US2999536A - Flow control device - Google Patents

Description

P 1961 J. c. SCHWALBACH 2,999,536

FLOW CONTROL DEVICE Filed Nov. 17, 1955 H M C 2 3 INVENTOR.

9 Jose 072 C Sc/mrafacfa BY W @Mmflach United States Patent i 2,999,536 FLOW CONTROL DEVICE Joseph C. Schwallbach, Wauwatosa, Wis., assignor to Baso Inc., Milwaukee, Wis, a corporation of Wiscon- Filed Nov. 17, 1955, Ser. No. 547,462 17 Claims. c1. 1534.23

This invention relates to improvements in modulating control devices, and more particularly to thermoelectrically powdered modulating fuel control devices. The invention disclosed and claimed herein is an improvement over those disclosed in my copending patent No. 2,874,904 granted February 24, 1959.

In the control of fuel flow to the gaseous fuel burners, it is necessary to provide a relatively large rate of fuel flow to safely ignite the fuel at a given burner, and once the burner is ignited a stable flame can be maintained at said burner even though the rate of fuel flow is reduced to a substantially smaller value. The minimum rate of fuel flow needed to maintain a flame is often designated as the minimum safe flow rate and the larger fuel flow rate necessary for safe ignition is designated as the safe ignition flow rate.

It is a general object of the present invention to provide a modulating fuel control device having fuel control means movable to positions affording fuel flow at said minimum safe flow rate and said safe ignition flow rate, said control means being movable to the position for said minimum safe flow rate only after ignition of the fuel.

Another object of the invention is to provide an improved fuel fiow control device of the character described which employs two electroresponsive operators for said flow control means, said flow control means comprising a pair of independently movable on-off and high-low valve means serially arranged in the fuel stream, the first of said operators being operable to move said on-off valve means between flow-preventing (off) and flow-permitting (011) positions, and the other of said operators being operable to move the high-low valve means between safe ignition (high) and minimum safe flow (low) positions.

A more specific object of the invention is to provide a control device of the type described for controlling the flow of fluid fuel to fluid fuel burning apparatus having main and pilot burners, the on-ofi operator of said device being responsive to the heat of burning fuel at the pilot burner and the high-low operator thereof being responsive to the heat of burning fuel at the main burner, whereby energization of the high-low operator and hence move ment of its valve means to the reduced flow-permitting (low) position may not take place until a stable flame exists at said main burner thereby insuring safe ignition.

Another object of the invention is to provide a control device of the aforementioned character which is provided with electromagnetic interlock means responsive to the heat of burning fuel at the main burner and operable on movement of the on-oif valve means to off position to overcall the on-oif operator and prevent subsequent movement of the on-off valve means from off to on posi-' tion as long as the high-low valve means is in low position, thus insuring that wherever the on-off valve means is moved to on position suflicient fue lis supplied to the burner for safe ignition.

A further object of the invention is to provide a device of the aforementioned character having first circuit controlling means in circuit with the on-ofl operator and operable to effect deenergizat-ion of the latter in response to a predetermined high limit temperature, said device also having second circuit controlling means in circuit with the high-low operator operable to cycle the latter Patented Sept. 12, 1 961 in response to normal fluctuations in the temperature, cycling of said second operator moving said second flow control means between said safe ignition and minimum safe flow positions to thereby afford modulation of the fuel flow.

Another object of the invention is to provide in a flow control device having the aforementioned characteristics safety shut-off means cooperable with the on-off valve means and with pilot fuel valve means, said safety shut-off means permitting cycling of the on-otf valve means when the safety shut-off means is cooked and energized, and being responsive to pilot burner outage to actuate said on-off and pilot fuel valve means to ofi position independently of the on-otf operator to shut off all fuel flow to both the main and pilot burners, said safety shut-off means over-calling the on-ofI' operator to prevent the latter from reopening the on-oif valve means during resetting of said safety shut-off means to thereby provide flow interruption.

