US2221667A - Ignition means for gas heaters - Google Patents

Description

Nov. 12, 1940. R BETZ 2,221,667. IGNITION MEANS FOR GAS HEATERS Filed Aug. so, 1955 TO CONTROL SYSTEM I E l EC TRICA LLLOPERATF 0 VA l-VE ELECTRICALL! ERA 'ED VALVE l WW E 60 J9 ZSmaentor Patented Nov. 12, 1940 PATENT OFFICE IGNITION MEANS FOR GAS HEATERS Paul L. Betz, Baltimore, Md., assignor to Consolidated Gas Electric Light and Power Company of Baltimore, Baltim Maryland ore, Md., a corporation of Application August 30, 1935, Serial No. 38,655

12 Claims.

This invention relates to safety devices for gas heaters of the type provided with a pilot for igniting the main burner or burners when gas is supplied to the heater.

Gas heating systems, such as for example the conventional type of gas water heater, usually include means to ignite the gas at the main burner or burners whereby the operation of the system may be initiated merely by turning on the gas, either automatically or manually. These means may comprise either gas flames or electric ignition devices such as incandescent wires. In connection with such systems, it is desirable to provide a safety device such that the supply of gas to the main burner cannot be turned on unless the pilot is in condition to function prop-' erly in igniting the main burner. For example, it has been proposed heretofore to provide an electromagnetically operated safety valve to- One of the objects of this invention is to provide a novel safety device in combination with the pilot of a gas heater and adapted to insure 35 valve in the event that ating condition.

Another object is to provide novel thermally responsive means in combination with the pilot of a gas-heater and constituting therewith a safety device to prevent operation of the heater unless the pilot is in operating condition which means will not be materially affected by heat from sources other than the pilot.

A further object is to provide a novel device of the type characterized above which is light, small and compact and inexpensive but at the same time reliable and dependable in operation.

A still further object is to provide a safety device of the type characterized above which if desired can be assembled with an electric pilot as a unit and can also be restored or replaced as a unit.

While a pilot in the form of a gas flame ordif narily burns continuously, an electric ignition the pilot is not in opergether with a thermocouple'subjected to the heat closing or to prevent opening of a gas supply.

device or pilot may readily be adapted for energization only during the operation of the burner,

or if desired for deenergization immediately following the ignition of the burner so that it is used only during the ignition period, with resultant decreased current consumption, economy and longer life. Further objects of the invention are to provide novel electrical control systems particularly adapted for the operation and control of an electric pilot and its associated safety device as characterized above, whereby'the pilot is operated only during operation of the heater and whereby the pilot current can be reduced following the ignition of the main burner, without interfering with the safety functions of said device.

The invention is illustrated in the accompanying drawing, but it is to be expressly understood that said drawings are for purposes of illustration only and are not to be construed as a definition of the limits of the invention, reference being had to the appended claims for this purpose.

In the drawing: Fig. 1 is a perspective view showing an apparatus embodying the invention which for purposes of illustration is associated with a conventional form of gas burner;

Fig. 2 is a sectional view of the device shown in Fig. 1; and

Figs. 3 and 4 illustrate two suitable control systems which may be employed in connection with a device of the type shown in Figs. 1 and 2. In Figs. 1 and 2, a combined electric pilot and associated safety device is shown in association with a portion of a gas burner I of a conventional type having a plurality of ports 2, this type of burner having sector-shaped openings 3 therein. As shown in Fig. 1, the combined pilot and safety device is disposed in one of these openings and two of the adjacent ports 2 are provided with pipes 4 which direct gas toward the pilot device to facilitate ignition of the gas. It will be understood, however, that the invention is not limited to this particular manner of installation and use of the device.

As shown in Figs. 1 and 2, the pilot comprises a coil of wire 5 which is adapted to become incandescent on passage of current to provide for the ignition of gas from the pipes or nozzles d. The coil 5 is connected at its endsto terminal strips 6 whereby current is conducted to and from the coil. This coil is mounted on a suitable base 1 by means of plates or blocks 8 assembled on the base in any suitable manner as by screws 9. Preferably blocks 8 are of metal and the terminals 6 are insulated therefrom in any suitable manner as by interposed strips of mica or other insulating material.

