US2407438A - Burner control - Google Patents

Description

Sept. 10, 1946. E. P. NEWMANl 2,407,433

`BURNER CONTROL. l

FiledJuney 15, 1944 2 Sheets-Sheet 1 /A/L/t'A/roe: Emo R Mew/VAN,

Err-0 R ME /6 Sept. 10, 1946.` E. P. NEWMAN BURNER CONTROLv Filed June 15, 1944 2 sheets-shet 2 Patented Sept. 10, 1946 BURNER CONTROL Eric P. Newman, Clayton, Mo., assig'nor to Automatic Control Corporation, St. Louis, Mo., a

corporation of Delaware Application June 15, 1944, serial No. 540,372

The present invention relates to a control, and particularly a control for burners andthe like. Y

It comprises vbroadly a main fuel'valve in a main fuel line, a pilot fuel valve in a pilot fuel line, and an igniter, all under control of some external control such as a space or room thermostat, with suitable switches and connections to operate the burners safely.'

An object of the invention is to provide a c'ntrol' wherein, in response to external demand for heat, the pilot name is ignited, andgin response to a substantial and rapid change in heat at the pilot, the main fuel line is opened. More particularly, an object is to provide a control wherein the pilot acts in a dual capacity of being a means to ignite a main burner andalso as the actuating means for a flame switch which controls the main valve actuating circuit. Y

A further object of the invention is to'provide a control wherein a failure of the flame switch to open or a short-circuitingof the flame switch at the time of av call for heat will result in a lockout of both main and pilot fuel valves, A further object is to provide a control system for a fuel burning system which is entirely automatic from one winter season to the next, which wastes no pilot gas when heat is not needed, and which is small and can be installed 'at avery reasonable cost.

Another 'object is a control Which'will operate regardless of changes invambient temperature in the furnacebefore, during, or after fuel combustion. i f

A further object is to provide a control system operable with either alternating or direct current.

Further objects of the invention include the provision of` a control wherein a momentary break of the pilot valve .relay circuit, such as vby the walking of or manual vibration of the room thermostat or a momentary power failure`,`wi1l cause a complete recycling to prevent escape of unburned fuel through the main Valve.

' Fig. -1l is a vdiagrammatic View of one type of the control employing arbucking coilzprinciple therein; Y

Fig. 2 is a rdiagrammatic `view of a modification of' Fig. 1;

Fig. 3 is a modification' thereof wherein a resistance combination is used;

Fig.'4 is a view of theame-switch preferably used herein; and Y Fig. 5 is a section on the line 5-5 of Fig. 4.

Referring to Fig. l, the mechanism includes broadly an external control, here shown as a room thermostat I Il. It includes also `a main burner 11 claims. (o1. 15s- 1171) v II, a pilot burner I2, an igniter I3, and afname switch I4. -In addition, it comprises a relay actuated'main Vvalve mechanism I5, and a relayv actuated pilot valve mechanism I6, and a transformer I1. e Y j .The main burner is fed from a fuel line 20, which leads tothe main valve mechanism I5, and thence by a line 2I to the burner I I. A pilot line 22 is connected into the main line 25 ahead oi-the main valve mechanism I5, the'line22 leading to the pilot valve mechanism I6, and'thence by a line 23 to the pilot burner I2. y. The main valve mechanism I5 includes a valve member 25 operating againsta valve seat 26 interposed between the fuel lines 20 and 2I. The valve is actuated by a'magnetic coil 2l, which, when energized, opens the valve.

The pilot valve mechanism I6 comprises ra ball type valve element 30 adapted to seat upon a seat 3|, toward whichvit is urged by a spring 32. The seat V3| is disposed between the lines 22 and 23. The valve is actuated by a pin 33 extending up beneath the valveseat. A flexible diaphragm 34, supported on thevalve housing and` secured in sealing relation tothe pin 33, seals the pin to prevent leakage of gas aroundit. The pinj33 is, in turn, attached to an armature 35, operated by a magnetic coil 36, the latter elements, together with a coil 66, forming 'a relay generally designated31.

" AThe flame actuated switch I4 is preferablyA of the rate of change type; An illustrativev form of it comprises archannel-shaped supporting mem...

