US1883242A

US1883242A - Oil burner control system

Info

Publication number: US1883242A
Application number: US333951A
Authority: US
Inventors: John C Bogle
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1929-01-21
Filing date: 1929-01-21
Publication date: 1932-10-18
Anticipated expiration: 1949-10-18

Description

oct; 1s, 1932. l J C, B'GLE 1,883,242

' OIL BURNER CONTROL SYSTEM 4 Filed Jan. 21. 1929 etv Patented Oct. 18, .1932

UNITED. STATES PATENT lOFFICE JOHN C. BOGLE, OF RIVER FOREST, ILLINOIS, ASSIG-NOR, BY MESNE ASSIGNMENTS, TO MINNEAPOLIS-HONEYWELL REGULATOR COMPANY, F MINNEAPOLIS, MINNESOTA,

A CORPORATION OF DELAWARE OIL BURNER CONTROL SYSTEM Application fled January 21, 1929. Serial No. 333,951.

This invention relates to an oil burner control system and has particulanrelatlon.

to circuits and apparatus for effecting desired predetermined operation of such systems.

The primary object of this invention is to provide means for effecting the occurrence of predetermined steps or operations in the cycle of operation ofv an oil burner control system in desired sequence. Q

Other objects and advantages of the invention will appear from a consideration of the following detailed description in connection with the accompanying drawing, in which:

Figure 1 is a diagrammatic representation of apparatus and circuits embodying .the invention, only those parts essential to a full and clear understanding of the invention being shown; and,

Fig. 2 is a schematic representation of the electrical circuits shownin Fig. 1.

Referring first to Fig. 1, a boiler or furnace 11 comprises a combustion chamber 12 Within which a burner 13 for oil or other liquid fuel is properly disposed. The burner 13 is connected through pipe or

conduit sections

14, 15, 16, and 17 to the discharge side of a pump 18, the intake side of which is connected througha pipe or conduit 19 to a tank 20 or other suitable source of' liquid fuel supply. The pump 18 is diagrammatically illustrated as being of the reciprocating type, but it will be understood that any other suitable form of pump may be utilized if desired.

The pump 18 is driven through a shaft 21 and suitable gears or v 'other mechanical means (not shown) from an electric motor 22, which also drives a blower 23. The blower 23 is provided with a conduit 24 for supplying air to the burner 13 for combustion purposes.V

An electromagnetically operated valve 25 is disposed between the ipe or conduit sections 16 and 17 in the uel supply line extending from the discharge side of the pump 18 tothe burner 13. This valve is normally closed and is adapted to be opened and held in its open position in response to the encrgization of its electromagnet. The valve 25 may be of the type disclosed in co-pending application Serial No, 226,730, filed October 17, 1927, by Lawrence E. Koch and Harris C. Roth, for magnetically operated valves, or it may be of any other suitable type operating in a similar manner.

A vertically extending pipe or conduit 26 is connected to the fuel supply line for the burner 13 between the pipe or'conduit sections and 16. The upper extremity of the pipe or conduit 26 is open to permit this conduit to function as a stand pipe to maintain uniform pressure upon the fuel line extending to the burner 13. The provision of this stand pipe equalizes irregularities of pressure due to the operation of the pump 18 or other causes, and thereby improves the operation of the burner 13.

A pressure relief valve 27 is disposed in a pipe or conduit line 28 which is connected to the section17 of the fuel supply line for the burner 13, between the discharge side of the pump 18 and the electromagnetically operable valve 25. The valve 27 may be of any well-known type of pressure relief valve and is provided to relieve the pressure created in the fuel supply line by the pump 18 while this pump is running and the electromagnetically operable valve 25 is closed. The

Y manner in which these conditions are caused to exist will be explained more .fully hereinafter. The pipe or conduit 28 extends from the pressure relief valve 27 back to the source of fuel supply and is thus adapted to return the liquid fuel delivered by the pump 18 to the source 20 when the valve 25 is closed. It will be understood that the valve 27 is closed at all times except when the pump 18 is operating and the valve is closed, and that it is adapted to be opened only in response tothe occurrence of an excessive fluid pressure in the section 17 of the fuel supply line.

