US2171860A

US2171860A - Electrically operated control

Info

Publication number: US2171860A
Application number: US181109A
Authority: US
Inventors: Ira E Mccabe
Original assignee: Individual
Current assignee: Individual
Priority date: 1937-12-22
Filing date: 1937-12-22
Publication date: 1939-09-05
Anticipated expiration: 1956-09-05

Description

Sept. 5, 1939. v E, MCCABE 2,171,860

ELECTRI CALLY OPERATED CONTROL Filed Dec. 22, 1937 4 Sheets-Sheet 1 IN VEN TOR. lK/I E. M C485 BY M A TTORNE Y.

Sept. 5, 1939. I. E. MccABE ELECTRICALLY OPERATED CONTROL 4 sheets sfieet 2 Filed Dec. 22, 1937 I N VEN TOR.

IRA E. M C1155 A TTORNEY Sept. 5, 1939. I. E. McCABE ELECTRICALLY OPERATED CONTROL 4 Sheets-Sheet 5 Filed Dec.

INVENTOR.

m E. m cm:

x f m M ATTORNEY.

Sept. 5, 1939. I. E. M CABE 2,171,850

ELECTRICALLY OPERATED CONTROL Filed Dec. 22, 1937 4 Sheets-Sheet 4 INVENTOR. F|[3 5 IRA 5.01am

MIJWn- M.

ATTORNEY Patented Sept. 5, 1939 UNITED STATES PATENT OFFICE 2,171,860 ELECTRIQALLY OPERATED CONTROL Ira E. McCabe, Chicago, Ill. Application December 22, 1937, Serial No. 181,109

14 Claims.

This invention relates to improvements in electrically operated fluid fuel burner heating devices and more particularly to an electrically operated control therefor.

It is an object of this invention to provide a control mechanism of simplified construction and operation which may be used in conjunction with the customary commercial switches responsive to the changes in temperature within the room and commercial switches responsive to the changes in temperature within the stack leading from the furnace or boiler to the chimney or with commercial switches responsive to the presence or absence of visible light from the burner flame and preferably for use with the light responsive switches such as disclosed in this applicants prior co-pending applications, Serial No.

94,352, filed August 5, 1936, and Serial No. 124,982, filed January 2, 1937.

The advantages of this improved mechanism are that it embodies only two high voltage switches, one in the burner operating-motor circuit'and the other in the ignition circuit when intermittent electrical ignition is employed, while the electrically actuated apparatus for operating these switches are connected in a secondary or low voltage circuit, in which only one switch is employed, thus reducing the cost of manufacture materially; it provides a normal period to produce combustion and if combustion occurs operation continues as long as combustion continues but if combustion fails to occur at the end of said period the burner operating mechanism is rendered inoperative until the control is manually reset; it will recycle to restore normal operation upon a failure and restoration of the commercial source of electricity when the room thermostat is calling for heat except when in the safety shut down position; it will recycle if the burner flame becomes extinguished as the result of abnormal conditions; and it will provide a purging or pre-ignition period prior to each time the operation of the burner mechanism is actuated.

This device is an improvement upon and a further development of controls of the type disclosed in this applicants prior Patent No. 1,817,635 dated August 4, 1931. v

- With these and other objects in view reference is made to the accompanying sheets of drawing which illustrate a preferred form of this invention with the understanding that detail changes may be made without departing from the scope thereof.

In the drawings:

Figure 1 is a view in front elevation of the panel mounting this improved mechanism, with the cover shown in section, and with the parts in the positions assumed during the idle or nonoperating period.

Figure 2 is a wiring diagram showing this improved mechanism connected in circuit with the commercial source of electricity and with the electrically actuated apparatus for operating it.

Figure 3 is a detail view in elevation illustrating the position assumed by the parts during the ignition period.

Figure 4 is a wiring diagram similar to Figure 2 illustrating in heavy lines the circuits energized or established during the ignition period.

Figure 5 is a view similar to Figure 3 illustrating the positions assumed by the parts during the normal operation of the burner mechanism.

