US3843308A

US3843308A - Heating control system

Info

Publication number: US3843308A
Application number: US00404575A
Authority: US
Inventors: M Graham; M Caparone
Original assignee: Robertshaw Controls Co
Current assignee: Robertshaw Controls Co
Priority date: 1973-10-09
Filing date: 1973-10-09
Publication date: 1974-10-22
Anticipated expiration: 1991-10-22

Abstract

A heating control system includes a control device for supplying fuel to a burner, a relatively large temperature sensing bulb disposed to sense an overheat condition of the heating system, and a relatively small temperature sensing bulb disposed to sense a flame roll-out condition at the burner, the temperature sensing bulbs containing an expandable fluid and being connected via a branched capillary tube with an actuator for operating a safety valve in the control device such that either the overheat condition on the flame roll-out condition closes the safety valve to prevent flow to the fuel to the burner.

Description

United States Patent [191 Graham et a1.

[ HEATING CONTROL SYSTEM [75] Inventors: Marvin M. Graham, Seal Beach;

Michael J. Caparone, Los Angeles, both of Calif.

Robertshaw Controls Company, Richmond, Va.

Filed: Oct. 9, 1973 Appl. No.: 404,575

Assignee:

US. Cl 131/22, 431/78, 137/65, 73/3682 Int. Cl. F23n 5/24 Field of Search 431/22, 78, 80, 85; 236/21 B, 78 B, 10; 137/65 References Cited UNITED STATES PATENTS 2/1953 McCarthy et al 431/17 1 Oct. 22, 1974 3,447,746 6/1969 Visos 236/21 B 3,682,188 8/1972 Randolph et a1. 431/81) Primary Examiner-Carroll B. Dority, Jr. Attorney, Agent, or Firm-Anthony A. OBrien [57] ABSTRACT A heating control system includes a control device for supplying fuel to a burner, a relatively large temperature sensing bulb disposed to sense an overheat condition of the heating system, and a relatively small temperature sensing bulb disposed to sense a flame rollout condition at the burner, the temperature sensing bulbs containing an expandable fluid and being connected via a branched capillary tube with an actuator for operating a safety valve in the control device such that either the overheat condition on the flame rollout condition closes the safety valve to prevent flow to the fuel to the burner. v

10 Claims, 4 Drawing Figures I IIIIIIIIIIII HEATING CONTROL SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention pertains to control systems and, more particularly, to heating control systems for automatically preventing fuel flow to a burner in response to hazardous conditions.

2. Description of the prior art It is desirable to utilize a safety energy cutoff device responsive to overheat conditions to prevent fuel flow to a burner, such safety energy cutoff devices normally including an electrical switch connected in series with a thermocouple and an electromagnet for pilot flame operated fuel burner apparatus. However, with the ac ceptance of electric ignition systems, as exemplified by US. Patents No. 3,318,358, No. 3,495,925, and No. 3,726,630, such thermocouple operation is not utilized;

and, additionally, it has been found that the use of safety switches to provide energy cutoff operation has the disadvantages of the switches becoming defective or shunted thereby allowing the heating system to obtain an extremely hazardous overheated condition.

A number of fluid expansion temperature responsive valves in the prior art, as exemplified by US. Pat. Nos. 2,055,133, 2,627,9l1, 2,787,130, and 3,386,065, have been employed in many applications other than as safety energy cutoff devices in a heating system; and, while the use of expandable fluid safety operators is desirable to provide such energy cutoff functionsin electric ignition heating systems, systems utilizing such valves have a number of deficiencies rendering them incapable of performing such safety cutoff operations.

Along with the hazardous condition created by overheating of a heating system, prolonged flame roll-out at the burner under certain draft conditions constitutes a serious fire hazard, and it is thus desirable to provide energy cutoff in response to prolonged flame roll-out to stop the flow of fuel to the burner.

SUMMARY OF THE INVENTION The present invention is generally summarized in a heating control system including a burner; a control device having an inlet adapted to receive fuel from a source, an outlet for supplying fuel to the burner, a flow passage between the inlet and the outlet, and valve means disposed in the flow passage for controlling fuel flow therethrough; a thermostat for operating the valve means to control the supply of fuel to the burner; and safety operator means including an actuator for operating the valve means to interrupt the supply of fuel to the burner, a first bulb containing an expandable fluid positioned to sense an overheat condition of the heating system, a second bulb containing an expandable fluid positioned adjacentthe burner to sense a flame roll-out condition and a tube connecting the first and second bulbs with the actuator whereby the first and second bulbs cooperate to control the valve means to prevent the supply of fuel to the burner in response to the overheat condition or the flame roll-out condition.

