US2470996A

US2470996A - Burner control system

Info

Publication number: US2470996A
Application number: US463340A
Authority: US
Inventors: William L Mcgrath
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1942-10-26
Filing date: 1942-10-26
Publication date: 1949-05-24
Anticipated expiration: 1966-05-24

Description

May 24, 1949. w. MCGRATH BURNER CONTROL SYSTEM Filed Oct. 26, 1942 Patented Mey 24, 1949 BURNER CONTROL SYSTEM William L. McGrath, Philadelphia, Pa., assilnor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware ApplicationOctober 26, 1942, Serial No. 463,340

Claims. (Cl. 236-1) The present invention is concerned with a burner control system and more particularly one of the type in which the burners are placed directly in an air stream of a Ventilating duct.

An object of the present invention is to provide a burner control system in which a plurality of fluid circulating means are provided for circulating heating fluid in heat transfer relation with a burner and in which means are provided for supplying fuel to the burner only when more than a predetermined number of such fluid circulating means are in operation.

A further object of the present invention is to Y provide a burner control system employing a plurality of burners in which means is provided for varying the fuel iiow to all of said burners, and in which an individual valve is provided for each burner, with means for closing all of the individual valves when the common fuel flow adjusting means assumes a predetermined minimum position.

A still further object of the present inveftion is to provide an arrangement such as set forth p in the last object in which individual valves are sequentially closed upon the main flow controlling means moving towards closed position and in Y which the individual valves are sequentially opened upon the minimum flow controlling means moving towards open position.

A still further object of the present invention is 'to provide a burner control system of the type discussed in the last two objects in which the means for controlling the individual valves is characterized by a relatively wide differential so that the valves are sequentially opened when the minimum flow controlling means is nearer open position than when the individual valves are sequentially closed.

A still further object of the invention is to provide a burner control system in which burners are located directly in an air stream being circulating to a space to be conditioned and in which provision is made for interrupting the ow of Other objects of the invention will be apparent from a consideration of the specification, claims and drawing in which the single figure is a schematic representation of my improved burner control system.

Referring to the drawing for a more detailed understanding of the invention, the reference numeral In is employed to indicate a Ventilating duct. As indicated by the arrows adjacent the inlet and outlet of the duct I0, the air is drawn in at the left-hand end of the duct lll and is forced out at the right-hand end thereof. The air is circulated through the duct by a plurality of propeller fans Il to 2 I, these fans being driven by motors 22 to 25. While the fans have been shown for convenience in illustration as disposed one above the other, it is to be understood that these fans will normally be arranged symmetrically of the duct. Located within the duct are a plurality of gas burners Il, l2, I3 and Il. The burners Il and |22 constitute one bank of burners and the burners I3 and Il a second bank of burners. While only two burners have been shown in each bank. it is to be understood that f each bank may consist of any desired number of burners. Associated with the bank of burners comprising burners il and l2 is a pilot burner i5. A similar pilot burner I3 is associated with the other bank of burners consisting of burners I3 and I4,

The burners Il, I2, I3 and I4 are connected by pipes 28, 29, 30 and 3| to a main gas supply pipe 32. Interposed in the pipes 28, 29, 30 and 3l are electrically operated valves 33, 34, 35, and 36. The valves 33 to 36 are of any suitable type which assume a closed position upon the operators being deenergized and winch move to an open position upon their operators being energized and remain in such position as long as such energization continues. The valves 33 to 36 serve individually to control the now of gas to the burners Il to I4. The flow of gas through main gas conduit 32 is controlled by a pneumatic valve 39. This valve is of the type in which an increase in the pressure of the pneumatic fluid moves the valve towards open position. Since the construction of the valve is entirely conventional, a detailed description thereof is deemed unnecessary.

The flow of fuel through conduit 32 is further controlled by an electrically operated valve 40. The valve 40 may be of any type in which the 'valve is maintained open only during the energization of the operator and moves to closed position as soon as the operator is deenergized. Associated with the gas conduit 32 on the inlet side of the valve 40 is a low pressure cut-olf switch 4|. This comprises a pressure chamber 42 operatively connected to a mercury switch 43. The pressure chamber is so related to the mercury switch 43 that as long as the pressure within conduit 32 is above a predetermined value, switch 43 will remain in closed position. Upon the pressure dropping below the predetermined value, however, the mercury switch 43 will move to open position. The low pressure cut-off switch 4|, as will be explained later, is employed to interrupt operation of the system when the gas pressure drops to an undesirably low value.

Connected in parallel with the pneumatic valve 39 by

pipes

45 and 46 is a conventional pressure regulating valve 44. 'I'his pressure regulating valve 44 serves to maintain a predetermined minimum pressure in pipe 32 regardless of the position of the pneumatic valve 39 to insure safe operation of any of burners |||4 whenever its respective solenoid valve is opened. It will be obvious that even when valve 39 is completely closed, it is possible for fuel to be supplied to the downstream portion of pipe 32 through valve 44, this fuel being at the pressure for which pressure regulator 44 is set, said pressure being the minimum at which the burners will properly operate.

The pilot burners l and I6 are connected to a pipe 41 which is connected to the main gas supply pipe 32 on the upstream side of the low pressure cut-off 4|. The flow of gas through pipe 41 and hence to the pilot burners l5 and I6 is controlled by a valve 48 which may be of the solenoid type.

The operation of the fan motors 22 to 25 is controlled by a plurality of fan switches comprising

switch blades

49, 50, 5| and 52. These switch blades 49 to 52 are adapted to be moved into or out of engagement with the associated fixed contacts 53, 54, 55 and 56. The switch blades 49 to 52 may be actuated by any suitable means.

