US2681693A - Pressure-atomizing oil burner having shaded-pole electric motor drive and oil pump unloading means - Google Patents

Description

June 22, 1954 J. A. LOGAN PRESSURE-ATOMIZING OIL BURNER HAVING SHADED-POLE ELECTRIC MOT Filed Jan. 50, 1952 OR DRIVE AND OIL PUMP UNLOADING MEANS 4 Shegts-She'et 1 INVENTOR -70JPff A. 4305A ATTORNEYS June 22, 1954 2,681,693

J. A. LOGAN PRESSURE-ATOMIZING OIL BURNER HAVING SHADED-POLE ELECTRIC MOTOR DRIVE AND OIL PUMP UNLOADING MEANS Filed Jan. 30, 1952 4 Sheets-Sheet 2 INVENTOR JbsEPH AJZoamv BY ATTORNEYS J1me 1954 J. A. LOGAN ,681,693

PRESSURE-ATOMIZING OIL BURNER HAVING SHADED-lfOLE ELECTRIC MOTOR DRIVE AND on. PUMP UNLOADING MEANS Filed Jan. 30, 1952 4 Sheets-Sheet 3 70 INVEN'TOR \IbJEPH A. Loan/v BY AME/9 ATTORNEYS June 22, 1954 J. A. LOG AN PRESSURE-ATOMIZING OIL BURNER HAVING SHADED-POLE ELECTRIC MOTOR DRIVE AND OIL PUMP UNLOADING MEANS Filed Jan. 30, 1952 TE NTHS OF SECONDS F|C5.Il

IIIII IIIIIIIIIIIIIIIIIIIIIII 6 I I52 20 25 TENTHS OF SECONDS FIG.I3

4 Sheets-Sheet 4 F I (3. IO

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- I ma 3 w I I I I I I I I I I I I I I l I I I I I I I I I I I I I I O 5 9 I5 TENTHS OF SECONDS TENTHS OF SECONDS F I 6. I4 /M' w //l' w /09 M IIIIIIIIIIIIIIIIIIIIIIIII||IIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 0 IO 20 4O 5O 58 0 IO 20 3O 4O 48 TENTHS OF SECONDS TENTHS 0F SECONDS INVENTOR JOSEPH A. LOGAN W BY ATTORNEYS Patented June 22, 1954 PRESSURE-ATOMIZING OIL BURNER HAV- ING SHADED-POLE ELECTRIC MOTOR DRIVE AND OIL PUMP UNLOADING MEANS Joseph A. Logan, Hadley, Mass, assignor to Gilbert & Barker Manufacturing Company, West Springfield, Mass., a corporation of Massachusetts Application January 30, 1952, Serial No. 269,076

1 Claim. 1

This invention relates to improvements in oil burners of the high-oi1-pressure-atomizing type, such as are designed for house-heating service and are subjected, in service, to frequent starts and stops under automatic thermostat control.

In burners of this type, it is desirable, for the reasons fully set forth in my prior Patent No. 1,985,934, granted January 1, 1935, to postpone the emission of oil from the nozzle of the burner until the fan has had time enough to establish a sufficient rate of air flow past the nozzle to produce good combustion and also to stop the emission of oil from the nozzle, as soon as possible after the power to the motor is out off and before the air flow ceases, allowing the air flow to continue after oil flow has stopped for the purpose of scavenging the air tube of the burner. The arrangement described was designed to enable the rate of air flow, during normal running periods of the burner, to be reduced to a value such as to result in high efiiciency of combustion without causing puffs of smoke or soot to be produced during the starting and stopping intervals of operation of the burner.

