US3017923A

US3017923A - Pot type burner apparatus

Info

Publication number: US3017923A
Application number: US716152A
Authority: US
Inventors: Kenneth S Jenson; Frederick W Suhr
Original assignee: Preway Inc
Current assignee: Preway Inc
Priority date: 1958-02-19
Filing date: 1958-02-19
Publication date: 1962-01-23
Anticipated expiration: 1979-01-23

Description

Jan. 23, 1962 K. s. JENSON ET AL POT TYPE BURNER APPARATUS 3 Sheets-Sheet 1 Filed Feb. 19, 1958 GDVDOOQOOOOOOOObOOOOOOOO 00000000 OOOOOOOOOOOOOOOUOO Jan. 23, 1962 K. s. JENSON ET AL POT TYPE BURNER APPARATUS 3 Sheets-Sheet 2 Filed Feb. 19, 1958 Jan. 23, 1962 K. s. JENSON ET AL 3,017,923

POT TYPE BURNER APPARATUS Filed Feb. 19, 1958 s Sheets-Sheet z 3,017,923 POT TYPE BURNER APPARATUS Kenneth S. Jenson and Frederick W. Suhr, Wisconsin Rapids, Wis, assignors to Preway, Inc. Filed Feb. 19, 1958, Ser. No. 716,152 8 Claims. (Cl. 158-91) This invention relates to burner apparatus, and more particularly to burners of the open pot type for burning liquid fuel.

Burners of the character mentioned have included an open pot having a cylindrical sidewall and a bottom wall forming a receptacle for a shallow body of liquid fuel usually supplied to the pot through an inlet situated near the bottom of the pot. Fuel admitted to the pot is ignited in some suitable manner and the heat generated during combustion vaporizes the liquid fuel into gases which mix with air to form a combustible gaseous mixture. Pots of this nature are usually of a substantial diameter, 8 to 12 inches for example, and the bottom is generally flat so that even a small quantity of liquid fuel in the pot spreads out over a relatively large area of the pot bottom. This gives rise to certain problems which it is desirable to eliminate.

More specifically, when heat is needed and burner operation desired, the fuel oil in the bottom of the pot must be ignited in some manner. In some cases frequent need for ignition is avoided by maintaining the burner in operation at low fire, or pilot fire, when there is no call for heat and merely increasing the fire when there is a call for heat. This has been described as a high-low operation. In other cases it may be desirable to allow the fire to burn completely out when there is no call for heat, and then to light the fire again when there is a call for heat. This has been described as an on-off operation. In the latter case ignition is frequently accomplished by means of an electric igniter which is placed above or in the fuel and gives off sutficient heat to vaporize some of the oil and to ignite the vaporized fuel. The igniter is a relatively small part compared to the area of the pot bottom and obviously can provide only a limited amount of heat, while the fuel may cover the entire pot bottom, thus constituting a relatively large volume of fuel having an extensive exposed surface area. As a result, on burner startup considerable difiiculty may be encountered in vaporizing and igniting the fuel due to the quantity involved.

When the fuel begins to burn combustion occurs principally in the lower portion of the pot, and as the fire grows it moves upwardly toward the top of the pot until eventually at high fire the entire combustion occurs near the upper rim of the pot. Due to the quantity of oil which may stand in the bottom of the pot on burner startup, during the initial stages of combustion, the tire frequently becomes very intense in the lower portion of the pot before it rises to the upper rim, creating excessive heat and a condition sometimes described as a red hot pot," with accompanying high temperature which may be dangerous and damaging to the burner parts.

Further, in prior open pot burners of the type described, during operation of the burner at a normal high fire rate, the rate of vaporization of the fuel depends primarily on the amount of heat generated by the fire. Thus, as the fire grows and the consequent heat increases, the rate of vaporization increases, and this causes the fire to grow still more. Such increases in fire and the rate of vaporization may continue uncontrolled except by the rate of fuel flow to the pot, and if fuel fiow to the pot becomes excessive because of faulty valving, or because of varying grades of oil or varying viscosity due to temperature changes, the fire may possibly attain uncontrollable proportions which may be dangerous and cause considerable damage.

3,l7,923 Patented Jan. 23, W62

ice

With the above and other considerations in mind, it is a general object of the invention to provide a new and improved burner of the open pot type which eliminates the undesirable conditions referred to.

