US2531538A

US2531538A - Air control unit for oil burners

Info

Publication number: US2531538A
Application number: US25403A
Authority: US
Inventors: Cecil W Smith
Original assignee: Individual
Current assignee: Individual
Priority date: 1948-05-06
Filing date: 1948-05-06
Publication date: 1950-11-28
Anticipated expiration: 1967-11-28

Description

Nw. 28, H950 c. w. sMlTH AIR CONTROL UNT FOR OIL BURNERS Filed May 6, 1948 m 3 0 5 e 2 fu G um INVENTOR. @ZM w @mim BY I Patented Nov. 28, 1950 UNITED STATES PATENT OFFC AIR CONTROL UNIT rouen', BURNEasf Cecil W. smith, waterman, nu Application May 6, 1948, Serial No. 25,?:03k l This invention relates generally to domestic oil burners and in particular to an air control unit adapted to be positioned Within an air sup- `ply tube, and about a fuel nozzle in the tube, to vary the pattern or shape of the burner flame and the action of the air within the flame.

The control of combustion air and the mixing of such air with fuel in an oil burner is an important factor in the heating efficiency of a burner, particularly oil burners of domestic type. About fourteen pounds (183 cubic feet) of air is required to burn one pound of fuel oil. The

-amount of air above that actually required to l haust gases having a low carbon dioxide reading.

- When an amount of air insuflicient for actually burning the fuel is used, the flame is generally sooty and smoky, and coats the furnace and boiler heating surfaces so as to thermally insulate such parts. It has been estimated that a coating of soot an eighth of an inch thick, on

` the boiler heating surfaces, can cause an increase in the fuel consumption of the burner of as much as twenty-five per cent. y

Because of the heat losses resulting from either excess air for burning, or insuicient air for burning, the air setting on an average domestic oil burner is adjusted so as to give the highest carbon dioxide reading possible without producing a smoky name or re. The percentage of carbon dioxide in the flue gases is generally recognized as an important factor in the combustion performance of a burner and the Federal Housing Administration requirements for a burner, to be financed by that agency, is that the burner shall be capable of producing and maintaining a carbon dioxide reading of not less than eight per cent. It will be appreciated that this reading is relatively low when based on a carbon dioxide reading of fifteen per cent which represents substantially perfect combustion with no excess air and no preventable fuel loss.

A further important factor in the efficient burning of fuel is the manner in which the fuel inthe `name is acted upon by the combustion air. ThusV many of the burners in commercial use l5 omms. (ci.V 15s-7e) have Va flame -pattern of a generally flat conical shape withaspiral twist Vin it. A llame with a spiral twist tends to provide for a more intimate mixing' of' the fuel with the air for combustion and lin -turnfora more efficient burning of the fuel.--In other words, where combustion airnis supplied in what may be called a straight now or stream, as contrastedy to a whirling or spiral motion lof ythe'air in the air stream,A the fuely and combustion air ,tend totravel in separate paths so that insuflicient air mixes with the fuel for burningpurposes. c ,f

However, when the spiral or whirling motion ofthe combustion air is excessive, the heavy ends ofthe fuel Lare thrown through the flame without being burned, rather thanbeing suspended in the fiameforgintimate mixing and burning with the combustion ,air. Fuel thus thrown out of the flame is usually evidenced by lan orange color in the flame and soot showings on the wall of the flrebox,V andnboiler surfaces. y It isseenmtherefore, thatthe volumeof combustion air supplied to the flame, to' reduce as far as possible the use of excess air, and the motion of the combustion air must both be` given consideration in the obtaining of an overall eiiicient burning of the name. s It is an object of this invention, therefore to provide an improved air control unit for an oil burner. f

A' further object of this invention is to provide an air 'control unit for an oil burner, whichv is capable of being adjusted to change both'ithe shape or pattern of the flame and the action or movement of the air in the flame. Yet another object of this invention is to pro"- Vid'e an air .control unit for van oil burner of 'a construction such that the burner is capableA of operating with substantially no excess air and with a carbon dioxide reading of fourteen per cent and higher. l

A still further object of this invention is to provide an oil burner in which an air control unit' is constructed Aand arranged relative to a fuel nozzle, such that a smooth flow of air is supplied tothe flame whereby the name burns evenly and without practically any galloping or pulsating action. y Another object of this invention is-to provide an air control unit for an oil burner adapted to burner arranged within an air supply tube for adjustable movement longitudinally of the tube, and constructed so as to form three separate air supplies to the burner nozzle for combustion purposes. The nozzle is disposed in a central .air passage, in which the -air flows with a spiral motion. A pair of annular passages are concentrically arranged about the central passage, one of which has straight flowing air andthe other spiral flowing air. The air inthe central passage constitutes the main combustion air and is maintained at a substantially constant voliume and velocity. The air inA the two annular passages is supplementary -air for combustion and, on adjustable movement of theV air control unit, the air in the annular passages is` relatively varied as to volume and velocity so as to produce a ame with pattern characteristics providing for. a highly efcient burning'V of the fuel in the flame.