Figure 6 is a wiring diagram similar to Figure 2 illustrating in heavy lines the circuits energized or established during the normal operation period. 7

Figure 7 is a view similar to Figure 3 illustrating the position assumed by the parts after an abnormal shut down with the room thermostat calling for heat, otherwise known as safety position.

Figure 8 is a wiring diagram similar to Figure 2 illustrating in heavy lines the circuits e ergized or established when a safety shut down occurs.

In the embodiment of the invention, as illustrated in Figure 1, the mechanism is mounted on a' panel I having a removable cover 2. As seen from the wiring diagram Figure 2, binding post 3 is connected to the commercial line L' and binding post 4 is connected to the commerical line L. Binding post 3 is also connected to one end of the winding of the primary coil PC of a commercial repulsion relay R, of the general type disclosed in this applicants prior Patent No. 1,973,925, dated September 18, 1934, by the lead 5 and the other end of the winding of PC is connected by lead 6 to binding post 4. Binding post 4 is connected by lead 'I to one terminal of the motor switch MS and the other terminal thereof is connected by lead 8 to binding postr9. Binding post 4 is also connected by lead I0 to one terminal of the ignition switch IS and the other terminal thereof is connected by lead I I to binding post I2. One end of the winding of the secondary or movable coil SC of the relay R is connected by lead I 3 to binding post I4 and the Y erably parallel to the arm 28.

nected by lead I1 to an electrical heating element E which in turn is connected by lead I8 to binding post I9.

As shown in the wiring diagram of Figure 2, a commercial. boiler control BC is connected in circuit with the commercial line L between the source and binding post 4. The motor M for operating the burner mechanism is connected by wire 20 to binding post 9 and by wire 2| to binding post 3. The commercial ignition device I for igniting the fluid fuel delivered by the operation of the motor M to the combustion chamber of the furnace or boiler is connected by wire 22 to binding post 9 and by wire 23 to binding post 3. Binding post I4 is connected by wire 24 to a commercial thermostat T which is connected by wire 25 to binding post I9. Binding post I9 is also connected by wire 29 to a commercial stack temperature responsive or burner flame light responsive switch SS which is connected by wire 21 to binding post IS.

The ignition switch IS is shown in section in Figures 1 and 3. The motor switch MS shown in full lines in all figures of the drawings is of the same type and construction as the ignition switch IS. Both are mercury tube switches of a commercial type and are supported in fixed relation upon the panel I. Each includes an electrode always in contact with the pool of mercury in the bottom of the tube and a movable electrode, normally out of contact with the mercury, supporting an armature responsive to a magnetic field to move the movable electrode into contact with the mercury to close the circuit therethrough, preferably of the type disclosed in the applicant's prior Patent No. 2,085,316.

It is preferable to mount the tubes of the switches IS and MS in spaced apart parallel relation to each other and at an angle to the side of the panel I. Each switch is provided with a magnet IM and MM, respectively, supported on swinging

arms

28 and 29, respectively, pivoted to posts 30 and 3 I respectively, upon the panel I to swing the magnets 1M and MM into and out of operative relation with the ignition and motor switches to close and open the circuits to the ignition device I and to the burner motor M, respectively. The post 39 pivotally mounts a de pending magnet actuator plate 32 connected to oscillate the arm 28 carrying the magnet IM and its weight normally maintains the magnet IM in inoperative position, as shown in Figure 1. The post 3I pivotally mounts a similar magnet actuating plate 33 to oscillate independently of the arm 29 carrying the magnet MM, however, this actuator plate 33 is provided with a stud 34 adapted to be engaged by the arm 29 when the magnet MM is in inoperative position and pref- The

actuator plates

32 and 33 are connected to each other by the pivoted link 35, causing the

actuator plates

32 and 33 to oscillate in unison into the operative position to cause the magnets IM and MM to close the ignition switch IS and motor switch MS at the same time.

