US2504250A - Control system for dual firing rate oil burners - Google Patents

Description

April 18, 1950 R. M. c'ocHRANE CONTROL SYSTEM FOR DUAL FIRING RATE OIL BURNERS Filed March 5, 1948 5 Sheets-Sheet l INVENTOR R/c/YARD BY 1?. Goa/Iraq ATTORN YS April 18 1950 R. M. COCHRANE 2,504,250

CONTROL SYSTEM FOR DUAL FIRING RATE on. BURNERS Filed March 5, 1948 5 Sheets-Sheet 2 INVENTOR 2% IY/Cl/ARD f7. Ca CHIPAIYE afw ATTORN YS April 18, 1950 R. M. COCHRANE 2,504,250

' comm. svs'rm FOR DUAL FIRING RATE on. BURNERS Filed March 5, 1948 5 Sheets-Sheet 3 INVENTOR i Raw/98011600134:

ATTORN EYS April 18, 1950 R. M. COCHRANE CONTROL SYSTEM FOR DUAL FIRING RATE on. BURNERS Filed March 5, 1948 5 Sheets-Sheet 4 W R S R Y mm M m R v w #0 mm H A M m w April 18, 1950 R. M. COCHRANE CONTROL SYSTEM FOR DUAL FIRING RATE OIL BURNERS Filed March 5, 1948 5 Sheets-Sheet 5 .z w v m m E W 3N m m w PSL b? mm NN ATTZNEYS faiented Apr. 18, 1956 UNITED STATES rssr OFFICE CONTROL SYSTEM FOR DUAL FIRING RATE OIL BURNERS Richard M. Cochrane, Longmeadow, Mass, as signor to Gilbert & Barker Manufacturing Company, West Springfield, Mass, a corporation of Massachusetts Application March 5, 1948, Serial No. 13,138

3 Claims. 1

This invention relates to improvements in control systems for dual firing rate burners, more particularly such burners as may be used in the heating equipment for houses for heating the rooms of the house and for heating water for the hot water supply system for the house.

The invention, in one important aspect, relates to controlling a burner, which has one firing rate for heating the rooms of a house and another firing rate for heating water for the hot water supply system.

The invention is closely related to a prior invention of Logan and Bills, disclosed in their pending application Serial No. 8,184, filed February 13, 1948, now Patent No. 2,464,697, dated March 15, 1949, in that the invention, herein to bedisclosed in the particular aspect above mentioned, is an improvement on that of said application, although in other aspects, it is independent. The disclosure of the present invention is, however, made without depending on said prior application to fully point out herein the utility of this invention in all its aspects. The scope of this invention will be distinctly pointed. out in the appended claims.

Among the purposes of the present invention are (1) to provide a way for a room thermostat to dominate a hot water thermostat so that an oil burner can be operated at a high firing rate for the purpose of room heating, whenever the room thermostat calls for heat, regardless of whether the hot water thermostat is or is not calling for the operation of the burner for the purpose of heating hot water, and, in addition, to operate the burner at a low firing rate, whenever the hot water thermostat operates to effectively call for operation of the burner for the purpose of heating hot water; (2) to provide a way for the burner, when used for firing a steam or hot water boiler, to always start up at the high firing rate, whenever the room thermostat calls for heat, and operate at such rate until the mains are filled with steam or hot water, as the case may be, and then operate at a low firing rate, if the weather is relatively mild, or at a high firing rate, if the weather is severe, as may be determined by a firing rate selector, which may be set manually or automatically for the firing rate needed; and (3) to provide in an oil burner, which has two nozzles, one with a high and the other with a low firing rate, and in which one or the other of these nozzles is selected for operation by a selector devicea way for operating the unselected nozzle briefiy at the end of each run of the burner to purge it of hot oil.

The invention will be disclosed with reference to the accompanying drawings in which-- Fig. 1 is a top plan view of one form of burner with which the control system may be used;

Fig. 2 is a diagrammatical view illustrative of the oil supply connections and controls and th air supply connections and controls; i

Fig. 3 is a diagrammatical view of a control sys-- tem embodying the invention;

Fig. 4 is a view, similar to Fig. 2, but showing alternative controls for the oil and air supply;

Fig. 5 is a diagrammatical View showing the control system adapted for use with the oil and air supply controls of Fig. 4;

Fig. 6 is a diagrammatical view of the control system as used when th nozzle purging feature of Fig. 3 is not desired;

Fig. '7 is a fragmentary diagrammatical view showing the change necessary in the Fig. 3 control system when the feature of always operating" the burner initially at the high firing rate, is not desired; and 1 Fig. 8 is another fragmentary diagrammaticalview, showing the change necessary in the Fig. 6 control system when the selector switch and sur-' face thermotat switch'of Fig. 6 are omitted.

Referring to these drawings; there is shown in Figs. 1 and'2 an example of one kind of oil burner, with which the control system of this inven-. tion may be used to advantage. The system is,- however, capable of use with other kinds of; burners and is not to be limited to use with the. single form of burner herein disclosed as one. illustrative example.

There is shown in Fig. 1, a burner of the socalled gun type, wherein air is supplied by a fan i located in a housing 2, to an air conduit 3, having an open end 4, adapted to be inserted into' th fire box of a suitable heating apparatus, such: as a steam boiler, hot water boiler, or hot air furnace, for example. The rear end of conduit 3 is closed. The fan I is driven by direct con-. nection to the shaft 5 of an electric motor 6, fastened to one side of the fan housing 2. I

The burner also includes two atomizing nozzles 1 and 8, which are adapted for connection one at a time to an oil supply pump 9 in a manner later tobe described. As shown, both nozzles are 10-. cated in the one air conduit 3, near the outlet end thereof. However, in some cases, the nozzles may be located in separate air conduits, both supplied by the same fan, and the control system of this invention will be useful with such an arrangement. Preferably, each nozzle is of the oil pressure atomizing type and. adapted to produce;

a substantially conical fog-like spray of oil to mix with the air supplied by the fan. The air and oil mixture, thus produced, will be suitably ignited, as by a pair of spark electrodes I3. The nozzles 1 and 8 preferably have different capacities. As a single illustrative example, the nozzle 1 may have a capacity of one gallon per hour and the nozzle 8 may have a capacity of one and one half gallons an hour, both at a pressure of say 100 pounds per square inch.

The oil pump 9 is fixed as indicated to the cross bar portion H of a yoke, the legs I2 of which are integrally connected to the fan housing 2. This pump is driven by the motor 5, preferably through the intermediary of a speed-responsive clutch, the driving and driven elements of which are respectively indicated at l3 and I4. As shown, the shaft |5 of the pump is connected to the driven element I4 of the clutch and the driving element l3 of the clutch is connected by a shaft l6 and a flexible coupling IT to the hub of fan The clutch arrangement is substantially like that shown in the Logan Patent No. 1,985,934, granted January 1, 1935, and enables the motor and fan to acquire considerable speed before the oil pump is started and enables the pump to be stopped before the fan, for the purposes set forth fully in said patent.

