US2315665A - Feed water control system for boiler furnaces - Google Patents

Description

April 6, 1943. c. w. SENGSTAKEN FEED WATER CONTROL SYSTEM FOR BOILER FURNACES Filed Dec. 2, 1938 3 Sheets-Sheet l Aivzrrn R M13 April c. w. SENGSTAKEVN 2,315,665

FEED WATER CONTROL SYSTEM BOILER. FURNACES Filed Dec; 2, 195a s SheetS Shet 2 115 r w a i ii I 114 117 55 90 Q5 m WH INVE TOR M MW April 6, 1943. c. WQQSENGSTAKEN FEED WATER CONTROL SYSTEM FOR BOILER FURNACES Filed Dec. 2, 1938 3 Sheets-Sheen 3 INVENTOR Patented Apr. 6, 1943 FEED WATER CONTROL SYSTEM FOR BOILER FURNACES Charles Sengstaken, Scarsdale, N. Y., assignor to John M. Hopwood, Mount Lebanon, Pa.

Application December 2, 1938, Serial No. 243,536

1 Claim.

This invention relates to boiler furnaces and more particularly to a control system for controlling the rate of delivery of feed water to the boilers in accordance with water level and in accordance with changes in the rates of combustlon as requiredby the demand for steam.

In the operation of a steam boiler best results, from the standpoint of thermal efficiency and the operation of turbines, engines, etc., supplied with steam, are obtained when the steaming rate can be caused to follow as closely as possible, the demand rate. Unless the rate of feed water delivery is properly controlled steam pressure and steam flow will fluctuate undesirably. Thus, for example, if under conditions where the load on the boiler is steady, the rate of steam flow out of the boiler and the steam pressure will decrease if the feed water regulator or regulating apparatus allows too much water to be forced into the boiler. If too little water is supplied under the at a value that will maintain a constant water level in the boiler. Such systems have a tendency to hunt because over-correction in the water rate, whether in the increasing or decreasing direction; exaggerates the very condition that is being controlled. In other words, since increased steam flow causes a reduction in pressure and water level, both elements of the control operate to increase the water rate, so that under conditions of increasing load the water rate would be increased so fast that the steaming rate could not keep up with the demand rate.

In the course of operation of a boiler demand for steam fluctuates, and the more abrupt these fluctuations are the more difficult it becomes to feed water to the boiler at a rate at which the required steam flow will result and the required steam pressure maintained.

If the steam demand suddenly increases and too much feed water is supplied, the steam pressure will decrease and it will be more difficult to produce the required steam flow because too much heat is taken out of the boiler water at a time when the steaming rate must increase. On decreasing steam demands the control must act toreduce the water rate before the water level responsive control starts to function to prevent the water level from rising too high.

It is an object of this invention, in part, to control the water rate in accordance with some variable that is independent of steam flow but dependent on the demand for steam, and in part, from boiler water level, it being preferred in the interests of safety, that ultimate control of the water rate shall be in response to and in accordance with variations in the boiler water level.

More specifically it is an object of this invention, in part, to control the rate of Water delivery to the boiler inversely in accordance with the rate of air flow to the furnace, and, in part, in accordance with water level variations.

A further object of the invention is to provide a control system of the character referred to above that will operate to momentarily decrease the rate of feed water delivery to the boiler in response to a demand for increasing rates of combustion on the boiler, preferably inversely in accordance with increasing rates of air flow to the boiler, and then subsequently to increase the water rate in response to Water level, ultimate control of the water rate being in accordance with water level.