The magnet arm 28 has a direct connection to the actuating plate 32 but the arm 29 is not connected with plate 33 so that if the magnet arm 29 is otherwise held in the operative position the return of

plates

32 and 33 to the inoperative or idle position causes only the opening of the ignition switch IS as the magnet IM is moved away. As arranged in the embodiment of this invention the power of both magnets are utilized, when the switches are closed, to hold them closed against gravity so that with the movement of the magnet IM to open the ignition switch the power of the magnet MM by itself will be insufficient to hold the motorswitch MS closed and will allow magnet MM to move away unless means, hereinafter described, are provided to lock the motor magnet arm 29 in the operative position.

The electric heating element E is normally receivable in a cup 36 of heat conducting material mounted upon a strip of bi-metallic or thermal metal 31 adapted to transmit the heat from the element E when energized to the strip 31. The heat 50 transmitted causes the strip 31 to deform, as shown in Figure 3. The actuator plate 33 is provided with a stud 38 adapted to normally engage the free end of the actuator strip 31 when cold and the magnets IM and M are in normal inoperative position and as the actuator strip 31,

deforms it imparts a movement through stud 38, plate 33, stud 34, link and plate 32 to move both

arms

28 and 29 to swing the magnets 1M and MM into position to close the switches IS and MS. The lower end of the actuator strip 31 is mounted upon a block 39 pivoted upon a stud 40 mounted upon the panel I. mounts one end of a strip of thermal metal 4| which acts as a compensator and the other end is adjustably secured to a block 42 mounted upon the panel I by means of a headed screw 43 and spring 44, whereby the position of the free end of the actuator strip 31 may be varied to establish the distance of travel required by that end to contact the stud 38 on the actuator plate 33 to move the

arms

28 and 29 to close the switches IS and MS.

The heating element E is mounted on the free end of an arm 45 pivoted upon the post 31 independently of the arm 29 and plate 33. The magnet carrying arm 29 is provided with a stud 46 adapted to engage the element carrying arm 45 and withdraw the heating element E from the cup 36 as the

actuator plates

32 and 33 are operated to closethe switches IS and MS. It is preferable to provide a magnet 41 supported upon the 1 base I beneath the actuator strip 31 and an armature plat 48 upon the element carrying arm 45 to coact therewith to retard the movement of the arm and also to providethe arm .5 with an ofiset to allow the stud 46 to travel a portion of the distance to its operating position before it engages the arm. When the arm 29 is free to return to its normal inoperative position, the weight of the element E upon the arm 45 assists in removing the magnet MM from its armature within the switch MS. The magnet 41 insures the po sitioning of the heating element E within the cup 36 as it assumes the idle position, as shown in Figure 1. When the actuator strip 31 is actuated to move the

actuator plates

32 and 33 in unison to close the switches IS and MS the movement after initiation is impeded by contact of the stud 46 with the arm 45 which is held by the armature 48 in engagement with the magnet 41. When the increased pressure exerted by the actuator strip 31 against the stud 38 is suficient to remove the armature 48 from the influence of its magnet 41 the arm 45 is released and, under the additional urge of the actuator moves the magnets IM and MM into operative position to close the switches IS and MS. As the actuator strip 31 cools its free end moves away from the stud 38 on the actuator plate 33 and to cause the removal of the magnet IM from its armature within the switch IS an adjustable stop 11 is provided on the actuator plate 33 to be en- The'adjacent side of the block strip 31, it snaps or quickly aged by the free end of the actuator strip 31 to initiate the movement of the plate 33 to its normal position and the adjustment thereof determines the period of ignition.

As shown in the wiring diagram in Figure 2, a commercial room thermostat T is connected by

wires

24 and 25 to binding posts l4 and I9 and theheating element E, which is of the high resistance type, is connected by wires l1 and I8 to binding posts It and I9 while the windings of the movable or secondary coil SC of the repulsion relay R are connected by wires l3 and I to binding posts l4 and I6. When the room thermostat closes in a call for heat or for operation of the burner mechanism, the circuit will be established through the secondary coil SC and heating element E and the current passing therethrough will energize the heating element E but because of the resistance of the element it will not be sufiicient to cause the repulsion of the coil SC. The distortion of the thermal actuator strip 31 will operate the actuator plate 33 and through its connections will close the switches IS and MS so that the motor M will supply fuel to the combustion chamber of the furnace of the boiler, not shown, and the ignition device I will ignite the fuel so supplied. The parts of the mechanism are then in the position shown in Figure 3 during the ignition period and the circuits so established are shown in Figure 4.

