US2702591A - dickey - Google Patents

Description

Feb. 22, 1955 P. s. DICKEY 2,702,

I CONTROL SYSTEM Filed Aug. 5, 1950 4 Shee'ts-Sheet 1 2| [ATMOSPHERE BURNERS SUPPLY RETURN INVENTOR.

PAUL S. DICKEY A ORNEY Feb. 22, 1955 P. s. DICKEY 2,702,591

CONTROL SYSTEM Filed Aug. 5, 1950 4 Sheets-Sheet 2 DEMAND DEMAND OIL PRESSURE PSI m D O I (D 500 1 500 S (v o 9% 4 LU D AQ 00 E 300 Q 300 E b fl g 200 200 t I ou RETURNED O 100 d L I00 o g/ O LBS. OF on. BuRNED/ BURNER HOUR IN V PAUL S. DICKEY FIG. 5 qgwmd/wn Feb. 22, 1955 s, DICKEY 2,702,591

CONTROL SYSTEM Filed Aug. 5, 1950 4 Sheds-Sheet s INVENTOR. PAUL S. DICKEY KWz/M Feb. 22, 1955 P. s. DICKEY 2,702,591

CONTROL SYSTEM Filed Aug. 5, 1950 4 Sheets-Sheet '4 DEMAND RETURN CONSTANT n c HEAD p p SUPPLY LIZO |2s INVENTOR.

PAUL s. DICKEY FIG. 7 BY United States Patent CONTROL SYSTEM Paul S. Dickey, East Cleveland, Ohio, assignor to Bailey Meter Company, a corporation of Delaware Application August 5, 1950, Serial No. 177,810

6 Claims. (Cl. 158-363) My invention relates to fuel burning systems and apparatus and particularly to the control of wide-range returnflow mechanical fuel oil burner atomizers.

It has been found desirable, in practice, to operate fuel burning systems over a wide range by utilizing a relatively small number of large capacity liquid fuel burners over the entire range rather than by selectively varying the number of burners in operation in accordance with the fuel demand. In addition, it has been found practically advantageous to provide multiple burner installations which can be operated under automatic control throughout a wide capacity range. These considerations have led to the use of wide-range return-flow liquid fuel burner atomizers of difierent constructions and with diiferent methods of and apparatus or systems for control thereof.

These atomizers and related fuel supply and control systems have, however, certain disadvantages. For example, it has been found necessary, with some types of installations, to manually or otherwise change the position of the atomizer relative to the burner throat opening in order to avoid carbon deposition upon the throat and impeller, with consequent loss in combustion efficiency, at the lower rates of operation. Other disadvantages, such as an execessive delivery of hot oil from the return passage of the atomizer to the storage tank, have involved the danger of vapor flashing in the supply pump. It has also been found that, when the recirculated oil is introduced at variable pressure to the oil inlet of the pump supplying the atomizer, mechanical difiiculties in attaining proper sealing of the pump have been experienced.

Wide-range high capacity return-flow atomizers are known and may have tangential passages and whirl chamber sizes selected for ellicient operation at maximum capacity. When such an atomizer is in operation with a reduced fuel input to the burner, impingement of atomized fuel particles from the outer portion of the cone upon the burner opening throat will usually occur at the lowermost portion of the fuel inlet range unless the atomizer is axially advanced toward the furnace from its maximum rate position. This occurs because the return-flow atomizer has a return fiow passage leading from its whirl chamber, whereby a portion of the fuel delivered into the whirl chamber is drawn off, leaving the remaining portion of the fuel entering through the tangential passages to be discharged through the orifice. Thus, with this type of atomizer the angular velocity component of the orifice discharge, which is a function of the flow through the tangential passages, does not decrease as rapidly with reduction in atomizer delivery as does the axial velocity component which is a function of the delivery rate. If the liquid fuel is supplied to the outer ends of the tangential passages at constant pressure and the rate of delivery through the atomizing orifice is controlled by regulation by the return-flow draw-off, the modification in whirl chamber pressure will be such that, at the lowermost portion of the atomizer range, the pressure of the whirl chamber will be substantially reduced, while the velocity through the tangential passages and the angular velocity will remain without eifective change. This lower range of velocities results in a greater spray cone angle and impingement as before mentioned.