The air inlet to the fanhousing 2 is shown at |8. It is controlled by an annular shutter I 9, the central opening of which receives the clutch elements l3 and I4, as best shown in Fig. 2. The shutter is supported by a screw 20, on which it is threaded, and this screw has smooth cylindrical portions, one near each end thereof, which are slidably and rotatably mounted, one in a bearing 2| in housing 2 and the other in a bearing 22 in the cross bar The screw 24 is bodily movable in the direction of its axis to carry the shutter l9 from a position suitable for high firing rate operation to a position suitable for low firing rate operation and vice versa. The screw has a shoulder 23 which is adapted to abut the adjacent end face of bearing 2| and limit the axially inward movement of the screw and thus define the low firing rate position of the shutter. Such position may be varied by rotating screw 25. Sliding movement of the screw in the opposite direction is limited by a second screw 24, with the inner end of which a circumferentially grooved collar 25-, fixed to screw 23, is adapted to abut and determine the high firing rate position of the shutter. The screw 24 is threaded into a circular end housing 26, secured to the cross bar II. By turning screw 24, the high firing rate position of the shutter may be adjusted. A part-cylindrical member 21 encloses the space between the member 26 and housing 2, except for suitable openings to enable air to enter and reach the inlet I8.

The air shutter I9 is shifted from one position to another by means of a lever 28, fulcrumed near its. lower end at 29 and having its upper end engaged in the groove in collar 25. The lower end of this lever is pivotally connected to the outer end of a piston rod 30, the inner end of which carries a piston 3|, slidably mounted in a cylinder 32. The inner end of this cylinder is closed and the piston is held in abutment with this closed end by means of a spring 33, coiled around rod 30 and acting between the outer face of piston 3| and a head 34, which is threaded into the outer end of the cylinder and slidably supports the piston rod. When the burner is not in operation, the shutter is held in high firing rate position by spring .33. When the burner is oper-.

ating at the high firing rate, the shutter is held in the same manner and in the same and illustrated position. When the burner is to operate at the low firing rate, oil is admitted to the inner end of cylinder 32 and the piston 3| is moved outwardly, rocking lever 28 clockwise and bodily moving screw 20 until the shoulder 23 abuts the adjacent end face of bearing 2|, thus carrying the shutter l9 into position for low firing rate operation and holding the shutter in such position.

The oil pump 9 includes a combined cut-off and pressure-regulatin valve housed within the pump casing. This valve is shown diagrammatically by a piston 35, pressed by a spring 35 against a seat 36, through which the pump outlet passage 31 extends. Oil drawn into the pump from a suction pipe 38 is forced by the pump into a chamber 39 and, when the oil reaches a predetermined minimum pressure, say pounds per square inch, the piston 35 is moved to the left away from seat 33, allowing oil to enter the outlet 31 and flow to one or the other of the nozzles 1 and 8 in a manner later to be described. When the oil inchamber 39 reaches a maximum predetermined pressure, say pounds per square inch, piston 35 will be moved to the left far enough to uncover a port 49 and allow oil from chamber 33 to flow through port 40 into a chamber 4| which is connected to the suction side of the pump. An example of one pump suitable for the purpose will be found in Wahlmark Patent No. 2,232,983, dated February 25, 1941, to which reference is made for a complete disclosure of the pump structure with its cut-off and pressure-regulating or by pass valves, if necessary or desired.

The flow of oil from the pump to the nozzles 1 and B is respectively controlled by two valves 42 and 43. The valve 42 is of magnetic material and is located within a tube 44 having an inlet in its peripheral wall, which is connected to the outlet 31 of the oil pump by means to be later described and having two outlets, one in each end thereof. This tube is made of non-magnetic material. The valve 42 is normally held by means of a spring 44 in the illustrated position against a seat 46 to close the outlet to a pipe 41, which extends to nozzle 1. A solenoid 48 surrounds tube 44 and is arranged in a casing 45 of magnetic material. When solenoid 48 is energized, it lifts valve 42 until it engages a seat 49 in the upper part of casing 45 and closes an outlet, which is connected to a pipe 5!], leading to the suction side of pump 9, as to pipe 38. The valve 43 is also made of magnetic material and is located in a tube 5| of non-magnetic material, having an inlet connected by a pipe 5| to the outlet 31 of the oil pump, and two outlets 53 and 51, one in each end thereof. Valve 43 is held by a spring 52 against a seat 53 to oiose an outlet, which is connected by a pipe 54 to nozzle 8. A solenoid 55 surrounds tube 5| and is located in a magnetic casing 56. When the solenoid 55 is energized, it raises valve 43, allowing oil to flow through pipe 54 to nozzle 8, and moves it against a seat 51 to close an outlet which is connected to a pipe 53. Pipe 58 has a branch 53 leading to the inner end of cylinder 32 and a branch 63 leading to the described inlet of tube 44 of valve 42. When valve 43 is positioned as shown, the inlet of tube 44 is connected to the outlet 31 of the oil pump by means of pipes 60 and 58, tube 5| and pipe 6|.

The solenoid valves have been shown merely in diagrammatical form. These valves per so are standard commercial articles, which can be bought in the market, and complete illustration '5 and description of them is therefore deemed unnecessary.

When the low rate nozzle 1 is to be operated, the solenoid 48 is energized and the solenoid 55 remains deenergized. The Valve 42 is raised to engage seat 49, while the valve 43 remains, as illustrated, engaged with seat 53. The pump 9 will force oil through pipe BI into tube 5| and thence through pipes 56 and 65 into tube 44 and thence through pipe 41? to nozzle 1. The raised valve 42 closes the outlet to pipe 56 and thus disconnects the cylinder 32 from the suction of pump 9. Oil from the pump, flowing into pipe 58 as described, will also flow through pipe 59 into the inner end of cylinder '32 and move piston 3| outwardly to shift the shutter I9 into low firing rate position. The closed valve 43 prevents oil from flowing to the high rate nozzle '8 When high firing rate operation is desired, the solenoid 55 is energized and the solenoid 49 remains deenergized. Accordingly valve 43 is raised to engage seat El and valve 42 remains engaged with seat 46 as illustrated. Oil from pump 9 will then flow through pipe 6I into tube 5! and from the latter through pipe '54 to the high rate nozzle 6. Oil cannot passto the cylinder 32 or tube 44 because the valve 43 engages seat 51. The lowered valve 42 closes the outlet to the nozzle 7 and enables cylinder 32 to communicate with the suction side of pump 9 by way of pipes 59 and 69, tube 44, and pipes 59 and 38. Accordingly, the piston will be moved to the illustrated position for high rate firing.