As it is desirable after ignition has been initiated to discontinue the operation of the ignition carrying the magnet MM, as shown in Figure 3, is arranged to be held in the operative position, by means rendered operative during periods of combustion. As shown in the wiring diagram Figure 4, a normally open commercial stack switch SS responsive to a rise combustion chamber, to close, is connected by wires 26 and 21 to binding posts l9 to It, respectively, to which the high resistance heating element Eis also connected by wires l1 and I8. Therefore upon establishment of combustion the switch SS closes and shunts the heating element circuit allowing more current to flow through the coil SC so that the coil SC is repelled. The movable coil SC is secured to a bracket 50 pivotally mounted at 5| upon one leg of a rectangular The relay may be so constructed that upon being energized, that is when the circuits including both coils are closed, low voltage is induced in the circuit of coil SC and upon repulsion of the coil the bracket 50 will be rotated about its pivot. The arm 29 carrying the magnet MM is provided with a finger 49 extending above and beyond its pivot post 3| in the direction of the top of the coil SC and the bracket 53 is provided with a catch'52 normally out of engagement with the finger 49 when the mechanism is idle, as shown in Figure 1, as long as the coil is in its lowermost position, as shown in Figure 3, but after the motor switch is closed and the coil SC moved to the upper end of its the panel I to extend stud 46 mounted on the lower extremity of the arm 29 will hold the heating element E in its removed position from the cup 36. As the thermal actuating strip 3'! cools it engages the stop 11 and through actuator plate 33, link 35 and actuator plate 32 moves the magnet IM to its inoperative position and opens the ignition circuit through the switch IS while the motor circuit is maintained closed through switch MS as the catch 52 on the repelling of the coil SC en gages the end of the finger 49 during the normal operation of the burner mechanism, The positions assumed by the parts during the normal operation of the burner are illustrated in Figure 5 and the circuits established are shown in the wiring diagram of Figure 6.

If there is a failure of the commercial current while the burner is operating with the room ther- T in closed position the coil SC will drop, releasing the finger 49 and if the ignition switch IS is open or upon the opening thereof by the cooling of the actuator strip 31, the power of the magnet MM is overcome by the

arms

29 and 45 to open the motor switch MS and the heater returns to be received within the cup 36, so that upon a current resumption thereafter the mechanism will recycle or repeat its initial ignition operation and assume the normal operation positions.

In the event that for any reason the fuel is not ignited during the predetermined time of the ignition period, provision is made to open the motor circuit and prevent operation until such time as the mechanism is manually reset. Under normal operating conditions, as previously described, it is necessary to maintain the magnet M in operative position and maintain the motor switch MS closed after the cooling of the actuator strip 31 has opened the ignition circuit. Therefore, as the parts move from the idle position, as shown in Figure 1, to the position assumed during the ignition period, as shown in Figure 3, provision is made to lock the heater arm 45 in the latter position during the time between the closing of the circuit through the room thermostat T and the repelling of the coil SC to engage the finger 49 of the magnet carrying arm 29 and, during normal operation thereafter, to unlock the arm 45, whereafter it is held by the stud 46 on the magnet arm 29 as long as the motor switch MS is closed and yet free to return to its idle position upon opening of the motor switch, but, in the event the coil SC is not repelled, then to hold the arm 45 in locked position, so that upon cooling of the actuator strip 31 to open the ignition switch and motor switch because the latter is not held by the relay lock 52, the element E is prevented from returning to its idle position until manually released and the mechanism reset to assume operation.