Another object is to provide a new and improved burner of the type described which is safe and efficient in operation over a wide range of fires.

A further object is to provide a new and improved burner of the type described including a novel pot bottom for containing the liquid fuel to be burned.

Another object is to provide a new and improved burner of the character described including a pot bottom for containing only a limited quantity of liquid fuel having only a limited fuel surface area exposed to thereby provide improved burner starting without the danger of a red hot pot.

A more specific object is to provide a new and improved pot type burner including a concentric annular fuel groove or well in the bottom of the pot having a diameter about one half the pot diameter, having a relatively narrow width and a sloping depth to permit a close control of the fuel quantity and the fire over a wide range from high fire to low fire.

Another object is to provide a new and improved burner of the type described wherein the rate of vaporization is controlled over a wide range of burner operation to prevent excessive vaporization, even though fuel flow to the pot may be excessive, to thereby minimize the danger of uncontrolled fires.

It is also an object of the invention to provide a new and improved burner of the type described including an igniter for starting the fire, and a novel igniter cover for concentrating igniter heat to expedite ignition and to protect the igniter from intense heats during combustion.

Other objects and advantages will become readily apparent from the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is an elevational view of a burner apparatus embodying the principles of the present invention;

FIG. 2 is an enlarged vertical sectional view through the center of the burner pot and ignition device illustrated in FIG. 1;

FIG. 3 is an enlarged vertical sectional view through the flow control unit illustrated in FIG. 1;

FIG. 4 is a fragmentary vertical sectional View taken at about the line 44 of FIG. 3, illustrating details of a switch mechanism for controlling the ignition device;

F G. 5 is a fragmentary plan view, partly broken away, of the burner pot illustrated in FIG. 2;

FIG. 6 is a fragmentary side elevation of the burner pot illustrated in FIG. 5, taken at about the line 6-6 of FIG. 5 with the ignition device omitted;

FIG. 7 is an enlarged fragmentary vertical sectional view through the burner pot side wall, taken at about the line 7-7 of FIG. 2;

FIG. -8 is an enlarged fragmentary vertical sectional view through the burner pot side wall, taken at about the line 8-8 of FIG. 2;

FIG. 9 is a plan view, similar to that in FIG. 5, showing the igniter element cover and its relation to the igniter element;

FIG. 10 is a left end elevational view of the cover illustrated in FIG. 9; and

FIG. 11 is a side elevational view of the cover illustrated in FIGS. 9 and 10.

While an illustrative embodiment of the invention is shown in the drawings and will be described in detail herein, the invention is susceptible of embodiment in many different forms, and it should be understood that the present disclosure is to be considered as an exemplifification of the principles of the invention and is not intended to limit the invention to the embodiment illustrated. The scope of the invention will be pointed out in the appended claims.

Referring now to the drawings, and particularly to FIG. 1, the invention is embodied in a burner apparatus including an open pot type burner 1i). Fuel oil in a liquid state is supplied to the bottom of the burner pot through

conduits

11 and 12 which lead from the outlet in a flow control unit 13 to the bottom of the pot. Fuel is supplied to the flow control unit 13 from a suitable tank or reservoir (not shown) having an outlet conduit 14 connected with the inlet to the flow control unit, the relative positions of the fuel tank, the flow control unit and the burner pot being such that fuel flows by gravity from the tank to the burner pot bottom under control of the flow control unit.

The flow control unit 13 is a device of conventional manufacture, and may comprise a construction similar to that illustrated in the Biermann et al. Patent 2,547,995. It includes an inlet valve which controls flow of fluid from the conduit 14 to an inner chamber in the unit 13 under control of a level responsive device such as a float. The unit includes an adjustable outlet valve which meters the flow from the control unit to the conduit 12 and the burner pot 10. In the embodiment chosen to illustrate the invention, the burner apparatus includes a thermostatic control unit 15 of the type illustrated in the McCarty et al. Patent 2,719,673 and de scribed therein as a conversion unit. The conversion unit is arranged to control the opening and closing of the adjustable outlet valve from the flow control unit in response to room temperatures.

Fuel in the burner pot bottom is ignited by an ignition device 16 which depends for energization upon a switch mechanism 17 mounted atop the flow control unit 13 and controlled by the conversion unit 15.

