US2377356A - Combustion control - Google Patents

Description

June 5, 1945. w. R. MILLER 5 CQMBUSTION CONTROL Filed Ma 1, 1941' :s Sheets-Sheet 1 INVENTOR.

HagZandHHiZlar wwomwzx June 5,1945. w, R, M|| ER 2,377,356

COMBUSTION CONTROL Filed May 1, 1941 3 Sheets-Sheet 3 5 BA/POMHP/C DA MPLV? INVENTOR.

MqyZand HMiZZEP Patented June 5, 1945 UNITED STATES. PATENT OFFICEv 2,377,356 J l V COMBUSTION CONTROL I Wayland R. Miller, Whitefish Bay, Wis., assignor to Perfex Corporation, Milwaukee, Wis., .a cor-.

porationof Wisconsin Application May 1,1941, Serial No. 391,280 30Clhims; (crass-s) This invention relates in general to automatic combustion control and ismore particularly con-' cerned with control of stoker fired'furnaces'.

In order to increase the efficiency of a furnace fired by fuel burners or stokers it has been usual" practice to utilize an automatic draft regulator which acts to maintain a predetermined draft in the furnace when the burner or stoker is in op eration. In large installations these draft regulators usually consist of a damper located in a'fiue and positioned by a reversible motor Whichis con'-' trolled by a draft responsive control. In smaller installations, the draft regulator consists ofa, sen: contained or "barometric damper.

the flue. In systems in which the burner or stoker is operated by on-off type'o'f controls,

these automatic draft'controls have sometimes been provided with supplemental control means for causing the draft control to assume a posi tion of minimum draft during' the off periods,

by air flow therethrough.

of the type described in which the draft control upon stopping of the burner or stoker is first moved to a position of maximum draft and maintained in this position for a period of time and This type of damper usually is formed of 'a'substantially balanced damper blade responsive to the'draftand controlling the admission of basement a'ir'into" then moved toward a position of minimum draft.

In stoker fired systems this novel control means and sequence of control s'ervesto minimize smoking and to prevent any discharge of smoke into the furnace room when the stoker is shut down.

In devices of this character, green 'coal is'con stantly fed to a retort in which it is burned under forced draft. While the stoker is in operation, the air being forced thereto causes good combustion of this green coal and thus only an insignificant amount of smoke is emitted from the fire.

However, when the stoker is shut down the forced draft is discontinued, With the result that incomplete combustion of the green coal occurs, thus causing considerable smoke to emit from the stack. By the arrangement of the present in- V vention, a maximum natural draftis provided for a-period of time after thestoker shuts down which causes a substantial flow of air through the coal bed, thus rendering better combustion of, the green coal in the retort andminimizing smoking. This positioning of the damper for obtaining maximum natural draft for a period of time also fire will pass through the stack, thus'avoiding' anyi discharge of smoke into the furnace-room when the stoker is shutdown. 'Infiuid fuel'bu'rningp. installations the-control sequence of the present invention has the advantage of providing a purg'v' ing period after each burner operation to insure removal of any unburned fuel before the burner is restarted. f x In stoker installations and also in some-types. of fluid fuel burning installations, air supply control'dampers are used which function to control the supply of air during the fon periods and to prevent the supply of air during the off periods. .1 It is a further object of this invention to provide a control system in which control means for the: draft control damper and the air supply control are interlocked or correlated in a manner (30'; maintain "the air damper open and the draft v damper in. a position of maximum draft for, a h period of .time' after the combustion means is shut down. This type of control of theair; damper and the draft damper insures a goodnat ural draft through the furnace for a period of time after the shutdown occurs, thereby reducing: smoking to a minimum or providing a'positive; purging operation. I '2 31-;

It is a further object of this invention to pro-. vide a control system for theair 'supplya'nd'fthe' draft damper of a, stoker fired systemwhichacts after starting of the stoker'tocausei relatively" quick movement of the damper'to aposition providing a substantial draft, .While delaying the initiation of a substantial air supply: This novel; sequence of control has the advantage of 'redu'c-iing fly ash toa minimum When the stoker firstl starts, and at the same time insu'ringthat all products of combustion are carried from thefur nace into the stack so as 'to avoid smoking up the furnace room. is? Another object of the invention is the provision of a draft damper control having a thermoT- static device responsive to thetemperature ofthe products of combustion and acting to" moviethe' damper froma, positi'on'of running or maximum draft toward a position'of minimum draft'upon a fall'in temperature A further object is the correlation ofa draft damper control syste'mi of this type with an air control damper also con-i trolled in accordance with the'te'mperature'of the productsof' combustion. 7 w i Another object of theinventid'n is the'provision of a draft dampercontrol system embodyinga relatively quick acting controldevice and a 'rfela tively slow acting device, which devices cooperate insures that all of the smoke emitted from the to cause movment'of thedampei ina predeterfi' mined sequence relative to stopping and starting of the stoker or burner.

A further object of the invention is the provision of a control system for a burner and a draft control damper which acts after normal stopping of the burner to cause movement of the damper to a position of minimum draft, but which acts upon stopping of the burner due to an abnormal condition to maintain the draft control damper in a position of substantial draft.

Other objects of the invention consist in the provision of various novel combinations and subcombinations of control apparatus and .will become apparent from the following description and the appended claims. v

For full disclosure of this invention reference is made to the following detailed description and to the accompanying drawings in which:

Fig. 1 illustrates diagrammatically an application of the invention to a control system for a large boiler installation;

Fig. 2 is a fragmentary view showing the air control damper of Fig. 1 in detail;

Fig. 3 shows diagrammatically an application of the invention to a boiler or furnace of relatively small size;

Fig. 4 is a section taken on line 4--4 of Fig. 3;

Fig. 5 is an elevational view partly in section of the stoker air control of Fig. 3;

Fig. 6 shows a modified form of stoker air control;

Fig. 7 shows diagrammatically another form ofthe invention; and

Fig. 8 is an elevational view partly in section of the stoker air control of Fig. '7.

Referring to Fig. 1, reference character I indicates a boiler or furnace which may be used in industrial or semi-industrial applications such as for supplying steam or heating buildings or for processing. Thi boiler is fired by a combustion producing means such as a stoker having a retort 2, a hopper 3, a fuel feed screw 4 and an air supply duct 5. This stoker may be driven by a motor 6 which serves to operate the feed screw and a blower I which forces air through the air duct 5. The stoker is also provided with a flow control device for controlling the flow of air to the fuel bed, this device being indicated at 8. v

This air control device is shown in Fig. 2 and may consist of a damper blade 9 which is pivoted at "I to the air duct, the damper blade 9 thus being adapted to open under the influence of air pressure from the stoker blower. When the stoker is out of operation this damper assumes the position shown for preventin the flow of air to the stoker by natural draft. This damper is provided with an arrangement for maintaining it in the open position when it is forced to this position by the air delivered from the blower. This holding means may consist of a lever H which is attached to the damper 9, this lever ll being adapted to engage a flexible latch member 12. The latch member i2 may be carried by the armature 13 of a relay having a coil or electromagnet l4. When the relay coil I4 is energized the armature I 3 is attracted to it thus causing the latch member l2 to assume the position shown in dotted, lines. When the damper 9 is blown to the open position, shown in dotted lines, the lever II also assumes the position shown in dotted lines and is latched in this position by the latch member l2. Thus when the stoker is placed out of operation the damper 9 will be held in open position until the relay coil I4 is deenergized. At this time the armature I 3' will rotate clockwise under the action of a suitable spring such as I5, this causing the latch member l2 to release the lever I I and permit the damper to close.

The furnace I is also provided with the usual flue or breaching for conveying the products of combustion to a stack I'I. Located in this flue is a draft control device or breaching damper II, this damper being positioned by a reversible electric motor I5. This motor 18 is controlled by a draft controller generally indicated as 20 and also by relays generally indicated as 2| and 22.