Other objects of theinvention will, in part,'be apparent, and will, in part, be obvious from the following description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a diagrammatic view of a boiler furnace and a control system embodying a form of the invention for controlling the rate of delivery of feed water to the boiler;

Fig. 2 is an enlarged view partly in section, showing the boiler drum, the feed water valve and the operating devices therefor;

Fig. 3 is a view partly in section of an air flow responsive regulator embodied in the system of Fig. 1 which controls and regulates the secondary air supply to the furnace in accordance with load requirements on the boiler;

Fig. 4 is a view in side elevation of the feed water control valve shown in Figs. 1 and 2;

Figs. 5 and 6 are views, in section of the valve taken on lines V-V and VI-VI of Fig. 4;

Fig. 7 is a view of the outlet port of the valve, the view being in the direction of the arrows VII-VII, Fig. 4; and

Fig. 8 is a diagrammatic view of the master regulator shown in Fig. 1.

Through the drawings and the specification like reference characters indicate like parts.

Referring to Fig. 1 of the drawings a boiler furnace l is shown in connection with which is illustrated a control system embodying what now appears to be a preferred form of the invention, for controlling the delivery of feed water to the boiler. The control system is applicable to any type of furnace so far as the kind of fuel burned is concerned and particularly to furnaces which are provided with means for automatically controlling the combustion rates in accordance with demand for steam.

In the particular illustration of Fig. 1, the furnace is supplied with pulverized fuel from a pulverizer 2. The primary or carrier air-being provided by a fan 2' having a control damper 3 in its inlet duct 4. Damper 3 is operated by a re ulator 5 which is controlled by a master regulator 6 in accordance with demand for steam. In order that regulator 6 may be more quickly responsive to changes in demand for steam, it is shown connected by a pipe 1 to a supply header 8 at a point remote from the boiler drum D.

The secondary air is, supplied by a fan or blower 9 of the vane controlled inlet type, the vanes being opened or closed by means of a regulator I 0. Regulator Ill isrunder the control of a device H which measures the rate of air flow or gas weight traversing the boiler and causes regulator ID to so adjust the inlet vanes that the secondary air supplied by fan 9 to the furnace will be maintained at a substantially constant value for any particular combustion rate that isrequiredtosatisfy the demand for steam. For a given demand for steam, device l operates to hold a substantially constantdifferential in pressure between say, two spaced points in the furnace passages, one beingsayat 2m the secondany air duct l3,-and the other being inside. the combustion chamber as at 14, these points being on opposite sides of burners I5. Becauseof such connection device ll responds to and measures the pressure drop across the burners which is a measure of theair flow.

Device H is, loaded in accordance with the demand for steam from. masterregulator B so that for each boiler load orrating device II will cause the rate of delivery of secondary air to change to the value required andwill .then regulate the air supply, to hold the rate constant at such value,

The combustion chamber pressure is, maim tained substantially constant at some predeterminedvalue, sayatmospheric or slightly below, by means ofa regulator 16 which is connected by a link I! to outlet dampers l8. Regulator I 6 is connected by a pipe I9 to the combustion chamber of thefurnace andoperatestoadjust dampers i8 when the pressure in the combustion chamber tends to riseabovethe desiredvalue, and moves then towards closed position if the pressure tends to decrease below this value.

Regulators and I0 ,mayube of any suitable form or construction, but as illustrated they are like the regulator shown and described in U. S. Patent No. 2,044,936, granted June 23, 1936, to Robert R. Donaldson, and regulator l6 may be of the type illustrated in U. S. Re. Patent 18,749, dated May 24, 1932. Since regulators 5 and I 0 are of the same type similar or corresponding parts will be given the same reference characters when the same are described subsequently herein. A brief description of regulator I6 is also given further on in this specification.

Feed. water is delivered to boiler drum D from a supply pipe 20 having a control valve 2| therein. This valve is provided with means 23 responsive to water level in the drum and means 24 'respo sive to regulator 6, which determines what the rate of air supply shall be, for operating the valve in a certain direction whenever a change in the rate of air supply and therefore a change in the rate of combustion, is required. A requirement for an increased rate of combustion and therefore an increased rate of air supply, is indicated when the pressure in header 8 decreases, and a reduction in the rate of combustion is indicated when there is a rise in steam pressure in header 8. Regulator 6 responds to departures in the steam pressure from the desired value and sends out control impulses to regulator 5 and device I! of such magnitude as will cause such combustion rates to be established in the furnace that the steam pressure will be maintained substantially constant.

