US3162234A

US3162234A - Burner control apparatus

Info

Publication number: US3162234A
Application number: US287433A
Authority: US
Inventors: William B Hamclink
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1963-06-12
Filing date: 1963-06-12
Publication date: 1964-12-22
Anticipated expiration: 1981-12-22

Description

W. B. HAMELINK BURNER CONTROL APPARATUS 2 Sheets-Sheet 1 mohumhwc INVENTOR.

Dec. 22, 1964 Filed June 12, 1963 @v F 3 E- k TkaFwv mokw NE En mm: Nam

Dec. 22, 1964 w. B. HAMELINK I 3,162,234

BURNER CONTROL APPARATUS Filed June 12, 1963 2 Sheets-Sheet 2 MAIN BURNER TRIAL PILOT TRIAL PURGE TIME IN SECONDS [is J INVENTOR.

MLL/AM B #4415; mm

Irma/5V United States Patent 3,162,234 BURNER CONTRQL APPARATUS William B. Hameiink, Richiield,Minn., assignor to Honeywell Inc, a corporation of Delaware Filed June 12, 1963, Ser. No. 287,433 8 Claims. (Cl. fill-28) The present invention is concerned with an improved burner control apparatus and more particularly with a burner control apparatus of the type wherein a timer is utilized to provide a sequence of operation of the burner system to safely bring the system from a stand-by condition to a run condition when there is a demand for heat from the burner and to bring the system from the run condition to the stand-by condition when this demand for heat is satisfied. Specifically this invention is concerned with a bur-ner'control system as described above wherein there is provided means for selectively interrupting the operation of the timer to facilitate operational adjustment of the burner system components, said means being operable only during certain portions of the time cycle wherein interruption of the timer operation will not result in an unsafe condition in the system.

It is well known in the art of burner control apparatus to provide a control system wherein a timer provides a sequence of operation of the burner components to safely bring the system from the stand-by to the run condition. In so doing the timer may provide aprepurge period during which combustion air is provided to purge the fire box of any accumulation of combustible fuel to thereby prevent an explosion when an attempt is made to establish combustion at the fuel burner unit. The prepurge period may be followed by a trial for pilot ignition period wherein fuel is supplied to a pilot burner and an igniter is energized to establish combustion at the pilot burner. At the initiation of the trial for pilot ignition period, a safety cut-out device which is effective to shut down the system a predetermined time after the initiation of this period may be energized. Combustion sensing apparatus such as a unit including a photocell for sensing combustion in the fire box is effective to render the safety cut-out means inoperative when combustion is established at the pilot burner. Following the trial for pilot ignition period a trial for main burner ignition period may be provided wherein fuel is supplied to the main burner as well as the pilot burner and during which the igniter may remain energized. During this period the combustion sensing means is effective to shut down the system in the absence of combustion in the fire box. At the end of the trial for main burner ignition period the fuel is shut off to the pilot burner and the igniter is tie-energized. If the combustion sensing means then detects combustion in the fire box the system continues into the run condition and operates as long as there is a demand for heat. The system continues to operate under the supervision of the combustion sensing means and, should a flame failure occur, the fuel supply is immediately interrupted. When the demand for heat is satisfied, the timer returns the system to the stand-by condition. This final portion of the time cycle may include a post-purge period wherein the blower is operated to purge the fire box of any unburned fuel which.

may remain there after the combination is terminated.

It has been found that it is often necessary to make operational adjustments to the components of the burner system after a time cycle has been initiated by the timer. To do so it is necessary to interrupt the operation of the timer and hence to prolong whatever period of the time cycle it happens to be in at the time. Such an interruption of the timer operation can safely be made during the prepurge period because at that time no fuel is being supplied to the pilot burner and an interruption of the timer merely expands the time during which the blower is operated alone. Similarly an interruption of the timer during the trial for pilot ignition period does not result in an unsafe condition because, if a flame fails to be established at the pilot burner within a predetermined time, the safety cutout is effective to shut down the system. This would occur before any dangerous amount of fuel accumulates in the fire box. However, as pointed out above, during the trial for main burner ignition period both the pilot and main burners are supplied with fuel. The combustion sensing means is effective to shut down the system during this period if there is a complete absence of combustion in the fire box but such combustion sensing apparatus is unable to distinguish between the presence of only a pilot flame and the presence of both a pilot and main burner flame. Hence, if the timer operation is interrupted during this period, it is possible that a pilot flame might exist but that the main burner would never ignite. Normally the timer would advance to the run period wherein the pilot burner would be shut oil and, if

there was no flame at the main burner, the entire system would be shut down. However, if the timer is interrupted during this period and the main burner does not ignite, an excessive amount of fuel might accumulate in the fire box which would result in an explosive condition.