The main object of my present invention is the provision of apparatus for and a method of operating a widerange return-flow mechanical liquid fuel atomizer whereby the angle of spray or atomization may be controlled with variable rates of fuel atomization so that carbon 2,702,591 Patented Feb. 22, 1955 deposition may be avoided without modifying the axial position of the atomizer relative to the furnace or burner throat, while at the same time providing an arrangement of piping, and pumping and control apparatus, effective to regulate the quantity of oil recirculated in the system to the end that undue heat input into the oil storage will be avoided, and the pump handling hot oil will receive oil at a pressure sufiiciently uniform that seal difliculties due to pressure variation are eliminated.

In the present invention, the flow of the liquid fuel through the tangential passages is effectively regulated along with a regulation of the return-flow draw-01f from the whirl chamber so that, for reduction in atomizer delivery rate, a reduction in the differential in pressure between the inlet and discharge ends of the tangential passages is effected, while the pressure in the whirl chamber is controlled in correlation with the differential to the end that the angular velocity of delivery is correspondingly decreased to the extent that the spray cone angle will not be disadvantageously increased at the lowermost fuel delivery rate.

To effect this result and to provide an atomizer of good efficiency for a wide range of fuel burning capacity, a ratio of tangential passage and orifice areas is selected such that, at the selected fuel supply pressure for maximum delivery, all of the fuel delivered through the tangential passages is delivered through the orifice, with the return-flow outlet shut off.

For operation below maximum delivery rate, both the pressure of the fuel delivered to the outer ends of the supply passages and the pressure in the whirl chamber are reduced, and with progressive reduction of delivery, the reduction is carried still further. The rate of reduction of the supply pressure is related to the rate of reduction of whirl chamber pressure, so that the difierential between these pressures will be of a variable degree, being maximum at the high fuel inlet rate and progressively smaller towards the low fuel rates.

The invention method of regulation effects not only an efiicient atomization of fuel over a wide range of fuel input rates without a disadvantageous spread of the spray cone at the lowermost load range, but also It is advantageous in that it minimizes the amount of oil which is delivered through the return-flow draw-01f, as the whirl chamber pressure is at a lower pressure for a given fuel delivery than if the control were solely by regulation of the return-flow draw-off. This is an advantage in reducing the heat carried back to the oil reservoir by the return-flow fuel. The pump which draws oil from the reservoir will thus not be required to handle oil of excessive temperature with the consequent hazard, to the continuous delivery, of vapor flashing.

A principal feature of my present invention is to prov1de a system and apparatus maintaining a differential between the oil supply pressure and the oil return pressure to a mechanical atomizer, which differential is varied 1n predetermined relation with rating or demand.

An object is to provide an oil fuel supply system and method of operation for wide-range return-flow mechanical fuel burner atomizers.

Another object is to provide such a system and method capable of varying the ratio of supply pressure to return pressure 1n accordance with variations in the oil supply pressure or rate.

These and further objects will be apparent from the description of the drawing.

In the drawings:

F1g. 1 is a diagrammatic showing of a wide-range return-flow mechanical atomizer fuel burner system embodying the invention.

F g. 2 shows a modification of Fig. 1.

F g. 3 illustrates a modification of Fig. 1.

F g. 4 illustrates a modification of Fig. 2.

Fig. 5 is a graph of operating conditions illustrative of the invention.

Fig. 6 is a schematic showing of a vapor generator fired by wide-range return-flow oil burners to which the invention has been applied.

Fig. 7 is a diagrammatic showing of another arrange ment of atomizer control.