The novel features that are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood by the following description of the specific embodiment disclosed when read in connection with the accompanying drawing, in which:

FIGURE 1 is a sectional view of a fuel control device constructed in accordance with the invention and operatively associated with the fuel burning apparatus, the electrical circuit of said device and parts of said apparatus being shown semi-diagrammatically, the thermostat being in a fuel shut-off position it assumes at room temperatures above the modulating range;

FIGURE 2 shows the thermostat in the position in which it calls for low fuel flow; and

FIGURE 3 shows the thermostat in a position in which it calls for high fuel flow.

The modulating fuel control device selected for illustration in the drawing is generally indicated by the numeral '10,.and controls the flow of fuel to a main burner 20 as well as to a pilot burner 49 disposed in igniting relation thereto. The device 10 comprises a valve body or casting 7 having an inlet 12 leading to an inlet chamber 16 and having an outlet 14 leading from an outlet chamber 18. The flow of fuel to the main burner 20 is under the control of an on-oif valve member 22 and a high-low valve member 24 which are disposed for coaction with annular valve seats 23 and 25 respectively formed in a valve partition 6 at opposite ends of a passageway 26 therein connecting the inlet chamber 16 I to the outlet chamber 18.

The valve member 24 when open (spaced away from seat 25 as shown) permits a relatively high rate of fuel flow sufficient for safe ignition of the fuel at the burner 20, there being a by-pass 3% around the valve seat 25 permitting, when the valve member 24 is seated, a low fuel flow suflicient to maintain a stable flame at the burner 20. A metering screw 32 is provided for adjusting the rate of fuel flow through the by-pass 30.

Suitable electromagnetic valve operators 34 and 36 are connected to operate the valve members 24 and 22 respectively. The operator 36 opens valve member 22 when energized and closes said valve member when deenergized, whereas the operator 34 operates the valve member 24 in the reverse manner, i.e. it closes the valve member 24 when energized and opens said valve member when deenergized. Operators 34 and 36 may be identical and may be of the form shown and described in the copending application of Adolph H. Hilgert, filed December 2, 1953, Serial No. 395,736, now Patent 3 No. 2,916,676, and assigned to the assignee of the present application.

The operators 34 and 36 will be described together, the even reference numerals referring to the high-low valve operator 34 and the odd reference numerals referring to the on-ofi operator 36, said operators comprising the frames 9091 for mounting permeable cores 92-93 and pivotal armatures 96-97 cooperable therewith. The cores 9293 have energizing windings 9 495 thereon. The valve members 22 and 24 are carried respectively by the valve arms 99 and 98, and said arms are operatively connected to the armatures 97 and 96 through links 105 and 104 and energy storing leaf springs 103 and 102. The arms 99 and 98 are biased to the left as viewed in the drawings by springs 93a and 94a which, through the aforementioned links 105 and 164, bias armatures 97 and 96 away from permeable cores 92 and 93. The operator 34 may be responsive to the heat of burning fuel at the main burner and is adapted to be supplied with energizing current from a thermoelectric generator 70 disposed adjacent the main burner 20 and connected in circuit with the energizing winding 94 through conductors 8 and 9 and the common ground connections shown therewith. The operator 36 may be responsive to the heat of burning fuel at the pilot burner 40 and is adapted to be supplied with energizing current from a thermoelectric generator 42 disposed adjacent the pilot burner 40 and connected in circuit with the energizing winding 95 through conductors 11 and 13 and the common ground connections shown therewith.

Condition responsive circuit controlling means is also provided for controlling the energization of operators 34 and 36 and hence the movement of valve members 24 and 22, said means comprising a plural staged thermostat 72 responsive to the temperature of the space heated by the burner 20. The illustrated thermostat 72 has a contact arm 73- grounded as at 74 and provided with duel blades 75 and 76 which are cooperable with fixed contacts 77 and 78 as shown. Contact 77 and blade 75 are connected in circuit with the energizing coil 95 of the operator 36 through conductor 13 as shown. The contact 78 and blade 76 are connected in circuit with the energizing coil 94 of the operator 34 through the conductor 9 as shown. It is, of course, apparent that neither operator can become energized if there is no fuel burning to heat the respective thermoelectric generators 70 and 42.