As is usual in burners of this kind (Fig. 3), the motor 6 and the primary 62 of an ignition transformer are connected in parallel in a burner operating circuit, which is controlled by a switch 63, operated by a relay or electromagnet 64, under the control of a suitable thermostat switch. This relay switch is part of a main control instrument, which is located within the dot-dash line in Fig. 3 and has terminals 65 and 56, adapted to b connected to the wires ii! and 68, of a suitabl supply source, usually 115 volts A. C., and a terminal 69, which is connected by a wire '19 to one terminal of the motor 6 and to one terminal of primary '62. The other terminals of the motor. and primary are connected by a wire I I to terminal 65. A wire l2 connects terminal 65 to the contact of switch 63 and the blade of the latter is connected by a wire it to terminal 69. A limit switch it, such as a steam-pressure-actuated switch, for example, may be included in series in the supply wire 61, if desired. The secondary of the ignition transformer is connected by wires 16 to the spark electrodes I0. When the electromagnet 64 is energized, switch 63 will close the burner operating circuit, comprising terminal 65, wire ?2, switch 63, wire l3, terminal 69, wire I0, motor 6 and primary 62, wire 'II and terminal 66. The motor 6 will be started to supply air and oil for combustion and the ignition transformer will be energized to supply ignition sparks between the electrodes I6. When the electromagnet 64 is deenergized, the switch 93 will open to stop the motor and deenergize the ignition transformer.

The main control instrument also includes a step down transformer having a primary 11, which is connected by wires I8 and 19 to terminals 65 and 66, respectively, and a secondary 80, which supplies low voltage for the control circuits for the electromagnet '64. The low voltage ciredits are shown by light lines to distinguish them from the high voltage circuits which are shown .by heavy lines. The electromagnet usually also 'actuates three switches 8|, 82 and B3 besides the burner control switch 63. The blades of these last three switches are interconnected by a conductor .84. All these three switches are closed, when the electromagnet 64 is energized, and they are all open, when the electromagnet is deenergized. There is also provided a heat-actuated safety switch 85, which when heated by an electric heating coil 86 for a predetermined time, say for example 90 seconds, will open and remain open until manually reset. This sort of switch is well known per se in control circuits and is only diagrammatically indicated here. The main control instrument also includes a thermostat responsive to combustion temperature, such as a stack thermostat, conventionally shown at 87, which actuates several pairs of contacts 88, 89 and 99. One of the pair of contacts 89 is connected to one of the pair of contacts 89 as indicated. When cold, the thermostat 8'! holds the pairs of contacts 88 and 89 engaged and the pair of contacts 99 separated as shown. On occurrence of combustion, the contacts 99 are first engaged, followed by the separation of the contacts 99 and then the separation of the contacts 88. On a subsequent failure of combustion, the contacts 99 will separate almost immediately and, in substantially two minutes, the contacts 89 and 38 will reengage.

One terminal of secondary 99 is connected by a wire 9| to one terminal of safety switch and the other terminal of the latter is connected by wires 92 and 92' to one terminal of the relay coil 64. The other terminal of the latter is connected by a wire 93 to one terminal of heater coil 86 and the other terminal of the latter is connected by a wire 94 to one of th contacts 88. The other contact 88 and that one of the contacts 89, fixed thereto, are connected by a wire 95 to one of the contacts 99 and the latter is connected by a wire 96 to the contact of switch 8|. The other contact is connected by a wire 9? to wire 93. The other contact 89 is connected to a wire 98 which connects with a wire 99 extending to the contact of switch 82 and to a wire I99 extending to the blade of a switch 59!, having two contacts I02 and I 93. The contact I92 is connected by a wire I94 to a terminal I85 of the main control instrument. The contact of the switch 83 is connected by a wire lot to on terminal of an electric heating coil Itl and the other terminal of the latter is connected by a wire Ial'8 to the blade of a switch I69 having two contacts H0 and III. The contact He is connected by a wire M2 to one terminal of a resistor I53 and the other terminal of the latter is connected by a wire II4 to a terminal H5. The secondary 80 has its right hand terminal connected by a wire IIE to a terminal Ill. The contact I93 is connected by a wire H8 to a wire H9 and by the latter to a terminal I29. The contact HI is connected bya wire I2I to a terminal I22.

The terminals I65, H5, H7, I29 and I22 of the control instrument are adapted to be connected to two thermostat switches one or the other of which starts the burner motor 6 on a demand for heat and stops the motor when such demand is satisfied. One thermostat switch comprises a bimetallic thermostat blade I23, which is responsive to the temperature of the water in the boiler and is used to control the burner for heating hot water, as for example, by an indirect heater through which the boiler water is circulated. This switch has contacts I24 and IE5 which are adapted to be successively engaged in the order named by blade I23, when the temperature of the water in '7 the boiler falls below a redetermined value, and to be successively disengaged in the reverse order, when the temperature of the boiler water exceeds a predetermined value. Th contacts 124 and I25 are" respectively connected by wires I26 and I2! to terminals II! and IE5. The blade IE3 is connected by a wire I28 to terminal IE5. The other thermostat switch, commonly called a room thermostat, comprises a bi-metallic blade I29, responsive to the temperature in the space to be heated by the burner. This thermostat switch has two contacts I30 and NI, adapted to be successively engaged in the order named by blade IE9 on a demend for heat and to be disengaged by the blade in the reverse order, when the demand is satisfied. These contacts I3 and i'cRI are respectively conhectedby wires I32 and I33 to terminals It? and I20. The blade I23 is connected'by a wire I31 to one terminal of a heating coil i'32 and the other terminal of the latter being connected by a wire I33" to terminal I22. The coil I32 is adapted at certain times to heat the blade I29 and accelerate its disengagement from contact E39 as will later appear.

While it has been common, heretofore, to control the one burner by a room thermostat and by a'hot water thermostat, the control system of this invention provides for the domination of the hot water thermostat by the room thermostat. If, for example,'the burner is operating, under the control of the hot water thermostat I23, for the purpose of heating hot water and there is a demand for room heating, which causes the room thermostat I29 to close, the hot water thermostat will be disconnected from the burner control circuit and the room thermostat will be connected into such circuit in place of the hot water thermostat. This result is efiected by the switches lei and I39, which are actuated by an electromaghet I34, being moved by this electromagnet, when energized, from their respective right hand contacts I52 and III) to their respective left hand contact we and III. The electromagnet I34 is connected at one end to the wire 32 and its other end is connected by a wire I35 to the wire I I3.