In the past various arrangements have been proposed which allow interruption of the timer operation without shutting down the entire system. But in each of these arrangements it has been possible to interrupt the timer at any portion of its cycle and hence the skill of the repair man has been relied upon to assure that he will not interrupt the timer at a portion of its cycle which might result in an unsafe condition. It has been recognized that to merely insert a simple switch which would interrupt the operation of the timer without shutting down the system would be unsatisfactory because anyone, skilled or unskilled, might operate the switch without realizing the possible disastrous consequences. In order to avoid this possibility, the prior art has provided means such as a special plug which is supplied only to qualified service personnel so that they can interrupt the timer without shutting down the entire system. Even this type of arrangement has been found to be unsatisfactory. First of all, the special plug or other device may fall into the hands of one who is not enqirely familiar with the system and the possible dangers inherent to it. Secondly, even the skilled serviceman may inadvertently or carelessly interrupt the timer during a period which could result in an unsafe condition.

The present invention overcomes these shortcomings found in the prior art in that it provides, in a control system of the type described above, means for selective interrupting the operation of the timer in combination with means for rendering the interrupting means effective tostop the timer only during the prepurge and trial for pilot ignition period. Thus the timer may be interrupted to facilitate adjustment of system components but it is impossible to interrupt the timer at a period which, by being prolonged, might result in an explosive or otherwise unsafe condition of the unit. This improved burner control apparatus combines the features of functionality by providing for selective interruption of the timer operation to facilitate adjustment of the burner components and safety by limiting such interruption of the timer to portions of the time cycle where extension of the portions of the cycle cannot result in the creation of a hazardous condition.

My invention will become apparent to those skilled in the art upon reading the following detailed description of a preferred embodiment of the invention in conjunction with the accompanying drawing wherein:

FIGURE 1 is a schematic showing of a burner control apparatus utilizing my invention and connected to control the operation of a typical fuel burner unit.

FIGURE 2 is a bar graph showing the time relationship of the operation of the contacts of a timer which forms a part of the control apparatus'of FIGURE 1.

Referring to FIGURE 1, reference numeral gener: ally designates a fuel burner unitwhich is adapted to be controlled by a burner control system constructed according tomy invention. The. burner system 10 includes a main burner 11, a pilot burner 12, and a blower or fan 13 for supplying combustion air to-the unit. Valves 14 and 15 control the'flow of fuel from a supply, not shown, g

; drawing. This movement of the lower end of bimetal 33 to the main burner and pilot burner respectively. An igniter 16 is adapted, when energized by an ignition transformer 17, to ignite the fuel at the pilot burner 12.

Reference numeral 20 designates an electronic flame detector which receives its operating voltage from atransformer 21 which has its primary winding connected across a pair of

mainconductors

22 and 23 which may be connected to a standard source of line voltage. The input to flame detector 20 is obtained from a pair of

conductors

24 and 25 which are connected to a flame sensing means such as a photocell 26. Photocell 26 is positioned in the wall of the fire box so as to sense the presence of a flame at either the pilot burner 12 or the main burner 11.. The output of'flame detector 20 includes a'main flame relay designated. 4R which has a normallyopen contact 4R1. When a flame is detected by photocell 26, flame detector 20 is effective to energize relay'4R to close contact 4R1.

The burner control apparatus is controlled bymeans' 4 run 'periodwher'ein timer T is de-energized until the stop button is depressed to de-energize the 1R relay or until a flame failure occurs at which time the system will be shut down by the flame detector. 2 p

During the trial for pilot'ignition period the 1R relay is placed under the control or supervision of a safety cutout or safety switch generally designated at 31. Safety cut-out31 includes an electrically energizable heater element 3?. which, when energized,'is effective to heat a bimetal element 31 which is fixed at its upper end as seen in FIGURE 1; Upon heating of bimetal'element 33, the lower end thereof moves to the right as indicated in the is sufliciently slow to provide a time delay in the safety switch; Safety switch 31 also includes a pair of fixed member 36. Whenthe bimetal elementis heated for a sufficient time so as to move its lower end to the right,

the element36 isreleasedand is causedto rotate by spring i '37 to a position wherein contact 38' is in electrical conof a start-stop station designated generally by the reference numeral 27. Start-stop station 2'7is etfectiveto control the energization of amain-control relay lRf'whichihas an electrically energizablef winding and normally open contacts 1R1, 1R2, and 1R3, and a normally closed contact 1R4. i i

As seen in FIGURE 1, the'winding of relay 1R has an intermediate tap or terminal 28, defining an upper portion 29 anda lower portion of thewinding, 'Energization of the lower portion 30 of the winding is effective to operatethe contacts 1R1, 1R2, 1R3, and IE4.