The valve arm 99 carries an armature 81 for cooperation with an electromagnet 8t fixedly mounted within the chamber 16 and having an energizing winding 79. One end of the winding 79 is connected as by conductor 17 to conductor 9 and grounded through the thermostat 72 at 74 as shown, and the other end thereof is connected to the main burner thermoelectric generator 70 in parallel circuit relation with the energizing coil of the high-low operator 34 by a conductor 19. The electromagnet 80 and armature 81 are adapted to provide an interlock which overcal-ls the on-off operator 36 to prevent opening of the valve member 22 whenever the armature 81 engages the pole faces of the magnet St? at a time when the winding 79 is energized. It will be observed that the circuit is so arranged that the highlow operator 34 and the electromagnet 80 are simultaneously energized so that the interlock is effective whenever the on-off valve member is closed while the highlow valve member is being held in low position, and said interlock remains effective as long as the high-low valve member remains in low position. The electromagnet 80 is substantially ineffectual, in so far as over-calling the operator 36 is concerned, at any time that the armature 81 is in a retracted position with respect to said electro- "means 38 is mounted within the chamber 16 for cooperation with the on-off valve member 22, said means com- "the thermoelectric generator 42 through'the conductor 11. An armature 41 is cooperable with the electromagnet 37 and is carried by an axially slidable stem 42 which projects through a suitable bearing in an end wall of the hood 39 and has fixed thereon, a cup-shaped member 44. A coiled compression spring 45 surrounds the stem 42 between the hood 39 and member 44 and biases the armature 41 away from the pole faces of the electromagnet 37, and the stem 42 toward engagement with an abutment member 22a carried by the valve arm 99. The electromagnet 37 when energized is adapted to hold the armature 41 and stem 42 in the cocked position shown when said parts are moved to this position against the bias of spring 45. When the safety shut-01f means 38 ,is cocked and energized. As shown, the on-otf operator 36 is free to cycle the on-off valve member 22. Upon deenergization of the safety shut-off means, however, the electromagnet releases the armature 41 and the spring 45 biases the tip 42a of the stem 42 into engagement with the abutment plate 22a to effect seating of the valve member 22 with substantial force thereby shutting off all fuel to the main burner. The bias of the spring 45 exerts a seating force on the valve member 22 which is greater than the opening force which the operator 36 is capable of exerting thereon when energized. Thus, the safety shut-off means, when deenergized, overcalls the operator 36.

The safety shut-off means 38 includes means for controlling the flow of fuel to the pilot burner 40, said last mentioned means comprising a valve member 52 biased toward a seat 53 by a compression spring 54. The valve member 52 is provided with a stem 5t having a head 51. An arm 46 is fixed to the cup-shaped member 44 and has an end portion engageable with the head 51. The arm 46 opens the valve member 52 during cooking of the safety shut-off means 38 and holds said valve member open as long as the safety shut-off means is cocked. On release of the armature 41 from the electromagnet 37, however, the arm 46 permits closure of said valve 52 upon seat 53 under the bias of spring 54.

A reset cam 60 mounted on a rotatable stem 59 which extends through the wall of the body 7, has fixed thereon a manually rotatable knob 61, shown in broken lines. Rotation of the cam 60 moves the arms thereof into engagement with both the cup-shaped member 44 and the abutment member 22a to simultaneously hold the on-otf valve member 22 against its seat while resetting the armature 41 to cocked position in engagement with the pole faces of the electromagnet 37 and thereby unseating the valve member 52 to allow pilot gas to flow to the pilot burner 40. This affords flow interruption during said cocking operation for safe ignition of the pilot burner 40 even though operator 36 may be energized at the time.