Switch blades 49 to 52 also control the energization of a plurality of

relays

58, 59, 60 and 6|. The relay 58 comprises a relay coil 62 and a plurality of switch blades 63, 64, and 65. The switch blades 53, 64 and 65 are adapted to engage contacts 66, 81 and 88, respectively. The switch blades 63 to 65 are normally biased out of engagement with contacts 69 to 68 by any suitable means (not shown). Upon energizatlon of the relay coil 52, the switch blades 53 to 65 are moved into engagement with contacts 66 to 68.

The relay 59 comprises a relay coil 10 and a single switch blade 1| which cooperates with a fixed contact 12. As with relay 58, the switch blade 1| is biased out of engagement with ecntact 12 and is adapted to be moved into engagement therewith upon the energization of relay coil 10.

The relay 60 comprises a relay coil 13 and a pair of switch blades 14 and 15 which are adapted to cooperate with contacts 18 and 11, respectively. Switch blades 14 and 15 are s'imilarly biased out of engagement with contacts 16 and 11 and are moved into engagement therewith upon energization of coil 13.

Relay 8| comprises a relay coil 18 and a single switch blade 19 adapted to be moved into engagement with xed contact 80 upon energization of relay coil 18.

Associated with the pilot burners I5 and IB are ignition electrodes 82 and 83. The ignition electrodes 82 and 83 are connected to ignition transformers 84 and 85. The ignition electrode 82 is connected to one secondary terminal of transformer 84 by a conductor 86. The other secondary terminal of the ignition transformer is connected to ground at B1. The pilot burner I6 is also connected to ground as indicated by the numeral 88. Similarly, the ignition electrode 83 is connected to one secondary terminal of ignition transformer by conductor 89. The other secondary terminal of transformer 85 is connected to ground at and the burner I6 is connected to ground at 9|.

A flame detecting apparatus 92 is associated with pilot burner I5 and a similar flame detecting apparatus 93 is associated with burner |6. These llamey detecting apparatuses 92 and 93 are of the electronic type in which the presence or absence of a llame is determined by the conductivity of a gap normally bridged by the pilot burner flame. The details of the apparatus have not been shown inasmuch as this type of ame detecting apparatus is well known in the art. A typical apparatus of this type is that shown in the Harrison Patent No. 2,224,119 granted December 3, 1940, The llame detecting apparatus 92 is provided with a pair of

power supply terminals

95 and 96, a ground terminal 91, and a flame electrode terminal 98. 'I'he ame electrode terminal 98 is connected by a conductor 99 to a flame electrode |00 disposed adjacent the. pilot burner |5. Associated with the apparatus 92 are a pair of relay switch blades |02 and |03. Switch blade |02 is adapted to be moved into engagement with a contact |04. The relay switch blade |03 is normally in engagement with a contact |05 and is adapted to be moved into engagement with a contact |06 upon the gap between llame electrode |00 and pilot burner l5 being bridged by a burner flame such as happens when pilot burner |5 is properly ignited. The mechanism for operating switch blades |02 and |03 is not shown, since this mechanism is conventional, as previously explained.

The flame detecting apparatus 93 comprises a pair of power supply terminals |08 and |09, a ground terminal ||0 and a flame electrode terminal The fia-me electrode terminal is connected by means of a conductor |2 to a flame electrode ||3 disposed adjacent the burner |6. Also associated with apparatus 93 are a pair of switch blades ||4 and H5. The switch blade ||4 is adapted to be moved into engagement with a fixed contact ||8. The switch blade ||5 is normally biased into engagement with a xed contact ||8 and is adapted to be moved into engagement with a contact I9 upon the gap between flame electrode ||3 and burner I6 being bridged by a burner name.

A pair of push button switches are provided for starting and stopping the system. One of these switches is a normally closed switch and comprises a, switch blade |22 'biased into engagement with a pair of contacts |23 and |24. Upon the push button being held inwardly, the blade |22 is held out of engagement with contacts |23 and |24. The other push button switch is a normally open switch and comprises a switch blade |26 adapted to be moved into engagement with contacts |21 and |28 upon the push button being moved inwardly.

A thermal timer |30 is provided for delaying the supply of fuel to the pilot burner until the fans |8 to 2| have been in operation for a pre determined period of time. This timer com-v prises a bimetallic element I 9| with which is assoelated an electric heater element |82. The bimetallic element is adapted to warp to the right upon being heated by heater |32. The bimetallic element |3| carries a contact |32 which is adapted to be engaged with a ilxed contact |34 upon the bimetalllc element being warped to the right. Such engagement of contacts |23 and |34 occurs a predetermined period of time after the initial energization of heater element |22.

A plurality of switches responsive to limiting conditions are provided for preventing a supply of fuel to the burners when the various limiting conditions assume undesired values. The low pressure cut-out switch 4|, previously referred to, is one of these switches. Another such switch is designated by the reference numeral |49. This switch comprises a mercury switch |4| which is positioned by a bellows |42 connected by capillary tubing |43 to a bulb |44 located outside of the space being conditioned. The switch |4| is biased by a spring |45 to switch open position. As long as the temperature outside the space, to which bulb |44 is subjected, is above a predetermined value, the bellows |42 is eilective to hold switch |4| in closed position, as lshown in the drawing. Upon the outside temperature dropping below this predetermined value, however, the biasingy spring |45 ls effective to move switch |4| to open position. While the value of this predetermined temperature will vary in accordance with the particular application of the burner control system, I have found it desirable in certain types of applications to have the switch set for a temperature of approximately 65.

