US2364591A

US2364591A - Controlling means

Info

Publication number: US2364591A
Application number: US430428A
Authority: US
Inventors: John L Stoughton; Walter S Landon
Original assignee: Detroit Lubricator Co
Current assignee: Detroit Lubricator Co
Priority date: 1942-02-11
Filing date: 1942-02-11
Publication date: 1944-12-05
Anticipated expiration: 1961-12-05

Description

Dec; 5, 1944- J. L. STOUGHTON EI'AL 2,354,591

I CONTROLLING MEANS Filed Feb. 11, 1942 INVENTORS BY 1%,). W

ATTORNEY Patented Dec. 5, 1944 CONTROLLING MEAN S John L. Stoughton and Walter S. Landon, De-

troit, Mich, assignors to Detroit Lubricator Company, Detroit, Mich., a corporation of Michigan Application February 11,1942, Serial No. 430,428

13 Claims. (01. 15s-2s) This invention relates generally to controlling means and is adapted among other uses to control the flow of fuel and air to a fluid fuel burner.

One object of this invention is to provide means responsive to changes in one condition to cause a change in a second condition.

Another object is to provide a control means for a fluid fuel burner for modulating the amounts of air and fuel to provide a desired combustible mixture.

Another object is to provide in such a control means, means to modulate the flow of fuel in accordance with changes in air flow.

Other objects will be apparent from a reading of the specification.

The invention consists in the improved construction of and combination of parts to be more fully described hereinafter and the novelty of which will be particularly pointed out and distinctly claimed.

In the accompanying drawing there is fully and clearly illustrated a preferred embodiment of the invention, in which drawing Figure l is a diagrammatic view of an oil burning system embodying the Invention.

Fig. 2 is a diagrammatic view showing a modi fied burner system embodyingthe invention.

Referring to Figure 1 of the drawing by characters of reference the numeral I designates gen erally a fluid fuel burner such as is known in the art as a pot type burner having an inner or vaporizing chamber 2 and an outer chamber 3 surrounding the chamber 2 for supplying air to the chamber 2 through a series of holes 4. Burners of this type are well known to the art and a more complete description thereof is not deemed necessary. A pressure or centrifugal type fan means 5 is driven by an electric motor 6 and discharges air under pressure into a conduit means I opening into thechamber 3 through its bottom wall for supplying a quantity of air under pressure to the chamber 3 from whence it flows through the holes 4 into the chamber 2.

Fuel such as oil is supplied from a suitable source of supply (not shown) through a conduit 8 leading to a strainer chamber 9 carried integrally with the bottom wall Ill of a fuel contro1- ling means generally designated II. The means II comprises a chambered casing having a fuel receiving reservoir I2 and a contro1 chamber I3 positioned above the reservoir I2 and separated therefrom by a plate-like member I4. Fuel is admitted from the strainer chamber 9 through a float controlled inlet valve means I5 which is operable to maintain the fuel level within the reservoir I2 substantially at the line L-L. The controlling means II has an outlet I6 opening from the reservoir l2 and opening into a fuel conduit I! which convey the fuel from the reservoir I2 to the chamber 2 of the fuel burner I for discharging the fuel adjacent the bottom wall of the chamber 2.

A reciprocal movable valve member l8 has the usual reduced diameter end portion received within'an outlet port in the outlet I6 and has a V-shaped slot I9 cooperable with the outlet port for controlling the flow of fuel supplied by the controlling means II to the burner I. Upward movement of the member I8 acts to position a greater area of the slot I9 above the outlet port to provide for increased fuel flow and downward movement acts to reduce the fuel flow to the burner I. A helical coil compression spring 20 is positioned concentric with the valve member I8 and has its upper end portion abutting the underof the valve member I8 is limited by a minimum fire adjustable stop member 23 positioned in the chamber I3 and which has at its lower end portion a radially outwardly extending flange 24 which is engaged by a radially outward extending flange 25 of the valve member stem portion 22.

i The stop member 23 is screw threadedly secured in an abutment or flange 26 extending into the chamber i3 from the front wall of the means I I. The upper end of the stem portion 22 is of reduced diameter and is received within an aperture extending through the flange 26 to guide the upper end of the valve member in its reciprocal movement. The upward, movement of the valve member I8 is limited by engagement of the flange 25 with'a radially outwardly extending flange 21 on the lower end portion of a high fire adjustable stop member.