Accordingly, it is a basic object of the present invention to overcome the disadvantages of the prior artby utilizing an expansible fluid, safety operator in a heating control system to prevent fuel flow to a burner in 2 responseto both overheat and fllame roll-out conditions.

An additional object of the present invention is to utilize a pair of temperature sensing bulbs to provide protection against overheat and prolonged flame roll-out conditions, the temperature sensing bulbs being connected with an actuator for a safety valve via a branched capillary tube such that the existence of either overheat or flame roll-out conditions closes the safety valve to provide energy cutoff.

A further object of the present invention is to balance the size and calibration of relatively large and small temperature sensing bulbs for operating a safety valve in response to different conditions such that while operation of the safety valve is a function of the temperature of both temperature sensing bulbs, a balance can be achieved between the interdependent operating temperatures of both bulbs to provide both flame rollout and overheat condition response.

Some of the advantages of the present invention over the prior art are that a safety operator utilizing an expandable fluid can be utilized to provide overheating and flame roll-out protection and the safety operator is simple in nature while providing fail-safe operation of a safety valve. v I

Other objects and advantages of the present invention will become apparent from the'following description of the preferred embodiment taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS 7 FIG. 1 is adiagram of a heating control system according to the present invention.

FIG. 2 is a cross section of the control device of the heating control system of FIG. 1.

FIG. 3 is a cross section of a fluid expansive actuator for controlling a safety valve of the control device of FIG. 2 in an unactuated position.

FIG. 4 is a view similar to FIG. 3 but illustrating the fluid expansive actuator in an actuated position.

DESCRIPTION OF THE PREFERRED EMBODIMENT A heating control system according to the present invention is illustrated in FIG. lfor use with a furnace 10 having a heat exchanger 12 vented to the atmosphere bya vent 14 and surrounded by a plenum chamber 16 receiving air through a return conduit 18 and forcing heated airthrough a supply conduit 20 by means of suitable filter and blower 21. A burner 22 is disposed beneath the heat exchanger 12 and receives fuel from a source (not shown) under the control of a control device 24 through a conduit 26. Ignition or establishment of a flame at the burner 22 is accomplished by an electric igniter 28, such as spark electrodes, under the controlofan ignition circuit 30 which includes an igniter driving circuit portion 32, such as a spark voltage generator, connected with the igniter 28, a flame or ignition sensingcircuit portion 34 disposed at a position to sense a flame at the burner 22, a timing switch circuit portion 36 which is disabled when. the ignition sensing circuit portion 34 senses a flame at the burner, and an input circuit portion 38. A thermostat 40, such as a space thermostat, has a switch therein connected in series with the secondary winding of a transformer 42 which has its primary winding connected to a suitable voltage source (not shown). Since many suitable electrical ignition circuits can be utilized with the heating control system and are known or described in the prior art, the circuit is not described in detail.

A recyclic, thermally operated limit switch 44 is mounted in a position to sense overheated conditions, for examplein or ,on the plenum chamber 16 of the furnace, and the switch 44 is connected in series with electrical leads from the timing switch portion 36 of the ignition circuit 30 to

terminals

46 and 48 of control device 24. The limit switch 44 is designed to operate, such as by opening the switch contacts, at a predetermined first overheat temperature.

A safety operator for the heating control system in cludes a pair of fluid expansion,

temperature sensing bulbs

50 and 52. Temperature sensing bulb 50 is large in size relative to temperature sensing bulb 52 and is disposed in the heat exchanger '12 to be responsive to a predetermined second overheat temperature higher than the overheat temperature at which switch 44 operates, and temperature sensing bulb 52 is disposed adjacent burner 22 so as to be responsive to flame roll-out, as indicated in dashed lines at 54, from the burner 22.

Temperature sensing bulbs

50 and 52 are connected with the control device 24 through a capillary tube 54 having

branches

56 and 58 communicating with

bulbs

50 and 52, respectively.