A pipe or conduit 29 is connected to a suitable source of combustible gasand extends throughY an electromagnetically o erable valve 30 to auxiliary burner 31 disposed Within the combustion chamber 12 of the boiler 11. The valve 30 may be of a type similar to the valve 25, but adapted for the control of a flow of gas instead of liquid. The valve 30 combustion c may also be of considerably smaller size or capacity than the valve 25. The o eration of the valve 30 is identical with t at of the valve 25, it bein normally closed and provided with an e ectromagnet, which, when energized, opens the valve and maintains `it in open position as long as the energization of the electromagnet is maintained.

The valve 30 is preferably shunted by a bypass 32 in which a manually adjustable valve 33 ma be disposed. rlhe by-pass 32 is regulated by means of the manually adjustable valve 33, or by a fixed initial adjustment when such a valve is not utilized, to permit a relatively slight consta-nt flow of combustible gas to the auxiliary burner 31, at which point this gas is ignited to maintain a pilot llame in the combustion chamber while the valve 30 is closed. p

When the valve 30 is open, the rate of supply of gas to the burner 31 is accordingly increased to ex and the pilot flame within the liamber 12 for purposes hereinafter set forth.

It may also be noted at this point that the by-pass y32 may be supplemented, if desired, by electrical ignition means such as a spark coil 34 and a spark gap 35 disposed in proximity to the auxiliary burner 31. In the event that such electrical ignition means are provided, they will be energized, as hereinafter set forth, concurrently with the opening of the valve 30, to ignite a relatively large gas llame in thecombustion chamber 12 as soon as the combustible' gas is supplied thereto. Under such circumstances it will be obvious that it is not necessary to maintain a pilot flame at' the burner 31 while the valve 30 is closed, and hence, if desired, the bypass 32 may be dis ensed with. The question of using a pilot game or a spark ga and electrical ignition means for the ignition of l the as at the burner 31 is one which may be etermined by practical considerations and has no effect upon the operation of the present invention.

A temperature responsive device 36 is preferably disposed in the room, building, or other space to be heated by the boiler 11, land `essentially comprises a switch 36 that is adapted to be closed in response to a demand for heat in such space. In other words, the switch 36a is closed in response to the existance of a predetermined temperature in the space to be heated, and is opened in response to the existance 'of a predetermined higher temperature in such space. vThe device 36 may be of any well-known t pe, such, for example, as that illustrated 1n Fig. 4: of the drawin s of co-pending application Serial No. 151, 04, filed November 30, 1926, by John C. Bogle, for electrically controlled heating systems. Hence, the structural details of the device 36 do not require illustration herein. The switch 36a is diagrammatically illustrated as being of the mercury contactor type, according to approved modern practice, but any desired type of switch which will operate 1n the manner above set forth may be utilized.

.A so-called boiler control` device 37 is associated with the boiler 11 and comprises a switch 37 that is adapted to remain in closed position as long as the boiler l1 is in normal operating condition. This switch is adapted to be opened, however, upon the occurrence of abnormal conditions in the boiler 11, such as excessive pressure or temperature. The device 37 may be of any well-known type, such, for example, as that illustrated in detail in Fi 5 of the drawings of the abovementione co-pending application Serial No;

151,704, and hence the structural details of this device are not illustrated herein. As in the case of the temperature responsive device 36, the switch 37* of the device 37 is illustrated as being of the mercury contactor type. 4

A combustion responsive device 38 comprises a bi-metallic or other thermostatic element 38 that is suitably. disposed within a stack 39 that is provided for conducting the gaseous products of combustion away from the combustion' chamber 12. These gases are still at a relatively hi h temperature as they pass through the stac 39 past the thermostatic element 38, and therefore this thermostatic element is actuated in accordance with the conditions of combustion obtaining in the combustion chamber 12. If the burner 13 is in operation and normal combustion conditions are obtaining in the combustion chamber 12, the thermostatic element 38a is actuated to open a switch 38", after first closing a switch 38, and to maintain these switches in these res ective conditions as long as the normal con itions of combustion exist in the combustion chamber 12. When these normal combustion conditions are non-existent, the thermostatic element 38* effects the closing of ,the switch 38 and the opening ofthe switch .38 for purposes hereinafter set forth. It is to be understood that the term normal combustion conditions as used herein, refers to combustion of liquid fuel in the burner 13, as the combustion of gas from the auxiliary burner 31 does not yield products of combustion in suicient volume or at a high enough temperature vto affect the thermostatic element 38.