The valve member I8 is moved upward against the force of the spring 28 by a bimetallic power element 29 having a. substantially cylindrical heat sensitive portion 30 with a longitudinally extending sidewall slot. The portion 30 adjacent its slot is rigidly secured as by welding to a upporting member 3| which is carried by the upper face of the plate-like member I4 and within the chember I3. A lip portion 32 extends from the portion 38 adjacent the other edge of the slot from the member 3| and is positioned to engage the underface of the flange 25. Normally the upward force exerted by the lip portion 32, with the portion at normal ambient temperature, is insufllcient to move the valve member I8 upward against the downward force of'the spring 28 so that the

flanges

24 and 25 remain in engagement. An

electric resistance heater unit 33 is positioned duit means I to the burner I is regulated or controlled by a damper 34 pivoted as at 35 and having an extending operating arm 35. A bimetallic power element 31 similar to th element 29 has a substantially cylindrical portion 38 supported on the supporting member 39 carried on a fixed abutment 48 rigid with the conduit means or air duct I and has a lip portion 4| engaging the top surface of the arm 35. Air pressure acting on the damper 34 acts to urge it in a counter-clockwise direction about the pivot 35 to maintain the arm 35 in engagement with the lip portion 4I. If desired, a biasing spring urging the damper 34 toward open position may be used. An electric resistance heater unit 42 is positioned in the cylindrical portion 38 and is operable to supply heat to the portion 38 so that the lip portion 4| will be moved to allow the damper 34 to pivot in a counter-clockwise direction thereby to permit a greater flow of air to the burner I.

'An electric resistance unit 43 having a high rate of increase in resistance with increase in temperature is positioned within the duct I intermediate the damper 34 and burner I and in a position to be in the path of the average air velocity flowing to the burner I. A transformer 58 has a primary coil 5I connected by

lead wires

52 and 53 to a suitable source of electrical energy and has a secondary coil 54 having its ends secured to

secondary terminals

55 and 55. Lead wires 52 and 53' connect the

lead wires

52 and 53 respectively to the motor Bwhich remains energized as long as the transformer 58 is energ'lzed. The terminal 55 is connected by a lead wire 51 to one terminal 58 of a modulating type thermostat diagrammatically shown at 59 and comprising a resistance element 60 and a bimetallic temperature sensitive blade or member bl,

The member 5| wipesagainst the element 50 making an electrical circuit therewith which utilizes more or less of the resistance element to form a variable resistance having its resistance dependent upon the temperature of the medium surrounding the blade 5|. The other terminal 52 of the thermostat 59 is connected by a lead wire 53 to one terminal of the unit 42. A lead wire 64 connects the other terminal of the unit 42 to the terminal 56. A branch lead wire 65 of the lead wire 54 is connected to one terminal of the unit 43 which has its other terminal connected by a lead wire 55 to one terminal of the unit 33. The other terminal of the unit 33 is connected by a lead wire 51 to the terminal 55.