Associated with the coil 5 is a safety device comprising two similar thermally responsive elements so disposed that with respect to ambient heat their response is equal and similar with no relative movement between them, but arranged so that one of them is more affected by heat from said coil than the other. The thermally responsive elements in the form shown comprise two bimetallic strips I0 and II which are supported at their ends between the blocks 8 and insulated therefrom as described above. The bimetallic strips I8 and II respectively carry contacts I2- and I3 and said strips are: so arranged that these contacts are normally separated. The two bimetallic strips are arranged to.bend in the same direction and to substantially the same extent under the same change of temperature so that any bending of the strips occurring as the result of equal changes in temperature of the two strips does not result in the closing of the contacts. Thus changes of temperature in the surrounding air, which affect both strips equally, do not result in closing the contacts. However, the adjacent strip I8 receives more heat from the coil 5 than the strip I I with the result that the deflection of strip I0 is greater than that of strip II, causing the contacts to close when the pilot coil is energized. As soon as the coil cools off, the bimetallic strips return to normal positions and contacts I2 and I3 are again opened. Preferably the safety device is suitably. shielded from air currents about the burner and through the opening 3 so that its operation is not affected thereby.

Devices embodying the invention can be employed in any suitable way to control electrically either a special safety valve or the usual automatically operated supply valve of a gas heating system, it being necessary only to make the proper circuit connections to the contacts I2 and I3, which connections can be varied depending upon the type of control system and valve that is employed. When so connected, the invention provides an electric pilot or ignition device which operates reliably and dependably but in the event of failure of the pilot to reach ignition temperature for any reason,- such as an open circuit, the safety feature is automatically provided by failure of the contacts I2 and I3 to close. The invention provides an additional advantage in that the safety device prevents opening of the gas valve until the pilot coil has reached the desired operating temperature, thus preventing the flow of gas during the brief period in which the pilot is heating up to ignition temperature and the consequent danger of explosion.

While devices embodying the invention can be used in association with any suitable control circuit, in many cases it is desirable to provide a control system such that the safety contacts are opened after the gas is ignited and while it continues to burn. Forexample, assuming that the safety contacts remain closed during the operation of the heater, if the control system is deenergized for any reason the gas is shut off and the.

pilot cools very rapidly, but the bimetallic operating members for the safety contacts may cool more slowly and the contacts may not open immediately. If the control system is again energized and the gas is turned on under this. condition, the heater may become filled with gas before the pilot has time to reach ignition temperature with consequent danger of an explosion. Hence it is desirable to connect the pilot and safety contacts in a-circuit controlled by a suitable relay in such a way that the gas cannot be turned on until the safety contacts close, but after the operation of the system is initiated, the safety contacts are permitted to open so as to be ready for another cycle without interrupting the operation of the system.

Fig. 3 illustrates a control system whereby op- .eration as above described can be provided.

Current is supplied to the system through leads I4, a control switch I5 and a transformer I6. A pilot device such as that described above is shown diagrammatically and comprises a pilot coil I8 and thermally operated contacts I9 and 20 which are normally open as shown but adapted to be closed when the pilot coil I8 reaches ignition temperature. The pilot coil I8 is connectedat one end to the secondary of the transformer I6 by wires 2| and 22 and at the other end in series with a resistance 23 and a resistance 24 which is preferably a second pilot coil and thence through wires 25 and 26 to the transformer secondary. A relay 21 of any suitable type is arranged normally to hold the bridging arm 28 across contacts 29 and 30, thereby short-circuiting resistance 23 by means of wires 3I and 32. One terminal of the relay 21 is connected to the transformer secondary through wires 26 and 33 and the other terminal is connected to the other side of the transformer through wires 34, 35, 36 and 22, this circuit including. contacts I9 and 28. An electrically operated gas supply valve of any suitable type is shown at 31, this valve being connected to Wires 26 and 34 in parallel with therelay 21.

