US2199214A - Liquid heater - Google Patents

Description

.April 30, 1940.v

H. VORKAUF v v LIQUID 'HEATER Filed may 17, l19:54

Wma-.Im

Avr-romainsr Patented Apr. 30,`

PATENT I olf-Fica uoUm Inman-n` Heinrich Vorkanf, Berlin,

La Mont Corporation, poration of New York "nomma (ci, 12a- 406) This invention `relates to feed preheater or v.apprit-1mm my 17,1934, seran rn ce economizer installations4 in connectionwith boilers or evaporators of the type in which the iiuid to be evaporated is .positively circulated. The in- 5 vention is particularly concerned with the method' and means of .maintainingflow of the uid through the'preheater or economizer. In the operation of boilers and evaporators frequently the feeding to the boiler or the,-

evaporator of vthe fluid to be evaporated, that is"- the make-up feed, is subject to variations corresponding with variations in the load on the boiler or the evaporator, or such variations may be due to other causes. In boilers for generating steam l5 from water, forfexample, the feeding of the makey up feed Vwater to the boiler commonly is reguw lated by a valve or other ow control device which is actuated from a water level regulator which substantially determines the amount of water to be maintained in the boiler and which is broughtintooperation upon a variation of this amount of water. Feed control,'however may be made dependent upon other factors such as variations in the temperature or in the quantity of the 3.5 steam delivered from the boiler. Suchmethods of feed control also have been utilized in connection with economizers or preheaters vthrough which the water or the fluid -to be evaporated is passed in order to heat the fluid before entering 3 0 the boiler or the evaporator'and to reduce 'the temperature of the heating gases or other heat vehicle so as to improve the eiliciency ofthe plant. v

In such preheater or economizer apparatus it is recognized that when the flow of the fluid to be heated is stopped by thecontrol deviceactuated `in accordance with the particular condiv tions-in 'the evaporator or the boiler, the preheater or economizer ,is subjected to adverse conditions. For example, 'if the feed is shut off at a time when the heating surfaces 'of vthe economizer are subjected to relatively hignhean, steam or vapor vmay be generated upon these sur.

faces or dissolved or entrained air may be libermade for the circulation of the fluid in the economizer so that the steam or vapor or the air may be freed from the water, this vapor'or. y

ated in the water or iiuid. lUnless provision .is .a

New York. N. Y., a ool'- N. uam

corrosion of such Moreover, 'the evaporationof the uid ,or 'water which carries vapor or air is avoided, continually wetted Vandy overheating, corrosionr is reduced o r.

and theydeposition of the scale-formingv n'ia'te'-- rials uponthe surfaces isi also prevented bythe.

thereby prevented from force of the ilowingiluid.

The present invention'yhas Afor its object .thc-A` prevention of these deleterious conditions'in' 'preheaters or economiaers. which are used inv connection with boilersor evaporators of .the type in which a positive circulation of the water or Voil-z.'A

the fluid vbeing heated'and evaporated is maintained. 'I'his positive circulation ofthe water may be accomplished inV a closed circuit -in'which N a positively acting nuid circulating means. such as a pump, may be connected also heating surfaces or heating elements for the Igeneration of the vapor or the steam are connected, to which and through which heating'surfaces or elements the positively acting fluidcir- Y .f

vculating means causes to iiow water or the fluid being heated. In such a boiler or vevaporator utilizing positive-circulation of the iiuid'beingf evaporated, accordingtothe-invention, a connecV tion vis so arranged between lthe circuit or conduit through which the positively acting circulating means forces the nuid and the conduit through whichthe makeup 'feed is delivered to the preheater or economizer and in-such relation $5 to the device controlling the feeding of the makel Vup feed to' said boiler or evaporator that, when the make-up feed is shut oif and, therefore, when the flow' of the water o r of the fluid to be evaporated. through the economizer or preheater is 40 stopped, water or iiuid` from said circuit may be 'delivered tothe preheater or economizer for flow 'therethrough so as to maintain lthe temperature 'of thev economizer at asumciently low degree to and the .deposition of `cicale-forming. materials re'- ferred to above. v v` I While heretoforeit` has been proposed to mainy tain circulation of the water through an econo- .mizer by .means offa water circulating device such as a pump, ina circuit in which, as-a. separate vcircuit'auxiliary toa steam generating or evaporator plant, the'pump and theeconomizer Felements are connected, according' to the presentv invention a connection is made. from the circutubes or heating scale-formingv materials, leaves the Vscale'deposited upon these surfaces; When, however. acontinuous now of -the'uid to be heated 6 is maintained, the vacc ulation of-steam 'or .g

