US2540866A - Draft-responsive controls for liquid fuel burners - Google Patents

Description

Feb. 6, 1951 R. w. DE LANCEY 2,540,866-

DRAFT-RESPONSIVE CONTROL FOR LIQUID FUEL BURNERS Filed Aug. 31, 1948 INVENTOR Pup m Dan/wear ZWM Patented Feb. 6, 1951 UNITED' PATENT OFFICE DRHFT RESPONSIVE CONTROLS FOR LIQUID FUEL BURNERS Ralph De; Lancey, Meriden, 001111., assignor to The Miller Company Meriden, Conn., a corporationof Connecticut Application August 31, 1948, Serial No. 46,971

The present invention; relates: toaburner: controls for'liquid fuel. burners; and.is.- more particularly directed toward controls for! intermittently operated gravity fed, liquid fuel burners under the control of a remote switch, such. as a room thermostat or an immersion thermostat, with a fuel valve adapted: to beiopened and closed by such thermostat; and employing forced draft produced by a motor driven blowerwhi'ch operates continuously over long: periods where pilot ignition is employed, or which operates ihtermittently where electric or: gas ignition is employed.

In such burners there is a. possibility that fuel supply may continue to the burner eventhough the forced draft producing apparatus has not been brought into operation or for some reason has failed to function.

The present inventioncontemplates a system including a normally open safety switch closeable by the moving stream of air employed for forced draft, this switch being in series with the fuel valve controls. According" to the present invention; it is also-contemplated thatthe safety switch may be shunted bya normally closed switch under the control of a time responsive element which opens the shunting switch at the proper time.

The employ-merit of thepresent invention assures the presence of forced draft whenever fuel is being fed to:the burner, except possibly during the starting period: when forced draftis not desired;

Otherand further objects will appear as the description proceeds;

The accompanying'drawingsshow, for purposes of illustrating the present invention; an embodiment in which the invention maytake' form; it being understood" that the drawings are illustrative of the invention rather than limiting the same.

Inthe accompanying drawings:

Figure 1 is a side elevationa'l view illustrating an oil burner'installation with controls;

Figure 2'is an enlarged vertical sectional View through the safetyswitch showing it -open;

Figure 3 is a still further enlarged sectional view showingthe switchclosed; and

Figure 4 is an inverted plan view of the safety switch.

In the drawings, a pot type burneris illustrated generally at It], fuel supply-pipeat H, and the forced draft duct at I2. Forceddraft is secured by blower'motor [3 operating a fan 14.

A combined constant level valve and metering valve of usualconstruction. isindicated at. l5. Through a pipe [6. and. fittings 11' it supplies fuel to the supply. pipe U 'Ihevalvastructurel5 also includesa metering valve indicated at 8; Thisiis under the control of a bi-metal element IS with electric heater 20.

Low voltage control current is obtained through a transformer T connected by a wire 2 l. The other side of the heater 2!) is connected by a wire 22 with a fixed contact 23 of the safety switch S The other side of the safety switch is connected by a wire 2 E. with the normally open contact 25 of the control thermostat 25. This thermostat is connected with the transformer by wire 26'. A thermal heater 2'? is connected between wire 2! and wire it. It is normally cold, but is heated whenever the thermostat 251 calls for burner operation. The lei-metal element 28 is connected with wire 2-3 and through a switch 29 and wire 3% with the wire 22, thereby provid ing circuit in shunt with the safety switch S.

The safety switch S is a unitary structure having an insulating mounting plate so adapted to be placed over an opening 39' in the top wall of the duct I2 so that it is readily available for inspection and adjustment.- It carries a binding post 3| connected with wire 22, a binding post 32 connected with wire 25, and an adjusting screw 33. The post 32 carries a conducting spring 34 which extends under the adjusting screw 33. This spring carries a U-shaped yoke to which is pivoted at at a rocker arm 3'! carrying a vane 38. The other end of the arm 31 carries pins 39 in which is pivoted movable contact carrying arm 43. The movable contact is indicated at 4| in the form of a rounded button opposite the fixed contact 23. The arm id is connected with pivot 36 by coiled spring if. The adjustment of the screw 33 determines the position of the vane at which the switch opens and closes.

The motor 13 operating the blower Id may be a continuously operated motor where pilot ignition is employed or may be an intermittently operated motor where electric ignition is employed. When the motor i3is not operating, the safety switch shifts to the open position, indicated in Figure 2, on account of the weight of the vane, which biases the fever 3'! in a counterclockwise direction. This moves the pivot 39 high enough for the over-the'-center spring s2 to snap the movable contact arm down against a stop l3. The circuit of the safety switch is open in the absence of forced draft.

