US2243715A

US2243715A - Combustion control system

Info

Publication number: US2243715A
Authority: US
Publication date: 1941-05-27
Anticipated expiration: 1958-05-27

Description

Filed July 1, 1937';

.Bzverz tor I land Riff-iller Patented May 27, 1941 COMBUSTION CONTROL SYSTEM Wayland R. Miller, oconomowoc, Wia, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis; a corporation of Delaware Application my 1, 1937, Serial No. 151,399

' 8 Claims. (01. 2365114) This invention-relates to combustion control systems.

An object of this invention is to provide a new and improved method for controlling a furnace equipped with fuel supplying means and damper means to maintain the dampermeans closed during standby periods to prevent heat losses through the stack, to open wide the damper late the draft through the furnace after combustion has been actually established.

Another object of this invention is to provide an automatic control system for accomplishing automatically the above sequence of operation.

Other objects and advantages will become apparent to those skilled in the art upon reference to the accompanying specification, claims and drawing.

For a more thorough understanding of the invention reference is made to the accompanying single sheet of drawing in which there is diagrammatically shown the preferred form of this invention.

l8 designates a boiler provided with a combustion chamber I The boiler is fired by means of an oil burner l2 in .a conventional manner. The products of combustion may pass from the combustion chamber over a bridge l3 to a back chamber I4 and thence through fire tubes l5 to a front chamber I8. The gases of combustion are drawn from the front chamber I8 through a breech or flue which connects into a chimney or stack (not shown). Steam is generated around the fire tubes I5 and is collected in a drum I8. The steam passes from the drum |8 through a pipe is to. a plurality of heat exchangers, one of which is shown at 28. The heat exchangers 20 may be utilized for heating a space or spaces. Condensed steam passes from the heat exchangers through a trap 2| and is returned to the boiler H1 in any suitable manner. An indirect heater 22 may be connected in the water space of the boiler to provide hot water for any desired use. Although I have shown a particular type of boilerfor purposes of illustration it is to be understood that any other type of boiler may be utilized withinthe contemplation of this invention.

Fuel oil is supplied to the oil burner l2 by means of a pipe 25 leading from a source of fuel oil (not shown) and the flow of fuel oil through the pipe 25 is controlled by anon and of! valve 28 operated by a solenoid motor 21 of usual de*- sign and by a modulating valve 28. The modulating valve 28 may be operated through a pitman 29 by a crank disc 88 mounted on a shaft of a motor 32. The motor 32 is preferably of the proportioning type and is adapted to modulate the valve 28 between a minimum position wherein a small flow of fuel oil is permitted. and a maximum position wherein a, large flow of fuel oil is permitted. The pitman 28 and the crank disc 30 are preferably arranged so that the proportioning motor 32 does not completely close the valve.

The proportioning motor 32 may comprise

motor rotors

33 and 34 for rotating the shaft 3| through a reduction gear train 35. The

motor rotors

38 and 34 are operated by

field windings

36 and 31. The shaft 8| also operates aslider 38 with respect to a resistance element 39. The slider 38 and the resistance element 39 form a balancing potentiometer, the operation of which will be pointed outmore fully hereafter. The shaft 3| also operates a cam 48 which in turn operates a mercury switch 4|. The arrangement is such that when the fleld winding 36 is energized thevalve 28 is moved toward the minimum position, the slider 88 is moved toward the left and the cam 40 is moved toward a position to cause closing of the mercury switch 4|. When the field winding 51 is energized the valve 28 is moved toward an openposition, the slider 88 is moved toward the right and the cam 40 is rotated in a clockwise direction to open the switch 4|. The cam 40 is so arranged that the switch 4| is closed only when the valve28 is in the minimum position as shown in the drawing. a