Referring now particularly to FIG. 3, the flow control unit 13 includes a casing or housing 21 which provides a chamber or reservoir 21 for fuel oil. Oil flows by gravity to the chamber 21 from the conduit 14, through a strainer 22 and through an inlet valve 23. The valve 23 is controlled by a float 25 in the chamber 21 which is supported by a pivoted lever 26 having a suitable connection with the valve stem 27 to close the valve 23 when fluid in the chamber 21 reaches a normal oil level indicated by the dot-dash line 28. The valve stem 27 is normally biased in an upward direction by a spring 29 to open the valve 23. Thus, when the level of the fuel in the chamber 21 falls, the float 25 also falls and allows the valve 23 to open to permit the flow of fuel into the chamber. When the level of the fuel rises, the float 25 rises to close the valve. In this manner, a substantially constant, predetermined level of fuel oil is maintained in the chamber 21 at all times.

It sometimes happens on rare occasions that the valve stem 27 fails to close the valve 23, because of grit or other extraneous material in the valve bore. On such occasions, if the valve fails to completely close, the fuel continues to rise and overflows into a safety chamber 31 provided by a wall 31a. An auxiliary safety float 32 is provided in the safety chamber and is suitably connected to a safety mechanism 33 which functions to hammer the valve stem 27 to a closed position in the event that fluid overflows the chamber 21 and rises in the chamber 32. The safety mechanism described functions to prevent the rise of fuel oil above an overflow level indicated by the line 34. Once actuated, the safety mechanism 33 must be reconditioned by means of a reset mechanism including an exteriorly accessible reset lever 35.

Fuel flow from the interior of the flow control unit to the conduit 12 is controlled by a metering valve mechanism generally designated 37. The metering valve includes a valve stem 38 which is controlled by a leverage 39 in turn controlled by a vertically disposed pin 40 which is reciprocable in the cover for the unit. The

pin 40 is in turn positioned to be controlled by a leverage 41 included in the thermostatic control unit 15. Movement of the leverage 41 is regulated by means of a reciprocable rod 42 having a connection with a bellows 43 positioned in a cylindrical bulb 44. The bulb 44 encloses a suitable gaseous medium which is responsive to room temperatures or the like and compresses the bellows on increases in temperature, and permits the bellows to expand with decreases in room temperatures. On decreases in room temperatures, the thermostatic control unit 15 permits the reciprocal pin 40 to rise, which in turn permits the leverage 39 to pivot upwardly, allowing the outlet valve 38 to open and permit the flow of fuel to the burner pot. Conversely, on increases in room temperature the thermostatic control unit is effective to move the reciprocal pin 40 downwardly, pivoting the leverage 39 downwardly to thereby move the valve stem 38 downwardly toward a closed position.

In the flow control unit 13, a screw 45 is adjustable to provide a compensation for variations in the grades of various oils which may be used with the burner apparatus, and the varying viscosities encountered with different grades of oil. An adjustable screw 46 is engageable by the leverage 39 on upward pivotal movement of the leverage, and provides an adjustment for determining the maximum opening movement of the valve 37 and thus determines the maximum fuel flow rate when the valve is fully open for high firing. In units of the type illustrated, the high firing rate could be varied, to accommodate most any conventional burner, within a range of 15 to 75 cc. per minute, for example. An adjustable screw 47 carried by the leverage 39 determines the maximum closing of the valve 37, and thus may be set to provide a low fire or pilot fire fuel flow rate when there is no call for heat at the thermostatic bellow 43. It should be understood however that in the preferred mode of operation for the burner apparatus described, it is not contemplated that the adjustment screw 47 would be utilized to provide a low fire or pilot firing rate, but rather it is preferred that the valve 37 be completely closed when there is no call for heat since the apparatus is intended for an on-oif type of operation.

In open pot burners of the type illustrated, liquid fuel supplied to the pot is vaporized and mixed with air to form a combustible gaseous mixture which burns in the pot. This characteristic mode of operation gives rise to the numerous problems previously described, particularly where the burner pot employed is formed with a generally flat bottom. The burner apparatus of this invention is designed to substantially eliminate the disadvantages encountered with prior burners.

Referring now particularly to FIGS. 2, 5 and 6, the burner pot 10 includes a cylindrical side wall 50 and a bottom wall 51 including an outer annular upturned flange portion 52 which is suitably joined to the bottom edge of the side Wall 50 as by Welding. The side wall and the bottom wall together define a generally cylindrical pot which is substantially open at the top. In the embodiment illustrated, the burner pot has a diameter of about 11 inches.