Referring now in particular to Fig. 1, my invention is illustrated as applied to wide-range return-flow mechanical oil burner atomizers generally indicated at 10. The particular construction of the atomizer head and burner box assembly may be of the well known spill type. In Fig. 1 I show three burner assemblies representative of a single or plurality of burners which may be used for heating any space such as a furnace.

Liquid fuel, preferably oil under a substantial pressure, is delivered to the burners 10 through a supply pipe 11. In return-flow atomizer constructions, a Portion of the fuel is by-passed and returned to the reservoir or fuel pump inlet to vary the capacity of the burner. In Fig. 1 such return oil enters the header 12.

The oil is delivered under pressure through a pipe 13 in which is located a capacity control valve 14 which may be positioned responsive to some indication of demand such as steam pressure, steam flow rate, temperature or similar demand factor. The outlet of the valve 14 is connected by a conduit 15 to a constant speed motor driven oil pump 16 elevating the pressure of the oil in supplying it to the header 11.

Spanning the pump 16 is a conduit 17 which joins the supply header 11 with the return header 12 through a by-pass valve 18 arranged to automatically control the rate of fiow of oil through the conduit 17.

The valve 18 has a spring 19 normally urging the valve to closed position. Also effective for positioning the movable valve members is a large diaphragm 20 and a small diaphragm 21. The principal purpose of this valve construction is to maintain a differential in pressure across the atomizers 10, between the supply header 11 and return header 12, varying in desired relation with rate of operation or rate of demand upon the system. For instance, the diaphragm area ratio and spring tension are designed and adjusted to maintain the following oil pressures or similar values.

Burner Burner Dif- Supply ferential Pressure Pressure P. s. i. P. s. i.

the burner side of the capacity valve 14. This is then an indication of rating or load and the upper side of the small diaphragm is open to the atmosphere.

The arrangement thus provides a constant differential pressure valve wherein the spring 19 and the diaphragm 20 cooperate to so position the throttling elements of the valve 18 that a constant differential pressure is maintained in the conduit 17 from one side of the valve 18 to the other. This effect is biased by the diaphragm 21, subjected to some indication of load or demand, and thus I maintain across the valve 18 a diiferential pressure varying in desired manner with rating or demand upon the system.

In general the capacity valve 14 controls the value of the return pressure in the conduit 12 while the by-pass valve 18 controls the pressure of the supply in the conduit 11. The operation of the two valves 14, 18 results in a discharge of oil from the burners 10 to satisfy the over-all demand on the system and at the same time to give a velocity discharge condition which as originally pointed out herein obviates the prior difficulties of carbon deposition, excessive return of heated oil, etc. In the arrangement of Fig. l the return oil is recirculated by the pump 16 and there is no discharge of return 011 to any storage tank or other pumping equipment than the pump 16. l

The over-all operation of Fig. 1 is that as rating mcreases, valve 14 opens, increasing the pressure in the headers 12, 15 and 17, and thereby effective upon the under-side of diaphragm 21, thus tending to close down valve 18 and increase the supply header pressure. As rating continues to increase the valve 18 closes until no oil is by-passed around the pump 16 through the conduit 17 and less and less oil is returned to the header 12 as the flow through the pipe 15, from the valve 14, increases through opening the valve 14.

In Fig. 2 I illustrate a modification of Fig. 1 wherein the pump 16 is driven by a controllable speed turbine 25 with its speed under the control of a valve 18A located in a steam supply line 26 for the turbine. The internal elements of valve 18A are reversed from those in the valve 18 to the end that pressure in the line 28, representative of return oil pressure in the conduit 12, tends to open the valve 18A. Supply header pressure acting through the pipe 27 upon the top of the diaphragm 20, while return header pressure acting through the pipe 28 acts upon the under-side of the diaphragm 20. Thus the differential pressure between the headers 11 and 12 is continually acting downward against the spring 19 in a direction tending to close the valve 18A while the return oil pressure acting upon the diaphragm 21 is continually effective in a direction tending to open the valve 18A. Opening the valve 18A increases the flow of steam to the turbine 25 with an increased operation of the pump 16 tending to build up the pressure in the supply header 11. The over-all result is that the differential in pressure between the supply and return headers increases with rating in predetermined manner.