The proportioning motor 32 is controlled by a relay generally designated at 43 and this relay may comprise series connected relay coils 44 and 45 for operating a switch arm 48 with respect to contacts 4] and 48. The arrangement is such that when the relay coil 44 is energized more than the relay coil 45 the switch arm 46 is moved into engagement with the contact 41 and when the relay coil 45 is energized more than the relay coil 44 the switch arm' 48 engages contact 48. When the relay coils 44 and 45 are equally energized the switch arm 48 is maintained spaced midway between the contacts 41 and 48. Power is supplied to the relay coils 44 and 45 by means of a step-down transformer 49. The secondary 50 of the step-down transformer is connected across the relay coils 44 and 45 and the primary 5| is connected across

wires

52 and 53 which in turn are connected to line wires 54 and 55 leading from a source of power (not shown). The transformer 49 is continuously energized and therefore power is at all times supplied to the relay coils 44 and 45. The energizations of the relay coils 44 and 45 are controlled by partially short-circuiting either or both of these coils in a manner well knownin the art.v

The operation of the oil burner I2 is controlled by a starter generally designated at 81 and this starter 51 may comprise: a relay coil 58 for operating switch arms 59 and 82. When the relay coil 58 is energized the switch arms 59 and 82 are moved into engagement with

contacts

88 and 83 respectively and when the relay coil 58 isldeenergized the switch arms 59 and 82 are moved out of engagement with

contacts

88 and 88 and the switch arm 59 is moved into engagement with contact 8I by means of springs, gravity or other means (not shown). The oil burner I2 is provided with an ignition transformer 84 for igniting in the usual manner the combustible mixture delivered by the oil burner I2.

The flow of combustion gases through the boiler I8 and therefore the draft within the boiler I8 is controlled by a draft or breeching damper 88. This damper 88 is operated by a link 81 and a crank 88 mounted on a shaft 89 of a motor 18. The motor 18 is shown to be a floating motor although any other type of motor may be utilized. The shaft 89 is operated through a reduction gear train H by motor rotors 12 and 13 which are in turn influenced by field windings 14 and 15 respectively. The arrangement is such that when the field winding 14 is energized the damper 88 is moved toward an open position and when the field winding 15 is energized the damper 88 is moved toward a closed position. The shaft 89 operates an abutment member 18 which is adapted to open limit switches 11 and 18 when the damper 88 is moved to an extreme closed position or an extreme open position respectively.

spect to contacts 88 and 81. When the relay coil 88 is energized more than the relay coil 84 the switch arm 85 engages contact 88 and when the relay coil 84 is energized more than the relay coil 88 the switch arm 85 engages contact 81 as shown in the drawing. Power is supplied to the relay 82 by means of a step-down transformer 88 having a secondary 89 connected across the series connected

relay coils

83 and 84 and a primary 98 connected by wires 9| and 92 across line wires 84 and 55. Power is therefore at all times supplied to the relay coils and 84 and the energizations of the

relay coils

88 and 84 are controlled by short-circuiting of the

relay coils

83 and 84.

A static pressure regulator generally designated at 94 is adapted under certain conditions to position the floating motor 18 and this static pressure regulator may comprise a casing 95 enclosing a diaphragm 98. The underside of the diaphragm 98 is connected by a pipe 91 to the combustion chamber of the boiler I8. The diaphragm 98 carries an operating stem 98 and is biased upwardly by a spring 88. The stem 88 operates a mercury switch I88 provided with a center electrode I8I, a left electrode I82 and a right electrode I88. As shown in the drawing, the damper 88 is closed and therefore the draft through the furnace is a minimum. The spring 99 therefore maintains the diaphragm 98 in its upper position so that the electrodes I8I and I88 are bridged. However, when the damper 88 is opened to increase the draft through the furnace the spring 99 is overcome and the diaphragm 98 moves downwardly to cause the mercury in the mercury switch I88 to bridge the electrodes III and I82.

