US2539789A - Air and fuel control for burners - Google Patents

Description

D. H. MGCORKLE 2,539,789

AIR AND FUEL CONTROL FOR BURNERS Jan. 30, 1951 Filed May 26, 1947 INVENTOR DONALD h. MC coma:

his A T TORNE Y Patented Jan. 30, 1951 2,539,789 AIR. AND FUEL, CoN'rRoL FOR nuances Donald; McCorkle, Berkeley, Galifi, assignor to D. H. 'McCorkle 00., Berkeley, Calif., a corporation of California Application May 26, 1947, Serial No. 750,609

1 Claim. 1'

The invention relates to a means of regulating the volume of air delivered to a vaporizing burner; and more particularly to a means for automatically regulating the amount of air delivered to the burner when operating on high fire, and means for regulating a smaller volume of air when the burner is operating on low fire.

One of the objects of this invention is to provide a simple, reliable and inexpensive means of automatically controlling the amount of air admitted to a burner blower. Another object is to provide automatically operating means for independently adjusting the amount of air admitted to the blower on high fire and on low fire. A further object is to provide a thermostatically controlled means for automatically reducing the speed of the motor on low fire and increasing the speed on high fire and controlling the volume of air admitted to the blower on high speed and low speed by utilizing the difference in static pressure developed by the blower on high speed and low speed.

The invention possesses other objects, some of which with the foregoing will be set forth at length in the following description wherein is explained that form of the invention which has been selected for illustration in the drawings accompanying and forming a part of this specification. In said drawings, one form of the invention is shown, but itis to be understood that it is not limited to that form, since the invention as set forth in the claim may be embodied in a plurality of forms.

It is common practice to use a blower in conjunction with a vaporizing oil burner, and to provide a thermostatic means arranged so that when the thermostat is satisfied, the fire will be reduced to a very low or pilot flame. When the thermostat calls for heat, the fire is automatically increased to full capacity. It will readily be seen that. in this type of burner, the regulation of the draft is highly important. If, when the burner isoperating on high fire, too much air is admitted to the burner, the stack losseswill be proportionately high. On. the other hand, if. too little air is admitted, improper combustion results; and the heat exchange surfaces are soon coated with carbon, thus reducing the efiiciency of the appliance. On the pilot flame, with the admission of too much air, there is a serious danger of extinguishing the small flame. If insuflicient air is supplied to the burner during the pilot fire stage, the burner will soot and carbonize, thus reducing its efiiciency on high fire. It is common practice to carry a pilot fire in excess of actual needs to prevent extinguishment. this often results in delivering heat to the rooms when such heat might be objectionable; My invention is calculated to obviate these undesirable features.

It is general practice to provide a smallcentrifugal b-0wer connected directly to a fractional horsepower shaded pole motor. It is important to note that in this type of blower the static pressure varies with the speed of the rotor, and that in a shaded pole motor; particularly of" the size used on vaporizing burners, the speed may be reduced by inserting resistance in series in the feed line. However, when the speed is reduced below approximately 40% of normal, it becomes erratic and undependable. In my invention I vary the speed of the motor, but do not reduce such speed below a controllable point.

Referring to the attached drawings: Figurel is a side view of a burner installation embodying my invention. Figure 2 is a front view, partly in section and showing the air control means. The electric circuits and mechanism for controlling the circuits and fuel valve are shown in diagram in Figure 3.

A typical burner installation in which myair 'control devices are embodied comprises a vaporizing burner 2, supplied with fuel through pipe 3. in which the conventional control valve 4 is interposed. This valve generally has a built-in adjustable by-pass so that when the valve is in the 0ffp0siti0n a small amount of fuel is fed through the supply line to the burner to maintain a pilot fiame. A conventional form of blower it forces air through the duct l to the burner; and is driven by the shaded pole motor 3, directly connected thereto. The motor is supplied by the feed lines 9 and iii, in one side ll of which a switch [2 and a resistance iii are inserted. When the switch is closed the resistance is shunted out and the motor runs at its rated speed. When the switch is open, the resistance cuts the voltage down so that the motor runs at a calcu ated. lower speed consistent with thenexisting conditions of fuel supply.

Fixed against the inlet side of the fan housing is the casing l6, having in the side thereof, a swinging shutter l1 suitably pivoted on an anti-frictional bearing 18. To the upper end of the shutter and on the outside thereof is fixed a lever arm I9, the upper end of which is threaded to mount a threaded counterweight 2|.