The operation of the apparatus is as follows:

The position of the contacts of the thermostat 72 shown indicates that the temperature sensed by said thermostat is sufficiently high so that the thermostat is not calling for heat. The blade 75 is out of engagement with contact 77, operator 36 is deenergized, and the on-oif valve member 22 is closed to shut-off the flow of fuel to the main burner 20. The blade 76 is flexed and in engagement with the contact 78, but since the thermoelectric generator 70 is cold, the operator 34 is deenergized and the high-low valve member 24 is in high position as shown.

As the temperature at the thermostat drops, the thermostat blade 75 moves to the right into engagement with contact 77 while the'bla'de 76 remains in engagement with contact 78 is shown in FIGURE 2, thereby energizing the operator 36 with current from the generator 42, said operator thereupon opening the on-otf valve member 22 to permit fuel flow to the main burner 20. Since the high-low valve member 24 is already in the high position shown when the valve member 22 is opened, full or high fuel flow is supplied to the main burner 20 on opening of the valve 22 for safe ignition thereof by the pilot burner 40.

After the thermoelectric generator 70 has been heated by burning fuel at the main burner 20 for a predetermined period, it generates a thermoelectric current sufficient to energize the operator 34 which thereupon actuates the high-low valve member 24 to low position and reduces the amount of fuel flowing to the main burner to that which can flow through the by-pass 30. If this reduced amount of fuel flow is insufficient to prevent the temperature at the thermostat from dropping, the blade 76 is moved to the right out of engagement with contact 78 and the blade 75 is flexed as shown in FIG- URE 3. This deenergizes the operator 34 which thereupon opens the high-low valve member 24 to high position wherein it again permits full fuel flow to the main burner 20.

As the temperature at the thermostat thereafter rises, the blade 76 reengages contact 78 as shown in FIGURE 2, to reenergize the operator 34 which thereupon pulls the high-low valve member 24 against its seat 25 to again reduce the fuel flow to the burner 20. Thereafter, the valve member 24 is cycled between high and low positions on disengagement and reengagement of the blade 76 with the contact 78 as long as the temperature at the thermostat does not go above a predetermined high limit temperature, occurrence of which causes disengagement of the blade 75 from the contact 77 as shown in FIGURE 1.

Whenever the blade 75 is disengaged from the contact 77, for example on occurrence of the aforementioned high limit temperature, the operator 36 is deenergized and closes the on-olf valve member 22 and thereby shuts off all fuel flow to the main burner 20. At the time the valve member 22 is closed in this manner, and until the main burner thermoelectric generator 70 cools, the high-low valve member 24 may also be held closed (low position) by energized operator 34, since the blade 76 is in engagement with the contact 78 completing the circuit to the winding 94. If, now, the thermostat knob is turned up, or the thermostat is subjected to vibration, or some other event causes the contact blade 75 to reengage the contact 77 and open the on-ofl valve member 22, an unsafe condition would exist because insufficient fuel is available to the main burner for safe ignition. To prevent such reopening of the valve member 22 while the valve member 24 is closed, electromagnet 80 and the armature 81 are provided to afford an interlock which overcalls the operator as and holds the on-olf valve member 22 closed as long as the electromagnet 80 and the operator 34 are energized by the thermoelectric generator 7%. When the main burner couple 7t cools to deenergize the operator 34 and open the valve member 24, the electromagnet St} is simultaneously deenergized to permit opening of the valve member 22 and afford safe ignition, said interlock thereafter permitting normal cycling of the on-off valve 22 by the operator 36.

In the event of failure of the pilot burner 40, the thermoelectric generator 42 cools to deenergize the operator 36 and the safety shut-off electromagnet 37, whereupon the armature 41 is released, to close the on-off valve 22 with sufiicient force for safety shut-off of the main burner fuel flow and to also effect closure of the pilot fuel valve member 52 thus providing 100% shut-off of the fuel.

