US2142059A - Safety pilot control system - Google Patents

Description

E938. L. KUEMPEL SAFETY PILOT CONTRQL SYSTEM Filed March 4, 1935 SHAW/14M Le0nL.Kiempel GUM;

Patented Dec. 27, 1938 PATENT OFFICE SAFETY PILOT CONTROL SYSTEM Leon L. Kuempel, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application March 4,

2 Claims.

This invention relates to a safety pilot control system.

It is an object of this invention to provide a system for a device having a main burner and a 5 pilot burner for igniting the main burner, comprising a valve for controlling the main burner, means for operating the valve, control means including a thermostat for the valve, electrodes adapted to be bridged by the pilot flame, and 10 choke means connected between the electrodes and control means to permit operation of the valve operating means under the command of the thermostat when the pilot flame bridges the electrodes.

Another object of this invention is to provide a control system for a main burner and a pilot burner wherein the control system comprises,

means for controlling the main burner including a relay, choke means for controlling the opera- 20 tion of the relay, and means associated with the pilot flame for controlling the choke meansto open the relay upon pilot flame failure.

A further object is to provide a yste'm for controlling an electric motor comp sing, a relay having a coil and a load switch operated thereby, a load circuit including the electric motor and the load switch, choke means, a circuit including the choke means and the coil, and means for decreasing the impedance of the choke means to energize the coil and permit operation of the motor.

More specifically, it is an object of this invention to provide a control system for a main burner and a pilot burner, the system comprising a valve for controlling the supply of fuel to the main burner, an electric motor for opening the valve upon energization thereof, a thermostatic switch, a relay having a coil and load switch operated thereby, a load circuit including the motor, the thermostatic switch and the load switch, a step-up transformer having a primary and a secondary, a primary circuit including the primary of the transformer and the relay coil and electrodes adjacent to the pilot burner adapted to be bridged by the pilot flame and connected to the secondary of the transformer whereby the primary circuit is energized when the electrodes arebridged by the pilot flame to close the load switch and permit energization of the motor when the thermostatic switch closes.

Other objects and advantages will become apparent to those skilled in the art by reference,

to the accompanying specification, claims and drawing in which drawing there is diagrammatically disclosed the preferred form of my 5 invention.

1935, Serial No. 9,208

Although my control system may be applied-to any type of system, it is shown for purposes of.

illustration as applied to a heating system wherein a warm air furnace is designated at In. The furnace I is provided with a bonnet I I having ducts I2 emanating therefrom for delivering warm air to spaces to be heated. Located in the furnace I0 is a combustion device which may take the form of a burner l3. Expanded gases of combustion are taken from the furnace l0 by means of a flue or duct M which leads to the usual stack (not shown).

A pipe l5 leading from some source of fuel supply terminates in a valve l6 and a pipe l1 leads from the valve 16 to the burner l3 whereby fuel is supplied to the burner l3 under the control of the'valve I6. Located adjacent the burner l3, so that'the burner I3 may be ignited thereby,

is a pilot burner l8. Fuel is always supplied to the pilot burner It! by means of a pipe I9 con- 20 nected into the pipe l5 ahead ofthe valve l6. The valve I6 is operated by means of a valve motor having a lever 2| pivoted at 22. A collar 23 is secured to a valve stem 24 of the valve [6 and is held against the upper surface of the lever 25 2| by means of a spring 25 abutting against a support 26. Pivoted intermediate the ends of the lever 2| is a hooked arm 2! which is adapted to be engaged by a pin 28 located on a gear 29. The gear 29 is rotated by means of a pinion30 30 which is in turn secured to the gear 3|. The gear 3| is rotated by means of a motor pinion 32 which is secured to the motor rotor 33. Themotor has a field diagrammatically shown at 34 and upon energization of field 34, the rotor 33 is 35 placed in operation to cause clockwise rotation of the gear 29 whereby the pin 28 engages in the hooked portion of the arm 21 to move the lever 21 in a counter-clockwise direction about its pivot 22, This movement of the lever 2| causes upward movement of the valve stem 24 against the actionv of spring 25 to open the valve Hi. When the valve I6 is completely opened, further movement thereof is prevented and the motor becomes stalled in this position. As long as the field 34 remains energized, the valve IE will remain in the open position. When the field 34 is deenergized, the spring 25 causes closing of the valve l6 and consequent reverse rotation of the gear train and motor rotor 33.