Upon energization of the lR-relay and the closing of contact 1R3 a timer, generally designated by T,' is energized. Timer T includes an electrically energizableactuator and a plurality of contacts identified as T1 through T9 which are controlled in a timesequence by the timer. A preferred time sequence for these contacts is shown in tact with fixed contact. to complete a circuit through an alarm 40 which may be any conventional electrically energizable audible or..visible alarm. Atthe same time,

contacts 39 and 34 are separated and the circuit to relay 1R is'interrupted. Obviously, oncebimetal 33 has been heated sufficiently to release the member 36, the safety switch must be rnanually reset before it is again operable.

As'will be explained in detail hereafter, safety switch heater 32 is energized only during the trial for pilot igniwhile the unshaded portion indicates the open condition of each particular contact. In actual practice, timer ,T

may include a synchronous motor which operates a shaft carrying a number of cams which may be adjustableto provide varying time periods, one of which may be the 7 Each of the cams is sequence shown in FIGURE 2. adapted to operate a corresponding switch or contact.

tionand, upon the establishment of a pilot flame, the 4R relay iseifec'tiye to close the 4R1 contact which in turn completes a circuit to av secondary flame relay designated 2R. Relay 2R includes a normally closed contact 2R1 and normally open contacts 2R2, 2R3, and 2R4. Uponienergization' of the 2R relay the 2R1 contact is opened and the safety switch de-energized and hence abrief portion of the timed'cycle. Actually, in the preferred form of my invention, contact T3 is opened'during a portion ,of the prepurge period and of thetrial for pilot The closing of contact 1R3, upon energization of relay IR, is also effective to energize a further relay designated 3R which has a normally open contact3R1. Energization of relay SR is effective to close the 3R1 contact and hence to energize the blower or fan 13.: i

ponents of the burner system including a prepurge period wherem only the blower 13 is energized, a trial for pilot ignition period wherein pilot valve 15 and ignition transformer 17 are energized to establish a flame at thepilot 7 burner 12, and a trial for main burner ignition period wherein pilot valve 15 and ignition transformer 17 are maintained energized and wherein main valve 14. is also energized to provide fuel atithe main burner. After the trialfor main burner ignition period, pilot valve 15 and ignition transformer 17 are de-energized, and, ifcombustion takes place 'at main burner 11, the system enters a ignition period. Thus, during the time that the timer contact T3 is open, the .timer may be de-energized by 'manually opening switch 41. It will "be seen that during the period when timer switch T3 is open the operation of the timer can be safely interrupted since, if the timer is in the prepurge portion of the cycle, only the blower is operating and, if the timer is in the trial for pilot ignition period of its cycle, the safety switch is effective to shut down the entire system if ignition is not accomplished v within the period provided by'the time delay in'the bimetal'33'. Contact T3 is again closed before the trial for main burner ignition period wherein, was explained. previously, a dangerous condition could exist if the timer were interrupted and a flame existed onlyat the pilot burner with no. combustion at the main burner.

During the time interval when contact T3 is open, manual switch 41 may be opened to stop the timer for any period of time desired so that the repair or service man may makeiadjustments to system components such as adjustment of dampers for regulating the air to the blower or adjustment of the pilot burner or igniter.

Hence timer operation can be interrupted to facilitate these adjustments without the danger of interrupting the operation during a period when such interruption might result in a hazardous condition at the burner unit.

Having described briefly the over-all operation of the system a detailed description of its operation will now be given. The system, as shown in FIGURE 1, is in a stand-by condition wherein there is no demand for heat from the burner unit. Relay-1R is de-energized and hence contacts 1R1, 1R2, and 1R3 are open and contact 1R4 is closed. Flame detector 2t? is energized through transformer 21 but, since there is no flame at the burner unit, flame relay 4R is de-energized and contact 4R1 is open. Consequently relay ER is tie-energized and its contact ER]. is closed and contacts 2R2, 2R3, and 2R4 are open. Relay 3R is de-energized and hence contact 3R1 is open. Timer T is at the zero or stand-by position as shown in FIGURE 2 and hence contacts T2, T3, T6, T8, and T9 are closed and timer contacts T1, T4, T5, and T7 are open.