cThe operation of the apparatus of Figure 1 1 as follows: The thermostat 59 Is preferably positioned within and responsive to the temperature of a room or other enclosed space which is heated by the burner I. Upon decrease in temperature of the space the bimetallic blade 8| warps to the left (see Fig. 1) to reduce the resistance offered to current flow through resistance 58 of the thermostat 59. A greater current then flows from the secondary coil 54 through lead wire '51, thermostat 59, lead wire 53,'unit 42 and lead wire 54 back to the secondary coil 54. This greater current causes the cylindrical portion 38 of the element 31 to increase in temperature, thereby raising the lip portion 4I allowing the damper 34 to move further toward open position to increase the rate of air flow to the burner I. It is to be noted that the fan means 5 is operated continuously. This increased rate of air flow to the burner I acts to cool ,-'the resistance unit 43. Cooling of the resistance unit 43 acts to reduce the resistance thereof to current flow and thereby reduces the voltage drop thereacross and increases the voltage drop across the unit 33 to cause the unit 33 to heat the cylindrical portion 30 of the element 29 to a higher temperature. The increase in temperature of the cylindrical portion 30 causes the lip portion 32 to move upward lifting the valve member I8 against the force of the spring 28 to increase fuel flow to-the burner I proportionately to the increased air flow. The increased flow of fuel and air to the burner I causes the output thereof to increase and raise the temperature of the space in which the thermostat was positioned. As the temperature of this space increases the bimetallic blade GI warps toward the right (Fig. 1) thereby increasing the resistance to current flow through the thermostat 59 and reducing the current flow through the unit 42. Reduced current flow through the unit 42 reduces its heating effect on the cylindrical portion 38 of the element 31 causing the lip portion M to move downward thereby moving the damper 34 toward closed position reducing the flow of air through the conduit means I to the burner I. As the flow of air through the conduit means I is reduced, the cooling efiect of this air flow on the unit 43 decreases, thereby allowing the unit 43 to increase in temperature. This increase in temperature of the unit 43 causes its resistance to increase, thereby increasing the voltage drop thereacross and decreasing the voltage drop across the unit 33. This decreased drop across the unit 33 causes the temperature of the cylindrical portion 38 to be reduced, thereby moving the lip portion 32 downward so that the spring 20 wll move the valve member I8 toward closed position to reduce the fuel flow to the burner I in accordance with the reduced air flow to the burner I.

It may now be seen that by this invention there is provided a means for balancing the fuel flow in accordance with the air flow to a burner to maintain a desired combustion in the burner the magnitud of which varies in accordance with the temperature of the heated space and which combustion rate is modulated to maintain the temperature of the space within a predetermined desired range. v

Referring to Figure 2 of the drawing the numeral III designates a pressure or centrifugal type fan means driven by an electric motor II and supplying air under pressure through a conduit means or duct 12 to a fluid fuel burner (not shown) similar to the burner I of Fig. 1. Fluid fuel for the burner is controlled by means of a valve member I8 which cooperates with a valve port I4 and which is intercalated in the fuel supp y to the burner similarto the intercalation of the valve member-I8 in the fuel supply to the burner I. The valve member I3 has a stem portion I5 extending upwardly through an aperture in a supporting member I6 held in fixed position relative to the port I4. A helical coil spring 'II ispositioned concentric with the stem portion I5 and has its lower end portion abutting the upper face of the supporting member I6 and its upper end portion abutting a radially outward extend ing flange I8 of the stem portion I5. The spring 1! acts due to its expansive force to urge the valve member 13 in an upward direction to increase the flow of fuel through the port I4. The upp r end portion I9 of the stem portion I5 is of reduced diameter and provides a shoulder 80 at its intersection with the normal diameter portion of the stem portion I5.

A plate-like supporting member 8| is held rigid with the fixed supporting member I6 and has a first screw threaded aperture therethrough aligned with said valve member for receiving in screw-threaded relation an adjustable high fire stop member 82 against which the top end portion of the valve member I3 abuts to limit its upward movement away from the port I4. The supporting member 8| has a second aperture extending therethrough in which is positioned a collar member 83 having spaced

shoulders

84 and 85 engageable respectively wlth the lower and upper surfaces of th member 8|. The distance between the