The proportion and arrangement of parts is such that the counterweight may be adjusted to place the center of gravity of the shutter structure on the inner side of its pivotal support. Also fixed on the shutter at its upper end but on the inside is a stop arm 22 arranged to engage the end of an adjusting screw 23, threaded into the top wall 24 of the casing it. By turning the adjusting screw the inward swing of the shutter may be limited to regulate the amount of air which can pass the shutter into the casing. Swing of the shutter in the other direction is limited by the adjusting screw 26 threaded into the upwardly turned edge 21 of the casing. Thus both maximum and minimum passages into the casing are provided; and these are automatically controlled by the static pressure determined by the fan speed, such fan speed of course corresponding to the motor speed.

Means are provided for varying the motor speed and also the amount of fuel supplied to the burner, in response to temperature changes in the space heated by the apparatus of which the burner Z is a part.

A room thermostat 3|, Figure 3 is connected to the secondary of a standard transformer 32, supplied by the house current over lines 33. The figure indicates the position of the component parts when the thermostat is satisfied. Assuming the room temperature to drop, the thermostat will close the contact 34 completing the low voltage circuit 36 which includes a suitable resistor heater 31. Heat radiated from the resistor heats a bimetal strip 38, rigidly secured to a fixed support 39.

As the temperature of the bimetallic strip rises, it flexes upwardly; raising the adjusting screw 4| from the end of the lever arm 42 which is pivotally mounted on the pin 43, and is urged downward by spring 44. The lever is connected to the valve stem 45 of the fuel control valve 4, either directly as shown or by simple linkage; and is also operatively connected to the switch i2 by which the high voltage circuit through the motor is closed. As the adjusting screw 4! rises, the spring loaded end of the arm moves downward. In so doing, the connecting device opens the valve 4 to admit the required amount .of fuel to maintain the burner on high fire. At the same time the switch 12' closes the motor circuit, shunting out the fixed resistor I3, and :allowing the motor 8 to develop its full rated R. P. M.

When the room thermostat is satisfied, the contact 34 is opened, the heat resistor 3'1 cools, .the bimetal strip 38 returns to the position shown in the figure, and the rocker arm 42 moves to partially close the valve to pilot fire, and open the switch l2, so that the fixed resistor I3 is once more in series with the motor, thus reducing its speed to the desired R. P. M. It is important to note that the resistor is so selected as to reduce the speed of the motor, buthot to such a point as to result in erratic and undependable speed. When the motor is thus operating at low speed, the static pressure created by the blower is correspondingly reduced; and the shut- ..ter- I1. rests against the adjusting screw 26 which static pressure.

is set at a point to supply the proper amount of air to the burner on pilot fire. The counterweight 2| is then set at a point where the shutter will bear lightly against the end of the adjusting screw.

On the high fire phase, the thermostat 3| closes the circuit, and as explained, the switch 12 shorts out the fixed resistor; and the motor operates at full R. P. M. This increase in motor speed results in an increase of static pressure. As the shutter I! has been nearly balanced for the low fire stage, the added static pressure will cause the shutter to swing inwardly until the arm 22 engages the lower end of the adjusting screw 23, which has been set to admit the proper amount of air at high fire.

It will be seen from the above that the amount of air admitted on high fire can be adjusted independently of the amount of air admitted on low fire; and that the amount of air admitted on .low fire 15 subject to adequate control independently of the control of the motor speed.

My invention permits the control of this air from complete shut-off to the full amount that would be admitted to the blower at the lower It is also to be noted that the volume of air admitted to the blower on full static pressure can be regulated from full capacity of the blower to a point equal to the low fire setting.

I claim:

An air and fuel control device for a fuel burner, comprising a fan for delivering air to the burner and having an air intake passage, a movable gate for varying the size of said intake passage, supporting said gate for movement by pressure of air flowing through said passage, a valve for controlling the flow of fuel to said burner, means responsive to changes in temperature of a space to be heated for varying the speed of the fan from a low speed to a high speed and vice versa and the setting of the valve whereby the How cl fuelincreases and decrease respectively with iii-- REFERENCES orrsn The following references are of record in the file of this patent:

UNITED STATES PATENTS Num er Name Date 1,655,246 Schermully Jan. 3, 1928 1,741,529 Marion Dec. 31, 1929 2,187,045 McCorkle Jan. 16, 1940 2,251,055 Howard et a1. July 29, 1941 2,351,878 Russell June 20, 1944 2,370,891

Thornquist Mar. 6, 1945

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