' ber 4l), having V.flanges 4I -thereon,by means of which it maybe securedproperly to the burner. This channel-shaped member 40 embraces and supports the pilot burner I2. The member 40 likewise has secured thereto an inner member 43 formed of metal of substantially the same coeflibottom part of the member 40, where it has 'an l insulated actuating button 43`that may be moved over to close the switch blade 5IlV against fthe switch blade 5I. n

This ame actuated switch is adapted to receive the pilot flame against the member 43, confined between the wings 46, When flame is applied thereto, the member 43 expands rapidly, increasing in length between the spot- welds 44 and 45. The outer member 46, within the corresponding length between the welds 44 and 45, receives heat only indirectly from the pilot name,v primarily by conduction through the small welded ears. As a result, the length between the welds of the outer member 40 expands less rapidly than the corresponding part of the inner member and does not attain the temperature of the inner member so long as heat is applied to the inner member in the relatively unlimited quantity represented by the pilot flame. Consequently, both will expand, but the inner will always be longer when the pilot flame is applied to it. Conversely, when the. pilot flame is extinguished, the two members rapidly equalize in temperature and assume their relative starting positions.

Thus, upon rapid temperature change applied to the inner member, as when the pilot flame comes on, the inner member 43 will expand rapidly relative to the outer, and warp the upper end of the device outwardly. As the blade 48 is rigidly secured to the upper part of the outer member 46, the lower end of this blade, through the button 49, will act to close the contacts 5U and 5I. And when the pilot flame goes off, the two members willv rapidly equalize in temperature, and when the temperature differential is below the operating differential, the switchwill reopen. 1 ,Y

It will be seen that changes in ambient temperature will not change the position assumed by this switch in response to the condition of the pilot flame, because ambient conditions expand or contract the distance between the welds on both inner and outer members in a similar amount. Although the changes in ambient temperature affect the amount of the differential in temperature to a small degree, they do not affect the existence of a substantial differential of a quantity to operate the switch. Hence the device operates in response strictly to pilot ame conditions, Vregardless of the starting temperatures of the two members 4B and 43 resulting from any changes in ambient temperature, and regardless of'changes in ambient temperature during main burner operation.

The foregoing switch is in principle the same as that disclosed in the patent of James A. Rodgers, 2,392,065, issued January l, 1946.

A relay switch 6I is provided for joint operation with the main valve 25 by thecoil 21.

The coil 35 operates through the armature 35, switches 64 and 65, these switches being for purposes to be described. The coil 36 also has associated therewith a `bucking coil 66 wound to oppose the magnetic pull of the main coil 36, but of lower power.

The connections are as follows: From the transformer I-1, a lead 10 is joined with a line 1I, that leads through a manual switch 12, to a line 13, connected into the room thermostat I0. When this thermostat cools to a predetermined temperature, it closes a switch 14l connecting the line 15 to the line 13. The line 15 leads to a limit switch 16, which comprises one of the familiar thermal devices for opening the circuit when the heat transfer medium does not remove heat suiciently rapidly to keep the furnace at a safe temperature. From the limit switch 16, the line 11 leads to the relay coil 36. The line 18 4 extends from the other end of the coil 36 to the other transformer lead 13.

From the line 1 6, there also leads a line 8B into the switch 65. From this switch, a line 8i leads into the coil 21, operating the valve 25 and the switch 6I. From the coil 21, the line 83 leads to a line 84. The line 34 leads to the contact 5I of the flame switch. The contact 50 thereof is connected by a line 9E! to the transformer lead 19. Thus the foregoing main valve operating circuit is directly across the secondary of the transformer in parallel with the room thermostat previously mentioned, but subject to controlby the room thermostat through the switch 65.

An additional circuit is provided in parallel with the coil 21 in the last described circuit. It comprises a line 93 connected to the lead 10, leading to a bucking coil 66, from which a line 94 leads into the line 84.

A lower Voltage line 95 leads from an inner point of the secondary of the transformer to the switch 64. From this switch, a line 36 leads to the igniter i3. From the igniter, a line 91 leads to the switch 6I, from which a line 98 connects into the return lead 19 of the transformer.

Operation The manual switch 12 is closed during any period in which the system is to be used. The limit switch 16 will normally be closed. At the start, the room thermostat switch 14 is open, the burner II and pilot I2 are off, the flame switch I4 is open, the switch 6I is closed, and the switches 64 and 65 are open.