shoulders

84 and 85 is so proportioned relative to the thickness of the plate-like member 8| that the collar member 83 can have predetermined reciprocal movement in the aperture, the purpose of which is to be described hereinafter. The collar member 83 has a screw threaded central aperture extending therethrough in which is screw threaded a thrust mem- I0 I Upon counter-clockwise rotation of the lever member 98 the strip 99 acts to rotate the blade ing the rod 91 and one end portion engaging the underside of the lever member 98 and its other end portion engaging the lower wall of the fixed member 94. The lever member 98 has a semicircular upwardly extending abutment I05 which engages the head 81 and which is held in engagement therewith by the sprin I04. The predetermined permissible reciprocal movement of the collar member 83 is so chosen that movement thereof from the position in which th shoulder 85 engages the member 8| to the position in which the shoulder 84 engages the member 8| is sulficient to cause the lever member 98 to rotate sufiiciently to move the contact members I02 and I03 into engaging relation. Conversely upon downward movement of the collar member 83, the predetermined distance is enough to separate the contact members E02 and I03. The thrust member 86 is screwthreaded relative to the collar member 83 with the shoulder 85 in engagement with the supporting member 8| until the switch is moved to circuit breaking position, i. e., contact members I02 and I03 in a separated position. Subsequent. to this adjustment, the collar member 83 is soldered to the thrust member 86 to hold the members83 and 86 in their adjusted position.

Referring again to the bimetallic power element 9|, the lip portion 95, with the cylindrical portion 92 at normal ambient temperature, exert a suflicient force in the downward direction to overcome the upward force of the spring 11 and ber 86 which extends downward therefrom toits side wall flattened as at 89 to provide a shoul A helical coil spring 89 is positioned der 90. concentric with the member 86 and is held under compression between the head 81 and the member 88 to prevent undesired relative rotation between the members 86 and 88. Numeral 9| designates generally a bimetallic heat actuated power element similar to the element 29 and having a substantially cylindrical portion SZ carried adjacent its split wall by a supporting member 93 rigidly secured to a fixed member 94 rigid with the fixed member 16 and having a lip portion 95 extending from the cylindrical portion 92. The lip portion 95 extends adjacent the flattened wall 89 overlying the shoulder 90 and terminating so that its end portion engages the shoulder of the valve member I3. The fixed member 94 has a downwardly projecting portion 96 in which is positioned a rod or fulcrum member 91 which has its longitudinal axis extending substantially perpendicular to the longitudinal axis of the thrust member 86. A switch actuating lever member 98 has one end portion pivotally secured to the rod 91 and has secured to its other end a strip 99 of insulating material such as .Micarta for engaging a current conducting movable blade I00 of a switch diagrammatically shown and designatedthe counter-clockwise force of the spring I04 so that the shoulder is maintained in engagement with the supporting member 8|. This position of the thrust member 86 maintains the switch I0| in open circuit position and the valve member I3 is maintained by the lip portion in minimum fire position. The minimum fire position may be adjusted to any desired fire by rotating the thrust member 86 so that the cylindrical member 88'which is held against rotation by the lip portion 95 of the element 9| due to the engagement of the flattened wall 89 with th edge of the lip portion 95. Rotation of the thrust member 86 in one direction will "cause the cylindrical member 88 to be moved upward on the member 86 to increase the low fir and rotation in the opposite direction will cause the member 88 to be moved downward on the member 86 to decrease the low fire. The operation of the switch |0| by the thrust member 86 will not be altered by this adjustment because the collar member 83 is held against changing its position relative to th thrust member 86 by the solder.

A second bimetallic heat actuated power element I06 is similar to the element 9| and has a substantially cylindrical portion I 01 and a lip portion I88. The portion I0! is secured adjacent one side of its split to. a supporting member I09 carried by a fixed member I I0 rigidly positioned relative to the supporting member I6. The lip portion I08 is carried by the cylindrical portion I0I adjacent the other side of its split. The extending free end portion of the lip portion I08 overlies andds engageable by the shoulder 80 of the valve member I3 and acts to limit opening movement of the valve member I3 under the influence of the element9l. An intermediate fire valve member I3 further in an upward direction.

