US2625216A

US2625216A - Control and ignition system for fuel burners

Info

Publication number: US2625216A
Authority: US
Inventors: Charles K Strobel
Original assignee: Robertshaw Fulton Controls Co
Current assignee: Robertshaw Controls Co
Priority date: 1948-12-30
Filing date: 1948-12-30
Publication date: 1953-01-13
Anticipated expiration: 1970-01-13

Description

Jan. 13, 1953 c. K. STROBEL. 2,625,216

CONTROL AND IGNITION SYSTEM FOR FUEL BURNERS Filed Dec. so, 1948 2 swans-swam 1 IN V EN TOR.

(bank's K. Jvobel 1953 c. K. STROBEL CONTROL AND IGNITION SYSTEM FOR FUEL BURNERS 2 SHEETS--SHEET 2 Filed Dec. 50, 1948 a V mM/Ww Maw W. W r/ v a Patented Jan. 13, 1953 UNITED STATES PATENT OFFICE CONTROL AND IGNITION SYSTEM FOR 1 FUEL .BURNERS 11 Claims. (01. 158-124) This invention relates to control and ignition wheneverthe automatic-pilot control operates to j shut off the fuel supply.

Another object of the invention is to rende an electric ignition-device operative as soon as the starting operation occurs.

Another object of the invention is to permit an automatic restarting operation under certain conditions without utilizing the electric ignition device.

Another object of the invention is to position the parts in such location to the oven or other heated compartment so as to secure efficient and satisfactory operation over long periods of time without-requiring repair or replacement;

Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawings, wherein:' I

Fig. 1 is a schematic view of a control andignitionsystem embodying the inventiornand v v Fig.2 is asimilar schematic view of -a modified control and ignition system.

Referring more particularly to Fig. 1 of the drawings a main .fuel burner is positioned in an oven or other compartmentto be heated, the outer wall of which is shown in broken lines in the drawing. A fuel supply. for the main burner Ill is provided from a manifold [2 having the usual main fuel-cock l4 controlling'the fuel supply therein and to which is connected a main fuel supply pipe l6 for the main burner.

Interposed inthe main fuel supply pipe [5 is a main valve device designated generally by the reference numeral It. The main valve device l8 includes a casing provided with a main valve seat '22 forming a partition between the inlet and outlet connections of the main fuel pipe 6 and having an opening'24 therein through which communication between said connections can be effected. A pilot valve seat 26 is formed in the casing 20in substantial axial alignment with the main valve seat 22 and having an opening 28 therein communicating with a by-pass passage 29 formed in the casing 20 and supplied with fuel from the main fuel pipe [6. A pair of diap'h-ra'gm valve members 3t] and 32 are carried in the casing 20 and overlie the valve seats'22, 28"to'conti'ol the

openings

24 and 28 respectively.

The

diaphragm valve members

30, 32 are spaced fromeach other and define first, second and third pressure chambers in the valve casing 20 which are designated respectively by the reference numerals 34, 36,-and 38.

Communicating with the first pressure chamber 34 is one end of a pilot supply conduit 40 which receives a supply-of fuel by way of'a connecting or branch conduit 42 from a pilot supply conduit 44. The oppositeend of the pilot conduit 49 communicates with one pilot burner 45 of a pair of pilot burners which are juxtaposed with the main burner H] and in lighting proximity to each other. Theother pilot burner 45 of the pair communicates by the way of a'conduit 48 with the third pressure chamber 38 and consequently receives a supply of fuel from the bypass passage 29 and valve seat opening 28 when the diaphragm valve member 32 is disengaged from the seat 26.