A further limiting switch is designated by the reference numeral |58. This switch is a high limit switch and comprises a switch |5| positioned by a bellows |52 to which is connected a fluid filled bulb |53. The bulb |53 is located in the path of the air leaving duct I and responds to the temperature of this discharge air. The switch is biased to closed position by a spring |54. Upon the temperature of the discharge air rising above a predetermined high limit value, the switch |5| is moved to open position `against the biasing action of spring |54.

A transformer |55 is employed to supply low voltage power for controllingthe electrical portion of the system. This transformer comprises a low voltage secondary |56 and a line voltage primary |51. The line voltage primary is connected to line Wires |58 and |59 leading to any suitable source of power (not shown).

As previously indicated, the valve 39 is controlled pneumatically.' Pneumatic means is also provided for controlling the energization of valves 33 to 36. The pneumatic portion of the system will now be described.

Air or other pneumatic fluid at a desired pressure such as pounds ls supplied to pipe |69 .from any desired source. A suitable restricting means |6| is located in the pipe. Connected to the pipe |60 is a branch pipe |62 terminating in a nozzle I 63 of a conventional pneumatic thermostat |19. Since this thermostat is entirely conventional and forms no part of the present invention, it has been shown schematically. In this schematic showing, a flapper valve |64 cooperates with the nozzle |63. The ilapper valve |64 forms an element of a bell-,crank lever |65. Cooperating with the other arm of the bell-crank lever |65 is a bellows |66 which is connected by capillary tubing |61 to a volatile iluid-lied bulb |68 located in the path of the air discharging from duct I9.

A plurality of pneumatic electric relays IBI, |82, |83 and |84 are provided for controlling the energization of solenoid valves 33 t-o36. The relay |8| comprises a bellows element |85 which is associated with a bell-crank lever |86. The right-hand end of the horizontal arm of the bell-crank lever is biased downwardly by a spring |89. The other arm -of the bell-crank lever is associated with a switch carrier |89 having a pair of spaced arms |90 and ISI. The carrier |80 carries a mercury switch |93.- The cooperating arm of the bell-crank lever |86 is adapted upon rotation of lever |86 to move the switch |93 between circuit-open and circuit-closed positions. The bellows |85 is connected by a conduit |95 to the conduit |19 so that the pressurewithin thel bellows I 85 corresponds to the pressure within conduit |19. It will be obvious that as this pressure rises, the bell-crank lever |8|B will be rotated in a counter-clockwise direction and as the pressure falls, the spring |88 will .be effective to rotate lever |86 in a clockwise direction. Upon the lever |86 being rotated in a counter-clockwise direction, the upstanding arm of lever |86 will engage the nger |99 to rotate switch |93 in a clockwise direction to circuit closed position. When, on the other hand, the lever |86 is rotated in a clockwise direction, the upstanding arm will engage nger |9| to rotate switch carrier |89 in a counter-clockwise direction to move switch |89 to circuitl open position. It will be apparent that after switch |93 has been once closed, it will not be moved to open position until the upstanding arm of bell-crank lever |86 has moved through a distance determined by the spacing of fingers and |9|. The spacing -of fingers |99 and |9| thus determines the differential of the switch or the difference between the pressure at which the switch is closed and the pressure at which the switch is opened.

A detailed description of relays |82, |83 and 7 |04 is not believed necessary in view of their similarity to relay III. I'hese relays comprise

mercury switches

200, 20| and 202 which are actuated by

bellows

204, 205 and 235 in the same manner as described in connection with relay |3|. As with the case of relay |8|. there is a predetermined diierential between the pressure at which the switch is closed and the pressure at which it is reopened. The four relays to |04 are adjusted so that they are operated at dierent values. This is indicated in the drawing by showing these switches tilted to different degrees. Thus, as the pressure rises due -to an increase in temperature, switch 202 will iirst be closed due to the fact that it is initially tilted less from the horizontal. Upon a further drop in pressure in conduit |19, switch will be closed. As the pressure rises, switches 200 and |93 will be successively closed. As the temperature adjacent bulb |58 again drops, the switches will sequentially open. Upon such a drop in temperature. switches |93, 200, 20| and 202 will be successively opened.

'The lingers of the relays |8| to |84 are so ad- A,iustedwith respect to the mechanism oi the relaysand the pneumatic valve 39 that the switches |93, 200, 20| and 202 are not opened until the valve 39 is nearly in full open position. As the temperature drops, however, the switches |93, 200,

20| and 202 are not reopened until the valve is in in the position they assume when the system is completely shut down.4 Before any of the elements of the system can be placed into operation, it is necessary to close the circuits to at least two of the fan motors 22 to 25. Let it be assumed tha-

t switch blades

49 and 50 are engaged with contacts 53 and 54. The engagement oi.' switch blade 49 with contact 53 establishes a circuit to fan motor 25 as follows: from the line wire |58 through conductor 2|0, switch blade 49, contact 53, conductors 2|| and 2|2, fan motor 25, and conductors 2 I3 and 2|4 to the other line wire |59. At the same time, an energizing circuit is established to the relay coil 52 as follows: from line wire |58 through conductor 2| 0, switch blade 49, contact 53, conductors 2|| and 2i5, relay coil 52, and conductors 2|1, 2|8, and 2|4 to the other line wire |59. The establishment of the circuitA just traced to fan motor 25 causes fan 2| to be placed in-to operation. The energization of relay coil 52 by reason of the circuit just traced causes switch blades 53, 54, and 65 to be moved into en- -gagement with contacts 56 tov 58. The engagement of these contacts alone does not result in the establishment of any energizing circuit, however.