This invention is primarily concerned with the control of the feed water rate, i. e. the rate of delivery of feed water to the boiler, as it operates under varying conditions of load. It is highly desirable, that the water rate be so controlled that the boiler may be available to deliver the required amounts ofsteam at the times when a change in the rate of steam delivery is called for without causing the steam pressure in theperiod of time that is long enough to allow the combustion rate to increase with the load demand and maintain a boiler steaming rate that will satisfy such increase in demand. If the water should be increased at such a time too much of the stored heat in the boiler would be utilized toheat the incoming feed water rather than serving as means of facilitating the required ing its steaming rate to prevent the steam pressure from rising too high, but this increased water rateshould persist only long enough to allow the combustion rate to be decreased to the value required to satisfy the steam demand; When sucha condition has been reached'the water rateis. controlled from water level until it is reduced to substantially the normal .level. Valve 2| and its control system accomplishes the above described functions as will be apparent from the following.

Valve 2| is so constructed that it may be adjusted towards open or closed position by either or both of the operating means 23 and 24. Means 23 operates in response to variations in boiler water level, opening valve 2| more and more as the water level falls and closing it more and more as the level rises. control of regulator 6, operates to shift the valve towards closed position when the demand for steam changes in an increasing direction and at which the valve may be actuated in either di- Means 24 being under rectlon for a given operating movement of means 23. 1

Valve 2| is illustrated in detail in Figs. 4 to 7 inclusive. It comprises a valve body 26 having an inlet '21 and an outlet port 28 of substantially rectangular shape, and a valve member 29 mounted for reciprocatory movement within the body. Plug 29 is in the form of a hollow sleeve or cylinder and is provided with an elongated rectangularly-shaped port 30. By moving member 29 either up or down and giving it a rotational motion at the same time, or giving it only rotational motion, port 30 may be caused to register with" port 28 with varying degrees of overlapping whereby port 28 may be either fully closed, opened wide OIj partially opened. The

up and down motion of member 29 is accomplished by means of a rod 3| which is operably connected to the waterlevel responsive means 23 through a lever 32, rod 33, bell crank 34 and link 35. Rotational motion of member 29 is accom plished by means of an angling bar 36 supported in a bracket 31 that is mounted for rotational movement on a shaft 38 journalled in supporting bracket 39 that extends upwardly from the top 5, in which position the center line of pin 43 is co-axial with the center line shaft 38 the turning of shaft 38 results merely in the turning of the angling bar 36, block 42 and bracket 31 about the axis of pin 43 without in any way turning or rotating stern 3| and the sleeve 29 connected thereto. If angling bar 36 is disposed at an angle with respect to stem 3| and the stem is moved downwardly, valve 28 will be rotated in a clockwise direction as is indicated by Fig. 6 and the extent of this rotational movement for a given downward movement of stem 3| will depend upon the angle at which the angling bar is set. If the angling bar is set in a vertical position, there will be no rotational movement but the more this bar is set at an angle in the direction of arrow 46 in Fig. 4 the greater will be the rotational movement of the'valve 29 as it moves downwardly. Also, if stem 3| is moved downwardly to a position Where pin 43 is below the rotational axis of shaft 38, sleeve or valve member 29 may be rotated in a clockwise direction when shaft 38 is turned in the direction of arrow 41, Fig. 4, or in a counter-clockwise direction when the shaft is turned in the opposite direction. When shaft 38 is turned in the direction of arrow 41, Fig. 4, assuming, of course, that pin 43 is below shaft 38, valve member 29 may be rotated either in a clockwise direction or in a counter clockwise direction whereby port 30 may be caused to register more and more to increase the opening of the valve or it may be closed more and more to decrease its opening.