Referring to the draft controller 20, this device may be of any suitable construction and is illustrated a comprising a diaphragm 23 closing one side of housing 24, the interior of which com- Inunicates through a draft tube 25 with the flue l6 ahead of damper I8. The diaphragm 23 is thus subjected to the sub-atmospheric pressure or draft within the flue l6 and hence within the combustion chamber of the furnace I. The tube 25 may obviously be connected at other points than the flue l6, such, for example, as directly with the interior of the combustion chamber. The diaphragm 23 may actuate a suitable operating member 21 which actuates switch arm 2| and 29. A biasing spring 30 may bias the diaphragm 23 against atmospheric pressure, this spring having an adjusting screw 8|. The switch arm 28 may cooperate with a pair of opposed " contacts 32 and 33 which are resiliently supported on contact blades as shown. This switch arm 28 and contact blades 32 and form a min mum draft control switch. The switch arm 29 cooperates with opposed contacts carried by flexible contact blades 35 and 36 to form a second draft control device which is adapted. to maintain a higher draft (lower pressure) than the first mentioned draft control device. The switch arm 28 and its associated contacts are placed in control of the damper motor I9 when the stoker is out of operation for mainta ning a minimum draft at this time. The switch arm 2! and its associated contacts are placed in control of the damper motor when the stoker is in normal operation and. serve to control motor I 9 for maintaining a predetermined draft which provides maximum combustion efllciency.

Referring to the relay 2!, this relay includes an clectromagnet including a coil 40 which operates a suitable armature 4i actuat ng the switch arm 42. The switch arm 42 is adapted to engage an overlapping type of contact mechanism which is shown as comprising a movable contact 43 carried by a contact blade 44 which in turn is biased against a fixed contact 45. When the relay coil is deenergized the switch arm assumes the position shown wherein it is disengaged from contact 43. At this time the contact blade 44 enages the fixed contact 45. When the relay coil 40 is energized the switch arm 42 first engages the contact 43 and then causes movement of the contact blade 44 in a clockwise direction thereby disengaging this contact blade from the fixed contact 45. By this arrangement the switch arm 42 always engages the contact 43 before the contact blade 44 disengages stationary contact 45. The relay 2| also includes a second switch arm 41 which is adapted to selectively engage an out contact 48 and an in" contact 49. The relay 22 includes a coil 50 which operates through a suit- I able armature a pair of switch arms 5| and 52,

the switch arm 5| cooperating with an "in" contact 539 and the switch arm 52 cooperating with engaged from contact. arms 32 and 33.

asvzsse:

control system also includes aimotor relay generally indicated as 51, this relay including a coil 63 which operates through a suitablearmature a pair of switch arms 58 and 59. The'switch arm 59 controls the stoker motor 6, this switch arm engaging a fixed contact 60 when the relay coil 50 is energized and being disengaged'from this fixed contact when the coil 50 is deenergized.

The switch arm 59 cooperates with an out contact 6| and an in contact 62.

Reference character 65 generally indicates a timing device which preferably is of the thermal type having a bimetallic element 66 secured to a fixed support 61 and having its fre end cooperating with a fixed contact 68. The bimetallic element 69 is arranged so that it engages the fixed contact 68 as shown when the element is relatively cold. This bimetallic element 66 is heated by means of a heater 69 and under the influence'of this heater moves downwardly so as to disengage the fixed contact 68.

Referring again to the damper motor I9, this motor may be of the type shown in the Cummings patent, No. 1,895,880. This is a motor of the shaded pole type having power supply wires 10 and a 3-wire control circuit comprising wires II.

' T2 and 73. When an electric circuit is completed from wire II to wire 12 the motor operates in a direction for opening the damper I8. When an electric circuit is completed from wire I2 to wire 13 the motor I9 operates in a direction for closing damper I8. When wire I2 is disconnected from both wires II and 13, the motor remains at rest in whatever position it happens to be. Th s motor is preferable provided with built-in limit switches which stop the motor when thedamper reaches either wide open position or closed position. .The damper motor I 9 is also provided withan auxiliary switch indicated generally at I5. This auxiliary 0r damper switch is shown diagrammatically as comprising a movable contact blade I6 which is adapted to be forced into engagement with a fixed contact IT by an extension IE on th lever arm of the damper motor. When the damper I8 is in wide open position the switch arm 16 engages contact TI. However for all other positions of the damper the switch arm 16 is disengaged from contact 11. The stoker and the draft damper are controlled by a heat demand responsive device 89. This device may be a thermostat if the boiler is supplying steam for heating purposes, or maybe a pressure responsive device or any other type of control device which closes a circuit when heat is required from the boiler or furnace I. The stoker is additonally controlled by a high limit control 8| which is shown mounted upon furnace I. This device may be a thermostat or pressure control which includes a switch which is opened whenever the pressure or temperature of heaterv I rises beyond a predetermined value.

Operation of Figure 1 switch contact 84, wire 85, switch arm 52, contact 55, wire 66, switch arm 41,-contact 48 and wire 87 to switch arm 28. .The draft (suction) within the furnace is at the proper stand-by value as indicated by the switch arm 28 being dis- If the draft should fall'zbelow ,t'h'ezdesired 3 811118312118. diaphragm '23 1 will move outwardly bringing switch arm 129' into engagement with 'the"contact"33. This contact, it will be noted, I'is connected by wires 88and 89 to the wire 1 I. Thusengagement of switch arm 28'with contact 33-will connect the motor control wires/II and I2 together which causes operation of the motor I9'in a direction for opening damper- I8.J..:This opening of damper I8 will permit a greater flow ofxair from the flue intothe stack thus increasing the draft (decreasing the pressure) within the'f-urnace combustion chamber; 1 When the draft is increased to the proper value the switch arm 28 disengages contact 33 and the damper motor I9 stops with the damper in'the new position- If the furnace draft becomes too high the'switchi arm 28 will engage contact 32 which contact is connected to. the

motor control wire I3 byuwires 90 and 9|; Thus at this time the motor control wires I2 and 73 are connected together which causes operation of the motor IS in a dir'ectipn fOrCIOSing thedamp inJa new position. From the foregoing it will beseen that when the device 80 is satisfied and the stoker is out of operation the draft controller20 serves to control the damper motor I9 in a manner .to' maintain aijpre'determined low draft When the device 80 calls-for heat a circuit will becompleted for. energizing coil-40 of relay 2I as followsr From secondary 93 of transformer; wire 95, control device 80, wire 96, wire 91, contact 45, switch blade 44, wire 98, wire 99, relay coil40,-wire I00, bimetal element 66 and wires IN and I02 to secondary 93." When the switch arm. 42 of relay 2I engages contact 43'it completes a holding circuit for coil 40 as follows; From secondary 93, wire 95,3wire. I03, switch arm 42,

' switch blade 44 and wires 98 and 99 to relay coil 40. 1 After the switcharm 42 engages contact 43 the switch blade 44 disengages contact 45. Thus when the relay 2 I' islpulled in thestarting circuit forthe relay coilis broken and the coil-is maintained energized by anindependent holding, circuit, this holding circuit serving to connect the wire 98 directly to the transformer secondary 93. At this time the coil 5001? relay 22- is also energized by a circuit extending from the wire 98 through coil 50, wire I05, contact 6l, switch arm 59 and wires I06 and I02 to secondary 93. The coil 63 of relay 51' at'thistime remains deenergized so that the stoker remains at rest. Due to the switch arm 52 of relay 22 now engaging its in contact 54 a circuit iscompleted-from control'wire 12 of dampermotor I9 to control Wire-II as follows: =Wire .12, selector switch arm 83, selector switch cont'act84; wire 85, switch arm 52,.contact'54and wire I0I-to'wire II. This causes the damper'motor I9 to run in damper opening direction'irrespective of the draft con troller 20. The damper motor now runsto move the damper to wide openposition at whichitime it is stopped by a built-in limitswitchmot shown. When the damper reaches this wide open position the auxiliary or draft switch I5 is closed which completes a starting circuit for rela coil 63 as follows: From secondary 93, wire 95, control device 80, wire 96, wire I08, coil 63, wire I09, contact I1, switch 'arm I6 and wires H0 and I02 to secondary 93. When the relay 51 pulls in its switch arm 58 engages contact 60 which energizes the stoker motor 6 as follows: From line wire III,

contact .80, switch arm 155,, wire II -'l2,.limit control BI, wire H3, and motor .6 to line wire I. The stoker is thus placed 'into operation. Also when relay 5! is :energized its switch arm 59 disengages contact SI and engages contact 82. When switch arm 55 disengages contact 6| it breaks the energizing circuit for coil 50 of relay 22, thus causing this relay to drop out. When the switch arm 59 engages contact 62 it completes a holding circuit for relay 0011 263 whichds independent of the damper switch I5, this circuit extending from wire I08, through coil 53, contact 52, switch arm 59, and wires I06 and I02 tosecondary 93. The damper I8 may therefore now be moved away from wide open position without affecting relay 51. As mentioned above'when the relay .5! becomes energized it, in addition to establishing a holding circuit for itself, also deenergizes the coil 50 of relay 22. As 'a result the 'switch arm 52 of this relay engages its out contact 55. At this time it will be noted that relay 2| remains energized thus causing its switch arm 41 to engage contact 49. A circuit is thus completed from the control wire I2 of motor I9 to the switch arm 29 of the draft control 20 as follows: From wire I2, switch arm 83, contact 84, wire 85, switch arm 52, wire 85, switch arm 41, contact 49, and wire H5 to switch arm 29. It will be noted that the contact arms 35 and 35 cooperating with the switch arm 29 are connected to the motor control wires 13 and II respectively. The draft controller 20 therefore now controls the damper motor I9 in a manner tomaintain a predetermined draft for'providing maximum efliciency of combustion.