.the heating'surfaces' eiiiilinated.V

and inl which circuit latingcircuit of the generator or evaporator itself to such a point in the path of the flow of the uid to the economizer as will cause water or the fluid being circulated to be delivered from the positively acting circulating means of the steam generator or the evaporator through the economizer to maintainthe fiow offluid therethrough. Whilesaid known installations have the advantage of maintaining the circulation of the water within the economizer itself, an aux iliary circulating device is required and the separation ofthe steam or vapor from the water, if generated, must be provided.

utilized to force the water or the fluid through vthe economizer, any steam or vaponfrmedbeingj-f1 carried with the uid into the steam and vsatery separating space of the steam generator orthe evaporator itself. l

Preheater installations for steam generators with forced circulation also heretofore have been known in which water is delivered through the preheater by the circulating pump `in order to prevent too low a temperature in the economizer.

In such a preheater installation it is necessary,

with a large amount of feed water flowing through the economizer, to deliver a large amount of` In a steam generator or evaporator having a closed circuit, by means of the positively acting circulating device the waterl or the fluid being evaporated is circulated through steam or vapor generating elements, which elements are connected to a steam and water separating space, such as a drum, and the water separated may be returned to the water circulating device for recirculation through the circuit. In such a case or in such apparatus as include a steam and water separating space, the economizer may be arranged to discharge the heated feed water or the heated make-up fiuidvinto such a space, any steam or vapor generated by evaporationv in the economizer beingl also. discharged to and separated in said space from the water, the water or fluid heated in the economizer being mixed with the water or fluid'of the circulation circuit for flow therethrough under the action of the positively acting circulating means or pump.

In such a plant within the scope of the invention there may be provided, as stated above, from the discharge of the circulating means or pump a connection to the pipe or conduit through which the feed is delivered to the economizer.v Such a connection is made ata pointbetween the water or fluid inlet end of the economizer and the controlling device, such asa valve, which controls the feeding of the make-up water or fluid to the economizer. In said connection from the circulating means to the feed conduit or pipe also may be included a valve or other device for controlling the flow of fluid or water from said circulating means to lsaid feed pipe. By suitably In the arrangef'f ment utilized in the present invention such aux-1 iliary circulating means are no, in ec'essaryasf the positively acting circulating device"niay'be" arranging'and connecting these valvesy or other fluid control devices in relation to each other and to the means actuating the feed control device subject to the variations in a selected vcondition within the steam generator or evaporator,

such. as the water level or the temperature, as referred to above, fluid may be delivered by the circulating device to th'e economizer when the l feed control device is shut off or when the flow therethrough isv reduced. On the other hand, when the make-up feed water or fluid to be evaporated is again to be delivered to the steam generator or the evaporator and the .feed control device or valve is accordingly open, the control 'devi'c'e'or valve in said connection from the circulating means or pump may be closed or throttled so as to stop or reduce to the desired degree the iflow` of the lwater or of the circulating uid from thecirculation circuit of the steam generator or the evaporator. f

It thus will be understood that, whereas the protection of the economizer or preheater is accomplished by the arrangement and1 method of the invention during the time when the feeding of the make-up feed water or fluid to be evaporated is stopped or so reducedas to cause the deleterious conditions to be present inthe economizer, the'invention also provides that when the feeding of the water or of the `fluid again takes place, the circulation of the waterfrom the generating circuit is stopped or is reduced to any desired degree. It thus will be clear that the function of the economizer or the preheater, as a fluid heating apparatus for improving the emciency by abstracting heat from gases or other heat ve- 'hicles which otherwise might be wasted, is maintained.

