US2417667A

US2417667A - Safety control system for fuel burners

Info

Publication number: US2417667A
Authority: US
Inventors: Charles K Strobel
Original assignee: Robertshaw Thermostat Co
Current assignee: Robertshaw Thermostat Co
Priority date: 1944-06-19
Filing date: 1944-06-19
Publication date: 1947-03-18
Anticipated expiration: 1964-03-18

Description

* 18, 1947. c. K. STROBEL 2,417,667

SAFETY CONTROL SYSTEM FOR FUEL BURNERS I Filed J une 19, 1944 2 Sheets-Sheet 1 40 44 60 m'zwzzy c'lomw Dela d em 52 1 l t'mz ySw m [me BallanRe/wzon mvanrbx C'liarlerlLStrvbel m1; 4110mm March 18, 1947. c, s o 2,417,667

SAFETY CONTROL SYSTEM FOR FUEL BURNERS Filed June 19,1944 2 Sheets-Sheet 2 66 4g m- J zg, Z 95' 93. 5% 74 60 54 46 99,

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ATTORNEY Patented Man 18, 1947 UNITED STATES PATENT OFFICE SAFETY CONTROL SYSTEM FOR FUEL BURNERS Charles K. Strobel, Pittsburgh, Pa., assignor to Robertshaw Thermostat Company, Youngwood Pa., a corporation of Pennsylvania Application June 19, I944, Serial No. 540,979 Claims. (Cl. 158117.1)

is arranged so that after a forced valve pick-up the current for holding the valve open is reduced below pick-up value to ensure quick closing-upon a small variation in resistance of the flame sensitive resistor. i

The apparatus described herein embodies several improvements'over the system disclosed in the earlier application and extends the field of usefulness of such controls in many ways; one object of the invention being to permit substitution of different types of fuel control devices of various fuel capacities and electrical characteristics without'requiring corresponding alteration in the circuit constants or the existing circuit elements.

Another object of the invention is to visibly signal the operating condition of the apparatus,

such as whether the fuel control device is in condition to supply fuel to the burner.

Another object of the invention is to avoid deterioration of the parts and consequent failure in operation as may occur from exposure to impuri-' tiesin the fuel.

Another object of the invention is to permit the use of commercially available fuel contrdl devices embodying means to permit manual operation during electric power failure and'automatic changeover on power resumption.

Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawing wherein Fig. 1 is a schematic view of a safety control apparatus for gaseous fuel burners embodying this invention, Fig. 2 is a similar schematic view of a modification.

Referring more particularly to the drawing, a

gaseous fuel burner III is supplied with fuel by a. main fuel pipe l2. The fuel supply is controlled by a main valve 14 which, in this instance, is arranged for manual operation by a suitable knob or handle IE but which may be arranged for thermostaticoperation, if desired. Interposed in the fuel supply pipe i2 between the main valve [4 and the burner I8 is an electromagnetic or solenoid gas valve l8 of any known type which is arranged to be opened by energization of the solenoid and closed by gravity upon deenergization'thereof. Preferably, the solenoid As disclosed in my valve I8 is of the commercially available manualset automatic-reset type in which the manual operation of a plunger 20 serves to open the valve uponpower failure but upon resumption of the power 'supply the .valve is automatically retained in open position under solenoid control. As will be apparent hereinafter, under normal operating conditions the opening of the solenoid valve l8 to admit fuel to the main burner I0 is contingent upon current of a predetermined value being supplied to a control relay 22 and is not, as in the disclosure previously referred to, dependent upon such current being supplied to'the solenoid valve itself.

A pilot burner 24 is provided for igniting the main burner l0 and is supplied with fuel from a conduit 26 connected to the main valve 14 to receive fuel from the pipe l2 when the main valve is opened. The pilot burner 24 is not under control of the solenoid valve l8 as is the main burner l0 and it will be apparent that the provision of a pilot burner is not essential to the successful operation of the control disclosed herein. In either event it is preferable to employ automatic lighting means shown as positioned adjacent the pilot burner 24 and comprising an electric resistance igniter 21 and associated resistor 29.

Electric current for the operation of the apparatus is supplied by the line wires28 connected to the primary of a transformer 30 which may receive commercial current at the primary at a voltage variation from to volts. In this embodiment, the main valve M has a main switch (not shown) combined therewith which is of the double-pole type having two terminals connected in series circuit with line wires Zii by wires 32 and- 34. The other two terminals of the doublepole switch are connected by wires 36-38 in series circuit with the primary of the transformer 3d.