The solenoid II of the stoker air damper 8 is connected to Wires 95 and I02. Consequently as long as the relay 2I "is energized this solenoid is energized. When the stoker motor I5 is started the air from the fan 1 forces the air damper 9 to open position and due to the solenoid ldibeing energized at such time this damper is latched in open position as shown inthe dotted lines of Fig. 2.

From the-description thus far it will'be apparent that during the stand-'byperiods, that is when the control device 80 is satisfied, the draft controller 20 serves to control the damper motor in 'a mannerto maintain a'predeterm'ined minimum draft. However, when the control device 80 calls for heat the relays 2I and 22 are energized, the relay 22 taking control of the damper motor away from controller 20 and causing the damper to be operated to wide open position during which time the stoker remains at'rest. When the dampor motor reaches wide open position the closure of the damper 'switchli energizes the relay 5! which places the stokerinto operation and deenergizes the relay 22, this returning'the control of the damper motor I9 to the draft controller 20, the relay 2| causing the high draft control-switch of this draft controller to be effective so as to maintain a relatively high draft while the stoker is in operation. Also the stoker air damper 9 is blown upon by the air from the fan 1 and is latched in open position due to the solenoid I4 being energized.

When the control device 80 becomes satisfied it will openits switch which deenergizes the coil of relay 51. This relay thus drops out and stops the stoker. The switch arm 59 of this relay now relay "2| engaging contact 143 the .relay coils II) and 5B are connected to secondary 3 independently of the control device an. Thus when the control device 80 becomes satisfied and causes relay 51 to drop out, the relay coil remains energized and the relay coil '50 becomes energized due to the dropping out of'relay 51. When the coil '50 of relay 22 becomes energized the switch arm 52 thereof engages contact 54 which once more directly connects control wires 'II and I2 of the damper motor I9 which causes this motor to run the damper to wide open position irrespective of the draft controller 20. When the damper reaches 'wide open position the damper switch I5 is once more closed and due to the switch arm 5I of relay 22 :now engaging contact 53 the heater of timer 65 is energized as follows: From secondary, wire 95, wire I03, heater 69, contact '53, switch arm Si, wire I09, damper switch 15 and wires 1 I0 and III2 to secondary 93. From the description thus far it will be apparent that when the "control device 80 becomes satisfied the stoker is immediately stopped. However, the solenoid I4 of the stoker air damper 9 remains energized which causes the air damper to remain latched in open position. Also whenthe stoker is placed out of operation the flue damper I8 is operated'to its wide open position irrespective of the draft controller for maintaining a maximum draft. Also when the damper reaches its wide open position .the heater 69 of the thermal timer 65 .becomes energized. Due to the dampers 8 and I8 both being in open position a maximum natural draft is provided when the stoker is first placed out of operation. This natural draft serves to provide for good combustion of the green coal remaining in the stoker retort and consequently reduces smoking of the fire to a minimum. In addition the opening of damper :I'8 insures that whatever smoke is emitted from the fire due to improper combustion of the green coal is drawn into the stack and thus prevented from escaping .into the boiler or furnace room.

After a period of time the volatile matter in the green coal is burned off and thus the tendency to smoke disappears. The thermal timer 65 is adjusted so as to open its contacts upon the expiration of the period of time required for burning off this volatile matter. At this time the bimetallic element 66 due to the influence of heat from the heater 89 disengages contact 68. This breaks the energizing circuit for coil 40 of relay 2I which causes the switch arm 42 to 'disengage contact 43 and causes switch arm 41 to engage contact 48 as shown. Due to the switch arm 42 disengaging contact 43 the energizing circuits for relay coil 50 and solenoid I4 are broken. Deenergization of solenoid I4 causes the latch member I2 to disengage lever II thus permitting damper 9 to close and stop or reduce to a minimum thenatural draft to the fuel bed. This reduces the rate of burning of the fuel to a minimum. Deenergization of coil 50 of relay 22 causes the switch arm 5| to disengage contact 53 which breaks the energizing circuit for heater 69. The switch arm 52 of relay 22 in disengaging contact 54 and engaging contact 55 places the switch arm 28 of draft controller 20 in control of the damper motor and thus causes the damper I8 to be returned from the wide open position to whatever position is necessary for maintaining the minimum predetermined draft. The draft controller 20 now maintains the furnace draft atwa minimum until "the device an again calls for heat at which time the control cycle described above is repeated.

At some timesit is desirable to open the damper I8 wide irrespective of the automatic control system. In such event the manual switch arm 83 is moved from the contact 84 into engagement with contact I I6 which directly connects control -to closed position.

From the foregoing description it willbe apparent that during the stand-by periods when the control device 80 is satisfied the stoker is out of operation, the air damper 9 is closed for reducing the rate of combustion to a minimum and the flue damper I8 is under automatic control for maintaining a minimum draft. When the device 80 calls for heat, the first result is the opening of the flue damper I8 to wide open position. When the damper actually reaches wide open position, and not until then, the stoker is placed into operation and the damper motor is again placed under the control of the draft regulator which now serves to maintain a predetermined relatively high furnace draft which provides for proper combustion. When the device 80 ;becomes satisfied it stops the stoker. However the air damper 9 remains in open position and the flue damper I8-is operated to its wide open position. These two dampers escape into the furnace room. When the volatile matter of the green coal is burned off the air damper 9 is closed and the flue damper I8 is returned to control by the draft controller which once more serves to maintain a minimum or stand-by draft.

In some installations it may be desired to operate the flue damper I8 to a fixed closed or minimum position during the stand-by periodinstead of a variable position. In such event the switch 28-32-33 of the draft controller 20 may be omitted, the wire 81 being directly connected to the control wire I3 of the damper motor. In other installations it may be desirable to maintain the same draft during the stand-by periods as during the running periods of the stoker. In such. case the low draft control switch of the draft controller may be omitted and also the relay switch arm 47 and contacts 48 and 49 may be omitted. In this case the contact 55 of relay 22 would be directly connected to the draft control switch arm 29.

Figures 3, 4 and 5 and operating mechanism, such as motor I25 and fan I26. The stoker is also provided with an air control generally indicated as I21 and which is diagrammatically shown in Fig. 5. Referring to this figure, the air control device I21 may include a butterfly type damper blade I28 which is pivoted to the sides of the air duct at I29. This damper blade is attached by a link I30 to a vane '.I3I, the link I30 passing through an opening I32 into the interior of a control housing I33 which is secured to the air duct I23 and which contains thevane I3I. The vane I3I fits closely to the sides of the housing I33 and ispivoted to the housing at I34. The freeend of this vane lies closely adjacent an arcuate member I35 which is fixed to the side walls of housing I33, this member. I35 having a curvature concentric .withthe path of movement of thefree end of vane I3I. This arcuate member I35 may carry a stop I36 at its upper end for preventing overtravel of vane I3:I. The vane I3I is attached by a spring, I31 to the free end of a bimetal element I38 by means of an adjusting screw I39. The bimetal element I38 may be supported by a U-shaped bracket I4n'which is secured to the side of housing I33, this bracket being provided withian' adjusting screw I4I for'adjustingthe position of bimetal element I38 with respect'to the housing I33. This bimetal element I38-is provided with a heater I 42, which heater is energized when the stoker is placed into operation.

