US3518034A - Burner safety control system - Google Patents

Description

June 30, 1970 L. BLOCK Erm.

BURNER SAFETY CONTROL SYSTEM Filed June 18, 1968 United States Patent O 3,518,034 BURNER SAFETY CONTROL SYSTEM Leo Block, Temple City, and Roy Frank Rafensten, La Canada, Calif., assignors to Raypak Company, Inc., El Monte, Calif., a corporation of California Filed June 18, 1968, Ser. No. 744,273 Int. Cl. F23q 9/10 U.S. Cl. 431-45 6 Claims ABSTRACT F THE DISCLOSURE In systems of this type safety considerations are, of course, paramount. The primary source of possible lire or explosion hazard has been the possible accumulation of gas in the combustion chamber when there is no flame t present, and then having an ignition spark applied possibly causing an explosion. The circumstance may occur in the event of a shut down in response to flame failure and restarting afterwards. It has been known in the prior art, of course, to provide for a purging period to purge the combustion chamber of gas before attempting to restart. A primary objective is, of course, to make possible a system that is safe under all conditions. Firstly, the system of the herein invention is of the 100% shutolf type meaning that in the event of automatic shut down the system shuts off completely (i.e.), both the main fuel supply and pilot burner fuel supply arecut off and this occurs in the event of llame failure at any individual pilot burner among plural burners. A further consideration is, of course, to assure that there is a purging period of adequate length after a shutdown before the attempt is made to restart. In the system of the herein invention, for reasons of economy and positiveness of action it is desired that the means responsive to llame failure, that is, the llame responsive switches be of the expansible bellows and capillary'tube ty-pe that require a period of cooling of perhaps 20 seconds to actuate after there is flame failure. Furthermore, it is desired that the purging period be provided by a mechanical timer which is inexpensive and positive in action. It is further desired and an objective of the invention that in a system using components of this type that the system will fail safe` under all circumstances, considering more particularly shut down in the event of llame failure; failure of contacts by reason of welding or the like; and/or failure of the timer itself. The primary object of this invention is thus to provide a system of the nature referred to possessing the characteristics that it is assured that it will fail safe under all circumstances particularly those enumerated.

Thus the system is one that even with plural pilot burners and main burners it will bring about one hundred percent shutoff in the event of failure of any pilot burner. With flame responsive switches of the type referred to, the mechanical timer will assure the adequacy of the length of the purging period. The system further embodies the extremely important fail safe consideration that upon restarting, which occasions opening of the pilot fuel Valve and energization of the spark ignition means that sparking is discontinued before it is possible to reopen the main ICC fuel valve. This arrangement is extremely important in the event of a momentary power failure. In the event of a momentary power failure and return of power the system will completely shut down, the pilot burners going out, and thus recycling of the timer means being necessary for restarting. Normally such an event does not produce a hazard, but it could produce a hazard in systems not embodying the characteristics of the herein invention. Momentary power failure could occur during the timing cycle at a point at which the ignition is on and the main fuel valve is open. Therefore, upon resumption of power the ignition would be on at a time when both the pilot fuel valve and main fuel valve are open so that the ignition means would ignite the main as well as the pilot burner which is a definite hazard, recognizing, of course, that in the event of momentary power failure and extinguishment of the pilot flames, the flame responsive switches do not have time to open and shut down. The system of the herein invention overcomes this particular hazard by Way of contact means in the timing cycle which assure that the sparking ignition means de-energized prior to opening of the main gas valve during the cycle. No possibility remains, therefore, for the system to attempt to ignite at a time when gas is being supplied to the main burners as well as the pilot burners. In the system, to fully insure the protection desired contact means are provided, particularly by way of a single pole double throw contacting mechanism having one contact which controls the main fuel valve and the other of which controls the pilot fuel valve thus assuring that both cannot be simultaneously energized and thus assuring in the system that before the main gas valve can be reopened after shut down, the pilot valve must have closed meaning that the timing cycle must have proceeded to that point, and that the main gas valve can now only open if the pilot valve has opened, and the main gas valve can only remain open if it is assured that the pilot flame is present. Accordingly, further objects of the invention reside in the achievement and securement of these particular characteristics in the system.

Further objects and additional advantages of the invention will become apparent from the following detailed description and annexed drawings, wherein:

FIG. l is a schematic circuit diagram of the system of the invention illustrating the principal components thereof;

FIG. 2 is a schematic view of a contacting device that controls the main fuel valve and pilot fuel valve.

Referring to the drawing'the numerals 10 and 10 designate typical gas burners supplied through a gas line 12 and electric control valve 14. Numerals 16 and 16 designate typical pilot burners associated with the main burners and supplied with gas through lines 20, 22 and 24 connected to a gas supply line 26 through the electric pilot gas control valve 30.

Adjacent to the pilot burners 16 and 16 in a position to ignite them are ignition contacts 32 and 32. Also adjacent to the pilot burners 16 and] 16' are temperature responsive devices 34 and 34' which in the exemplary form of the invention are elements containing expansible fluid such as mercury which expands in response to heat generated by the pilot flames.