V The combustion control system may be placed in operation by means of a room thermostat designated at I88 and this thermostat may comprise a bellows I88 containing a volatile fluid for operating a mercury switch I81. Upon a decrease in space temperature the bellows I88 contracts to close the switch I81. The system may also be placed in operation by means of a temperature responsive controller I88 which may comprise a bellows I89 connected by a capillary tube II8 to a bulb III located in the water space of the boiler I8. The bulb and capillary tube preferably contain a volatile fluid so that upon a de-' hereafter, these two switches are connected in parallel with respect to each other so that either may place the combustion control system in operation. The temperature responsive controller I88 therefore maintains the boiler water at a predetermined temperature-to provide hot water for any desired purpose and to maintain the boiler water temperature Just under the boiling point so that the time lag following a call for heat by the room thermostat I and the generation of steam is decreased to a minimum.

The oil burner l2 and its associated mechanism is controlled by an oil burner relay system which may comprise a relay generally designated at H4 and another relay generally designated at H8. The relay II4 comprises a relay coil I I8 which when energized moves switch arms H1, H8, H9 and I28 into engagement with contacts I2I, I22, I28 and I24 respectively. When the relay coil I I8 is deenergized the switch arms are moved out of engagement with their respective contacts by means of springs, gravity or other means (not'shown). Likewise therelay II5 comprises a relay coil I25.which when energized moves switch arms I28, I21 and I28 into engagement with contacts I29, I88 and I8I respectively. When the relay coil I28 is deenergized the switch arms are moved out of engagement with their respective contacts by means of springs, gravity or other means (not shown). Power is supplied to these two relays H4 and H5 bymeans of a step-down transformer I88 having a secondary I84 and a primary I85. The primary I85 is connected by a wire I88 to the line wire 55 and by a wire I81 through a mercury switch I38 operated by a low water out of! I89 and through a switch I48 operated by a high limit pressure controller I to the other line wire 54. The mercury switch I98 of the low water. out 011189 is moved to an open position in case the water level within the boiler is too low. The high limit pressure controller may temperature increase.

comprise a bellows I42 connected by a pipe I43 to the pipe I5 and the arrangement is such that when the pressure in the pipe I8 and consequently in the-boiler I becomes excessive the switch I40 is opened. Since the switches I38 and I40 are in series with the primary I35 of the step-down transformer I33, power is supplied to the transformer I33 only when the boiler water is at a safe level and the steam pressure is not excessive.

Associated with the oil burner relays H4 and I I5 is a safety switch generally designated at I45 and this switch may comprise contacts I45 operated by a bimetallic element under the influence of a heater I41. The safety switch I45 may be of the type disclosed in F. S. Denison Patent No. 1,958,081, and therefore a further description is not considered necessary it being sufficient to state that when the heater I41 is energized for a given period of. time the contacts I45 open and require manual resetting. Also associated with the oil burner relays H4 and H5 is a combustion responsive device generally designated at I48. This device may include a thermostatic element extending into the path of gases of combustion as at I49 for operating a switch arm I50 with respect to contacts I5I and I52. The switch -arm I50 and the contacts I5I and I52 are so arranged that they provideoverlapping action upon a By this it is meant that when the thermostatic element is cold the switch arm I50 engages the contact I5I and as the thermostatic element increases in temperature the switch arm I50 engages the contact I52 before it disengages the contact I5I. However, upon a decrease in temperature the switch arm I50 disengages the contact I52 before it reengages the contact I51. Such a construction is well known in the art. and a further description thereof is not considered necessary.

The temperature responsive controller I08 and the room thermostat I05 control a relay generally designated at I54. This relay may comprise a relay coil I55, which when energized, moves switch arms I55 and I51 into engagement with contacts I58 and I59. When the relay coil I55 is deenergized the switch arms are moved out of engagement with their respective contacts and the switch arm I 51 is moved into engagement with a contact I by means of springs, gravity or other means (not shown). Power is supplied to the relay I54 by means of step-down trans? former I52 having a secondary I53 and a primary I54 connected across wires I35 and ,l31. It fol-- lows then that the transformer I52 is supplied with power as long as the water level in the boiler is normal and also the steam pressure in the 1 boiler is normal. I

A secondcombustion responsive switch is generally designated at I55 and may include a thermostatic element extending into the boiler in concertain conditions, positions the proportioning motor 32 is generally designated at I12 and this controller may comprise a bellows I13 suitably connected to the steam pipe I8 for operating a slider I14 with respect to a resistance element I15. The slider I14 and the resistance element I15 form a control potentiometer for the proportioning motor 32. Upon an increase in pressure the slider I14 is moved upwardly and upon a decrease in pressure this slider is moved downward- 1y.