According to the invention, the bottom wall 51 is formed with an annular depression or groove which forms an annular fuel well concentrically disposed within the cylindrical burner pot and positioned approximately midway between the center of the pot and the pot side wall. In the pot illustrated, the outer diameter of the groove 53 is about 5 inches. The groove is of relatively narrow width, about and slopes from a shallow portion 53a at one side of the pot center, the right side as illustrated in FIGS. 2 and 5, to a deeper portion 53b at the opposite side of the pot center, which has a constant depth for a substantial length of the groove 53. The shallow portion 53a is about /2" deep, and the portion 53b is about 1%" deep. The fuel inlet conduit 11 opens into the groove at the deeper portion 53b.

The groove 53 forms a well for holding a limited quantity of fuel having a limited, predetermined surface area exposed. The sloping bottom in the groove further reduces the capacity of the well to hold only a limited quantity of fuel for ignition. As seen in FIGS. 1, 2 and 3, the oil level 28 normally maintained by the float 25 is about Ms below the top of the annular groove 53 in the pot bottom. By virtue of the limited quantity of oil which may be held in the pot bottom, ignition is effected in a more expeditious manner, and there is never a sufficient quantity of fuel to incur a red hot pot as may occur with substantially flat bottom pots. Further, the well provides only a limited quantity of fuel during burner operation, but still provides a wide range of operation and permits an element of control over the combustion.

The remaining portions of the bottom wall 51 include a central portion 55 which is conically shaped to slope upwardly toward the center of the pot from the inner edge of the annular well 53. The radially outer portion of the bottom wall slopes upwardly from the outer edge of the annular groove to the corner of the pot where it joins the side wall 50 at substantially the level of the center of the pot. The center of the pot and the outer edge of the bottom wall of the pot are positioned substantially at the overflow level indicated by the line 34 in the control unit 13, and thus in the rare instances when fuel may overflow the chamber 21, the inclined central and outer portions of the burner pot bottom wall function to reduce the quantity of oil which may be held in the pot because of the inclination of these portions of the bottom wall.

The burner pot side Wall St is provided with a plurality of air inlet openings arranged in horizontal, vertically spaced rows. Beginning at the bottom of the burner pot side wall and proceeding upwardly, there are six rows of air inlet openings 57 in which the openings are rather widely spaced horizontally in the rows. Adjacent the top of the pot there is a seventh row of openings 58 wherein the openings are closely spaced. In the embodiment illustrated, the bottom row of openings 57 is positioned about /8 from the bottom edge of the side wall, and thereafter upwardly, the rows 57 and the row 58 are vertically spaced apart on centers of 1%". In the rows 57, the separate openings are spaced apart horizontally around the pot sidewall on 1 centers. In the upper row 58, the openings are spaced on .273 centers. In each of the rows, the openings are .113" in diameter.

As illustrated in the sectional view of FIG. 7, the burner pot sidewall is deformed around each of the air inlet openings 57 in the bottom row in a manner such that the openings provide a downwardly directed passage inclined at about 30 from the vertical, so that these inlet openings serve to direct air entering therethrougn downwardly and toward the center of the pot. As seen in FIG. 8, the pot is deformed around each of the openings in the upper row 58 in a manner such that the openings provide upwardly directed passages inclined at about 30 from the vertical, so that these openings serve to direct air upwardly and toward the center of the pot. The openings in the intermediate rows are all substantially horizontally directed through the vertical sidewall.

The air inlet openings '7 and 58 are sized and arranged in proportion to the annular well 53 and the burner pot bottom wall so as to impose a limit on maximum rate of vaporization, even in the event of an excessive flow through the metering valve 37 to the burner pot. This safety feature virtually eliminates the danger of uncontrolled fires in the event of excessive fuel flow to the pot, eliminates excessive heat which contributes to a red hot pot," and minimizes the danger of explosion in the burner. Further, the float control of the unit 13 is superimposed 6 on the controlled rate of vaporization to prevent flooding in the burner pot during operation. Thus, these features, with others, contribute to provide an extremely safe burner apparatus.