On a. demand for hot water heating, the hot water thermostat switch blade I 23 will first engage contact E24 and shortly after engage Contact 25. When both these contacts are engaged by the blade, a starting circuit will be closed to the relay 64 for closing switch 63 and operating the burner motor and ignition means. This circuit may be traced as iollo'wsirom the right hand terminal Of secondary Bil, by wire 4 I6, terminal Ii'I, wire I26, contact i2 3, blade I23, contact I25, wire I27, terminal I35, wire I34, contact 62, switch IOI, wires I06 and t8, engaged pairs of contacts 89 and 88, wire'il l, heating coil 85, wire 93, rela coil 64, and wires 92 and 92, switch 85 and wire 9! to the left hand terminal of secondary 8E The relay coil 64, being energized, the switch 63 closes to start the motor and ignition means and at the same time, the switches 35, 82 and 53 also close.

The switches 85 and 32, when closed, prepare alternate or running circuit which is completed,

when combustion occurs, by the action of the stack thermostat 81. Very soon after combustion occurs, the contacts 98 will engage and complete this running circuit by shunting out the heating coil 85 of the safety switch 35. This running circuit is the same as the starting circuit through the wire IE and then extends by wire 39, closed switch 82, conductor 35, closed switch SI, wire -93, the contacts 30, which are then engaged, wire 9'! to wire 33, down wire 93 to the relay coil 54 and atria-s50 thence as heretofore described. The heating coil 86 is thus put out of action to prevent the safety switch from o ening. In about two minutes following the start of combustion, the contacts 89 open, followed shortly by the openings of contacts 8 8. If combustion does not occur within say seconds after the relay coil 84 was energized, the safety thermostat switch 85 will be opened by the heat received from coil 86 and the burner will stop and can be started up again, only after switch 85 has been manually reset. If combustion initially occurs and there is a'later failure while the motor 6 is operating, the burner will be stopped almost instantly b the opening of contacts 90-. Then, after a scavenging period of about two minutes, the pairs of contacts 88 and 89 will reengage and establish the starting circuit, above described, whereby the burner motor will automatically be started. If combustion then occurs, the running circuit will be established, as above described. If combustion does not occur within 90 seconds, the safety switch 85 will open and stop the burner until the switch is manually reset.

When the demand for heat is nearly satisfied, the blade I23 will have moved to the right far enough to disengage from contact I25 but not from contact I2 1. This does not stop the burner because of an'alternate branch, which was established, when switch 83 closed. This branch eX- tends from blade I23 by Wire I28, terminal II5, wire IIE, resistor II3, wire II2, contact IIO, switch 39, wire I68, heating coil I01, wire I06, closed switch 83, and conductor 84, to closed switch 8I. Previous to the separation of blade I 23 from contact I25, no current fiowed in thisbranch because of its relatively high resistance, due to the coil I01 and resistor H3 (if used), and the fact that the other branch, comprising contact I25, wire I21, terminal I05, wire I04, contact I02, switch IiII, wires I30 and 99 and closed switch 82, has relaatively low resistance. Thus the heating coil I01 can be energized only during the last few moments of each run of the burner and this is made use of for a purpose later to be described.

'When the demand for heat is satisfied, the blade I23 leaves contact I24 breaking the circuit to relay coil, and causing switch $3 to open and stop the burnei. The switches BI, 82 and 83 also oben. Soon after combustion ceases, contacts 90 open breaking the running circuit in another place so that if the thermostat switch I23 should close, the burner could not be immediately started. The starting-of the burner will be postponed until the combustion chamber has cooled enough to allow safe starting because of the delay of about two minutes, which is necessary for the stack thermostat 81 to cool enough to engage the contacts '88 and '89. When these contacts reengage the above described starting circuit will be reestablished.

The operation of the control, as thus far described, is the usual one. Anovel arrangement, now to be described, enables the room thermostat to dominate the hot water thermostat. Assume for example that the burner is operating under hot water thermostat control, as already described, and that a demand for room heating occurs, causing the room thermostat switch I29 to engage the-contacts I30 and I3I, 'a circuit will be closed to relay coil I34, as follows-from secondary 83, by wire IIB, terminal 'I I1, wire I32, eontaetls'fl, blade I 29, contact 'I3I, wire I33, terminal #20, wires H9 and I35, coil I34, wire '92, closed switch'8'5 and wire 9| to the secondary' flfl.

The relay 34 will be energized and move switches IUI and I09 away from contacts I02 and III] respectively to disconnect the hot water thermostat I23 from the burner circuit and cause suchswitches to engage their respective contacts I83 and III to connect the room thermostat switch I28 into the burner circuit. The interruption of the circuit to relay coil 84, caused by the movement of each of the switches I DI and I88 from one contact to the other, is of course so short as not to cause opening of any of the switches controlled by the relay, nor will there be time for the stack thermostat to cool sufficiently to open the contacts 98.

If the call for heat originates with the room thermostat I28, the relay I34 will be energized as just above described, and the switches NH and I89 will be moved to engage their respective contacts I83 and I I I. A starting circuit to the relay 84 will be closed, which extends from the secondary 88, by wire I I5, terminal I I1, wire I32, contact I38, blade I23, contact I3I, wire I33, terminal I28, wires II?) and H8, contact I83, switch IIlI,-wire I88 and thence as before traced in connection with the hot water thermostat control. If combustion occurs, the running circuit is established, as before described, by shunting out the heating coil 85. If combustion does not occur, the coil 88 opens switch 85 and stops the burner, as before described. Near the end of the run of the burner, under room thermostat control. blade I28 disengages from contact I3I and allows current to flow through the heater I 81. Current now flows from blade I29, by wire I3I', heating coil I32,

wire I33, terminal I22, wire IZI, to contact III,

switch I89, wire I88, coil I81, wire I85, closed switch 83, and conductor 84 to closed switch 8|. The heating coil I32 heats up blade I29 and causes it to disengage from contact I38 at an earlier time than it otherwise would. This breaks the circuit to relay 64, causing switches 8!, 82, 83 and 63 to open to stop the burner, and breaking the circuit to relay I34, causing switches NH and I89 to resume their illustrated positions.