Figs. 3 and 4 are modifications of Figs. 1 and 2 differing thereform in that the capacity valve 14 has been omitted and the demand factor other than return header pressure is applied directly to the diaphragm 21. This simplification is possible under certain arrangements and conditions of operation where the oil supplied through the conduit 13 does not need control by a capacity valve 14. The demand factor effective upon the diaphragm 21 may be some variable in the operation of the system as a whole, indicative of the amount of oil to be burned from the burners 10. Reference may now be had to Fig. 5 which illustrates a number of graphs in the operation of mechanical wide-range return-flow atomizers. For maximum or full rating operation of the atomizer, the by-pass valve 18 (Fig. l) is closed while the capacity valve 4 is open to thereby supply the requisite amount of oil and at the desired differential in pressure between that of the supply header 11 and that of the return header 12. Under such arrangement the atomizers will operate as a straight mechanical atomizer without any return oil flow or at least a very minor amount will enter the header 15 from the header 12. Under this condition a predetermined supply pressure and pressure differential for that supply pressure will exist. This may be as illustpr atecsl at the high rating end of curves A, B and C of For elfective Wide range operation down to a minimum capacity, a predetermined reduction of pressure differential between the supply header and the whirl chamber is attained as shown by curve C of Fig. 5 through manipulation of valves 14 and 18.

In Fig. 6 is shown a vapor generator which may be of the divided furnace type having a group of atomizing burners 10 supplied from a conduit 11 and returning oil to the conduit 12. The conduit 11 has fuel, such as oil, supplied thereto at a constant pressure, and it as well as the return conduit 12 are adapted to be connected in communication with the various burners by means forming no part of the present invention. Air is supplied from a fan or blower 30 through a passage 31 to the furnace for supporting combustion of fuel discharged from the burners 10, and a boiler 32 is heated by the combustion of the fuel for generating steam which is delivered through a conduit 33 to a point of use. The pressure of the steam discharged from the boiler may be employed in this case as an indication of demand on the furnace, a drop in pressure indicating an increase in demand, and an increase in pressure indicating a decrease in demand. it will be appreciated that the furnace may be employed for heating something other than the boiler. and that the demand may be indicated by changes in temperature of some object or material being heated. Connected in the fuel supply conduit 11 and the return conduit 12, as shown in Fig. l, are valves 35 and 36 which are controlled by pressure actuated 5. diaphragms 37 and 38 respectively. The valve 35 is so designed that it is moved towards its open position as the pressure supplied to the diaphragm 37 is increased and the valve 36 is designed to close on an increase in the pressure supplied to the diaphragm 38.

The fan or blower 30 is driven by a power unit 40, such as a turbine, and a conduit 41 delivers operating fluid to the power unit under the control of a valve 42 which is adapted to be moved towards its open position by a diaphragm 43 when the pressure supplied thereto is increased. Arranged in the air passage 31 is a damper 44 connected by a link 45 to a control mechanism 46 which operates when pressure supplied thereto is increased to move the damper toward its open position.