The two switches 38" and 38c are embodied in the combustion responsive device 38 and are diagrammatically illustrated as being of the mercury contactor type. The details of construction of the device 38 do not constitute an essential. part of the present invention, as any desired type of device .which will operate in the manner described may be utilized. By way of example, however, reference may be had to Figs. 7 ,`8, and 9 of the-130 the like, havmg four electrodes therein, two

of which are provided with a common electrical connection. In the present invention, two separate contactors, each comprising only two electrodes having no common electrical connection, are utilized, but the mechanical details of construction of the device may be the same as' those of the device disclosed in the said co-pending application if desired. The switches 38b and 38c are so mounted that the actuation thereof in respense to the heating of the thermostatic element 38 causes the switch 38 to be closed before the switch 38b is opened. This socalled overlapping action is utilized for a purpose hereinafter set forth, and is in accordance; with the invention of co-pending application Serial No. 284,340, filed November 19, 1927, by John C. Bogle, forelectrical switch and control circuit therefor.

The remaining control apparatus of the present invention is shown herein as being mounted upon a common panel 40 for convenience in manufacture and installation, it being understood, however, that the-mounting of the remaining devices about to be described may be varied as desired Without affecting the present invention. One of the devices mounted on the panel 40 is an electrically-heated thermostatic device, which preferably comprises a bi-metallic strip 41 pivotally mounted at 42 and supported at a pointdisplaced from the pivotal mounting 42 by an adjustable screw 43.' An electrical heating element 44 is suitably associated with the bimetallic strip 41 to cause the righthand extremity of said strip to be deliected downwardly in response to a predetermined electrical energization and resultant heating of the element 44. The said right-hand extremity of the strip 41 carries a. switch 44n of the mercury contacter type, this contacter being normally so tilted that the two contact members thereof are electrically connected by the body of mercury or other conducting fluid within the container of the switch.

The device is so adjusted that when the heating element 44 has been electrically energized for a predetermined interval of time, the bimetallic strip 41 is so deiiected as to tilt the switch 44a a sufficient distance to cause the body of mercury or other conducting fluid in said switch to move to the right-hand eX- tremity of the container therefor. This extremity is extended downwardly to form a well into which the conducting fluid iows under these conditions. When the conducting fluid has flowed into this well, it will remain therein until the right-hand extremity of the strip 41 has been manually lifted a substantial distance abovethe normal position of this member corresponding to the de-cnergized. condition of the heater 44. Dui-Eng such manual actuation of the strip 41 the saine pivots about its mounting 42 and moves away from the adjusting screw 43 a slight distance. Upon'inanual release of the strip 41, it returns to the position illustrated in the drawing, thecomlucting fluid in the switch 44 then having been returnedto circuit-making engagement with the contact members oi'v the switch 44. It will be understood that the panel'40 may be provided with a casing and cover and that the manipulation of the stri p l 41 to reclose the switch 44a may be facilitated by the provision of a resetting handle or the like extendingthrough a wall of the box or cover for the panel 40.

The details of construction of the switch 44al and the actuating mechanism therefor are shown more or less diagrammatically, as such details do not form an essential part ot the present invention. For a more detailed understanding of the structure of a suitable device of this character, reference may be had to Fig. 6 of the drawings of the above-mentioned co-pending application Serial No.

151,704, or to Figs. 1, 2, and 4 of the drawings of co-pending application Serial No. 235,147, filed November 23, 1927, by John C. Bogle, for electrical switches. The thermostatically-operated switch shown diagrammatically herein may be of the typel disclosed in either of these co-pending aplications or of any other suitable type. l