If there is a demand for heat from the burner unit, the start button is depressed to close a circuit which may be traced from main conductor 22, through the start button, timerswitch T2, normally closed contact 2R1 of the secondary flame relay 2R, heater 32 of the safety switch,

terminal 28 and lower portion 30 of the Winding of relay 1R, contacts 34 and 3h and contact carrying member 36 of the safety switch member, and through a. conductor 42 to main conductor 23. From this circuit it is seen that heater element 32 of safety switch 31 and the lower portion 30 of the winding of the 1R relay are connected in series. The relative impedances of heater 32 and of portion 34 of the winding of the 1R relay are selected, with a given line voltage, such that so long as these two members are connected in the series relationship described above, the current flow is such that heater 32 is operatively de-energized but relay IR is energized to that this circuit acts as a holding circuit for relay 1R.

The'closing of the 1R2 contact is effective to place the energizing circuit for the main valve 14, pilot valve 15, and igniter 16 in a condition to be completed upon oper alion of timer contacts as will be described hereinafter.

Closing of contact 1R3 completes a circuit from main conductor 22 through contact 1R3 to the winding of relay SR and to the other main conductor 23. Hence the relay 3R is energized and contact 3R1 is closed, thus completing a circuit to the motor of blower 13. This circuit can be traced from conductor 22 through contact 3R1, the blower motor, and through a conductor 43 to main conductor 23. The closing of contact 1R3 also completes a circuit to the timer motor which may be traced from main conductor 22, through contact 1R3, a conductor 44,

timer contact T9, timer contact T3, and the motor winding of the timer T to conductor 23. Hence the timer is set into operation and is effective to begin its time cycle defining the sequence of operation of the system components to bring the burner unit from a stand-by condition to a run condition.

As seen from the bar graph of FIGURE 2 the first switching accomplished by timer T is the closing of timer contact T1 which occurs at approximately four seconds after the beginning of the time cycle. The closing of this contact shunts contact 1R3 and hence is effective to complete a circuit to the timer motor T and the relay coil of relay 3R even if relay 1R should be de-energized. As noted in the graph of FIGURE 2 the period from zero to forty seconds after initiation of the time cycle constitutes a prepurge period wherein only the blower of the burner unit is energized. During this period the blower is effective to purge the burner unit of any accumulated combustible mixture.

After approximately ten seconds of timer operation timer con-tact T2 is opened and hence depression of the start button after this time will have no effect upon the system until the cycle is completed.

Sometime after the initiation of the prepurge period, for example after approximately thirty-five seconds as shown in FIGURE 2, timer contact T3 is opened. However, timer motor T remains energized as long as manual switch 41 is closed. At this time a circuit can be traced from conductor 22 through contacts T1 and T9, through a conductor 44, switch 41, a conductor 45, and through the timer winding to the other conductor 23. During the period when contact T3 is open it will be seen that the timer may be de-energized by the opening of the manual switch 41. Thus, during this interval when contact T3 is open, the timer may be stopped so that operative adjustments may be made to the burner components if required. It will be noted that the contact T3 will again close prior to the completion of the trial for pilot ignition period, for example shortly before fifty seconds of the time cycle have elapsed. Thus the manual switch 41 is rendered effective to interrupt the operation of timer T only during a portion of the prepurge period and the trial for pilot ignition period, the system during these two periods being such that extension of the time for either of these periods cannot possibly result in a hazardous condition at the burner unit.