The improved control device provides full fuel flow to the main burner for ignition thereof at all temperatures within the range of temperatures in which modulation is afforded by the device, and therefore does not require that the room temperature modulate down to the lower end of said modulating range after closure of the on-ofi valve 22 before the burner 20 can be reignited. More specifically, when the temperature of the room drops from above the modulating range into said range just far enough to cause reengagement of blade 75 with contact 77 (while blade 76 and contact 78 are in engagement), a normal low fuel flow situation is sensed by the thermostat 72, yet the improved flow control device affords safe reignition on high fuel flow. This is true, since a condition precedent to ignition is deene-rgization of the electromagnet 80 and release of armature 81 to permit opening of on-oflt' valve 22, such deenergization occurring substantially simultaneously with deenergization of the operator 94 and the resultant opening of highlow valve 24. Thus, a high fuel flow is provided for reignition of the main burner, even though the thermostat senses a temperature normally requiring a low flame. Further, the high-low valve member 24 cannot be moved to closed (low fuel flow) position until the thermoelectric generator 70 is heated by the flame at the main burner. Thus, the existence of the flame at the main burner is determinative of the actuation of the high-low valve member 24 to low fuel flow position, as distinguished from apparatus wherein means, such as timing means, effects movement of the high-low valve to low position after predetermined interval of time following opening of said high-low valve, regardless of whether or not the main burner has ignited within the time period.

Although a single specific embodiment of the invention has been shown and described, this was done with full awareness that many modifications thereof are possible, and the invention is therefore not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

What is claimed as the invention is:

1. A flow control device for fluid fuel burning apparatus having a burner comprising, an on-off first flow control member having flow-preventing and flow-permitting positions, electroresponsive operator means for said flow control member, a second flow control member having increased flow-permitting and reduced flow-permitting positions, and interlock means associated with said first flow control member and responsive to the heat of burning fuel at said burner for overcalling said operator means and preventing movement of said first flow control member from flow-preventing to flow-permitting position when said second flow controlling member is in reduced flow-permitting position.

2. A flow control device for fluid fuel burning apparatus having a burner comprising, an on-off first flow control member having flow-preventing and flow-permitting positions, first electroresponsive operator means for said first flow control means, a second high-low flow control member having alternative increased flow-permitting and reduced flow-permitting positions, second operator means responsive to heat of said burner for moving said second flow control member to reduced flow position, and interlock means associated with said first flow control member and also responsive to the heat of burning fuel at said burner for overcalling said first operator means and preventing movement of said first flow control member from flow-preventing to flow-permitting position when said second flow controlling member is in reduced flow-permitting position.

3. A flow control device for fluid fuel burning apparatus having a burner comprising, a first flow control member having flow-preventing and flow-permitting positions, first electroresponsive operator means for said first flow control means, a second flow control member having increased flow-permitting and reduced flow-permitting positions, second electroresponsive operator means respon- 7 at said burner for overcalling said first operator means and prevent movement of said first flow control member from flow-preventing to flow-permitting position when said second flow controlling member is in reduced flow-permitting position, and independent condition responsive circuit controlling means in circuit with both said interlock means and said second operator means operable for controlling both said last named means in response to a predetermined condition.

4. A flow control device for fluid fuel burning apparatus having main and pilot burners comprising, a first flow control member biased to a flow-preventing and movable to a flow-permitting position, first electromagnetic operator means energizable in response to heat of buming fuel at said pilot burner for moving said fiow control means from said flow-preventing to flow-permitting position against said bias, a second flow control member biased to increased flow-permitting position and movable to reduced flow-permitting position, second electromagnetic operator means energizable in response to heat of burning fuel at said main burner to move said second floW'control member from increased flow-permitting to reduced flow-permitting position, and electromagnetic interlock means associated with said first flow control member and energizable in response to said heat of burning fuel at said main burner, said interlock means when energized preventing movement of said first flow control member from flow-preventing to flow-permitting position.

