US2930364A - Method of and apparatus for regulating the delivery of feed water to steam boilers - Google Patents

Description

MalCh 29, 1960 G. R. ANDERSON METHOD OF AND APPARATUS FOR REGULATING THE DELIVERY OF FEED WATER TO STEAM BOILERS Filed Dec. 9. 1955 3 Sheets-Sheet 1 E@ R m w 5 mw @www m m n N www mm q R1 @um mw mh R 1 m m l \mm\ wm. R, A'Y m w R QQ 5 S B wm NQ h mN mz: 2&5, s@ mm mi um@ Nm, n Q WARN www QP u mw QN uw? MW l v 5% N. a nw n .MQ I f .wml h. Mm w \R NN QW WM. wh Qu NNI @hm Nw @n uw NQ R. Mw. \m. kmwm m, W om Wm, o uw. Nm. n Mm, E vm. Qw `$ml L 5 m w A. md h1- F\ Mandi 29, 1960 G. R. ANDERSON 2,930,364

METHOD 0F AND APPARATUS FOR REGULATING THE DELIVERY 0E FEED WATER To STEAM EoILERs Filed/Dec. 9, 1955 3 Sheets-Sheet 2 AIR SUPPLY /66 INVENTOR.

GEORGE ANDERSON States i` METHon or AND APPARATUS non lnaGULAfr-` ING run DELIVERY or FEED WATER To STEAM Bomans George R. Anderson, Mount' Lebanon Township, Allegheny County, Pa., assignor to Hagan ChemicalsV di Controls, Inc., acorporatiou of Pennsylvania This invention. relates to a method of and apparatus for.. controlling the rate of supply of feed water to a plurality of steam boilers supplying steam to a common steam-header. Y

In the operation of steam boilers whichsupply steamv toy a common steam header it i`s not uncommon to operate at least one of such boilers at or near its capacity and to vary the heat input to other boilers at suchrate thatthe total demand for steam is met while at the same time maintaining the required steam pressure inthe header.` The system of this invention has to do, withv the. regulation of the supply of feed water to the boilers regardless of whetheryone or another is operating.y at or near. capacity and others are operating. at less than capacity and at times evenuat standby or zero output.

, YWhere thev feed water pumps are driven. by steam turbines and the pumps are of the centrifugal type, thepower' input to theturbines will vary with the cube of the speed at.. which the pump is driven. It is therefore important that theA power input to the turbines be controlled. accurately so as to avoidthe waste of steam. Also' there are cases where waste steam is usedfor process or for` heating feed. water or for other purposes and Where the load on one or more of the boilers may fluctuate drastically,` the amount of steam supplied to the pumpturbine's should be so controlled as to avoid any excess .wastage of steam. Where reciprocating feed pumpsare employed the. input to the prime movers driving them does'not vary Y as the vcube of the speed at which the pumps are operatedz so that the control of the turbines or other drives' for such pumps are more easilyI regulated inA so far as steaml economy is concerned.

An object of this inventionis to provide a method of supplying feed water to a plurality of boilers one or more of whichv may bev generatingsteam at capacity andothers at much less than capacity in which thefeed line^ to' each boiler is providedwitha.feedline regulating valve-oper-y ated fromboiler level and inwhich method the control;v

of.. the delivery ofY the feed water is-soregulated as to maintain the pressure differential across the feed line valves at or above a predetermined minimum value and to controlthe supply of feed water in accordance with the changesVv in differential across' theV valvehaving the lowest differential at any particular time.

Another object is to provide .a system for regulating the supply of feed water as in the preceding object in which the control system functions automatically from rat whichever feed line valve has the lowest pressure differential across it thereby 'avoidingvthe'necessity of vboiler roorn=operators switching the control system from one to thev other of the feed line valves according to which ofI lines that consist in adjusting'the' owopening in a valve inteach- Aline-fromv the level. of'fwatenin the boiler supplied:

by that line', rrleasuring thelpressureV difference across the'. e valve havingthe lowest pressure differential and controlling the rate of- 'supply of. water to all the lines 1n,

such manner that the pressure difference across said valve is maintained at valuesabove predetermined minimums;

Another object is to provide apparatus for controlling the delivery of feed Water to a' plurality of steam boilers that includes a feed line' for each boiler, a valve in each feed line provided with means for operating the same in accordance with changes in boiler. water leve1,means responsive to the pressure difference acrossV the valve having the lowest pressure differential` for developing a control force that varies with the' differential,A a plurality of feed water pumps for the feed lines,` adjustable power inputl prime movers for driving the pumps, arcgulator responsive to the pressure differential control force for developing a control forceu that is proportional to the deviation of the pressure Vdifferential from apredetermined y minimum value, a master: sender responsive to said reg-' ulator control force` and the pressure. of the-feed water Y line for each boiler, thatincludes a valvein eacli feed y line provided with an: operatorcontrolled from changes in. water level in its associated boiler,` a prime ifxoveryfor4 driving each feed pumpV and provided with means for` controlling the power input thereto', and meansy con-f trolled from changes in differential across' theA4 feed line valve having thelowest differential ata'nymoment for so adjusting the power input to-*theV primel movers that the differentials across said feed linevalves are maintained at or above predetermined minimums. e

f Other objects of the'invention will beappa'r'en't to those' of ordinary skill in the arttto which the invention per"-4 tains from the followingV description and the'` accompany`` ing drawings. j Y

In the drawings: i l

. Figure 1'is a moreo1'- less-ediagrarnmaticV View. of a kplurality of steam boilersfprovidedwithi feed water supply and control apparatus.: arranged and constructed in vac? cordance with an embodiment. of the invention; l

Fig. 2 is a view in vertical section' of-a pilot-valv ent# bodied in' thevsystemoff` Eig. 1;.