For controlling the supply of fuel and air to the burners 10, in response to changes in demand on the furnace, there are provided means operating in response to changes in steam discharge pressure for regulating the pressure supplied to the diaphragms 37, 38, 43 and the control mechanism 46. This means comprises a pressure responsive device 50, such as a Bourdon tube, subjected to the steam pressure in the conduit 33 through a pipe 51. A pilot valve 52 is connected to the Bourdon tube and controls the supply of pressure fluid to a chamber 53 of a relay 54 for moving a member 55 against the action of a spring 56 to position a pivoted beam 57 which regulates fluid supply and discharge valves 58 and 59. The positions of these valves determines the pressure in a chamber 60 which communicates through a restricted connection 61 with an opposing chamber 62. When the pressure supplied to the chamber 53 balances the tension of the spring 56, the beam 57 assumes a position to close the supply and discharge valves, and the pressure in the chamber 60 is held at the value existing when the balance was reached. An increase in the pressure supplied to the chamber 53 results in an operation of the beam 57 to open the supply valve 58 and eifect a continuing increase in the pressure in the chamber 60. If the pressure in the chamber 53 drops below the value balancing the spring 56, the discharge valve 59 is open to effect a continuing decrease in the pressure in the chamber 60. The relay 54 is disclosed in the Gorrie Patent Re. 21,804 and need not be described further herein.

The pilot valve 52 is connected so as to increase the pressure in the chamber 53 when the Bourdon tube operates on a drop in the steam pressure in the conduit 33. An increase in the steam pressure causes the Bourdon tube to position the pilot valve so as to reduce the pressure in the chamber 53. This pilot valve is like that described in the Johnson Patent 2,054,464.

The pressure in the chamber 60 of the relay 54 is delivered through conduits 65 and 66 to the diaphragm 43, and is delivered through a branch conduit 67 to the control mechanism 46 for the damper 44. The pressure is also delivered from the conduit 65 to a chamber 68 in a relay 69 which operates to supply a pressure to a conduit 70 communicating with a branch conduit 71 leading to the diaphragm 38, and communicating with another branch conduit 72 leading to a chamber 73 in a relay 74 which controls the flow of pressure fluid through a conduit 75 to the diaphragm 37. An operation of the relay 54 to increase the pressure supplied to the conduit 65 results in an opening of the valve 42 to increase the speed of the turbine for driving the blower 30 to supply more air to the passage 31, and operation of the control mechanism 46 to open the damper 44, and an operation of the relay 69 to increase the pressure in the conduit 70 for effecting a closing movement of the valve 36 in the fuel return line 12. The pressure increase in the conduit 70 is also delivered through the conduit 72 to the relay 74 and causes the latter to operate so as to increase the pressure in the conduit 75 for opening the valve 35 in the fuel supply line.

As the valve 36 is closed and the valve 35 is opened, the pressures at the burner sides of these valves are increased so that more oil is forced through the burners to satisfy the demand on the furnace. It is desirable that the valves 35 and 36 be operated so that the differential in pressure between the supply and discharge sides of the burners is varied in desirable manner with rating or demand. For maintaining the desired interrelation there is provided a relay 80 having bellows 81 and 82 subjected through conduits 83 and 84 to the pressures at the supply and discharge sides, respectively, of the burners. The bellows operate against spring loaded ful- 'crumed levers 85 and 86 respectively. An adjustable roller fulcrum 87 for the levers 85, 86 compares the pressure effects of the bellows 81, 82 and the system controls the position of a linkage 88 arranged to position the movable element of the pilot valve 89, for establishing in a conduit 90 a fluid pressure representative of the desired differential in pressure between the supply oil and the return oil, or departure therefrom.

The size and location of the bellows 81, 82, as well as the length and pivoting of the linkage 85, 86, 88, is determined by the expected range in pressures of the supply oil and of the return oil. The spring adjustments 91 and 92, as well as the movable fulcrum 87, may be manually manipulated during operation to establish the desired difierential in pressure which may be arranged to have desired functional relation with rating or demand on the unit as a whole.

The pressure result of the relay 80, applied within the pipe 90, is effective within a chamber 93 of the relay 74 to aid the pressure in the chamber 73 in operating the relay 74 to determine the pressure supplied to the diaphragm 37.