When the room thermostat Ill closes its switch 14 a circuit from the lead 'I3 of the transformer is closed through the line 1 I, the room thermostat II) and its switch 14, the line 11, the main coil 36 of the pilot valve I6, the line 18, the lead 19, back into the transformer. Thereupon the coil 36, being energized, lifts its armature, causing the rod 33 to lift the ball valve 3! from its seat and admit gas from the supply line 20 through the pilot line 22', past the valve, and by the line 23 to the pilot burner I2. Energizing the coil 36 also closes the switches 64 and 65. The closing of the switch 64 closes a circuit from the inner tapped line 95 of the transformer through the aforesaid switch 64, the line 96, to the igniter i3, and thence by the line 91 through the now closed switch 6I, by the line S8 to the return lead 1S to the transformer. The igniter I3 will then glow and ignite the pilot ame Vof the pilot burner I2. This flame will then act upon the flame switch i4, expanding the inner member 43 relative to the outer member 46, and warping the blade 43 to close the contacts 50 and 5I. This latter will occur only if the pilot flame ignites and remains ignited. The closure of these two contacts after such ignition of the pilot burner completes a circuit through the other switch. 65r of the coil 36 as follows: From the transformer lead 1U, aline 86 leads through the switch 65, and by a line 8l into the coil 21 of the main valve I5, and thence by a line 83 to the line 84 through the flame switch I4', and by the line 96 back to the return lead 'I9 of the transformer.

Energizing of the coil 21 causes it to lift its armature, opening the valve 25 to admit fuel to the main burner Il, which is ignited by the pilot burner I2. The coil 21 also opens the switch 6I' to break the circuit to the igniter I3 and to deenergize the same.

84, and thence through the flame switch and back to the transformer. The bucking coil is of insufficient strength to f overcome the holding force of the main coil 36, 'but is of sumcient force to prevent the main coil from moving its armature. 1

When thus started, the burner II will operate for a running period. The pilot burner will likewise Vburn during this period. Thereafter, when the room thermostat I is 'heated by the heat from the burner, it will break the contacts of the 1 switch 14, which will open the circuit through circuit t'o the igniter, which, during the running period, is aiready open at the switch 6 I; Opening of the switch 65 breaks the circuit to the main valve :coil 2l, so that the main valve 25 immediately closes, and the switch 6Iv also recloses. However, as noted, the closure of the switch 6I does not close the circuit to the igniter'at this time, since it is now open at the switch 64. With both the main and the pilot valve closed, the main and pilot burners Il and I2 stop operating, and the ame switch I4 cools. With the type of flame switch shown, and which is preferred, this openingof the contacts 50 and'5l will occur within a few seconds after the pilot burner goes out, as this control responds immediately to an abrupt change of temperature on the inner member 43, regardless of the ambient temperature applying equally to both members.

As noted, the bucking coil 66 opposes the main coil 36, but is of insufficient power to'cause a release of the armature.V -Since itis of sufficient power to prevent the armature from being pulled in when both coils are energized, any instantaneous break of the principal circuits, such as by vibration of the room thermostat contacts or an instantaneous power failure either of which are of insufficient duration to vpermit the" flame switch contacts to open, will, nevertheless, result in aY complete recycling of the control. This occurs because any such ,action deenergizes the main coil 3B and its armature falls out.` If this .3

break of the circuit of the main coil 36 occurs by jiggling of the thermostat, the coil 66 will remain in circuit and will act to open the switches 64- and 65 and close the pilot valve`30. If, however, the main coil 36 is deenergized because lof a momentary power failure,the, armaturewill fall, and upon restoration of power the coils 36 and 66 willV become simultaneously energized providingY the contacts 50 and 5I remain closed. Insuch case, the coil 66 is energized at the same time the coil 36 becomes reenergized, and, although the algebraio sum of the forces produced by the opposed coils will hold the armature 35 up once it is raised, this force is not ygreat enough 'to pull the armature up from its lower position.

Thus, with the armatureofthe coil 36 down, the pilot valve is closed and the circuit to the mainv valve coil 2'I is broken through the switch 65. Therefore, the main valve closes upon such instantaneous circuit failure, and it is prevented from reopeninguntilthe switch I4 coolsand'th'e bucking effect of the coil 66 is destroyed by the opening -of the contacts 50 and 5I, whereupon the coil 36 is effective again to close the 'switches 64 and 65,toopen the pilot vvalve 30, to 'start the c a 6 igniter I3, and, Ain short, to produce a complete recycling from the starting condition.