Yet another` feature. of this invention isfound in the provision of anV air control unit for the airvsupply tube of an oil*V burner, which is adjustable tovary-the action of supplementary air for combustion on the'main air for combustion to elongate orA shorten'. the length of the burner flame, concurrently with varying the angle of twist or spiralin the nameu to provide a flame with highly eiiicient burning: characteristics.

Further objects, features and advantages of this invention will become'apparent from the following description when taken in connectionwith the accompanying drawings, inwhich:

Fig. 1 is a perspective viewof the front end portion of an air supply tubeA of an oilwburner, showing the assembly thereinv of the air control unit ofv` this invention, with certain parts being broken away to more clearly show such assembly;

Fig; 2 is a longitudinalsectional ViewY taken on the line 2-2 of Fig. l;

Fig. 3 is illustrated' similarly to Fig. Zand shows the' air lcontrol unit ina changed position therefor;

Figs. 4 and 5 are transverse sectional views as seen along the lines 4-4 .and 5-5, respectively, in Fig. 3`; and

, Fig. 6 is a diagrammatic; showing of the ame pattern when the air control unit is in its adjusted position shown in Fig. 2.

With reference to the drawings, the air control unit of this invention, designated generally as I0, is shown in Figs. 1 and 2 in assembly relation within the front end of a cylindrical air supply tube |A formingy part of a domestic oil burner. The rear end I t ofthe air supply tube is in suitable uid connection with a source of combustiony air such as a fan or the like. (not shown). Mounted about the front end of the tubev is a hood or skirt l1 provided with a contracted outlet I8 which has its deiining wall or surface I9 tapered or-inclined in -arearward and outward direction.

A fuel nozzle 2|, centrally located within the front of the air supply tube |5 and to the rear of the outlet I8, has a rearwardly extended fuel supply tube 22 adapted. to be connected with a source (not shown) of an air and fuel mixture. The nozzle 2| is equipped with usual electrodes 23 for initiating combustion of the mixture discharged from the nozzle.

The ail` control unit I6 comprises a pair of

tubular members

24 and 26, arranged in a concentric relation. with the tubular member 26 within the vtubular member 24. The outer tubular member 24, from its rear end 21, is formed in succession with a straight cylindrical section 28, an inwardly and forwardly curved section 29, a forwardly and outwardly inclined section 3| and, finally, an inwardly and forwardly inclined front end section 32. It will be noted, for a purpose to appear later, that the front end section 32 and inclined section 3| are reversely inclined so that their junction 33 constitutes a circumferential peak about the outer tubular member 24.

The inner tubular member 261 is constructed in succession from its rear end 34, with a straight relatively short section 36, a forwardly and inwardly tapered or flared section 31, and a forwardly and outwardly tapered section 38. Mounted about the front end of the tapered section 3S is a combination air deilector and air cushioning member 39 of an irregular shape, formed with a rear section 4| mounted about the front end of the tapered section 38 and secured thereto as by welding or the like. The section 4| terminates at its rear end in av laterally projected flange 42. Forwardly from its section 4I, the combination member 39- has a laterally inwardly extended section 46 which terminates in a front end section 43 which is inclined forwardly and inwardly. As best appears in Figs. 2 and 3, the

front end sections

32 and 43 of the

tubular members

24 and 26, respectively, are at an inclination corresponding substantially to the inclination of the side Wall I9 of the outlet4 I8.

An air cushioning membery 44 is arranged within the combination member 39 and is formed with a front end section 46. adapted to. be,v secured to the inner side of the front end'v sec.- tion 43 of the inner tubular member 26, and a straight rearwardly extended section 41 which is in -a spaced relation with the front end of the tapered section 38 of the inner tubular member 26, so that an air pocket or chamber 48, open at its rear end, is formed between the tapered section 3B, the straight section 41 at theV rear end of the air cushioning member 44, and the intermediate section 40 of the combination member 39.

