US2491125A

US2491125A - Safety control system for fuel burners

Info

Publication number: US2491125A
Application number: US728893A
Authority: US
Inventors: Philip R Marvin
Original assignee: Milwaukee Gas Specialty Co
Current assignee: Milwaukee Gas Specialty Co
Priority date: 1947-02-15
Filing date: 1947-02-15
Publication date: 1949-12-13
Anticipated expiration: 1966-12-13

Description

Dec. 139 1949 P. R. MARVIN 2,491,125

SAFETY CONTROL SYSTEM FOR FUEL BURNERS Filed Feb.. 15. 1947 f fm/gm,-

P/zzo E www@ Patented Dee. 13, 1949 2,491,125 SAFETY coN'rnor. SYSTEM Fon FUEL mmm-ms Philip R. Marvin, Wauwttosa, Wis., assigner 'to Milwaukee Gas Specialty Company, Milwaukee,

^ l, Wis., a corporation o! Wisconsin Application February l5, 1947, Serial No.'728,'893

Claims. (BLISS-1173.)

This invention relates, in general, to a burner control sysem, and has particular relation to burner control systems employing means .for interrupting the supply of fuel to a main burnerln the event a pilot burner is extinguished.

While the particular system which I shall d'escribe hereinafter in connection with the drawing is, in general, of the type in which an electric circuit for an electroresponsive valve in the fuel conduit has contacts under the control of a relay in the controi circuit, it 1ste be understood that the invention in its broader aspects is not limited to this particular type of system but may be embodied in other types of systems as suitable or desired;

Prior systems of the type with which the present invention is concerned -have proposed the use in position, for example, where it is subject to the heat of a pilot burner, of a thermistor which has a negative temperature coeiilcient of resistivity and operates, when heated by the pilot burner, to pass suilicient current to maintain an electroresponsive valve -in the fuel conduit open when the pilot burner is burning and the circuit including the electroresponsive valve is otherwise closed, and to reduce the current so that the electroresponsive valve operates to Aclosed position when the pilot iiame is extinguished.

` In these prior schemes however, the thermistor has usually'been subjected, for example, to the heat within the burner compartment and/or to the heat 0f the main burner or other ambient temperature. As a result, prompt actuation of the valve to closed positionv when the pilot iiame is extinguished is not assured because the ambient temperature mayv heat the thermistor an amount to pass suiiicient current to maintain the electroresponsive valve in open position for a considerable period of time after the pilot flame is extinguished.

With the valve in the fuel condit open and the pilot ilame extinguished, fuel may ilow in considerable volume 'to the main burner. As a re'- sult the burner compartment may be filled, -foiexample, with a highly explosive gas-air mixture, thus presenting the possibility of serious Aand disastrous explosion when it is attempted to relight the pilot burner. These things can happen and have happened in using defective so-called safety devices, and, profiting by experience, 'the requirements of the American Gas Association that such-devices be safe have become increasingly stringent.

One of the main objects of the present invention is to provide an improved burner control system in which the problems previously presented are overcome.

Another object of 'theinvention is to'provide a 'burner control system inwhich prompt actuation of the valve in the fuel conduit to closed position "when the pilot, name is -extinguished is assured, and, more particularly, a system in which the valve cannot be maintained open or its closing retarded, for example, by heat within the burner compartment and/or the-heat of the main burner or other ambient temperature.

Another object of the invention is to provide I -a burner control system 'using thermistor type and contacts ln'the first circuit controlled by energization of the coil, a pilot burner, a rst thermistor -having -a negative coeiiicient of resistivity connected in'series with'the -relay coil and positioned to be subjected to the heat of the pilot ilame so as to pass 'suilicient current through the coil to cause the valve to be opened and maintained open when the pilot burner is lighted, said thermistor reducing 'the current through said relay coil to cause closing of the valve when the pilot name is extinguished, a shunt circuit connected to the second circuit around the relay coil, and a second thermistorfhaving a negative coleilicient of resistivity positioned to be subjected to ambient temperature and connected into -th'e Ashunt circuit in series with the relay coil with the circuits for the first and second thermistors so calibrated that, when the system is in proper operation, the holding current for the relay is reduced to such value that the 'relay is just maintained energized to close the contacts in the circuit for the valve due to shunting fof current through the -shunt circuit including the second thermistor. y

Another object of 'the invention is lto provide a system vas set -forth inthe `preceding paragraph wherein there is a iirst resistor in the second circuit in series with the relay coil and the iirst thermistor and a second resistor in the shunt circuit in series with the r'elay coil and the second thermistor for calibrati'ng and adjusting the system.

shown at I is a main burner.

its simplicity in construction, its economy in manufacture, its eifectiveness in use, and the absence of moving contacts and the like in the devices subjected to the heat of the pilot flame and to the ambient temperature.