At approximately thirty-eight seconds after the iuitiation of the time cycle timer contact T4 is closed. This completes a circuit in parallel with the heater 32 of the safety switch which can be traced from main conductor 22, through the stop button, contact 1R1, contact T4, and through the upper portion 29 of the winding of relay 1R to terminal 28 on the 1R relay winding. At this time, through transformer action of portion 29 of the winding of relay 1R, safety switch heater 32 is operatively energized and is efiective to heat the bimetal element 33. Hence at this time the lower end of the bimetal element begins to move toward the right and is effective after a time delay, if the heater remains energized, to release the contact carrying member 36. Shortly after the closing of contact T4, for example at forty seconds after the initiation of the time cycle, timer contact T5 is closed and hence completes a circuit to the pilot valve 15 and the ignition transformer 17. This circuit can be traced from main conductor 22 through the stop button, a conductor 49, contact 1R2, timer contact T8, contact T5, and through the pilot valve actuator 15 to conductor 43 which is in turn connected to main conductor 23. A parallel circuit can be traced from timer contact T5 to the ignition transformer 17 which is in turn connected to conductor 23. Hence at this time the pilot valve is opened to allow fuel to be supplied to pilot burner 12 and at the same time the ignition transformer is effective to energize the igniter 16. Normally a flame is established at the pilot burner during this pilot ignition period and if this occurs the flame is sensed by photocell 26 and in turn flame detector 20 is effective to energize the 4R relay which in turn closes its contact 4R1 completing a circuit through the secondary flame relay 2R. This circuit can be traced from conductor 22, through the closed timer contact T6, through the winding of relay 2R, andcontact 4R1 to conductor 23. Energization of relay 2R is effective to open contact 2R1 and hence to de-energize the safety switch heater 32. At the same time contact 2R2 is closed and hence shunts timer contact T6. Similarly contacts 2R3 and 2R4 are closed, contact 2R3 then shunting timer contact T8 in the circuit to the pilot valve and the ignition transformer and contact 2R4 placing the circuit to the main fuel valve in position to be completed when the timer contact T7 closes.

contacts 35 and 38, contact carrying member 36 and through conductor 42 to the other main conductor 23. It

should be noted that shut-down of the system by the safety switch would be effective to de-energize relay 1R which in turn would open the contact 1R2 hence de:energizing the fuel valves 14 and 15 and the igniter 17. However both timer T and relay 3R would remain energized until the system had run through a complete cycle due to the fact that contact T1 is now in a closed position. This is important since the fan would continue to run and to be effective to purge the system of unburned fuel and also the timer would continue through its timed cycle without can be traced from conductor 22, through the alarm 40, a

burner, the photocell would be unable to detect this problem. For this reason, it is important that timer contact T3 is now' closed so that it is impossible to stop the timer during this period. If it were possible to stop the timer, it ispossible that fuel might continue to be supplied to the main burner for a long period of time without the establishment of combustion as long as the flame was maintained at the pilot burner. Hence it would be possible to build up a large-amount of unburned fuel in the fire "box which might result in a hazardous condition.

But since timer contact T3 is closed during this period, opening of manual switch 41 will have no effect upon the timer and it is impossible to create such a hazardous condition in the fire box.

At the completion for the trial for main burner ignition period, for example at approximately eightly seconds after the initiation of the time cycle, timer contact T5 is opened "which then de-energizes pilot valve 15 and ignition transformer 17. Hence the flame is extinguished at'th'e pilot burner and combustion then takes place only at the main burner. 11. If the condition previously described should occur, that is should the main burner fail actuating any of the burner components and hence return to its start position so that another ignition period might be begun.

Shortly before the end of the trial for pilot ignition l period,for example at approximately, forty-eight seconds after the initiation of the timed cycle, timer contact T6 is opened, removing the shunt around contact 2R2 and hence render-ing the completion of a' circuit through the winding of relay 2R dependent upon energization of that relay. Assuming that a' flame is established at the pilot burner during the trial for pilot ignition period, timer contact T7 closes at approximately 50 seconds after the initiation of the time cycle and hence is effective to energize main fuel valve 14 to cause it to supply fuel'to the main burner 1-1.- This circuit canbe traced from the mainconductor 22,- throughthe stopswitch, conductor 49, contact 1R2, timer contact T7, contact 2R4,'the actuator of valve 14, and conductor 43 which in turnis connected to the other main conductor 23; The system is now in the trial for mainv burner ignition period which may continue for a period of approximately thirty seconds. It will be noted that during this period fuel is supplied to both the main 'andpilot burners and the igniter is maintained energized.

Normallyduringthis period a? flame will'be established at the main burner -It's'hould also be noted that the system is now under control of the flame detector and, upon failure of combustion in the fire box, flam erelay 4R will be de-energized which in turn opens the 4R1 contact to interrupt the circuit to secondary flame relay 2R which is then effective to interrupt the flow of fuel to both the pilot and main burners. This is true because at the'same time that timer contact T7 was closed to complete a circuit to the main valve, timer contact T8 is opened and hence a circuit to the pilot valve is completed only through contact 2R3. Thus, if burner relay 4R is ie-energized, opento ignite, at this time when the pilot'flame is extinguished, flame relay 4R would be de-energized and as described previously, the system would'be shut down. assumingthat a flame has been-established'at the main burner, the system enterswhat may be called the run period, that is wherein combustion is maintainedat the main burner to satisfy the need for heat; "If this combustion is maintained satisfactorily, timer'contact T9 is opened at approximately one hundred. and five seconds after the initiation'of the time cycle and hence the timer is'renderedinoperative duringthetime when the coming contacts 4R1 and therebyde-energizing the secondary flame relay 2R, contacts 2R3 and 2R4 are both opened breaking the circuit to the pilot valve 15 and the main valve 14 respectively. As pointed out above, this interruption of the fuel to the burner would not'b'e effective to interrupt operation of the timer T or of the blower since timer T and the 3R relay will remain energized until the timer has run through its complete cycle.