5. A flow control device for fluid fuel burning apparatus .having main and pilot burners comprising a first valve member biased to flow-preventing and movable to a flow-permitting position, a first electromagnetic operator means energizable by a thermoelectric generator responsive to heat of burning fuel at said pilot burner for moving said valve member from said flow-preventing to flowpermitting position against said bias, a second valve member biased to increased flow-permitting position and movable to reduced flow-permitting position, a second electromagnetic operator means energizable by a thermoelectric generator responsive to heat of burning fuel at said main burner to move said second valve member from increased flow-permitting to reduced flow-permitting posi tion, and independent manually resettable safety shut-ofl means having a shut-off position preventing movement of said first valve member from flow-preventing to flowpermitting positions upon pilot burner outage.

6. A flow control device for fluid fuel burning apparatus having main and pilot burners comprising a first valve member biased to a flow-preventing and movable to a flow-permitting position, a first electromagnetic operator means energizable by a thermoelectric generator responsive to heat of burning fuel at said pilot burner for moving said valve member from said flow-preventing to flowpermitting position against said bias, a second valve member biased to increased flow-permitting position and movable to reduced flow-permitting position, a second electromagnetic operato-r means energizable by a thermoelectric generator responsive to heat of burning fuel at said main burner to move said second valve member from increased flow-permitting to reduced flow-permitting position, and independent manually resettable safety shut-off means co- I operable with said first valve member and having a shut-off position and a free cycling position, said safety shut-off means when in shut-off position, overcalling said first operator means and preventing movement of said first valve member from flow-preventing to flow-permitting positions upon pilot burner outage.

7. A flow control device for fluid fuel burning apparatus having main and pilot burners comprising a first valve member biased to a flow-preventing and movable to a flow-permitting position, a first electromagnetic operator means energizable by a thermoelectric generator responsive to heat of burning fuel at said pilot burner for moving said valve member, from said flow-preventing to flow-permitting position against said bias, a second valve member biased to increased flow-permitting position and movable to reduced flow-permitting position, a second electromagnetic operated means energizable by a thermoelectric generator responsive to heat of burning fuel at said main burner to move said second valve member from increased flow-permitting to reduced flow-permitting position, a third valve member for controlling fuel flow to said pilot burner having flow-permitting and flow-preventing positions, and independent manually resettable safety shut-off means cooperable with said first and third valve members and having a shut-off position preventing flow of fuel to both said main and pilot burners, a manual reset position preventing flow to said main burner and permitting flow to said pilot burner, and a free cycling position permitting flow of fuel to both said burners, said safety shutoff means preventing movement of said first and third valve members from flow-preventing to flow-permitting positions when in said shut-off position upon pilot burner outage, said shut-off means when in said manual reset position permitting flow of fuel to the pilot burner and overcalling said first operator means when the latter is energized to thereby interrupt the fiow of fuel to the main burner.

8. A flow control device for fluid fuel burning apparatus having main and pilot burners comprising a first valve member having a first and movable to a second position, a first cycling electromagnetic operator means energizable by means responsive to burning of fuel at said pilot burner for moving said valve member from said first to its second position, a second valve member biased to increased flow-permitting position and movable to reduced flow-permitting position, a second cycling electromag netic operator means energizable by means responsive to burning of fuel at said main burner to move said second valve member from increased flow-permitting to reduced flow-permitting position, and independent manually resettable safety shut-off means having a shut-off position preventing movement of said first valve member from its first to its second position upon pilot burner outage.

9. A fuel flow control device for fuel burning apparatus having main and pilot burners comprising relatively movable first and second flow control member serially arranged in the path of the fluid fuel to said main burner, said first flow control member being biased to a fiowpreventing and movable to a flow-permitting position, first electroresponsive cycling operator means energizable in response to burning of fuel at said pilot burner for moving said first flow control member from said flowpreventing to flow-permitting position, said second flow. control member being biased to an increased flow-permitting position and movable to a reduced flow-permitting position, second cycling operator means operatively associated with said second flow control member and having a flame sensing portion exposed directly to the heat of burning fuel at said main burner, said second operator means being responsive to burning of fuel at said main burner for moving said second flow control member from increased flow-permitting to reduced flow-permitting position, wherefore said second flow control member may be moved to reduced flow-permitting position by said second operator means only after ignition of fuel at said main burner.