Fig. Y 3 is-.a view iny section lof' a' master sender einY Fig. 7 is an enlarged View showingthe construction of`-v signal valves embodied in the feed water ow responsive devices of Fig. l.

The boiler feed apparatus and the` controllsys'tem embodying the invention, as shownlin'fFig. 1., comprises ai' plurality of steam boilers Aand B each of :which supplies-f steam through a super heater SH. to acommon header. CH. Y Each boiler is supplied with feed water tl'irouglr feed lines l and 2 connected tothe steamdrums andlj v of the respective boilers. The feed lines are provided .with feed water valves 5 and 6. respectively. Valve 5 isv positioned by a4 boiler water level regulator 7 and valve' t? by a water level regulator 8.` The boiler levelrespon-` sive regulators 7 and 8y actuate/their respective valves5f and 6F towards openposition as the water" level iitle` estranea.k Maa, 29; ileso with reference to a predetermined normal level. Regulators 7 and 8 may be of the type disclosed in the application of Otto B. Vetter, Serial No. 537,797, filed September 28, 1955, now Patent No. 2,805,907, and assigned to Hagan Corporationv of Pittsburgh, Pennsylvania, although other regulators may be employedif desired.

The feed lines 1 and 2 are applied with feed water by a plurality of pumps 9, 10 and 11 that are driven respectively by prime movers such as steam turbines 12, 13 and 14. The output of each pump is controlled by regulating the power input to the turbine that drives it.

The outlets of the feed pumps 9, 10 and 11 are connected to a header 15 to which the feed lines 1 and 2 are also connected. Thus each pump works against the same head or pressure. The intakes of the pumps are connected to a source of feed water not shown.

The steam inputs to the respective turbines are controlled by valves 16, 17 and 18 (see details in Fig. 6) in the steam lines therefor. These valves are separately operated by power cylinders or operators 19, 20 and 21, respectively, to each of which suitable operating fluid at controlled but variable pressure is delivered by pneumatically operated pilot valves 22, 23 and 24.

As will be explained infra, means 25 and 26 are provided for measuring the pressure differentials across the feed water valves 5 and 6, respectively. Means 25 and 26 are so connected that the output of means 25 will be linearly proportional to the lower of the differentials across valves 5 and 6. The boiler generating the most steam will determine whether the differential across valve 5 or valve 6 is the lower. For example, if boiler A is generating steam at or near capacity, and boiler B is generating no steam or only a portion of its capacity, the drop across valve 6 will be high and approach a value equal to the difference between the boiler feed line pressure in header 15 and the pressure in line 2 between valve 6 and the boiler. The differential across valve 6 is higher than that across valve 5 because under the conditions stated, valve 6 will be near its closed position. Since boiler A generates more steam it requires more feed water; therefore valve 5 will be in a wider open position and the pressure differential across it will be lower.

As stated, the means 25 and 26 are so interconnected that the regulation of the feed water pumps will be governed automatically from the feed line valve differential which is the lowest and will maintain the differential acoss each valve at or above a predetermined minimum va ue.

As connected, means 25 supplies the output control force utilized in the regulating system to effect such con` trol of the input to the pump turbines that the differentials across valves 5 and 6 are maintained above a predetermined minimum.

As shown, means 25 and 26 are pressure differential transmitters connected to respond to the differential across the valves 5 and 6, respectively. The output of transmitter 26 is connected to and used as the supply pressure for means 25. The output of transmitter 25 is utilized to load a regulator 27. Transmitter 26 can be used in lieu of transmitter 25 when necessary as when boiler A is taken out of service; similarly transmitter 25 may be used alone as when boiler B is taken out of service. The transfer of control from one to the other of transmitters 25 and 26 can be effected by three way valves 25a and 25h. The output of transmitter 26 may be measured with a gauge 26' for indicating the pressure differential existing across valve 6 at any time. As shown, valve 25a is in a position to connect the output of transmitter 26 to the supply connection of transmitter 25.

lf it be assumed that boiler A is generating steam at or near capacity and that boiler B is generating very little steam as on standby for example, that the pressure differentials across valves 5 and 6 are to be maintained above a predetermined minimum of say 75 p.s.i., then under the assumed conditions, the feed water supplied will be regulated from the differential across valve 5. When the differential is at p.s.i., transmitter 25 will de velop an output control force pressure of say 30 p.s.i.

.The output pressure will increase from 30 p.s.i. to say 60 p.s.i. as the differential across valve 5 increases, to say p.s.i., and will decrease from 30 p.s.i. to zero if the differential across valve 5 decreases to zero.

Since transmitter 26 provides the input air supply to transmitter 25, the value of that input pressure will vary from a maximum of say 60 p.s.i., as when the differential across valve 6 is at a maximum, to zero p.s.i. as when the differential across valve decreases to zero. The value of the output pressure of transmitter 26 will vary between zero and 60 p.s.i. with variations between maximum and zero differential across valve 6. Thus it follows that the output control pressure of transmitter 25 can never exceed the output pressure of transmitter 26. It also follows that because of the above'mentioned connections of transmitter 26 to transmitter 25, the feed water supply system will be regulated automatically from the lowest pressure differential existing across either valve 5 or valve 6, and maintain such a rate of supply of feed water that the differential across each valve will be maintained at or above the preselected minimum of say 75 p.s.i.