The means of the prior patent tends to produce substantially the same amount of time delay on starting as on stopping. That is, the time between the closing of the switch to the burner motor and the building up of oil pressure, following almost instantaneously after engagement of the clutch, is about the same as the time between 1 the opening of this switch and the closing of the cutofi valve by drop in oil pressure, following almost instantaneously after disengagement of the clutch. Assuming, for example, that the clutch engages, when "10% of full speed is reached,

and disengages, when the speed decreases to 70% of full speed, the motor, without the load of the pump, will accelerate its own rotor and that of the fan to 70% of full speed in about the same time required for the rotors of the motor, fan and pump, moving by their momentum, to decelcrate from full speed to 79% of full speed. Actually, the sooner the oil cut-ofi valve closes, after opening of the switch to the burner motor, the better are the results obtained. An ideal condition would be to close the cut-off valve simultaneously with the opening of the motor switch. Also, another desirable condition is to get a longer time delay on starting. These two conditions are incompatible and cannot be obtained in the burner of the prior patent solely by means of the speed-responsive clutch, or other pump unloading means. For example, if the mass of the motor rotor, which operates by its momentum, after the switch to the motor has been opened, to

drive the pump rotor, is reduced in an attempt to secure increased deceleration and thus a quicker disengagement of the clutch and a resulting quicker closure of the oil cut-oil valve, then quicker acceleration is had on starting which is the reverse of what is needed.

This invention has for its object the provision in an oil burner, having a means for relieving the motor of the load of the oil pump at speeds below a predetermined value, of an improved driving means for the air-supply fan and oil-supply pump, characterized by less mass to secure more rapid deceleration and quicker closing of the oil cut-oh valve, and by such poor starting torque that a longer time is needed to accelerate the lessened mass. With such an arrangement, the time delay on starting may be double that of the time delay on stopping. As compared to the means of the prior patent, the time delay on starting may be nearly doubled and the time delay on stopping reduced at least one third.

The invention will be disclosed with'reference to one illustrative example of it in the accompanying drawings, in which:

Fig. 1 is a side elevational view of an oil burner embodying the invention;

Fig. 2 is a sectional plan view taken on the line 2-2 of Fig. 1;

Fig. 3 is a sectional elevational view thereof;

Fig. 4 is a cross sectional View taken on the line 44 of Fig. 1;

Figs. 5 and 6 are sectional views taken on the lines 55 and tt, respectively, of Fig. 4;

Fig. 7 is a sectional view of the pressure-regu lating valve;

Fig. 8 is a sectional view of another form of pump-unloading means;

Figs. 9 and 10 are graphs showing the time which elapses between the closing of the motor switch and the admission of oil to the burner nozzle, as effected by the means of the prior patent alone and by such means when modified by the means of this invention, respectively;

Figs. 11 and 12 are graphs showing the time elapsed between the opening of the switch to the burner motor and the cutting off of oil flow to the burner nozzle as effected by the means of the prior patent alone and by such means when modified by the means of this invention, respectively; and

Figs. 13 and 14 are graphs respectively showing the time required for the motor of the prior patent and the motor of this invention to come to a stop after opening of the switch to the burner motor.

Referring to these drawings; the burner includes a body casting i (Fig. 1), suitably supported, as by the floor plate 2 and standard 3. This body, as shown in Fig. 3, provides in its upper portion a fan housing 4, the outlet 5 of which opensinto the front end of a horizontallydisposed cylindrical conduit 6, provided .in the lower portion of the body. Mounted to rotate in this housing l is a fan 1. The rear end of con duit 6 is closed by a coverfig,w ich is easily.li movable. Fixed to casingfl is ;a :tube .9,'Whi0h is located coaxially, and formsa .prolongationof the conduit 6, the rear end of the tube communieating with the front end 'D'f the conduit. The front end of tube 9 is adaptedto be inserted through the wall of the combustion chamber of a heating apparatus and to be in open communication with such chamber. Tube 9-qhasfixedqto its front end a suitable air director IE) and, inside the tube, near the front end thereof, is-a turbulator, consisting of, a circular series of angullarly-spacedspira1 vanes lrl fixed to an annular ring l2, which has sliding engagementwith theiinterior peripheral wall of tube ,9. ,An oil- ,atomizing nozzle 13 of the 'high-oil pressureatomizing type is supported centrally of tube '9 near its front and outlet end. This nozzle will have a-discharge rate of from one to three gallons per hour when supplied with oil at pressures of .theorder of 100 p. s. i. It will be seen that fan 1 will force air, whichis drawn into its housing 4, in a manner to be later described, through the outlet 5 into conduit 5 and thence forwardly through such conduit and through tube 9, past the spiral vanes H, which whirl the air stream,

and then to air director it}, which directs the rwhirling air stream into the spray of atomized oil emitted from thenozzle 13. The mixture of air and oil, thus produced, is ignited by anelec- ;trical spark, produced betweena pair of electrodesM.