The panel 40 also carries a switching device comprising two

solenoids

45 and 45 ywhich are adapted to control the operation of a switch 45a. This switch is also shown as being of the mercury contacter type and comprising two contact members which are disengaged by a cooperating body of mer- `cury or other conducting fluid when the

solenoids

45 and 45 are de-energized. These two solenoids are respectively provided with core members 45b and 45, each of which is pivotally connected at its lower extremity to an armature member 45d that is pivotally supported at 45e on the panel 10. The elec tromagnet winding of the solenoid 45 has sufficient ampere turns and the core member 45b is so disposed with respect thereto that energization of the solenoid 45 will result in the actuation of the armature member 451 from the position shown in the drawing to a position in which the switch 45a is so tilted that the mercury or other conducting iuid therein flows into circuit-making engagement with the contact members of this switch. The solenoid 45', however, has an insulicient number of ampere turns to effect such actuation, but is adapted to maintain the armature member 45jl and switch 45a in actuated position after they have been thus actuated by the solFor an accurate understanding of the structural details of a suitable device of this char'- acter, reference may be had to F ig. 12 of the drawings ofthe above-mentioned co-pending application Serial No. 151,704. The abovementioned co-pending application Serial No. 235,147 also shows a device which functions in the same manner as that described herein,

although the structural details of the device are of a different design. The device shown in the last-mentioned copending application may likewise be utilized in the system of the present invention if desired, or any other suitable device capable of operating in the same manner may be so used, regardless of the type of switch and details of construction of the actuating means therefor.

A time delay device preferably .comprising a bimetallic strip 46 is also mounted upon the panel 40 and is providedwith an electrical heating element 47 and contact menibers 47a. When the heating element 47 is deenergized, the strip 46 occupies the posi- ,tion illustrated in the drawing, in which the .Contact members 47a are separated. When the heating element 47 has been energized for a predetermined interval of time, the righthand extremity of the strip 46 is deflected downwardly a sulicient distance-to eect enagement between the contact members 47 tem of the present invention may tfor a purpose hereinafter set forth. It will be readily understood that the air break con-l tact members of this device may be replaced with a mercury contacter or other suitable form of switch, the selection of the type of switch to be utilized depending upon the type of installation or other practical considerations. y

Electrical energy for operatino the sys- Lbe derived from any suitable source to which suppl

conductors

48 and 49 are properly connecte The supply conductor 48 extends to one terminal of the switch 44, the other terminal of which is connected through a conductor 50 to one terminal of the switch 45 and through a conductor 51 to one terminal of the switch 36a. The other terminal of the switch 45a is connected through a conductor 52 to one Aterminal of the motor 22 and through a conductor 53 to one terminal of the switch 38C. The other terminal of the motor 22 is connected to the supply conductor 49, thus completing the circuit of said motor. r1`he other terminal of the switch 38 is connected through a conductor 54 to one terminalof the hold coil 45', the other terminal connected through a conductor 56'zto one ter' minal of the electromagnet of the valve 25, the other terminal of which electromagnet is connected to the supply conductor 49.y The last-mentioned terminal of the switch 37 is also connected, through a conductor 57, to-

one terminal of the switch 38", the other terminal of which is connected through a conductor 58 to one terminal ofthe electromagnet of the valve 30, the other terminal of this electromagnet being connected to the` supply conductor 49. The conductor 58 is also extended to make connection with the bimetallic strip 46 and to one terminal of the heating element 47 for said bimetallic strip, the other terminal of the heating ele'l ment 47 being connected to the supply conductor 49.

Since one of the contact members 47a is 'mounted on the right-hand extremity of the blmetalhc strip 46, this Contact member is in electrical connection with the conductor 58 which is connected to the op osite extremity of said bime'tallic strip. T e other one of the contact members 47 a, which is a fixed contact member, is connected through a con-A ductor 59 to one terminal of the heating element 44 for the bimetallic strip 41. The other terminal of heating element 44 is connected through a conductor 60 to one terminal of the pull coil 45, the other terminal of which is connected to the supply conductor 49, thus completing the energizing circuit for the heating element 44 and the pull coil 45.

When electrical ignition is to be utilized, one of the primary terminals of the ignition device 34 will be connected through a conductor 61 to the terminal of the switch 38b to which the conductor 58 is connected. The other primary terminal of the device 34 will be connected through a conductor 62 to the supply conductor 49, and the secondary terminals of the deviceV 34 will be connected through conductors 63 and 64 to the opposite sides of the spark gap 35, to establish an igniting arc across this gap when the primary circuit of the ignition device 34 is energized.