The arrangement, as thus far described, is capable of general use with any electrically-operated burner for room heating and hot water heating. The burner, to be controlled by the described arrangement, need not necessarily have two nozzles as shown. However, the arrangement is particularly desirable in connection with a burner having relatively low and relatively high firing rates. It is, for example, desirable and more efficient to operate the burner at the low firing rate than at the high rate, when the burner is being operated for the purpose of heating hot water, and as another feature of the control system, there is provided an arrangement whereby the burner, when controlled by the hot water thermostat, will always operate at the low firing rate. For this purpose there is provided an energizing circuit for the solenoid 48. which controls the flow to the low rate nozzle I. and a control switch I35 for this circuit, which is normally closed and opens only when the room thermostat switch I29 controls the burner. The blade of switch I35 is connected by a wire I3? to the blade of motor switch 83. SwitchI35 en gages a contact I38, when relay coil I34 is deenergized. This contact I38 is connected by wires I38 and I45 to a switch I4I, which engages a contact I42, connected by wires I43 and I44 to a terminal I45. The latter is connected by a wire I 55 to one terminal of solenoid 48. The other terminal of the latter is connected by wires 10 I4! and I48 to wire II. Thus, when the hot water thermostat I23 closes on a demand for heating hot water, the relay 64 is energized, as before described, to close switch 83 and start the motor 8 and energize the primary 62 of the ignition transformer. The closing of switch 83 will close an energizing circuit to solenoid 48, as follows--from terminal 85, by wire I2, closed switch 83, wire I 3?, switch I38, contact I38, wires I39 and I48, switch I4I, contact I42, wires I43 and I44, terminal I45, wire I48, solenoid 48, wires I41 and I48 to wire II and up wire II to terminal 86. The solenoid 48 will thus be energized to cause the low rate nozzle I to be connected to the oil pump. As long as the hot water thermostat switch I23 is in control of the burner, the described energizing circuit will be closed, whenever the motor switch 83 is closed, and low firing rate operation will result. However, whenever the room thermostat switch I29 closes, the relay coil I34 will be energized and switch I36 will be moved away from contact I38 to break the described energizing circuit and to engage another contact I48 to establish another energizing circuit to the solenoid 48 or 55, as selected by other controls to be described.

One of these controls consists of a firing rate selector switch, herein shown as a pivoted tube I58, having a pair of terminals I5I and I52 near one end of the tube and a pair of terminals I53 and I54 near the other end of the tube. One pair or the other of these terminals is adapted to be connected by mercury I55 in the tube, according to the position to which the tube is tilted. The tube may be moved from one position to another either manually or automatically as desired. It may for example, be actuated by a thermostat, such as an outdoor thermostat, conventionally indicated at I58. The terminals I5l and I54 are interconnected, forming a single supply terminal for the switch, which supply terminal is connected to a supply wire I56. The terminals I52 and I53 are output terminals and are adapted to be connected to the solenoids 48 and 55, respectively. The terminal I52 is connected by a wire I5? to a terminal I58 of the main control instrument and such terminal is connected by a wire I 59 to the described wire I40. The output terminal I53 is connected by a wire I88 to a terminal I6! of the main control instrument and such terminal is connected by a wire I52 to a switch I83, engaging a contact I54, which certain advantages later to be described. Such,

switch consists of a tube I68, closed at both ends and containing mercury I68, which is adapted to connect one or the other of two pairs of contacts, arranged one pair near each end of the tube.

ply terminal I'EI, to another position in which the mercury connects a supply terminal I I2 'to another output terminal I73, which is connected to the supply wire 955 of the selector switch. The supply terminals iii and I72 are connected together and these interconnected terminals are connected by a wire I14 to a terminal I15 of" The latter is pivoted and can move from the position shown, in which an output terminal I75 is connected by the mercury I59 to a sup the control instrument. The terminal I is con-- nected by a wire I16 to the contact 1480f switch I36. Thus, when the tube I68 is tilted to its lastnamed position, the supply terminal of the selector switch will be connected to contact. I43 and, if the latter isengaged by switch I35, tothe motor switch 63. And if the tube I68.-is not used, the wires I14 and I56 will bepermanently connectecLasshown in Fig. 7.

Assuming that these wires I14 and I 56 are connected by the mercury I69, and that the selector switch is positioned as shown for low firing, rate operation, on a call: for heat by the room thermostat switch I26, switch I36? will be moved by electromagnet I34 to engage contact. I49: and switch 63- will be closed by the electromagnet 54, as alreadydescribed', and a. circuit will be closed to energize'solenoid 48 and cause the nozzle 1 to be connected to the oil pump. This circuit may be traced as follows-from terminal 65, by wire 12, closed switch 63, wire I31, switch I36, contact I 49, wire I16, terminal I15, wire I14, terminal E12, mercury I69, terminal I13, wire I55, terminal I5I, mercury I55, terminal. I52,.wire I51, terminal I58, wires I59 and I40, switch I4-I, contact I42, wires I43 and I44, terminal I45, wire I46, solenoid 48, wires I41 and I48 to wire H, and up wire I I to terminal= 66.

Assuming now that the selector switch is positioned for high firing rate operation the terminals I53 and I54-will be connected bythe mercury I55 and a circuit will be closed to energize solenoid 55. This circuit is the same as that just described up through wire I56 and then extends as followsterminal I54, mercury I55, terminal I53, wire I68, terminal I6I, wire I62, switch I63, contact I64, wire I65, terminal I66, wire I61, solenoid 55, wire I48 to wire HI and up wire 1i to terminal 6. The solenoid 55 may thus be energized to cause the high rate nozzle 8 to be connected to the oil pump.

The switch, involving tube I68, is used where it is desired to secure rapid firing during the initial part of each run of the burner. This switch is actuated by a thermostat I68, Which 5;

may be responsive to temperature of the steam in the end of the steammeain, supplied by the boiler, heated by the burner described. Or the thermostat may respond to the temperature in the return line of a hot water boiler. The switch willbe positioned as shown, when the bLuner starts and will be moved to its other position only after the temperature at the selected location has risen to a predetermined value. When this thermostat switchis positioned as shown, the solenoid 55 will be.- energized when the burner starts, through the following circuit-from terminal 65, by wire 12, closed switch 63, wire I31, switch I36, contact I49, wire I16, terminal I15, wire I14, terminal I'II, mercury I69, terminal I16, awire I11, which connects the output terminal I16 to terminal I5I, terminal I5I, wire I62, switch I63, contact I64, wire I65, terminal I66, wire I61, solenoid 55-, wire I48, to wire H, and up wire 1! to terminal 66'. Thus, the solenoid 55 will be energized to cause the high firing rate nozzle to be connected to the oil pump. The burner will operate at the high rate until the mains are filled with steam. or hot water, as the case may be, when the thermostat responding to a predetermined temperature of the steam or water, as the case may be, will move tube I68 to its other 'position,.breaking. the described circuit to solenoid 55 and connecting supply wires I14 and I56 so that the selector switch now becomes operative,

12 whereupon the burner will continue to operate but at whatever rate is selected by the selector switch.