Regulator 27 is provided with proportional band and automatic reset features and develops a control force only after the output of transmitter 25 is above a preset value of say 30 p.s.i. Because of these features of proportional band and automatic reset, regulator 27 will send out a pressure increasing towards a maximum or a pressure decreasing towards a minimum or zero gauge so long as the pressure delivered by transmitter 25 is above or below the preset value of say 30 p.s.i.

The output of master sender 28 is proportional to the pressure in header 15 when the output of regulator 27 is zero gauge and responds to both the pressure in the header and to the output of regulator 27 when the latter is above zero p.s.i. gauge. The output of master sender 28 is transmitted to the pilot valves 22, 23 and 24 causing them to so operate power cylinders 19, 20 and 21 that the inputs to the turbines 12, 13 and 14 will be so adjusted as to produce, by the resulting changes in the rates of ow of feed water, a differential across valve 5 that is within the controlled range. The outputs of the pumps are such that by holding the differential across valve 5 substantially constant, the feed water will be delivered to all boilers at the rates required to maintain the desired water levels in the boilers at all times.

THE FEED WATER VALVES 5 AND 6 Valves 5 and 6 as shown are of the diaphragm type and may be of any form or construction. Valves 30 thereof and valves 16, 17, and 1S may be considered to be constructed as shown in Fig. 6. Therefore, the illustrations thereof are schematic only. Each of the diaphragm valves 5 and 6 comprises a valve 30 (see Fig. 6) having a valve stem 31 connected to a diaphragm 32 disposed within a housing 33 to which pneumatic pressure from regulator 7 is supplied through a pipe 34. Thus as the water level in boiler A decreases below the operating level desired, regulator 7 responds and transmits an increasing pressure to the diaphragm 32 and increasing the opening of the valve. As the level rises, this pressure is decreased and the Valve moves towards a more closed position. The same is true of regulator 8 and its valve 6.

As the positions of valves 5 and 6 change for a given rate of flow through each of the feed lines, the pressure differentials across them change. Thus, if at a given ow the valves are opened to a wider position, the differential decreases. Likewise, if the valves are moved more towards a closed position, the differentials will rise. In operation of the system assuming boiler A is the chief producer and boiler B is on standby or generating only a small part of its capacity, valve 5 is adjusted to such aisladas@ a: positionat a selected rate of" new through-y the feed line 1 as will establish a differential across it of say 75 p.s.i". That differential will be assumed to be that' corresponding to the feed water flow rate required at a givenV load which is somewhere between a maximum and minimum load on the boiler. VThe 75 pound-differential selected becomes the reference or control. pointl` and be'- ingy the minimumA differential for both valves 5 and 6, the regulation of the feed water supplyl will maintain the differential above that value.

BOILER WATER LEVEL REGULATORS' 7 AND 8 Regulators 7 and 8 as illustrated are identical in con-v struction and operation;y therefore, similar and corresponding parts willv be designated by the same reference characters.

Regulator 7 comprises a pressure differential responsive means 35, a constant head producing means 36 and an escapement valve 37.

The level responsive means 35 comprisesV a hollow ring mounted for rotation on a frictionless bearing 36located .at the center of the ring. The interior of the'ring is;

provided with a partition 37' at the top thereof. The ring contains a quantity of heavy liquid such as-mercury 38 which with the partition 37 divides the ring into pressure chambers 39 and 40.

Constant headv device 36 supp-lies a head h1 to chamber. 39 and the chamber `d0' is connected to, for example,A the datum water level in the boiler, that is, at a point nearthe bottom of the drum 3. Thecolur'nn or headI of water from the datum level to the boilerA level at any.' time may be represented as h2. Thus as the column h2 varies with respect to the column h1, the ring will rotate from a zero position clockwise on falling levels. and towards its zero positioncounterclockwise on risin levels.

The ring may be provided with counter weights W1; and W2 that will give it the proper motion in response` to changes in true level. The zero position of the ring may beadjusted by means of a stop 42.

Asthe ring rotates clockwise in response to decreasing boiler levels, the escapement valve 37 is so positioned that the press-ure in line 34 increases. As the ring rotates counterclockwise in response to rising levels, the pressuredelivered by valve 37 to. line 34'decreases. The valve 37 is supplied with air pressurev at constant' value through an inlet 44 port. t The valve has an er@V haust port 45 and an outlet port which is connected to the pipe 34. The position ofV the valve withv respectl to the inlet port 44 and'exhaust port 45 determines;

the pressure in pipe 34 and that pressure can vary from. zero gauge to a maximum pressure equal to the pressure: of the supply source.

The constant head means 36 comprises aclosed cylinder, or vessel 47 which is connected near itsv upper; end by a pipe 4S to the steam space in the boiler. The lower end of. the vessel is connected by a pipe as shown to the` ring chamber 39. Since the vessel 47 Vis exposed to the;

MITTERS 25 AND 26 As shown, the transmitters 25 and 26Y are identical in construction. Therefore, only one of them need be described in detail.. However, similar and corresponding parts will be identitied by the same reference characters.