The straight rear section 36, of the inner tubular member 26, is adapted to fit against the inner peripheral surface of the straight section 28 of the outer tubular member 24, and is secured thereto as by welding. The

tubular members

24 and 26 are thus assembled together in xed relative positions, with the straight section 28 of the outer tubular member 24 extending rearwardly beyond the straight section 36 of the inner tubular member 26, and with the

front end sections

32 and 43 terminating in substantially a common vertical plane at the forwardend of the air control unit I0.

The unit ID, comprising the

tubular members

24 and 26, is slidably supported for longitudinal movement within the air supply tube I5 by the provision of means including a series of longitudinally extended ns 5| (Figs. 2 and 4) spaced about the straight section 28 of the outer tubular member 24. By virtue of the fins 5|, the air control unit I8 is supported in a concentrically spaced relation within the air supply tube I5.

Located rearwardly. of the nozzle 2| is a nozzle supporting member 52, of a cylindrical shape, having a rear end 53 of a reduced section (Figs. 2 and 3). The nozzle supply line 22 and holders 54I for the electrodes 23 extend through the nozzle support 52. A series of inclined air deecting vanes 5!) are spaced about the front end of the nozzle support52, which is adapted to be positioned within the straight rear end section 28 of the outer tubular member 24, such that the free or outer sides 56 of the vanes 50 are in slidable contact with the inner peripheral surface of such rear end section. With the nozzle support 52 thus positioned, the nozzle 2l is concentrically located within the inner tubularmember 26.

It is seen, therefore, that the assembly of the air control unit i6 within the air supply tube I5 forms within the air supply tube a central air passage 5l, dened by the inner tubular member 26 and the rear end 28 of the outer tubular member 24, an inner annular air passage 58 formed between the

tubular members

24 and 26, and an outer annular passage 59 formed between the air supply tube l5 and the outer tubular member 24. From a consideration of Figs. 4 and 5, it is seen that the

annular air passages

58 and 59 are concentrically arranged relative to the central air passage 51. Air to the inner annular passage 58 (Figs. 3 and 4) is supplied from the outer annular passage 59 through a series of circumferential holes 6| formed in the straight section 28 of the outer tubular member 24, at a position forwardly of the rear straight section 36 of the inner tubular member 26.

The vanes 50 (Figs. 2 and 4) on the nozzle support 52, provide for the movement of the air iiow in the central passage 51 with a spiral or whirling motion. A straight flow of air takes place in the innerannular passage 53. The air ow in the outer annular passage 59 is substantially straight up to the openings 6i in the outer tubular member 24. A whirling or spiral motion is then imparted to the air by the provision of inclined vanes 63 spaced about the tapered section 3l of the outer tubular member 24. As a result spiral or whirling air is discharged from the central passage 5l and the outer annular passage 59, while a straight now of air is discharged from the inner annular passage 58.

The air flow in the central passage 51 is the main combustio-n air and constitutes about thirty-five per cent of the total air ow in the air supply tube i5. The air flow in the

annular passages

58 and 59 is the supplementary air for combustion and constitutes about siXty-ve per cent of the total air ilow in the air supply tube, which supplementary air is relatively varied between the annular passages 58 and 5S on adjustment of the air control unit l longitudinally of the air supply tube.

Adjustment of the control unit l] is accomplished by means including a rod member 64 having its front end in looped engagement, as indicated at 65 (Figs. 2 and 4), with one of the fins I and which extends rearwardly through the air supply tube l5 such that its rear end (not shown) is accessible from the outside of the rear end of the air supply tube. Thus by merely a push and pull manipulation of the rod 64, the control unit I6 is adjustably moved forwardly and rearwardly within the air supply tube.

As previously explained, the front section 43 of the inner tubular member 26, andthe front section 32 of the outer tubular member 24 are at an inclination corresponding substantially to the inclination of the outlet side Wall I9. A foremost adjusted position of the air control unit Ill is dened by the contact of the front section 32 with the outlet wall I9, which parts are adapted for a substantially seated engagement, as shown in Fig. 3. Thus when the control unit is` in its foremost position, no air is discharged from the outer annular passage 59.