If the pressure at the discharge side of the burners should increase for some reason, more than the pressure desirably increases at the supply side, the bellows 82 would operate to lower the movable element of the pilot 89 to increase the pressure supplied to the chamber 93 of relay 74. The relay 74 would be operated by this increased pressure to increase the pressure supplied through the conduit 75 to the diaphragm 37 for opening the valve 35 and increasing the pressure at the supply side of the burners. If the pressure at the discharge side does not increase as much as it did on the supply side, then the bellows 82 would operate the linkage 88 to reduce the pressure supplied to the chamber 93 and the relay 74 would operate to reduce the pressure on the diaphragm 37 tending to close the valve 35 so as to reduce the pressure at the supply side of the burners. It will be appreciated that the bellows 81, 82 may be positioned, as shown, to maintain any desired equal or functional relation in differential in pressure between that of the oil in the supply conduit 11 and that of the oil in the return conduit 12. Thus I may match the curves A, B, C of Fig. 5 or other desired plotted conditions.

In the installation from which the operating characteristics of Fig. 5 were obtained, the desired relation of supply pressure to whirl chamber pressure, as determined by the relative indications of pressure gages in the supply conduit 11 and return conduit 12, is obtained in the fuel burning range from 4500 lb. per hour down to approximately 2500 lb. per hour by the throttling of valves 35 and 36. However, the latter valve is opened to such a slight degree that the amount of return oil flow is so small that it is not possible to determine its rate by the customary orifice meter and so the curve D is not extended to show return oil flow for the higher output range.

However, below a 2500 lb. per hour rate, and in order to avoid undue reduction in the velocity of oil introduction through the tangential slots into the whirl chamber while reducing the rate of delivery to the furnace, control of the pressure differential is further effected by simultaneous manipulation of valves 35 and 36, through progressive throttling of the supply by control valve 35, while progressively manipulating valve 36 to permit a progressive increase in return oil flow. The rate of return oil flow for the lower range of burner output, below 2500 lb. per hour, is shown by curve D of Fig. 5. This correlated regulation of valves 35 and 36 results in a relationship as shown by curve A for supply pressure and curve B for the return or relative whirl chamber pressure. Curve C depicts the relative differential between these two pressures.

Thus the invention provides a method of straight mechanical atomizer operation at maximum burner output, and return flow operation from the maximum rate down to the minimum. As before stated, the rate of return oil fiow at a burner rate above 2000 lb. per hour, for example, is negligible and the rate of return oil flow at the minimum burner rate does not rise to 'a troublesome quantity, as will be clear from curve D. On the other hand, the reduced pressure diiferential, occurring through the lower rate burner output range, avoids a wide spray angle from the atomizer.

The amount of oil returned to the conduit 12 is substantially less at any atomizer delivery rate than with any other prior art methods of return fiow atomizer control. This is graphically demonstrated in Fig. wherein the curves A and B represent the supply pressure and return pressure, respectively, of an actual operating installation using the same atomizer controlled to maintain a substantially constant differential pressure (curve C) from 2300 lb. of oil per burner per hour to 250 lb. of oil per burner per hour, the supply pressure at the top rating being 1000 p. s. i. and the return pressure 870 p. s. i. It will be noted that the recirculated or return oil rate, shown by curve D, is much greater, at all ratings, than that for the invention system, as shown by curve D.

For obtaining a high operating efficiency of the furnace, there is provided control means for additionally regulating the valves 35 and 36 in the fuel line so as to maintain a predetermined ratio between the total air flow and the total fuel supplied to the burners. This control means includes a relay 100 having diaphragms 101 and 102 acting in opposition upon a lever system 103 for positioning the movable element of a pilot valve 104. Arranged in the fuel conduits 11 and 12 are devices 105 and 106 for measuring the flow rate of fuel oil through the conduits. Each of these devices may be like that disclosed in my Patent No. 2,459,689 and need not be described herein as it forms no part of the present invention. A device 107 is connected to the devices 105, 106 and operates to supply to a conduit 108 a pressure which is proportional to the difference between the measurements of fuel fiow. It will be appreciated then that the pressure in the conduit 108 is directly proportional to the total fuel consumption at the burners 10. Pressure in the conduit 108 is subjected on the diaphragm 101 so as to urge the linkage 103 in a counterclockwise direction. Arranged in the air passage 31 is an orifice 109 and pressures at opposite sides of the orifice are subjected through pipes 110, 111 on a device 112 which operates in response to differential pressures for supplying a pressure to a conduit 113 directly proportional to the total air flow to the furnace. The pressure in the conduit 113 is delivered to the diaphragm 102 for opposing the action of the diaphragm 101.