Interposed in the pilot conduit 40 between the branch pipe 42 and the-pilot burner 45 i a control valve device designated generally by the reference numeral 50. The control device .50 includes a magnet casing 52 within which a horseshoe-type .permanentmagnet 54 is secured. Extending across the pole faces of the magnet 54 is a plate 560i Curie point metal which may also serve as a fluid-tight seal to prevent passage of fuel into the magnet casing 52. Depending from the magnet-casing 52 is a valve casing 58 to which inlet and outlet connections of the pilot conduit 49 are made. A valve seat 60 is formed in the valve housing 58 adjacent the outlet connection of the conduit 40 and a ball valve 62 is adapted for-engagement with the seat 60 to control the flow of fuel between the inlet and outlet connections of the conduit 49. The ball valve 62 is madeof metal,- preferably steel, and is normallybiased to a closed position relativeto the seat-60 due to gravity, spring or other means.

A third pilot burner 64 is located in heating proximity with the magnet casing 52 and is supplied with fuel by way of a conduit 66 connected to the manifold I2 through the main fuel cock. l4. As indicated in the drawing, both the control valve device and the third pilot burner 64 are located exteriorly of the oven or other heating compartment which contains the main burner I0 and the pair of

pilot burners

45, 46. A short flash-tube 68 projects through the oven Wall from between the pair of

pilot burners

45,46 to the third pilot burner .64 for conducting ignition operations therebetween as will be apparent hereinafter.

In the embodiment disclosed in Fig. l of the drawings, electric ignition means are provided for the pilot burner 46 of the pair and takes the form of a coil of resistance wire 10 located within the oven in igniting proximity with the pilot burner 46. A transformer T2 of the step-down type and limiting resistor I4 are connected in circuit with the igniter 10. Moreover, automatic switching means are employed for causing energization of the igniter 16 at predetermined times.

The switching means for the igniter l include a main switch means 16 which is normally open but which is positioned to be closed upon operation of the fuel cook 14 to open position. Such combined main switches and fuel cocks are well known to the art so that the schematic showing and brief description herein are considered ample.

A control switch means 78 is also provided for the igniter Ill and comprises a relatively fixed contact 88 positioned for cooperation with a relatively movable contact 82 which is carried on a movable partition 84 extending across the first pressure chamber 34 and serving to exclude aseous fuel from the vicinity of the

contacts

89, 82. The movable partition 84 has spaced relation with the diaphragm valve member 38 and the pilot conduit 40 is connected therebetween. As indicated in Fig. 1 of the drawings, the mov able partition 84 is subject to the pressure existing on its underside in the first pressure chamber 34 for moving to a position for closing the

contacts

80, 82; it being noted that thecasing on the opposite side of the partition 84 is open to the atmosphere. The electrical circuit for the igniter H3, including the main switch means It and the control switch means 18, will be described in connection with the description of the operation of the improved control and ignition system which now ensues.

. The system is shown in Fig. l of the drawings in the running condition, that is, with the main burner Ill producing a flame and the one pilot burner 45 of the pair and the third pilot burner 64 also producing flames. In order to bring the system into this running condition, a starting operation is conducted by opening the main fuel cock l4 and simultaneously closing the main switch means 16. The pilot supply conduit 44 is assumed to be supplying fuel to conduits 42 and 45'. Since the movable partition 84 and the diaphragm valve member 34 are exposed to the fuel pressure existing in the pressure chamber 34 and derived from the pilot conduit 49, then the pressure on the underside of the movable partition 84 is greater than that existing on the opposite side thereof. Concurrently, the pressure in the chamber 36 on the underside of diaphragm valve member is less than that existing on the opposite side thereof. Consequently, the movable partition 84 and the diaphragm valve member 34 are in such positions as to close the

contacts

80, 32 and the valve opening 24 respectively. However, since the side of the diaphragm valve member 32 in chamber 36 is exposed to atmospheric pressure and the side in chamber 38 to approximately diaphragm valve member 32 is moved to open position.

Fuel now flows by way of main fuel pipe It, bypass 29, valve opening 28, and pilot conduit 48 to the other pilot burner 46 of the pair. It is to be observed that fuel is concomitantly admitted by way of the pilot supply conduit 44, branch pipe 42, and pilot conduit 40 to the valve housing 58 of the control valve device 50. However, such fuelin the valve housing 58 cannot be supmanifold pressure by way of by-pass 29, then this 6,

plied to the one pilot burner 45 of the pair, as the ball valve member 62 is occupying a closed position relative to its seat 60 in this starting operation.