As previously indicated, the operation of the solenoid valve ii! is controlled by the control relay 22. This relay may include a magnetizable core 40 in the form of a floating plunger which moves into attracted position relative to an operating coil 42 in response to current above a predetermined minimum value being supplied to the coil 42 cannot retain the core 40. Movement of the core 40 into and out of attracted relationwith the coil 42 serves to operate a hinged contact arm 44 as indicated in broken lines in the drawing. In the attracted position of the core 40, that is, when energizing current above the predetermined minimum value is being supplied to the coil 42, engagement is made by a contact 45 carried by the contact.arm 44 with a fixed contact 48. In the released position of the core 48, that is, when current of less than the predetermined minimum value is being supplied to the coil 42, the contact arm 44 will be moved to the position shown in broken lines in the drawing, causing separation of the contacts 48-48.

A ballast resistor 58 having normally a relatively low resistance and a positive temperature coeflicient of resistance is positioned to be exposed to the flame of the pilot burner 24 for causing, either directly or in cooperation with other devices to be described, operation of the relay 22, to move the contact arm 44 from one position to the other.- It will be understood that although the ballast resistor 50 is thermally responsive to the passage of current therethrough, it is primarily the heating thereof by the pilot burner flame which causes the variation in resistance relied upon in this embodiment.

A second or control resistor 52 is provided for cooperation with the ballast resistor 58 to control operation of the relay 22 and serves to render the adjustment of the circuit constants less critical.

In order to accelerate the operation of the relay 22 upon a change in the value of the current supplied thereto, the control resistor 52 may also have normally a relatively low resistance and a positive temperature coeflicient of resistance as in the case of the ballast resistor 50. The resistor 52 is not, however, exposed to the heat of any flame but is adapted to become heated upon passage of electric current therethroughand will change its resistance appreciably in accordance with changes of temperature causedby changes in the value of the current flowing through it.

A cut-out 54 is also included in the relay circuit and is preferably of the thermal type having time-delayed operation for a purpose which will be apparent hereinafter. Such devices are constructed with predetermined time-current charswitch 58 having a timing element and forming one of a pair of such devices of the mercury tube type both operable by a single actuating coil 60. The other switch 58 of the pair also has a timing element which serves to deenergize the igniter 21 after a predetermined period. Both switches and 58 open after a specified time-delay and are initially closed. In this embodiment of the invention the switch 58 may have a time-delay of eighteen seconds before opening after the main switch of valve I4 is closed and is adapted for instantaneous closing upon opening of the main switch of valve i4 or other deenergizing of the actuating coil 58. The switch 56 may have a time-delay oi five seconds for opening following the closing of the main switch of'valve i4 and also have instantaneous closing. It is not essential, however, that the switch 58 having the longer time-delay period alsohave an instantaneous closing upon operation of the main switch of the valve H to open position or other deenergizing of the coil 68, it being only necessary that it assume a closed position before the switch 581s again actuated to open position. In this embodiment where such a short time delay as flve secends is established for opening of the switch 58 it is preferable to arrange the switch 58 with an instantaneous closing action as will be apparent.

An electric visible signal is provided to indicate the opened or closed position of the solenoid valve I8 and may take the form of a signal lamp -82 having a resistor 84 associated therewith.

pipe l2 as far as the electromagnetic or solenoid valve l8 which is initially closed. As the main switch combined with the main fuel valve I4 is also operated to closed position when the main fuel valve is opened, the electrical circuit is established as follows: From the lower terminal of the secondary of the transformer by wire to junction A of the bridge, wire 68, series resistor 28, wire 68, ign'iter 21, wire 18, switch 58 and wire 12 to junction 3 of the bridge. The adjacent arm of the bridge is connected-by wire 14 to 11inction B, coil 42 of control relay 22, wire 18, to Jun:-

tion C of the bridge, the next adjacent arm being connected by wire 18 to junction C, ballast resistor 50, and wire 88 to junction D-of the bridge; and the fourth arm of the bridge being conne :ted

by wire 82 to junction D, control resistor 52, wire 84 and wire 88 to junction A of the bridge. A wire 85 connects Junction C of the bridge to the upper terminal of the secondary of transformer 38. v p

The cut-out 54 is conne :ted as the detector arm of the bridge in this initial or starting period circuit by a wire 86 connecting one terminal thereof to junction D and a wire 88 connecting the other terminal thereof to the wire 14 from junction B. The temporary short-circuiting of coil 42 is established by connecting one terminal of the switch 56 to junctionB of the bridge by a wire 88 and connecting the other terminal thereof to wire I8 by a wire 92, The actuating coil 80 of the switches has one terminal connected by wire 83 to wire I8 and the other terminal connected by wire to junction A.