-Transmitter 25 comprises a beam 50' mountedV onv a substantially frictionless double acting fulcrumY 51; TheV The member SS-is connected by a pastir rodE 54?' ter-the l `as a bellows 56 which is connected by a push rod" 57 to beam 5t) at a point opposite to that at Iwhich thepusfi` rod 54 is connected. On the opposite side of the fulcruntf 51 is a pressure ,receiving and transmitting unit 58l ('sfe- Fig. 7). The unit 58 comprises a housin'g59`- having` therein a pressure deectable bellows 60. The closed end of the bellows is provided with an exhaust port valvel seat 61 and a push rod 62 that engages the beam 501` As shown, the push rod 62 has a passageway therein" leadingV from the exhaust seat to the atmosphere at 62'11: The housing 59 is also provided with a valve stem 62',` one end of which controls the exhaust port 61 land the other end of which controls an inlet port 62a to whichv aE supply pipe 63 is connected. Pipe 63 is supplied with compressed air by transmitter 26 through valve 25d.`

. The pressure in line 63 will be proportional to the differential across valve 6. The housing 59 is provided with an outlet pipe 65 that leads to the regulator .27i

Ar closed volume or ballast chamber V is also connected i to pipe 65 to stabilize the operation of unit 58.

W-hen beam 50 is in neutral position the ValvestemI 62' is in a position where both the exhaust port 61 and;v the inlet port' 62a are closed. If the beam 50 tilts clock`v wise about the fulcrum 51, the valve stem is uns'eated from the inlet seat 62a, the exhaust seat being then held closed, whereby pressure is admitted to the/housing 597v device includes a pressure tight housing 52 inl which a deectableV member such as a bellows 53 is' disposed..

until a force exerted by the bellows 60 on beam 50 is suc'ient to balance the force which caused the bem to tilt clockwise. If the beam tilts counterclockwise as" a result of a decrease in the force acting'on the left# hand side of the fulcrum 51, the inlet seat 62a remains closedwhile the exhaust port is uncovered; `thereby reducing the pressure in the housing 59 until the forcey exerted by the bellows 60 on beam 50 is reducedV toA equality with the counter force acting on the left-handk side of the fulcrurn.

The housing 55 is connected to the feed line 1 at the" upstream or high pressure side of valve 5 and the housing` 52 is' connected to the feed line 1 at the low side of the valve. Therefore, the pressure difference acting on bel` lows 56 and 53, respectively, will be such as to exert clockwise turning force on the beam 50. Therefore, as" the pressure difference increases, the turning moment" produced by the pressure dilerential will increasemore and more and the pressure developed in the housing 5.9wx will increase correspondingly. Therefore, the pressure output from housing 59to the pipe 65 will be proportional to the pressure difference acting on bellows 56 and 53, respectively.

REGULATING DEVICE 27 Regulating device 27 comprises a beam 70 mountedrioxrl a double acting fulcrum 71. Connected to the' beamats the left-handside of the fnlcrum 71 is a pressure receive v particular case that the tension in spring 79 is such ask to exert a downwardly acting force on bearn70 of sayA 30 pounds. Therefore, the pressure admitted` to the hous-y ing 73 must reach `a value where the force of that pressurek will equal or exceed the force ofthe spring before the beam 70 will tilt clockwise. If the unit area of diaphragm 74 is one square inch, a pressure of 30 p.s.i. will balance` the spring force. The spring force tends to tilt the-beamk counterclockwise. 1 Y r ,f

On the opposite end of beam 70 is a pressure receiving device 82 and a pressure developing and sending device 83. Devices 72, 82 and 83 are illustrated more in detail in Figs. 4 and 5, respectively. Device 83 comprises a housing 83 having a flexible diaphragm 84 at one end thereof secured at its margin to the housing in a pressure tight relationship therewith. The center, of the diaphragm is connected to a bolt or push rod 84', the head of which is clamped to the central portion of Vthc diaphragm and provided with a seat 85 that communi cates with a passageway 86 to the atmosphere. A valve stem 87 controls exhaust port seat 85 and an inlet port 88 which is connected to a pipe 89 to which compressed air at constant pressure is supplied by a source not shown. The valve stem 87 as shown is urged towards the position in which the inlet port 88 is closed by a spring 90. The bolt as shown engages the beam 70 and will transmit to the beam a force that is proportional to the area of the diaphragm 84 and the magnitude pressure in the housing.

Device 82 comprises a housing 90 having a diaphragm 91 associated therewith and which is connected to the beam 70 by a push rod 92. The housing 90 is connected by a pipe 93 to the interior of housing 83'. The pipe 93 has a needle valve or orifice 94 therein and it is also connected to a volume or ballast chamber 95. The needle valve 94 depending upon its degree of restriction and the chamber 95 provide rate response and automatic reset action for the regulator 27. The rate response is controlled by the closeness of the setting of the needle valve 95 and the automatic reset action is controlled by the rate at which the pressure in housing 90 can be equalized with the pressure in housing 83', and that is controlled by the setting of the needle valve and the volume of chamber 95.

