US2085195A - Automatic starting device and safety shut-off for gas-fired industrial furnaces - Google Patents

Description

' 2,085,195 SHUT-OFF W. J. KERR AUTOMATIC STARTING DEVICE AND SAFETY FOR GAS-FIRED INDUSTRIAL FURNACES Filed May 16, 1935 June 29, 1937.

I INVENTOR.

W/Lu/m .JT AfiRR BY I H I (IIIII/I/I/III/IIA ATTORNEY.

Patented June 29, 1937 PATENT OFFICE AUTOMATIC STARTING DEVICE AND SAFE- TY SHUT-OFF FOR .GAS-FIRED INDUS- TRIAL FURNACES William J. Kerr, Waterbury, Conn., assignor to The Bristol Company, Waterbury,

Comm, a corporation of Connecticut Application May 16,

5 Claims.

This invention relates to electrically operated control mechanism for gas-fired industrial furnaces, and more particularly to automatic starting devices embodying safety shut-off means perative in case of extinguishment of the flame or electrical failure. The invention is concerned more especially with that type of control system in which the shut-off means is actuated by relay means governed in turn by a heat-sensitive elernent exposed to the influence of a flame in the heating system of such a furnace.

In industrial furnaces of the gas-fired type it is essential in the interests of safety that there be at no time an accumulation of unburned gases which may become ignited at one time and cause an explosion. To this end, it is necessary that .gas be not admitted to the combustion chamber unless there be present an igniting agent, whereby complete combustion of the gas will be assured.

It is an object of this invention to provide means for automatically starting up a gas-fired industrial furnace, and at all times during the starting cycle preventing the accumulation of unburned gases. Y

A further object lies in the provision of means for interlocking the occurrence of the various events comprising the startingcycle, and introducing such time delays therein as may be expedient.

Still another object is to provide means whereby, in the event of interruption to the fuel supply or the extinguishment of the flame for any reason whatsoever, valves controlling the admission of fuel to the furnace will be closed and may not be reopened until the normal starting cycle is again initiated.

The invention has for an object, also, the provision of an electrically operated device of the above nature so embodied that, in event of failure of the essential circuits incorporated therein, or of the source of electrical energy for any such circuits, the system will revert to a condition in which no hazard exists.

The accompanying drawing is a diagrammatic representation of an industrial furnace having a starting and safety system in which one form of the invention is embodied.

As indicated in the drawing, 10 designates the combustion chamber of a furnace adapted to be heated by the combustion of gaseous fuel admitted through a burner H, the flow of the fuel being controlled by a solenoid valve 12. Adjacent to the burner II is placed a smaller burner or pilot light 13, having incorporated therewith a spark plug l4, and receiving gas through a flow- 1935, Serial No. 21,756

controlling solenoid valve 15. The spark plug I4 is connected to one terminal of the high-tension winding of an ignition transformer I6 having the other terminal grounded onthe piping system. A thermocouple .I1 is located within the furnace in close proximity to the pilot light I3, so that only when the gas from this burner is ignited will there be an appreciable electromotive force developed by the couple.

A control panel indicated at l8 carries the several relays and automatic devices (together with their electrical wiring and terminals) necessary to effect the interlocking and safety features hereinafter set forth.

Thus, a sensitive relay 20, of the type having an electrical winding 2| and contacts 22 adapted to be maintained in an open relationship by the influence of a unidirectional exciting current flowing in said winding, is actuated from the thermocouple l1. The said winding to this end is connected thereto through a series resistor 23 having an ohmic value selected to suit the critical temperature at which the relay is to become operative.

This relay is so adjusted that the maximum current which will flow in its electrical winding 2| under operating conditions will not be sufficient to open the contacts when they are in a closed position, but when mechanically moved to an open position by an externally applied force. said contacts wfll remain open so long as a maintaining current continues to flow. A relay suitable for this purpose is the Weston Sensitro relay-model 705.