.Thenozzle +3 and electrodes M are supported in any suitable manner. For-example, a pair of rods 3.5 (Fig. .2) are fixed at one end to ring 12, at diametrically opposite points thereon, and extend 'rearwardly :through tube -9 into conduit .6 and terminate with ends -l 6,'which ,are bent :filltwfdldly at right angles and inserted in holes formed in the peripheral wall of the conduit. :liixed :to and spanning these rods, is a cross piece 1 7, through which 'extendsthe oil-conducting tubular support is for nozzle 13. "The cross :;piece H also has fixed-therein two insulating tubes [9, in which the described electrodes 1. 3 are supported. The nozzle support It, and insulators is are adjustable in cross piece 11, as indicated. .By removing cover Bythe ends it of rods l5 may be pulled out of their retaining holes and then .the rods may be drawn rearwardly of conduit 6 to remove the nozzle i3, electrodes M and air-whirling vanes I i, all in assembled rela- -tion.

The electrodes M (Fig. 3) are connected by wires to the high tension terminals 2! of a suitable ignition transformer 22 (Fig. 2), which is fixed to and located outside body I with its high tension terminals 2i and insulators '23 pro- =jecting through an opening in the wall of conduit-fi into the interior thereof.

' -A flexible copper tub-e 2:; (Fig. 3) is connected at one end to the oil-conducting nozzle support '18' and extends rearwardly through tube 9 and conduit 5-, emergingtherefrom through a passage in cover 8, as indicated in Fig. l, for con' nection to the oil-supply means, to be described. The oil-supply means comprises a suitable able cut-off and pressure-regulating valves. shown, this pump and these valves are combined 4 pump, which has a high discharge rate and is capable of supplying oil to nozzle I3 at a rate at least six times the discharge rate of the nozzle and at a pressure of at least p. s. i. and suitinto a single unit 25 (Figs. 1 and 4), which may, ;for example, be constructed as disclosed in Wahl- ,mark Patent No. 2,309,683, A suction pipe 26 (Fig. .1), connected at one end to the inlet of the pump, is adapted for connection at its other end to a suitable supply of liquid fuel. The other .end of the-described tube 24 (Fig, l) is connected to the outlet ofthis oil-supply unit. This unit (Fig-'4) is bolted to the outer end face of a bracket 27, which is disposed in spaced parallel 'relationwith'one-end wall 28 of the fan housing and is integrally connected thereto by two sidearms 29.

The pump unit is supported with its driving shaft '39 in substantially coaxial relation with the fan 1. Shaft Si! is fixed to the driven ele :ment13l of a speed-responsive clutch, the driv- 1in element 32 of which is connected by a flex- ,ible coupling33 to the hub of fan I. This clutch :is designed to relieve th driving motor (to be later described) of the load of the oil pump until "themotor an the fan have acquired considerable'speed, say for example around?!) per cent :of full speed. One example of 'a clutch'suitable V for the purpose is shown in Fig. 6. The driven element 3! is in the form of .a drum .and the driving element .32 ,isin the form of a face plate,

to which are fixed in diametrically opposedrela- 'tion a pair of fulcrum pins 34. Pivotallymounted at one end, one on each pin 34, are weight arms .35 having arcuate surfaces adapted, when the arms are thrown outwardly b centrifugal force, to engage :and grip the internal periphery cfithe .drum 3| and drive the same and the oil pump. The weight garmsare drawninwardly out .of-contact with the drum-by springs 36. Each spring connects "the fulcrum pin '34 of one weight arm 35 to a pin 31 on the other Weight'arm. Initially, the weight arms are held by their springs :out of contactwith the-drum 31, being moved into such contact only after the motor and fan have reached a predetermined high speed, which should be as nearly as'feasible to full speed, usu

.ally about I0 of full speed.