If the force produced by the pressure on diaphragm 74 is less than the spring force of spring 79, the inlet port seat 88 will be closed and the exhaust port 85 will be open. As the pressure in the housing 73 is increased to a point where the force of the pressure on diaphragm 74 exceeds the spring force, a pressure develops in chamber 83. The intensity of the pressure in chamber 83 will be proportional to the net force acting clockwise on the beam, the net force being the difference between the force of pressure acting on diaphragm 74 and the opposing force of spring 79. The pressure developed in chamber 83 is delivered to the master sender 28 (see Fig. 3). Regulator 27 will continue to supply pressure to the master regulator 28 until the differential across valve 5 has been reestablished to its control point, namely, 75 p.s.i.

MASTER SENDER 28 The master sender 28 is shown more in detail in Fig. 3. That sender comprises a beam 100 mounted on a iiexible fulcrum 101. As shown, the fulcrum is of substantially L-shape having one leg 102 secured to the base 103 of the machine and its vertical leg 104 secured to the beam. A relatively thin section 105 joins leg 104 to leg 102. The thin section exes to provide rocking motion of the beam 100. Regulator 28 includes a bellows or pressure defiectable member 106 disposed within a housing 107 to which pressure is supplied by pipe 93 from the regulator 27. Device 28 also includes spaced pressure deectable members such as bellows 108 and 109 disposed in housings 110 and 111, respectively, disposed on opposite sides of fulcrum 101. The housings 110 and 111 p rovide automatic reset and rate action for the regulator as will be shown infra.

Bellows 106 is provided with a push rod 112 having a rounded lower end that is seated in a seat 113 in an adjustable bearing member 114 secured to beam 100. The bearing member 114 embraces the beam and is clamped to it by means of a set screw 115.

Bellows 109 is provided with a push rod 116, the lower end of which is rounded and is seated in a seat 117 in abearing member 118. The bearing member 118 embraces the beam and is secured to it by a screw 119.

8 Bellows 106 and 109 because of their locations act on the left-hand side of the fulcrum 100.

Bellows 108 is provided with a push rod 121, the lower end of which is rounded and received in a seat 122 in a bearing member 123. Member 123 is adjustable along the beam 100, embraces it and is provided with a screw 124 for clamping it to the beam.

Sender 28 is also provided with a pressure deectable member such as a bellows 125, the lower end of which is secured to a supply fitting 126 secured to the base 103. The fitting 126 is provided with a cup 127 within which the bellows is disposed. The bellows responds to the pressure in header 15. The pressure connection from header 15 to the bellows 125 is through a pipe 128 which leads to a sediment collecting chamber 129. The upper portion of the chamber is connected by a pipe 130 to the fitting 126 as shown.

The bellows 125 as shown acts on the right-hand side of the fulcrum 101 and the force exerted by it is resisted by a relatively strong tension spring 132, the upper end of which is hooked over the beam 100, the lower end being connected to a nut 134. The spring is disposed within a tubular support through the closed bottom 137 of which an adjustment screw 138 extends. The screw is threaded into the nut 134 so that the tension in spring 132 may be adjusted. The spring 132 causes the beam 100 to take a definite position for each value of pressure supplied to the bellows 125. The position of the beam, however, will be augmented by the pressure supplied by pipe 93 to bellows 106.

Device 28 also includes an escapement valve 140 that comprises a body 141 having an exhaust port seat 142 at one end and an inlet port seat 143 at the opposite end. The body also includes an outlet port 144 which is connected to a sending line 145 that supplies the pilot valves 22, 23, and 24, as shown in Fig. 1. Pipe 145 is also connected to the housings 110 and 111 by a branch pipe 146. In the branch pipe is a needle valve 147 for controlling the rate at which pressure is transmitted to the housing 111 and the rate at which pressure is relieved therefrom. A volume chamber 148 is connected to the branch pipe 146 preferably at a location between the needle valve 147 and the connection to housing 111. The chamber 148 gives ballast to the housings 110 and 111 and acts to control, in conjunction with the needle valve 147, the rate action of sender 2S and its automatic reset function.

Valve includes a valve 149, the opposite ends of` which are tapered to register with and control the exhaust and inlet port seats 142 and 143. Ail. pressure at substantially constant pressure is supplied to the inlet port seat through a supply pipe 150.

The pressure at the outlet of the valve is proportional to the relative restrictions of the inlet and exhaust port seats. The extreme conditions occur when the exhaust port seat 142 is closed and the inlet port 143 is open and vice versa. In the former case the pressure suppliedl to pipe and to branch pipe 146 is equal to the pressure of the supply pipe 150; and in the other case aswhere the inlet port is closed the pressure will exhaust from the pipe 145 and branch pipe 146 to the atmosphere. For intermediate positions of the valve 149 the pressure in pipes 145 and 146 will be proportional to the relative restrictions at the inlet and exhaust ports and vary between atmospheric and maximum.

Housings 107, 110 and 111 are shown mounted on a lframe member 152. They may be moved lengthwise of member 152 in accordance with the particular positions of the bearing members 113, 118 and 123 on beam 100.

The beam is provided with stops 154, 155 and 156 to prevent overtravel of the beam 100 in either direction about its fulcrum 101.