The element 9| is actuated by means of an electric resistance heater unit H3 positioned in the cylindrical portion 92 and which acts to raise the temperature thereof sufllciently so that the spring I! will be able to move the valve member I3 upward until the shoulder 80 engages the lip portion I08. Continued energization of the unit H3 will continue to raise the temperature of the element 9| and cause the lip portion 95 to leave the shoulder 80 and move out of the path of movement of the valve member I3. The element I08 is actuated by an electric resistance heater unit H4 positioned within the cylindrical portion I 01. Upon energization, the unit H4 acts to raise the temperature of the portion II to permit the lip portion I08 to control the positioning of the valve member I3 by the spring 11. The higher the temperature to which the portion I0! is heated the further the valve member I3 will be moved from the port I4 and the greater the fuel flow to the burner; the maximum flow being limited by the engagement of the valve member I3 with high fire stop member 82. v

The electric resistance unit H4 has a low rate of increase in resistance with increase in temperature while an electric resistance unit H5 positioned in the duct I2 has a high rate of increase in resistance with increase in temperature relative to the unit H4. The unit H5 is positioned within the duct I2 so that it is in the path of the average flow velocity through the duct I2.

Electrical energy is supplied through lead wires II 8, ill to a primary coil H8 of a transformer H9, The transformer H9 has a secondary coil I20, one terminal of which is connected by means of a lead wire I2I to one terminal I22 of a room thermostat diagrammatically shown at I23. The other terminal of the secondary coil I is connected to a terminal I24. A lead wire I connects the terminal I24 to one end of the resistance unit H5. The other end of the unit H5 is conheated by means of a lead wire I25 to one end of the unit II 4. The other end of the unit H4 is connected by means of a lead wire I2I to a second terminal I28 of the room thermostat I23. The

.to one end of the resistance unit H3 and the other end of the resistance unit H3 is connected by means of a lead wire I33 to the terminal I28.

A branch lead wire I 34 of the lead wire H6 is I connected to one terminal of the electric motor II. The other terminal of the electric motor II is connected by means of a lead wire I 35 t the a switch blade I00 which carried the contact member I02. The contact member I03 of the switch IOI is connected by means of a lead wire I38 to the lead wire I I1.

I The operation of the apparatus as disclosed in Fig. 2 is as follows: The burner (not shown) acts to heat the space or, room in which the room thermostat I23 is positioned. Upon decrease in temperature of the air surrounding the thermostat I23 to a predetermined minimum temperature, the bimetallic blade I3I will move the contact member I30 into engagement with the contactmember I29, thereby completing the following electrical circuits: Current flows from the secondary'coil I20 of the transformer through lead wire I2I, thermostat I23, lead wire I33, resistance unit H3, lead wire I32 back through the terminal I 24 to the transformer secondary coil I20. secondary coil I20 through lead wire I2I, thermostat I23, lead wire I2I, unit H4, lead wire I28,