The temperature responsive element 34 connects by capillary tube 36 to temperature responsive switch 38 which is a single pole double throw switch 40 actuatable by bellows element 42 connected to tube 36. The temperature responsive element 34 is similarly connected to another temperature responsive switch 38 which corresponds to the switch 38.

The controls as shown are preferably operated from a 24 volt supply as designated by the terminals 44. Numeral Si) designates a single pole double throw manual switch and numeral 52 is a similar single pole double throw switch for purposes which will be described. Numeral 54 designates a temperature responsive single pole double throw switch which may be a room thermostat or other comparable control instrument controlling the system.

Numeral 60 designates a component which is a high voltage generator for purposes of providing voltage for actuating or energizing the spark gaps 32 and 32'. This component may be of a conventional type which is powered by relatively low voltage as described and generates high voltage in its output circuit generated indicated at 62. The component 60 is duplicated at 60 having an output circuit 62', both of the circuits being connected in parallel to the circuit 64 which connects to the spark gaps 32 rand 32 which are in parallel.

Numeral 70 designates a low voltage timer motor which may be of conventional type connected across the 24 volt supply as will be described. Numerals 71, 72, 74, 76 and 78 designate timer operated switches. These switches may be operated lby cams on the shaft of the timer motor, this mechanism being in itself conventional. Contacts 76 and 78 are part of a single pole double throw contacting mechanism as shown in FIG. 2 so that when one of them is closed the other is necessarily open and vice versa.

In normal operation both the -main gas valve 14 and the pilot valve 30 are open supplying gas to the main burners and 10 and the pilot burners 16 and 16. The circuit for the main gas valve is through the manual switch 50, the temperature responsive or flame responsive switches 40 and 40', wire 77 normally closed timer contact 78, condition responsive switch 54, the valve 14 and wire 79 back to the other side of the line.

The pilot valve 30 is energized by a similar circuit through the :manual switch 52 and valve 30 back to the other side of the line. During normal operation as may be observed the main gas valve may be opened and closed in response to operation of the condition responsive switch 54, pilot valve 30 remaining open at all times supplying gas to the pilot burners 16 and 16.

As pointed out in the foregoing, the system is of the 100% shut off type so that in the event of a pilot burner going out the system will shut down, shutting down all pilot burners and all gas burners, it being understood that there may be any number of each.

The operation of the system in the event of pilot flame failure at any pilot burner, will best be understood from the following example. For clear understanding the cycle is taken `as beginning at time zero, which is the time at which either one of the flame responsive switches 40 or 40 engages its upper contact after pilot flame failure. The time for operation of one of these flame responsive switch is taken as 20 seconds so that the time at which a pilot flame goes out would be 20 seconds before one of the switches 40 or 40 engages its upper contact.

EXAMPLE Time minus 20 seconds: pilot blows out.

Time-zero: flame switch 38 lmoves to upper Contact position, energizing timer motor 70 through wires 80, 82, 84 and 86 back to the other side of the line. The timer motor now starts operating driving its various cams to actuate its contacts in accordance with the following. All pilot and main burners are cut off.

Time-10 seconds: contact 78 opens and contact 76 closes. This isolates the main gas valve 14 from the pilot valve that is, it lbecomes possible to energize the pilot valve but not the main gas valve.

Time-one minute: contact 71 closes producing a further circuit for the timer motor including wire 88 and wires 84 and 86 so that the timer motor will complete its cycle without interruption.

Time-five minutes: contact 72 closes and opens the pilot valve through a circuit including wire 82, contact 72, wire 92, AContact 76, manual switch 52, pilot valve CTI 4 30, and back to the other side of the line. (It will be noted that the sparking components or panels 60 and 60 are not yet energized at the time because of the presence of the contact 74 which has not closed and the significance of which will be made apparent presently.)

Time-five .minutes l0 seconds: contact 74 closes energizing the components 60 and 60 providing ignition at spark gaps 32 and 32' so that the pilot burners are reignited.

Time--five minutes 25 seconds: Contact 74 opens disconnecting the sparking components 60 and 60.

Time-five minutes 30 seconds: (assuming the 20 second warm-up time for the flame switches); switches 40 and 40 engage their lower contacts and supply power to Wire 77.

Time-five minutes 45 seconds: contact 76 opens :and contact 78 reclosed completing the circuit to the main gas valve 14 bringing about restarting of main burner 10 so that the system is back in regular operation, assuming that sparking, and re-ignition of pilot burner 16 have properly occurred as normally expected.

Time-six minutes: contacts 72 and 71 open and timer stops.

The contact 74 is a very important contact in the system or circuit as can be understood from the following example illustrating the hazard that could occur in the absence of this contact, in the event, for example, of a momentary power failure at a particular time.