Upon initial closing of the main switch of valve l4 the elements comprising the bridge circuit are unheated and the relay coil 42 is short-clr cuited by the switch 58,-consequently the bridge networlr is considerably unbalanced. The current through the

wires

88 and 85 to the cut-out 54 is large until the circuit elements heat up and the bridge balance is improved, but, due to the time lag of the cut-out 54, the large inrush current upon initial closing of the main switch permitted by the attraction of the core 48 to rent therethrough only.

move to close the contacts 44-49 and energize the solenoid valve circuit which may be traced as follows: From junction C, wire 16, contact 45, contact 48, wire9'4, resistor 54, wire 98. the coil of solenoid valve i8, wire 98 and wire 69 to lunction A, all in series'with the transformer secondary. Energization of the valve through the circuit described will permit fuel to flow from the main fuel pipe I2 to the main burner N where it is ignited by the flame from the pilot burner 24. The ignal lamp 52 which is connected across the resistor 64 by wires 99 and Hill is also energized and provides visible indication that the solenoid valve I8 is in open position.

The energizing of the relay coil 42 at the ex- 15 piration of the five second time-delay period as described is effectuated by supplying current of sufllcient or pick-up value thereto. This current may be of greater value than that supplied to the coil 42 after the pick-up has been made and which is required only for holding purposes. As the igniter 21 is still connected in the circuit when the pick-up occurs and is establishing a relatively low impedance therein, it is apparent that the required value of current is available even if the ballast resistor 591 s unheated by the pilot burner flame and is of relatively low resistance.

It may be assumed that the ballast resistor 50* and the control resistor 52 have now become heated, the former due to the flame from the pilot burner 24 and the passage of current therethrough and the latter due to the passage of our- Consequently, the bridge balance is improved to such an extent that current through the cut-out 54 is reduced to a value insufficient to cause operation thereof regardless of whether the main switch of valve i4 is manipulated in on-ofi-on cycles at this period of starting operation. The cut-out will now operate only on passage of. overcurrent and thus protects the circuit against failure of the ballast resistor during the running operation. Atv the expiration of the eighteen-second time delay of the switch 58, the igniter 21 and series resistor 29 become deenergized by operation of the switch 58 to open position. The bridge nature of the circult is thus eliminated, unless the network is considered a bridge with infinite impedance in one arm.

This operation of the switch 58 having the longer time delayed action to open position is entirely automatic and occurs regardless of whether the ballast/resistor 50 is heated by the pilot burner flame or even whether the pilot burner has become ignited. As previously indicated, the current to the relay coil is now reduced below pick-up value and need be only at the predetermined minimum value suflicient to retain the core ill in attracted position. However, when the witch 58 opens, unless the ballast resistor 50 has become heated and its resistance increased sumciently to raise the resistance of the shunt established thereby around the relay coil 42 and cut-out 54 to compensate for the increase in total circuit resistance, then the current to the relay coil 42 will decrease below the predetermined minimum value for holding purposes and the core 40 will be released to actuate contact arm 44 to open contacts 46-48. It will be understood that the predetermined minimum current value referred to herein is established by adjustment of the circuit constants and takes into account the fluctuations in the line voltage.

- Such action of the core 40 will open the circuit of the solenoid valve l8 and deenergize the valve,

causing it to close to shut-off the fuel supp y to the main burner |0. Moreover, if at any time during the operation of the apparatus the flame of the pilot burner 24 ceases then the ballast resistor 59 will cool and its resistance be lowered in consequence so that the current 'through the relay coil 42 is rendered insumcient to retain the core 40 in-attracted position whereupon closure 10 of the solenoid valve 19 will occur. Whenever the solenoid valve thus becomes closed the. signal lamp 62 will be deenergized and provides vis- .ual indication that the main burner is not in operation. s

It will be apparent from the foregoing description that the provision of the relay 22 permits the use of control valves of difierent types and capacities without limitation to those which a v will operate on small variations in current values. The principle of using" such. small variations in current values to control supply of fuel to a burner is retained by providing the relay to open and close the valve circuit. The control relay which is the primary safety device of the appa- 25 ratus i not exposed to the fuel passing to the burner as is the solenoid valve, so that any impurities such as gum cannot cause sticking of the movable parts and defeat the safety purposes.

could be arranged for 100 per cent shut-oil by placing the coils 21 and 50 either in the main burner flame where a pilot burner is dispensed with as previously noted herein or in the flame of a pilot burner supplied by a conduit connected with the outlet side of the solenoid valve l9 as disclosed in the alternative arrangement illustrated in Fig. 2. Thus, during the first delay period no fuel would flow and at the end thereof.