10. A fuel flow control device for fuel burning apparatus having main and pilot burners comprising relatively movable first and second flow control members serially arranged in the path of the fluid fuel to said main burner, said first flow control member being biased to a flowpreventing and movable to a flow-permitting position, first electroresponsive operator means energizable in response to burning of fuel at said pilot burner for moving said first flow control member from said flow-preventing to flow-permitting position, said second flow control member being biased to .an increased flow-permitting position and movable to a reduced flow-permitting position, second operator means operatively associated with said second flow control member and responsive to burning of fuel at said main burner for moving said second flow control member from increased flowpermitting to reduced flow-permitting position only after ignition of fuel at said main burner, and independent condition responsive safety shut-off means operatively associated with said first valve member and operable to overcall said first operator means and move said first valve member toward its flow-preventing position in response to pilot burner outage irrespective of energization of said first operator.

11. A fuel flow control device for fuel burning apparatus having main and pilot burners comprising relatively movable first and second flow control means disposed to control the flow of fluid fuel to said main burner only, said first flow control means having a flow-preventing and movable to a flow-permitting position, first electroresponsive cycling operator means energizable in response to burning of fuel at said pilot burner for moving said first flow control means from flow-preventing to flow-permitting position, said second flow control means being biased to an increased flow-permitting position and movable to a reduced flow-permittjng position, second cycling operator means operatively associated with said second flow control means and having a flame sensing portion exposed directly to the heat of burning fuel at said main burner, said second operator means being operable in response to burning of fuel at said main burner for moving said second flow control means from increased flow-permitting to reduced flow-permitting position, wherefore said second flow control means can be moved to reduced flowpermitting position by said second operator means only after ignition of fuel at said main burner.

12. A fuel flow control device for fuel burning apparatus having main and pilot burners comprising relatively movable first and second flow control means disposed to control the flow of fluid fuel to said main burner only, said first flow control means having a first and movable to a second flow controlling position, first cycling operator means operable in response to burning of fuel at said pilot burner for moving said first flow control means from said first to its second position, said second flow control means being biased to an increased flow-permitting position and movable to a reduced flow-permitting position, and second cycling operator means operatively associated with said second flow control means and having a flame sensing portion exposed directly to the heat of burning fuel at said main burner, said second operator means being operable in response to burning of fuel at said main burner for moving said second flow control member from increased flow-permitting to reduced flow permitting posi tion, Wherefore said second flow control means can be moved to reduced flow-permitting position by said second operator means only after ignition of fuel at said main burner.

13. A fuel flow control device for fuel burning apparatus having main and pilot burners comprising an on-off and a high-low valve serially arranged in the path of the fluid fuel to said main burner only, said on-oif valve being biased to an off and movable to an on position with respect to the fuel flow, first electroresponsive cycling operator means energizable in response to heat of burning fuel at said pilot burner for moving said onoif valve from said off to on position, said high-low valve being biased to high flow-permitting position and movable to a low flow-permitting position with respect to the fuel flow, second cycling operator means having a flame sensing portion exposed directly to the heat of burning fuel at said main burner, said second operator means being responsive to heat of burning fuel at said main burner for moving said high-low valve from high flow permitting to low flow-permitting position only after ignition of fuel at said main burner.

14. A fuel flow control device for fuel burning apparatus having main and pilot burners comprising relatively movable first and second flow control means serially 10 arranged in the path of the fluid fuel to said main burner said first flow control means having a first and movable to a second position, first cycling operator means operable in response to burning of fuel at said pilot burner for moving said first flow control means from said first to its second position independently of said second flow control means, said second flow control means being biased independently of said first flow control means to an increased flow-permitting position and movable to a reduced flow-permitting position, second cycling operator means having a flame sensing portion at said main burner and operable in direct response to burning of fuel at said main burner for moving said second flow control means relative to said first flow control means from increased flow-permitting to a reduced flow-permitting position, and a two stage thermostat in circuit With both of said operator means for rendering one of said operator means inoperative in response to one temperature and the other operator means inoperative in response to another temperature.