Assuming that the differential across the valve 5 is stable at the control point value, namely, 75 p.s.i. and

desde@ that the pressure in the header 15 is in equilibrium 'at l the value required to maintain the differential across valve 5, then it will be apparent that the pressure sup to the pipe 145 and the brauch pipe 1146. That pressureY will be transmitted to the pilot valves 22, 23, and 24 and bring about a reduction in the pressure in the header 15 and inthe feed lines V1 and 2 as will be explained infra. Any change in pressure in bellows 125 will produce a change in the 'output pressure to Lines 145 and 146 at a rate determined by the restriction of the needle valve 147 and the volume of chamber 148. The bellows. .1% as shown resists increasing pressures to bellows 125. But as the time factor takes its effect, the pressures in chambers 110 and 111 are equalized so that eventually at stable conditions the pressure to bellows 125 is balanced f by the spring force of spring 132.

When there is a change in the differential across valve 5 suicient to cause differential transmitter 25 to deliver a control force to device 72 of regulator 27, and assum- Y ing that that force exceeds the spring force of springy 79, then there will be an increase in the `pressure supplied to housing 107. That increased pressure will act in the same direction as an increase in pressure on the bellows 125, whereupon a higher pressure is established in the,

sending line 145. That pressure is delivered to the piloti valves 22, 23, and 24. These pilot valves will therefore act upon the power cylinders 19, 20 and 21 and cause them to decrease the power input to turbines 12, 13 and 14. As will appear from the description of the pilot valves 22, 23 and 24, infra, increasing pressures incontrol line 145, causes the control pressures to the power operators 19, 2t), and 21 to decrease. That decrease causes the operators to shift Valves 16, 17 and 1S towards more closed positions, thereby decreasing the steam input to the turbines and thereby reducing the output of the feed water pumps. Therefore, the rate of supply of" feed water to the feed lines 1 and 2 and to the interconnecting header 15 will be such that the pressure'is reduced to a value that lwillreestablish theV differentialVV across valve 5 to the control point. Thus it is apparent' that regulator 27 will so control the pressure to housing'y 107 that the master sender 28 will provide the required control force for the pilot valves 22, 23 and 24 to accomplish the constant differential desired across valve 5. lnV that manner the feed water is supplied to the boilers at a precisely controlled rate.

PILOT VALVES 22, 23 and 24 In Fig. 2 the construction of each 'of' the pilot valves 22, 23 and 24 is shown. Since these valves are identical, the description of the valve shown in Fig. 2 will sufice for the three of them.

As shown, the pilot valve comprises a body 160 having a supply port 161 to which a pipe 162' is connected that carries oil at a relatively high pressure.- The port 161 leads to a chamber 163 having an outlet port 164 associated with a drain port 165 in a cap 166. Port 165 Y is connected to a pipe 167 that leads to a sumpfor supply tank not shown. The pressure at which the oil dis'- charges through the pipe 167 is atmospheric. The port 164 is controlled by a valve 168 suspended from a spring 169. The upper end of the spring is connected to a valve stem or rod 170, the turns at the `upper ends` of the spring being wrapped around the enlargement of the stem and secured thereto by a screw 171. vEmbracing the stern 170 at the upper end of the chamber 163 isga.

v ahead of pipe 190 which leads to the respective power isr whichis ,securedk tothe top of the` body* 1.60. by" welding: or other suitable means, the lowerk vend being securedtcr` a bushing plate 173. The bushing plate' as shownha's a snug fit with the stem; The valve: stern. is actuatedy by.-

apressure dellectable member such as arv bellows 176' dis.- posed on a housing 177, the lower end ofwhich is bolted@ to the valve body as shown. The housing 177-pro-4v vides a pressure tighty chamber `whereby the bellowsL may be deflected according to the pressure supplied.l toitv by pipe 145. Deflection of the bellows 176 in. response to' the. control pressure from pipe V145 isresisted by a rela tively heavy spring 178 disposed between acap plate 1.79: of thebellows and the upper end of the valve body 160.Vr

The housing 177 is provided with a boss 180 having a threaded bore therein through which a screw threaded operating stern 181 extends and which is provided with a handwheel 182. By means of the haudwheel' and screw'A 181 the valve 168may be operated manually.

In the event that oil should leak past the bushing 173. into the interior of the'bellows 176 that oil may* bex drained olf'through a drain passage 184 leading to the' drain port 165.

The valve port 164 as shown is formed' in a plate` 185. In that manner a plate having the size ofy the opening required may be selected. The pressurel in lineV 162 varies in accordance with the amount that valve 1687 is open. When that Valve is wide open the pressure in` line 162 drops to substantially zero gauge pressure in.-l asmuch as an orifice 187 is provided i'n the supply piper cylinders 12,713 and 14. y

They power `cylinders supplied by the pipes 190, each comprise, as schematicallyl illustrated, Va' cylinder 191y having a piston 192 therein. The oil pressurev from the respective pipes is supplied tol lower end of the cyl indery causing the pistonsto move upwardly. Each piston moves against the force of a spring 193 so that for every value of pressure suppliedv to the respective cylin ders there will be a corresponding position of thel pistonsV `therein. Therefore, the steam valves supplying the turbines will havea position for every' valueY of controlpres# sure suppliedI by the master sender line 145.

OPERATION' I. Boiler- A the pressure generator-Boiler B on stand-` By-dierential across valve 6 substantially zero n When boiler A. handles thebase steam loadv andboiler` Bison standby, the pressure. differential across valve is at a'y maximum value whenv in fully closed position. Therefore, transmitter 26 will deliver maximum pres'-` sure from its air supply through its valve supply' port" 62a, housing 59, pipe 63 and valve 25a to the valve iii-.-

let port 62a ofV transmitter 25. Thepressur'e output ofV transmitter 25 to line;651wil1` therefore vary from! the value of'thepressure in line 63, whichmay be-assurnetk` to be 60 p.s.i. for the conditions stated",l to zero at zero" differentialY across valve 5.