both main and pilot burners wouldreceive fuel (where a pilot burner is used). In its broad aspects the invention is not to be deemed limited to the provision of an igniter and time-delay control switches although a complete system has been disclosed including such features. While the signal lamp and the solenoid valve have been disclosed in the preferred embodiment as connected in the secondary circuit of the transformer, it is apparent that the valve could be connected to the primary of the transformer or power supply line and the signal lamp connected across the valve coil as also disclosed in the embodiment shown in Fig. 2. As the arrangement.

and construction of parts and the operation of the embodiment shown inFig. 2 are in all other respects identical with those described in con-.

nection with Fig. 1, similar reference numerals made by connecting wire 98 from one terminal of the valve to wire 38 instead of to wire 66 as in and changes can be made in the arrangement and combination of parts and in the details of construction herein disclosed within the scope of,

It will further be apparent that the system was previously made from contact 46 to wire 15 is now made by a wire lili from contact 46 to. wire 36. The other connection of this valveisthe previous embodiment. All such modifications controlling the supply of fuel to the burner, an

' energizing circuit for said device including the source, a control relay having contacts connected in said circuit and operable for energizing and deenergizing said device for movement thereof between said positions in response to variations in the current value supplied to said relay, and circuit means connecting'said relay to the source, said circuit means including a ballast resistor having a preselected temperature coefliclent of resistance electrically connected to said relay and located to be heated by the burner flame, said resistor. being adapted to vary in resistance according to the presence or absence of said flame for causing said current variations upon extinguishment of said flame suflicient to effect movement of said device position. Y

2. Safety ontrol apparatus for fuel burners having a source of electrical energy, comprising an electrically operable device movable between fuel flow permitting and preventing positions for controlling the supply of fuel to the burner, an energizing circuit for said. device including the source, a control relay having contacts connected in said circuit and operable for energizing and deenergizing said device for movement thereof between'said positions in response to variations in the current value supplied to said relay, and circuit means connecting said relay to the source, said circuit means including a ballast resistor having a preselected temperature coefllcient of resistance electrically connected in shunt with said relay and located to be heated by the burner flame, said resistor being adapted to vary in resistance according to the presence or absence. of said flame for causing said current variations upon extinguishment of said flame sufficient to efiect movement of said device to said fuel flow preventing pos tion.

3. Safety control apparatus for fuel burners having a source of electrical energy, comprising an electrically operable device movable between fuel flow permitting and preventing positions for controlling the supply of fuel to the burner, an energizing circuit for said device including the source, a control relay having contacts connected in said circuit and operable for energizing and. deenergizing said device-for movement thereof between said positions in response to variations in the current value supplied to said relay, and

circuit means connecting said relay to the source,

said circuit means including a ballast resistor having normally a relatively low resistance and a positive temperature coefficient of resistance connected in shunt with said relay and located to said fuel flow preventing and including a ballast resistor having a preselected temperature coefficient of resistance electrically connected to said relay and located to be heated by the burner flame, a second resistor connected by said circuit means in circuit with said relay and adapted for cooperation with said ballast resistor to cause said current variations according to the presence or absence of said flame and sufllcient to effect movement of said device to fuel flow preventing position upon extinguishment of said flame, and means electrically connected to said second resistor for rendering the second resistor effective after a predetermined period during which said ballast resistor has time to become heated.

'5. Safety control apparatus for fuel burnershaving a source of electrical energy, comprising an electrically operable device movable between fuel flow permitting and preventing positions for controlling the supply of fuel to the burner, an energizing circuit for said device including the source, a control relay having contacts connected in said circuit and operable for energizing said device for movement thereof to said fuel flow permitting position when current of at least a predetermined minimum value is supplied to said relay, circuit means connecting said relay to the source and including a ballast resistor having a preselected temperature coefficient of resistance electrically connected to said relay and located to be heated by the burner flame, a second resistor connected by said circuit means in circuit with said relay and adapted for cooperation with saidtween an initially closed and an open position to I control the supply of fuel to the main burner, electromagnetic means for operating said valve member to open position and maintaining it open, an energizing circuit for said means including the source, a control relay having contacts connected in said circuit and being operable for causing energization of said means when current of at least to be heated by the burner flame, said resistor being adapted to vary in resistance according to the presence or absence of said flame for causing said current variations upon extinguishment of said flame suflicient to effect movement of said device to said fuel flow preventing position.