The circuit connections of the system embodying the present invention and the op-v eration of the apparatus embodied in said system will be better understood by reference to Fig. 2 of the drawing, in which like reference characters are applied tothe schematic representations o f the corresponding devices o shown in Fig. 1. Upon reference to Fig. 2, it will be seen that the motor 22 is connected between the

supply conductors

48 and 49 in series with the switches 44a and 45. The hold coil 45 for the switch 45l is connected in series with the switch 38c and in a circuit parallcling the motor. 22. One terminal of the electromagnet of the valve 25 is connected to the supplyy conductor 48 through the switches 44, 36a and 37, and the other ter' minal of this electromagnet is connected directly to the supply conductor 49. A branch circuit paralleling the electromagnety of the valve 25 is derived through the conductor 57 and the switch 38b and supplies -energy to the clectromagnet of the valve 30, the rimary side of the ignition device 34 v(w en` this device is used), and the heating element l 47, which 'controls the contact members 47a through the bimetallic strip 46. These three

devices

30, 34, and 47 are directl connected in parallel relation to each ot er in this branch circuit, one terminal of each of these devices bein connected to the supply conductor 49. i circuit comprising the switch 47 the conductor 59, the heating element 44, the conductor 60, and the pull vcoil 45, all connected in series relation to each other, is also connected in parallel relation to the

devices

30, 34, and 47.

It will be seen that all of the electrical apparatus of the system derives energy throughl the switch 44, which is normally closed. The

operation of the system is. initiated by closure ofthe switch 36l in response to a demand for heat in the space to be heated, it being understood, however, that this switch 36IL may be replaced, if desired, with a manually operable switch or other desired type of switch. When this switch l36'L is closed, the electromagnet of the valve 25 is energized, since the switch 37 a, which is connected in series with the switch 36, is closed except under abnormal boiler conditions, as heretofore explained. The devices 30, 34 (when used), and 47 are also immediately energized upon closure of the switch 36, since the switch 38b is closed because the thermostatic member 38 is cold during the period of inactivity of the burner 13.

Upon the energization of the electromagnet of the fuel supply valve 25, this valve is opened preparatory to lthe starting of the motor 22 and fuel pump 18 to supply fuel to the burner 13. This supply of fuel is not immediately initiated, however, as will presently appear. The energization of the electromagnet of the gas valve 30 increases the rate of supply of combustible gas to the auxiliary burner 31 in the combustion chamber and results in the. expansion of the gas pilot flame normally burning in this auxiliary burner by reason of the opening in the bypass 32 when said by-pass is utilized. If the electrical ignition device 34 andspark gap 35 are utilized in place of the by-pass 32, the supply of gas to the auxiliary burner 31 is ignited by the spark at the gap 35, which is created immediately upon the energization of the ignition device 34, concurrently with the opening of the gas valve 3,0 in response to the energization of the electro-magnet thereof.

The gas flame from the aux1liary burner 31, which is expanded by opening the valve 30 when the by-pass 32 is utilized and initiated by opening the valve 30 when electrical ignition is utilized, is of sufficient size and intensity to heat the combustion chamber 12 and the burner 13 to-a relatively high temperature in a relatively short interval of time, without, however, materially affecting the thermostatic element 38a. This heating of the combustion chamber and fuel burner prior to the supplying of liquid fuel thereto places the burner in condition for immediate operation upon the su ply of liquid fuel thereto and eliminates t e danger of failure of ignition which would be likely to result from the supplying of liquid fuel to a cold burner and combustion chamber. Such a .failure of ignition in systems of the prior art frequently results in the fouling of the burner nozzles and in vthe accumulation of liquid fuel in the bottom of the combustion chamber.

. The danger of explosions and inoperativeness the burner and combustion chamber by the gas flame.

During the period while the combustion chamber 12 and the fuel burner 13 are being heated by the gas 4fiame from the auxiliary burner 31, the electrical heating element 47 is continuously energized. After this energization has continued for a certain interval of time, which may be determined by calibration and adjustment of the bimetallic strip 46 and contact members 47 the strip 46-is deflected suiiiciently by the heat created by the electrical heating element 47 to effect circuit-making contact between the contact members 47 When such contact is made, a series circuit comprising the heating element 44 and the pull coil 45 is connected in parallel relation to the

devices

30, 34, and 47 to be energized in similar manner. The energization of the pull coil 45 in this manner results in the actuation of the switch 45a to closed position, thereby establishing the energizing circuit for the motor 22. The motor thereupon starts to operate to cause the pump 18 to supply liquid fuel from the source 20 to the burner 13 and to cause the blower 23 to supply air to the burner for the combustion of the li uid fuel. As the liquid fuel and air are supp ied to the burner, combustion is immediately established by the gas flame from the auxiliary burner 31, and the normal operation of the heating system is thus initiated.