The control device 24, as illustrated in FIG. 2, includes a casing 60 having an inlet 62 adapted to receive fuel from the fuel supply and an outlet 64 for supplying fuel through conduit 26 to the burner 22. A flow passage extends within the casing between the inlet 62 and the outlet 64 with a main valve 66 and a safety valve 68 disposed therein. Main valve 66 includes an annular valve seat 70 and a diaphragm valve member 72 cooperating with the valve seat 70 to control flow therethrough. A bleed chamber 74 communicates with the flow passage through the casing upstream of main valve 66 via a restrictive passageway 76 and an unrestrictive passageway 78 branching from a bleed port 80 and communicates with the flow passage through the casing downstream of main valve 66 via a bleed passage 82. A bleed valve 84 controls communication between the

bleed passages

78 and 82 and the bleed chamber 74 v and includes a valve member 86 movable by means of an actuator mechanism 88 between an on position, as illustrated in FIG. 2, wherein communication is established between bleed passage 82 and bleed chamber 74 through a pressure regulator 90 and a bleed valve seat 92 and an off position wherein bleed passage 78 communicates with bleed chamber 74 due to movement of valve seat 92 against a spring bias by valve member 86. The actuator mechanism 88 includes an armature 93 and an electromagnet 94 having a winding connected to

terminals

46 and 48, the actuator mechanism 88 being illustrated in FIG. 2 with armature 93 pulled in by electromagnet 94. Bleed chamber 74 communicates with a main valve operating chamber 96 via a passage 98, the main valve operating chamber 96 being defined on one side by the diaphragm valve member 72 and by a bottom wall 100 of the casing 60. A coiled spring 102 is mounted in compression between the diaphragm valve member 92 and the bottom wall 100 to bias the main valve member toward the main valve seat 70.

A cock valve 104 is positioned in the flow passage between the safety valve 68 and the main valve 66 and is operated by a rotatable knob 106 having an upwardly spring biased stem 108 with splines or the like slidably joining the stem with the cock valve 104.

The safety valve 68 includes a valve seat 110 disposed upstream of the cock valve 104 and a valve member 112 cooperating with the valve seat 110 to control flow therethrough. The valve member 112 is mounted on an arm 114 which is pivotally mounted in the casing on a pin 115 and has a protrusion 116 extending therefrom underlying and aligned with a flange 117 extending from stem 108. A torsion spring 118 engages the arm 114 to bias the valve member 112 away from the valve seat 110.

Capillary tube 54 communicates with a safety valve actuator 120 mounted in the casing 60. The actuator 120 has a plunger 122 extending therefrom to engage the arm 114, and, as illustrated in FIGS. 3 and 4, the safety valve actuator 120 includes a threaded support member 124 mounting the end of capillary tube 54. A fluid expansion device 126 is secured to and communicates with the end of the capillary tube 54 and has a movable wall 128, such as a bellows or diaphragm, formed from a suitable elastic material biased toward an outwardly bowed position, as shown in FIG. 4, such that with an internal pressure about equal to atmo' spheric pressure, the wall 128 assumes the outwardly bowed position. An abutment member 130 is centrally mounted on the wall 128 and engages a tubular member 134 slidably receiving an end 136 of plunger 122. The lower end of tubular member 136 engages a bowed spring 138 having an end 140 mounted in a recess 142 in a support plate 144. The support plate 144 is mounted within a housing 146 attached to the threaded force produced by the elasticity of the movable wall 128. The lower end of the plunger 122 carries a flange 156, and acoiled spring 158 is mounted in compression between theflange 156 and the lower end of the housing 146. A C-ring 160 issecured to the plunger 122 in a position to abut the bottom of support plate 144 and limit upward movement of the plunger.

The

temperature sensing bulbs

50 and 52, the capillary tube 54 and

branches

56 and 58 and the expansion device 126 contain an expandable fluid, such as a gas or a liquid which generates a vapor pressure equal to atmospheric pressure when temperature sensing bulb 50 is exposed to the second overheat temperature, for example 350F., with the temperature sensing bulb 52 at a normal operating temperature, for example F., or when the temperature sensing bulb 52 is exposed to sustained heating at a temperature commensurate with flame roll-out at theburner, for example 700F., with the temperature sensing bulb 50 at a normal operating temperature, for example 150F. Of course, the vapor pressure is a function of the temperature of both of the temperature sensing bulbs in that as temperature sensing bulb 50 approaches the second overheat temperature or as temperature sensing bulb 52 approaches the flame roll-out temperature, the other temperature sensing bulb will have its normally responsive temperature decreased. By proper selection of size and calibration, a balance can be obtained to provide protection against both overheat and flame roll-out conditions. The

charge of fluid in the

temperature sensing bulbs

50 and 52, the

capillary tubes

54, 56 and 58 and the fluid expansion device 126 is selected to have, at normal temperatures less than the overheat and flame roll-out temperatures, a pressure which is sufficiently less than atmospheric pressure to allow atmospheric pressure to force the wall 128 to the retracted or unactuated position of FIG. 3.