Near the upper rim of the burner side wall 50, but spaced slightly therebelow, the side wall is provided with an inwardly extending annular lip or flange 60. The flange 60 is turned inwardly from a short cylindrical sleeve 61 which may be welded or otherwise suitably secured to the sidewall Stl. During operation of the burner, combustion air enters the burner pot through the

various openings

57 and 58 to mix with the vaporized fuel for combustion. While the major portions of such air are suitably mixed and burn during combustion, the concentration of cooling air along the burner pot sidewall sometimes prevents complete combustion of the gaseous mixture along the sidewall. Accordingly, the lip 60 is provided to direct the cool, unburned gases adjacent the sidewall inwardly toward the center of the pot to insure a complete combustion.

At the upper rim of the sidewall 50, the pot is formed with a horizontally disposed, outwardly extending rim 62, having at its outer periphery, an upwardly turned flange 63. As illustrated, the

rim portion

62, 63 is formed integrally with the sleeve portion 61 which may be welded to the burner pot sidewall. The outwardly extending rim portion 62, d3 facilitates handling of the pot, and also affords a support means for an annular upper high fire ring of a conventional type, if such a ring is found desirable or necessary under peculiar conditions of operation. It should be understood however that in the preferred mode of operation, no high fire ring is necessary as the burner is capable of operation over a wide range of high fires without a high fire ring.

While the intended mode of operation described for the burner apparatus illustrated contemplates the use of ignition means and an on-off cycle of operation wherein the fire dies completely when there is no call for heat, and is ignited again when there is a demand for heat, provision is made for use of a low fire pilot ring in the burner pot 10 if a low fire or pilot fire type of operation is desired wherein the fire is merely lowered rather than extinguished when there is no call for heat. Accordingly, somewhat above the lower row of air inlet 57, low fire baffle ring supporting pins 65 in the form of rivets or the like may be secured in the burner pot sidewall to project radially inwardly to afford a support for a low fire pilot ring such as that illustrated at 66. The ring 66 may be employed to add stability to a low fire where extended periods of pilot fire operation are contemplated, though no such ring is necessary with the contemplated mode of on-off operation.

Adjacent the fuel inlet to the annular fuel well 53, the well is formed with an enlarged well portion 69 which, as viewed in FIG. 5, is generally V shaped in plan, and which as viewed in FIG. 6, is generally V shaped in vertical cross-section. The well portion 69 tapers from a deep portion at the deep side of the main well 53 upwardly and outwardly toward the outer portion of the burner pot sidewall, as seen plainly in FIG. 2. The enlarged portion 6% of the fuel groove forms an inlet well portion over which an igniter element 70 is positioned for use in igniting the fuel.

The igniter element 79 is an elongated U shaped element which is electrically energized to supply heat which vaporizes fuel in the fuel well and heats such vapor to the point of ignition. As seen best in FIGS. 2 and 5, the igniter element projects through an opening 71 in the burner pot side wall where suitable gasket means (not shown) may be provided, and is positioned over the inlet well portion 69 with the tip of the igniter disposed substantially over the end of the inlet conduit 11. Because of the limited quantity of oil which may accumulate in the burner pot bottom, and because of the limited exposed surface area of the body of oil in the well, ignition '2 is expedited and occurs with a high degree of certainty.

In order to concentrate the heat of the igniter element 70 and to protect the igniter heat from excessive temperatures during extended periods of high fire operation, an igniter cover 75 is provided to enclose the igniter element 70. The cover 75 is of an inverted channel shaped cross-section, having upright sidewalls 76 which rest at their bottom edges on the outer portion of the burner pot bottom wall 51. The sidewalls 76 extend from an inner end substantially even with the tip of the igniter element 70, outwardly to engage the burner pot sidewall 56. At the outer end, the upright edges of the side wall are formed with laterally turned flanges 77 which abut against the burner pot side wall. The upper edges of the side walls 76 taper upwardly from the inner ends to the outer ends, and are joined by a top wall 78. Like the side walls, the top wall extends from an inner end substantially even with the igniter tip outwardly to the burner pot sidewall. At the outer edge, the top wall is formed with an upwardly extending flange 79 which is joined to the flanges 77 and abuts the side wall 56 It will be understood that the lower edges of the side walls 76 fit the burner pot bottom wall 51, and the

flanges

77 and 79 fit the burner pot side wall so as to substantially enclose the igniter element in a chamber which is open at the inner end adjacent the igniter tip. Thus, the heat of the igniter element is concentrated under the cover and over the inlet well portion 64 to expedite ignition.