Engagement of switch blade with contact 54 establishes the following energizing circuit to fan motor 24 to cause operation of fan 20: from line Wire |58 through conductor 220, switch blade 50, contact 54. conductors 22| and 222, fan motor 24, and conductors 225, 225, 2|3 and 2|4 to the other line wire |59. At the same time, an energizing circuit is established to relay coil 10 as follows: from line wire |58 through conductor 20, switch blade 50, contact 54, conductors 22| and 228, relay coil 10, and conductors 229, 230, 2 I8 and 2 I4 to the other line wire |59. The establishment of the circuit just traced to relay coil 10 causes contact blade 1| to be moved into en sagement with contact 12. A

yiN)

It will be noted 'that two of the relays 50 to 5| have now been energized. Upon any two of these relays being energized. itis possible to establish a circuit to the electrical heating element |32 'of timer |30. The following circuit is established upon theenerglzation of relay coils 52 and 1l, as hasjust been described. From the right-hand terminal of secondary through conductors 233, 234 and 235, contact 12, contact blade 1l, conductors 235 `and231, contact blade 53, contact 55, conductors 238 and 239, heating element |32and conductors 24|, 242, 24,3, 244, 245, 243. 241, 248, 249, and 250 to the other terminal of secondary |55. It will be noted that the circuit Just traced to heating element |32 depended upon the establishment of a conductive path between conductors 233 and 239. The various relay switches of relays 58 to 5| are so arranged that it is necessary to have two relays energized before a. circuit can be established between conductors 233 and 239. Before proceeding with the further description oi' the operation of the system, various possible circuits between the conductors 233 and 239 and the conditions under which they are established will be considered in more detail.

Let it be assumed that insteadof switches 43 and 50 being engaged with contacts 53 and 54, switches 49 and 5| will engage with their associated contacts. The engagement of switch 43 with contact 53, of course, causes energization of the fan motor/25/and the relay coil 52 in the manner previ/ousjl described. Engagement of switch bladgy/fr'r/with contact 55 results in the following/fdiruit being established to fan motor 23: from line wire |58 through conductors 253. switch blade` 5|, contact 55,

conductors

The energization of relay coil 13 results in switch blades 14 and 15 being moved into engagement with contacts 15 and 11. Relay coils 52 and 13 are now energized. Under these conditions, it is possible to trace a circuit between conductors 233 and 239 asfollows: from con.

ductor 233 through conductor 255, contact 11, switch blade 15, conductors 255 and 251, switch blade 55, Contact 68, and conductors 259 and 210 to conductor 239. The establishment of this connection again makes possible the establishment of a circuitto heater coil |32.

If, on the other hand, switch blades 5| and 52 are closed, it is also possible to establish a circuitbetween conductors 233 and 239. The effect of the closure of switch blade 5| with its contact 55 has been discussed. When switch blade 52 is engaged with contact 55, the fan motor 22 is energized through the following circuit: from line wire I 58, through conductor 212, switch blade 52, contact 56, conductors 213 and 214, fan motor 22, and conductors 215, 251, 225, 2|3, and 2 I4 tothe other line wire |59. At the same time, a circuit is established to relay coil 19 as follows: from line wire |58 through conductor 212, switch blade 52, contact 55, conductors 213 and 211, relay coil 18, and conductors 219, 25|, 230, 2|8 and 2|4 back to the other line wire |59.' Fans |8 and i9 will now-be in operation and relay coils 13'a'nd'15 will be energized. Under these conditIons, it is possible for a circuit to be established between conductors 233 and 239 as follows: from conductor 233 through conductor 265, contact 11, switch blade 15, and conductors 266, 230 and 28|,

v switch blade 19, contact 88, and conductors 282,

conductors 234 and 235, contact 12, switch blade 1|, conductors 236, 285 and 286, switch blade 14, contact 16, and

conductors

281, 283 and 218 to conductor 239. Again, a circuit is established to heater |32. If fans I8 and 2| are the ones that are operated, relay coils V18 and 62 will be energized and a circuit will be established between conductors '233 and 239 as follows: from conductor 233 through conductors 234 and 289, contact 61, switch blade 64, conductors 298 and 28|, switch blade 1I, and

conductors

282, 283 and 218 to conductor 239. Again, a circuit is established to heater |32,

It will be seen from the foregoing paragraphs that regardless of which two fans are energized a circuit -is established between conductors 233 and 239 so as to. cause a circuit to be established through heater |32, the remainder of this circuit being identical to that first traced. It is to be furthermore noted that this circuit through heater element |32 can only be established upon the closure of at least two fan switches. Each one of the circuits which was traced above included the relay contacts of two separate relays.

Upon heater |32 being energized as a result of the establishment of any of the above circuits, the bimetallic element |3| is heated so as to warp to the right. After a predetermined period of time this warping results in the engagement of contacts |33 and |34. The engagement of contacts |33 and |34 results in the establishment of the following circuit upon the engagement of push button switch blade |28 with contacts |21 and |28: 4from the right-hand terminal of secondary |56 through conductor 233, through any of the combinations of relay circuits previously traced to conductor 239, bimetallic element I3I, contact |33, contact |34, conductor 295, low pressure cut-out switch 43, conductor 296, outdoor temperature responsive switch I4 I conductor 291, high limit switch I5I, conductor 298, contact |24,