The switch means 16 being closed, a circuit is established for the igniter 10 which may be traced as follows: line wire L, wire 85,.primary of transformer 12, wire 88, contact 82, contact 80, wire 90, switch means 76, and wire 92 to line wire Ll. Since the igniter 18 is connected in circuit with the secondary of the transformer 12, the establishment of the primary circuit thereof causes energization of the igniter 1B and consequent ignition of the fuel flowing from the pilot burner 45. The third pilot burner 64 receives a supply of fuel from the manifold [2 by way of conduit 56 due to the open position of the main fuel cock I4. Such fuel is ignited by operation of the flash tube 68 from the flame existing at the pilot burner 46.

The magnet casing 52 of the pilot control valve 56 becomes heated by the flame from the third pilot burner 64 and the heat is conducted to the plate 56 of Curie point metal. The plate 56 soon becomes heated above its Curie point whereupon it becomes substantially nonmagnetic and incapable of shunting the flux from the magnet 54. Thus, substantially all the flux from the magnet 54 passes through the plate 55 and attracts the ball valve member 62 against its bias into the open position shown in Fig. 1 of the drawings. Consequently, fuel now flows in this open position of the ball valve member 62 from the conduit 48 to the pilot burner 45 which thereupon becomes ignited by the flame from the other pilot burner 46 of the pair.

The fuel pressure existing in the first pressure chamber 34 is soon relieved due to opening'of the ball valve member 62 and the movable partation 84 resumes a position for opening the

contact pair

80, 82. Simultaneously therewith, the diaphragm valve member 30 resumes a position out of engagement with the valve seat 22 and fuel from the main fuel pipe 16 passes through the valve opening 24 to the main burner 10. The fuel from the main burner IE is ignited by the pilot burner 45. The opening of the

contact pair

80, 82 serves to cause deenergization of the igniter 10. The flow of fuel through the valve opening 24 to the main burner I 0 is sufficient to establish a pressure inthe second pressure chamber 36 similar to that existing in the third pressure chamber 38. Consequently, the dia-' phragm valve member 32 moves to a position in engagement with the valve seat 26 and shuts off the flow of fuel to the other pilot burner 46. The system is thus set in its steady or running condition.

In the event that the third pilot burner 64 becomes extinguished, then it'will be reignited from the one pilot burner 45 through the flash tube 68. A similar operation, but in reverse, will also occur should the one pilot burner 45 become extinguished while the third pilot burner 64 re-.

mains in operation. However, in case of a complete failure of fuel flow in the steady state operation of the system, then the control valve device 50 will be brought automatically into operation. Thus, the magnet casing 52 will become suihciently cooled to cause a corresponding cooling of the plate 56 of Curie point metal. The flux from the magnet 54 Will tend to pass through the plate 56 due to its increased permeability, and is thereby shunted from the ball valve member 62. The ball valve member 62 is seated under its bias and the pressure condition existing in the first pressure chamber 34 reverts to that of the starting operation. Consequently, the diaphragm valve member becomes seated on the valve seat 24 and shuts off the flow of fuel to the main burner it. It will be observed that the system is thus placed automatically in condition for another starting operation due to closure of the contacts 86. 82 simultaneously with the seating of the diaphragm valve member '36 on the valve seat 22. f I