With the parts in the position shown in the drawing, the room thermostat I05 and the temperature responsive 1 controller I08 are satisfied and thereforeithe control system is shut down. The valve 26 in the fuel supply line is closed and the valve 28 is in a minimum position. The oil burner is inoperative and the draft or breeching damper 55 is in a closed position to prevent the escape of heat from the boiler through the breech or fliiel1 to the chimney. The draft or breeching damper 55 is in a closed position since the relay coil 83 of the relay 82 is short-circuited whereby relay coil 84 is energized more than relay coil 83 to maintain the switch arm 85 in engagement with the contact 81. Likewise the valve 28 is in a minimum position since the relay coil 45 is short-circuited by the switch arm 59 engaging the contact 5| of the starter 51.

Assume now that the space temperature decreases so as to close switch I01 of the room thermostat I05 or that the boiler water temperature decreases to such a value as to closeswitch II2 of the temperature responsive controller I08. A circuit is therefore completedfrom the secondary I53 through the switch I01 and relay coil I55 or through the switch H2 and relay coil I55 to cause energization of the relay coil I55. As a result switch arms I55 and I51 are moved into engagement with contacts I58 and I59. -Movement of the switch ann I51 out of engagement with the contact I50 breaks the short circuit through the relay coil 83 and movement of the switch arm I55 into engagement with the contact I58 at this time has no effect. Movement of the switch arm I51 into engagement with the contact I59 completes a short-circuit for the relay coil 84 of the relay 82 extending from the junction of the relay coils 83 and 84 through switch arm I51, contact I58, switch arm I58 and cold contact I59 of the combustion responsive switching mechanism. I55 and through a protective resistance to the right end of the relay coil 84. By reason of this the relay coil 83 becomes energized more than the relay coil 84 and the switch arm 85 is moved into engagement with the contact 85 to complete a circuit from the wire 8| through switch arm 85, contact 85, limit switch 18 and field winding 14 back to the other wire 82. Com pletion of this circuit energizes the field winding 14 to move the damper 55 towards an open position.

When the damper 55 is moved toan extreme open position the limit switch 18 is opened to break the circuit through the field winding 14 and the switch operated by the cam 18 is closed. Closure of the switch 80 completes a circuit from the secondary I34 through safety switch contacts I46, mercury switch 80, mercuryswitch 4I operated by the proportioning motor 32, safety switch heater I41, relay coil II5, cold contact I5I of the combustion responsive switching mechanism I48 and switch arm I50 back to the secondary I34. Completion of this circuit causes heating of the heater I41 and energization of the relay coil II5. Energization of the relay coil H5 moves switch arms H1, H8, H8 and m into engagement with contacts m, m, m and I24.

Movement of the switch arm II1 into en gagement with the contact I2I completes a maintaining circuit for the relay coil II4 which circuit may be traced from the secondary I44 of,

step-down transformer I33 through safety switch contacts I44, contact I54 and switch arm I54 of relay I54, contact I2I and switch arm 1 of relay II4, heater .I41,. relay coil IIS, cold contact I5I and switch arm I54 back tothe secondary I44. This maintaining circuit shunts out the switch 44 operated by the floating motor 14 and the switch 4I operated by the proportioning motor 32 and therefore therelcy I1! miI-Y remain pulled in even though the draft damper I4 is moved away from the wide open positioneor the valve 24 is moved away from its minimum position. Summing up, in order to pull. in the relay H4, both switches 44 and 41 operated by the floating motor 14 and the proportioning motor 32 respectively must be closed, but after the relay II4 has once been pulled in it makes. no difference whether these switches are opened or closed as long as the spacethermostat I45 or Movement of the switch arm II! into engageare connected in parallel back to the wire :44.