It may be desirable in a burner of this type,

, which operates at different firing rates, to periodica-lly purge the nozzle, which is not selected for operation, of the oil therein, which has become heated bythe operation of the other and selected nozzle. For example, if the selector switchis" set for low firing rate operation, then near the end of each run of the burner, the high rate nozzle will be operated for a brief, period to purge it of hot oil. And if the selector switch is set for high firing rate operation, then near the I end of. each run of the burner, the low'rate nozzle, will be operated for a brief period to clear it of the heated oil therein. This is efiected by shown for low firing rate operation, the current flow to solenoid 48 will be cut off and directed to solenoid instead. The circuit will be the same as for low firingv rate operation, under control of the room. thermostat switch, up to switch MI and then it extends through contact I18, wire I65, terminal I 56 and wire I61 to solenoid 55 and thence by wire I 48 to wire 1| and up wire H to the other supply terminal 66. If. the selector switch is set for high firing operation to energizesolenoid 55, then, when switches MI and IE3 move to' engage contacts I18 and I19 respectively, the solenoid 48, which causes low firing rate operation will be energized. The energizing circuit will be the same as for high firing rate operation under room thermostat control from terminal up to the switch I63'and then will extend through contact I19, wires I88 and I44, terminal I45, wire I46,.so1enoid 48, wires I41 and I48 to wire II and up wire H to the other supply terminal 56.

The switches I 'iI- and I63 are simultaneously moved by an electromagnet I8 I-being positioned as shown when the electromagnet isv not energizecl and moving into engagement with the contacts I18 and I19, respectively, when the electromagnet I8! is energized. This electromagnet is controlled by a thermostat switch I82, normally open but movable toclosed position after it has been heated for a predetermined time by the described electric heating coil I61. Switch I82 controls a high voltage circuit for energizing electromagnet I-8I. The blade of switch I82 is connected.- by a wire I83 to terminal 66. The contact of switch I92 is connected by a wire I84 to one terminal of electromagnet I8I, while the other terminal of the latter is connected. by a wire I85 to wire 19 and thus to terminal 66. When switch I82 closes, the electromagnet will be energized. through the following circuit-from one supply terminal 65- by wire 12, closed switch 63, wire 13, terminal 89, wire I83, closed switch I82, wire I84, electromagnet I8i, wire I85 to wire 19, down wire 19 and across to the other supply terminal 66. Thus, the relay I8I will be actuated to move switches MI and I63 to reverse the connections to the solenoids 48 and 55 to energize the one which previously had been deenergized and vice versa.

It will be recalled that heater I61 is energized only after the room thermostat switch 29 has moved away from its contact I3I or after the hot water thermostat switch I23 has moved away from this contact I25, according to which switch is controlling the burner. Thus, the purging of the unselected nozzle will occur at the end of each run of the burner just prior to stopping the burner. The time interval, between the disengagement of blade I29 from contact I3I and its disengagement from contact I39 and the time interval, between the disengagement of blade I23 from contact I25 and its disengagement from contact I29, will not necessarily be equal. For present purposes, this time interval may be assumed to be at least two minutes. Of this time, one minute may be consumed in heating up switch I82 to close it and the balance for the purging of the unselected nozzle.

It may be desirable that the current flow through the heating coil I01 should be substantially the same whether the burner is operating under the control of the room thermostat or under the control of the hot water thermostat This will insure closure of switch I82 in about the same time in each case. It will be noted that, when the room thermostat controls, the two'relay coils 64 and I34 are connected in circuit in parallel. However, when the hot water thermostat controls, the relay 64 is energized, but the relay I 34 is deenergized. I provide a coil 295, having the same impedance as relay I34, and connect it by wires 266 and 291 to wires 92 and I04, respectively. When the hot water thermostat controls, the coil 206 will be connected in parallel with relay 64 and take the place of relay I34. Also, when the room thermostat controls, the circuit includes in series the usual anticipating heater I32, while the hot water thermostat has no such heater. To compensate for this, the resistor I I3 of the same value as resistor I32 may be added in series to the hot water thermostat circuit. Thus, the same current flow through coil I01 may be secured whether the room thermostat v or the hot waterthermostat is in control of the circuit.

In Fig. 4, a single solenoid I84 controls a three way valve I85 which is operable to connect the oil supply pipe 6! either to a pipe I66, leading to the low firing rate nozzle 1, or to a pipe I91, leading to the high firing rate nozzle 9. A spring I68 normally holds valve I85 in position for oil to flow to nozzle 9 but, when the solenoid E64 is energized, valve 985' is lifted to close the outlet to pipe I81 and open the outlet to pipe I86 and the nozzle 1. The valve I85 is located within a nonmagnetic tube I89. The air-shutter-operating cylinder 32 is controlled by a second valve I96, moved in one direction by a spring I9I and in the other direction by a solenoid I92, when the latter is energized.' The valve slides in a nonmagnetic tube !93. The inner end of cylinder 32 is connected by a pipe I94 to the space within tube I93. A pipe I95 connects the lower end of the tube I93 to the space within tube I39 and thus to the oil supply pipe 6|. The upper end of tube I93 is connected to the described suction pipe 53. When solenoid I92 is not energized, valve I99 prevents fiow of oil to cylinder 32 and opens pipe 59 to allow pipe I94 and thus cylinder 32, to communicate with the suction side of the pump. When solenoid I92 is energized, valve I99 is lifted to allow oil to flow through pipe I94 to cylinder 32 to move the air shutter to low firing rate position and to close the connection to pipe 59. Both solenoids I84 and I92 will be energized simultaneously to secure low firing rate operation. High firing rate operation is secured, when both these solenoids are deenergized.

Substantially the same control system may be used to control the solenoids I34 and !92, except that many connections can be omitted, because neither solenoid is energized for high firing rate operation. Fig. 5 shows the circuits necessary to the operation of these solenoids. The other circuits for controlling the relay coils 54, I34 and It! by the hot water thermostat and thermostat switches are the same as in Fig. 3. It will be noted, however, that the solenoids I84 and I92 are connected in parallel by two wires I96 and I91, former being connected to terminal I45 and the latter to wire H. The wires I65 and I61,

terminal I66, wire I11, and the terminals I10 and Ill of the thermostat switch I 68 of Fig. 3 are omitted.