As doon as combustion is thus established, the hot gases resulting therefrom are conducted away through the stack 39 past the thermostatic member 38'* of the combustion responsive device 38. The thermostatic member 38 thereupon actuates the switches 38b and 38c to close the latterand then to open the former. The opening of the switch 38b interrupts the energizing circuits for .the

devices

30, 34, 47, 44, and 45, the energizatlon of these devices not being required after the normal operation of the heating system 1s initiated.

The closing of the switch 38, which, as above described, precedes the openingof the switch 38", connects the hold coil 45 in parallel relation to the motor 22 and thus establishes the energizing circuit for the hold coil, which circuit is maintained as long as the burner 13 is operating. The energization of the hold coil 45 causes the switch 45 to be maintained closed, thereby maintaining energization of the motor 22 and of the hold coil 45. It will be observed that the overlapping action of the device 38, inclosing the switch 38 before opening the switch 38", is necessary in order that the hold coil 45 will be energized before the pull coil 45 is de-energized, thus insuring that the switch 45 is continuously maintained in its closed position.

In the event that combustion is not properly established in the combustion chamber 12 within a reasonable interval of time after the pump 18 starts to supply fuel to the burner 13, the switch 38b remains in its closed position for an abnormal length of time, during which time the heat-ing element 44 is continuously energized. After a predetermined period of such energization the bimetallic strip 41 is sunciently deflected to effect opening of the switch 44'?, which can be reclosed on y by manual operation, as hereinbefore described. The opening of the switch 44L de-energizes all ,of the electrical apparatus of the control system, as will be readily apparent upon referring to Fig. 2 of the drawmg.

Since manual reclosing of the switch 44n is prerequisite to the restoring of the control system to operative condition, it isnecessary that someone attend to this matter personally, at which time a proper inspection may be made to determine the cause of the failure of combustion. The fact that the system failed to establish combustion within the proper interval of time will be shown by the fact that the body of mercury or other conducting fluid in the switch 44'* will have flowed into the well at the right-hand extremity of the container of this switch, where it is visible through the glass walls of the container.

In the normal operation of the system, however, and particularly in view of the fact that the combustion chamber is thor- 1,ass,24a

oughly heated by the gas flame from the.'

auxiliary burner 31 before fuel is supplied to the burner 13, the proper combustion conditions will be established in much less time than that required for the described operation of the switch 44, and this switch will alwa s remain in its closed position. The provision of this additional safety feature,

owever, is desirable in view of modern standards of safety in systems of this char acter. p

After the heating system has been in operation for a suicient length of time to raise the temperature of the space to be heated to the desired degree, the temperature-responsive device 36 causes the switch 36a thereof to be opened, thereby interrupting the enerizing circuit for the electromagnet of the uel supply valve 25. This .valve is thereupon closed to terminate the flow of fuel from the pump 18 tothe burner 13.

The opening of the switch 36 does not affect the energizing circuit for the motor 22, however, and this'motor continues in operation until combustion in the chamber 12 is terminated. During this time the blower 23 is maintained in operation and supplies air for the combustion of the liquid fuel remaining in the pipe or

conduit sections

14, 15, 16, and the stand pipe 26, at the time the valve 25 is closed. This fuel remaining in the pipes continues to flow by gravity into the burner and combustion is maintained until this supply is entirely drained off. This feature provides an additional element ofsafety in the operation of the heating s stem by preventing the extinguishment o the burner flame before all of the fuel remaining in the pipes has been drained off, -which extinguishment would result from the termination of operation of the blower 23 prior to the complete drainage of the fuel supply pipes. It will be seen, therefore, that combustion is terminated in the system of the present invention only by reason of the termination of fuel supply to the burner, which means that there is no fuel vremaining in the supply pipes.