The top wall 78 of the igniter cover is formed with a V-shaped recess 78a extending outwardly from the inner end of the wall to permit circulation of air and oxygen around and under the igniter element. The circulation of air thus provided permits a complete combustion in the area adjacent the igniter element in a manner such that any carbon formed is consumed about as rapidly as it forms. Thus, an accumulation of carbon on the igniter element in sufificient quantities to cause difliculty is effectively prevented and failures due to carbon formation on the igniter are avoided.

Centrally of the upwardly extending flange 79, it is formed with an upwardly projecting handle portion 80 which facilitates manipulation of the cover. The igniter cover is held in position by means of headed rivets 81 secured to the burner pot side wall 50 with the heads of the rivets spaced somewhat from the side wall to receive the flanges 77 which may be inserted by moving the igniter cover vertically downwardly between the rivets.

Energization of the igniter 70 is controlled by an ignition circuit including a micro switch 85 (FIGS. 4 and forming a part of the switch mechanism 17. The switch 85 is supported in a switch housing 84 suitably secured to the top of flow control unit 13 and including a bottom wall 86, having upwardly turned end walls 87, and formed with short upwardly turned side wall portions 83. A closure member is fitted on the end walls 87 and includesa top wall 89 and side walls 90.

The switch 85 includes a switch actuating arm 92 which extends outwardly from the switch for engagement under the thermostatic control leverage 41 and over the reciprocal pin 40, so that actuation of the switch is controlled by the thermostatic control unit 15. A spring 93 biases switch arm 92 upwardly in a switch closing direction. The operation is such that when the thermostatic unit indicates a need for heat and the control leverage 41 rises to open the outlet valve 37 from the float control unit, the switch 85 is closed at the same time to efiect energization of the igniter element 70. When there is no longer a call for heat at the thermostatic control unit 15 the leverage 41 is lowered to the valve 37, and the micro switch 85 is opened to break the circuit through the igniter.

The igniter switch is wired in a circuit including a wire 95 which leads from a suitable source of power to the micro switch, a wire 96 which leads from the micro switch to the ignition device, a wire 97 which leads from the ignition device, and a wire 98 connected to the wire 97 and returning to the source of power.

The

wiring

96 and 97 leads from the micro switch housing to an igniter housing lltit) suitably secured to the outside of the burner pot side wall 50. The igniter housing includes a removable end cover M21 which permits access to the interior of the housing, and includes a detachable bracket M2 to which the igniter element 70 is secured as by screws 1G3 to support the igniter element with the tip of the igniter projecting into the burner pot as previously described. The wire 96 leads to one end of the U shaped igniter element, and the wire 97 leads to one side of an ignition control switch 165. The opposite side of the control switch 105 is connected by a wire 106 which leads to the opposite end of the U shaped igniter element.

The control switch M is a commercially obtainable item of conventional construction which includes one movable switch contact of bimetal composition which is responsive to heat generated by the current flowing through the igniter circuit. The operation is such that the bimetal contact normally closes against a stationary contact, but after energization of the circuit for a short period of time bends to open the switch thereby deenergizing the igniter. After the switch is open for a short time, the bimetal cools and again closes to energize the igniter. In this manner the igniter is cycled between on and off conditions until such time as ignition is established in the burner pot.

The switch 165 incorporates a bimetal disk which is responsive to the heat of combustion in the burner pot, and after ignition is established flexes to open the movable switch contact to thereby deenergize the igniter, and maintain the igniter deenergized so long as the burner remains in operation.

To summarize the operation briefly, when the room temperature or other control temperature drops below a desired minimum, the thermostatic bellows 43 expands sufliciently to effect operation of the leverage 41 to open the metering valve 37 and to close the micro switch 85. Opening of the metering valve permits the flow of fuel from the flow control unit 13 to the fuel well 53 in the burner pot. At the same time, closure of the switch 85 completes a circuit to energize the igniter element 70. The energized igniter element heats the oil in fuel well 53 and in the inlet portion 69 to vaporize a portion of the fuel and to heat such vapor to a point of ignition. The vaporized fuel mixes with combustion air entering through the air inlet openings, particularly the lower openings 57, and the mixture of vapor and combustion air burns at first in a small candle like flame. Because of the limited quantity of fuel in the burner pot bottom, and because the heat of the igniter element is concentrated by the igniter cover 76, ignition is readily accomplished in a short period of time. I

Gradually the flame grows entirely around the annular fuel well, burning in an annular wicklike flame having a base located substantially at the surface of the oil. At this stage of the operation, the fuel has risen to a level such that the surface is approximately Ms below the top groove, though ignition may occur with the fuel at a lower level. As the flame grows, the fuel may burn down as much as /2" in the annular groove. After a short period of operation, the ignition control switch opens in response to burner heat to deenergize the igniter.