Further objects and advantages of the invention will appear from the following detailed description, taken in connection with the accompanying drawing in which thesingle gure is a diagram showing schematically the parts and circuit connections of one form of system embodying the present invention.

Referring now to the drawing, the burner It may be the main burner for a room or space heater, or it may be the burner for a water heater or for a iloor furnace, an over burner, one or more top burners for a gas range, or any other burner, and of any suitable construction.

A fuel supply pipe or conduit 2 leads to the burner i for the delivery of gaseous or other fuel thereto, for example, through a mixing chamber 3 to which air is admitted through adjustable aid inlets (not shown), as well understood in the art. The flow of gas through the conduit 2 is controlled by a valve 4 of any suitable electroresponsive or electrically operated type. For purposes of illustration, the valve 4 may be a solenoid valve operated to open position by the iiow of current through its coil Band to closed position by a spring 1.

The pilot burner 8, which is located in juxtaposition to the main burner I to maintain a pilot flame 9 for igniting the main burner, is supplied with gaseous fuel by a pilot supply pipe IIl. The pilot supply pipev I may be connected, for example, to the pipe 2 anterior of the valve 4, or through this valve, or in some cases posterior of the valve, or to any other source of fuel supply.

Power for operating the valve 4 is supplied from a suitable source, for example the line wiresA I2 of a source of alternating current such as the type of alternating current linewhich averages about 115 volts. The circuit through the coil i of the valve 4 is controlled, for example, by a relay I3 having a coil I4 and a pair of contacts I5. One contact I5 is connected in circuit with one of the line wires I2. The other contact I5 is connected by a conductor I6 to one side of the coil 6, and the other side of the coil 6 is connected in circuit with the other line wire I2.

A thermistor I8 is positioned so as to be heated by the pilot ilame I9 when the pilot llame is burning. The thermistor I 3, which is preferably not positioned dire/ctly in the llame, has a negative temperature coeiilcient of resistivity, i. e., it is a non-conductor, or relatively a non-conductor, when not subjected to the heat of the pilot name or a corresponding temperature, and changes to an electric conductor when heated by the pilot flame or a corresponding temperature.

One side of the thermistor I3 is connected by a conductor 2l to one side 2I of a suitable voltage source. A conductor 22 connects the other side of the thermistor I8 through an adjustable resistor 23 and the coil I4 of the relay I3 to the other side 24 of the voltage source. 'I'he coil I4 of relayI3. adjustable resistor 23, and thermistor I8 are thus connected in series in an electric circuit leading, for example, from one side of the voltage source through the thermistor, adjustable resistor, and relay coil to the other side 24 of the voltage source.

'Ihe adjustable resistor 23 is preferably adjusted to pass just enough current to cause the the thermistor I8 is heated by the pilot flame and there is suilicient diierential in the pilot llame temperature and the ambient temperature, as will presently appear.

A second tlf.` ermistor 26 is connected in a shunt circuit around the coil I4 of the relay I3, and the shunt circuit includes a resistor 2'I in series with the Athermistor 26. This second thermistor 26 has a negative temperature coeflicient of resistivity. The shunt circuit comprises a conductor 28 connecting one side of the thermistor 26 to the conductor 2I to one side of relay coil I4, and a conductor 29 connecting the other side of the thermistor 26 to the conductor 22 on the other side of the relay coil I4.

The thermistor 26 is positioned so as to be subjected to the ambient temperature which may be the heat within the compartment (not shown) for the main burner and/or the heat of the main burner or other ambient temperature. As previously stated, the adjustable resistor 23 is preferably adjusted to pass just enough current to cause the relay I3 to maintain the contacts I5 closed and thereby to maintain the valve 4 open as long as the thermistor is heated by the pilot flame and there is sufficient differential in the pilot name temperature and the ambient temperature. The desired balance can be obtained by connecting suitable milliameters in the circuits for the respective thermistors I8 and 23 and noting the readings in adjusting the resistor 23.

In operation, with the heat' of the pilot flame I9 heating the thermistor I8 and the heat of the ambient temperature on the thermistor Il suihciently lower than the heat to which this thermistor is subjected by the pilot ilame the thermistor I8 passes current through the relay coil I4 suilicient to close contacts I5. 'I'he voltage across the line wires I2 is thus applied to the coil 6 of the valve 4, opening this valve and holding it open for the supply of fuel to the burner I as long as this condition exists.

Ihe resistor 23 constitutes an adjustable protective device for the thermistor I8, and the resistor 21 constitutes a suitable protective device for the thermistor 26. The resistors constitute current limiting devices for preventing destruc- 50 tive overheating of the thermistors.