The invention will be more clearly understood from a description of the drawing in which:`

Figure 1 shows a steam generating'plant with an economizer and embodying the features of the invention.

Figure 2 shows a section through the make-up feed valve. l

Figure 3 shows a section through the valve controlling the flow of circulating water to the economizer.

Figure 4 shows a` modification of the control apparatus utilized in the invention.

Figure 5 shows another modification of the control apparatus of the invention. y

In Figure 1 is shown a boiler plant having a furnace space I enclosed by furnace walls 2. Fuel burners such as, for example, those which may bum powdered fuel or those which may burn oil, are shown at 3 in the rear wall 4 of the furnace.

y In the space above the furnace constituting a Y passage for the gases from the furnace and enclosed by the upper portions'- of the walls 2 and I and by the front wall of the structure are mounted extensions I2 of tubes I0, which in the furnace, extend along the face of the walls 2. The extensions I 2 of said tubes are arranged in serpentine form in each half of the space to form generating plant illustrated, are formed as con-y tinuous tubes which, at theirlower ends, are connected to headers I4 and I5. It will be noted that some of the tubes from the header I4 extend downwardly alongr the wall 2 and along the botillustrated in Figure I may be of the type in which tom wall of the furnace and upwardly along the opposite wall 2 to` form part of vthe bundle of tubes onthe opposite side of the gas space. Others of the tubes extend from the header I8 in like liv arrangement to form part of the bundle of tubes I2 on the opposite side of the structure from the header I5.

' The discharge ends of the tubes in the installation shown-in Figure 1 are connected at the boti0 tomvportion of a//drum or steam and water sep-i arator I8 within'which is mounted a bame 28 be tween the' walls of which the steam and water may `be discharged upwardly against adee'ctor 2|, the water being thrown to either side of the 15 name zc'and the .steam being liberated into the space 22 of the drum I8.

From the water space of the drum I8 a connecs. tion is made' by .the pipe 24 to the suction of the circulating pump 26 suitably mounted'and driven ailuid pressure is produced by the steam or vapor contactingthelement of the regulator,

whichsteam o r vapor is condensed whenr the water or fluid in the drum I8 rises and vcorre- 'spqndin'giy .the water rises within said-element in contact therewith,- thecondensation reducing the pressure within the element.' Conversely 4a Ifallin the water, level increases the-steam contact with the element and .evaporates more fluid -within the element, thus raising thefpressure.

The increase or decrease of the pressure is transmitted through 'the pipe or lead 64 to the diaby 'a motor or otherepower means 28. The dis- Icharge of the pump is connected by thepipe- 88 and its .extension 3| tothe headers I6 and I4 to. which, as described above, the .water inlet ends of the tubes are connected. Said water inlet ends may be provided with wate`r restricting'devices"` or orices to limit the amount o f water entering each tubedn the manner and for the purposesv of steam generation as described in the United States LettersJ Patent No. 1,884,979 granted. October 25, 1932. v 'Ihe p ump may draw the water from thewater space of the drum I8 through thev pipe 2 4 a.nd

deliver the water to the headers I 4 and I6 from `The water llevel regmator .I s "cerates', in 'the usual'man'ner underv variation of thewater level with load von the steam generator and many different devices may for this purpose. `In .the particular device illustrated, as will -be clear c -fromFlgure 2, the'fluid pressure which is brought to bearon thiediaphragm 52 through the lead 64 connected tc tl 1e waterlevel regulator 46 causes the diaphragm to bear uponv a flange 66 at vthe upperend of the stem 38.0f the valve SII and acts againstthejpressure of the spring 68 tending to closethezzvalve. The `stem 38 passes through a stufiing'bdx 82v and carries at its lower extremity the valve discs-64M a balanced valve, the discs 64 bearing, vwhen closed, upon seats-86 and 68 of thevalvestructure in the usual manner.