'switch blade, |22, contact |23, contact |28, switch blade |26, contact |21, conductors 299 and 388, solenoid valve 48, and conductors 38|, 243, 244, 245, 246, 241, 248, 249, and 258 back to the other terminal of secondary |56. The energization of solenoid valve 48 as a result of the establishment of this circuit, causes gas to ilw to the pilot burners |5 and I6. At the same time, a circuit is established to the primary of ignition transformer 84 as follows: from the right-hand terminal of secondary |56 through conductor 233, through the relay circuits previously traced to conductor 239, bimetallic element I3I, contacts |33 and |34, conductor 295, switch 43, conductor 296, switch |4I, conductor 291, switch I5I, conductor 296, contact |24, switch blade |22, contact |23, contact |28, switch blade |26, contact |21, conductors 299, 383, 384, switch blade II5, conl0 tact |I8, conductors 381, 388 and 388. the primary of ignition transformer 84, conductors 3|8, 3| I, 248 and 258 back to the other terminal of secondary |56. It is also possible to establish a similar circuit through switch blade |83 and contact |85. This circuit will be traced only from switch contact |21. Proceeding from this contact, current may flow through conductors 299, 383, 3I5, 3I2, and 3I3, switch blade |83, contact |85, conductors 3I4 and 389, the primary oi' ignition transformer 34, and conductors 3|8, 3| 249 and 258 back to left-hand terminal of secondary |56. It will be obvious that the primary oi' ignition transformer 85 is connected in parallel with the primary of ignition transformer '84. Thus the two ignition transformers are energized simultaneously so that an ignition spark is produced between ignition electrode 82 and pilot burner I5 and also between ignition electrode 83 and pilot burner I6.

As a result of the establishment of the circuits traced, gas is supplied to the pilot burners vI5 and I6 and an ignition spark is produced for igniting these pilot burners. Under normal conditions-the pilot burners I 5 and I6 will be quickly ignited. The flame detecting apparatus 92 is designed to detect the establishment of a iiame at the pilot burner l5 and the flame detecting apparatus 93 is designed to detect the establishment of a llame at pilot burner I6. The movement of push button switch blade |28 into engagement with contacts |21 and |28 also caused energizing circuits to be established to the power supply terminals of the two flame detecting apparatuses. Tracing the circuits only from contact |23 of the normally closed push button switch, a circuit is established through the

power supply terminals

95 and 96 of apparatus 92 as follows: from contact |23 through contact |28, switch blade |26, contact |21,

conductors

299, 383, 3|5, 3|,2 and 3|1,

input terminals

conductors

299, 383, 3| 5, and 328, power supply terminals |89 and |88, and conductors 32|, 3I9 and 258 to the left-hand terminal of secondary |56.

'I'he operator will maintain switch blade |26 engaged with contacts |21 and |28 until the apparatuses 92 and 93 have indicated the establishment of a flame by the movement of switch blades |82, |83, II4 and ||5 from the position shown to their other circuit making positions. Usually such an apparatus is provided with a signal light to indicate when this has happened. As soon as switch blades |82, |83, I|4 and |I5 have moved to their opposite circuit making positions, it is possible for the operator to release switch blade I 26 and the solenoid valve 48 will remain enerare terminated, however, as soon as switch blades |03 and ||5 move out of engagement with contacts |05 and |8. It will be noted that the ignition circuits proceed through the contacts |05 and ||8 in parallel so that as soon as both switch blades |03 and I|5 have separated from these contacts, the ignition circuit is completely interrupted regardless of whether push button switch blade |26 is in engagement with the contacts |27 and |28 or not.

A permanent circuit is also now established to the power supply terminals of the flame detecting apparatuses 92 and 93. The circuit to

terminals

power supply terminals

A circuit is now established to the electropneumatic relay |12. This circuit will be traced from the contact |23 of the normally closed push button switch and is as follows: from contact |23, through conductor 324-, contact H6, switch blade H4, conductor 325, contact |06, switch blade |03, conductors 3|3, 3|2, 3|5 and 304, switch blade H5, contact H9, 'conductor 330, switch blade |02, contact |04, conductors 33|, and 326, coil |15 and conductors 321, 248, 249 and 250 back to the left-hand terminal of secondary |56. The establishment of the above traced circuit results in the electro-pneumatic relay being moved to open position so that the pressure existing in the line |1| is caused to exist in line |19. Thus, the pressure in line 19 assumes a value determined by the discharge temperature responsive thermostat |10. Under normal conditions, this discharge shut down will be suiliciently low that valve 39 will move to a partially open position, at least.

A circuit is now also established to the main shut-off valve 40. Again, this circuit will be traced only from closed push button switch. This circuit is as follows: from contact |23, through conductor 324, contact H6, switch blade H4, conductor 325, contact |06, switch blade |03, conductors 3|3, 3|2, 3|5, and 304, switch 4blade H5, contact ||9, conductor 330, switch blade |02, contact |04, conductors 33| and 332, shut-off valve 40,

conductors

333, 242, 243, 244, 245, 246, 241, 248, 249 and 250 back to the left-hand terminal of secondary |56.

The establishment of the above circuit causes shut-off Valve 40 to be opened so that gas is suppliedto the inlet side of pneumatic valve 39. Since the rise in pneumatic pressure following the energization of the relay |12 takes much longer than the opening of valve 40, pneumatic valve 39, initially closed, will gradually open. This prevents a sudden increase in the gas iiow to the burners. Even with pneumatic valve 39 completely closed, a certain minimum ilow of gas will temperature following a the contact |23 ofthe normally 12 be established through pipe 45, pressure regulator 44, and pipe 46 to the gas supply pipe 32. With the various elements of the pneumatic system in the position shown in the drawing, however, all of the solenoid valves 33 to 36 will be closed so that no gas may flow through the individual burners. Let it be assumed now that the temperature adjacent bulb |63 drops so as to increase the pressure continually in pipe |19. As this pressure continues to increase, valve 39 will move to open position. As it approaches open position, switches 202, 20|, 200 and |93 will be successively moved to closed position, as previously described. The movement of switch 202 to closed position will cause an energizing circuit to be established to solenoid valve 36 as follows: from the right-hand terminal of secondary |56 through conductor 334, switch 202, conductor 335, solenoid valve 36, and

conductors

336, 241, 248, 249 and 250 to the left-hand terminal of secondary |56, The energization of solenoid valve 36 permits gas to now through conduit 3| to burner I4, this gas being ignited by the pilot burner I6.