Therefore, when the relay II4 pulls in the valve 26 is opened and the relay coil 54 is energized to move switch arms 59 and 42 into engagement with contacts 64 and 43 respectively. Movement of the switch arm 42 into engagement with the contact 63 completes a circuitdrom wire 52 through switch arm 52, contact 44 and oil burner motor back to the wire 53. The oil burner motor is therefore placed in operatiomto supply a combustible mixture to the boiler I4. Movement of the switch arm 59 outpt engagement with the contact 6| breaks the short circuit for the relay coil 45 and movement of the switch arm 54 into engagement with the contact 44 connects the junction of the relay coils 44 and 45 with the slider I14 and places the relay 44 under the control of the pressure controller I12. The proportioning motor 32 and consequently the valve 24 will be moved to a position corresponding to the position of the slider I14 of the control potentiometer and since this slider I14 is positioned inaccordance with variations in steam pressure the motor 32 and consequently'the valve 24 will be positioned in accordance withvariations in steam pressure. As the steam pressure decreases the slider I14 moves downwardly-todecrease theenergization of the relay coil 44 and increase the energization of the relay coil 45 to move the switch arm 46 into engagement with the contact 44. This completes a circuit from the wire 52 through switch armlfi, contact 48 and field winding 31 back to the other wire 53. The valve 24 is therefore moved toward an open position. As the valve is moved toward an open position the slider "is moved toward the right to decrease the energization of the relay coil 45 and increase the energization of the relay coil 44. When the slider 38 has moved sufficiently far to the right to rebalance the energizations of the relay coils 44 and 45, the switch arm 45 is moved out of engagement with the contact 44 to break the circuit through the field winding 31. In this manner the valve 24 is modulated toward m open position inaccordance with the amount ofdecrea'seinsteam pressure. Conversely, an

increase in steam pressure causes upward move-- ment of the slider I14 to-decrease the energization of the relay coil 45 whereupon the switch arm 44 is moved into engagement with the contact 41 to complete a circuit through the field winding 44. This causes. movement of the valve 24 towards aclosed position and also left hand movement of the slider 44. This leftzhand move.-.

ment of the slider 44 decreases theenergization' of the relay coil 44 and increases the energization of the relay coil 44 and when :thesliderdll has moved sufficiently far to the left so as torebalance the energization of the relay coils 44 and 45 the switch arm 44 is moved out of engagement with the contact 41 to break-the circuit through the field winding 24. It follows then that when the switch arm 44 of the starter 51 engages the contact 4|, the valve 24 is maintained in. a minimum position but when the starter 51 is pulled in to move the switch arm 54 into engagement with the contact 44, the pressure responsive controller I12 modulates the valve 24 in accordance with variations in steam pressure. Therefore the supply of fuel to the oil.burner I2 is increased as the steam pressure decreases and the supply of fuel is decreased as the steam pressure increases in order to maintain a substantiallyconstant steam pressure during operation of the system.

Movement-of the switch arm I24 of the relay II4 into engagement with the contact I24 completes a circuit from the wire I41 through contact I22, switch arm II4, switch arm I24, contact I24 and ignition coil 44 back tothe wire I44. A combustible mixture is therefore supplied to the boiler I4 and is ignited. In case this combustible material is not ignited within a predetermined time the heater I41 causes opening of the safety switch contacts to cause the relay I I4 to drop out to stop further operation of the oil burner I2, the ignition transformer 44 and also to close the valve 24 and to move the valve 28 to a minimum position.