The pilot valve 104 is positioned by the linkage 103 for controlling the pressure in a conduit 115 to a chamber 116 of the relay 69. The pressure supplied to the chamber 116 aids the pressure in the chamber 68 for determining the pressure supplied through the conduit 70 to the diaphragm 38 and to the chamber 73 of the relay 74. As long as the ratio of the total fuel supply to the total air supply remains constant, the pressure supplied from the relay 100 to the chamber 116 will be held at some predetermined value and the supply of fuel and air to the furnace will be varied only with changes in steam pressure. If the supply of fuel becomes too great for the amount of air supply the pressures delivered to the diaphragms 101 and 102 will effect a positioning of the pilot valve 104 to decrease the pressure supplied to the chamber 116 of the relay 69. This relay then operates to decrease the pressure supplied through the conduit 70 so as to effect a closing of the valve 35 and an opening of the valve 36 for reducing the total fuel discharged from the burners until the ratio of total fuel to total air reaches the value at which the relay 100 is balanced. If the quantity of fuel discharged to the burners is insufiicient relative to the air supply the relay 100 is unbalanced in the opposite direction to increase the pressure delivered to the relay 69 and effect an increase in the pressure supplied to the diaphragms 37 and 38. The valve 35 is then opened and the valve 36 is closed to increase the discharge of fuel from the burners.

It will be seen that the control system of Fig. 6 operates to automatically control the supply of fuel and air to the burners responsive to a demand factor such as steam pressure developed by the vapor generator which is heated by the burners. If the rate of total fuel supply is not in desired proportion to the rate of total air supply the ratio relay 100 effects a modification of the steam pressure control in the positioning of the fuel control valves 35 and 36. Each and all of the atomizers 10 are subjected to a differential pressure between the pressure of the oil supply and the pressure of the oil return which follows a predetermined relation with rating. If the instantaneous pressure differential between the oil supply and oil return is not in accordance with the adjustment of the relay then the control of the supply oil valve 35, which is basically from steam pressure as a demand index and further responsive to total air flow-total fuel flow relation, is further modified by departure of fuel oil differential pressure from the desired value for that operating level.

In Fig. 7 I show a modification including a demand or capacity valve 121 in the return header 12 from a plurality of wide-range return-flow mechanical atomizers 10. The valve 121 is continuously positioned in accordance with some index of demand upon the system, such as flow, pressure, temperature or the like. Oil is supplied to the supply header 11 by a constant head pump feeding a control valve 122 through a conduit 123. The control valve 122 is of a special construction performing the function of maintaining a differential in pressure between the headers 11, 12 varying in desired relation with rating or demand. This valve is shown in somewhat diagrammatic fashion as having a lower control plug 125 and an upper plug 126. The two plugs are carried by a stem 127 in turn positioned by a dual-area piston 128 which is acted upon by a spring 129.

The pump inlet pressure at 123 may be approximately constant at 1000 p. s. i. giving a high drop across the valve at low rating, decreasing as the rating increases. It is necessary to use pistons having two different effective areas, the smaller being connected to the burner inlet pressure, and the larger to the return pressure, while a differential is set up in accordance with the difference in areas of the two plugs in the valve cage and the loading of the compression spring 129.