When the control switch I5 is closed, current passes through wires 22 and 2| and pilot coil I8, then through wire 3|, arm 28 and wire 32 in parallel with resistance 23, and then through pilot coil 24 and wires 25 and 26. At this time the relay 21- and the valve 31 are not energized as the contacts I9 and 28 are open. When the coils I8 and 24 reach ignition temperature, contacts I 9' and 28 close and valve 31 opens to supply gas to the burner. At the same time relay 21 is energized and shifts bridging arm 28, opening the circuit between contacts 29 and 30 while at the same time. closing the circuit between contacts 29, 38 and 39. This operation does not deenergize the relay 21 or valve 31, and it establishes the circuit between wires 34 and 22 by way of wire 40, contact 39, arm 28 and contact 38 in parallel with the circuit through wire 35, contacts I9 and 20 and wire 36. At the same time the arm 28, by bridging contacts 38 and 29, establishes a shortcircuit around pilot coil I8 by way of wire 22, arm 28 and wire 3|. Current then passes through wire 22, arm 28 and wire 3|, and thence through resistance 23, pilot coil 24 and wires 25 and 26. Pilot coil-24 therefore remains heated, but as the coil I8 cools 01! due to the reduction in current flow, contacts I9 and 20 open without affecting relay 21 or valve 81. As soon as the switch I5 is opened, however, valve 31 closes and relay 21 restores the arm 28 to its original position so that the system is ready for another operation.

During the initial ignition period, the resistance in the pilot circuit between wires 22 and 26 includes the resistance of pilot coils I8 and 24, resistance 23 being short-circuited. As the two pilot coils I8 and 24 are preferably substantially similar, they both become heated to ignition temperature by the time that contacts I 9, 20 close and the gas is turned on. Then on operation of the relay and gas valve the pilot coil I8 is short-cit cuited so that it cools off and contacts 19, 20 open so that they are ready for another cycle of operation. However, pilot coil 24 remains energized and inoperating condition as long as the control system is energized. If resistance 23 has the same value as the resistance of pilot coil IS, the

current through pilot coil 24 is the same both before arid after the operation of the relay. It

will be seen that it is not essential that coil I8 be a pilot coil but this is preferable in order that the element which is associated with the safety contacts shall be in condition to insure ignition of the burner before the safety contacts are closed.

If the resistance 23 is of greater value than coil l8, the current consumption after the ignition period can be reduced substantially to any extent while at the same time the coil l8 cools off, thus reducing current consumption and resulting in increased economy of operation and longer life of the pilot coil. The reduction in pilot cur rent may be proportioned to leave the pilot 24 at a temperature sufiicient to ignite the. gas in the event of momentary interruption of the gas supply for any reason, the initial high pilot temperature'insuring ready ignition in normal operation, or the current may be further reduced to any desired extent. In this case, however, it is desirable to provide for opening the gas valve shortly before the relay operates, in view of the fact that the pilot current is decreased at this time. This can readily be accomplished, for example, by employing a relay of any known type wherein the operation of the relay contacts is delayed for an interval after energization of the relay, which will not change the pilot circuit until a suitable interval has elapsed after the gas valve is opened. Various types of relays having time delayed operation are known, and a relay suitable for this purpose is shown in U. S. Patent No. 2,087,216 of Paul L. Betz issued July 13, 1937.

It will be perceived that the system as described above can be associated with other safety devices 45 and automatic controls which are adapted to prevent the operation of valve 31 or to close said valve in the event of flashback or excessive temperature, etc. Since the details of such devices constitute no part of the present invention, they 50 are not shown herein. Such devices may be connected with the system above described in any suitable way which does not interfere with the intended operation thereof, as for example at the point indicated in the wire 26 by the words To 55 control system.

Fig. 4 illustrates another control system which can be employed. The current flowing through the pilot coil is discontinued after the gas has been ignited, but with a single pilot coil. In

60 this system current is supplied to the transformer 4| by the leads 42 and control switch 43. The electric pilot coil 44 is connected at one end to the transformer secondary by wires 45 and 46 and at the other end by wire 41 with a contact 65 48. The bridging arm 49 normally connects contact 48 with contact 50 whereby the circuit through the pilot coil is completed to the other side of the transformer secondary through wires 5| and 52.