unit H5, lead wire I25, and terminal I24 back to the transformer secondary coil I20, Current flow through these two circuits acts to cause the resistance units H3, H4 and H5 to increase in temperature. As the temperature of the unit II 3 increases, the temperature of the cylindrical portion 92 of the element 9| will increase and upon a predetermined increase of temperature of the portion 92 the lip portion 95 will be moved upward to permit the springs 11 and I04 to move the valve member I3 toward open position and to move the switch IOI to closed position respectively. During the time interval required to raise the temperature of the portion 92 sufficient to permit the valve member I3 to be moved upward, the temperature of the unit H5 will have increased sufliciently so that the voltage drop thereacross will be so great that the voltage drop across the unit H4 will be reduced sufliciently so that the unit H4 is ineffective to heat the cylindrical portion I01 of the element I05 suiiiciently to cause the lip portion I08 to move out of engagement with the flange H2 of the intermediate fire adjustment member III. The intermediate adjustment member II I is preferably so adjusted that the fuel supplied by the valve member I3 when the member I3 is limited in its movement by member III may be burned in the burner either at forced draft or natural draft conditions. Upon closure of the switch IOI an electrical circuit will be completed from the lead wire I38, through the switch IOI, through lead wire I35, through the motor II and lead wire I34 back to the lead wire H6, thereby energizing the motor II causing the fan means I 0 to supply air under pressure through the duct I2 to the burner (not shown). This airflow through the duct I2 will act to reduce the temperature of the resistance unit H5, thereby decreasing the voltage drop thereacross and increasing the voltage drop across the unit H4. This increased voltage drop across the unit H4 permits the unit "4 to raise the temperature of the portion I0I sumciently to permit the lip portion I08 to move upwards so that the valve member I3 will be moved toward open position by the spring 11. Upon sufllcient coolinz of the unit I I5 by the air flowing through the duct I2, the voltage drop across the unit I I4 will increase sufliciently so that the lip portion I08 will permit movement of the valve member I3 to its maximum open position, i, e., engagement of the valve member I3 with the high fire stop member 82. Should the air supplied by the fan means II to the burner vary for any reason whatsoever the cooling efiect of the air flow will vary and the temperature of the unit II! will v ry to chan e the temperature of the element I08. This change in temperature of the element I08 will move the Current also flows from thetransformer' valve member I3 relative to the port 14 modulating the fuel flow according to air flow.

After a predetermined time interval, the burner will have heated the space in which the thermostat I23 is positioned to a suificiently high temperature to cause the bimetallic blade I3I to move the contact member I3Ilout of engagement with the contact member I29, thereby deenergizing both the secondary circuits. Upon'deenergization of the resistance unit H4, the cylindrical portion lll'l will cool and decrease in temperature so that the lip-portion I08 will be moved downward,moving the valve member 13 toward closed position until the lip portion I08 engages the flange N2 of the intermediate fire adjust-.

ment member III. Meanwhile, the unit 3 and the cylindrical portion 92 having increased to a substantially higher temperature than the tem-' perature reached by the unit I I4 and cylindrical portion I01 reduces in temperature so .that a short time after the lip portion I08 has engaged the flange II! the lip portion 95 will engage the shoulder 80. Continued cooling of the cylindrical portion 92 will act to move the valve member 13 further toward closed position. Substantially at the same time the lip portion 95 engaged the shoulder 80, the lip portion 95 also engaged the shoulder 9|) so that as the valve member 13 was moved towards closed position, the thrust member 86 was moved downward causing engagement of the shoulder 85 with the top surface of the platelike member BI and causing the switch I01 to be moved to open circuit position deenergizing the circuit to the motor II and reducing the supply of air through the duct I2 to the burner.

It may now be seen that with the apparatus as shown in Fig. '2 and with the room thermostat I23 satisfied, i. e., open circuit position, there will be no heaters actuated and the motor II will be deenergized. Upon dissatisfaction of the thermostat I23, i. e., engagement of the contact members I29, I30, the burner will-be placed in operation and the unit II willact to modulate the flow of fuel controlled by the valve member I3 in accordance with the air supplied by the fan means III to maintain a predetermined desired fuel air ratio at the burner. This apparatus also acts as a safety device to prevent high fire fuel flow before high fire air fiow and in the event of failure of high fire air flow to automatically reduce the fuel flow to that fiow which will burn by natural draft.