In the case of a rapid off-on operation of the main fuel cock I l under steady state condisons, the third pilot burner 55 and the main burner H3 will be reignited from the one pilot burner which serves as a constant pilot burner until the control valve device 5%! has released the ball valve member 52 to its closed position. Hence, before the plate 555 of Curie point metal is cooled, reignition can be cfiected even though the electric circuit is deenergized by the open position of the

contacts

80, 82. However, if the ball valve member 62 has already moved to its closed posi- 'tion in such case, the starting operation will be similar to that which occurs under cold start as those described in connection with the previous embodiment. Consequently, similar characters of reference have been employed for corresponding parts and further description is deemed unnecessary. The main valve device 18 includes a casing 28 having a valve seat 22 provided with a valve seat opening '24 with which a diaphragm valve member 38 is adapted to cooperate as in the previous embodiment. A second valve seat 26 is provided in the casing 29 having a valve opening 28 with which a diaphragm valve member 32 is designed to cooperate also as in the previously described embodiment. Thus, apart from the omission of the movable partition 84 and the contacts as, 82 of the previously described embodiment the main valve devices i8 may :be identical in all respects. Similarly, the control valve device 55! includes a permanent magnet 55, a plate 55 of Curie point metal and the ball valve member 62, all as described in connection with Fig. 1 of the drawings.

The ignition system of the embodiment disclosed in Fig. 2 does not require switch means such as disclosed in the previous embodiment as will now be apparent. A catalytic type igniter 94 is positioned exteriorly of the oven compartment, as indicated in Fig. 2 of the drawings, and a second short flash tube 95 extends through the oven wall from between the pair of pilot burners 45, 4'6 and to igniter Q4. The igniter $4 is arranged for continuous energization and is thus preheated, but below the temperature required for effective ignition. It has been found that, by heating the igniter 94 to a temperature of approximately 900 F. by'continuous energization from the secondary of the transformer "E2, the temperature will rise to the ignition point only when unburned fuel from the flash tube 96 impinges thereon. Such sof-c'alled hot-type catalytic igniter S4 and the relatively short flash tube 98 employed in conjunction therewith operate quite satisfactorily with any of the usual gases consumed in domestic use. In this embodiment, the primary of the transformer 72 is connected by wire 58 at one end to line wire L and by wire mo at the opposite end to line Ll.- As previously mentioned no 6 switch means is employed due to continuousene'r gization of the igniter 94.

As the operation of the system disclosed in Fig. 2 of the drawings is identical in all respects to that of Fig. 1 except insofar as the render is concerned, detailed description is deemed unnecessary Thus, the fuel issuing from the pilot burner news not only through the flash tube 68 to the third pilot burner 64 but also through the second flash tube 96 to the ignitr 94. Ig'hit ich of the pilot burner 46 is thus effected as in the case of the Fig. l embodiment Where the resist ance type igflitei' T0 was employed. It is apparent, therefore, that both embodiments of the imvendor-mas initial pressure established the first pressure chamber 34 serves to condition an igmter "for an ignitingoperation.

Various modifications maybe made in the details of construction and arrangement of parts disclc'sed herein. The -magnet casing 52 cduld itself be made of Curie oint metal and the plate 56 of non-ma netic material to prevent the ball Valve member 62 from sticking to the pole faces of the magnet 54. These and other modifications are intended to be included within the scope of this invention and the specific embodiments-dis closed in the drawings and described herein'are to be taken merely for illustrative purposes while the invention is limitd' only by the scope or the appended claims.

1. A control and ignition system ror fuel burnas having a main burner, a pair of pilot burners juxtaposed with the main burner, a main valve device having means including a pair of diaphrag'm members defining first, second and third pressure chambers, said first and third chambers being adapted for connection with one and the other or said pilot burners respectively, said second chamber being adapted for connection with the main burner, means for supplying fuel under pressure to said chambers, valve means movable between open and closed positions and opera tively associated with one of said diaphragm members for controlling the supply of fuel to said second chamber, said one diaphragm having one side thereof subject to the fluid pressure 'in the said first chamber. second valve means movable between open and closedpositions and operatively associated with the other of said diaphragm members for controlling the supply of fuel to said third chamber, said other diaphragm member having one side thereof subject to the fluid pressure in said second chamber, a control valvedevice adapted to be responsive to a flame originating at said other. pilot burner and being movable between positions for controlling the connection to said one pilot burner and the pressure in said first chamber, said control valve device being biased to a position for establishing an initial pressure in said first chamber sufii cient for causing said one diaphragm member to close said first named valve means thereby limit ing the initial pressure in said second chamber for causing said other diaphragm member to open said second valve means, an electric igniter for said other pilot burner, means operative upon establishment of said initial pressure for conditioning said igniter for an igniting operation, and magnetic means operatively associated with said control valve device and being effective upon said control device becoming responsive to said flame for overcoming said bias and opening said connection to said one pilot burner thereby reducing the pressure in said first chamber for causing said one diaphragm member to open said first named valve means and establish a pressure in said second chamber sufficient for causing said other diaphragm member to close said second valve means.