Assuming that the hot water thermostat I23 calls for heat, the switch 63 will be closed as be- -fore by relay 34 but the switch I36 will remain in engagement with contact I39 because relay l34 is not energized. Also, the switches MI and IE3 will engage their respective contacts I42 and I64 because relay I8I is not energized. A

circuit will. be established, on closing of switch 63, to energize both solenoids I84 and I92 to secure operation of the burner at the low firing rate. This circuit may be traced as follows from terminal 65 by wire 12, closed switch 63, wire I31, switch I36, contact I 33, wires I39 and E49, switch I4I, contact I42, wires I43 and I44, terminal I45, wire I96, solenoids I94 and I92, wire I91 to wire II and up wire II to terminal 66. Near the end of the run of the burner, the relay IBI will be actuated, as before, to simultaneously move switches I 4! and I63 into engagement with their respective contacts I18 and I19, with the result that the burner will operate at the high firing rate because the described circuit for the solenoids I 34' and I92 is broken by the disengagement of switch II from contact I42. The engagement of switch I4! with contact I18 accomplishes nothing because there is no wire connecting with this contact. The engagement of switch I63 with contact 119 does not accomplish anything because switch I63 has its source of power broken at the switch I59. At the end of the purge run, the hot water thermostat I23 opens, causing relays 64 and IBI to drop out, opening switch 63 to stop the burner and moving switches MI and I63 back to their illustrated positions.

Assuming now that the room thermostat I29 calls for heat, and that the switches I56 and I68 are in the position shown, the relay !34 will be energized to move switch i356 to contact I49 and then the relay 54 will be energized to close switch 63. The burner motor will start but the solenoids I84"and I92 will not be energized. Starting from terminal 65 as before and passing through wire 12, closed switch 63, wire I31, switch I 36, contact Q49, wire I16, terminal I15, and wire I14 there is a break between the terminals I12 and I13 of thermostat switch I66. Consequently the burner operates at the high firing rate. Such operation will continue until the thermostat switch I39 moves to its other position to cause the mercury I39 to connect the terminals I12 and I13. Then the burnerwlll operate at the high or low rate, whichever is determined by the selector switch I50. As shown, this switch is setfor. the low firing rate and both solenoids will be energized; The circuit is the same as beforetraced to terminal I12 and their. extends through mercury I66, terminal I13, wire E56, terminal 5I', mercury I56, terminal I52, wire I63, terminal I56, wires I56 and I46, switch I4I, contact 542, wires I43 and I44, terminal I45, wire I66, solenoids I64 and I92, wire I31 to wire II, and up wire1l to terminal If the burner continues to operate at the low rate until the demand for. heat is nearly satisfied, an automatic switch to high rate operation will occur, when relay IBI is energized by the thermostat I26 disengaging from contact 31. The switches I iI and I63 will be moved. to engage their respective contacts I16 and I16 and the last described circuit to the solenoids i 34. and I62- will be'broken by the disengagement of switch MI from contact 542;

Assuming now that the selector switch I56 is set for high firing rate operation. and that the thermostat switch I66, after being satisfied, moves to cause the mercury I66 to connect the terminals I12 and 513, no circuit will be established to the solenoids I84 and I92 and thus high firing rate operation will continue. If one follows along from wire I16, through terminal I12, mercury I69, terminal I13, wire I56, terminal I54, mercury I55, terminal E53, wire I68, terminal I6I, wire I62, to switch I63, there is a. break'in the circuit to the solenoids because the contact I64, which is then engaged by this switch, has no connection leading. therefrom. However, when the relay I6I is energized near theend oi the high fire run, as before described, theswitch I6-3willbe moved to engage contact I15 and complete a circuit by wires I86 and I64, terminal I45, wire I66, solenoids I64 and I92, Wire I91 to=wire 1i and up wire 1| to terminal 66. Thus, the solenoids wiil be energized to produce ashort low firing rate run for purging the nozzle 1.

When the burner is used with a. warm air furnace and it is desired to. use a. fan for circulating the warm air, when the burner is operating under the control of the room thermostat 526, the motor for such fan, designated I98 in Fig. 3, may have one of its. terminals connected to a contact I93 of switch I36 by a wire 206, terminal 26I and a wire 202 and its. other terminal connected by a wire 203 to wire II. When room thermostat I26 closes, relay I34 is. energized as before described and. this will cause switch I36 to engage contact I33, whereby a circuit will be closed to motor I98 as follows-from terminal 65, wire 12, closed, switch 63, wire I31,.switch I36, contact [39, wire 200, terminal 20!, wire 202, motor I98, wire 203,, and wire H to terminal 66.

In the event that the feature of purging the unselected nozzle near the end ofeach run of the burner is not desired, the switches MI and I63, with their actuating relay NH and the relay control switch I82, with its heating coil I01 and the. resistors IOI and H3 may be omitted, together with the wires III, I40, I43, I44, I62, I65 and I80. The arrangement is shown in Fig. 6. The wires I06 and. I08. will be connected and the. wires H2 and H4 will be connected. The wires I39 and. I51 will extend directly to the terminal I45 and thus to the low firing rate solenoid 48, while wires I60 and I11 will extend directly to the terminal I66 and thus to the high. firing rate solenoid. 55. The. other circuits are the same as. in Fig. 3.

Assuming that the hot water thermostat I23 calls for heat, the relay 64 is energized as be.- fore to close switch 63 and switch. I36 remains engaged with contact I38 because relay I34 is. not energized. The burner will operate only at the low firing rate as is desired through the. following oircuit-from terminal 65, wire 12,. closed switch 63, wire I31, switch I36, contact. I38, wire I39, terminal I45, wire I46, solenoid 48, wires I41 and I48 to wire H and up wire. H to terminal 66. The circuit to solenoid 55' by way of wire I51, terminal I 52, mercury I55,. terminal I 5I-, wire. I56, and terminal I13, is broken. by the gap. between the terminals I13 and I12. In the event that switch I68 is in the "hot. position so that terminals I12 and I13 are connected by the mercury I63, the circuit will extend by wire I14, terminal I15, wire I16,

to contact I49, where there is a break because the switch I36 is disengaged. If the selector switch should be in the high firing rate position, the circuit to solenoid 55 would be broken by the gap between the terminals I52 and I5I.

Assuming now that the room thermostat I20 calls for heat and that switch I68 is in the position shown, then the relay I34 will be energized to move switch I36 into engagement with contact I49 and the initial operation of the burner will always occur at the high firing rate regardless of the rate for which the selector switch I50 is set. The circuit is as followsfrom terminal 65 by wire 12, closed switch 63, wire I31, switch I36, contact I49, wire I16, terminal I15, wire I14, terminal I1I, mercury I69, terminal I10, wire I11, terminal I66, wire I61,

solenoid 55, wire I48 to wire H, and up wire H to terminal 66. When the thermostat switch I68 moves to its other position, the described circuit will be broken by the gap between the terminals I10 and HI but the terminals I12 and I13 will be connected by the mercury I69 and the circuit now extends by wire I56, terminal I5I, mercury I55, terminal I52, wire I51, terminal I45, wire I46, solenoid 48, wires I41 and I48 to wire H, and up wire H to terminal 66.. Thus, the low firing rate solenoid 48 will 'be energized. However, if the selector switch I50 were set for the high firing rate, the solenoid 55 would be energized to continue the high firing rate operation through a circuit which is the sameas last described, through wire I56 and then extends through terminal I54, mercury I55, terminal I53. wire I66, terminal I66, wire I61. solenoid 55, wire I48 to wire 1!, and up wire 1! to terminal 66.