The driving elements for the oil pump (Fig. 4) extend out of the fan housing through a large hole 38 which forms the air inlet to fan 1. Cooperating with this inlet is a shutter .39, which 'ismovable to adjustthe effective area of the fan dental-rotation of the screw. "A casing it encases' the shutter, screw and clutch and is provided with air inlet slots 43 of adequate aggregate area. The shutter is prevented from rotating by a rod Ml, with'which it is slidably engaged, this rod jbeing fixed at its outer-end inbracket 2.1.

The provisions for regulation of oil pressure are shown in Fig.7. The passages :55 and 46 respectively connect the outlet and inlet sides of the oil pump to a cylindrical bore 4'! at lonsitudinally spaced locations. Fixed in this bore between such locations is a sleeve 48. The ends of bore 41' are closed by plugs 49 and each having its inner end spaced from the adjacent end of sleeve 48, thereby forming chambers 5i and 52, respectively communicating with outlet and inlet passages 45 and 46. Slidably mounted in sleeve 48 is a hollow piston 53, having fixed to its outer closed end a valve 54, adapted to engage a seat 55 on closure plug 49 and close off communication between chamber 5! and an outlet passage 56 in plug 49, to which passage the described oil tube 24 is connected. A spring 5? acts between the closed end of piston 53 and a seat 58 to urge valve 5A into engagement with its seat 55, whereby outflow of oil to tube 24 and nozzle i3 is prevented. Seat 58 is adjustable by means of a screw 59, threaded into closure plug 50 and normally covered and concealed by a cap nut 65, which is threaded on a hollow hub on plug 50. The valve 54 will be opened by pressure of the oil on the outer end face of piston 53, when such pressure reaches a predetermined minimum value, which may for example be 95 p. s. i. When the pressure of the pumped oil reaches a somewhat higher predetermined pressure, say for example, 100 p. s. i., some oil wi l be by-passed back to the suction side of the pump in order to maintain the pressure of the oil supplied to nozzle l3 substantially constant. A hole 6| in the peripheral wall of piston 53 will move into communication with a circumferential groove 62 in the interior peripheral wall of sleeve 48, when the oil pressure rises to the second predetermined value, and some oil from chamber 5| can then flow through a passage 63 in sleeve t8 into groove 62 and thence through hole 6| to the interior of piston 53, which constantly communicates with chamber 52 and thus with the inlet side of the oil pump.

The burner structure, as thus far described, is substantially the same as that of the prior patent, above identified. l

An alternative arrangement for unloading the pump is shown diagrammatically in Fig. 8. As there indicated, the oil pump shaft 36 is directly connected by a flexible coupling 64 to the hub of fan 1, whereby it starts and stops coincidentally therewith. The pump unit, including the pump and pressure regulating means, are the same as heretofore described, whereby the outlet to pipe 24 and to oil-atomizing nozzle i3 is closed by valve 54 until the relatively high predetermined P pressure has been built up. However, the pump is initially unloaded by a small by-pass 55, formed in a disk 55, fixed to a diaphragm Bl, which is clamped along its marginal edge by and between two cup-shaped casing sections 58 and 559. Conduits ill and H respectively connect the inlet and outlet sides of the oil pump to the casings 68 and 69. A valve 12, carried on the inner end of an adjusting screw it, which is threaded into casing 68, lies in the path of disk 56. A spring 74 tends to move diaphragm 6'! to carry disk it away from valve l2. Initially, the pumped liquid will by-pass through hole 65 and this by-passing will continue until enough pressure is created in the casing 69 to move the diaphragm 81 to carry disk 65 into abutment with valve T2, whereby the by-pass will be closed. This occurs onlyafter the fan has acquired considerable speed, which may be about the same as that attained when the above described clutch engages. Thus, the pump,

6 although started with fan 1,15 unloaded and can be started with little driving torque.