Should the thermostat 25 call" for heat, a circuit will'be establishedthrough the wire 21, heater 20', wire 3%, switch 29; bi metal" 28; to the thermostat 26 and wire 26. This will start heating thebi-metal [9 which thereafter opens the metering valve l8. Current will also flow through the heater 21' andstart heating the bi-metal 28. The fan motor 13 is then started either manually orthrough suitable timing controls set into operation by the thermostat ZS-so that ablast of air passes intotheburner. This blastof air reacts against the. vane 38; lifts it. from the positionuof Figure 2 to the position of Figure 3. This car ries the pivot 39 below the spring 42 and causes the switch to snap closed. 1 The closing of the safety switch S completes a second circuit for the heater 29 of the metering valve, so that the metering valve continues to be held open even though the bi-metal 29 has opened the contact 29. Such opening takes place after a predetermined time which normally is sufficient for the blower to have been brought into operation. If

for any reason the blower has not been brought into operation, the fuel valve heater 29 will in due time have been disconnected by the switch 29 and the flow of fuel stopped.

If for any reason the forced draft is not available because of power failure, motor failure or fan failure, the switchS will remain open so that it is impossible to flood the burner or supply fuel when there is inadequate draft.

During the time that the blower is in operation, the vane 38 will move back and forth slightly as indicated by the arrows at the left of Figure 3, and this will cause a back and forth horizontal movement of the contact 9! over the contact 23 as indicated by the short arrows near these elements. This serves to dislodge dirt particles which might collect and impair the low voltage circuit and to keep the contacts clean.

Since it is obvious that the invention may be embodied in other forms and constructions within the scope of the claims, I wish it to be understood that the particular form shown is but one of these forms, and various modifications and changes being possible, I do not otherwise limit myself in any way with respect thereto.

What is claimed is:

i. In combination, a gravity fed, forced draft, liquid fuel burner, a metering valve for controlling flow of fuel to the burner and biased toward closed position, a fuel flow control circuit including a low voltage transformer, a condition responsive switch, an operator for the metering valve and a draft responsive switch all in series, a forced draft blower, a duct connecting the blower to the burner, a lever extending lengthwise of the duct and pivotally mounted intermediate its ends, a vane carried by the end of the lever remote from the blower, the vane being biased by gravity toward a position to obstruct air flow and movable upwardly by the air stream to a variable, less obstructing position, a ductcarried, downwardly facing, fixed contact forming one part of the draft responsive switch, a movable contact interconnected with the lever on the end opposite the vane and cooperable with the fixed contact to form the other part of the draft responsive switch, the interconnections between the lever and movable contact including a horizontal pivot which moves down and up as the vane moves up and down and an over-the center spring connecting the free end of the movable contact and the pivot for the lever and acting, when above said pivot, to urge the movable contact upwardly, the movable contact moving across the face of the fixed contact when the vane shifts position in its upper range of movement so as to wipe dirt off the contacts and maintain the low voltage circuit.

2.-'Ihe combination of claim 1, wherein the vane, the switch contacts and the snap spring are supported on an insulating member which covers an opening in the duct.

3. The combination of claim 1, having a normally closed switch in shunt with the vane controlled switch, and a thermally responsive means for opening the. normally closed switch after a predetermined time whereby the metering valve may be initially opened irrespective of blower operation.

4. The combination of claim 1, having means for vertically shifting the lever pivot to adjust the sensitivity of the switch.

5. In combination, a gravity fed liquid fuel burner, a fuel line leading to the burner, an air duct for supplying air for combustion, a blower connected to the air duct to provide forced draft through the same to the burner, a metering valve for supplying fuel to the fuel line, a bimetallic operator for the metering valve, a heater for the bimetallicoperator, a low voltage source for the heater and two switches in series with the heater, onebeing a condition responsive, thermally operated switch, the other a forced draft responsive switch mounted in the air duct and including a lever pivoted on a horizontal axis in the duct and carrying at one end a vane which swings down under the influence of gravity and is lifted by the air stream from the blower, and at the other end a pivoted movable contact, an overthe-center spring interconnecting the lever and movable contact, and a ,fixed contact against which the spring holds the movable contact when the vane is raised and over the surface of which it moves the movablecontact with movement of the vane so long as it is high enough to keep the spring axis above the pivot of the movable contact, so that contact surfaces of the second switch are kept clean over long periods of blower operation. I

6. In combination, a gravity fed, forced draft, liquid fuel burner having a forced draft blower and air duct which delivers a continuous blast of air characterized by small irregularities in velocity of the air' stream, a vane movably mounted in the duct, the vane being biased in the absence of the air blast to a position to obstruct flow of air to the burner and movable by the air stream to less obstructing positions which varywith the velocity of the air stream, a fixed contact in the duct, a movable, vane-operated contact in the duct, a snap spring which snaps the movable contact away from the fixed contact when the air stream is discontinued and holds the contacts in engagement when the blower is in operation, there being connections between the vane and the movable contact whereby the movement of the vane due to varying velocity of the air stream shifts the movable contact back and forth over the surface of the fixed contact 'while the spring maintains the engagement of REFERENCES CITED The followingre'ferences are of record in the file of this patent:

I UNITED STATES PATENTS Number Name Date Re. 21,950w Valiean Nov. 18, 1941 2,197,746 irMatthes Apr. 6, 1940 2,237,041

Schreuder Apr..1, 1941 2,251,055 Howardet a1. July 29, 1941

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