'which the water is distributed into the vdifferentv tubes .I 0 connected tothese headers. The steamf as it is generated flows through the tubes together with the water and is discharged into the .drum I8, the excess water being separated in the drum I8 to be drawn again by the pump for delivery to' 0' the headers 'I4 and |6..-1The circulation of the water thus occurring through the steam generaring tubesv and through the circuit is produced,

In the arrangement shown vin Figure 1 'said economizerl tubes have one end thereof connected tothe drum I8. Conveniently, as illustrated in the drawing, these ends. of ,the tubes may bel connected to the space between the bailles 28 vsc that any steam or-'vapor discharged from these `economirer tubes may be separated fromthe water dis'- w charged therewith in the manner. vdescribed above with the steam generating tubes,A the other ends being connected-tc headers 36 to bear upon the diaphragm 12 of the valve 10 `acting through the flange 16 and the stem 18 vagainst the spring 60, the valve discs 84 are moved in connection and31.

'rc the .headers '3s-ane a1 through ajpipe an and its extension 4I the feed' pump 42 cr'other feedy pipe 40 lis ing device may be connected. '11n-the, inserted la. feed controlling device or `valve 50 and delivered to the drum.

Thus it 11 be clear that when the `waterlevei lrises" in the drumi condensation will take place in the element ofthe water level regulator 46 and the pressure inthe lead 54 and, therefore, the

vprsure uponfthe diaphragm 52 will be reduced.v

'Ihe spring 6 0, acting against this pressure, therefore, may act to throttle or close the valve $0 so that its 'discs 64 approach or become seated upon the seats and 66. Conversely, when the water level in the drum I8 fallsthe fluid pressure withinthe .element o f the water level regulator 46 is *raisedv and pressure is brought upon vthe diavphragm' 52. When this pressure becomes'sum-v cient toovercome the spring 68 the valve discs 84' are moved away fr om their seats and the valve is opened permitting fluid or water from the feed pump 42 to be delivered through the pipe 48 and its extension 4I to the headers 36 and 31 of the economizer. From these headers the water then isforced through the tubes 34 of the economizr Also .connected to the lead 54 is discharge pipe 30 from the circulating pump and the pipe 46, being connected to said pipe 40 at a point thereon between the headers 36 and 31 and the control valve 18 in the pipe 1I connected between the the valve SII.v As will be clear from Figure 3, the

construction of the valve 10 may be substantially the same as that of the valve 58 with the exception that thevalve discs and their -seats are in reverse relation'to the steam and'its motion/to that of Figure 2. Thus, when pressure is brought against their seats 85 and 86. Conversely, when which may be of any convenient type. Inv the" particular embodiment shown in thev drawing the? valve 50 is connected tc a water level regulating device 46 suitably mounted onf and connected to the steam and water spaces of the drum I8'to be subjected to variations in the water level within vsaid drum.

The water level regulator diagrani'xnatically pressure is'relieved from the diaphragm 12 the valve discs 84 will be lifted from their seats 85 and 86 by the action of the spring 80, thus permitting water to flow from the discharge-pipe 38 through the pipe 1I to the feed pipe 40 and to be delivered by the pump 26 .Y 'a AL through.y 'It will, therefore, beunderstood that. `when the flow of the feed water through the economizer is stopped or reduced by the closing of the valve 60 under the action of the water level regulator 46, circulation of", water through the economizer is maintained by the opening of the valve 10, permitting flow of the circulating water 'to and through the economizer under the action of thecirculating pump. l

Instead of the water level regulator'of the type utilizing an element within which a'. fluid pressure is generated, as illustrated in Figures 2 and 3, mechanical water level regulating apparatus having a float mechanically operating a valve may be used, as shown in Figure 4. As shown in the gure, a float 90 mounted at the end of a lever 6| may be positioned within the drum I8. Thelever 9| may be pivoted upon a shaft 92 extending through the wall of a box 93 mounted upon the drum I8. At the outside of the wall of the box 93 yis the lever 94. Connected to the lever 94 is a link 95 having its other extremity connected to the stem of the valve 60. Also connected to the lever 94 is the upwardly extending link 96 having its other extremity connected through a reversing lever 91 pivoted at 96. To the opposite extremity 99 of the reversing lever by means of link |00 connection is made to the stem of the valve 10. 'Ihe valve 60, as in the embodiment previously described, is located in the feed line to the economizer, the valve 10 being located in the connection between the discharge pipe of the circulating pump and the feed line, as above described. In the arrangement shown in'Figure 4, thev valves 50 and 10 may be alike.