70 has one terminal connected to wire 52 and the other terminal connected to a wire 54 which leads to one of the contacts 55 of a safety device associated wtih the pilot coil 44, the other contact 55 being connected by wires 51 and 46 to the 75 transformer secondary. A relay 58 having time The electrically operated valve 53 delayed operation of any suitable known type,

such as that shown in the Betz patent referred to above, is connected across wires 52 and 54 in parallel with the valve 53, this relay normally maintaining the bridging arm 49 inc. position relay 58 are open because the contacts 55, 56 are open, but the circuitof pilot coil 44 is closed as described above. The coil, therefore, heats up to ignition temperature and causes contacts 55, 56 to close, thereby energizing the valve 53 and relay 58. Valve 53 immediately opens supplying gas to the burner to be ignited by the pilot 44. The operation of relay 58, however, is delayed for an interval sufficient to insure ignition of the gas, and thereafter the relay operates to swing the arm 49 -to-its opposite position. This operation of the relay is utilized to interrupt the current to the pilot coil 44 by opening the circuit between arm 49 and contact and to establish a short-circuit in parallel with the contacts 55 and 56 by way of wire 46, contact 59, arm 49, contact and wire 6|. The interruption of the current through the pilot coil causes the pilot coil to cool thereby permitting contacts 55, 56 to open. This does not, however, affect the valve 53 nor the relay 58 because the circuits of the same are completed by way of wire 54, wire 6|, contact 60, arm 49, contact 59 and wire 46. The system, therefore, continues to operate until the valve and relay are deenergized as by opening the switch 43 or by the operation of any suitable control devices which may be employed. In this eyent,-valve 53 closes and the relay 58 returns the arm 49 to its initial positionv whereby the system is ready for further operation in the manner described above.

While the use of the relay 58 as shown in Fig. 4 is generally desirable together with the contacts 55 and 56, the latter of themselves provide the safety feature that the valve cannot be opened until the pilot device reaches ignition temperature, and this function is normally accomplished independently of the relay operation and hence for some purposes the contacts may be used alone and the relay omitted.

It will be seen from the foregoing description that the invention provides a combined electric pilot and safety device which is small and compact and relatively inexpensive and which, if desired, may constitute a unit for installation or replacement. With respect to the safety device, the use of two thermally actuated devices which respond equally and in the same direction in the event of equal changes of temperature provides for safety operation that is substantially independent of all heat affecting both devices to the same extent. Hence, when the device is properly installed, it is inoperative except in response to heat from the pilot itself, but is reliable and dependable in performing its intended function as a safety device. The combined electric pilot and safety device is particularly adapted for use in electrical control systems such' as those described above, wherein the contacts act as a safety device to prevent opening of the gas valve until the pilot reaches ignition temperature, but then after being closed to effect opening of the valve and turning on of the gas, are opened while the burner continues in service. Thus, the safety device is restored to normal condition and is ready for the next cycle of operation in con-- dition to accomplish its intended function. Further, current consumption can be reduced and greater economy of operation obtained without in any way interfering with the accommplishment of the safety function.

While the invention has been described and illustrated in the drawings with particularity, it will be understood that the invention is not restricted to the embodiments so described andillustrated, but changes may be made in the form, details of construction and arrangement of the parts and in the circuits employed without departing from the spirit of the invention. Reference is, therefore, to be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. In an electrical ignition system for a gas burner, the combination of an electrically operated valve, a valve circuit including valve operating means and a pair of normally open contacts, a circuit including an electric pilot and an impedance, means responsive to heat from said pilot for closing said contacts, a circuit in parallel with said pilot, a circuit in parallel with said impedance, a circuit is parallel with said normally open contacts and relay means energized simultaneously .with the closing of said contacts for completing said first and last named parallel circuits and for opening. said second named parallel circuit.

2. In an electrical ignition system for a gas burner, the combination of an electrically operated valve, a valve circuit including valve operating means and a pair of normally open-contacts, a circuit including an electric pilot and an impedance, means responsive to heat from said pilot for closing said contacts, a circuit in parallel with said pilot, a circuit in parallel with said impedance, a circuit in parallel with said normally open contacts, and relay means having time delayed operation energized simultaneously with the closing of said contacts for closing said .first and last named parallel circuits and for opening said second named parallel circuit.