Maximum opening of the valve occurs when ports 28 and 30 are in register, as shown by Fig. 6, and minimum opening occurs when the valve member 29 is in the position shown in 5. The angling bar mechanism of the valve maybe so set that when valve member 29 is in its uppermost position there will be a slight opening as indicated at 49 and the size of this opening may be through the valve. In the case of the control of feed water to the boiler this minimum opening would be set to take care of the feed water requirements of the boiler at minimum load or rat-- Shaft 38 of valve 2| is provided with a crank arm 50 that is operatively connected to operating means 24 and which, as stated previously herein, is under control of master regulator or device 6. When the load on the boiler increases, device 5 transmits an operating pressure medium such as compressed air to device 24 causing it to turn shaft 38 in a counter-clockwise direction whereby sleeve 29 is moved in a direction to decrease the flow opening through valve 2|. This, therefore, tends to reduce the rate at which feed water is delivered to the boiler at the time when an increased demand for steam is imposed on it. This allows the stored heat in the boiler to be made available for generating and releasing steam during the period that the combustion rate is being increased to the value required to meet the increased demand on the boiler. This will result in a reduction in the water level in the boiler but means 23 responds to this lowering of water level a and causes valve member 29 to be moved downwardly to increase the opening of the valve until the water rate has increased to the value required or called for by the steaming rate established at the higher load.

If the load on the boiler is decreasing, which results in an increase in the steam pressure to which device 6 responds, then pressure impulses are transmitted to device 24 which cause it to turn shaft 38 in a clockwise direction whereby valve member 23 is rotated in a direction to increase the opening of the valve and thereby inell crease the feed of water to the boiler. This increased rate of feed water delivery tends to counteract the tendency for the steam pressure in the boiler to rise suddenly by utilizing the stored heat in the boiler to heat the incoming feed water. This increased opening of the valve is maintained during the time that the combustion rate is being decreased to the value called for by the reduction in load on the boiler at which time device 23 will come into play to adjust the valve opening in valve 2| to a value that will establish such a rate of delivery of feed water as will maintain the level in the boiler substantially constant at normal level.

Device 24 comprises a pressure-tight housing or chamber 52 in which a diaphragm 53 is mounted. The diaphragm is provided with plates 54 and 55 on its top and bottom respectively, which are suitably secured together. Plate 55 is provided with a lug 56 to which a ten sion spring 51 is operatively connected at its upper end. The lower end of the spring is connected to a block 58 having threaded engagement with an adjusting screw 59 whereby the tension or downward pull exerted on diaphragm 53 by spring 51 may be adjusted to any value de- 7 sired. Plate 54 is provided with an upwardly projecting lug 6D to which a link BI is connected at its lower end. The upper end of the link is connected to a lever 82, one end of which is pivotly connected to a support 63 carried by housing 52. The other end of lever 62 is connected by a link 64 to crank arm 50.

When the load on the boiler is increasing and the steam pressure is tending to decrease, device 3 reduces the pressure acting on the under side of diaphragm 53 whereby spring 5! pulls the diapre-set to allow any desired minimum flow phragm downwardly, moving the free end of lever 62 downwardly and causing crank 59 to turn shaft 38 in a counterclockwise direction to decrease the flow opening in valve 2|. If the load on the boiler is decreasing and the steam pressure is tending to rise, device 6 tranmits increased pressure impulses to the under side of diaphragm 53 whereby lever iii is caused to move upwardly and turn shaft 32 in a clockwise direction whereby the flow opening through valve 2| is increased.

Operating device 23 comprises a substantially noneexpansible support 66 and a thermally expansible tube ii? that is rigidly connected to the support as at This tube is disposed at an angle, as shown, with its upper end connected by a tube Gil to the steam space of boiler drum D, and its lower end is connected by a tube or pipe to the water space of the boiler at a point well below the level L which may be designated as the normal boiler water level. Thus, the lower portion of tube 5'1 will be filled with water and the upper portion will be filled with steam. If the water level in the tube varies, tube 5? will either expand or contract. If the water level is relatively high, the tube will tend to contract and when relatively low, it will expand. The lower end of tube 6? is connected to a lever ll one end of which is pivotly connected as at E2 to rigid support 6'5 and the free end of the lever is connected to link Thus, as the water level in the boiler drum rises, tube El contracts whereby lever H is turned in the direction of arrows 13. This results in lever being turned in a clockwise direction to raise valve member 29 and decrease the flow opening through valve 25. The opposite action takes place when the water level in tube 51 falls, i. e. tube 6i expands causing lever 32 to turn in a counter-clockwise direction and move valve member 29 downwardly to increase the opening in the valve.