What is claimed and is desired to be secured by Letters Patent of the United States is:

1. In an apparatus of the character described, a fluid fuel burner, means controlling the supply to said burner of a combustion supporting fluid medium, electric resistance means positioned in the path of flow of at least a portion of the fluid medium and having its resistance responsive to the cooling effect caused by the flow of the fluid medium, fuel supply controlling means for said burner, heat operated means for actuating said fuel supply controlling means, and electric heating means heated in accordance with the resistance of said electric resistance means and controlling said heat operated means thereby to actuate said last-named controlling means in proportion to the cooling effect of the fluid medium flow. 2. In an apparatus for supplying fluid fuel and air to a burner, a first electric resistance unit having a high coeflicient of resistance with increase in temperature, a second electric resistance unit having a relatively low coeflicient of thereby to decrease the voltage drop thereacross and to increase the voltage drop across said second unit, fluid fuel supply controlling means, heat responsive means for operating said controlling means in response to the heating effect of said second unit, said second unit acting to heat said responsive means in inverse ratio to the temperature of said first unit thereby to proportion the air and fuel.

3. In a control system for a fluid fuel burner, an electrically operated air supplying means for the burner, means for supplying fuel to the burner, flow regulating means intercalated in said fuel supplying means, a first control means for said flow means, a switch actuatedby said control means upon actuation of said flow means toward an increased fuel flow, a first circuit means electrically connecting said switch to said air means and operable to energize said air means upon actuation of said switch, a heat actuated control means for said flow means and operable in one position to limit the amount of said increased fuel flow and operable in a second position to actuate said flow means for a further increased fuel flow, an electric resistance unit positioned to heat said heat actuated means and having a low coefficient of increase in resistance upon increase in temperature, a second electric resistance unit positioned in the air path of said air supplying means and operable to be cooled by air flow, said second resistance unit having a high coefiicient of increase in resistance 'upon increase in temperature, a second circuit means connecting said resistance units in series circuit, and control means for said first circuit means.

4. In a control system for a fluid fuel burner, means for supplying air under pressure to the burner, means controlling the flow of air to be supplied by said air means to the burner, movable means controlling the supply of fuel to the burner, a heat actuated power element operatively connected to and for moving said movable controlling means, a first electric resistance unit positioned in heat exchange relationship with said power element and having alow coeflicient of increase in resistance with increase intemperature, a second resistance unit having a high c0- eflicient ofincrease in resistance with increase in temperature and positioned in the path of air flow supplied by said air means to the burner, a source of electric potential having a substantially constant value, and circuitmeans connecting said units in series circuit with each other and with said source of potential.

5. In a fluid fuel burner control system, means supplying air to the burner under pressure, mea'ns controlling flow of fuel to the burner and having an operating portion, a first resistance member positioned in the path of and cooled by the air supplied by said air means and having a. high coefiicient of resistance with increase in temperature, a heat actuated power element operatively connected to said operating portion and operable to actuate said flow controlling means.

a second resistance member positioned in heat exchange relation with and for heating said power element, said second resistance member having a low increase in coefiicient of resistance to electric flow with increasing temperature, an electric circuit connecting said resistance members in series, the coefllcient of resistance of said resistance members being so proportioned relative to each other that said first resistance member acts to vary the heat supplied to said power element in proportion to the air supplied to the burner thereby to maintain the desired fuel and air flow ratio to the burner.

6. In a fluid fuel burner control system, means for supplying air to the burner under pressure, means controlling flow of fuel to the burner and having an operating portion, electric current controlling-means cooled by at least a portion of the air supplied by said air means and operable to modulate a flow of electric current in proportion to air flow through said air supplying means, an electrically operated power element operatively connected to said operating portion and operable to actuate said flow controlling means in proportion to the current flow through said element, an electric circuit connecting said electrically operated element and said electric controlling means, said current controlling means acting to modulate the electric current supplied to said electrically operated element proportionately to the rate of air flow supplied by said air supplying means thereby to maintain the desired fuel and air flow ratio to the burner.