It should also be noted that during the'trial for main burner ignition period normally the combustion will exist at both the pilot and the main burner. Photocell 26 is effective to sense the existence of combustion in the fire box but it is. unable to distinguish between the existence of combustion at both the pilot and main burner and the'existenceof a flame at only one of the burners.

bustion takes place at the main burner'to satisfy the need for heat. Unless an accidental flame failure occurs, timer T will remain de-energized until the need for heat is satisfied and'the system is to be shut down. During this period the system will remain under the supervision of the flame detector and, of course, should the combustion at the main burner be interrupted flame relay, 4R would be de-energized to effectively interrupt the fuel to the burners.

Assume now that theneed for heat haslbeen satisfied and it is desired to end the period'of operation of the:

burner unit, The stop switch is depressedand the circuit to relay IR is interrupted causingits contacts 1R1, .1R2, Hence the bustion at the main burner is extinguished. At this time timer contact T1 is still closed and a circuit is now established from main conductor 22, through contact Tl,

conductor 46, and a conductor 47, 'to the winding of relay 3R 'to maintain it energized and. thus .to maintain the fan in an energized position to provide a post-purge period for the fuel burner. At the same time a circuit is established in parallel with the winding of relay 3R, from conductor 47, through contact 1R4, the timer motor, and

to the other main conductor 23. Hence the timer is again energized and enters a shut down portion of its time cycle. Since there is no longer combustion in the fire box, flame detector 20 de-energizes-its flame relay 4R,

opening [contact 4R1 and de-energizing the secondary flame relay'2R. Thus contact 2R1 closes and contacts.

' 'Thus the circuit to the fuel valves and the igniter is now Hence it is possible that, should the pilot flame con- 7 in a stand-by position ready for a new cycle. Also at approximately the 111 second position of the timer, contact T9 is again. closed, and at approximately the 115 second position contact T6 is again closed to shunt contact 2R2. At approximately the 116 second position contact T2 is again closed. Therefore it can be seen that at this time the system can return to its stand-by condition and when the timer reaches the 120 second However,

9 position, Contact T1 opens interrupting the circuit to the timer motor. It can be seen that the system is now in the start or zero time position and upon a demand for operation of the burner the system can again be placed in operation by depressing the start button.

From the foregoing description, tracing a complete cycle of opera-tion of the apparatus of my invention, it can be seen that I have provided an improved burner control apparatus which utilizes a timer to sequence the operation of the burner components in bringing the system from a stand-by to a run condition and wherein means have been provided for interrupting operation of the timer only during certain portions of the time cycle. Through the cooperation of manual switch 41 and timer contact T3, it is possible to interrupt the timer operation only during the prepurge period and the trial for pilot ignition period which, as described above, are periods wherein extension of the period cannot result in an unsafe condition at the burner. During other portions of the time cycle it is impossible to interrupt the timer operation by opening manual switch 41. Thus it is possible to interrupt operation of the timer to facilitate operational adjustment of the burner components only during portions of the cycle wherein such interruption cannot result in an unsafe condition. I

Various modifications to my burner control system can obviously be made without departing from the present invention, for example the components of the burner unit itself are shown by way of example only and various burner components may of course be substituted. Similarly the flame detector is not limited to a photocell type but various other types might be used. Safety switch 31 may also be of any acceptible type and need not be limited to the type specifically shown and described herein. It is therefore intended that the scope of the present invention be limited solely by the scope of the appended claims.

I claim as my invention:

1. In a fuel burner control system having means including a program timer to provide a given sequence of operation of a fuel burner system including, in order of occurrence, prepurge of the burner, trial for pilot ignition, and trial for main burner ignition, followed by a run period of the fuel burner system when said sequence of operation results in satisfactory combustion at the burner, the improvement comprising: manually operable switch means constructed and arranged to interrupt said sequence of operation only at a time within the period comprising the prepurge period and the trial for pilot ignition period to then facilitate operational adjustment of components of the fuel burner system.