If, however, combustion is established the switch arm I54 of V the combustion responsive switching mechanism I44 moves into engagement with the contact I42 to complete a circuit fromthe secondary I24 through safety switch contact I44, contact I54, switch arm I44, contact I2I, switch arms III and Ill, contact I22, relay coil I25 of relay III, hot contact I42 of the combus' tion responsive switching mechanism I44, and switch arm I54 back to the secondary I44. Completion of this circuit energizes the relay coil I25 to move the switch arms I24, I21 and- I24 into engagement with the contacts I24, I44 and Iii. Movement of the switch arm I24 into engagement with the contact I24 completes a maintaining circuit for the relaycoil I25-which is switch contacts I48, contact I58, switch arm I88, contact I20, switch arms I28 and H1, contact I80, relay coil H8, cold contact I5I and switch arm I80 back to the secondary I84. This circuit maintains the relay coil I I8 energized and shunts out the heater I4'I whereupon opening of the safety switch contacts I48 is prevented.

A second circuit for the relay coil 58 of the starter 81 and the solenoid motor 21 is completed when the switch arm I28 engages the contact I3I and this second circuit may be traced from the wire I81 through contact I8I, switch arm I28, solenoid motor 21 and relay coil 58 which are connected in parallel back to the wire I88. This circuit is entirely independent of the relay II4.

When the thermostatic element of the combustion responsive switching mechanism I48 becomes suiiiciently heated to separate the switch arm I50 and the cold contact I5I all circuits through the relay coil H8 and the heater I" are broken and the relay II4 drops out. As a result switch arm I20 disengages the contact I24 to break the circuit through the ignition transformer 84 whereupon ignition is terminated after combustion has been satisfactorily established. In this manner the solenoid valve 28 is maintained opened and the oil burner I2 is maintained in operation until such time as both the space thermostat I08 and the temperature responsive controller I08 are satisfied. When this occurs the relay I84 drops out and since switch arm I88 thereupon disengages contact I58 the relay II5 will drop out to stop the oil burner I2 and close the valve 28. The oil burner I2 and the valve 28 cannot again be placed in operation until such time as the thermostatic switching mechanism I48 has cooled suillciently to move the switch arm I80 into engagement with the contact I8I.

When combustion has been established in the manner pointed out above the switch arm I88 of the combustion responsive switching mechanism I88 is moved out of engagement with the contact I80 and into engagement with the contact I10. Movement of the switch arm I88 out.

of engagement with the contact I89 breaks the short-circuit through the relay coil 84 and movement of the switch arm I88 into engagement with the contact I10 connects the junction of the relay coils 88 and 84 to the center electrode IOI of the pressure regulator 04. The relay coils 88 and 84 of the relay 82 are thereupon connected to the electrodes IOI, I02 and I03 of the pressure regulator 04. Upon a decrease in furnace pressure as the result of an increase in furnace draft the electrodes I i and I02 of the pressure regulator 84 are bridged to complete a shortcircuit for the relay coil 83 to decrease the energization thereof and increase the energization of the relay coil 84. This causes movement of the switch arm 88 into engagement with contact 81 to complete a circuit from the wire 8| through switch arm 88, contact 81, limit switch I1 and field winding I back to wire 82. This causes energization of the field winding I8 to move the damper 88 towards a closed position to decrease the draft through the boiler I0. Conversely, when the pressure in the boiler I8 increases as the result of a decrease in draft the electrodes III and I03 are bridged to complete a short-circuit for the relay coil 84 whereupon the switch arm 88 engages the contact 88 to complete a circuit from the wire 8i through switch arm 85, contact 88, limit switch I8 and field winding I4 back to the wire 92. This causes opening movement of the damper 88 to increase the draft through the furnace. By reason of this arrangement a floating control of the draft or breeching damper 88 is obtained to maintain the draft through the furnace substantially constant.