Power is supplied to the control system of my invention by means of line wires 35 and 36. A wire 31 connects the line wire 35 to one end of a primary 38 of a step-up transformer 39, preferably of the power type, which has a secondary 49. The other end of the primary 36 of the transformer 39 is connected by means of a wire 4| to one end of a relay coil 42. The other end of the relay coil 42 is connected by means of a wire 48 to the line wire 36. The secondary 49 of the transformer 39 is connected to electrodes 65 and 66 which are located in the pilot flame of the pilot burner l8.

As is known in the art, a power type transformer places a high impedance in the primary thereof when the secondary thereof is in open. circuit position so that substantially no current is allowed to pass through the primary. However, when the secondary of such a transformer is shorted, the impedance of the primary is greatly reduced to permit a large current flow therethrough. From this it is seen that such a transformer forms a very good choke device which prevents substantially the flow of current through a circuit and which, under certain conditions, allows the flow of a large current through the circuit.

It is also known in the art that flame conducts electricity much better than air. This principle is used in my invention to complete a circuit through the secondary of the step-up transformer 39 to, in efiect, short-circuit the secondary thereof to permit a large flow of current through the primary 38.

Since the relay coil 42 is located in series with the primary 38 of the power type transformer 39, burning out of the transformer 39 is thereby prevented when the secondary 49 is short-circuitedby reason of the pilot flame bridging the two electrodes 65 and 66.

From the above discussion, the operation of this portion of the invention becomes self-evident, it being sufficient to state that when the pilot flame bridges the electrodes 65 and 66, the relay coil 42 becomes energized by reason of the flow of current from line wire 35 through wire 31, primary 38, wire 4|, relay coil 42 and wire 43 back to line wire 36. When the pilot flame becomes extinguished, the impedance in the coil 38 is greatly increased which will prevent flow of current through the above circuit and cause deenergization of the relay coil 42.

A' step-down transformer is indicated at 45 and comprises a primary 44 and a secondary 46. The primary 44 is connected to some source of power and for purposes of convenience, it is shown as connected across the wires 43 and 31. A condition responsive means which may take the form of a thermostat 41 responsive to space temperature, has contacts 48 and 49 contained thereon. These contacts 48 and 49 are adapted to sequentially engage contacts '59 and respectively since the distance between contacts 48 and 59 is less than the distance between contacts 49 and 5|. The thermostat 41 is held in place by means of a binding post 52. The binding post 52 is connected by means of a wire 53 to an electrode located in a mercury switch 44 which in turn is secured to the lever 2| by means of a bracket 55. The other electrode of the mercury switch 54 is connected by means of a wire 56 and a wire 51 to the contact 5|. The contact 59 is connected by means of a wire 58 to one end of the secondary 46 of the step-down transformer 45. The other end of the secondary 46 is connected by means of a wire 59, to a contact 69. Switch arm 6| which is operated by the relay coil 42 is connected by means of a wire 62 to the field 34 of the valve motor. The other end of the field 34 is connected by means of a wire 63 to the Junction of wires 69 and 61. The switch arm 6| is normally urged away from the contact 69 by means of gravity or springs or like mechanisms. The contact 99 and the switch arm 6| form a load switch operated by the relay coil 42. The load switch and the relay coil form a relay of the usual design.