K Were it not fory the coil 66 or its equivalent, an instantaneous failure ofthe principal circuits, re-

sulting in at least momentary closing ofthe valves, might be accompanied by a failure of flame at Zboth burners followed by an immediate re` opening of both valves with lthe igniter I3 in an open circuit. Thus, when the power fails, the armature 35 drops outand the switches 64 and 65 open. Resumption of power before the switch I4 cools, and without the coil 66 in operation, would close the switch 65, open the valve 25 and break the igniter circuit at 6 I. Thereafter, when the contacts'50 and 5I open upon the cooling of the switch I 4, the coil 21 is deenergized, the valve 25 isA closed and the igniter I3 is madeA operative by the vclosing of the switch 6I. The igniter circuit'is thus completed after a substantial amount of unburned gas had been delivered by the main Y burner to the furnace, which action could easily causev an explosion even though the main burner had been shut off before the ignition carne on. If the' pilot isf extinguishedfduring operation, and is notv relit by the main burner llame, this will normally result in opening of the"contacts 56 and 5l of the flame switch, followed immediately by closing of the main valve 26 and closing of the switch 6I, so that the igniter I3 may again be put in the circuit for re-ignition. If fuel pressure falls substantially, the pilot flame will not Ygenerate sufficient heat to maintainV the switch I4 closed, and the main valve 25 will close due to the opening ofthe circuit to the coil 2'I.

If there is a failure of the igniter or of pilot ignition at the start o-f a cycle, the main burner valve 25 will not open and theescaped gas will be only in the limited volume running through the pilotline.4

If the room thermostat remains, closed, either by failure or otherwise, so that the burner attains an excessive temperature, the limit switch 'I6 will be 'opened inV conventional Ffashion. This will bre'althe-circuit to the coil 36, resulting in closure of the -main and pilot Valves, which will remain in circuit until the contacts and 5I are opened. Thereafter the control will be required to recycle completely upon any reclosure of the .control will operate to complete the cycle started,

but after the `cycle ends a new one cannot be' instituted because the bucking coil 66'is energized whenever the contacts 50 and 5I are closed.

Obviously, too, if the flame switch fails in open position, the main burner valve can never open. These two failures are controlled inthe foregoing manner, regardless of an additional failure of the room thermostat.

MOdifi'CatiO'n 0f Fig. 2

@ou sea.

The main valve switch coil is at 21a, and the iiain valve operating coil it at 2lb.` These two 7 coils are directly in parallel for simultaneous energization, wherebythe valve 26 and the switch Si; will .he openedA simultaneously.

It will be seen that: the transformer leads 10,

IS; and 95 remain as before, as do the leads 84 E@ to the name switch. The line 11 from the thermostat lil branches into a line 11a leading tothe coil 35a, and into a line 11b leading to the coil 35o, by way of a switch 63.

' When the room thermostat I 0 closes', `current hows from the transformer lead 'lll through the line 1l, the thermostat l0 and the line 11. In this modification, the line 11 branches into a line 11o and a line 11b. The current flows through the line 11a, and thence through the coi-l 36a, whence it iows by a line 18av to the other transformer leadv 13. Thus the coil 36a is put in circuit as soon as the roomV thermostatV closes, in the same manner as before. It then closes the three switches 63, S4, and 55. When the switch 63 is closed, it closes a circuit from the line 11 through a line 11b to the coil 36h, and thence back to the transformer lead 19. This puts the coil 36h for operating the pilot valve3llv in parallel with the coil 35a but under control of the switch 63 of the latter coil.

When the switch 64- closes, it establishes the ignition circuit through the line 95 as ibefore, and the line 91 and the closed switch 8|, and the line 98: back to the transformer lead 19. As the coil '21aV is then out of circuit, as was the fcoil 21 at a corresponding time in the4 other illustration, the igniter will become operative. Thus the pilot burner may lbecome ignited.

When the switch 65 closes, the line 8l is connected'with the transformer lead 10, and this line through its connections Bla and 8lb leads to the two coils 21aand 21h, and thence by the two leads 83o and 83h. These two parallel leads merge in the line 83, which is connected with the lines 94 and St as before. Thus the two Icoils 21a and 2lb are directly in parallel and operate in unison whenever the switch 55 is closed and the name switch also is closed, the two operating in the same mannerfas the single coil 21 in the earlier illustration. l

The bucking coil 66a is connected directly across the transformer leads and through the flame switch as before. Its operation is the same as before, but the third switch 63 is employed so that when the bucking coil is effective it not only breaks the circuits through the switches 64 and. G5, controlling the main valve and igniter, but also is eiective through the switch B3 to open the circuit to the pilot valve coil 36h and insure closing of that valve.

It will further be evident that the choice of one or two coils, either for the pilot valve control or for the main Valve control, does not affect the overall operation of the mechanism where the connections are made as shown in Figs. 1 and 2. Sometimes, for mechanical reasons such as efficiency of manufacture or the desire for separating the switch operation or control from the valve operation or controls, it may be desirable to use separate coils to actuate one or more of the valves and switches.