To accomplish this the heater carrying arm 45 is provided with a prolongation 53 extending beyond' its pivot post 3| in an upward direction and a latch 54 is mounted upon a pivot post 55 upon over the free end of the extension 53. The under side of the latch is cut out to form a shoulder 56 adapted to engage the free end of the extension 53 when it has assumed the igniting position, as shown in Figure 3. As shown in Figure 1, the latch is normally held in lifted or inoperative position by an arm 51 having extending under the free an adjutsable half round stud 58 mounted upon its free end adapted to engage the flat surface thereof under the body of the latch 54, which arm extends from a pivoted plate 59 with its main body arranged on the opposite side of its pivoted post 60 upon the panel I to normally hold the latch in inoperative position. To release the latch 54 to assume its operative position, the plate 59 is provided with an arcuate arm 6| extending below the pivot pin 60 in the same direction as the arm 51 and is normally held with its free end in engagement with the free end of an additional thermal actuator strip 62, the other end of which is secured to the block 39 mounting the actuator strip 31 so that it will also react to the compensating action of the thermal member M. It s preferableto mountthe thermal actuator strip 62 adjacent the thermal actuator strip 3'! in such a manner that the thermal element E may be reciprocated through an opening provided therefor in the strip 62 and so arranged that when the arm 45 has been moved to withdraw the heating element from the cup 36 it will be actuated within and its heat will be transmitted to the actuator strip 62 causing the free end'thereof to be deformed to engage the arm SI and through it rotate the plate 59 to withdraw or drop the stud 58 to free the latch 54, and yet when the heating element is received within the cup 36 the actuator strip 62 is sufficiently spaced apart therefrom so that it is not materially affected by the heat therefrom.

Inasmuch as the strip 3? has acted to withdraw the heating element E from the cup 36 in rotating the magnet M to close the motor switch MS, the free end of the extension 53 of the arm 65 is in pos tion to be engaged by the latch 55 when the action of the actuator strip 62 allows it to drop and the shoulder 56 will hold or lock the arm 45 in the position shown in Figure 3 during theignition period. When normal ignition does not occur the actuator strip 3! will cool and rotate the

actuator plates

32 and 33 to allow the arm 28 to open the ignition switch IS whereupon the motor mag-.

net arm 29 not being held also moves to open the motor switch, by means of the fact that the motor magnet MM lacks suflicient'power by itself to maintain the. switch closed, but the latch 5% prevents the reiurn of the heating element E to be received in the cup 35 until the latch 55 is lifted. A manual release or reset is provided which includes, a rotatable plate 65 pivoted upon the panel above and at one side of the pivot post 65 opposite the ex ension 57. The plate 66 is provided with a notch 65 and an angular surface 56 therebelow adapted when the parts are in the idle position, as shown in Figure 1, to be engaged by an adjustable stud 61 mounted on the plate 59. The stud 61 will ride over the surface 65 upon the further movement of the'actuator strip 62 as the heating element E continue to be energized through the closed thermostat circuit after the normal ignition period has passed and engage in the notch 65, as shown in Figure 7, to prevent the rotation of the plate 59 to raise the latch 5t and unlatch the heater arm 45 in the event the heater element E should become de-energized, as by a failure of current, to permit the actuatorstrip 52 to cool until the knob, marked on the drawing reset which is mounted upon the reset plate 65 above its pivotal point, is rotated in the direction of the arrow to take the notch 65 and body of the plate therebelow from under the stud 67. The reset plate 64 is also provided with a portion 68 end of the latch 54 energization of the heater element E as by a power I or current interruption which, upon the subse-' quent cooling of the thermal member 62, would otherwise be followed by the return of the arm 51 to idle position which action would disengage extension 53 and latch 54 to free the heater element arm 45 whereupon the heater would be restored within the cup 35 to cause a resumption of operation upon the restoration of current with the thermostat calling for heat. v

When normal ignition of the fuel occurs and switch SS is closed the movable coil SC of the relay R is repelled and this movement is utilized to free the latch 54 by providing the bracket 50 with an upstanding arm 68 mounting a roller 69 adapted to engage and ride over an angular surface ill to engage under a depending portion H of the latch 55 to rotate it about its pivot to lift the shoulder 56 above the end of the extension 53 so that the arm 65 is free to return the heating element E to the cup 36 while thecatch 52 engages the end' of the finger 49 to maintain the motor switch MS closed, as shown in Figure 5; It is to be noted that by the movement of the coil SC, as shown in Figure 5, it is also lifted out of contact with the stud 58 of the arm 51.