Assume 'now that both the space thermostat I05 and the temperature responsive controller I08 are satisfied, the relay I54 drops out and as a result the relay coil 88 is short-circuited by the switch arm I51 engaging the contact I and the draft damper 88 is thereupon moved to a complete closed position. Also as a result of dropping out of the relay I54 the oil burner I2 is stopped and the valve 28 in the fuel line is closed. The valve 28 is moved to a. minimum position by engagement of the switch arm 58 of the starter 81 with contact 8|. The parts are therefore returned to the position shown in the drawing.

Summarizing briefly, the sequence of operation is as follows: when there is no call for heat by either the space thermostat I05 or the temperature responsive controller I08 the oil burner I2 is inoperative, the ignition transformer 84 is inoperative, the on and off valve 28 is closed and the modulating valve 28 is in a minimum position. Also the draft or breeching damper is in a closed position to prevent losses to the stack, sometimes termed standby losses. When either the temperature responsive controller I08 or the space thermostat I08 calls for heat the relay I54 is pulled in and the draft or breeching damper Y 88 is moved to a wide open position. When the damper 88 moves to the wide open position, the oil burner I2 and the ignition transformer 84 are operated and the valve 28 is opened providing the modulating valve 28 is in minimum position. This proviso is extremely beneficial since in large installations it is not desirable to start up an oil burner with too large a flow of fueloil since serious explosions may occur. When the oil burner I2 is placed in operation the proportioning motor 82 which positions the modulating valve 28 is placed under the control of the pressure controller "2 and the valve 28 is modulated in accordance with variations in steam pressure to maintain the steam pressure substantially constant when the system is in operation. As

soon as the oil burner I2 is placed in operation a maintaining circuit for the oil burner I2 is established, which maintaining circuit is in parallel with the switch 80 operated by the floating motor I0 and the switch 4I operated by the proportioning motor 32. Therefore the oil burner I2 may be maintained in operation even though the draft damper 88 is moved away from the wide open position or the valve 28 is moved from the minimum position.

After combustion has accordingly been established the draft damper 68 is moved out of the wide open position and placed under the control of the pressure regulator 94 to maintain the draft through the boiler I0 substantially constant whereby the system operates most efliciently. When the system is operating, the draft through the boiler I0 is maintained substantially constant and the fuel supply to the oil burner I2 is modulated in accordance with the variations in steam pressure. When the space temperature becomes satisfied and when the temperature responsive controller I08 becomes satisfied the oil burner is stopped, the valve 28 is closed, the valve 28 is returned to its minimum position, and the draft or breeching damper 88 is moved to -a closed position.

Since in starting the system thevalve 28 is in the minimum position, a large supply of fuel cannot be supplied to the oil burner l2 when the. oil burner i2 is started up, since it is impossible to start the oil burner l2 until the breaching damper 66 is wide open and since it is impossible to place the breeching damper 56 under automatic con trol until combustion has been actually established, an extremely safe mode of operation is provided. The provision of the low water out off I39 and the high pressure controller III which shut down the system during abnormal water level and steam pressure conditions also adds to the safety of the system. I

Since the fuel supply to the oil burner I2 is modulated in accordance with the load on the boiler, since the draft damper 66 is positioned in accordance with the draft through the boiler when the system is operating and since the draft damper 56 is closed when the system is out of operation an extremely eflicient mode of operation is provided. These features when taken in combination with each other form a control sys--,

tem whichgives safe and efficient control of a boiler.

Although for purposes of illustration I have shown one form of my invention, other forms thereof may become apparent to those skilled in the art upon reference to this specification and therefore this invention is to be limited only by the scopeof the appended claims and prior art.

I claim:

1. In a control system for a furnace having fuel supplying means and damper means, the combination of, control means for moving the damper means to a wide open position to provide unobstructed draft through the furnace, means associated with the damper means for starting operation of the fuel supplying means and igniting the fuel when the damper means reaches a wide open position, means for maintaining the fuel supplying means in operation even though the damper means is moved away from the wide open position, means for controlling the damper means in accordance with the draft through the furnace, and means responsive to the establishment of combustion in the furnace for placing the damper means under control of the draft responsive control means.