This invention provides as a means for driving the air-supply fan and the oil-supply pump, a single-phase induction motor of the shadedpole type. This particular motor (shown full size in Fig. 5 and half-size in Fig. 4) is adapted for operation from a 110 volt, cycle, alternating-current supply and is rated at horsepower and 1750 R. P. M., being the largest motor of this type now available in the market. This motor includes a stator, made up of a stack of punched laminations 15, suitably clamped together and mounted between two end bells 16 and Ti, which carry the bearings 18 for the shaft 19 of the rotor 88 of the motor. A mounting plate 3! is suitably fixed to end bell 17. As shown, a plurality of bolts 32 pass through the end bell i laminations #5, end bell Ti and mounting plate 8! and these parts are held together by nuts 83 on the ends of the bolts. The mounting plate 8i fits in and closes an opening 84 in an end wall of the fan housing l which opening is large enough to permit insertion of a fan I into the housing. The plate 8! is held to this end wall by a plurality of screws 85. The fan is fixed to shaft 19 and then inserted through hole 84 into the housing and then the plate 8! is fastened in place. The rotor is of the squirrel cage type consisting of a stack of iron laminations 8t, carrying a circular series of copper rods 87, the ends of which are riveted to copper rings 88, one on each end of the rotor. The latter has a series of ventilating holes ea therethrough and carries a ventilating fan 38, which draws in air through holes 95 in end bell is and through the holes in the rotor and then forces it outwardly through holes 52 in end bell H. In Fig. 5, the stator is shown as having four inwardly-extending radial poles 93 spaced apart, each pole carrying a main winding 94. The shading coils are shown at 95 as endless loops of copper, each loop encircling a small portion 96 of each pole. These shading coils function in the Well known manner to displace a portion of the magnetic flux flowing through each pole out of phase with the remainder of the flux and thus to create a small starting torque to turn the rotor in the direction illustrated.

Motors of this type have never before been utilized, so far as I am aware, to drive oil burners of the pressure-atomizing type. Such motors are usually employed only for driving small fans, clocks, program shafts and similar very light loads. They could not be used for driving an oil pump which develops pressures, of the order herein described, unless provisions were made for relieving the motor from the load of the pump at starting. The largest motor of this type, now made, does not have sufficient starting torque to start the pump described, if it is coupled to the motor shaft at starting and not unloaded. There are other types of single-phase induction motors, which afford much. greater starting torque, such as the split-phase type. the capacitor-start type and the repulsion-start type, and which would normally be chosen for the work in hand, if selected from considerations of emcient driving. The shaded-pole type of induction motor was not, however, chosen from these considerations but because it enables a materially improved efiect in the oil burner operation during the starting and stopping intervals to be obtained. The most ineflicient type of single-phase induction motor now known was purposely chosen be- '7 cause of the very fact that it has the poorest and a very low starting torque, whereby a rotor having a mass much less than that of the conventional motor will be accelerated more slowly. Thus, by intially uncoupling the pump from the fan or initially unloading the pump, which is desiredin any case to delay the supply of oil. to the atomizing-nozzle, one can use this type of motor and convert one of its disadvantages, so far as efficient driving is concerned, into an advantage so far as oil burner operation is concerned, be-

cause the slow acceleration prolongs the interval between the starting of the air-supply fan and the emission of oil from the nozzle. A substantial increase in the time delay of the oil feed is secured'over what can be secured by the arrangement of the prior patent. And this advantage "is secured by the use of a smaller and cheaper motor so that a better result in time delay is had on starting at substantially less cost.