When the heater 2 is cold, asyduring a stand-by period, the bimetal element I38 assumes the position shown in which it applies-a slight compressive force to the spring I31, this forcing the vane I3I downwardly and forcing the damper blade I28 to closed position.- When the stokerf'is startedthe heater I42 isenergized, but the bimetal element I38 -requires an appreciable time to'heat. Thus when the stoker first starts,.t'ne damper I28 is held in closed position so as .to restrict the flow of air to the retort. As the bimetal element I38 becomesheatedit warps upwardly, this removing the compressive force from spring I31 and now applying, tension to this spring for pulling vane, I3I upwardly thus opening the damper I28. As damper I28 opens the pressure on the down-stream side rises, this pressure building up under vane I3I, thus forcing the: vane I3I upwardly against spring I3]. The air leaking around the'edgesv of the vane I3I passes from the housing I33 through an adjustable opening I44 in the cover for this housing and thus the pressure at the top of vane I3I re mains substantially atmospheric. The bimetal element I38. when'fully heated engages a stop- I43. At thistime the air control device I21 functions tomaintain the proper supply of air to the retortas to maintain the fuel bed at the desired thickness and thus proportions the air flow with the fuel feed. Thus if the air flow is more than necessary'to burn the coal in the retort, the thickness of the fuel bed will decrease which decreases the resistance to flow of air therethrough. This would normally result instill further increasing the flow of air to the retort. However, as the resistance to air fiowthrough the fuel bed decreases; the pressure 'on the down-stream si'de of the damperl28 decreases correspondingly which causesithe' vane I3I to, lower under the action of gravity and/or spring I3] therebyreducing the flow of air to the re-, I

sure urges vane I3I upwardly until the spring I31 is compressed sufilciently to resist further movement, this motion of the vane I3I causing opening movement of the damper I28 for increasing the supply of air to the retort. It should now be apparent that the function of the air control device I21 is to delay the supply of air to the stoker when the stokeris first started, this having the effect of preventing or substantially reducing fly ash. When the stoker hasoperated a short time so that new fuel is delivered to the retort and the danger of. fly ash eliminated, the air damper I28 is gradually opened and during normal operating of the stoker is variably positioned so as to proportion the air supply to the fuel feed. When the stoker is placed out of operation the heater 142 is deenergized. However due to the residual heatof the bimetal element I38, this element stays in its hot position for a substantial period of time which maintains the damper I28 in at least partially open position. For a more complete description of the stoker air damper of Fig. 5, reference is made to the application of Clifford Hotchkiss, Serial No. 350,715, filed August 3,

In Fig. 3 the flue dampermay be of the socalled barometric type, this damper being located in an air inlet to the fine and serving to regulate the pressure in the flue by varying the amount of air admitted. This damper may be of any suitable type and is shown diagramatically as comprising a damper blade I45 which is pivoted offcenter in an air passage I46 of a damper housing I41 in flue I48. In Fig. 3 the damper mechanism is shown for convenience as having the air inlet passage I46 extending from the bottom of the flue. In actual practice, however, the damper I45 and its passage should be located at one side of the flue so that the axis of rotation of the damper I45 is substantially vertical. The damper I45 is positioned by the conjoint action of a solenoid I50 which may be mounted on the damper housing, this solenoid cooperating with an armature II which is pivoted at I52, this armature operating an abutment lever I53 which is arranged to abut a lever I54 attached to the shaft of the barometric damper I45. .The lever I53 is biased in a clockwise direction by means of a spring I56. When the solenoid I 50 is energized it attracts the armature I5I, causing counterclockwise rotation .of lever I53 against the tension of spring I56, the

lever I53 in turn causing clockwise rotation of the lever I54 and movement of the damper I45 to its completely closed position. When the solenoid I50 is deenergized the parts assume the position shown in which the damper I45 may open completely. The damper operating lever I54 also may be actuated by a resilient or yieldable abutment lever arm I58 which is attached to the shaft I59 (Fig. 4) of a stack temperature responsive device which may include a spiral bimetallic element I60. When the temperature at thermostat I60 is at a value such as 125 F. indicating that the stoker is out of operation, and when the solenoid I50 is deenergized, the yieldable lever arm I58 assumes the position shown in which it forces the barometric damper I45 to its wide open position. However, when the temperature at thermostat I60 rises to a higher value indicating operation of the stoker, the lever arm I58 rotates counterclockwise thereby leaving the damper I45 free to adjust itself for maintaining the predetermined draft. The shaft I59 also operates a suitable form of switching mechanism in accordance with the temperature of the products of combustion. This switching mechanism is illustrated diagrammatically as comprising an arm I62 attached to shaft I59 and to an insulating member I63 which operates switch arms I64 and I65, these switch arms engaging contacts I66 and I61 respectively when the stack temperature is low and engaging contacts I68 and I69 respectively when the stack temperature is high. Preferably the actuation of switch arms I64 and I65 is effected with snap action by suitable means diagrammatically illustrated as a permanent magnet I10.

The control system of Fig. 3 additionally includes a heat demand responsive device such as I12 which in this case might be a thermostat responsive to the temperature of a space heated by the furnace I20. This thermostat may be of a. type well known in the art which closes its contacts upon fall in temperature to a predetermined value and which opens its contacts upon rise in temperature above such value. This thermostat may also include an anticipating heater I18 which functions to add false heat to the thermostat during a call for heat thereby shortening the length of the on periods of the stoker. This thermostat controls a relay generally indicated as I14 which includes a coil I15 which operates through a suitable armature a pair of switch arms I16 and I11. When the coil I15 is energized the switch arm I16 engages a contact I18 and the switch arm I11 engages a contact I19. When the relay coil is deenergized the switch arm I11 engages a contact I and the switch arm I16 is disengaged from contact I18,

Operation of Figures 3, 4 and 5 With the parts in the positions shown the thermostat I12 is satisfied as indicated by its contacts being open. The relay I14 is also deenergized which causes the stoker to be out of operation and which also causes the solenoid I50 of the stack damper control to be deenergized. The temperature of the stack gases is also relatively low as indicated by the stack thermostat assuming a position in which it forces the barometric damper I45 to wide open position and causes the switch arms I64 and I65 to engage contacts I88 and I61 respectively. The bimetallic element I36 of the air damper control I21 is also cold which causes the air damper I28 to be closed.

If the thermostat I12 now calls for heat it will close its contacts and energize the relay coil I15 as follows: From secondary I8I of transformer I82, wire I83, thermostat I12, wire I84, coil I15 and wire I to secondary I8I. The energizing current for the relay also passes through the anticipating heater I13 for causing false heat to be applied to the room thermostatic element. Energization of coil I15 causes switch arm I16 of relay I14 to engage contact I18 which energizes the stoker motor I25 as follows: From line wire I86, contact I18, switch arm I16, wire I81, high limit control I88, wire I89 and motor I25 to line wire I90. Energization of coil I15 also causes the switch arm I11 to engage contact I19 which immediately energizes the heater I 42 of air damper control I21 as follows: Secondary III, wire I9I, wire I92, switch arm I11, wire I93, wire I94, contact I66, switch arm I64, wire I95, heater I42 and wire I96 to secondary I8I. Thus the heater I42 is energized simultaneously with the stoker motor. At the same time the solenoid I50 of the flue damper control is energized as follows: Secondary I8I, wire I9I, wire I92, switch arm I11,

'withicontacts. I68 and: I69 respectively. Disencontact I19, wire I93, contact I61, switch arm I65, wire I98, solenoid I50, wire I99 and wire I96 to secondary I8I. Energization of solenoid I50 causes the armature II to be attracted, thereby rotating lever I53 counterclockwise against the action of spring I56, 'this in turn rotating the damper lever I54 so as to substantially or completely close the barometric damper I45. At this time the lever I58 yields and thus permits the damper to close even though the stack temperature is low.

From the description thus far it will be apparent that when the thermostat I12 calls for heat it starts the stoker, energizes heater I42 of the air damper control and energizes the-solenoid I50 of the flue damper control which causes the barometric damper to be moved from wide open position to completely closed position. The bimetal element I38 of the air damper control I21 requires an appreciable time to heat, for example, a minute or two. Thus when the stoker is first started the air delivery to the stoker retort is prevented or maintained at a minimum while the barometric damper is heldclosed. This delay in supplyin air to the stoker permits a certain amount of coal to be fed to the stoker retort thus building up an appreciable fuel bed before air is supplied. The purpose of this delay in air supply is to avoid fly ash. If the fire has burned down during a stand-by period to a considerable extent the resistance of the fuel bed would be quite low and ash would be blown from the retort if the air were delivered thereto immediately upon starting of the stoker. By delaying the supply of air the stoker is given an opportunity to feed some coal into its retort before air is delivered thereto, this increasing the resistance of the fuel bed and preventing or substantially reducing fly ash when the air supply is commenced. At the same time the barometric damper being completely closed provides maximum draft and also closes communication between the furnace room and the flue during this starting period. This provision of maximum draft insures that no products of combustion will enter the furnace room if for some reason the stack draft is very low due, for example, to the stack being cold. This arrangement also permits the barometric damper to be adjusted to maintain a lower draft than would otherwise be possble. In other words, in prior barometric damper installations the damper cannot be adjusted to maintain the ideal draft as such a setting would result in the damper opening too easily, permitting products of combination to be discharged into the furnace room if the stack is cold. The present arrangement, however, permits the damper to be adjusted for maintaining the ideal draft and at the same time prevent discharge of products of combustion into the furnace room.