When, in the course of operating the burner, combustion is established and then fails it is desirable to restart it in an effort to supply the call for heat. In the event of such failure being the result of a power failure a resumption of current is the only remedy required. Should such failure be caused by a clogging of the fuel line or fuel supplying apparatus or of some possible self correcting cause another operation of the burner apparatus may of itself eliminate or dispose of the factor contributing to the failure of the flame. For this purpose a pivoted catch 12 in the form of a plate is pivotally mounted on a post 13 above the latch 56. The catch 12 is provided with a notch it adapted to engage a stud 15 provided therefor upon the latch 54 and is provided with a depending portion 15 extending into the path of travel of the free end of the extension 53 of the arm 35, so that-when the latch 54 has been lifted by the movement of the coil SC the catch l2 will hold it in that position, as illustrated during the normal operation of the burner mechanism and shown in Figure 5. Should there be a current interruption in the commercial line or the flame fails allowing switch SS to open after the motor switch MS has once been locked in running position, as shown in Figure 5, the coil SC will fall to release both the finger 59 of the magnet,

when the latch 55 is lifted What I claim is:

1. In an electrically operated and controlled fluid fuel burning mechanism, a motor circuit and a switch in said circuit, electrically controlled means for opening and closing said switch including a room thermostat and a resistance heating element and switch operating means coacting with thermal means responsive to heat from the heating element to actuate the switch operating means, in combination with means cooperating with the switch operating means in closing the switch to-withdraw the heating element from operative association with said thermal means, a switch responsive to the presence or absence of combustion adapted upon the establishment of combustion to shunt out the said heating element, and means actuated upon the shunting of the heating element to lock the motor switch in closed position as long as the shunt circuit remains closed. I

2. The structure of claim 1,- wherein the source of current is connected in series with the primary windings of a repulsion relay and the motor circuit is connected in parallel therewith, and wherein the room thermostat and heating element are connected in series with the secondary movable coil of the repulsion relay, and wherein" the resistance of the heating element is sufiicient to prevent the repulsion of the secondary coil of the relay until said heating element is shunted out by the closure of the combustion responsive switch and wherein the repulsion of the secondary coil operates the motor switch lock.

3. The structure of claim 1, wherein the switch operating means includes a pivoted actuato 4. The structure of claim 1, wherein the switch operating means includes a pivoted actuator plate from the heating element.

5. The structure of claim 1, wherein means are provided to hold theheater when placed in withdrawn position, said heater'holding means ren- .dered operative when the locking means for holding the motor switch closed is actuated.

' oted arm, and wherein a latch is provided to engage the free end of said arm when the heating element is withdrawn, said latch normally released when the locking means for holding the motor switch closed is actuated, and wherein a 7. The structure of claim 1, wherein the means to withdraw the heating element includes a pivoted arm, and wherein a pivoted latch is provided adapted to engage the free end of the arm when the heating element is withdrawn, and wherein means is provided to normally hold the latch out of engagement therewith adapted to be operated by a second similar actuating strip of bi-metallic metal responsive to the heat from the heating element when in the withdrawn position to release the latch to hold the arm with the heating element withdrawn from the first mentioned actuating strip.

8. The structure of claim 1, wherein the means to withdraw the heating element includes a pivoted arm, and wherein a pivoted latch-is provided adapted to engage the free end of the arm when the heating element is withdrawn, and wherein means is provided to normally hold the latch out of engagement therewith adapted to be operated by a second similar actuating strip of bi-metallic metal responsive to the heat from the heating element when in the withdrawn position to release thelatch to hold the arm with the heating element withdrawn from the first mentioned actuating strip, said last named means upon continued heating of said second actuating strip adapted to engage a pivoted lock to prevent said means from again releasing the latch from the heating element arm until the pivoted lock is manually released.