The closure of switch 20| causes the following circuit to be established to solenoid valve 35: from the right-hand terminal of secondary |56 through

conductors

334 and 338, switch 20|, conductor 339, solenoid valve 35, and

conductors

340, 246, 241, 248, 249, and 250 back to the left-hand terminal of secondary |56. The energization of solenoid 35 results in burner 3 being placed in operation.

A closure of switch 200 causes the following circuit to be established to solenoid valve 34: from the right-hand terminal of secondary |56 through conductors334, 338, 342, switch 200, conductor 343, solenoid valve 34, and conductors 344 and 245 to 250 back to the left-hand terminal of secondary |56. The energization of solenoid valve 34 results in burner I2 being placed in operation.

The closure of switch |93 results in the establishment of the following energizing circuit to solenoid valve 33; from the right-hand terminal of secondary |56 through

conductors

334, 338,

342, and '345, switch |93, conductor 346, solenoid valve 33, conductor 341, and conductors 244 to 250 back to the left-hand terminal of secondary |56. The establishment of the traced circuit causes energization of solenoid valve 33 so that burner il is placed in operation.

In the above paragraphs, it has been assumed that all of the burners were brought into operation sequentially. It is of course entirely possible for the temperature to assume an intermediate valve at which only burners I3 and I4, for example, are placed into operation. In any event, the burners will raise the temperature of the air being circulated through the duct I0 by those of the fans I8 to 2| in operation. This will cause a rise in the discharge temperature to which bulb |68 is subjected so as to cause the pressure within conduit |19 to decrease. A decrease in pressure will result in pneumatic valve 39 being moved towards closed position so as to reduce the ow of gas to the burners. Any tendency of this to decrease the discharge temperature will cause a rise of the pressure in tube |19 so as tocause pneumatic valve 39 to move back towards open position. It can be readily seen that under normal circumstances, the ilow of gas to the burners will be modulated so as to maintain a substantially constant discharge temperature, The number of burners in opera- 13 tion will depend to a large extent upon the heating load.

Under normal conditions, the burners will continue to remain in operation as long as it is desired to have the system operating. The flow of gas will be modulated tothe burners in the manner described. If the temperature of the discharge duct rises suiilciently high as to cause the pneumatic valve 39 to approach its minimum position, however, the valves 33 to 36 will be successively closed. Thus, as this discharge temperature rises, the pressure Within pipe |19 will decrease to decrease the pressure within bellows |85, 204, 205, and 206. This will successively cause reopening of switches |93, 200, 20|, and 202 and closure of valves 33 to 36. This will, as indicated above, not occur during normal circumstances and will occur only when there is a major change in load as indicated in a rise or fall of outside temperature or by a variation in the amount of air handled by the system.

When any one burner is placed out of operation due to a rise in discharge temperature, there will be a consequent reduction in discharge temperature which will cause the pneumatic valve 39 to open slightly again and increase the iiow of gas to the burners remaining in operation so that the system will balance oi again but with fewer burners in operation. The fact that the pneumatic electric switches |8| to |84 are set with a relatively wide differential is very important in preventing short cycling of the system. If this differential were too narrow, the solenoid valves 33 to 36 would be continually opening and closing. The result is that the discharge temperature would be continually varying. By providing these valves with a wide differential, the control of the discharge temperature is, under normal circumstances, taken care of solely by adjustment of the pneumatic valve 39.

If during the operation of the burners, any of the various limiting conditions occur, the system will be immediately shut down. For example, if the gas pressure falls below a predetermined minimum value, the switch 43 will be opened. The opening of this switch will interrupt all of the circuits traced through push button switch |22, which circuits include all of the switches to the various valves and to the ame detecting apparatus. The result is that the entire system will be shut down until the gas pressure is restored' to the desired value.

Again, if the outdoor temperature rises to a value such that operation of the system is no longer needed, switch |4| will move to an openA position. This again Will interrupt the various circuits traced so as to cause termination of the operation of the system. Again, if the discharge temperature rises to an unduly high value, switch 15| will opento interrupt the circuits to the

solenoid valves

40 and 49 and to terminate operation of the system.

If, at any time, either of the pilot burners I5 and I6 is extinguished, the switch blades of the particular flame detecting apparatus will move to their deenergized position. It will be noted that all of the circuits traced through the name de tecting apparatus involve the in contacts of both flame detecting apparatuses. As an added precaution. the circuit traced to the main shut-off valve 40 includes .both sets of in contacts of both of the flame detecting apparatuses. It will be obvious that as soon as either pilot burner is extingushed, the solenoid valves 40 and 48 will be closed to interrupt flow of gas to both the main and pilot burners.

Under all conditions, when the system has once been shut down, it is necessary to reclose switch |26 manually before the system can be again placed into operation.

It will be seen that I have provided a burner control apparatus in which provision is made for initially preventing the operation of the system unless at least two of a plurality of circulating fans are placed into operation. Furthermore, it will be seen that the apparatus provides for a delay after the fans have been placed into opera tion before the burners can be placed in operation. The system, furthermore, provides for modulation of the flow of gas to the burners with means for sequentially closing individual valves to individual burners as the main modulating valve is modulated below a minimum position. It will also be seen that provision is made for maintaining these individual valves closed until the main modulating valve reaches a position close to wide open position. This insures that gas will initially be supplied at substantially full pressure to the burners so that there will be no danger of the gas popping back in the mixer.

It will, furthermore, be seen that I have provided a system employing a combination of electric and pneumatic controls in such a manner as to reduce the apparatus to a minimum for the functions performed.