To move mechanically the said contacts, a cam member 25, having a contour 26 of uniform radius and a single depressed portion or indentation 21, is provided. The cam is to be driven at a constant speed by a motor 28, and serves to actuate two followers 29 and 30. The follower 29 takes the form of a lever member adapted to actuate mechanically the relay 20 in a sense to open 7 its contacts 22 as the follower traverses the indentation 21 in the contour of the cam. The follower 30 is adapted to control the contacts 3| of a lever switch 32 in a sense that these contacts are caused to close when the follower rests'upon the greater radius of the cam or contour 26 and to open as it passes over the indented portion 21.

In addition, the panel I8 carries three relays 35, 36 and 31, the relay 35 having a contact arrangement of the double-pole, single-throw, normally-open type and embodying the two sets of contacts 38 and 39. Relays 36 and 31 are both of the single-pole, double-throw type, the former embodying the sets of contacts and 4|, and the latter the sets of contacts 42 and 43, with contacts 4| and 43 of the respective relays normally closed.

A manually actuated, normally open push-button switch 44 is placed in a position convenient for the operator of the furnace I0; and a source 45 of alternating current supply is made available to the system. The interconnections of the several devices on the panel I 8 and their connections to the solenoid valves l2 and IS, the ignition transformer IS, the push-button switch 44 and the current supply 45, are as follows: Designating the conductors forming the two sides of the supply circuit by the numerals and 5|, the conductor 50 is connected to one terminal of the operating coil of each of the relays 35, 36 and 31, and also to one side of the low-tension winding of transformer l6 and to one side of the winding of motor 28. Theoperating coil of relay 31, the low-tension winding of transformer l6 and the winding of motor 28 are connected in parallel between conductor 50 and a common conductor 52 adapted to be brought into connection with the conductor 5| through the normally open contacts 39 of the relay 35. The operating coil of relay 35 is connected between conductor 50 and a conductor 53 from which a circuit may be completed to the conductor 5| through the switch 44 or the contacts 38 of the relay 35 relay 36 when'thelatter is energized. The operating circuit of relay 36 is completed between conductors 50 and 5| through the contacts 22 of relay 2|. The actuating coil 41 of solenoid valve I5 is connected between the conductor 50 and a conductor 54, from" which a circuit may be completed to conductor 5| through either the contacts 4| of relay 36'or contacts 42 of relay 31. The actuating coil 49 of solenoid valve I2 is connected between conductor 50 and a conductor 55, and the circuit completed therefrom' to conductor 54 through the normallyclosed contacts 43 of relay 31. The contacts 3| of lever switch 32 serve to provide a connection between conductors 5| and 52 when the follower 30 is resting upon the portion of the periphery radius.

Operation The operation of the system is as follows:

The various elements are shown in an inactive condition but with power applied, the cam 25 being located in its normal position of rest, and electrical power being applied to the terminals 46 of the system. The contacts 22 of relay 20 being closed, current will flow in the actuating coil of relay 36, causing its upper contacts 40 to remain closed-and its lower contacts open. All other windings of the system will be dead.

In order to start the furnace the operator presses the switch 44, energizing the relay 35 and causing both sets of its contacts 38 and 39 to be closed. The upper contacts 38, receiving current through the upper contacts 40 of relay 36, serve to lock the'relay 35 in position, whereupon the push-button switch 44 is released, reverting to its normally open position.

Current through the lower contacts 39 of relay 35 will energize in parallel the motor 28, the relay 31 and the ignition'transformer Hi. The motor 28 will start, causing the cam 25 to rotate in the sense indicated by the arrow shown in the drawing. The actuating'coil of relay 31 being energized, its lower contacts 43 will open and its upper contacts 42 will close, the latter serving to enerin series with contacts 40 of 1 of cam 26 having the maximum the event of the said relay 35 becoming de-energized. This action will continue without further change as the cam 25 performs the greater part of its revolution, or for a predetermined time, say approximately one minute. During this time, if conditions are normal in the furnace, the couple l1 will have become heated by the flame from the pilot light |3, and will be causing to circulate in the winding 2| of relay 2|] a current tending to actuate therelay, but magnitude to cause the contacts 22 of this relay to be opened.