9.'In an electrically operated and controlled fluid fuel burning mechanism, a source of electricity connected in circuit to the primary windings of a repulsion relay, a motor switch therein connected in parallel with the first circuit, thermally actuated means for operating the motor switch including a pivoted switch actuator plate, a pivoted switch operator arm adapted to be-engaged and rotated in one direction by the actuator plate to close the switch, a bi-metallic actuating strip having a free end adapted to engage the actuator plate, an electric resistance heating element, a pivoted arm normally supporting the heating element adjacent the actuating strip and adapted to be engaged by the switch operator arm to rotate the heating element away from the actuating strip, a secondary circuit connected to the windings of the secondary movable coil of the repulsion relay, said heating element and a room thermostat connected in series in the secondary circuit, with the resistance of the heating element suflicient to prevent movement of the coil when the room thermostat is closed, a switch responsive to combustion, conditions to close upon the establishment of combustion connected'in a shunt circuit to shunt out the resistance heating element, whereby the closing of the room thermostat energizes the heating element to cause the bi-metallic actuating strip to rotate the actuator plate to close the motor switch and withdraw the heating element from the actuator strip and upon establishment of combustion to shunt out the heating element and thereafter .allow the secondary coil of the relay to be repelled, a catch on the secondary movable coil of the-relay adapted to engage the switch operator arm when in the repelled position to maintain the motor switch closed as the actuating strip cools to return the actuator plate to its normal position.

10. The structure of claim 9, wherein a pivoted latch is provided adapted to engage the free end of the heating element arm when the heating element is in its withdrawn position, a latch a motor circuit having 1 repulsion relay adapted when the relay is repelled to lift the latch to release the free end of the heating element arm, a pivoted catch adapted to engage the latch and hold it in its releasing position, said catch having a portion depending in the path of the heater element arm to be engaged thereby to release the latch as the heating element arm returns to normal starting position upon the release of the switch operator arm.

11. The structure of claim 9, including an ignition circuit connected in parallel to the first named circuit and including an ignition device and an ignition switch connected in series therein,

an ignition switch operator arm, and an operating connection between the motor switch actuator plate and the ignition switch operator arm, whereby the ignition switch is closed in unison with the motor switch and the ignition switch til opened independently of the motor switch upon the cooling of thermal actuating strip.

12. In a fluid fuel burning system, an electrically operated and controlled fuel burning mechanism, a circuit therefore, a switch in circuit therewith, thermally actuated means and a movable electric resistance heater therefore, said means when heated operative to close the switch and disassociate the heater therefrom and thereafter upon cooling to allow the switch to open, electrically operated means for holding the switch closed and the heater removed from the'thermal means, a circuit for the electrical means including a thermostat and said heater, the latter,

when energized, preventing operation of said elecoperator mounted upon the movable coil of the trical means, a shunt circuit around the heater, and a combustion responsive switch therein operating upon the establishment of combustion to close to deenergize the heater and render the electrical holding means operative.

13. The structure of claim 12 wherein safety lock-out means are provided operating, upon removal of the heater from heating relationship .with the thermal means and failure of the combustion switch to close, to lock the heater in the removed position, means actuated by the electrically operated holding means upon closing of the combustion switch to render the safety lockout means inoperative, and means for resetting the safety lock-out means actuated by the movable heater when released by the electrical holding means.

14. In a fluid fuel burning system, an electrically operated and controlled fuel burning mechanism, a circuit therefore, a thermally actuated switch in circuit therewith responsive to heat to close, an electrical resistance heater movable into and out of heating proximity with said thermally actuated switch, means associated with the closing of the thermally actuated switch to move the heater from its heating proximity therewith, a thermostat in circuit with v said heater, a combustion responsive switch and electrical means controlled thereby upon establishment of combustion for holding the thermally actuated switch and heater, in their thermally actuated positions.

IRA E. McCABE.