While I have shown a detailed embodiment of my invention, it is to be understood that this is for purposes of illustration and that my invention is to be limited only bythe scope of the appended claims.

I claim as my invention:

1. In a fluid fuel burner control system, a burner, an electrically operated shut-off valve for controlling the flow of fuel to said burner, a pneumatically operated valve for also controlling the ow of fuel to said burner, means responsive to a controlling condition indicative of the demand for burner operation for gradually controlling the pressure of the pneumatic uid associated with said pneumatically operated valve so as to cause said valve to be modulated between maximum and minimum open position, an electro-pneumatic relay for causing said pneumatically operated valve to move to minimum open position independently of said condition responsive means when deenergized, energizing means for both said 'electrically operated valve and said electropneumatic relay, andmeans including a main controlling switch effective when moved to one position to cause simultaneous deenergization of said electrically operated valve and said electropneumatic relay.

In a. fluid fuel burner control system. a plurality of burners, an electrically operated shut- 01T valve for controlling the ow of fuel to all of said burners, a pneumatically operated valve for also controlling the flow of fuel to all of said burners, means responsive to a controlling condition indicative of the demand for burner operation for gradually controlling the pressure of the pneumatic duid associated with said pneumatieally operated valve so as to cause said valve to be modulated between maximum and minimum 'open positions, further electrically operated valves individually controlling the flow of fuel to said burners, pneumatically operated switches controlling said further valves to cause them to open sequentially as the pneumatic pressure changes, an electro-pneumatic relay for causing said further valves to close and said pneumatically operated valve to move to minif mum position independently of said condition responsive means when said relay is deenergized, energizing means for both said electrically operated valve and said electro-pneumatic relay, and means including a main controlling switch effective when moved to one position to cause simultaneous deenergization of said electrically operated valve and said electro-pneumatic relay.

3. In a iiuid fuel burner control system, a burner, a conduit leading to said burner, a main controller for varying the flow of fuel to said conduit, and a pressure regulating valve connected in parallel with said main controller to maintain a minimum pressure of fluid in said conduit, said pressure being the minimum required for safe operation of said burner.

4 In a nuid fuel burner control system, a plurality of burners, a main conduit leading to all of said burners, means individual to each burner for individually controlling the ow of fuel from said conduit to said burners so as to vary the number of burners in operation, a main controller for varying the flow of fuel to said main conduit and hence to all of said burners, and a pressure regulating valve connected in parallel with said main controller to maintain a predetermined minimum pressure of fluid in said conduit sufficient to insure safe operation of said burner.

5. In a temperature control system, a duct leading from the outside to a space to be heated, controllable means circulating air from the outside to said space through said duct, a plurality of burners in said duct, an electrically operated shutolf valve for controlling the flow of fuel to all of said burners, a pneumatically operated valve for also controlling the ow of fuel to all of said burners, means responsive to a controlling condition indicative of the demand for burner operation for gradually controlling the pressure of the pneumatic uid associated Ywith said pneumatically operated valve so as to cause said valve to be modulated between maximum and minimum open positions, further electrically operated valves individually controlling the now of fuel to said burners, pneumatically operated switches controlling said further valves to cause them t0 open sequentially as the pneumatic pressure changes, ain electro-pneumatic relay for causing said further valves to close and said pneumatically operated valves to move to minimum position independently of said condition responsive means, energizing means for both said electrically operated valve and said electro-pneumatic relay,

means preventing energization of said valve and relay until means lor causing a predetermined circulation of air in said duct has been energized, and means including a main controlling switch effective when moved to one position to cause simultaneous deenergization of said electrically operated valve and said electro-pneumatic relay.

6. In a temperature control system, a duct leading from the outside to a space to be heated, controllable means circulating air from the outside to said space through said duct, a plurality of burners in said duct, means responsive to the temperature of the outside air, further means responsive to the temperature of the air leaving said duct, an electrically operated shut-off valve for controlling the flow of fuel to all of said burners, a pneumatically operated valve for also controlling the now of fuel to all of said burners,

means responsive to a controlling condition indicatlve of the demand for burner operation for gradually controlling the pressure of the pneumatic fluid associated with said pneumatically operated valve so as to cause said valve to be modulated between maximum and minimum open positions, further electrically operated valves individually controlling the ow of fuel to said burners, pneumatically operated switches controlling said further valves to cause them to open sequentially as the pneumatic pressure changes, an electro-pneumatic-relay for causing said further valves to close and said pneumatically operated valve to move to minimum position independently of said condition responsive means, energizing means for both said electrically operated valve and said electro-pneumatic relay, means including said outdoor temperature responsive means and said further means permitting said energization only when said outlet air temperature is below a predetermined value and the temperature of the air leaving said duct is below a second predetermined value, additional means preventing said energizatio until means for causing a predetermined circulation of air in said duct has been energized, and means including a main controlling switch effective when moved to one position to cause simultaneous deenerglzation of said electrically operated valve and said electro-pneumatic relay.

'7. In a temperature control system for a space, an air passage to said space, controllable means circulating air through said passage to said space, a plurality of temperature changing units disposed in said passage, means supplying fuel to said units, flow control means controlling said fuel supply, means causing said flow control means to open only after suicient operation of said controllable means to establish a predetermined circulation of air, modulating valve means in series with said now control means also controlling said fuel supply, an on" and oi control for each of said temperature changing units, temperature responsive means within said space, said temperature responsive means controlling said modulating valve means, and means for sequentially controlling said on and on controls in such a manner that said temperature changing units are sequentially placed into operation as said modulating valve means approaches one of its extreme positions and are sequentially placed out of operation as said modulating valve approaches the other of its eXtreme positions.