2. A control and ignition system for fuel burners having a main burner, a pair of pilot burners juxtaposed with the main burner, a third pilot burner spaced from said pair of pilot burners, a main valve device having means including a, pair of diaphragm members defining first, second and third pressure chambers, said first and third chambers being adapted for connection with one and the other of said pilot burners respectively, said second chamber being adapted for connection with the main burner, means for supplying fuel under pressure to said chambers, valve means movable between open and closed positions and operatively associated with one of said diaphragm members for controlling the supply of fuel to said second chamber, said one diaphragm having one side thereof subject to the fluid pressure in said first chamber, second valve means movable between open and closed positions and operatively associated with the other of said diaphragm members for controlling the supply of fuel to said third chamber, said other diaphragm member having one side thereof subject to the fluid pressure in said second chamber, a control valve device adapted to be responsive to a flame at said third pilot burner and being movable between positions for controlling the connection to said one pilot burner and the pressure in said first chamber, said control valve device being biased to a position for establishing an initial pressure in said first chamber sufiicient for causin said one diaphragm member to close said first named valve means thereby limiting the initial pressure in said second chamber for causing said other dia phragm member to open said second valve means, an electric igniter for said other pilot burner, means effective upon establishment of said initial pressure for conditioning said igniter for an igniting operation, a flash tube extending between said other pilot burner and said third pilot burner, and magnetic means operatively associated with said control valve device and being effective upon said control valve device becoming responsive to said flame for overcoming said bias and opening said connection to said one pilot burner thereby reducing the pressure in said first chamber for causing said one diaphragm member to open said first named valve means and establish a pressure in said second chamber sulficient for causing said other diaphragm member to close said second valve means.

3. A system as claimed in claim 2 wherein said control device includes an element of Curie point material for preventing said magnetic means from overcoming said bias as long as said element is below a predetermined temperature.

4. A control and ignition system for fuel burners having a main burner, a pair of pilot burners juxtaposed with the main burner, a third pilot burner spaced from said pair of pilot burners, a main valve device having means including a pair of diaphragm members defining first, second and third pressure chambers, said first and third chambers being adapted for connection with one and the other of said pilot burners respectively, said second chamber being adapted for connection with the main burner, means for supplying fuel under pressure to said chambers, valve means movable between open and closed positions and operatively associated with one of said diaphragm members for controlling the supply of fuel to said second chamber, said one diaphragm having one side thereof subject to the fluid pressure in said first chamber, second valve means movable between open and closed positions and operatively associated with the other of said diaphragm members for controlling the supply of fuel to said third chamber, said other diaphragm member having one side thereof subject to the fluid pressure in said second chamber, a control valve device including a magnet casing adapted for juxtaposition with said third pilot burner, said control valve device having open and closed positions for controlling the connection to said one pilot burner and the pressure in said first chamber, said control valve device being biased to a closed position for establishing an initial pressure in said first chamber suflicient for causing said one diaphragm member to close said first named valve means thereby limiting the initial pressure in said second chamber for causing said other diaphragm member to open said second valve means, an electric igniter for said other pilot burner, means operative upon establishment of said initial pressure for conditioning said igniter for igniting operation, a flash tube extending between said other pilot burner and said third pilot burner, a magnet in said magnet casing for overcoming said bias and holding said control valve device in said open position, and an element of Curie point material interposed between said magnet and said control valve device for shunting the flux from said magnet as long as said element is below its Curie point.