From the above it will be seen that if the load on the boiler is increasing device 2e will so operate valve 2! that the rate of feed water delivery to the boiler will be decreased for a time long enough to allow the combustion rate of the furnace to increase to the rating required to hold the steam pressure in the boiler at the desired value and that as the combustion rate approaches the required value, device 23, responding to a decrease in water level in the boiler, will operate to open valve 2! sufficiently to establish a water rate that will satisfy the demands on the boiler. If the load on the boiler decreases device 24 tends to increase the rate of delivery of feed water'to the boiler by opening valve ill, but by the time the combustion rate has been decreased to the rate required by the decreased load on the boiler, device 23 will have moved valve 2i towards closed position or to such a position that will satisfy the water rate demanded by the boiler.

Device H is illustrated in detail in Fig. 3, and comprises a pressure sensitive diaphragm 75 which is mounted within a pressure-tight housing it, a beam 'i'i mounted on a roller fulcrum I8, the lever being connected at one end to the diaphragm by a connecting member l9, an a loading device Sil which is operatively connected by a spring 8! to the other end of the lever. Device i! also includes a control element 32, such as an escapement valve, which is disposed for operation by beam l! for transmitting control forces, such as compressed air pressure impulses, through a sending line 83 to a diaphragm chamjust slightly above piston 98.

ber 8d of regulator Iii. diaphragm which operates a pilot valve that controls the direction and extent of movement of a piston rod 36 which carries a frame 81 that is connected by a link 88 to the shutters that control the size of the opening on the inlet side of blower 9.

Beam T5 is operatively connected to valve 32 by means of a push rod 89 that rests on the lever at its lower end and which supports at its upper end valve member The dead weight of beam ll, diaphragm i5, rod 89 and such other parts as are carried thereby, is balanced by tension springs 95 and 552 one being attached to one end of the lever and the other tothe other end thereof. The upper ends of these springs are anchored to supports 93 and M respectively which are adjustable up or down whereby the tension f in the springs may be adjusted to the proper degree.

In order that the operation of device ll may be stabilized, i. e., to prevent it from overor under-controlling device it in response to changes in secondary air flow or in changes in the degree of loading imposed by device 80, a time delay device, in the form of a dashpot 95 is provided.

Dashpot db comprises a cylinder 9'? having a piston 98 therein which is connected by a spring $9 to the underside of diaphragm T5. The lower end of cylinder 9? is connected to a variable volume chamber such as may be formed by a bellows Hi3, mounted in a pressure-tight housing l5 The dashpot is filled with such a quantity of fluid that when bellows I86 is expanded to its maximum capacity the level of the liquid will be The upper end of cylinder 9? is provided with an overflow chamber Hi2 having a flow connection with the lower end of the cylinder by means of a by-pass I03 provided with a needle-valve I04 therein. The interior of housing It! is connected by a pipe I05 to sending line 83 so that as the pressure impulses in line 33 increase bellows I 60 contracts displacing fluid which tends to move piston 98 upwardly. The force of the fluid on the piston is gradually dissipated, however, because the fluid will be gradually displaced through by-pass Hi3 into overflow chamber Hi2, and finally there is no force exerted on the piston at all so that it will return to its normal position.