8. In a temperature control system for a space, air passage means to said space, controllable means circulating air through said passage to said space, a plurality of main burners in said passage, means for supplying fluid fuel to said burners, a main electrically operated valve for controlling the flow of fuel to all of said burners, means opening said valve only after a suiicient operation of said controllable means to establish a predetermined air circulation, a proportioning valve in series with said electrically operated valve for controlling said fuel iiow, temperature responsive means for controlling said proportioning valve` a pilot burner associated with each of said main burners, ignition means for said pilot burner, apparatus associated with each pilot burner for detecting whether said pilot burner is ignited, said apparatus comprising a relay having in contacts and out contacts and being operable upon the associated pilot burner being ignited to cause said relay to open said out contacts and close said in contacts, an energizing circuit for each of said ignition means controlled by out contacts of all of said relays in parallel, and an energizing circuit for said valve controlled by in contacts of all of said relays in series.

9. In a Ventilating system in which a stream of air is caused to flow through a conduit, a burner of sectional structure adapted to heat the air as it ows in such conduit, a gas supply pipe, leads from the gas supply pipe to the several sections of the burner, a pneumatically operated control valve arranged in the supply pipe, controlling gas ilow to all of the sections of the burner, cut-oil valves in the leads to the several sections of the burner, means for operating the cut-orf valves severally, each such means including a pneumatically driven element, and the pneumatically driven velements being severally responsive to different degrees of pressure, a source of pneumatic pressure eiective upon the control valve and upon the pneumatic elements of the cut-oil valves, and means for varying the degree of pneumatic pressure so effective, in response to variation in temperature of the heated stream of air.

10. In a Ventilating system in which a stream of air is caused to flow through a conduit, a burner of sectional structure adapted to heat the air as it flows in such conduit, a gas supply pipe, leads from the gas supply pipe to the several sections of the burner, a pneumatically operated valve arranged in the supply pipe and controlling the tlow of gas to all of the sections of the burner, and solenoid valves arranged in the leads to the sections of the burner, the valves opening in response to the energizing and closing upon the deenergizing of the solenoids, a pneumatic-electric switch associated with each solenoid valve and adapted to close the solenoid-energizing circuit in response to pneumatic pressure, the switches severally being so responsive to diierent degrees of pressure, a pneumatic pressure line leading to said pneumatically operated valve and to the said switches, a control member responsive to the temperature of the stream of heated air arranged in the pneumatic pressure line and establishing the effective value of the pressure in accordance with such temperature.

11. In a Ventilating system in which a stream of air is caused to ow through a conduit, a burner of sectional structure adapted to heat the air as it flows in such conduit, a gas supply pipe, leads from the gas supply pipe to the several sections of the burner, a control valve arranged in the supply pipe, controlling gas ilow to all of the sections of the burner, cut-0H valves in the leads to the several sections of the burner, means for operating the cut-oir valves severally, each auch means including a pneumatically driven element, and the pneumatically driven elements being severally responsive to diierent degrees of pressure, a source of pneumatic pressure effective upon the control valve and upon the pneumatic elements of the cut-ott valves, and means for varying the degree of pneumatic pressure so effective, in response to variation in temperature of the heated stream of air.

12. In a temperature control system, temperature changing. apparatus. at least three iluid circulating means for circulating fluid through said temperature changing apparatus. means'for controlling said circulating means, a relay associated with each iluid circulating means and operable by said controlling means, each of said relays including electrical contacts positioned said pipe, a prcportionlng valve in said pipe downstream Il'om said solenoid valve, conduits individually connecting said burners to said pipe, a solenoid valve in at least one of said conduits, means r'or insuring a predetermined minimum pressure in said pipe downstream from said pro- 4 portioning valve whenever said main solenoid valve is open, and a pair of thermostatically controlled devices connected in controlling relation to said solenoid valves and proportioning valve for operation thereof lll a sequence wherein said main solenoid is opened and said pro-f portioning valve partly opened before the sole nold valve in said conduit is opened.

i4. In a temperature control system, temperature changing apparatus, a solenoid valve and a proportioning valve serially arranged for controlling said temperature changing apparatus, at least three fluid circulating means for circulating iluid through said apparatus, means for controlling said circulating means, a relay associated with each ud circulating means, each of said relays including electric switch contacts positioned thereby, temperature responsive means for controlling said proportioning valve, and a plurality o'f energizing circuits for said solenoid valve, each of said energizing circuits including inseries the contacts of two of said relays.

15. In a condition changing apparatus, a plurality of devices for changing said condition, a iluid supply pipe, a shutoii valve in said pipe. conduits individually connecting said devices to said pipe, a proportioning valve downstream from and in series with said shutoff valve and arranged to control flow through said supply pipe and thus control ilow to said devices, a pressure regulating valve in by-pass relation to said proportioning valve for maintaining a predetermined pressure in said pipe and said conduits whenever said shuto valve is open, a valve in at least one of said conduits, and control means responsive to saidcondition connected to control said shutoff valve, proportioning valve and the valve in said conduit in a predetermined sequence.

WILLIAM L. MCGRATH.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 2,048,162 Kriechballm July 21, 1926 2,119,153 Dallenbach May 31, 1938 2,127,172 Hermitte Aug. 16, 1938 2,127,445 Hardgrove Aug. 16. 1938 2,139,344` Anderson Dec. 6, 1938 2,150,113 Wunsch Mar. 7, 1939 2,168,688 Nordgren Aug. 8, 1939 2,188,775 Locke Jan. 30, 1940 2,245,730 Sparrow June 17, 1941 2,331,476 Jones Oct. 12, 1943 2,362,045 Bliss Nov. 7. 1944