When the pressure in line65 to regulator 27 is above: 30 p.s;i., the output pressure in line 93 to master sender 28 will vary from 30 p.s.i.. to maximum, sayl 60 p.s.i., and when the pressures in housings 83' and 90a-reequal, the pressure in line 93 will be equal to the difference' befI tween the force of spring79 and the force developed by` the pressure on diaphragm 74. That pressure acting on bellows 106 causes master sender 28A to transmitv increased pressure to the pilot valves 22, 23 and 24, cans` ing them to open wider and thereby reduce the steam.

input tothe turbines 12, 13 and 14. The feed water delivery rate is thus reduced and eventually sender-28 through the action of regulator 27 establishes affeed" water rate that is proportional to the steam output of' the boilers.

Whenthe pressure in. line 65 falls belowl 30' p.s,

the output pressure of regulator 27 to line 93 `will fall below 30 p.s.i. and may go to zero until the pressure differential across valve is restored to the minimum of 75 p.s.i. When the output pressure to line 93 and sender 28 is zero, bellows 125 of master sender 2S will adjust valve 140 in a direction to decrease the control pressure to pilot valves 22-24 causing them to decrease the discharge to drain. In that event the power cylinders increase the openings in the steam valves and thus the power input to the turbines is increased, The resulting output of the feed pumps will increase the feed water ow rate to the boiler A and reestablish the mni mum differential.

II. Boiler A the prime generaron-steam generation n boiler B increasing from standby If boiler A generates at capacity and the load on boiler B increases from standby, the differential across valve 6 will decrease as its flow opening increases. That decreasing differential causes transmitter 26 to decrease its output pressure to the valve 62a of transmitter 25. Since the output of transmitter 25 can never be greater than the output pressure of transmitter 26, the effect on regulator 27 and master sender 28 is to increase the steam input to the turbines and the output of the feed pumps. Thus the supply of feed water to both boilers will be at such a rate that the minimum differentials on valves 5 and 6 are maintained. If boilers A and B go to full capacity, the supply pressure to valve 62a of transmitter 26 will decrease to a minimum, say zero p.s.i., in which event the output of regulator 27 will be zero and master sender 28 will so control the pilot valves 22-24 that the inputs to the turbines are increased tothe extent necessary to provide the required ow of feed water to the boilers.

III. Boiler A on standby-boiler B the principal steam generator When boiler A is on standby and boiler B is the principal steam generator, the differential across valve 5 will be a maximum, say of the order of 150 p.s.i., or higher. Since that differential is so high valve port 62a. of transmitter 2S will be wide open so that the pressure output of differential transmitter 26 will pass through valve port 62a of transmitter 25 into line 65 to regulator 27. Under those conditions the control force to regulator 27 as received in housing 73 will be linearly proportional to changes in the differential across valve 6. Thus it can be seen that whichever boiler, that is, boiler A or boiler B is on standby or operating at full capacity, the system will automatically regulate the feed water supply by and in accordance with changes in the differential across the feed water valve having the lowest differential.

IV. Boiler alone generating steamboiler B off line When boiler A is operating alone and boiler B is out of'service, valve 25a may be rotated 90 clockwise thereby connecting valve 62a to a supply pipe 64 to which a source of compressed air at substantially constant pressure of say 60 p.s.i. is connected. Transmitter 25 will then operate in accordance with the dilerential across valve 5 and the source of supply of air pressure for the valve 62a will corne from an independent or auxiliary source indicated by the pipe 64. The transmitter 25 through the regulator 27 and the master sender 2S will in the case stated so control the power input to the turbines 12, 13 and 14 that the proper rate of supply of feed water to the `boilers is effected.

V. Boiler A a Iine-boiler B generating the steam load When boiler A is ofi the line valves 25a and 25b are rotated counterclockwise 90 whereby the output of transmitter 26 passes from line 63 through a branch line 63a through valve 25b to line 65 and thence to regulator 27. When this transfer has been made, the regulating system 12 will operate to maintain the pressure dilerential across valvey 6 at or above the preselected minimum of say 75 p.s.i. In other respects, the system functions to control the power input to the turbines driving the feed water pumps in the manner already explained.

If the character of the load supplied with steam by boilers A and B is relatively steady with no great searches or fluctuations from maximum to minimum load, the master sender 28 may be omitted and the output of regulator 27 may then be connected directly to the sending line 145. With that connection the steam then put to the turbines 12, 13 and 14 would be regulated directly by regulator 27.

However, where the boiler load on either or both boilers may be fluctuating drastically and the rate of iiuctuation is very high, then the master sender 28 is highly desirable because it is designed as shown to act more promptly and is more sensitive to changes in the pressure output of the regulator 27 and of changes in the boiler feed pressure in header 15.

Having thus described the invention, it will be apparent to those of ordinary skill in the art to which the invention pertains that various modifications and changes may be made in the illustrated embodiments without departing from either the spirit or the scope of the invention.