This improvement will be clear from a comparison of the graphs shown in Figs. 9 and 10, which indicate fuel pressure at the noz re plotted against time in tenths of a second. The same burner, which had the clutch shown in Fig. 4, was used in each case and the only difference wasjin the motor used to drive the fan and pump. The Fig. 9 graphs were made with a burner, having the conventional split-phase induction motor, which is 110 volts, 60 cycles, rated at ,4; horsepower and 1750 R. P. M. Ihe graphs of is were made with the same burner but driven by ,a shaded-pole motor, having the characteristics above described. These graphs are tracings made from the screen of an oscilloscope. apparatus used to produce the graphs on the oscilloscope included a strain gauge, subjected to fuelprcssure adjacent the atomizing nozzle, and the resistance wire of this gauge was included in a bridge circuit, the input terniinals'oi whicwere connected to a source of direct current. Pressure stretched "the resistance wire of the strain gauge, increasing its resistance and upsetting the balance of the bridge circuit, thereby producing a signal in the output circuit of the bridge. This D. C. signal was chopped up by a chopper or vibrator, operating at 100 cycles a second, and the chopped-up signal was amplified and the amplified signal transmitted to the oscilloscope to be further amplified and then produced on the screen of the oscilloscope. The lines its and NH really represent the horizontal components of the chopped-up wave. The space between these two lines would be filled with nearly vertical lines representing the vertical components of the waves, which rise and fall very V steeply and are very closely spaced (about .01"

apart). These waves occur so rapidly that they show only faintlyon the oscilloscope screen and they have been omitted from the drawing. The vertical distance between the lines itil'and lei represents pressure in pounds per square inch. The line Hi2 indicates zero pressure. In Fig. '9, the motor switch closed at zero time and zero pressure continued until the clutch engaged and drove the oil pump. Then the pressure built up very rapidly, almost instantaneously, as indicated by the line H93, until the pressure (around S5 pfs. i.), necessary to open the cutoff valve and allow oil to flow to the nozzle, was established.

' This occurred in .5 second. In Fig. 10, parts of the graphs, which correspond with those of Fig. 9, have beengiven the samereference numeral with the addition of a prime. Fig. shows how the time delay is nearly doubled, being .9 second.

The

' mass and thus less inertia than the rotor of the conventional motor and, with equal torque would be accelerated more rapidly but the extremely poor starting torque of the shaded-pole motor acting on the rotor of less mass, produced a greater time delay. It should be noted that the fluctuation of the lines Hill and till are of no significance here. These are due to a peculiarity of the measuring instrument and. occur following the building up and also after the letting down of pressure. These lines soon straighten out and become horizontal but, whether curved or horizontal, the pairs of lines its and it! or H35 and till are parallel and the vertical distance between them is constant, representing constant pressure and in this case p. s. i.

When the switch to the burner motor is opened, the rotors of the motor, fan and pump turn for awhile by momentum. After a certain decrease in speed, the clutch will disconnect the oil pump, which will thereupon come to rest very rapidly. the rotors of the motor and tan continuing to turn at gradually decreasing speed until they finally come to rest. A's soon as the pump is uncoupled from the motor, the oil pressure drops rapidly, almost instantaneously to zero. Imme diately following the uncoupling of the pump, the oil pressure will drop enough to close the cut-off valve and prevent further flow of fuel to the atomizing nozzle. A much improved cut-off is obtained with the shaded pole motor drive,.as will be clear from a comparison or Figs. ll and 12, which were produced with the same burner but driven by the conventional split-phase motor and the described shaded-pole motor, respective- 1y. In each of these figures, the switch to the pump motor was opened at zero time. full pressure, of say 100 p. s. i., represented by the vertical distance between the lines its and 5&5, was had for about half a second. Then the pressure dropped slightly until the cut-off valve closed at .Gsecond, after which the pressure dropped to zero, almost instantaneously, as rep-' presented by the line Hit. The line lill' represents zero pressure and becomes horizontal in about 2 seconds. In Fig. 12, parts of the graph, which correspond with parts of the graph of Fig. 11, have been given the same reference numerals with the addition of a prime. The much improved cut-ofi of .4 second is obtained. Figs. 13 and 14 show the time required for the rotors of the motor and fan to come to rest, in the respective cases of the described split-phase motor and the shaded-pole motor drive. The lines m8 and its of Fig. 13, and the corresponding lines ass and tilt of Fig. 14, represent the extremes of a 60 cycle A. C. signal. The lines Hil and llil' represent zero speed. The motor switch was continueolto turn longer than the motor rotor of less mass and less momentum. The result is a re duction in time of cut-01f to the very low value of l second, about one third'less than that oh" tained with the structure of the prior patent alone.