In the adjustment of the air control unit, the fins 5l on the outer tubular member 24 are in slidable contact engagement with the air supply tube I5, while the outer or free sides 56 of the vanes 50, on the nozzle support 52, are in slidable contact with the inner peripheral surface of the straight section 28 of the outer tubular member 24. Stated otherwise, the air control unit, during adjustment, is moved relative to the air supply tube l5, the nozzle 2l and its support 52.

In the operation of the air control unit, assume the unit to be in its position shown in Fig.- 2 at which the outer annular passage 59 is open to the outlet i3. As shown diagrammatically in Fig. 6, the whirling or spiral air from the outer annular passage 59 follows a path indicated b-y 4the spiral at 5l. The whirling air discharged from the central air passage 5l through the outlet i8 follows a path indicated by the spiral at 63. The straight air from the inner annular passage 58 tends to converge forwardly of the outlet i8, as illustrated by the lines` 69.

Without the straight air from the annular passage 58, the spiral air from the central passage 5l and the outer annular passage 59 would tend to spread outwardly frlorn the outlet I3 to in turn reduce the pitch or distance between adjacent flights of the spirals. In other words, the flow of combustion air outwardly from the outlet I8, and in turn the shape and pattern of the resultant burner flame, would result in a relatively short flame having a sharp twist or spiral and a relatively large diameter. Such a. high whirling motion of the combustion air acts to throw the fuel discharged from the nozzle 2l outwardly from the flame without completely burning the fuel.

By virtue of the straight air from the inner annular passage 58, tending to converge at a point forwardly of the outlet lB, the twist or spiral as well as the diameter of the spiral are decreased and the resultant flame is elongated. I'he fuel discharged from the nozzle 2l by virtue of the air from the passage 58 crossing the paths of the spiral air from the passages 5l and 55, is thus more intimately mingled with the combustion air and is retained in suspension within the flame for complete burning. A relative variation in the velocity and volume of the supplementary air discharged from the

annular passages

53 and 59 is thus effective to concurrently vary the angle of twist in the flame, the diameter of the flame and the length of the flame.

A maximum elongation or axial projection of the flame from the outlet IB is obtained on adjustment of the air control unit l5 to its foremost position shown in Fig. 3. At this position a maximum volume and velocity of straight air from the inner annular passage 58 acts only upon the spiral air from `the central passage 5? in a manner such that this spiral air is substantially confined within the straight air discharged from the inner annular passage.

As the air control unit is moved rearwardly from its foremost position shown in Fig, 3, and toward its position shown in Fig. 2, the volume yand velocity of straight air from the inner passage 58 is progressively decreased concurrently with a progressive increase in the volume and velocity of spiral air discharged from the outer annular passage 59. In turn, the flame pattern is progressively shortened along with an increase in its angular twist.

On adjustment of the air control unit I0, therefore, the flame pattern is capable of being varied over a relatively wide range of lengths and corresponding angular twistsso to obtain a desired'. flame having a high burning efficiency. It will be noted further that the volume and velocity of the spiral air discharged from the central air passage. l is substantially constant for all adjusted positions of the control unitL lll, and that the air discharged from` the annular passages 58 and 5S is relatively varied as to velocity and volume with each adjustedv position of the air control unit.

In one embodiment of the invention the flame starts at a position of about one and one-half inches.` away from the outlet I8 and maintains substantiallythe same position for all adjusted positionsof the air control unit l0.

It has been found that the heatfrom the flame is radiatedv to the hood or skirt Il and then conducted to the vanes 63. The heat, thus conducted to the vanos 63 is carried away by the airy flow through the outer annular passage 59. Further, the heat from the flame is continuously carried away from the nozzle 2l by the action of the air flowing through the passages 5'! and 58. .As a-.result the nozzle 2.! is always retained cool so that any clogging of its discharge orifice by fuel caking is substantially eliminated. The flame pattern, and in turnthe burning efciency of the` flame, are thus capable of being maintained substantially constant over prolonged periods of burner operation.

The usual action of a fan or blower, now generally used in domestic oil burners for supplying combustion air, results in the air being moved with a pulsating or wave action. Unless this pulsating action is eliminated or substantially reduced, the flame tends-to pulsate or gallop. The flame pattern is thus irregular and the variation in combustion air supplied to the flame acts to reduce the overall heating efficiency of the flame.

