off valve is open and time delay means preventing the closing of the pilot burner valve for a predetermined time interval after closing of said main shut-off valve' to provide a time delay for the extinguishment of the pilot burner after said main burner has been extinguished and permitting the closing of said pilot burner valve to extinguish the pilot burner after said predetermined time interval has elapsed.

2. A- burner control system for a gas burning appliance, said system comprising a main burner, a main shut-off: valve controllingthe supply of gas to said main burner, a. pilot burner in igniting relation to said main burner, a normally closed pilot burner valve connected to" receive' gas independent of said main shut-off valve and controlling the supply of gas to the pilot burner, means responsive to the opening of said main shut-off valve for openingsaid. pilot burner valve substantially simultaneous with the opening of the main shut-off valve to supply gas to the-pilot burner and for maintaining said pilot burn.- er valve open aslong as said main shut-off valve remains open, electrically energized" ignition means operative to ignite the pilot burner in response to said opening, of said main shut-oil valve, a thermal switch. positioned adja'cent the-pilot" burner and operative when heated thereby to deenergize said ignition means, and time delay means coacting with said pilot burner valve for maintaining said pilot burner valve open for a predetermined time interval after closing of said main shut-off valve to provide a time delay for the extinguishment of the pilot burner in response to extinguishment of said main burner and permitting the closing of said pilot burner valve to extinguish the pilot burner after said predetermined time interval has elapsed.

3. A burner control system for a gas stove, said system comprising a plurality of top burners, a plurality of manually operated main shut-off valves each controlling the supply of gas to a respective one of said top burners, a pilot burner in igniting relation to said top burners, a normally closed pilot burner valve connected to receive gas independent of said main shut-E valve and controlling the supply of gas to the pilot burner, means operative when a first one of said main shut-off valves is opened to open said pilot burner valve to supply gas to the pilot burner, an electrically energized igniter operative to ignite the pilot burner, circuit means for energizing said igniter upon said opening of said pilot burner valve, a thermal switch in said circuit means positioned adjacent the pilot burner and operative when heated thereby to deenergize said igniter, means operative to maintain said pilot burner valve open as long as any of said main shut-01f valves is open, and time delay means coacting with said pilot burner valve to prevent the latter from closing for a predetermined time interval after closing of the last of said main shut-oft" valves to provide a time delay for the extinguishment of the pilot burner after the extinguishment of the last of said top burners and permitting the closing of said pilot burner valve to extinguish the pilot burner after said predetermined time interval has elapsed.

4. A burner control system for a gas burning appliance, said system comprising a main burner, a main shut-off valve controlling the supply of gas to the main burner, a pilot burner in igniting relation to the main burner, a normally closed solenoid valve connected to receive gas independent of said main shut-off valve and controlling the supply of gas to the pilot burner, means for energizing the solenoid coil of said solenoid valve for opening the latter to supply gas to the pilot burner in response to the opening of said main shut-01f valve and for deenergizing said solenoid coil in response to the closing of said main shut-01f valve, an electrically energized igniter operative to ignite the pilot burner, circuit means for energizing said igniter in response to said opening of said main shut-off valve, a normally closed thermal switch in said circuit means controlling the energization of said igniter positioned adjacent the pilot burner and operative to open when heated thereby to deenergize said igniter after ignition of the pilot burner and to maintain said igniter deenergized while the pilot burner remains lighted, the solenoid coil for said solenoid valve remaining energized to maintain said solenoid valve open as long as said main shut-off valve is open, and a dashpot coacting with said solenoid valve to delay the closing thereof for a predetermined time interval after the closing of said main shut-off valve to provide a timedelay for the extinguishment of the pilot burner after said main burner is extinguished and permitting the closing of the solenoid valve after said time interval due to the deepergization of the solenoid coil in response to the closing of said main shut-off valve.

5. Apparatus as in claim 4, wherein said thermal switch includes a fixed contact, a stop spaced from said fixed contact, a contact movable between said stop and said fixed contact to open and close the switch, a thermal element subject to a flame at the pilot burner and connected to the movable contact to controlthe position of the latter, and a friction clutch connected between the thermal element and said movable contact for taking up the continued expansion or contraction of the thermal element after the movable contact has been moved to either extreme limit of movement and insuring immediate movement of the movable contact in response to the ignition or extinction of said fiame at the pilot burner.

6. A top burner ignition system for a gas stove, said system comprising a pilot burner for igniting a top burner, an electrically energized igniter for igniting the pilot burner, and a normally closed thermal switch controlling the energization of the igniter positioned adjacent the pilot burner and operative to open when heated by a flame at the pilot burner to de-energize said igniter after ignition of the pilot burner and to maintain said igniter de-energized while the pilot burner remains lighted, said thermal switch including a mounting bracket, a fixed contact attached to said bracket, a stop on said bracket spaced from said fixed contact, a contact movable between said the bimetal helix and said mounting bracket taking up stop and said fixed contact to open and close the switch, a two-sectioned bimetal helix with one section having the high expansion on one side being subject to a flame at the pilot burner and the other section having the high expansion on the other side being shielded from the flame at the pilot burner, said helix having one end thereof connected to the movable contact to control the movement thereof, said two-sectioned construction of the bimetal helix with the high expansion on opposite sides of the helix in the respective sections thereof being operative to compensate for the ambient temperature of the stove and to prevent movement of the movable switch contact in response to ambient temperature changes, and a friction clutch connected between the other end of the continued expansion or contraction of the helix after the movable contact has been moved to either extreme limit of movement and insuring immediate movement of the movable contact toward its other extreme limit of movement in response to the ignition or extinguishment of said, flame at the pilot burner.

7. A burner control system for a gas stove, said system comprising a plurality of top burners, a plurality of manually actuated main shut-cit valves each controlling the supply of gas to one of said top burners, a pilot burner in igniting relation to each of said top burners, a normally closed pilot burner valve controlling the supply of gas to the pilot burner and connected to receive gas independent of said main shut-01f valves, means responsive to manual actuation of any one of said main shutone of the main shut-off valves is open, and time delay means operatively associated with said pilot burner valve to maintain the latter open for a time interval after closing the last of said main shut-01f valves to provide a time delay for the extinguishment of the pilot burner after the extinguishment of all of the top burners and permit ting the closing of said pilot burner valve to extinguish the pilot burner after said predetermined time interval has elapsed.

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