15. A fuel flow control device for fuel burning apparatus having main and pilot burners comprising relatively movable first and second flow control members serially arranged in the path of fluid fuel to said main burner, said first flow control member being biased to a flow preventing and movable to a flow-permitting position, first electroresponsive operator means energizable in response to burning of fuel at said pilot burner for moving said first fiow control member from said flowpreventing to flow-permitting position independent of said second flow control member, said second flow control member being biased to an increased flow-permitting position and movable relative to said first flow control member to a reduced flow-permitting position, second operator means operatively associated with said second flow control member and having flame sensing means at said main burner rendering operation of said second operator means responsive to burning of fuel at said main burner such that movement of said second flow control member by said second operator means from increased flow permitting to reduced flow-permitting position can occur only after ignition of fuel at said main burner is sensed by said flame sensing means, and temperature responsive circuit controlling means in circuit with said first and second operator means and operable to effect de-energization of said first operator means in response to a predetermined high limit temperature, said circuit controlling means being also operable to cycle said second operator means in response to normal fluctuations in temperature, cycling of said second operator moving said second flo-W control member relative to said first flow control member between increased flow-permitting and reduced flow-permitting positions to thereby afford modulation of the fuel flow.

16. A fuel fiow control device for fuel burning apparatus having main and pilot burners comprising relatively movable on-oif and high-low valves serially arranged in the path of the fluid fuel to said main burner, said on-oif valve being biased to an off and movable to an on position With respect to the fuel flow, first electroresponsive cycling operator means energizable in response to burning of fuel at said pilot burner for moving said on-oif valve from said off to on position independent of said high-low valve, said high-low valve being biased independently of said on-off valve to a high flow-permitting position and movable to a loW flow-permitting position, second electroresponsive cycling operator means including a source of electrical energy having flame sensing means at said main burner and responsive to heat of burning fuel at said main burner such that energization of said second operator means and movement of said high-low valve from high flow-permitting to low flowpermitting position can occur only after ignition of fuel at said main burner is sensed by said flame sensing means, and a two stage thermostat in circuit with both said electroresponsive operators for controlling the energization of said operators and thereby movement of said valves, said thermostat aifording the circuit for said first operator at a predetermined temperature control point and afiording the circuit for said second operator at a predetermined second temperature control point which is lower than said first control point.

17. A fuel flow control device for fuel burning apparatus having main and pilot burners comprising relatively movable first and second flow control members serially arranged in the path of the fluid fuel to said main burner, said first flow control member being biased independently of said second flow control'member to a flow-preventing and movable to a flow-permitting position, first electrore'sponsive operator means energizable in response to burning of 'fuelat said pilot burner for moving said first flow control member from said flowpreventing to flow-permitting position independent of said second flow control member, said second flow control member being biased independently of said first flow control member to anincreased flow-permitting position and movable to a reduced flow-permitting position, second electrorespons'ive operator means operatively associated with said second flow control member and energizable in response to burning of fuel at said main burner for moving said second 'flow control member relative of said first flow control member fromiincreased flow-permitting to reduced flow-permitting position, and a two stage References Cited in the file of this patent UNITED STATES PATENTS 1,991,863 Morrow Feb. 19, 1935 2,005,224 Dunham et a1. June 18, 1935 2,164,511 Furlong a- July 4, 1939 2,478,386 Gauger Aug. 9', 1949 2,494,737 'Borst Jan. 17, 1950 2,627,911 McCarty et a1 Feb. 10, 1953 2,678,814 Geldhof et al. May 18, 1954 2,687,738 Thornbery Aug. 31, 1954 2,710,181 Parrett June 7, 1955 2,767,973 Matthews Oct. 23, 1956 2,919,858 Matthews Jan. 5, 1960

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