A pulsating or galloping action of the flame is substantially eliminated in the present invention by means including the combination member 39 and the air cushioning member M. The inner tubular member 2li is formed with a series of circumferential openings il (Figs. 2 and 5) which are arranged rearwardly of the lateral flange 42 on the combination member S9. The flange 42 acts to cushion or choke the air passing through the inner annular passage 53 while the openings 'ii provide for an equalizing of the velocity pressures of the air fiowing through the central passage 5l and the inner annular passage 58. The resultant overall effect is the cushioning of the air in the inner annular passage '53 so that it flows evenly from such passage.

The spiral air in the central pal sage 5?, by virtue of the action of centrifugal force, tends to travel about the inner peripheral surface of the inner tubular member 2 ,This air on moving into the cushioning chamber 48 is cushioned or choked so as toeliminate any pulsating action therein prior to its iiow outwardly from the oentral passage 5i. It is seen', therefore, that the air cushioning member ai and the flange 62 are arranged substantially opposite each other on the inner tubular member 2t and, in conjunction with the equalizing action provided by the open ings il, provides for a smooth and even flow of the air through the passages 5l and 5t. A 'cushioning action of the air passing through the outer annular passa-ge 59 is accomplished by the choking action of tie varies in conjunction with the openings ti. Also a choking effect of the air flowing through the central passage 5'? isY obtained. by the nozzle support 52, it being understood `that the air'admitted into the passag. 51: initially flows about the nozzle supportfor `travel about the vanes 50.

As previously mentioned, the junction 33 between the sections 3ly and 32 on the outer tubu-y lar member 24 constitutes a circumferential peak on such member. It is also seen (Figs. 2 and 3) that. theV nozzle is of an irregular shape and formed at its front end with reversely inclined sections S and 8i which form a circumferential peak at their junction 82.

In theA stopping and starting of burner operation, drops of fuel tend to form at the discharge orifice 85 (Fig. l) of the nozzle 2l. In the present invention these drops flow downwardly on the nozzle section to the peak 82, and then fall downwardly by the action of gravity into the in- IierY tubular member 26. From the inner tubular member 26, the fuel drops flow through the openings. l l on to the inclined section 3l of' the outer tubular member 24 and then through an opening 83 formed' in the peak 33 at the lower side of the outer tubular member 243. From the opening 83.the fuel dropsto the lower side ofy the air supply tube l5.- The hood l'.' is formed with an upwardly and rearwardly slanted opening 84', the rear end 8% of which is in substantial alignment'with the lower side of the air supply tube l5; As al result any. fuel drops accumulating on the nozzle 2l follow thevabove described path for passage into the burner fire box. This drainage of the fueldrops from the nozzle eliminates any accumulation of free fuel within the air supply tube.

From al consideration of the above description, it is seen that the invention provides an air control unit for an oil burner which is of a simple and compact construction, and capable 0f adjustment to obtain a flame pattern having a high burning efhciency. Air for combustion is supplied. from three different sources, one of which remains constantA as. to the velocity and volume, and the other two of which are relatively variable as to velocity and volume in direct response to an adjustment of the control unit. The air from such three sources are combined at the outlet. of the air supply tube for a complementary action on each other to produce a controlled air flow for mixing and intermingling with the fuel mixture supplied from the burner nozzle. By controlling the combustion air in accordance with this invention, flames of a substantially white color and with practically no smoke are consistently obtained. Further, carbon dioxide readings from the products of combustion of these flames as high as 14.2% have been obtained. Adjustment of the air control unit is predicated on achieving a white flame, and by virtue of the nozzle 2| being relatively cool at all times, and thus free from clogging, no further adjustment is required over a-prolonged time period of burner operation.

Although the invention has been described and' illustrated with respect to a preferred ernbodiY ment thereof, itis to be understood that it is not to be so limited since changes and modificationsv can be made therein which are within the full in. tended scope of this invention, as dened by the appended claims.

I claim:

1. In an Oil burner, an air supply tube havingl a contractedoutlet at its front end, a fuel nozzle within saidv air supply tube at' the forward end' thereof, a first tubular member movably supported'in a spaced relation within said air supply tube for. adjustable movement longitudinally ofv said air supply tube, a second tubular member arranged in a spaced relation within said first tubular member for movement therewith, means for imparting a spiral motion to the air flowing through said second tubular member, other means for imparting a spiral motion to the air flowing in the space between said air supply tube and said first tubular member, means for admitting a portion of the air from said last mentioned space into the space between said first and second tubular members at all adjusted positions of said first and second tubular members, and means for moving said rst and second tubular members to an adjusted position, with the forward ends of said two tubular members and the outlet of said air supply tube being relatively constructed and arranged such that the first tubular member is movable into a seated engagement with the air supply tube at said outlet to stop the flow of air between said rst tubular member and said air supply tube.