In manufacture of a fail-safe liquid filled safety operation, a vacuum is drawn in the

temperature sensing bulbs

50 and 52, the

capillary tubes

54, 56 and 58 and the fluid expansion device 126, which are then filled with the selected liquid. The

temperature sensing bulbs

50 and 52 are placed in a temperature medium at slightly below a balanced temperature corresponding to the second overheat temperature and the flame rollout temperature. The plunger 122 is pushed to its upward or latched position, and the

temperature sensing bulbs

50 and 52, the

capillary tubes

54, 56 and 58 and the fluid expansion device 126 are sealed.

In a gas filled safety operation, the temperature sensing bulbs contain an adsorbent material, such as any of the activated adsorbent materials or a porous decomposed carbonaceous material formed from a compound of carbon and a non-carbon component by removing the non-carbon component leaving cavities of sufficient size to adsorb substantial quantities of the gas. The

temperature sensing bulbs

50 and 52,

capillary tubes

54, 56 and 58 and the fluid expansion device 126 contain a charge or quantity of gas, such as a noble gas selected from helium, neon, argon, krypton or xenon. Other gases which are non-reactive at the temperature of use can be employedso long as the gases have a molecular size which is readily adsorbed by the adsorbent material. The particular gas used is selected 'byconsidering the cost and the desired pressure or volume change per degree temperature change, which pressure or volume change increases directly with the molecular weight of the gas. For example, xenon produces a greater pressure or volume change per degree temperature change than krypton.

One acceptable decomposed compound is formed from a synthetic polymer having volatile components such as hydrogen and a halogen, which can be driven off by heat leaving a porous carbonaceous skeletal structure. Suitable synthetic polymers are polyvinylidene chloride or polyvinylidene fluoride. Granules of polyvinylidene chloride or polyvinylidene fluoride are formed into adsorbent carbonaceous granules by carbonizing or pyrolytic decomposition in a purifying atmosphere, such as a vacuum or a purging flow of inert gas. carbonizing is performed by heating to a temperature less than the melting point but greater than the temperature at which decomposition can be initially observed. For polyvinylidene chloride, carbonizing is performed at a temperature in the range from 138C (280F) to 177C (358F). The duration of heating required for complete carbonization of the synthetic polymer is dependent upon the size of the granules of the synthetic polymer and the temperature employed.v

Along with utilizing a predetermined temperature and duration for a certain size of granular synthetic polymer, observation of a reduction in gas being removed by a vacuum system or the gas being evolved from the granular material are other methods of determining complete carbonization. During carbonization, the non-carbon components, that is hydrogen and the halogen, are volatilized and removed from the synthetic polymer structure leaving a carbon skeletal structure which is highly porous..After the synthetic polymer is carbonized, the carbonized polymer can be subjected to a higher temperature up to about 1510C. (275F) to outgas hydrogen and halogen gases which may have been adsorbed. Outgassing can be completed in a short duration, for example 15 minutes.

In manufacture of a gas filled actuator, the adsorbent material is placed within the bulbs and 52. The

bulbs

50 and 52, the

capillary tubes

54, 56 and 58, the fluid expansion device 126 and the support member 124 are assembled together with the rest of the actuator 120. The

temperature sensing bulbs

50 and 52 are evacuated and heated to outgas air adsorbed by the adsorbent material. The temperature of the temperature sensing bulbs is then adjusted to a balance corresponding to the second overheat temperature and the flame roll-out temperature, and a charge of gas is supplied to the temperature sensing bulbs until the actuator is operated by the movement of the: sliding plate 152 disengaging the abutment 150. At this point the open ends of the

temperature sensing bulbs

50 and 52 are selaed, and the actuator is completed. the operating temperature of the actuator can be lowered by crimping the

temperature sensing bulbs

50 and 52.