This above-described action take place when diaphragm E5 is moved downwardly either as the result of an increased pressure differential acting thereon or because loading device 80 has moved beam I! in a counter-clockwise direction. When this happens valve 82 increase the pressure in line 83 and the action of the dashpot is to resist movement of the diaphragm in such a manner that regulator it will have sufiicient time to make its adjustment on blower 9 before the regulator functions to effect further adjustments. If diaphragm 15 moves upwardly causing beam '52 to turn clockwise or if the beam turns in this direction because device 38 exerts a suflicient downward pull on the beam, valve 82 is adjusted to decrease the pressure impulses in line 83 and in housing i i 2. Initial upward movement of diaphragm i5 is resisted by spring 59 and by the drag of piston, but as soon as the pressure impulse in housing it)! decreases the volume of the bellows increases whereby a downward pull is exerted on piston 98 further increasing the resistance imposed on diaphragm l5 to'upward In this chamber 84 is a make up forthe increase in volume. When this occurs piston 98 will occupy its normal position:

Device 80 comprises a. pressure-tight housing I01 in which a bellows I08 is disposed. A strong compression spring I09 is mounted within the bellows and bears against a thrust plate IIO urging the bellows toward its expanded position. A push rod III connects bellows I08 to spring 8 I. Housing I81 is supported by a cup-like member I01 and a tube '1 from a plate P extending outwardly from diaphragm housing 16.

Loading pressure is delivered to the interior of housing I01 by regulator 6 through sending line H2 and for each value of pressure bellows I08 will hold rod III in a definite position whereby a. definite tension will be imposed on spring 8I. Spring I09 is of such stiffness that full travel of the bellows, in a compression direction, may take place when the pressure in housing I01 is varied from atmospheric to the maximum pressure that will be delivered to it by regulator 6. Spring BI is light in character and will stretch or compress under much lighter forces, but its characteristic is such that each value of force exerted by it on beam 11 must be balanced by a given but different value of pressure differential acting on diaphragm 15 in order that a balance may be maintained between differential and loading of device 80. Thus spring 8| gives to device II the gradient required for regulation of the secondary air supply over the full range of secondary air requirements from no load to full load.

Valve 82 comprises a valve body I I4 having an inlet II5 to which a source of compressed air at constant pressure is connected, an exhaust port II6, an outlet II1 to which line 83 is connected, and valve member 90. The inlet and exhaust port seats are shaped to cooperate with the conical or tapered surfaces at the ends of valve member 90, so that as it is moved towards the inlet port and away from the exhaust port, a lesser pressure will be established in sending line 83. When the exhaust port seat is closed, the inlet being wide open, maximum pressure is delivered to the sending line; when the inlet is closed and the exhaust port is wide open, the pressure in line 83 decreases to a minimum, i. e. atmospheric, and when member 90 occupies intermediate po sitions, intermediate values of pressure will be built up or established in sending line 83.

When maximum steam demand is imposed on the boiler, the steam pressure will tend to decrease so that at the maximum demand regulator 6 will so adjust the loading of device 80 that device II will cause regulator I to open the shutters on the blower for maximum secondary air. The arrangements of regulator 5, and device II are such that device transmits the minimum loading impulse to housing I01 and to the pilot valve mechanism of regulator 5 when the load on the boiler is at a maximum, maximum control impulses are delivered thereto at minimum load on the boiler. Device II is also so constructed that at minimum load maximum operating pressure is transmitted by valve 82 to diaphragm chamber 84 of regulator I0 at maximum load minimum pressure is delivered thereto.

Thus at maximum load on the boiler, bellows I08 will be fully expanded and maximum tension will be imposed on spring 8|. This will require that the air flow through duct I3 be increased to a value at which the pressure differential acting on diaphragm will balance the maximum force exerted by spring 8| on beam As the load decreases on the boiler, then pressure in housing I01 is increased, compressing bellows I08, moving rod III upwardly and decreasing the tension in spring BI. This decrease in pull of'spring Ill on beam 11 will unbalance it whereby the control impulse sent to regulator I0 will effect a reduction in the secondary air supply rate until a balance is restored between the pressure differential acting on diaphragm 15 and the pull of spring 8I on beam 11. But for any given steady load on the boiler, diaphragm 15 will be operated to control regulator I0 to maintain the secondary air supply rate substantially constant.