After the lapse-ofa time interval determined by the rotation of the cam 25, the follower 29 will enter the indentation 21 on the cam contour, and will be caused to engage the relay 20 through a not in itself of sufficient I stem 48 thereof, mechanically actuating it in a 7 sense to open its contacts 22. This will cause the relay 36 to be de-energized and released, opening its uppercontacts 40 and closing its lower contacts 4|.

The opening of the upper contacts serves to de -energize the locking circuit of relay 35, thereby releasing that relay, while the closing of the lower contacts of relay 36 serves to shunt. the

upper contacts of relay 31. The release of relay 35 serves also to open both its sets of contacts, the upper set or locking contacts 38 having already been de-energized by the release of relay 36.

The opening of the lower contacts 39 of relay 35 transfers to the switch 32, still maintained in thermocouple |1 will be causing to flow in thewinding 2| of relay 20 sufficient current to main tain the contacts in their open position after having been disengaged by the cam follower 29. Furthermore, as soon as the follower 29 has disengaged the relay 20, the follower 30 will enter the indentation 21 in the contourof the cam, opening the contacts 3| of switch 32, and thereby de-energizing the ignition transformer l6, the relay 31 and the driving motor 28, thus. bringing the cam to rest.

Assuming the relay 20 tohave been maintained in its open-circuitposition asabove set forth,

the release of relay '31 will open its upper contacts 42 (already bridged by. the lower contacts relay 36) and will close its lower contacts 4| of 43, thereby energizing the solenoid 49 of the main fuel valve l2. This causes gas to be admitted to the main burner II, where it will be ignited by the flame from the pilot burner l3, thus establishing a normal condition of operation, with both'the main and pilot burners operating, the ignition transformer l6 de -ene'rgized, and the cam 25 in its normal position of rest.

In the event of the gas failing to ignite during the preliminary part of the cycle, or of the thermocouple or its circuit proving defective, there will be no current flowing in the winding of the relay 2!] at the time of the release of its contacts 22 through the action of the follower 29, so that its said contacts will re-close, re-energizing relay 36, whose lower contacts 4i, being thus opened, no longer serve to shunt the upper contacts 42 of relay 31. Thus, as the cam continues its rotation, and the switch 32 is opened, releasing relay 31, there will remain no alternative circuit for the current to the solenoid valves, so that the pilot burner will at once be shut off and the valve I2 to the main burner will not be opened. The ignition transformer will then be de-energized and the motor 28 will come to rest in the normal manner. 1

In the event of a fault developing in the thermocouple circuit during operation, the relay will immediately be de-energized and released, energizing relay 36 and closing both fuel valves as hereinbefore set forth. If an intermittent contact should develop in the thermocouple circuit, the first interruption of the current will release the relay 20, and as a return of current will not alone be able to actuate the relay to reopen its contacts, the fuel will remain shut off until there is initiated a normal starting cycle, including a complete rotation of cam 25.

In the event of an interruption to the fuel supply to the pilot, the cooling of the thermocouple will again cause the relay 20 to be released, closing the fuel valves, which will not bev reopened until the normal starting cycle is carried out. Should an interruption to the electrical supply occur, the fuel valves will automatically close and remain closed so long as the power supply is interrupted. If power should be restored before the couple I! has cooled sufficiently to release relay 20, the valves will be reopened; and if flame be present in the furnace, the burners will be re-ignited and normal operation resumed. If, on the other hand, the bumers are not re-ignited, the couple will quickly reach a temperature at which the relay 20 will be released before there can accumulate sufficient fuel to introduce a hazardous condition, thus closing the fuel valves, which then cannot be reopened without carrying through the normal starting cycle.

Thus, 'there have been provided automatic means whereby the furnace must be carried through a definite starting cycle in order to establish normal operation, and in the event of the occurrence of any one of a group of events likely to introduce operating hazards, the system reverts to a condition of safety.

While throughout the specification and claims the term "gas-fired has been utilized in connection with the furnace, it is to be understood that the furnace may be fired with a liquid fuel such as oil and control efiected thereof as set forth Without requiring any change other than, of course, in the nature of the burner means.