When combustion in the chamber 12 is terminated in the manner described, and all of the hot gases resulting therefrom have been conducted away through the stack 39, the thermostatic member 38 is permitted to cool off, which results in the closing of the switch 38b and the opening of the switch 38. The closing of the switch 38b establishes the connections for initiating the next 'cycle of operation ofl the system and the opening of the switch 38c interrupts the energizing circuit of the hold coil 45', resulting in the opening of the switch 45EL by the action of gravity. When the switch 45 is thus opened, the energizing circuit ofthe motor 22 is interrupted and the operation of the motor and the blower 23 is terminated.

Duiiing the interval between the closing of valve in response to the opening of ther temperature responsive switch 36 a and the time when the motor 22 is denergized inrer spense to the opening of the switch 38", the fuel supply pump 18 continues to be operated by the motor 22. Since the valve 25 is closed, the fuel suplied by the pump'18 18 to be returned to the source 20 through the pipe or conduit line 28.

From the foregoing description itwill be seen that the present invention provides additional features of safety in the operation of heating systems of the character described and insures the occurrence of predetermined steps in the cycles'of suoli operation in desired sequence. y

It will be apparent to those skilled in the art that various changes and modifications may be made in the details of structure and circuit connections of the apparatus herein described without departing from vthe spirit and scope of the inventionas set forth in the appended claims.

What is claimed as new and is desired to secure by Letters Patent is:

1. In a heating system, in combination, a. fuel burner, a combustion chamber therefor, a source of liquid fuel supply, a pump for supplying liquid fuel from said source to said burner, a .blower for supplying air to said burner for combustion purposes, an electric motor for operating said pump and said blower, a normally closed valve for controlling the iiow of fuel from said pump. to said burner, an electromagnet for opening said normally closed valve, a switch responsive to the temperature of the space to be heated, means responsive to combustion conditions in said combustion chamber, a switch for controlling the energization of said electric motor, means for actuating said motor switch to closed position, and means for maintaining said motor switch in closed position, said space -temperature responsive `switch controlling said means for actuating said motor switch to closed position and also controlling the period of energization of said valve-opening electromagnet, and said combustion-condition-responsive means controlling said means for maintaining said motor switch in closed position.

2. In a heating system, in combination, a fuel burner, a combustion chamber therefor, a source of liquid fuel supply, a pump for supplying liquid fuel lfrom said source to said burner, a blower for supplying air to said burner for combustion purposes, an electric to the temperature of the space to beheated motorfor operating said pump and said blower, a normally closed valve for controlling the flow of fuel from said pump to said burner, an electromagnet for opening said normally closed valve a switch responsive to the temperature of tI e space to be heated, means responsive to combustion conditions in y-said combustion chamber, a switch for controlling the energization of said electric motor, means for actuating said motor switch to closed position, and means for maintaining said motor switch in closed position, said space-temperature-responsive switch controlling said means -for actuating said motor switch to closed position and also controlling the period of energization of said valve-opening electromagnet, and said combustion-condition-responsivek means controlling said means for maintaining said motor switch in closed position and rendering said maintaining means lneffective only upon the termination of combustion in said combustion chamber.

3. In a heating system, in combination, a fuel burner, a combustion chamber therefor, a sourcefof liquidvfuel supply, a pump for supplyiiigliquid fuel from said source to said burner, a blower for supplying air to said burner for combustion purposes, an electric motor t for operating said pump and said blower, a normally closed valve for controlling the flow of fuel from said pump to said burner, an electromagnet for opening said normally closed valve, a switch responsive 3 means responsive to combustion conditions in said combustion chamber, a switch for controlling the energization of said electric motor, a pull coil' for actuating said motor switch to closed position, and a hold coil for maintaining said motor switch in closed po- ',sition, said space-temperature-responsive means controlling the energization of said pull coil and of said valve-opening electromagnet, and said combustion-condition-responsive means controlling the energization of said hold coil.