7. In' a fluid fuel burner control system, means for supplying air to the burner under pressure, means controlling flow of fuel to the burner and having an operating portion, electric current controlling means positioned in the path of and cooled by the air supplied by said air means and operable to modulate a flow of electric current in proportion to air flow through said air supplying means, a heat actuated power element operatively connected to said operating portion and operable to actuate said flow controlling means, a resistance member positioned in heat exchange relation with and for heating said power element, an electric circuit connecting said resistance member and said electric controlling means in series, said current controlling means acting to modulate the electric current supplied to said resistance member proportionately to the rate of air flow supplied by said air supplying means thereby to vary the heat supplied to said power element to maintain the desired fuel and air flow ratio to the burner.

8. In a fluid fuel burner control system, means for supplying air to the burner under pressure, means controlling flow of fuel to the burner and having an operating portion, electric current controlling means positioned in the path of and cooled by the air supplied by said air means and operable to modulate a flow of electric current in proportion to air flow through said air supplying means, a heat actuated power element operatively connected to said operating portion and operable to actuate said flow controlling means, a resistance member positioned in heat exchange relation with and for heating said power element,

an electric circuit connecting said resistance temperature of a space heated by the burner and operable to acutate said damper means, means controlling flow of fuel to the burner and having an operating portion, electric current controlling means positioned in the path of the air supplied by said air means to the burner and operable to modulate a flow of electric current in proportion to air flow to the burner, a heat actuated power element operatively connected to said operating portion and operableto actuate said flow controlling means, a resistance member positioned in heat exchange relation with and for heating said power element, an electric circuit connecting said resistance member and said electric controlling means, said current controlling means acting to modulate the electric current supplied to said resistance member proportionately to the rate of air flow supplied to the burner thereby to vary the heat supplied to said power element to maintain a desired fuel and air now ratio to the burner.

10. In an apparatus of the character described a fluid fuel burner, fluid propelling means controlling the supply to said burner of a combustion supporting fluid medium, electrically heated means positioned in the path of flow of at least a portion of the fluid medium and cooled by the flow of the fluid medium thereover, fuel controlling means for supplying fuel to said burner; and bimetallic heat actuated means for controlling said fuel controlling means and controlled by said electrically heated means,'said electrically heated means being operable to reduce the heat supplied to said bimetallic heat means thereby to regulate the fuel supplied to said burner in accordance with the fluid medium supplied to said burner.

11. A heating apparatus comprising a fluid fuel burner, a duct to supply combustion supporting air to said burner, means controlling air flow through said duct, a bimetal heat motor controlling said controlling means, an electric heater for actuating said heat motor, a thermostat controlling the circuit of said heater, a fuel'valve controlling the supply of fuel to said burner, a bimetal heat motorcontrolling valve, an electric heater for operating said valve motor, an electric resistance member in said duct and cooled by air flow to said burner, electric circuit means including said second-named electric heater and said resistance member, said resistance member controlling the current flow to said valve motor electric heater thereby to control the ratio of fuel to air supplied to said burner.

12. A heating apparatus comprising a fluid fuel burner, a duct to supply combustion supporting air to said burner, 9, motor driven fan controlling air flow through said duct, a switch controlling the circuit of said fan, a bimetal heat motor for closing said switch, an electric heater for actuating said heat motor, a thermostat controlling the circuit of said heater, a fuel valve controlling the supply of fuel to said burner, a bimetal heat motor controlling said valve, an electric heater for operating said valve motor, an

- electric resistance member in said duct and cooled said supplying means, means responsive to the by air flow to said burner, electric circuit means including said second-named electric heater and said resistance member, said resistance member controlling the current flow to said valve motor electric heater thereby to control the ratio of fuelto air supplied to said burner.

13. A heating apparatus comprising a fluid fuel burner, a. duct to supply combustion supporting air to said burner, a fan for supplying air to said to said burner, electric circuit means including said second-named electric heater and said resistance member, said resistance member controlling the current flow to said valve motor electricheater thereby to control the ratio of fuel to air supplied to said burner.

JOHN L. STOUGHTON! WALTER s. LANDON.