Upon a decrease in temperature affecting the thermostat 41, contact 49 is first moved into engagement with contact 59 and upon a further decrease in temperature contact 49 is moved into engagement with contact 5| to complete a starting circuit from the secondary 46 through wire 58, contacts 59, 48, 49 and 5|, wire 51, wire 63, field 34, wire 62, switch arm 6|, contact 69 and wire 59 back to the secondary 46. Completion of this circuit causes rotation of the rotor 33 and consequent raising of lever 2| and opening of the valve l6. When the valve I6 is opened and the lever 2| is moved to its upper position, the mercury in the mercury switch 54 bridges the con tacts contained therein and completes a holding circuit from secondary 46 through wire 58, contacts 59 and 48, thermostat 41, binding post 52, wire 53, mercury switch 54, wire 56, wire 63, fleld 34, wire 62, switch arm 6|, contact 69 and wire 59 back to the secondary 46. The motor will remain energized and the valve l6 will be held in the open position until an increase in temperature causes the thermostat 4! to move the contact 48 away from the contact 59 whereby the above holding circuit will be broken and the spring 25 will move the valve l6 to closed position.

The above operation has been set forth upon the assumption that switch arm 6| is in engagement with contact 69. The switch arm 6| is held in engagement with the contact 69 when the relay coil 42 is energized and as pointed out above, the relay coil '42 is energized and the switch arm 6| is held in engagement with the contact 69 only when the pilot flame bridges the electrodes 65 and 66. From this it is seen that only when the pilot flame bridges the electrodes 65 and 66, the motor for opening the valve l6 may be energized under the command of the condition responsive device 41. However, if the pilot flame becomes extinguished, the switch arm 6| will be moved out of engagement with the contact 69 and the motor may not be energized to open the valve l6 even though the thermostat 41 should be calling for heat.

From the above it is seen that I have provided a safety pilot control system wherein it is impossible to open the control valve to the main burner if the pilot burner should be extinguished thereby preventing the accumulation of large amounts of combustible gases within the furnace l9. However, in my system, if the pilot flame is burning properly and bridges the electrodes 65 and 66, the valve I6 is opened and closed under the direct command of the condition responsive means or thermostat 41. Further, since the valve I6 is closed by means of a spring, power failure protection is also provided in my system since upon the failure of power in the lines 35 and 36 it will be impossible to open or maintain open the valve |6.

While one embodiment of the present invention has been shown and described in detail, many modifications will occur to those skilled in the art. It is intended in this application to cover all such modifications as fall within the scope of this invention as defined by the appended claims.

I claim as my invention:

1. In a system of the class described, a main burner, a pilot burner for igniting said main burner, a valve for controlling the supply of fuel to said main burner, an electric motor for opening said valve upon energization thereof, a thermostatic switch, a relay having a coil and a load switch operated thereby, a source of power, a load circuit including the source of power, the motor, the thermostatic switch and the load switch, a stepup transformer having a primary and a secondary, a primary circuit including the source of power, said primary of the transformer and said relay coil, and electrodes adjacent the pilot burner positioned to be bridged by the pilot flame and connected to the secondary of the transformer whereby the primary circuit is energized when the electrodes are bridged by the pilot flame to close the load switch and permit energization of the motor when the thermostatic switch closes, said electrodes being so spaced relative to the voltage of said secondary that in the absence of flame no current passes therebetween.

2. In a system of the class described, a main burner, a constantly burning pilot burner for igniting said main burner, a valve for controlling the supply of fuel to said main burner, an electrically controlled motor for opening said valve upon energization thereof, a thermostatic switch, a relay having a coil and a load switch operated thereby; a source of power; a load circuit including the source of power, the motor, the thermostatic switch and the load switch, a step-up transformer having a primary and a secondary, a continuously closed primary circuit including the source of power, said primary of the transformer and said relay coil; and electrodes adjacent the pilot burner positioned to be bridged by the pilot flame and connected to the secondary of the transformer whereby the primary circuit is maintained energized so long as the electrodes are bridged by the pilot flame to maintain the load switch closed and permit energlzation of the motor when the thermostatic switch closes, said electrodes being so spaced relative to the voltage of said secondary that in the absence of flame no current passes therebetween.

LEON L. KUEMPEL.

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