I claim:

1. The combination with a fluid fuel burner, an electrical igniter for the same, and electrical means controlling the supply'of fuel to said'burner; of a control system comprising in circuit a main switch, said igniter, said fuel-supplycontrolling means, a motor-operated sequential switching mechanism, and a plurality of interdependent relays, whereby in response to closure of said main switch, energization of one of said relays effects operation of said igniter, the fuelwinding permanently in circuit with supply-controlling means and the motor-operated sequential switching mechanism; a mechanically controlled relay subsequently and momentarily mechanically actuated from the motor of the sequential switching mechanism; a switch forming a part of said switching mechanism to de-energize said motor, said one relay and the igniter; and a temperature-sensitive element responsive to the burner and operative to maintain said mechanically actuated relay in its actuated position, whereby upon release of said onerelay with said mechanically actuated relay remaining energized, said fuel-supply-controlling means continues to supply fuel to said burner.

2. The combination with a fluid fuel burner, an electrical igniter for the same, and electrical means controlling the supply of fuel to said burner; of a control system comprising in circuit a main switch, said igniter, said fuel-supplycontrolling means, a motor-operated sequential switching mechanism, and a plurality of interdependent relays, whereby in response to closure of said main switch, energization of one of said relays effects operation of said igniter, the fuelsupply-controlling means and the motoroperated sequential switching mechanism; a mechanically controlled relay subsequently and momentarily mechanically actuated from the motor of the sequential switching mechanism; a switch forming a part of said switching mechanism to de-energize said motor, said one relay and the igniter; and a temperature-sensitive element responsive to the burner and operative to maintain said mechanically actuated relay in its actuated position, whereby upon release of said one relay with said mechanically actuated relay remaining energized, said fuel-supplycontrolling means continues to. supply fuel to said burner and upon release of said one relay with said mechanically actuated relay not electrically energized by the temperature-sensitive element, said fuel-supply-controlling means ceases to supply fuel to said burner.

3. In a control for a fluid fuel furnace having a main burner and a pilot light: a temperaturesensitive element thermally associated with said pilot light, shut-ofi means for said main burner, means associated with said shut-off means for actuating the same to an open position and including an electromagnetic element having a said temperature-sensitive element and tending under the influence of current therefrom to maintain said electromagnetic element in a position to permit actuation of said shut-off means to an open position, said winding being so proportioned that current therein representing normal operating temperature at said pilot light is sufflcient to maintain said electromagnetic element in said permissive position but insufficient to give it motion to said position, together with motor-driven timing means establishing a definite time cycle and exerting a transient influence for mechanically effecting said motion and subsequently terminating said influence, and for causing said shut-off means to be moved to an open position upon maintenance of said electromagnetic element in said permissive position after the termination of said transient influence.

4. In a control for a fluid fuel furnace having a main burner and a. pilot light and separate electrically operated means for governing the supply of fuel to each: a.temperature-sensitive electrical element thermally associated with the pilot light, a relay provided with contacts to efiect the operation of said means and having a maintaining winding in circuit with said element,

manually operable additional contacts for ener-' gizing said pilot-light means, a motor-operated" timing mechanism for mechanically positioning main switch; said igniter, said fuel-controlling 20 means, a motor-operated sequential switching mechanism, a. plurality of interdependent relays so arranged and connected in circuit that in response to closure of said 'rnain switch, energize.- tion of one of said relays efiects operation 01' said igniter, the fuel-controlling means 'for the pilot burner and the motor for the sequential switching mechanism to subsequently and momentarily mechanically actuate another of 'said relays and the switch of said switching mechanism, which latter serves to de-energize said motor, said one relay and the igniter, and the said other relay being in circuit with said temperature-sensitive element and adapted to be maintained thereby in its actuated position; and

a further one of said relays controlling the supply of fuel to the main burner and, upon release of said one relay with said mechanically actuated relay maintained in its actuated position, serving to establish and maintain the supply of fuel to said main burner. V

' WILLIAM J. KERR.

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