After the stoker has operated a short time the bimetal element I38 of the air control I21 will become heated which causes opening of the air damper I28 and the automatic positioning of this damper for proportioning the air supply to the fuel feedin the manner previously described; This operation of the stoker will result in the temperature of the products of combustion rising which will cause the stack thermal element I60 to rotate the arms I58 and I62 in a counter-clockwise direction. This rotation of lever I58 causes it to swing clear of the damper lever I54. Corresponding rotation of lever I62 causes the switch arms I64 and I65 to be disengaged from contacts I66 and I61 andtobe brought-intoen'gagement gagement of the switch arm I65 fromcontact I61 deenergizes the solenoid I50 which causes the lever I53. to be swung clear of the damper lever I54. I The barometric damper I55 is now free to float and thus position. itself for maintaining the draft for which it is adjusted. Disengagement of the switch arm I64 from contact I 66 and engagement thereof with contact I68 establishes a new energizing. circuit-for the heater I42 of the air damper control, this new circuit being independent of. the relay I14 and as follows: Secondary I8I. wire 200, contact I68, switch arm I64, wire i95,heater I42 and wire I96 to secondary I8I. The stoker will now operate with the air damper control I21 automatically proportioning the supply of air and the barometric damper I45 automatically maintaining a constant draft. As a result the stoker will operate at maximum efii- .ciency. When the thermostat I12 opens its contacts the relay I14 will be deenergized, the switch arm I16 bec'omingdisengaged from contact I16 for stopping the stoker. The switch arm I11 will also engage contact I80 which will establisha new energizing circuit for solenoid I as follows: From secondary I8I, wire 'I9'I, wire I 92; switch arm I11, contact I80, wire'20I, contact I69,

. switch arm I65, wire I98, solenoid I50, wire I99 v and wire I96 to secondary I8I.' Thus when the stoker is .flrst'placed out ofoperation thebarometric damper" I45 is moved to closed. position by energization of .relay. I50, this relay now being energized due to thestack thermostat being in its hot, position. Also the heater I42 of the air control I21 remains energized due to the stack thermostat being inits hot position. Consequently upon stopping of the stoker the draft is increased to a: maximum and the air damper is maintained open which permits a supply of air to the stoker by natural draft. This rovides for burning off the volatile matter of the green coal in the stoker retort without substantial smoking and also insures that any smoke emitted is prevented from passing into the furnace room through the check damper passage. I

Due to the' stoker being out of'operation the stack temperature will 'fall after a period of time, thus causing the stack arms I58 and I62 to return to positions shown in Fig. 3, the switch arms I64 and I65 being disengaged from contacts I68 and I69 and being reengage'd with contacts I 66 and I61. 'Disengagement of the switch arms I64 and I65 from contactsll68 and I69 will deenergize the solenoid I50 and also the heater I42 of the air damper control. The. reengagement of these switch arms with contacts I66 and I11 will have no effect due to switch arm I11 of relay I 14 being now disengaged from contact I 19. Deenergization of solenoid I50 will permit the re silient stack arm I58 to move the check damper from completely closed position to open position. Deenergization of the heater I42 will permit the bimetal element I38 to cool for closing the air damper-I28. Thus the draft during the standby period will be reduced to a minimum and also the air damper will be closed which reduces burning of the fire by natural draft to a minimum. This substantially reduces the heat delivered by the stoker during the ofif or stand-by periods and also retards the fire from burning out at this time.

From the foregoing description it will be ap-- damper is closed.- andthe barometric or-flue-damp be consumed.

er is wide open. When the thermostat calls for heat the barometric damper is immediately moved from wide open position to completely closed position, and while the heater I42 is immediately energized a substantial period of time is required before the air supply damper begins to open. Thus the stoker is operated for a short period of time with a reduced air supply and with the barometric damper completely closed for providing maximum draft. After a short period the air control damper opens and assumes automatic operation in which it proportions the flow of air to the fuel feed. Also the stack temperature rises which causes the barometric damper to be placed under automatic control for maintaining a constant draft. When the stoker is placed out of operation the barometric damper is immediately closed and the air damper is maintained in open position, the dampers being held inthese positions until the stack temperature falls, at which time the air damper is permitted to close and the barometric damper is moved from closed position to wide open position It will be noted that the heater I42 of the air damper control is' energized immediately upon energization of relay I14, this result being provided by the switch arm I64 and contact I66 of the flue damper control. This arrangement is desirable in installations where the air damperpermits sufllcient flow of air to cause the fire to pick up and in installations where an anticipated type of thermostat is used or when some other form or heat demand responsive control is employed which provides fairly short on" periods. It will be apparent that if the air control is designed to prevent any material flow of air until the heater I42 is energized, the stack temperature might not rise suihciently to cause energization of this heater. It will also be apparent that the on period and thus the stoker air damper would never open. By the arrangement described, however, the heater I 42 is energized simultaneously with the stoker which insures that the air damper opens before the "on period of the thermostat ha expired. In installations in which the on" periods are sufilciently long and in which a substantial flow of air may occur when the air control damper is in its minimum position, the heater I42 may be controlled solely by the stack thermostat, being energized when the stack temperature rises and being deenergized when the stack temperature falls. In other words, the arrangement for energizin the heater I42 through the in contact I19 of relay I14 and cold contact I66 of the stack damper control may be omitted.

In some applications of the inventionit may be desirable to design the bimetallic element I38 and heater I42 so that the element I33 both heats and cools very slowly. In this event the heater I42 could be controlled directly by the relay I'I4, the stack thermostat contacts thus being omitted. In other words, instead of positively holding the air damper open until a fall in stack temperature occurs, the'air damper control may be designed so as to require a substantial period of time in closing the damper such as will usually permit the volatile matter in the green coal to It will also be apparent that in low priced installations the solenoid I56 may be omitted. In this case the barometric damper would be controlled solely by the stack thermal element which also controls the air damper.

If desired a solenoid and armature may be substituted for the bimetal element I 38 and heater I42 of the stoker air damper. This modification is shown in Fig. 6. In this figure the construction of the air damper is substantially the same as in Fig. 5 except that a lever 2IIl is substituted for the bimetal element I38, this lever being pivoted at one end and carrying an armature cooperating with a solenoid 2I2 attached to the top of the housing. The solenoid 2I2 may be connected to the wires I and I96 of Fig. 3. This arrangement will operate in the same manner as the arrangement first described with the exception that no delay in air feed will be provided, which is satisfactory for certain types of installations. If a delay in air feed is desired while at the same time utilizing a solenoid type air control this result may be obtained by omitting the contact I66 of Fig. 3 so that a rise in stack temperature must occur before the air damper is moved from its minimum position.

Figures 7 and 8 Another form the invention may take is shown in Figs. 7 and 8. In Fig. 7 the furnace 2I6 is provided with a stoker as in the modifications previously described, this stoker having a motor 2 I 6 and an air damper control generally indicated as 2II. As shown in Fig, 8 the stoker air control 2II may be of generally the same construction as the air control I21. of Fig. 5. In this case, however, the bracket 2I8 which supports the bimetal element 2I9 is formed of insulating material and actuates a suitable switching mechanism. This switching mechanism may comprise a pair of stationary contacts 229 and 22I which cooperate with contact point secured to the end of element 2 I9. Preferably the bimetal element 2I9 operates at least the switching mechanism with snap action. This snap action may be provided by any suitable form of mechanism and is illustrated diagrammaticall as comprising a permanent magnet 222 which is adapted to cooperate with an armature carried by bimetal element 2 I9. The bimetal element 2I9 is heated by a heater 223 which is as shown in Fig. 7 connected directly across the terminals of motor 2I6 by wires 224 and 225. In this embodiment of the invention, therefore, the heater 223 is energized when the stoker is in operation and is deenergizedwhen the stoker is out of operation. The heater 223 and the bimetal element 2I9 are preferably designed so that the heater 223 must be energized an appreciable time before the bimetal element 2I9 moves from its cold position in which it engages contact 22I and closes the air damper, to its hot position in which it causes opening of the air damper and engages contact 220. Also the bimetal element 2I9 is designed so as to require an appreciable time to cool off after the heater is deenergized whereby the air damper 226 is maintained in open position and the contact engaged for a substantial period of time after stopping of the stoker.