2. In a combustion control system, in combination, means forming a combustion chamber, means comprising a first valve and a second valve in series therewith for controlling a supply of fuel for the combustion chamber, said first valve having a minimum open position, switch means associated with said first valve, said switch means being closed when said first valve is in minimum position, control apparatus comprising means for causing said second valve to open provided said switch is closed and means and supervisory combustion responsive control means associated with said automatic means and control means whereby said draft responsive means are in active control during the progress of combustion and in the absence of combustion during a demand for operation of the system said control means are in control for maintaining said damper means wide open responsively to said automatic means.

4. In a combustion control system, in combination, a combustion chamber having damper means controlling the eduction of gases therefrom, fuel supply control means and automatic means for initiating operation of the system, control means responsive to said automatic means for closing said damper means when the system is shut down and for opening said damper means wide open when operation of the system is to begin, means associated with said damper means whereby operation of said fuel supply control means is dependent upon said damper means being in wide open position, draft responsive means for variably adjusting said damper means during operation, and supervisory combustion responsive control means associated with said'automatic means and control means whereby said draft responsive means are in active control during the progress of combustion and in the absence of combustion during a demand for operation of the system said control means are in control for maintaining said damper means wide open responsively to said automatic means.

5. In a combustion control system, in combination, a combustion chamber having damper means controlling the eduction of gases therefrom, fuel supply control means and automatic means for initiating operation of the system,

control means responsive to said automaticmeans for closing said damper means when the system is shut down and for opening said damper means wide open when operation of the system is to begin, means associated with said damper means whereby operation of said fuel supply control means is dependent upon said damper means being in wideopen position, draft responsive means for variably adjusting said damper means during operation, supervisory combustion recombustion responsive control means.

responsive to the establishment of combustion of fuel supplied by said valves for completing an electrical circuit whereby said second valve remains open independently of said switch.

3. In a combustion control system, in combination, a combustion chamber having damper means controlling the eduction of gases therefrom, fuel supply control means and automatic means for initiating operation of the system, control means responsive to said automatic means for closing said damper means when the system is shut down and for opening said damper means wide open when operation of the system is to begin, draft responsive means for variably adjusting said damper means during operation,

6. In a combustion control system, in combination, means forming a combustion chamber, means comprising a first valve and a second valve in series therewith for controlling a supply of fuel for the combustion chamber. said first valve having a minimum open position, switch means associated with said first valve, said switch means being closed when said first valve is in minimum position, control apparatus comprising means for.causing said second valve to open provided said switch is closed, means responsive to the establishment of combustion of fuel supplied by said valves for completing an electrical circuit whereby said second valve remains open independently of said switch, means for variably adjusting said first valve and means whereby said adjusting means actively controls said first valve in response to establishment of combustion.

7. In a combustion control system, in combination, means forming a combustion chamber, means comprising a first valve and a second valve in series therewith for controlling a supply of fuel for the combustion chamber, said first valve having a minimum open position, switch means associated with said first valve, said switch means being closed when said first valve is in minimum position, control apparatus comprising means for bringing about opening of said second valve and operating said system provided said switch means are closed, and means responsive to a condition within the combustion space produced as an incident to starting of the system and dependent upon said switch having been closed for completing an electrical circuit whereby said second valve is rendered independent of said switch.

8. In a combustion control system, in combination, means forming a combustion chamber, means comprising a first valve and a second valve in series therewith for controlling a supply of fuel for the combustion chamber, said first valve having a minimum open position, switch means associated with said first valve, said switch means being closed when said first valve is in minimum position, air flow varying means, control appa-' ratus for bringing about operation of said air fiow varying means, and for bringing about opening of said second valve provided said switch means are initially closed, said control apparatus inciuding'means responsive to operation of said air flow varying means for producing an operating condition in said combustion space, and

means responsive to said condition for rendering said second valve independent of said switch means.

WAYLAND R. MILLER.