2. Apparatus for controlling the operation of a fuel burner system including a burner, a blower, an igniter, and valve means for controlling the flow of fuel to the burner, the apparatus comprising: combustion sensing means; means including a program timer to provide a given sequence of operation of the burner system including a prepurge period wherein the blower is operated to purge the burner of unburned fuel, an ignition period wherein combustion is established at the burner, and, if combustion is established, a run period wherein the system is placed under the control and supervision of said combustion sensing means; manually operable switch means constructed and arranged to interrupt the operation of said timer to facilitate adjustment of burner components; and means operable by said timer to render said switch means effective to interrupt said timer only at a time within said prepurge period.

3. In combination with a fuel burner system; means including a timer for providing a sequence of operation of the system including a prepurge period, a trial for pilot ignition period, a trial for main burner ignition period, and a run period; safety cutout means adapted to be energized during said trial for pilot ignition period and effective after a time delay to shut down the system; combustion sensing means responsive to the presence or absence of combustion in the burner system and effective to render said safety cut-out means inoperative upon establishment of a pilot flame; means operable by said combustion sensing means to shut down the system upon the absence of combustion during said trial for main burner ignition period and said run period; manually operable switch means for interrupting the operation of said timer to facilitate adjustment of components of the fuel burner system; and means operable by said timer to render said manual switch means effective only at a time within the period comprising said prepurge period and said trial for pilot ignition period.

4. In combination with a fuel burner unit having a pilot burner, a pilot valve for controlling the supply of fuel to the pilot burner, igniting means for the pilot burner, a main fuel burner, a main valve for controlling the supply of fuel to the main burner, and a blower to supply air for purging the unit and for supplying combustion air thereto, control apparatus comprising: timer means operable to define a time cycle including a purge period, a pilot ignition period, a main burner ignition period, and a run period; means operable when there is a need for operation of the burner to energize the blower and to render said timer means operable; means operable by said timer means to energize the pilot valve and the igniting means during said pilot ignition period and said main burner ignition period and to de-energize said pilot valve and said ignition means at the end of said main burner ignition period; means operable by said timer means to energize said main valve during said main burner ignition period and said run period; combustion sensing means adapted to sense the presence or absence of combustion in the unit; means including means operable by said timer means to render said combustion sensing means effective during said main burner ignition period and said run period to de-energize said main valve and said pilot valve in the absence of combustion in the unit; manually operable means for interrupting the operation of said timer means; and means operable by said timer means to render said manually operable means effective only at a time within the period comprising said purge period and said pilot ignition period.

5. Apparatus for controlling a fuel burner system including a main burner, a pilot burner and a blower, the

apparatus comprising: means including a program. timer to provide a sequence of operation of the system including a purge period, a trial for pilot ignition period, a trial for main burner ignition, and a run period; means including means operable by said timer for supplying fuel to the pilot burner during the trial for pilot. ignition and trial for main burnerignition periods; means including means operable by said timer for supplying fuel to the main burner during said trial for main burner ignition period and said run period; means including safety cut-out means rendered operable by said timer to interrupt the supply of fuel to the burners upon failure to establish combustion at the pilot burner; combustion sensing means effective to render said last named means inop erable upon establishment of a pilot flame; means including said combustion sensing means effective to interrupt the supply of fuel to the burners in the absence of combustion during said trial for main burner ignition period and said run period, said combustion sensing means being unable to sense the absence of only a main burner flame during said trial for main burner ignition period; manually operable means for interrupting the operation of said timer to facilitate adjustment of system components; and means constructed and arranged to render said manually operable means effective only at a time within the period comprising said purge period and said trial for pilot ignition period.