The furnace 2I5 is also provided with a barometric damper control unit generally indicated as 228.. This unit includes a, barometric damper 229 which during normal operation of the stoker serves to maintain a constant draft in the furnace. This damper 229 is at certain times controlled by electro-magnets 230 and 23 I. The electro-magnet 230 cooperates with an armature 232 which actuates an abutment lever 233 which is arranged to abut a damper lever arm 234, the lever 233 being biased in a counter-clockwise direction by spring 235. The electro-mag'net 231 is arranged to operate an abutment lever.236 which is also arranged to abut the damper lever 234 and which is biased in a clockwise direction by a spring 231. It will be noted that when both solenoid 233 and 231 are deenergized the abutment levers 233 and 236 assume thepositions shown wherein the barometric damper 223 is held in substantially wide open position. When the solenoid 233 is deenergized and the solenoid 231 energized the levers 233 and 236 becomesubstantially spaced apart, this giving a substantial range of free movement for the damper lever 234 which permits the barometric damper 223 to adjust itself so as'to-maintainzthe predetermined draft in the furnace. When solenoids 233 and 231 are both energized the damper lever 234 is urged in a clockwise direction and held in a position in which the barometric damper 229' is substantially closed. The stoker and flue damper unit may be controlled by means of a thermostat :or pressure controller 243 which controls a relay generally indicated as 241,, this relay including. a coil 242 and switch arms 243, 244 and245. When the coil 241 is energized theswitch arms 2-43, 244

and 245 engage contacts 246, 241 and 248 respectively. Whencoil 242 is, deenergized the switch arms 244 and 245. engage contacts. 243. and 253 respectively. i

Operation of Figures 7 and 8 With the partsin the positions shown, the com trol device 243 is satisfied and the relay 241 is deenergized. The stoker motor 216 isoutof operation andthe heater 223 of the air control unit 211 is deenergized. The bimetal element 213 is also cold, this element now engaging contact 221 and holding the air damper 226 in closed position. The solenoids 233 and 231 of the barometric damper unit are also both deenergized, causing the barometric damper223 to be held in wide open position. Thus the air supply to the stoker is reduced to a minimum and also the draft is reduced to. a minimum,-. thereby causing the fire the retort to burn at a minimum rate. r a 7 When the device 243 calls for heat the coil 242 of relay 241 is energized as follows: From secondary 253 of the transformer 254, wire 255, control device 243, wire 256, relay coil 242 and wire 251 to secondary 253. ,Energization of coil 242 causes the switch arms 243, 244 and 245 to engage their respective fin contacts 246, 241 and 243, Elm gagement of the switch arm 243 with contact 246 establishes an energizing circuit for the stoker motor 216 and the heater 223 of the stoker air control, this circuit extending through the high limit control 258. Engagement of the switch arm 244 with contact 241 energizes the solenoid 233' as follows: From secondary 253, wire 255, wire 263, bimetal element 213, contact 221, wire 261, contact 241, switch arm 244, contact 262, solenoid 233, wire 263 and wire 251 to secondary 2533, En. gagement of the switch arm 245 with contact 248 wide open position to substantially closed position. At this time the bimetal element219 is cold and requires a substantial periodv of time in which to heat. During this period of time the stoker air damper 2261s closed to at least a minimum position and the barometric damper 229 held in closed position.

After a period of time in which the stoker is given an opportunity to deliver coal to the retort, the bimetal element becomes sufiiciently heated to move from its cold position to its hot position in which it engages contact 223 and causes the air damper 226 to open and operate automatically for proportioning th flow of air to the retort in accordance with the requirements for. such air. When the bimetal element 2 I 9 disengages contact 221 it breaks the energizing circuit for solenoid 233, The solenoid 231, however, remains enersized as its, circuit does not extend through the bimetal element 219. Consequently the damper lever 234 is freed from contact with the abutment lever arms 233 and 236 and thus left free to position itself so as to maintain the draft for whichit it adjusted. Thus after the stoker has operated for a period oftime the air damper 226 is freed for automatic control and also the barometric damper 223is freed for automatic control. This operation in whichthe air supply and draft are controlled automatically continues until the control device 243 becomes satisfied. At this time the relay 241 becomes deenergized thus stoping the stoker motor 216 and deenergizing the heater 223. The switch arms 244 and 245 now engage their out contacts 243 and 253, this causing energization of both solenoid 233 and solenoid 231 through the contact 223 of the stoker air control unit. Thus solenoid 233 is energized as follows: ,From secondary 253, wire 255, wire 263, bimetal element 219, contact 223, wir 266, wire 261, contact 243, switch arm 244,.wire 262, solenoid 233, wire 263 and wire 25'! to secondary 253. The energizing circuit for solenoid 231' extends from wire 266 through contact 253, switch arm 245 and wire 265 to solenoid 231;, When the stoker first stops the bimetal element 213 is heated to an appreciable extent and remainsin'its hot'positionj for a substantial periodoi tim after the heater 223 be,-

- comes deenergized. Thus the air damper 226 is held in open position and also the solenoids 233 and 231 are both energized forcausing the barometric damper 223 to be held in substantially closed position. As a result the smoking of the fire is minimized and whatever smoke is emitted from the fire is prevented from entering the furnace room. After a period of time in which the'volatile matter in the green coal in the retort is burned ofi the bimetalelement 219 again'assumes its cold positionin which it causes closing of the air damper 226. The bimetal element in disengaging contact 223 deenergizcs solenoids 233 and 231, causing them to assume the p sitions shown in which the barometric damper is held in wide open position. Thus after the energizes solenoid 231 as follows; From secondary 253, wire 255, wire 263, wire 264, contact 248, switch arm 245, wire 265, solenoid 231 and wire 25'! to secondary 253.

From the description thus far it will be apparent that when the control devic 243 calls for heat the stoker motor is placed into operation, the heater 223 is energized and the solenoids 233 and 231 are energized. Energization of solenoids 233 and 231 causes the damper 223 to be moved from stokeris stopped the air damper is held open and thebarometrie damper moved to closed position, the dampers being held in these positions for a period of time, the dampers then being caused to assume positions providing for minimum burning of the fire during the off*or stand-by period.

While the present invention is especially suitable for stokerfired installations, its utility'is not limited to installations .of this type and certain features of the invention have utility in other types of systems, such as oil fired installations or even hand fired installations in which automatic draft control is' provided. Whilethe use of the complete control systems shown and described is desirable, certain sub-combinations of control apparatus have utility apart from'the complete combination. Also it will be apparent that many changes may be made without departing from the scope of the present invention, Forthis reason it is desired to be limited only by the scope of the appended claims. I

. What'is claimedis:

1. In a control system for a furnace having combustion producing meansand a flue, the combination of, control means influenced by the demand for heat from the furnace for selectively placing the combustion producing meansinto and out-of operation, damper control meansincluding damper means associated with the flue, said damper control means including means actuated upon placing of the combustion producing'means into operation for causing movement of the damper meansfrom a position of minimum draft to an-intermediate position providing sufficient draft for satisfactory operation of the combustion producing means, means operative as' an incident to the placing of the combustion producing means out of operationfor causing movement of said damper means to a position provid ing maximum draft, andmeans for causing movement of said damper means to'a position providing minimum draft after a substantial period of time. 2. In a control system for afurnace'having combustion producing means'and a flue, the come bination of, control means. influenced by the demand for heat from the furnace'for selectively placingthe combustion producing means into and out of operation, damper control means including damper means associated with.,the"flue',"said damper control means including meansactuated as an incident to'the placing of the combustion producing means into operation 'for causing movement of the damper means fromaposition of minimum draftto a position lof maximuinid'raft andfor thereafter causing ihov'nient of f said damper means to and stopping it at an intermediate position'providing satisfactory draft for normal operation of the "combustion producing means, and means'operative upon placing ofthe combustion producing means out 'of operation for causing said damper meansto remain in position for providing'a substantial draft for a substantial period'of time and for then causing the damper means to assume a position of'mi'nimum draft. I

3. In a control system fora furnace having combustion producing meansand a flue, the combination of, control means influencedby the demand for heat from 'the'furnace for selectively placing the combustion producing means intoand out of operation, damper control means including damper means associated with the, flue, said placingthe combustion means into orout of opdamper control means including means actuated as 'an incident to the placing of the combustion producing means into operation for causing movement of the damper means from. a, position of minimum draft to a position of maximumwdraft and for thereafter causing movement of said damper means to an, intermediatepositionproviding satisfactory draft for-normaloperation'of the combustion producing means,means operative as an incident to the-placing of the combustion producing means out of operation for causing movement of said damper :means 'roa position providing maximum draft; and means for eration,.damper means associated with the flue for controlling the draft, means actuated-as an incident to the combustion means being -placed out of operation for causing movement of-the damper means to a position providing increased draft and for maintaining it in such position, and means actuated a substantial period: of time thereafter for causing movement of the dampe means toa position of reduced draft; a

5. In a control system fora furnace having combustion producing means and a flue, the combination of, control means influenced by the demand for heat from the furnace for selectively placing the combustion producing means into and out of operation, pressure responsive damper control means including damper means associatedwith the flue arranged to maintain a predetermined draft in the furnace when the combustion producing means is in operation, means actuated asan incident to the combustion producing means being placed outof operation for causing movement of thedamper means to a position maintaining maximum draft, and means operative a substantial period of time after the combustion producing means is placed out of operation for causing movement of the damper meansfrom said position of maximum draft.