2. In an oil burner, an air supply tube having an outlet at its forward end, a pair of tubular members arranged in a concentric relation within the forward end of said air supply tube so as to form a central air passage and a pair of annular passages about said central passage, a fuel nozzle in said central passage, means for imparting a spiral motion to the air flow in said central passage, other means for imparting a spiral motion to the air flow in the outer one of said annular passages, means for adjustable moving said pair of tubular members as a unit toward and away from said outlet, means for admitting air from said outer annular passages into said inner annular passage at all moved positions of said tubular members, and means for stopping the flow of air through said outer annular passage when said unit is moved to an extreme forwardly moved position therefor.

3. In an oil burner, an air supply tube having a contracted outlet adjacent its forward end, a first tubular member movably supported in a concentrically spaced relation within said air supply tube having its front end portion extended inwardly and forwardly, means for adjustably moving said first tubular member longitudinally of said air supply tube, with a forwardly moved position of said tubular member being defined by the seated engagement of its front end portion with said outlet, a second tubular member arranged in a concentrically spaced fixed relation within said first tubular member having a flared rear portion in contact engagement with the inner peripheral surface of said first tubular member, said rst tubular member having a series of circumferential openings therein located forwardly of the rear end of said second tubular member, a nozzle supporting member arranged in a concentrically spaced relation within said first tubular member at a position rearwardly of said second tubular member, a fuelnozzle within said second tubular member having a fuel supply portion carried in said supporting member, means for imparting a spiral motion to the air flowing in the annular space between said air supply tube and said rst tubular member, other means for imparting a spiral motion to the air flowing through said second tubular member, and means for moving said first and second tubular members as a unit toward and away from said outlet to provide for a relative variation in the ow of air through said annular space and said second tubular member.

4. In an oil burner, an air supply tube having an inwardly and forwardly tapered outlet in its front end, an air control unit movably supported within the front end of said air supply tube for adjustable movement longitudinally of said air supply tube, said air control unit being constructed to form within said air supply tube a central air passage and a pair of annular air passages concentrically arranged about said central air passage, a fuel nozzle within said central air passage, means at the front end of said air control unit adapted to engage the tapered portion of said outlet at a forwardly adjusted position of said air control unit to stop the flow of air through the outer one of said pair of annular passages, means providing for the admission of air from said outer annular passage into the inner annular passage of said pair of air passages at all adjusted positions of said air control unit whereby to relatively vary the volume flow of air through said two passages in response to an adjustment of said control unit, and means for imparting a spiral motion to the air flowing through said central passage and the outer one of said annular passages.

5. In an oil burner, an air supply tube having a contracted outlet at its front end, a nozzle within said air supply tube adjacent the front end thereof, a pair of tubular members arranged in a concentrically spaced relation over their forward sections and with the rear section of the inner tubular member being of a flared construction and secured to the inner peripheral surface of the outer tubular member, with the outer tubular member having a series of circumferential openings therein located forwardly of the rear end of said inner tubular member, means supporting said outer tubular member in a concentrically spaced relation within the front end of said air tube so that said nozzle is within said inner tubular member, with the front ends of said tubular members being inclined inwardly and forwardly at positions ahead of said nozzle, and said inner tubular member being formed with a series of circumferential openings rearwardly of the inclined front end portion thereof, oppositely arranged air cushioning means on said inner tubular member arranged forwardly of the openings therein, and means for imparting a spiral motion to the air owing through said inner tubular member, and in the space between said air supply tube and said outer tubular member.

CECIL W. SMITH.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,396,086 Anthony Nov. 8, 1921 1,679,830 Lang Aug. 7, 1928 2,120,387 Bargeboer June 14, 1938 2,127,866 Haase Aug. 23, 1938 2,215,941 Smoot Sept. 24, 1940 2,220,603 Hirtz et al Nov. 5, 1940 2,256,080 Eweryd et al. Sept. 16, 1941 2,262,525 De Lancey Nov. 11, 1941 2,325,444 Vroom et al July 27, 1943 2,368,178 Turpin Jan. \30, 1945 FOREIGN PATENTS Number Country Date 655,055 Germany Oct. 12, 1938