Modification of Fig. 3

In Fig. 3, there is shown a control that accomplishes the same objective but uses a resistor instead of the bucking coil 66. In this arrangement, the parts are the same except for this substitution. It comprises the introduction of a rst resistor Rl in the line 11 leading from the thermostat. The line from the resistor RI' into the coil 3621s designated 11o. From the line 11o, a line 1165' leads through a resistor R2 to the line 84.

When the room thermostat l0 closes, the same circuit from the line 10 through the line 1l, the room thermostat l0, the line 11, the resistor Rl, the line 11o, the coil 36, the line 18 and the line 19' is effected. This closes the switches 64' and as heretofore. When the switch 64 closes, the igniter i3 is energized because the switch 6|, operated by the main valve coil' 21, is closed. The pilot valve 30 is open and the pilot flame ignites, whereupon the flame switch I4 closes the contacts 5i) and 5f. This closes the circuit from the line 1G through the line 80, the switch 65, the line 8i, the coil 21, the line 83, the line 84, the switch I4, the line 90, and the lead 19, whereupon the main valve 21 is opened and the switch 6I is also opened to cut the igniter I3 out. Thus the out out of the igniter and the opening of the main valve are, as before, dependent upon the existence of a pilot name.

At the same time this last circuit is closed, the parallel circuit from the line 11o, through the line HB5 and the resistor R2, is closed by way of the line 84, the switch I4 and the line 9i). The resistor R2 introduces a circuit drawing current in parallel with the coil 36. This current increases the voltage drop across the resistor R! (which resistor may comprise in whole or in part the inherent resistance in the circuit). The increased voltage drop across the resistor Rl reduces the voltage available to the coil 35, so that its current drop and its magnetic pull is lowered. The reduction in magnetic pull is insufficient to cause the coil to drop its switches open, but is sufficient to preventl the coil from pulling the switches from an open position.

In this circuit, it will be seen that the same results as in Fig. l' attain, except that the parallel voltage reducing circuit Vis open whenever the room thermostat opens. It acts to prevent the main Valve from returning to open position upon break in current through the coil 35 until the llame safety switch I4 has cooled.

It will be understood that the control may be employed with other controlling elements, such as diaphragm valves, in which case the-particular Valves illustrated become relay or pilot valves controlling the bleed lines of the familiar diaphragm type valves.

For use with D; C., the system may beY modified', as by employing voltage dividers of conventional types, in which case, the bucking coil has the advantage of opposing the lifting of the armature, as well as diminishing the force of the main coil.

In some installations, it may be desirable to use a separate transformer for the igniter instead of a center tap on the main transformer. In such case the primary of the second transformerv could be energized in parallel iwith the circuit including the coil 21 and flame switch i4, and the primary circuit would include the switch 6|. Obviously this would eliminate one switch 64 of the relay 31, as the voltage into the switch '6| and the primary would be the same as that through the switch 65, permitting interconnection of the circuits.

What is claimedr is:

1. In a control for use with a main burner, a pilot burner, and a main control device including a power element, electrical means operatedy through the main control to supply fuel to the main burner, a flame-responsive switch opanos-188 9. erated by combustion at ,the pilot burner, and means controlled by vsaid flame-responsive switch for reducing the power of said element to'render .the same effective to hold said control device in a closed position once, this position is attained, but ineffective to move ksaid device from an opento a closed position. c

2. In a control for use with a main burner, a pilot burner, Vand a main control device, a flameresponsive switch operated upon existence oi" combustion at the pilotburner, an electrical fuel supply means energizable to operate the main burner, means `responsive to operation of the main control device to cause operation of the pilot burner, means operated in response to operation of the pilot flame switch to energize the main burner fuel supply means, and means operated in response to operation of the pilot vilaine switch to prevent reoperation of the main burner fuel supply Vmeans when the llame-responsive switch is in operative position.

3. In a control for use with a `main burner, a pilot burner, anda kmain control device, a amcresponsive switch operated upon existence of combustion at the pilot burner, rst means responsive to operation of the main control device to effect operation of the pilot burner, said means including mechanism concurrently operated to control actuation of the main burner, said mechanism being also dependent upon operation of the flame-responsive switch, and safety means operated upon closing of the pilot flame switch to render the first means incapable of shifting from inoperative to operative position when the iiame switch is in operative position.