FAIL SAFE CHARACTERISTICS Power failure It will tbe noted that in the event of a power failure, that is, a momentary power failure causing closing of the gas valves, the pilots will be extinguished upon resumption of power andafter cooling of the ame switches, the timing cycle will re-start requiring a purging period before there can be re-ignition. That is there cannot tbe reignition until timer contacts 72 and 74 have closed. Failure of either or any pilot flame will shut down the entire system.

The presence of the contact 74 has signicance as may be understood from the following.

(Because of mechanical considerations the timer contact 78 will reclose after ve minutes and 45 seconds.) The timer contact 72 opens after six minutes so that without contact 74 there would be a period of l5 seconds during which the contact 78 would be closed and the main gas valve open during which there would be sparking. If there should be a power failure, that is, a momentary failure during this period everything would shut off and when the power returned there would be sparking with the main gas valve and pilot valve both open at the same time, and this would give rise to a dangerous condition, that is, with sparking and igniting of the main burner or burners directly from the spark gap or gaps rather than from the pilot flame or flames. As will be seen, upon resumption of power after momentary failure the arne switches have not had time to open.

Contact failure As may be seen from the foregoing failure of any pilot ame shuts down the complete system requiring a positive purging period under control of the timer before there can be restarting. In the event of failure of contacts causing shut-down restarting is prevented. Contacts 76 and 78 are critical inasmuch as contact 76 controls the pilot valve 30 and contact 78 controls the main gas valve 40. These contacts are part of a single pole double throw device so that in the event one of them is closed the other must necessarily be opened (see FIG. 2). As a result, if, for example, contact 78 should weld in a closed position, this prevents closing of contact 76 and it is then not possible to open the pilot burner valve 30. On the other hand if Contact 76 should weld shut it then becomes impossible to close contact 78 and the m'ain gas valve 14 cannot be opened and in either event the system fails safe.

Timer failure If the timer fails, it cannot go through its cycle and thus the system cannot be restarted after shut down. Thus it fails safe.

The pilot valve 30 may be opened by closing the two manual switches 50 and 52 which complete the circuit through the wires 90, 92 and switch 5 2 and valve 30 back to the other side of the line. The ignition sparking may be started first. Closing manual switch energizes the two sparking components 60 and 60 through the circuit including the Wire 90 after which the valve 30 is opened by way of the manual switch 52.

From the foregoing those skilled in the art will readily observe and understand the nature and construction of the invention and the manner in which it achieves and realizes all of the objects and advantages as set forth in the foregoing as well as the many additional advantages that are apparent from the detailed description.

The foregoing disclosure is representative of a preferred form of the invention and is to be interpreted in an illustrative rather than a limiting sense, the'invention to be accorded the full scope of the claims appended hereto.

What is claimed is:

1. In an automatic ignition control system of the type having a pilot burner for igniting a main burner, a main fuel supply control device and a pilot fuel control device, and electrical means for igniting a pilot burner comprising, in combination, control means including flame responsive contacting mechanism responsive to pilot flame whereby to interrupt fuel supply upon flame failure after a period of cooling, means for restarting the system after shut down comprising a timer and contacts actuatable thereby in a predetermined sequence, said contacts including a first contact which controls the said fuel supply device for the main burner to render it inoperative, a second contact operable `to `open said pilot fuel control device, a third contact operable to energize the ignition means for igniting a pilot burner, said timer having means for actuating said first contact to control said control device for the main fuel to allow supply of fuel after a predetermined time, and means whereby the timer reopens said contact energizing the ignition means prior to the reactivation of said control device controlling fuel to the main burner, whereby it is not possible to ignite the main burner fuel by the electric igniting means.

2. A system as in claim 1 including means whereby said timer controls said second contact to supply fuel to the pilot burner during the time that said ignition means is operating, and means to deenergize said pilot fuel control device when the main fuel supply device is energized.

3. A system as in claim 1 wherein said third contact is actuated to operate said control device controlling the pilot fuel prior to the actuation of said contact controlling the ignition means, said flame responsive means resuming control upon ignition of the pilot burner.

4. A system as in claim 1 including plural pilot burners, and plural llame responsive devices, each of said flame responsive devices being connected to be operable to shut down the system and to bring about a restarting sequence.

5. A system as in claim 1 wherein said first and third contacts are part of a single pole double throw contacting mechanism precluding simultaneous energization of the pilot fuel and main fuel control devices.

6. In a control system of the type having a main burner and a main fuel supply control device, a pilot burner, and a pilot burner control device, a control system comprising in combination, a contact controlling the main fuel supply device and a contact controlling the pilot fuel supply device, said contacts being part of a single pole double throw contacting means whereby if one is closed the other is opened thereby rendering it impossible to energize both of said control devices simultaneously through said contacts, and means whereby in the event of shut down of the system restarting is dependent upon said contacts.

References Cited UNITED STATES PATENTS 3,064,719 11/1962 Graves 431-45 X 3,181,592 5/1965 Krajc et al. 431-45 3,185,203 5 1965 Hassa 431-45 EDWARD G. FAVORS, Primary Examiner U.S. C1. XR..

Images