In Fig. 11,

The shaded pole type of induction motor is devoid of the governors, switches and brushes that are necessary with induction motors, having the other known and above-named provisions for starting. The elimination of switches, such as governor-controlled switches, eliminates a source of frequent trouble. If these switches fail to open, when they should, the starting winding will not be cut out, as it should be, and will soon burn out. Hence, an overload switch must be provided to take care of this contingency. Should the motor stall from any cause, and it might because of breakage of clutch springs for example, the overload switch is a necessity with singlephase induction motors of any other type. However, the shaded-pole motor, when stalled, consumes no more current than when it is running and no overload switch needs to be provided. While the ventilating fan stops and the heat from the motor will be dissipated more slowly, resulting in a heat rise, this rise occurs so slowly that no damage will be done in the short interval, such as 90 seconds for example, which is required by the usual combustion-safety switch of the burner to open the circuit of the motor after failure of combustion.

Thus, the burner operation is rendered more nearly fool proof by using a type of single-phase induction motor that eliminates the switches, which are a source of trouble, and the expense thereof. A simpler and cheaper motor results in more fool proof operation and improves the operation of the burner, so far as prevention of soot is concerned by prolonging the interval during acceleration when the oil supply is out oh and shortening the interval during deceleration when the oil supply is on.

The invention utilizes an undersize motor for driving the oversize high-pressure oil pump of an oil burner. The motor isn't even capable of starting the oil pump from a rest condition. However, the undersized motor has enough less mass in its rotor to efiect the desired quick deceleration to the speed at which the pump is unloaded and the cut-off valve closes to stop the flow of oil to the nozzle. Ordinarily, the lower mass of the rotor would also mean increased acceleration of the rotor of the motor and this would be incompatible with the desired time delay of oil feed on starting of the burner. The

adverse effect of low mass at starting is oifset by the notoriously poor starting torque of a shadedpole motor and, actually, the time delay on starting has been almost doubled over what could be secured with the type of motor heretofore used for the purpose.

This application is a continuation-in-part of 10 my now abandoned application serial No. 230,171, filed June 6, 1951.

What is claimed is:

In an oil burner for house-heating service, a nozzle of the high-oil-pressure-atomizing type rated to discharge atomized oil at from one to three gallons an hour when supplied with oil at a pressure of the order of pounds per square inch, an oil conduit connected at one end to said nozzle, a positively-acting pump connected to the other end of said conduit and capable of pumping oil at a rate at least six times the discharge rate of said nozzle and at a pressure of at least 100 pounds per square inch, a cut-off valve in said conduit responsive to the pressure of the pumped oil and opening only when the oil attains a pressure slightly less than that for which the nozzle is rated, a by-pass valve in said conduit responsive to the pressure of the pumped oil and opening only when the oil attains the rated pressure, a conduit connecting the outlet of the by-pass valve to the inlet side of the pump, a fan for supplying air at relatively low pressure, an air conduit connected to the outlet of the fan for conducting air from the fan to said nozzle to mix with the atomized oil, a single-phase induction motor of the shaded-pole type for driving the fan and pump and having low starting torque insufficient to start the pump and relatively small mass in its moving parts, an unloading device for relieving the motor of the load of the pump to enable the motor to start and until the motor has acquired a predetermined high speed, the characteristically low torque of said motor resulting in slow acceleration of its moving parts notwithstanding the low mass thereof and a relatively long interval for the fan to establish air flow in the air conduit before the pump is started and before the latter can build up sufficient oil pressure for atomized oil to be emitted from said nozzle; the pump being driven by the relatively low momentum of the moving parts of the motor, fan, and pump after the power to the motor is out oh and said moving parts having selected inertias such as to produce deceleration to the speed at which the unloading device unloads the pump and efiects a closure of the cut-oil valve in less than half the time of the aforesaid interval.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,985,934 Logan Jan. 1, 1935 2,485,207 Logan Oct. 18, 1949

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