When the control is used for a burner having the high and. low firing rate nozzles firing into separate combustion chambers, the surface. thermostat switch I68 and the selector switch I5Ilmay be omitted. together with the wires I61, I60, I14 and I11. The arrangement can be that of Fig. 6 with the described switches and wires omitted and the terminal I15 connected to the terminal I66 by a wire 28I, as indicated in Fig. 8. With this modified arrangement, whenever the hot water thermostat switch I23 calls for heat the solenoid 48, controlling low rate nozzle 1', will be energized by way of switch I36, contact I38, wire I39, terminal I45, and wire 546.. and whenever the room thermostat switch I29 calls for heat the solenoid 55, controlling the high rate nozzle 8, will be energized by way of switch I36, contact I49, wire I16, terminal I15, wire 20I, terminal I66 and wire I61.

Whenever the hot water thermostat control.

is not desired, the switch m and the wires I20,

I21 and I28 may be omitted.

switch, which may be set manually or automatically for the firing rate best suited for prevailing weather conditions. Regardless of the firing rate for which the selector switch is set, the burner, when controlled by the room thermostat, will always start up at the high rate and a the control by the selector switch will be postponed until the mains have been filled with steam or hot water, as the case may be. When the boiler is also used for heating the domestic hot water supply, as by circulating the boiler water through an indirect heater, the control system enables the burner to always operate at the low rate, when controlled by the hot water thermostat. If a call for room heating occurs, before the hot water thermostat is satisfied, the room thermostat will dominate the hot water thermostat and control the burner until the need for room heating is satisfied. The control can also be used for a dual firing rate burner, which fires a warm air furnace, by eliminating the surface thermostat used with steam and hot water boilers to secure initial fast firing, and the hot water thermostat used for control of the burner when heating a domestic supply of hot water. The control can also be used for a burner, having two nozzles located in difierent combustion chambers which have outlets into a common stack in which the stack thermostat 81 is located. In this case, the surface thermostat switch I68 and selector switch I50 can be dispensed with. The low rate nozzle can fire into the combustion chamber of a hot water heater and the high rate nozzle can fire into the combustion chamber of a warm air furnace. The invention also provides, as a desirable adjunct,

an automatic means for purging the unselected nozzle of a dual firing rate burner, where both nozzles are used to fire into the same combustion chamber. If the two nozzles fire into different combustion chambers, obviously the purging feature will not be needed.

The invention thus provides a control system for an electrically operated burner used for house heating service, which provides for room thermostat or hot water thermostat control, with preference to the room thermostat; low rate operation for hot water heating; initial high rate firing for the burner, when used with steam or hot water boilers; high or low rate burner operation for space heating to meet the prevailing weather conditions; and automatic purging of the unselected nozzle when required.

What I claim is:

1. An electrical control system for a dual-firing-rate boiler-firing oil burner of the type wherein a fan and pump, driven by an electric motor under the control of a room thermostat switch, respectively supply air and oil for combustion and electromagnetically-operated valve means are provided to vary the rates of air and Cir oil supply from those adapted for the relatively low firing rate to those adapted for the relatively high firing rate and vice versa; a control circuit for said means, a selector switch in said circuit movable from one position to another to control said means to effect low or high firing rate operation, a second switch in series with said selector switch in said control circuit and operable to open and close said circuit thereby respectively rendering said selector switch operable and inoperable to control said means and operable when opening said circuit to control said means to effect high firing rate operation, and a thermostat for actuating the second switch and maintaining it open until the temperature at the last mentioned thermostat exceeds a predetermined value. 1

2. An electrical control system for a dual-firing-rate boiler-firing oil burner of the type wherein a fan and pump, driven by an electric motor under the control of a room thermostat switch, respectively supply air and oil for combustion and electromagnetically-operated valve means are provided to vary the rates of air and oil supply from those adapted for the relatively low firing rate to those adapted for the relatively high firing rate and vice versa; a control circuit for said means, a selector switch in said circuit movable from one position to another to control said means to efiect low or high firing rate operation, a second switch in series with said selector switch in said control circuit and operable to open and close said circuit thereby respectively rendering said selector switch operable and inoperable to control said means, a second circuit for controlling said means and operable when closed to actuate said means for high firing rate operation, a third switch connected to move with the second switch and operable to close and open the second circuit when the second switch is moved to open and close the first circuit, and a thermostat for actuating said second and third switches to open the first circuit and close the second circuit until the temperature at the last mentioned thermostat exceeds a predetermined value, whereby operation of the burner at the high rate is had independently of the rate for which the selector switch is set until the temperature at the said last mentioned thermostat exceeds said value.

3. An electrical control system for a dual-firing-rate boiler-firing oil burner of the type wherein a fan and pump, driven by an electric motor under the control of a room thermostat switch, respectively supply air and oil for combustion and electromagnetically-operated valve means are provided to vary the rates of air and oil supply from those adapted for the relatively low firing rate to those adapted for the relatively high firing rate and vice versa; said means including a first electromagnet operable, when energized, to effect high rate firing, and a second electromagnet operable, when energized, to efiect low rate firing; a second switch, a thermostat for actuating the second switch, the latter having a supply terminal and two output terminals and movable from a "cold position, in which one output terminal is connected to the supply terminal and the other output terminal is disconnected from the supply terminal, to a "hot" position in which the supply terminal is disconnected from the first terminal and connected to the other terminal; a selector switch, having a supply terminal connected to the sec ond output terminal of the second thermostat switch and two output terminals connected one to the first elebtromagnet and the other to the fsf'e'con'd eiectromagnet and movable from one position, in which one output terminal is connected to its supply terminal and the other output terurinal "is disconnected therefrom, to a second position, in which the supply terminal is disconnected from the first-named output terminal and connjetzted to the other output terminal; and supply wires connected one to the supply terminal of the first thermostat switch and the other to "the other terminal of both electromagnets, whereby on a call for heat by the first thermostat switch the burner will operate at the high rate uirder the control of the second switch until the temperature at the second thermostat rises to a predetermined value.

RICHARD M. COCHRANE 20 REFERENCES CITED The following references are 'of record in the vfile of this patent:

UNITED STATES PATENTS Number Name Date 1,683,485 Res 6k Oct. 23, 1928 1,932,269 Harrington Oct. 24,1933 2,155,255 Cra'go Apr. 18, 1939 10 2,319,703 Smith May 18, 1943 2,451,964 Logan 'Oct. 19, I948

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