After an annular flame is established, this flame grows slowly and may reach a height of 4 or 5 inches while retaining the annular wick like shape. Because of the limited quantity of oil which may accumulate in the fuel well, and the limited exposed surface of this fuel, the flame never reaches sufiicient proportions and temperatures to give a red hot pot. The initial stages a burner operation are thereby accomplished in a safe and relatively cool fashion.

During operation, while burning occurs in the burner pot, some heat from the flame established radiates downwardly to heat the fuel in the annular fuel well, particularly the fuel at the upper surface, and this contributes toward vaporization of the fuel which continues'to flow to the pot. Principally however the heat of the flame heats the walls of the burner pot, particularly the large central and outer expanses of the bottom wall which are exposed, and the heat of the bottom wall portions is conducted by the metal to the side walls and the bottom wall of the narrow annular fuel groove. The heat thus transmitted to the fuel functions to heat and vaporize the fuel and to maintain the desired rate of vaporization during burner operation.

As the flame grows, more heat is produced, and the rate of vaporization increases to further increase the flame. Eventually, the flame rises from the surface of the fuel, firstly to a position where the base of the flame is about even with the lowest row of air inlet openings 57. As combustion continues, the fire gradu ally moves upwardly, to the succeeding rows of air inlet openings if the rate of fuel flow is suflicient to permit this, moving eventually to a final position at the upper rim of the pot with the base of the flame approximately at the level of the upper row of the air inlet openings 58. When the flame burns at the upper rim of the pot, the lip 60 functions to direct the cool unburned gases at the burner pot sidewall inwardly toward the flame to insure complete combustion.

The sizing and location of the

air inlet openings

57 and 58 in the burner pot side wall are, of course, calculated to provide suificient air to support combustion in the burner within the range of operation varying from a firing rate of 15 cc. per minute to 75 cc. per minute. Additionally, these air inlet openings permit a sufficient flow of air to provide a substantial cooling effect which imposes a limit on the maximum possible rate of vaporization to thereby hold the fire down even in the event of excessive fuel flow to the burner through a faulty metering valve. The burner thus provides a safe, controlled operation without the danger of uncontrolled fires.

When the demand for heat is satisfied, the bellows 43 is compressed, and the leverage 41 forces the pin ltl downwardly to eifect closure of the metering valve 37, at the same time opening the micro switch 85, thereby ter minating operation of the burner.

We claim:

1. In a burner for liquid fuels, an open top burner pot having a cylindrical side wall and a circular bottom wall joined thereto and closing the same at the bottom thereof, said bottom wall having a single concentric annular depression therein providing a well for liquid fuel, said annular depression having side walls and being spaced approximately midway between the center of the pot and the pot side wall, and having a relatively narrow width as compared to the radius of the bottom wall to thereby hold only a limited quantity of liquid fuel, means forming a fuel inlet to the well, the central portion of said bottom wall being free of obstructions and sloping from the inner edge of the fuel well upwardly to the center of the pot at an inclination less than that of the adjacent depression side wall, the outer portion of said bottom wall sloping from the outer edge of the fuel well upwardly toward the pot side wall at an inclination less than that of the adjacent depression side wall and meeting the side wall at substantially the level of the center of the bottom wall, and the space above the central portion of the bottom wall being open.

2. In an apparatus for burning liquid fuel, an open top burner pot having a cylindrical side wall and bottom wall, said bottom wall having a concentric annular depression spaced approximately midway between the center of the pot and the pot side wall to provide a well for liquid fuel, the space above the central portion of the bottom wall, within the bounds of the well, being open, said annular depression having a relatively narrow width and a bottom sloping downwardly from a shallow portion at one side of the pot center to a deeper portion at the opposite side of the pot center to thereby hold only a limited quantity of liquid fuel, means forming a fuel inlet to the deepest portion of the well, a fuel well portion extending outwardly from the annular depression adjacents the fuel inlet and sloping upwardly from the bottom of the depression adjacent the inlet, and an igniter element projecting through the burner pot side wall over the outwardly extending fuel well portion with the end of the igniter element over the fuel inlet.