It will be apparent that as the water level rises in the drum I6 the lever 94, acting through the'link 95 will press downward the stem of the valve 50. The valve 50, therefore, should be so constructed as to close under this motion of the mechanism. When the float thus -moves the lever 94, through the link 96, the lever 91 and the link |00, the stem of the valve 10 will be raised. As in the particular arrangement being described the valve 10 is like the valve 50. the valve 10 will be opened upon this motion of the mechanism. It will be clear, therefore, that when the water level rises to the point where it is necessary to shut `olf the feed by closing the valve 50, at the same time the valve 10 will beopened and flow of the water through the pipe 1| may take place to thev economizer as described above.

While in the `illustrated embodiments of the control devices the valves controlling the flow of the feed and of the circulating water which is by-passed from the discharge of the circulating pump to the economizer are actuated by a single water level regulator, each of said valves may be controlled by separate water level regulators or may be actuated separately or together generation.

is stopped or is so reduced as to cause the deleterious conditions above 'referred to to rise, the water or circulating fluid is by-passed through the economizer under the action of the circulating pump to maintain sufficient flow in the economizer to prevent such conditions. And

conversely, when the normal flow of the feed.

feed water through the economizer.

water through the economizer or sumcient flow` to prevent said undesirable conditions occurring is established, then the delivery of the circulating water to and through the economizer may be stoppedgor so reduced as tosccure the desired economizing effect obtainable with the flow of In some cases it may be desirable to maintain a flow of the circulating water through the economizer in addition to the flow of the feed water in order that a sufciently high velocity of flow in the tubes or over the surfaces of the economizer may be maintained.

Instead of the control valve 10 in the pipe 1| a back pressure or check valve may be utilized, as shown in Figure 5, which permits flow only in the direction from the discharge pipe of the circulating pump toward the feed pipe 40. When a normal amount of feed water is being delivered to the economizer the resist- Vance in the economizer corresponding with such an amount of flow may be sufilcient to require a pressure' of the feed water in the feed pipe 40 which is higher than that in the discharge pipe 30 of the circulating pump. It thus will be seen that a back pressure valve or a check valve |20 arranged at 10 as just described, will. prevent flow of the feed water through the pipe 1| toward the circulation circuit and also ilow of the .circulating Water toward the feed pipe 46 will be prevented by the excess pressure of the feed water. Such a valve |20, however, may open when the pressure in the feed pipe falls to a point below that of the pressure on the other side of the back pressure valve 20 caused by the circulating pump. Flow then may take place from the circulation circuit under the action of the circulating pump through the check valve |20 to the economizer. In this embodiment a check valve |22 may replace valve 50 in pipe 40 to prevent flow of the circulating water in the feed pipe 40 toward the pump 42 or the supply when the pressure of this feed supply falls.

In order more easily to control the conditions of pressure in the feed pipe 40 or in the by-pass pipe 1| which may be utilized for the purposes just described, orice plates may be installed at ||0 in the feed `pipe 40 and at ||2 in the bypass connection 1|. 'I'he oriilcey ||0Vadds to the resistance of the economizer itself which must be overcome by the feed Water pressure and thus the pressure of the feed Water may be maintained -sufficiently high under normal feeding to be greater than the pressure in the discharge pipe 30 of the circulating pump. 'I'he orifice provided by the plate ||2, however, may be utilized to limit the amount of water which is delivered by the circulating pump to the economizer.