.6. In a controlsystem for a furnace-having combustion producin means and a flue, the combination of, control means influenced by the demand for heat from the furnace for selectively placing the combustion producing means into or out of operation, pressure respons'ivedamper control means including damper means associated with the flue arranged to maintain a predetermined draft inv the furnace when the combustion producingzmeans is in operation, said damper control means including means actuated as an incident to the placing of the combustion producing meansinto operation for causing movement of .the damper means from a position of minimum draft to a position of maximum draft and for thereafter causing movement of the-damper means to a position providing saidpredetermined draft, and means actuated upon placing of the combustion producing means out of operation for causing .said damper means to maintain at least said predetermined-draft for a substantial period of time and for then causing said damper means to assume a position of minimum draft.

, ,7. In a control system fora -furnace having combustion producing means and a flue, thecombination of,'control means influenced by the demand for heat from the furnace for selectively placing'the combustion producingmeans into or out of, operation, pressure responsive damper control means including damper means'associated with the flue arranged to maintaina predetermined draft in the furnace when the combustion producing means is in operation, said damper control means including means actuated-asan incident to the placing of the combustiomproducing meansinto operation for causing movement of the damper means from a position'of minimum draft to a position ofmaximurndraft and for thereafter causing jmov'ement 'of the damper means to a position providing said predetermined draft, means actuated as an incident to the placing of the combustion producing means out of operation for causing movement of the damper means to a position maintaining a maximum draft, and means operative a substantial period of time-after the combustion producing means is placed out of operation for causing movement of the damper means to a position providing a minimum draft while the combustion producing means is out of operation.

8. In a control system for a stoker fired furnace having a flue, the combination of, control means influenced by the demand for heat from the furnace for selectively placing the stoker into and out of operation, an air control damper associated with the stoker, a draft control damper associated with the flue, means actuated upon starting of the stoker for causing movement of said dampers from positions providing a minimum air supply to the fire and a minimum draft to positions providing a substantial supply of air to the fire and a. substantial draft for withdrawing products of combustion, and means operative upon placing of the stoker out of operation for maintaining said dampers in positions for permitting air flow to the fire and providing substantial draft for a substantial period of time to minimize smoking, said last mentioned means causing said dampers 'to return to positions providing minimum air supply and minimum draft after said period of time.

the furnace for selectively placing the stoker into and out of operation, an air control damper associated with the stoker, a draft control damper associated with the flue, means actuated upon starting of the stoker for causing movement of said dampers from positions providing a minimum air supply to the fire and minimum draft to positions providing a substantial supply of air to the fire and a substantial draft for withdrawing products of combustion, means operative upon placing of the stoker out of operation for maintaining said air control damper in position to permit flow of air to the fire, means operative as an incident to such placing of the stoker out of operation for causing movement of said draft damper to a position of maximum draft for a substantial period of time to minimize smoking, and means for causing said dampers to return to positions providing minimum air supply and minimum draft after said period of time.

10. In a control system for a stoker fired furnace having a flue, the combination of, control means influenced by the demand for heat from the furnace for selectively placing the stoker into and out of operation, an air control damper associated with the stoker, a draft control damper associated with the flue, means actuated upon starting of the stoker for causing movement of said dampers from positions providing a minimum air supply to the fire and minimum draft to positions providing a substantial supply of air to the fire and a substantial draft for withdrawing products of combustion, means operative upon placing of the stoker out of operation for maintaining said dampers in positions for permitting air flow to the fire and providing substantial draft for a substantial'period of time to minimize smoking, said last mentioned means in-' cluding a control device common to both of said dampers and actuated after said period of time for causing said dampers to return to positions grogding minimum air supply and minimum ra I 11. In a control system. for a stoker fired fun nace having a flue, the combination .of,-. control means influenced by the demand for; heat from the furnace for selectively placing thestoker into and out of operation, an air control damperuase sociated with the stoker, a draft control damper associated with the flue,- means actuated upon starting of the stoker for causing movement. of said dampers from positions providing a minimum air supply to the fire and minimum draft to posi-. tions providing a substantial'supply of'airto the fire and a substantial draft for withdrawing pr0d+ ucts of combustion, means operative upon p1ac ing of the stoker out ofv operationfor maintaim ing said air control damper in position to permit flow of air to the fire, means operative as an incident to placing of the stoker out of operation for causing movement of said draft damper to a position of maximum draft to minimize smoking, and means including a control device common to both of said dampers and actuated after a substantial period of time following the placing of the stoker out of operation for causing said dampers to re turn to positions providing minimum, air supply and minimum draft. 12. In a control system for a furnace'having combustion producing means and a flue, thecombination of, a combu'stionair pressure controlled air damper associated with the combustion pro-.- ducing means for maintaining a controlled supply of air for combustion, a draft controlled draft damper associated with the flue for controlling the draft for the furnace, and interlocking control means for said dampers and the combustion producing means for placing said combustion producing means out of operationand causingz'said dampers to assume positions of minimum air supply and draft, and for placing the combustion producing means in operation and rendering said dampers operative to maintain said controlled supply of air and said controlled draft,

13. In a control system for astoker fired'furnace having a flue, the combination of, control means influenced by the demand for heat from the furnace for selectively placing the stoker into and out of operation, an air control damper associated with the stoker, a draft control-damper associated with the flue, first motor means jfOl controlling the air damper, second motor means for controlling the draft damper, means operative upon placing of the stoker into operation for causing the second motor means to move the draft damper from a position of minimum draft to a position of maximum draft and for thereafter moving said draft damper to an inter mediate position, means operative upon placing of the stoker out of operation to cause said first motor means to control the air supply damper in a manner to maintain a supply of air to the stoker and to cause the second motor means to move the draft damper from an intermediate position to a position of maximum draft, said last mentioned means including a single control device actuated after a substantial period of time following placing of the stocker out of operation, said single control device controlling both of said motor means and operative when actuated to cause said motor means to return thedampers to positions of minimum air supply and draft.

14. In a control system for a stoker fired furnace havinga flue, the combination of, damper means associated with the flue for controlling the damper means, a pressure actuated control device influenced by the products of combustion and adapted to control said motor means, means responsive to the demand for heat from the stoker for placing the same into and out of operation, means actuated upon the stoker being placed into operation for placing said control device in control of said motor means, said last recited means being actuated upon the stoker being placed out of operation for causing the motor means to operate the damper means to a position of maximum draft to thereby minimize smoking, and a control device actuated a substantial period following the placing of the stoker out of operation for causing said motor means to operate the damper means to a position of minimum draft.

15. In a control system for a stoker fired furnace having a flue, the combination of, damper means associated with the flue for controlling the furnace draft, motor means for positioning said damper means, a pressure actuated control device influenced by the products of combustion and adapted to control said motor means, means responsive to the demand for heat from the stoker for placing the same into and out of operation, means actuated upon the stoker being placed into operation for placing said control device in control of said motor means and actuated upon the stoker being placed out of operation for causing the motor means to operate the damper means to a position of maximum draft to thereby minimize smoking, and timing means in control of said motor means and operative at the expiration of a timed period after the stoker is placed out of operation for causing the motor means to operate the damper means to a position of minimum draft.

16. In a control system for a stoker fired furnace having a flue, the combination of, damper means associated with the flue for controlling the furnace draft, motor means for positioning said damper means, a pressure actuated control device influenced by the products of combustion andadapted to control said motor means, means responsive to the demand for heat from the stoker for placing the same into and out of operation, means actuated upon the stoker being placed into operation for placing said control device in control of said motor means, and actuated upon the stoker being placed out of operation for causing the motor means to operate the damper means to a position of maximum draft to thereby minimize smoking, and means including a thermostatic device which changes in temperature as an incident to the stoker being placed out of operation for controlling said motor means, said thermostatic device causing the motor means to operate the damper means from said position of maximum draft to a position of minimum draft.