3. In a burner for liquid fuels, a burner pot having a cylindrical side wall and a bottom Wall, said bottom wall having a continuous, relatively narrow groove surrounding the central portion of the pot to form a well for liquid fuel, means forming a fuel inlet to the well, an igniter element projecting through the burner pot side wall over the fuel well with the tip of the igniter element over the fuel inlet, and an igniter cover of inverted channel shape comprising, spaced side walls along opposite sides of the igniter and a top wall joined to the side walls and over the igniter, said cover side walls and top wall having outer ends abutting the adjacent burner pot side wall and closing the outer end of the cover, said cover side walls and top wall extending from the outer ends to inner ends substantially even with the igniter tip, the cover being open at the end adjacent the igniter tip.

4. In an apparatus for burning liquid fuel, a burner pot having a cylindrical side wall and bottom wall, said bottom wall having a concentric annular depression spaced approximately midway between the center of the pot and the pot side wall to provide a well for liquid fuel, said annular depression having a relatively narrow width and a bottom sloping downwardly from a shallow portion at one side of the pot center to a deeper portion at the opposite side of the pot center to thereby hold only a limited quantity of liquid fuel, means forming a fuel inlet to the deepest portion of the well, a fuel well portion extending outwardly from the annular depression adjacent the fuel inlet and sloping upwardly from the bottom of the depression adjacent the inlet, an igniter element projecting through the burner pot side wall over the outwardly extending fuel well portion with the end of the igniter element over the fuel inlet, and an igniter cover of inverted channel shape comprising, spaced side walls having bottom edges fitting on the burner pot bottom wall on opposite sides of the igniter element and upper edges sloping upwardly from the inner ends to the outer ends, and a top wall joined to the upper edges of the side walls and sloping upwardly from the inner end to the outer end, said cover side walls and top wall having their inner ends substantially even with the end of the igniter element and their outer ends abutting the burner pot side wall to form a chamber enclosing the igniter element, said cover top wall having a V-shaped recess therein extending outwardly from the inner end thereof to permit circulation of air around the igniter element.

5. A burner as defined in claim 3, wherein the top wall of said igniter cover has a V-shaped notch therein at the end over the igniter tip.

6. In an apparatus for burning liquid fuel, a burner pot having a cylindrical side wall and bottom wall, said bottcm wall having a concentric annular depression spaced approximately midway between the center of the pot and the pot side wall to provide a well for liquid fuel, said annular depression having a relatively narrow width and a bottom sloping downwardly from a shallow portion at one side of the pot center to a deeper portion at the opposite side of the pot center to thereby hold only a limited quantity of liquid fuel, means forming a fuel inlet to the deepest portion of the well, an igniter element projecting through the burner pot side wall over the deep portion of the fuel well with the tip of the igniter over the fuel inlet, and an igniter cover of inverted channel shape having side walls on the bottom of the pot along opposite sides of the igniter, and a top wall joined to the side walls 11 and over the igniter, said cover side walls and top wall having outer ends abutting the adjacent burner pot side wall and closing the outer end of the cover, said cover side walls and top wall extending from the outer ends to inner ends substantially even with the igniter tip, the cover being open at the inner end.

7. The combination as defined in claim 1, including means for introducing liquid fuel through the fuel inlet to the fuel Well including flow control means to prevent the level of fuel from rising above the top of said well so as to leave the relatively wide central portion of said bottom wall, within the bounds of said well, and the relatively wide outer portion of said bottom wall, between the well and the pot side wall, exposed during operation of the apparatus to conduct heat from the fire to the walls of said well to cause vaporization of the liquid fuel.

8. The combination as defined in claim 1 comprising, means including a metering valve for introducing liquid fuel through the fuel inlet to the fuel well for vaporization, and said side Wall having air inlet openings arranged in rows extending circumferentially around the Wall and spaced vertically along the wall to admit air for mixture 12 with vaporized fuel to form a combustible gaseous mixture.

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