4. In a control for use with a main burner, a

Vpilot burner, and a main control device having a power element, a name-responsive switch operated upon existence of combustion at the pilot burner, pilot fuel supply means operated by said main control device, first means responsive to opf eration of the main control device to effect ignition of the pilot burner, said means including mechanism concurrently operated to control actuation of the main burner, said mechanism being also dependent upon operation of the pilot name switch, and safety means operated upon closing of the pilot flame switch to render the iirst means incapable of shifting from inoperative to operative position when the iiame switch is in closed position, said safety means comprising a power reducing means adapted to reduce the power of said element below that required to operate the iirst means from an open to a closed position, but not less than that required to hold the first means in a closed position once this position is attained.

5. In s, control for use with a main burner, a pilot burner, and a main control device including a relay, a, flame-responsive switch operated upon existence of combustion at the pilot burner, pilot fuel supply means operated 4by said main control device, rst means responsive to operation of said relay to effect ignition of the pilot burner, said means including mechanism concurrently operated to control actuation ofthe main burner,

said mechanism being also dependent upon op- 6. In a control for Vuse with a main burner, a pilot burner, and a main control device including a relay and coil, a flame-responsive switch operated upon existence of combustion at the pilot burner, pilot fuel supply means operated by said maincontrol device, flrstineans responsive to operation of said relay to effect ignition of the pilot burnery said means including mechanism concurrently operated to control actuation of the main burner, said mechanism ,being also dependent upon operation of the pilot llame switch, and safety means operated upon closing ofthe pilot flame switch Vto render said relay incapable of shifting said first means from an inoperativepto an operative position when the ame switch is in a closed position, said rst means comprising a switch device and said safety means comprising-a bucking coil producting a magnetic force in opposition to that of the relay coil.

7. In a control for use with a main burner, a pilot burner, and a main control device including a relay, a name-responsive switch operated Yupon existence of combustion at the pilot burner, pilot fuel supply means operated by said main control device, first means responsive to operation of said relay to effect ignition of the pilot burner, said means including mechanism concurrently operated to control actuation of the main burner, said mechanism being also dependent upon operation of the pilot fiame switch, and safety means operated upon closing of the pilot flame switch to render said relay incapable of shifting said flrst means from an inoperative to an operative position when the flame switch is in a closed position, said first means comprising a, relay switching device and said safety meansincluding a current reducing device to lower the current through a coil of said relay.

8. In a control -for use with a main burner, a pilot burner, and a main control device including a relay, a name-responsive switch operated upon existence of combustion at the pilot burner, pilot fuel supply means operated by said main control device iirst means responsive to operation of said relay to effect ignition of the pilot burner, said means including mechanism concurrently operated to control actuation of the main burner, said mechanism being also dependent upon operation of the pilot flame switch, and safety means operated upon closing of the pilot ilame switch to render said relay incapable of shifting said rst means from an inoperative to an operative position when the flame switch is in a closed position, said first means comprising a switching device and said safety means including a resistance to reduce the current through the relay.

9. In a control for use with a main burner, a pilot burner, a pilot igniter and a main control device, a rst means .to admit fuel to the pilot burner upon operation of the main control device,

said means being also adapted to operate the pilot burner, a pilot igniter and a main control 1i device, first means to Yadmit fuel to the pilot burner upon operation of the main control device, said means being also adapted to operate the pilot igniter, second means including a device operated -to actuating position upon existence of combustion at the pilot burner and the rst means to admit fuel to the main burner, said second means being also Aadapted to render the igniter inoperative, said combustion device being operable in response to combustion or combustion failure at the pilot regardless of ambient temperature variations, and said device, upon failure of pilot combustion, being adapted to render the second means inoperative, means to effect shutoff of the lmain burner fuel supply means upon ,l

coil capable of actuating said device "to burner operating' position, and a buckingrcoil'operatively vassociated with the main coil and adapted, when both coils are energized, to reduce the power of the relay to a value suiiicient to holdthe device in operating position, but incapable of pulling it to said position, the main coil being adapted to be energized and to operate the actuated device to provide burner operation when the space thermosta-t demands heat, a combustion-responsive switch movable to a combustion-indicating .position when combustion exists at the burner, the bucking coil being connected with the combustion-responsive switch to be energized When the same moves into combustion-indicating position in response to existence of combustion at the burner, whereby when said thermostat demands heat and the combustion-responsive switch is in combustion-indicating rposition the relay can hold the actuated device., but cannot pull the same to operating position.

ERIC P. NEWMAN.

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