The lowermost and smaller area of the piston 128 is acted upon by pressure in the supply line 11. The uppermost or large area of the piston 128 is acted upon by pressure in the return header 12 through a pipe 130. Any leakage to the space between the heads of the piston 128 is drained to a low pressure return by a pipe 131.

It will be noted that the valve plug 125 is of a smaller effective area than the valve plug 126. The plug 125 is positioned relative to a single sharp V-notch port having curved edges to provide full capacity with decreasing pressure drop. The difference in areas between the two pistons provides the increasing differential with rating with allowance being made for the change in pressure drop through the valve with increased rating.

In the pipe 130 and in the pipe 131 I provide throttle valves 132 and 133 respectively for controlling the pressure flow therethrough.

In operation, as the return flow control valve 121 is closed, increasing the return oil pressure, this tends to open the valve 122 by building up the pressure above the piston 129 thus increasing the burner inlet pressure in the header 11 until a balance is established between the pressures on one side of the valve piston and the other which due to the selection of piston areas and spring rate and valve seat unbalance are designed to approximate the desired characteristics.

While I have illustrated and described certain preferred embodiments of my invention it will be understood that this is by way of example only, and that I do not expect to be limited except as to the claims appended hereto.

This application is a continuation-in-part of my copending application S. N. 36,353 filed July 1, 1948, now Patent 2,540,778.

Certain subject matter of this application is disclosed and claimed in divisional application S. N. 471,763, filed November 29, 1954.

What 1 claim as my invention and desire to secure by Letters Patent of the United States, is:

1. A liquid fuel burner system including, a burner structure, a fuel supply conduit for the burner, a fuel return conduit for the burner, a source of liquid fuel under pressure for the supply conduit, a valve in the system controlling the fuel fiow in the system, a first motor applying a positioning force to the valve in accordance with the pressure differential between the supply and return conduit, and a second motor of a size different from that of the first motor applying positioning force to the valve in one direction in accordance with demand upon the burner and through a connection common with the first motor.

2. The burner system of claim 1 wherein, the two valve motors apply their forces to position the valve in maintaining an increasingly higher pressure differential as demand increases.

3. The burner system of claim 1, wherein; the source of liquid fuel under pressure for the fuel supply conduit includes, a liquid pressure pump having an inlet joining the fuel return conduit and an outlet joining the fuel supply conduit, and controllable pressure fluid motive means driving the pump; and the valve in the system controls the pressure fluid motive means.

4. The burner system of claim 3, wherein; the second motor is responsive to the pressure in the supply conduit as an index of demand upon the burner.

5. A liquid fuel burner system including, a mechanical atomizing liquid fuel burner, a fuel supply conduit connected to the burner, a fuel return conduit leading from the burner, a pump for the liquid fuel with its inlet joining the return conduit and its outlet joining the supply conduit, a source of power for the pump, a source of liquid fuel conducted to the pump inlet, a valve between the source of fuel and the pump inlet responsive to demand for the liquid fuel, a by-pass conduit around the pump joining the supply and return conduits, a regulating valve in the by-pass, a first motor applying a positioning force to the regulating valve in accordance with the pressure differential between the supply and return conduit, and a second motor sized differently from the first motor and arranged to apply a positioning force to the valve in a predetermined direction in accordance with demand through a common connection with the first motor.

6. The burner system of claim 5 wherein, the two valve motors apply their forces to position the regulating valve to maintain an increasingly higher pressure difierential as demand for the fuel increases.

References Cited in the file of this patent UNITED STATES PATENTS 1,425,338 Ray Aug. 8, 1922 1,683,371 Peabody Sept. 4, 1928 1,762,133 Harris, Jr. June 3, 1930 1,824,952 Graham ct al. Sept. 29, 1931 2,115,665 De Florez et al. Apr. 26, 1938 2,290,350 Olches July 21, 1942 2,334,679 Mason et al. Nov. 16, 1943 2,616,254 Mock Nov. 4, 1952

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