In operation, a demand for heat is initiated by the closing of the switch in thermostat 40 to activate the igniter switch 30 which initiates atiming' period for the timing switch circuit portion 36. During the timing period, acircuit is established through the limit switch 44 to the

terminals

46 and 48 of the control device 24 to energize the electromagnet 94 and pull in the armature 93 to place the bleed valve 84 in the on position illustrated in FIG. 2. With the bleedvalve 84 in the on position, bleed chamber 74 will be exposed to outlet pressurethrough bleed passage 82; and, accordingly, main valve operating chamber 96 will have outlet pressure therein while the chamber above. the diaphragm valve member 72 will have inlet pressure therein with the pressure differential across the diaphragm moving the valve member 72 away from valve seat 70 against the bias of spring 102 to supplyfuel through outlet 64 and conduit 26 to the burner 22. Simultaneously withthe supply of fuel to the burner, the igniter driving circuit portion 32 of the igniter circuit 30 applies a spark generating voltage to the spark electrodes 28 adajcent the burner 22 to ingite the fuel. The ignition sensing circuit portion 34 of the igniter circuit 30 senses the presence of ignition orflame at the burner to prevent the timing function of the timing switch portion 36 from opening the circuit established between

terminals

46 and 48 of the control device 24. Should the ignition sensing circuit portion 34 fail to sense ignition or flame within the timing period of the timing switch circuit portion 36, the timing switch circuit portion 36 will open the circuit to

terminals

46 and 48 thereby deenergizing the electromagnet 94 and returning the bleed valve 84 to its off position. In the off position, bleed chamber 74 is exposed to inlet pressure through bleed passage 78 and, accordingly, since main valve operating chamber 96 will be subject to inlet pressure, therewill be no pressure differential across the diaphragm thereby permitting spring 102 to move valve member 72 against valve seat to close the main valve and prevent fuel flow to the burner 22.

If operation of the heating system causes an overheat condition'wherein the temperature increases above the first overheat temperature, the limit switch 44 will open to open the circuit to

terminals

46 and 48 thereby deenergizing electromagnet 94 to return bleed valve 84 to its off condition to close main valve 66 and prevent further flow of fuel to the burner 22. In the event of failure of limit switch 44 to operate or failure of the control device 24 to stop fuel flow in response to opening the circuit to

terminals

46 and 48, the fluid in temperature sensing bulb 50 will expand sufficiently in response to increase of temperature to the second overheat temperature to-terminate the flow of fuel to burner 22 in that the expansion of the fluid increases the pressure in the expansion device 126 to atmospheric pressure to thereby permit the elasticity of the movable wall 128 to force the tubular member 134 downward against the force of bowed spring 138 to move the slide plate 152 to the right, as shown in FIG. 4, disengaging the slide plate from the abutment 150 to allow the plunger 122 to be moved downward under the force of spring 158. The downward movement of the plunger 122 pivots the arm 114 causing valve member 112 to engage valve seat 1 toprevent fuel flow through the control device 24. A leak in either of the

temperature sensing bulbs

50 or 52 or in the

capillary tubes

54, 56 or 58 or the fluid expansion device 126 will allow air to enter the expansible chamber formed by wall 128 to increase the pressure therein to atmospheric pressure thereby operating the actuator 120 to prevent fuel flow through the control device.

Temperature sensing bulb 52 operates the safety actuator 120 in the same manner as described above when subjected to prolonged flame roll-out such that when a prolonged flame roll-out condition exists, the safety actuator 120 closes the safety valve 68 to prevent fuel supply to the burner 22. For exemplary purposes, when the larger temperature sensing bulb 50 is at 150F., the smaller temperature sensing bulb 52 has a size such that with sustained heating at 700F., which temperature is commensurate with prolonged flame roll-out, the safety actuator 120 will be operated to close the safety valve. Further to this example, if the temperature sensing bulb 52 is at 150F., the temperature sensing bulb 50 has a size so that at 35091 which temperature corresponds to the second overheat temperature, the safety actuator 120 will operate to unlatch and close the safety valve. Since the unlatching or closing of the safety valve 68 is a function of the temperature of both of the larger and smaller

termperature sensing bulbs

50 and 52, as one of the bulbs approaches its operating temperature, the operating temperature of the other bulb will be decreased; however, a balance can be obtained to provide both flame roll-out and overheating protection by balancing the size and calibration of the bulbs.

In order to reset the safety valve actuator 120 after the safety valve 68 has been closed and the cause of overheating corrected, the knob 106 and stem 108 are depressed such that the flange 117 engages the protrusion 116 on the arm 114 thereby pivoting the arm clockwise against the force of spring 158 to move the plunger 122 back into the housing 146 until the bowed spring 138 forces the sliding plate 152 back into the notch 148.