Therefore, what is claimed as new and desired to be secured by Letters Patent is:

l. A feed water supply and control system for a plurality of steam boilers, comprising a feed water line for each boiler, a supply header interconnecting said feed lines, a plurality of feed pumps connected to said header, a prime mover for driving each pump, regulating means controlling the power input to each of said prime movers, a feed water control valve provided with a positioner, for each feed line, each boiler having a water level responsive means for so actuating the valve positioner that the valve is opened as the water level falls and moved towards closed position as the level rises, a pressure differential responsive means for each feed line valve, each of which means has a signal supply input and an output control force means and Awhose output control force is proportional to the pressure difference across its associated valve, the supply input of one pressure differential responsive means and the output of another of them being interconnected so that the output signal of the one forms the input supply for another thereof, whereby a control force is developed that is proportional to and limited by the lowest of the pressure differentials across said valves, a regulator responsive to said differential control force for developing a corrective control force whose magnitude is proportional to thevalve of the diiferential control force, a master regulator responsive to the sum of thc water pressure in the supply header and to said corrective control force for developing and delivering a regulating control force to said prime mover regulators, increasing and decreasing values, respectively, of said master regulator control force causing the power input regulators to respectively decrease and increase the power input to said lprime movers.

2. A system as in claim 1 in which the corrective control force regulator is provided with means rendering it non-responsive to the output control forces of said pressure differential responsive means until said dilerential output control forces reach predetermined values.

3. A system as in claim 1 in which the master regulator alone controls the prime mover input regulator means so long as the value of the input signal to the corrective control force regulator isvkbelow a predetermined value.

4. A feed water supply and control system for a plurality of steam' boilers, comprising a feed water line for each boiler, an interconnecting supply header for said feed lines, a plurality of feed pumps connected to deliver to said header and feed lines, a prime mover for driving each pump, means responsive to a variable control force for,` vregulating the power input to said prime movers, a

control forces of said pressure dilerential responsive means being so connected that the output force of one of said pressure differential responsive means forms the signal supply input for another of said pressure differential responsive devices whereby a control force is developed by said another pressure' differential responsive device that is proportional and limited by the lowest responsive means being so connected that the output of one of the pressure dilferentials across said valves, a regulator responsive to the control force of said valve pressure difference responsive means whose input is limited by the output of the other and provided with rate responsive means and automatic reset means, for developing a corrective control force proportional to the change and rate of change of the control force of said pressure difference responsive means lhaving the limited input, a master regulator responsive to the sum of the feed water pressure delivered to said lines and the corrective control force of said regulator for developing and delivering a control force to the prime mover power input regulating means, the power input regulating means decreasing the power input to the prime movers in response to the increasing values of said master regulator control force and increasing the power input in response'to decreasing values thereof. I

5. A system for controlling the rate of supplyl of feed water to a plurality of steam boilers provided with separate feed water lines and a common steam header to which the steam space of the boilers are connected, comprising a iiow control valve in each boiler feed line, means responsive to the water levels in each boiler for opening and closing said valves in inverse relation to variations in such boiler water levels so as to maintain the level in each boiler substantially constant, a transmitter for each valve responsive to the differential thereacross for generating a control force proportional to said pressure differential, each transmitter havingan air control valve provided with an inlet for air supply and a pressure outlet, the pressure outlet of the valve of one transmitter being connected to the supply inlet of the other transmitter, regulating means controlled by theoutlet pressure of said other transmitter for developing a corrective control force proportional to the change and rate of change ofthe control force of said other transmitter, boiler feed pumps connected to the feed lines through a feed line supply header, steam powered prime movers for driving said pumps, means responsive to the Asum of said corrective control force and the pressure in the feed line supply header for developing a prime mover steam input regulating control force that varies directly with the values of said feed line header pressure and corrective control force, and said means responsive to said` prime mover power regulating control force for decreasing the steam input to said prime movers as said control force increases and increasing the steam input as said control force decreases.

6. A system according to claim 5 in which the range of pressure output of the said other transmitter is between zero p.s.i. and the value of output pressure of the transmitter which supplies it.

7. Apparatus for supplying feed water to a plurality of steam boilers each having a feed water line, a valve in each feed line across which a pressure difference develops with ow of feed water therethrough, boiler level responsive means for each boiler for controlling the flow opening of each valve in inverse relation to variations in the .boiler water level so as to increase the ow opening as the said level falls below and to decrease said flow opening as the level rises above a predetermined level in the boiler, a feed water supply header connected to said feed lines, a feed pump for supplying Water to the header at controllable rates, an adjustable power input prime mover for driving the pump having control means, means responsive to the pressure difference across each valve, each said pressure difference means having a control element provided with a supply input and a signal output means for developing a signal proportional to said pressure difference, means so connecting the control elements of said feed valve pressure difference means that the signal output of one of the pressure dierence means constitutes the supply input for the other feed valve pressure difference responsive means, whereby the signal output of one of them is caused to be proportional to the pressure difference across its water feed valve but which is limited in its maximum output value to the value '.of the signal output of the other, means responsive to the sum of the feed water pressurefin said header and the signal output of the pressure difference means whose maximum signal output is limited by the output signal of the other feed valve pressure difference means for developing a regulating force for said power input controlling means,

the power input controlling means decreasing the power j input to the prime mover as the regulating force thereto increases and increasing the power input as the regulating Aforce decreases. Y

References Cited in the tile oftliis patent Y y UNITED STATES PATENTS` Great Britain Oct. 6, 1942 Bristol Mar. 6, 1934

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