5. A control and ignition system for fuel burners having a main burner, a pair of pilot burners juxtaposed with the main burner, a third pilot burner spaced from said pair of pilot burners, a main valve device having means including a pair of diaphragm members defining first, second and third pressure chambers, said first and third chambers being adapted for connection with one and the other of said pilot burners respectively, said second chamber being adapted for connection with the main burner, a movable partition in said device responsive to the pressure in said first chamber, switch means operable between open and closed positions by said partition, means for supplying fuel under pressure to said chambers, valve means movable between open and closed positions and operatively associated with one of said diaphragm members for controlling the supply of fuel to said second chamber, said one diaphragm having one side thereof subject to the fluid pressure in said first chamber, second valve means movable between open and closed positions and operatively associated with the other of said diaphragm members for controlling the supply of fuel to said third chamber, said other diaphragm members having one side thereof subject to the fluid pressure in said second chamber, a control valve device adapted to be responsive to a flame at said third pilot burner and being movable between positions for controlling the connection to said one pilot burner and the pressure in said first chamber, said control valve device being biased to a position for establishing an initial pressure in said first chamber sufficient for causing said one diaphragm member to close said first named valve means thereby limiting the initial pressure in said second chamber for causing said other diaphragm member to open said second valve-means,- an electric igniter for said other pilot burner adapted to be energized in said closed position of said switch'means, a flash tube extending between said other pilot burner and said third pilot burner, and magnetic means operatively associated with said control valve device and being efiective upon said control valve device becoming responsive to said flame for overcoming said bias and opening said connection to said one pilot burner thereby reducing the pressure in said first chamber for causing said one diaphragm member to open said first named valve means and establish a pressure in said second chamber suflicient for causing said other diaphragm member to close said second valve means.

6. A system as claimed in claim wherein said control valve device includes an element of Curie point material for preventing said magnetic means from overccming said bias as long as said element is below a predetermined temperature.

7. A control and ignition system for fuel burners having a main burner, a pair of pilot burners juxtaposed with the main burner, a third pilot burner spaced from said pair of pilot burners, a main valve device having means including a pair of diaphragm members defining first, second and third pressure chambers, said first and third chambers being adapted for connection with one and the other of said pilot burners respectively, said second chamber being adapted for connection with the main burner, means for supplying fuel under pressure to said chambers, valve means movable between open and closed positions and operatively associated with one of said diaphragm members for controlling the supply of fuel to said second chamber, said diaphragm having one side thereof subject to the fluid pressure in said first chamber, second valve means movable between open and closed positions and operatively associated with the other of said diaphragm members for controlling the supply of fuel to said third chamber, said other diaphragm member having one side thereof sub- .ieot to the fluid pressure in said second chamher, a movable partition in said device responsive to the pressure in said first chamber, switch means operable between open and closed positions by said partition, a control valve device includim a magnet casing adapted for juxtaposition with said third pilot burner, said control valve device having open and closed positions for controlling the connection to said one pilot burner and the pressure in said first chamber, said control valve device being biased to a closed position for establishing an initial pressure in said first chamber sufficient for causing said one diaphragm member to close said first named valve means thereby limiting theinitial pressure in said second chamber for causing said other diaphragm member to open said second valve means said initial pressure in said first chamber being suflicient for causing said partition to close said switch means, an electric igniter for said other pilot burner adapted to be energized in said closed position of said switch means. a flash tube extending between said other pilot burner and said third pilot burner, a, magnet in said magnet casing for overcoming said bias and holding said control valve device in said open position, and an element of Curie point material interposed between said magnet and said control valve device for shunting the flux from said magnet as long as said element is below its Curie point,