Master regulator 6 comprises beam I I8, a steam pressure responsive element II9 such as a bellows disposed within a pressure-tight housing I20, an escapement valve I2I such as valve 82, and a gradient spring I22. Regulator 6 includes also a stationary rigid knife-edge fulcrum I23 that bears on the upper side of beam I I8, and a push rod I24 secured to bellows II9, the push rod having a knife-edge I25 bearing against the underside of beam H8 at a point near fulcrum I23 but between it and spring I22. Spring I22 is connected at its upper end to a link I26 having at its upper end a knife-edge I21 bearing on the upper side of beam II8.

Regulator 6 also includes a dashpot D. P., the movable element or piston P of which is yieldingly connected by a spring S to beam H8. The dashpot operates to yieldingly restrain movement of beam H8 thereby giving stability to operation of the regulator, and is of the fluiddisplacement type. The displacement of fluid is accomplished by a bellows B located in a housing H and which is acted upon by the pressure impulses sent out by valve I2I. The restraining or stabilizing effect of the dashpot depends upon the magnitude of these pressure impulses and the length of time that it persists is controlled by a needle valve N. V. located in a passageway P. W. which communicates with the top of the dashpot cylinder and with the space below the dashpot piston.

Spring I22 is so adjusted that when maximum steam pressure (i. e. a pressure corresponding to minimum load) is acting on bellows II9, valve member 90 will be in a position to close exhaust port I28, at which time inlet port I29 is Wide open and maximum control pressure is delivered to regulator 5 and loading device thereby calling for minimum rates of supply of fuel and secondary air to the furnace. When regulator 6 is thus properly adjusted, inlet port I29 will be closed when maximum boiler load occurs, in which case the steam pressure will have decreased to a predetermined minimum valueand the control pressures or impulses acting on loading device 80 and transmitted to regulators 5 and I8 will be a minimum, 1. e. atmospheric in this case, whereupon the rates of fuel and air supply delivered to the furnace will be increased to maximum. For intermediate boiler loads, the pressure impulses delivered by regulator 6 to the above described will be of corresponding intermediate values.

From the foregoing, it will be observed that the impulses sent out by regulator 6 will determine what the rate of air supply to the furnace for combustion purposes shall be for any given load demand. These same impulses are utilized to operate device 24 to initially vary the water rate means 2% acts to initially and temporarily ad just valve 21 to decrease the rate of delivery of feed water to the boiler, and if the loa d change is in a decreasing direction device 24 operates to initially and temporarily adjust valve 2| to increase the water rate, but in either case means water rate through its operation of valve 2| to establish or maintain the required water level in the boiler. Because of the gradient in device 23, the steady water levelsfor the higher boiler loads will be lower than those that will be es-" tablished at the lower boiler loads or ratings, this, however, allows some leaway for device 24 to increase the water rate to the boiler when the load is decreasing.

' liaving thus described the invention what I r claim as new and desire to secure by-Letters-Patentisl w A system for controlling combustion, in boiler iurnaces in accordance with the demand for steam andcontrolling the rate ofjdeliveryof feed water tothe boiler,,.said system comprising means for developing a control forcethat is a measure of the rate of supply of combustion air required bythe furnace for a given demand for steam, means responsive to said; control force for controlling the rate of sup ply oi air tothe furnace a valve for controlling the. supply; of

- W l t the i hsmean responsi to chan .15 23 will eventually and primarily control the in water level for so operating; saidvalve that thq rate of delivery of ;fee d water to the boiler is t such that a substantially constant water level is maintained inthe boilerat substantially constant load, and, means responsive to saidcontroljorce r operatingsaidvalve and efiecting a change in the rate of delivery of water substantially I simultaneously with a change in the rate of. air

supply to the furnace said water level responsive meansbeing arranged to have ultimate control of the rate of delivery of water and particularly at substantially constantloads.

CHARLES W. SENGSTAKEN.

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