The use of two diverse types of safety controls in the heating control system of the present invention has the advantage that failure of one type, such as by an electric short, crimped tube, or the like, will not ordinarily cause failure of the other type. The fluid expansion safety operator does not use energy whereas electric safety devices usually require a constant current or electrical power, and the three-foot maximum electrical lead length presently existing for thermoelectric limit devices does not apply in that capillary tube length is not so limited.'The design of the fluid expansion safety operator allows it to be used in place of many electro-magnetic safety valves.

One advantage of using a gas charge with an adsorbent material in the

bulbs

50 and 52 is that the temperature of actuation or operation can be set at any temperature within a wide range of temperature, whereas a liquid charge in the bulb is limited to the particular boiling point of the liquid. Of the adsorbent materials, a decomposed unactivated synthetic polymer, such as carbonized polyvinylidene chloride or carbonized polyvinylidene fluoride, produces a greater volume or pressure change per degree of temperature change than activated materials, such as activated charcoal. The greater volume or pressure change per temperature change insures that the gas expansion operated safety control has sufficient ability to do work to respond reliably to the overheat temperature of operation, particularly when used in conjunction with a heavier gas, such as krypton and xenon.

Inasmuch as the present invention is subject to many variations, modifications and changes in detail, it is intended that all matter described above or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A heating control system comprising a burner;

a control device having an inlet adapted to receive fuel from a source, an outlet for supplying fuel to said burner, a flow passage between said inlet and said outlet, and valve means disposed in said flow passage for controlling fuel flow therethrough; thermostat means for operating said valve means to control the supply of fuel to said burner; and safety operator means including actuator means for operating said valve means to interrupt the supply of fuel to said burner, first bulb means containing an expandable fluid positioned to sense an overheat condition of said heating system, second bulb means containing an expandable fluid positioned adjacent said burner to sense a flame roll-out condition and tube means connecting said first and second bulb means with said actuator means whereby said first and second bulb means cooperate to control said valve means to prevent the supply of fuel to said burner in response to said overheat condition or said flame roll-out condition.

2. A heating control system as recited in claim 1 wherein said first and second bulb means are charged to a pressure less than atmospheric pressure and said actuator means is operated by pressure equal to atmospheric pressure.

3. A heating control system as recited in claim 1 wherein said valve means includes safety valve means and main valve means, said thermostat means operating said main valve means and said actuator means operating said safety valve means.

4. A heating control system as recited in claim 3 wherein said safety valve means includes a valve seat, a valve member cooperating with said valve seat to control flow through said flow passage and pivotal arm means supporting said valve member, and said actuator means includes an expansible chamber communicating with said tube means and expandable in response to said fluid in said first and second bulb means to abut said arm means to move said valve member against said valve seat to close said safety valve means.

5. A heating control system as recited in claim 1 wherein said first and second bulb means and said tube means contain a gas adsorbent material and a charge of gas.

6. A heating control system as recited in claim 5 wherein said gas adsorbent material includes a carbonized polymer selected from polyvinylidene chloride and carbonized polyvinylidene fluoride, and said gas is selected from krypton and xenon.

7. A heating control system as recited in claim 1 wherein said actuator means includes an expansible chamber, said tube means includes a capillary tube communicating with said expansible chamber and having first and second branches communicating with said first and second bulb means, respectively, and said first bulb means is larger than said second bulb means.

8. A heating control system as recited in claim 7 wherein said first and second bulb means, said capillary tube and said expansible chamber contain a gas adsorbent material selected from carbonized polyvinylidene chloride and carbonized polyvinylidene fluoride, and a charge of gas selected from krypton and xenon.

9. A heating control system as recited in claim 8 and further comprising electric ignition means connected with said thermostat means for igniting said burner.

10. A heating control system as recited in claim 9 wherein said valve means includes main valve means operated by said thermostat means and safety valve means operated by said expansible chamber of said actuator means.

Claims

1. A heating control system comprising a burner; a control device having an inlet adapted to receive fuel from a source, an outlet for supplying fuel to said burner, a flow passage between said inlet and said outlet, and valve means disposed in said flow passage for controlling fuel flow therethrough; thermostat means for operating said valve means to control the supply of fuel to said burner; and safety operator means including actuator means for operating said valve means to interrupt the supply of fuel to said burner, first bulb means containing an expandable fluid positioned to sense an overheat condition of said heating system, second bulb means containing an expandable fluid positioned adjacent said burner to sense a flame roll-out condition and tube means connecting said first and second bulb means with said actuator means whereby said first and second bulb means cooperate to control said valve means to prevent the supply of fuel to said burner in response to said overheat condition or said flame roll-out condition.