17. In a control system for a furnace having combustion producing means and a flue, the combination of, control means influenced b'ythe demand for heat; from the furnace for placing the combustion producin means into and out of operation, damper means associated with the flue, thermostatic means influenced by the temperature of the products of combustion and tending to cause said damper means to assume a position of minimum draft when said thermostatic means is relatively cold, whereby the draft through the furnace is maintained at a minimum when the combustion producing means is out of operation, electromagnetic meansassociated with said damper means and operative to cause movement of the damper means from the position of minimum draft to a position of maximum draft upon placing of the combustion producing means into operation, and means controlled by said thermostatic means for causing movement of said damper means to an intermediate position when the thermostatic means becomes relatively hot.

18. In a control system for a furnace having combustion producing means and a flue, the combination of, control means influenced by the demand for heat from the furnace for placing the combustion producing means into and out of operation, damper means associated with the flue. thermostatic means influenced by the temperature of the products of combustion and tending to cause said damper means to assume a position of minimum draft when said thermostatic means is relatively cold, whereby the draft through the furnace is maintained at a minimum when the combustion producing means is out of operation, electromagnetic means associated with said damper means and operative upon placing of the combustion producing means out of operation to cause movement of the damper means to a position of maximum draft, and means controlled by said thermostatic means for causing movement of the damper means from said position of maximum draft to a position of minimum draft when the thermostatic means becomes relatively cool.

19. In a control system for a furnace having combustion producing means and a flue, the combination of, control means influenced by the demand for heat from the furnace for placing the combustion producing means into and out of operation, damper means associated with the flue, damper control means including an electro-magnet and a slow-acting device for positioning said damper means, said damper control means being controlled by said first mentioned control means and acting upon placing of the combustion producing means out of operation to cause movement of the damper means from an intermediate position to a position of maximum draft, said slow acting means a period of time thereafter causing movement of saiddamper means from said position of maximum draft.

20. In a control system for a stoker fired furnace having a flue, the combination of, control means influenced by the demand for heat from the furnace for selectively placing the stoker into and out of operation, and air control damper associated with the stoker, a draft control damper associated with the flue, and thermostatic means influenced by the temperature of the products of combustion for controlling both of said damper means, said thermostatic means when relatively cold tending to position said dampers for providing a minimum air supply and a minimum draft. and when relatively hot tending to cause said damper means to provide a substantial air sup ply and a substantial draft.

21. In a control system for a stoker fired furnace having a flue, the combination of, control means influenced by the demand for heat from the furnace for selectively placing the stoker into and out of operation, an air control damper associated with the stoker, a draft control damper associated with the flue, means actuated upon starting of the stoker to cause relatively quick movement of the draft control damper from a position of minimum draft to a position of maximum draft and a substantial period of time thereafter to cause movement of the air control damper from a position of minimum air supply to a position of substantial air supply, and means for causing said dampers'to return-totheir positions of minimum air supply and minimum draft after the stoker is placed out of operation."

'22. In a control system for 'a stoker fired furnace havinga flue, the combination of, control means influenced by'the'demand forheat from the furnace for selectively placing the stoker into and out of operation,.an air control damper associated with the stoker, a draft control damper associated with the flue, a slow acting device for controlling said air control damper, said device being :rendered effective substantially when the stoker isplaced into operation and causing'movement of the air control damper from a position of minimum .air supply to'a position of substantial air supply asubstantial period of time after the stoker is placed into operation whereby the air to the stoker is delayed until a quantity of coal is delivered to the stokerretort, motor means for positioning said draft control damper, said motor means being controlled by said control means and serving to cause movement of the draft control damper from a position of minimum draft to a position of substantial draft upon call for heat by said control means.

23. In a control system for a stoker fired furnace having a flue, the combination of, control means influenced by the demand for heat from the furnace for selectively placing the stoker into and out of operation, an air control damper associated with the stoker, a draft control damper associated with the flue, means including a thermostatic element associated with said aircontrol damper for causing movement of the same from a position of minimum air supply to a position of substantial air supply as said element changes in temperature in a predetermined direction, an electric heating element for influencing said thermostatic element, said heating element being arranged under the control of said control means in a manner to cause movement of the air control damper from the position of minimum a'irsupply to a position of maximum supply after the stoker is placed into operation, an electro-magnetfor positioning said draft control damper, and means for controlling said electromagnet in a manner to cause the draft control damper to move from a position of minimum draft to a position of maximum draft upon call for heat by said control means.

24. In a control system for a stoker fired furnace having a flue, the combination of, control means influenced by the demand for heat from the furnace for selectively placing the stoker into and out of operation, an air control damper associated with the stoker, a draft control damper associated with the flue, means including a slow acting timing device for actuating said air control damper, said timing device being rendered effective substantially when the stoker is placed into operation and causing movement of the air control damper from a position of minimum air supply to a position of substantial air supply a period of time after the stoker is placed into operation, motor means for positioning said draft control damper, and switching means actuated by said timing device for controlling said motor means.

25. In a control system for a stoker fired furnace having a fine, the combination of, control means influenced by the demand for heat from, the furnace for selectively placing the stoker into and out of operation, an air control damper associated with the stoker, a draft control damper associated with the flue, means including a slow acting timing'device foractuating said air control dampeLsaid-timing device being rendered effective substantially when the stoker is placed intooperation ancl'causing movement of the air control damper from aposition of minimum air supply toa position of substantial air supply a periodof time after the stoker is placed into operation, switching means actuated by said timing,

device, motor means comprising a pair of electromagnets :for actuating said draft control damper,

one electroema'gnetbeing efiectiveto move the and out of operation, an air control damper associated with the stoker, a draft control damper associated with the flue, means including a slow acting timing device for actuating said air control damper, said timing device causing movement of the air control damper from a position of minimum air supply to a position of substantial air supply a period of time after the stoker is placed into operation, means for causing movement of the draft control damper to a position of maximum draft upon stopping of the stoker, and control means actuated by said timing device for causing movement of said draft control damper away from said position of maximum draft a substantial period of time after stopping of the stoker.

27. In a control system for a stoker fired furnace having a flue, the combination of, control means influenced by the demand for heat from the furnace for selectively placing the stoker into and out of operation, an air control damper associated with the stoker, a draft control damper associated with the flue, means actuated upon starting of the stoker for causing movement of said dampers from positions providing a minimum air supply to the fire and minimum draft to positions providing a substantial supply of air to the fire and a substantial draft for withdrawing products of combustion, said last mentioned means including timing means for delaying movement of the air control damper in draft increasing direction upon starting of the stoker until a quantity of fuel is supplied to the stoker retort, and for delaying movement of the draft damper in draft decreasing direction for a period of time upon stopping of the stoker.

28. In a control system for a furnace having combustion producing means and a flue, the combination of, control means influenced by the demand for heat from the furnace for placing the combustion producing means into and out of operation, a barometric damper associated with the flue and adapted to maintain a, constant draft, electric motor means adapted in a first position to hold said damper substantially closed and in a second position to release said damper for normal operation, means for causing said motor means to move to saidfirst position upon starting of the combustion producing means, and means including a slow acting device for causing said motor means to move to its second position a combustion producing means and a flue, the combination of, control means influenced by the demand for heat from the furnace for placing the combustion producing means into and out of operation, a barometric damper associated with the flue and adapted to maintain a constant draft, electric motor means adapted in a first position to hold said damper substantially closed and in a second position to release said damper for normal operation, means for causing said motor means to move from said second position to said first position upon stopping of the stoker, and means including a slow acting device for causing said motor means to move from said flrst'position toward its second position a period of time thereafter.

30. In a control system for a furnace having combustion producing means and a flue, the combination of, control means influenced by the demand for heat from the furnace for selectively placing the combustion producing means into and out of operation, a damper in the flue, a reversible motor for positioning the damper, a device responsive to the draft in the furnace for controlling the reversible motor, means controlled by said control means for placing the reversible motor under the control of the draft responsive device when the combustion producing means is in operation and for causing the reversible motor to operate the damper to a minimum draft position when the combustion producing means is out of operation, means for causing the damper to move to wide open position upon call for heat by the control means before the combustion producing means is placed in operation, and means for causing the damper to move to wide open position before moving to said minimum draft position, when the combustion producing means is placed out of operation,

WAYLAND R. MILLER.

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