3. In an electrical ignition system for a gas burner, the combination of an electrically operated valve, a valve circuit including means for operating said valve and a pair of normally open contacts, a circuit including an electrical pilot device, thermally responsive means subject to heat from said pilot device to close said normally open contacts, a circuit in parallel with said pilot device and including a pair of relay contacts, a relay for closing said relay contacts, and a relay circuit including said normally open burner, the combination of an electrically operated valve, an operating circuit including valve operating means, relay means having time delayed operation, anda pair of normally open contacts, a circuit including an electric pilot, means responsive to heat from said pilot for closing said contacts, a circuit in parallel with said pilot,

a circuit in parallel with said normally open contacts, and means operated by said relay means for closing said parallel circuits.

6. In an electrical ignition system for gas burners, the combination of an electrically operated valve, a relay, an operating circuit including means for operating said valve and said relay and a pair of normally open contacts, a circuit including two electric pilots, thermally responsive means operated by one of said pilots for closing said contacts, and a circuit having relatively low resistance in shunt with said one pilot and including circuit closing means operated by said relay.

'7. In an electrical ignition system for gas burners, the combination of an electrically operated valve, a relay having time delayed operation, on operating circuit including means for operating said valve and said relay and a pair of normally open contacts, a circuit including two electric pilots, thermally responsive .means operated by one of said pilots for closing said contacts, and a circuit having relatively low resistance in shunt with said one pilot and including circuit closing means operated by said relay.

8. In an electrical ignition system for a gas burner, the combination of an electrically operated valve, a relay, an operating circuit includ-- ing means for operating said valve and said relay and a pair of normally open contacts, a circuit including in series two electric pilots and a resistance, thermally responsive means operated by one of said pilots for closing said contacts, two circuits one of which is in parallel with said one pilot and the other with said resistance and each of which includes relay contacts, said relay being adapted to normally close the circuit in parallel with said resistance and on operation of said normally opeh contacts to open the circuit in parallel with said resistance and to close the circuit in parallel with said pilot.

9. In an electrical ignition system for a gas burner, the combination of an electrically operated valve, a relay, an operating circuit including means for operating said valve and said relay and a pair of normally open contacts, a circuit including in series two electric pilots and a resistance, thermally responsive means operated by one of said pilots for-closing said contacts, two circuits one of which is in parallel with said one pilot and the other with said resistance and each of which includes relay contacts, said relay being adapted to normally close the circuit in parallel with said resistance and on operation of said normally open contacts to open the circuit in parallel with said resistance and to'close the circuit in parallel with said pilot, said resistance being substantially equal to the resistance of said one'pilot.

10. In an electrical ignition system for a gas burner, the combination of an electrically operated valve, a relay having time delayed operation, an operating circuit including means for operating said valve and said relay and a pair of normally open contacts, a circuit including in series two electric pilots and a resistance, thermally responsive means operated by one of said pilots for closing said contacts, two circuits one of which is in parallel'with said one pilot and the other with said resistance and each of which includes relay contacts, said relay being adapted to normally close the circuit in parallel with said resistance and on operation of said normally open contacts to open the circuit in parallel with said resistance and to close the circuit in parallel with aaaacer said pilot, said resistance being greater than the resistance of said one pilot.

11. In an electrical ignition system for a gas burner, the combination of an electrically op erated valve, a valve operating circuit including a pair of normally open contacts, a circuit including two electric pilots and a resistance in series, means responsive to heat from one of said pilots to close said contacts, a low resistance circuit in parallel withsaid resistance, a low resistance circuit in parallel with said one pilot, a circuit in parallel with said contacts, a relay circuit energized upon closure of said contacts, and. relay means for opening said first parallel circuit and closing said other parallel circuits.

12. In an electrical ignition system for a gas burner, the combination or an electrically operated valve, a valve operating circuit including a pair of normally open. contacts, a circuit including two electric pilots and a resistance in series, means responsive to heat from one 01' said pilots to close said contacts, a low resistance circuit in parallel with said resistance, a low resistance ciredit in parallel with said one pilot, a circuit in parallel with said contacts, a relay circuit energized upon closure of said contacts, and relay means for opening said first parallel circuit and closing said other parallel circuits, said resistance being greater than said one pilot and said relay means having time delayed operation.

PAUL L. nnrz.

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