-8. A control-and ignition system for fuel burners having a main burner, a pair of pilot burners juxtaposed with the main burner, a third pilot burner spaced from said pair of pilot burners, a main valve device having means including a pair of diaphragm members defining first, second and third pressure chambers, said first and third chambers being adapted for connection with one and the other of said pilot burners respectively, said second chamber being adapted for connection with the main burner, means for supplying fuel under pressure to said chambers, valve means movable between open and closed positions and operatively associated with one of said diaphragm members for controlling the supply of fuel to said second chamber, said one diaphragm having one side thereof subject to the fluid pressure in said first chamber, second valve means movable between open and closed positions and operatively associated with the other of said diaphragm members for controlling the supply of fuel to said third chamber, said other diaphragm member having one side thereof subjectto the fluid pressure in said second chamber, a control valve device adapted to be responsive to a flame at said third pilot burner and being movable between positions for controlling the connection to said one pilot burner and the pressure in said first chamber, said control valve device being biased to a position for establishing an initial pressure in said first chamber suflicient for causing said one diaphragm member to close said first named valve means thereby limiting the initial pressure in said second chamber for causing said other diaphragm member to open said second valve means, a catalytic igniter positioned remote from said other pilot burner, a first flash tube extending between said igniter and said other pilot burner, a second flash tube extending between said other pilot burner and said third pilot burner, and magnetic means operatively associated with said control valve device and being effective upon said control valve device becoming responsive to: said flame for overcoming said bias and opening said connection to said one pilot burner thereby reducing the pressure in said first chamber for causing said one diaphragm member to open said first named valve means and establish a pressure in said second chamber suificient for causing said other diaphragm member to close said second valve means.

A system as claimed in claim 8 wherein. said catalytic igniter is preheated below the temperature required for efiective ignition and said first flash tube being adapted to convey unburned fuel from said other pilot burner for increasingsaid igniter temperature sufficiently to produce a flame at said other pilot burner.

19. A system as claimed in claim 8 wherein said magnetic means includes a magnet casing adapted for juxtaposition with said third pilot burner, a magnet in said magnet casing for overcoming the bias of said control valve device and holding the same in said open position, and an element of Curie point material interposed between said magnet and said control valve device for shunting the flux from said magnet as long said element is below its Curie point.

11. A control system for furner burners having a main burner, a pair of pilot burners juxtaposed with the main burner, a main valve device having means including a pair of diaphragm members defining first, second and third pressure chambers, said first and third chambers being adapted for connection with one and the other of said pilot burners respectively, said second chamber being adapted for connection with the main burner, means for supplying fuel under pressure to said chambers, valve means movable between open and closed positions and operatively associated with one of said diaphragm members for controlling the supply of fuel to said second chambensaid one diaphragm having one side thereof subject to the fluid pressure in said first chamber, second valve means movable between open and closed position and operatively associated with the other of said diaphragm members for controlling the supply of fuel to said third chamber, said other diaphragm member having one side thereof subject to the fluid pressure in said second chamber, a control valve device adapted to be responsive to a flame originating at said other pilot burner and bein movable between positions for controlling the connection to said one pilot burner and the pressure in said first chamber, said control valve device being biased to a position for establishing an initial pressure in'said first chamber sui-ficient for causing said one diaphragm member to close said first named valve means thereby limiting the initial pressure in said second chamber for causing said other diaphragm member to close said second ,valve means, and means operatively associated with said control valve device and being effective upon said control valve device becoming respon sive to said flame for overcoming said bias and opening said connection to said one pilot burner thereby reducing the pressure in said first chamber for causing said one diaphragm member to open said first named valve means and establish a pressure in said second chamber suincient for causing said other diaplnagm'member to close said second valve means.

CHARLES K. STROBEL.

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

UNITED STATES PATENTS Number Name Date 1,636,770 Fox July 26, 1927 2,233,659 Wittmann Mar. 4, 1941 2,250,738 Wittmann July 29, 1941 2,275,279 Beam Mar. 3, 1942 2,408,673 Moorhead Oct. 1, 1946 2,506,403 Witzel May 2, 1950 2,512,173 Ray June 20, 1950