f1. In a heating system, in combination, a fuel burner, a combustion chamber therefor, a source of liquid fuel supply, a pump for supplying liquid fuel from said source to said burner, a blower for supplying air to said burner for combustion purposes, an electric motor for operating said pump and said blower, a normally closed valve for controlling the flow of fuel from said pump to said burner, an electromagnet for `opening said normally closed valve, a switch responsive to the temperature of the space to be heated, means responsive to combustion conditions in said combustion chamber, a switch for controlling tlie energization of said electric momaintaining said motor switch in closed po.-

supplying liquid fuel from said source to said burner, a blower for supplying' air to said burner for combustion purposes, an electric motor for operating said pump and said blower, a normally closedvalve for controlling the flow of fuel from said pump to said burner, means for relieving the pressure created by said pump while the same is operating and said normally closed valve is closed, an electromagnet for opening said normally closed valve, a switch responsive to the temperature of the space to be heated, means responsive to combustion conditions in said combustion chamber, a switch for controlling the energization of said electric motor, means for actuating said motor switch to closed position, and means for maintaining said motor swltch in vclosed position, said r space-temperature-responsive switch controlling said means for actuating said motor switch to closed position and also controlling the period of energization of said valve-opening electromagnet, andsaid combustion-condition-responsive means controlling said means for maintaining said motor switch in closed position.

6. In a heating system, in'combination, a fuel burner, a combustion chamber therefor, a source of liquid fuel supply, a pump for supplying liquid fuel from said source to said burner, a blower for supplying air to said burner'for combustion purposes, an electric motor for operating said pump and said blower, a normally closed valve-for controlling the flow `of fuel from said pump to said burner, means for relieving the pressure created bysaid pump whilev the same is operating and said normally closed valve is closed, an electromagnet for opening said normally closed valve, a switch responsive to the temperature of the space to be heated, means responsive to combustion conditions in said combustion chamber, a switch for controlling the energization of said electric motor, means for actuating said motor switch to closed position, and means vfor maintaining said motor switch in closed position, said space-temperatureresponsive switch controlling said means for actuating said motor switch to closed position and also controlling the period of energization of'usaid valve-opening electromagnet,

and said combustion-condition-responsivc means controlling said means for maintaining said motor switch in closed position and rendering said maintaining means ineffective only upon the termination of combustion in said combustion chamber.

7. In a heating system, in combination, a fuel burner, a combustion chamber therefor, a source of liquid fuel supply, a pump for suplying liquid fuel from said source to said urner, a blower for supplying air to said burner for combustion purposes, an electric motor for operating said pump and said blower, a normally closed valve for controlling the iow of fuel from said pump to said burner, a connection including a relief valve between the discharge side of said pump and said 'source of fuel supply for relieving the pressure created by said pump and for returning the fuel pumped thereby to said source while said pump is operating and said normally closed valve is closed, an eleotromagnet for opening said normally closed valve, a switch responsive to the temperature of the space to be heated, means responsive to combustion conditions 'in said combustion chamber, a switch for controlling the energization of said electric motor, a pull coil for actuating said -motor switch to closed position, and a hold coil for maintaining said motor switch in closed position, said space-temperature-responsive means controlling the energization of saidv pull coil and of said valve-opening electro-magnet, and said combustion-condition-responsive means controlling the energization of said hold coil.

8. In a heating system, in combination, a fuel burner, a combustion chamber therefor, a source of liquid fuel supply, a pump for supplying liquid fuel from said source to said burner, a blower for supplying air to said burner for combustion purposes, an electric motor for operating said pump and said blower, a normally closed valve for controlling the flow of fuelfrom said pump to said burner, a connection including a relief valve between the discharge side of said pump and said source of fuel supply for relieving the pressure created by said pump and for returning the fuel pumped thereby to said source while said pump' is operating and said normally closed valve is closed,.an electromagnet for opening said normally closed valve, a switch responsive to the temperature of the space to be heated, means responsive to combustion conditions in said combustion chamber, a switch for controlling the energization of said electric motor, a pull coil for actuating said motor switch to closed position, and a hold coil for maintaining said motor switch in closed position, said space-temperature-responsive means controlling the energization of said pull coil'and. of said valve-opening electromagnet, and said combustion-condition-responsive means' controlling the energization of said hold coil and maintaining said hold coil energized independently of the operation of sai ace-temperatureresponsive means until the termination of combustion in said combustion chamber. n In witness whereof, I have hereunto sub- Cul scribed my name.

JOHN c. BOGLE.