6. In combination with a fuel burner system: means including an electric timer for providing a sequence of operation of the system including a prepurge period, a

adapted to be energized during said trial for pilot igni-' tion period and efiective after a time delay to shut down the system; combustion sensing means responsive to the presence or absenceof combustion in the burner system" and efiective to render, said safety cut-out means inoperative upon establishmentof' a pilot flame; means operable by said combustion sensing means to shut down the system upon the absence oficombustion during said trial for main burner ignition period and said'run period;

circuit means including control means adapted to connect said timer to a source of power, said circuit means further including the parallel combination of manually operable switch means and normally closed movable contact means; and means operable by said timer means and efiective to open saidcontact means only at a time within the period comprising said prepurge period and said trial forpilot ignition period to render said switch means selectively operable to interrupt the operation of said timer means. I

l 7. Control apparatus for a ing a main burner and a pilot burner comprising: means including a programming timer for providing a" predeter mined sequence of operation of the system including a first time period wherein fuelis supplied only to the'pilo't burner, 'aisecond tirne periodwherein fuel is supplied to both the pilotand the main burner, and a third period wherein 'fuel is supplied only tothe mainbur'ner; safety cut-out means constructed and arranged torinterrupt' the operationof the system a predetermined time afterthe beginning of said first period; combustion sensing means;

responsive to the presence or absence of combustion in the unit and effeotive to interrupt thesu'pply of fuel to the burners in the absence of combustionduring said second and third periods, said combustion sensing means being eflective to interrupt the operation of said safety cut-oft means upon the establishment of a pilot flame during said first period, said combustion sensing means further being unable to sense the absence of combustion at the main burner when there is combustion at the pilot burner-during; said second period; manually operable means for interrupting the-operation of said timer to facilitate adjustment of system components; and means operable by said timer and constructedandarran'ged to render said manually operable means ineffective at any fuel burner system includtime within said second period so that it 'is impossible to interrupt the operation of said timer aridtherebye14 :tendf the length of said second period tojcreate a danger: ous condition by theaccumulation of fuel should the main burner fail to ignite during said second period.

8. Apparatus for controlling the operation of a fuel burner system including .a main burner, a pilot burner,

igniting means .for the pilot burner, main valve means i and pilot valve means for controlling the flow of fuel to the main burner and the pilot burner respectively, and a blower 'to" supply air for purging the unit and for combustion air, the apparatus comprising": electrically energizable timer means to provide a time cycle for controlling th'e sequence of operation of the system'including a prepurge period, a trial for pilot ignitionperiod, a trial for main burner ignition period and a run period; electric power supply means; means operable in response to a demand for heat from the burner to connect said timer means to said power supply means to initiate said time cycle; means operableby said timer means to connect said blower to said source of power during the entire time cycle; means operable by said timer means to connect the pilot valve means and the igniter means to said Source of power during said trial for pilot ignition period and said trial for main burner ignition period to establish combustion at the pilot burner; further means operable by said timer means to disconnect the pilot valve means and the ignite'r means from sourcev of powerupon completion of said trial for main burner ignition period; means operable by said timer means for connecting the main valve to said source of power duringsaid trial for main burner ignition period and said run period to supply fuel to the main burner to facilitate the establishment of combustion at the main burner; safety cut-out means including meansrendered operable by said timer means and effective to shut down the system a predetermined time after the initiation of said trial for pilot ignition period; means including combustion sensing means constructed and arranged to render said safety cut-out means inopervtimer means and said esource of power, said circuit means including the parallel combination of manually operable switch means and normally closed movable contact means; and means operable by said timer meansand effectiveto open said contact means only at a time within the periodcomprising said prepurge period and said trial for pilot ignition period to render said switch means selectively operabletointerrupt the-operation of said timer means, e

References Cited in the'fileof this patent UNITED STATES PATENTS 2,388,666 Bower Nov. 1-3, 1945 3,082,813 Hamelink Mar.26, 1963

Claims

1. IN A FUEL BURNER CONTROL SYSTEM HAVING MEANS INCLUDING A PROGRAM TIMER TO PROVIDE A GIVEN SEQUENCE OF OPERATION OF A FUEL BURNER SYSTEM INCLUDING, IN ORDER OF OCCURENCE, PREPURGE OF THE BURNER, TRIAL FOR PILOT IGNITION, AND TRIAL FOR MAIN BURNER IGNITION, FOLLOWED BY A RUN PERIOD OF THE FUEL BURNER SYSTEM WHEN SAID SEQUENCE OF OPERATION RESULTS IN SATISFACTORY COMBUSTION AT THE BURNER, THE IMPROVEMENT COMPRISING: MANUALLY OPERABLE SWITCH MEANS CONSTRUCTED AND ARRANGED TO INTERRUPT SAID SEQUENCE OF OPERATION ONLY AT A TIME WITHIN THE PERIOD COMPRISING THE PREPURGE PERIOD AND THE TRIAL FOR PILOT IGNITION PERIOD TO THEN FACILITATE OPERATIONAL ADJUSTMENT OF COMPONENTS OF THE FUEL BURNER SYSTEM.