4. Safety control apparatus for fuel burners having a source of electrical energy, comprising an electrically operable device movable between fuel flow permitting and preventing positions for controlling the supply of fuel to the burner, an energizing circuit for saiddevice including the source, a control relay having contacts connected in said circuit and operable for energizing and deenergizing' said device for movement thereof between said positions in response to variations in the current value supplied to said relay, cir cult means connecting said relay to the source a predetermined minimum value is supplied to said relay, circuit means connecting said relay to the source and including a ballast resistor having normally a relatively low resistance and a positive temperature coefficient of resistance connected in shunt with said relay and located to be heated by the pilot burner flame, asecond resistor in series v circuit with said relay and cooperable with said control the supply of fuel to the main burner, electromagnetic means for operating said valve member to open position and maintaining it open, an energizing circuit for said means including the source, a control relay having contacts connected in said circuit and being operable for causing energization of said means when current of at least a predetermined minimum value is supplied to said relay, circuit means connecting said relay to the source and including a ballast resistor having normally a relatively low resistance and a positive temperature coefficient of resistance connected in shunt with said relay and located to be heated by the pilot burner flame, a second resistor in series circuit with said relay and cooperable with said ballast resistor for causing said current value to fall below said minimum in the absenceof said flame, an electric igniter for said pilot burner and adapted for shunting said second resistor and preventing said cooperation thereof, and switching means for electrically disconnecting said igniter and thereby discontinuing the shunted nature of said shunted resistor and rendering it cooperable after a predetermined period during which said ballast resistor has time to become heated.

8. Safety control apparatus for fuel burners having a source of electrical energy and main and pilot burners comprising an electrically operable device for controlling the supply of fuel to the main burner, an energizing circuit for said device including the source, a control relay having contacts adapted to open and close said circuit and an operating coil therefor-adapted to be supplied with current of at least a predetermined minimum value, circuit means connecting said relay to the source and including a ballast resistor connected in shunt with said coil and located to be heated by the pilot burner flame, a second resistor in series circuit with said coil and cooperable with said ballast resistor to cause said current value to fall below said minimum in the absence of said flame, an electric igniter for said pilot burner connected in shunt with said second resistor, switching means having a timing element for short-circuiting said relay coil for a predetermined period during which said igniter is adapted to produce said flame, said energizing circuit being closed by operation of said contacts at the expiration of said period, and second switching means having a timing element for electrically disconnecting said igniter after a second predetermined period during which said ballast resistor has time to become heated by said flame, said energizing circuit remaining closed or becoming open by operation of said contacts at the expiration of said second period according to the heated orunheated condition of said ballast resistor.

9. Safety control apparatus for fuel burners having a source of electricalenergy comprising an electrically operable device movable between fuel flow permitting and preventing positions for controlling the supply of fuel to the burner, an energizing circuit for said device including the source, a control relay having contacts connected in said circuit and operable for energizing and deenergizing said' device for movement thereof between said positions in response to variations inthe current value supplied to said relay, circuit means connecting said relay to the source and including a ballast resistor having a preselected temperature coeillcient of resistance electrically connected to said relay and located to be heated by the burner flame, a second resistor connected by said circuit means in circuit with said relay and adapted for cooperation with said ballast resistor to cause said current variations according to the presence or absence of said flame, means for renderinglthe second resistor effective after a predetermined period during which said ballast resistor has time to become heated, and an electric visible signal responsive to operation of said relay contacts for indicating the position of said electrically operable device.

10. Safety control apparatus for fuel burners having a source of electrical energy and main and pilot burners comprising an electrically operable device movable between fuel flow permitting and preventing positions for controlling the supply of fuel to the main burner, an energizing circuit for said device including said source, a control relay having contacts adapted to open and close said circuit and an operating coil therefor adapted to be supplied with current of at least a predetermined minimum value, a ballast resistor having a preselected temperature coefficient of resistance connected in shunt with said coil and located to be heated by the pilot burner flame, a second resistor in series circuit with said coil and cooperable with said ballast resistor to cause said current value to fall below said minimum in the absence of said flame thereby causing operation of said contacts to open said circuitand efiect movement of said device to said fuel flow preventing position, an electric igniter for said pilot burner connected in shunt with said second resistor, switching means having a timing element for short-circuiting said relay coil for a predetermined period during which said igniter is adapted to produce said flame, said energizing circuit being closed by operation of said contacts at the expiration of said period, a second switch ing means having a timing element for elec-- trically disconnecting said igniter after a second predetermined period during which said ballast resistor has time to become heated by said flame, said energizing circuit remaining closed or becoming open by operation of said contacts at the expiration of said second period according to the heated or unheated condition of said ballast resistor, and an electric signal lamp connected in said energizing circuit in series circuit with said device for indicating the position thereof.

CHARLES K. STROBEL.

1 REFERENCES CITED vThe following references are of record in the file of this patent:

uNrrEn STATES PATENTS- British l. 1932