If during operation of the system with the thermistor I8 heated by the pilot flame sumciently to maintain the valve 4 open and the ambient temperature is sinsuillcient to heat the 55 thermistor 26 sufilciently to by-passfthe current around the relay I3 so as to cause closing of the valve 4, and the pilot flame is extinguished, the following action occurs. The thermistor I8 immediately cools and becomes non-conducting or 6o sumciently non-conducting so that it will not pass sumcient current to cause relay I3 to hold contacts I5 closed. These contacts then open the circuit for the valve 4, which operates to closed position shutting oif the supply of fuel to 65 the burner I.

To close the circuit which opens the valve 4 and maintains it open, the pilot burner is lighted and the ilame I3 issuing therefrom heats the thermistor I8 and causes it to pass suillcient cur- 70 rent through the relay I3 to close contacts II. This energizes the coil 6 of the valve 4, which thereby operates to open position to pass fuel to the main burner I. It is thus'apparent that no passage of gas to the burner I can occur un- 75 less the pilot flame is burning and the ambient It is to be understood that the electric circuit for controllingthe valve l may have a thermostat, limit device, or other control means therein, in which case the .valve 4 will be caused to open and to be held open by the heat of the pilot iiame on the thermistor I8 only when such thermostat, limit device, or other control is in position closing the circuit which includes the thermistor I8 and the, thermistor 26 is not heated by the ambient temperature suillciently to by-pass the coil I4 of the relay I3.

The thermistors I8 and 26 may be of any suitable form. Such devices are well known and will not be described in detail. Sumce it to state that the thermistor elements may be formed, for example, of ierric oxide (FezOs) with about 1% of titanium dioxide (T102), of suitable particle size, or by mixing oxides with an organic binder and solvent and applying suitable contacts, or otherwise as desired.

The embodiment of the invention shown in the drawing is for illustrative purposes on1y, and it is to be expressly understood that said drawing and the accompanying speciiication are not to be construed as a definition of the limits or scope of vthe invention. reference being had to the appended claims for that purpose.

I claim:

1. In a system of the class described, in combination, a fuel conduit, an electroresponsive valve in said conduit. a iirstelectric circuit for said valve, a second electric circuit. a relay having a coil in said second circuit and contacts in said iirst circuit controlled by energization of said coil, a pilot burner, a first thermistor having a negative coeilicient of resistivity connected in series with said relay coil and positioned to be subjected to the heat of the pilot iiame so as to pass suiilcient current through said coil to cause said valve to be opened and maintained open when the pilot burner is lighted, said thermistor reducing the current through said relay coil to cause closing of said valve when the pilot iiame is extinguished, a shunt circuit connected to said second circuit around said relay coil, and a second thermistor having a negative coemcient of restivity positioned to be subjected to ambient temperature and connected into said shunt circuit in series with said relay coil. the circuits /for said ilrst and second thermistors being so calibrated that when the systeml is in proper operation the holding current for the relay is reduced to such value that the relay is just maintained energized to close the contacts in the circuit for the electroresponsive valve due to shunting of the current through the shunt circuit including said second thermistor.

2. A system according to claim 1 wherein there is a iirst resistor in said second circuit in series with said relay coil and said rst thermistor, and

a second resistor in said shunt circuit in series with said relay .coil and said second thermistor for calibrating and adjusting the system.

3. A system according to claim 1 wherein there is a main burner in juxtaposition to said pilot burner and wherein said second thermistor -is ing a negative coeiicient of resistivity connected in series with said relay coil and positioned to be subjected to the heat of a dame so as to pass sumcient current through said coil to cause said electroresponsive device to be operated when the llame is burning, said thermistor reducing the current through said relay coil to cause operation of the electroresponsive device to inoperative position when the iiam'e is extinguished, a shunt circuit connected to said second circuit around said relaycoil, and a second thermistor having a negative coeilicient of resistivity positioned to be subject to ambient temperature and connected into said shunt circuit in series with said relay coil, the circuit for said first and second thermilstors being so calibrated that when the system is in proper operation the holding current for the relay is reduced to such value that the relay is Just maintained energized to close the contacts in the circuit for the electro-responsive device due to shunting through th shunt circuit including said second thermistor.'

5. A system according to claim 4 wherein there is a first resistor in said second circuit inseries with said relay coil and said iirst thermistor, and a second resistor in said shunt circuit in series with said relay coil and said second -thermistor for ealibrating and adjusting the system.

PHILIP R. MARVIN.

REFERENCES crrED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Certificate of Correction Patent No. 2,491,125 l December 13, 1949 PHILIP R. MARVIN It is hereby certified that errors appear in the printed specification of the above numbered patent-,requiring correction as follows:

Column 5, line 49, for restivity read resistivity; column 6, line 3,6, for th" read the; i l

land that the said Letters Patent should u,be read with these corrections therein that the same may conform to the record of the cas in the Patent Office.

Signed-and sealed this 11th day of April, D. 1950.

s im] THOMAS F. MURPHY,

Assistant Uommzssz'oner of Patents.