The arrangement shown and described vabove in which the economizer tubes discharge into the space between the baflles 20, into which space also the steam generating tubes discharge the mixture of steam and water, has the advantage that in the normal operation of the economizer and steam generating plant the feed water may become f fully heated to the steam generating temperature. Moreover, when any steam is generated in the economizer either during the normal feeding of the feed water or when the feed water is shut oif and the circulating water is passing through the economizer, the steam and water mixture thereby produced,`if any, will have v feed water to said preheater.

which the water is forced for circulation in the steam generatoror evaporator to flow through the economizer so as to maintain a flow through the economizer for the purposes described. Y

Having thus described my invention I claim:

l. Steam generating plant comprising a steam generating circuit in which the Water being evaporated is circulated by a positively actingA circulating means, a feed lwater preheater connected to discharge into said circuit the feed water after being heated in said preheater, means for delivering circulating water from said circuit to said preheater and causing it to fiowtherethrough, and means for controlling the ow of said circulating water so, delivered, said controlling means being constantly and directly actuated in accordance with variations in the rate of flow of feed water flowing through the preheater so that flow of water through the preheater in amount sufdcient to protect said preheater is maintained with varying amounts of feed water delivered to the preheater.

2. Steam generating plant comprising a steam generating circuit in which the water being evaporated is circulated by a positively acting circulating means. a feed water preheater connected to discharge into said circuit the feed water after being heated in said preheater, aA

connection between the discharge of said circulating means and the water inlet side of the preheater, a flow controlling device in saidconnec tion, means for conducting feed water to said preheater, a device controlling the flow of feed in said conducting means, and meansconnected to said devices for actuating said flow controlling device in said connection in a predetermined relation to the operation of said device controlling the flow of feed to said preheater.

3. Steam generating plant comprising a steam generating circuit. in which the water being evaporated is circulated by a positively acting circulating means, a feed water preheater connected to discharge into said circuit the feed Water after being heated inl said preheater, a connectionvbetween the discharge of said circulating means and the water inlet side of the preheater, a flow controlling device in said connection, means for conducting feed water to said preheater, a device controlling the flow of feed in said'vconducting means, and means for actuating -said iiow controlling device in said connection, said actuated means being connected to and being arranged in such'relation to the operation of said devicel controlling the flow of feed water to said preheater that flow of circulating water is caused through said connection to said preheater in inverse relation to the ow of 4. Steam generating plant comprising a steam generating circuit in which the water being evaporated is circulated under a pressure produced by a positively acting water circulating means, a feed water preheater connected to discharge into said circuit the feed water after passing through said prereater, means for delivering to said feed water heater the 4feed water under s 1*/ I l s pressure sufficient to produce flow lthrough the preheater, and means constantly responsive to variations in said pressure for causing circulating water to flow from said circuit through said'preheater when the pressure of said feed water is reduced to a predetermined amount inl relation to the pressure of said circulating water.

5. Steam; generating plant according to claimA fi in which flow restricting means are provided for modifying the now producing pressure .rela- 6. Steam generating plant comprising a steam generating circuit in which the water being evaporated is circulated by a positively acting circulating means, a feed water preheater connected to discharge into said circuit the feed 'water Lafter being heated in said preheater. a

connection between the discharge of said clrculating means and the water inlet side of the preheater, a valve in said connection, a conduit carrying feed water to said preheater, a-valve in said conduit, and means connected to said valves for opening said valve in said rconnection upon closing operation of said valve in said feed carrying conduit. s

7. Steam generating plant according to claim 6 in which the operation of the feed valve is dependent upon a predetermined condition in the steam generator related to the requirement of water to be fed into the generator.v

8. Steam generating plant comprising a steam generating circuit -in which the water being evaporated is positively circulated, a feed water preheater connected to discharge into said circuit the feedvwater after passing through said preheater, means for causing water from said circuit to flow through said preheater, and means actuated yin accordance with variations inl the volume of `water within said steam generating circuit and arranged to vary. constantly in direct yrelation to variations in said volume. the flow of water from said circuit through said preheater. 9. A heat exchanger plant comprising a heat exchanger `of the type in which a fluid is positively circulated .in a circuit, a duid heater of the type in which the fluid being heated flows therethrough, said fluid heater being connected to discharge tosaid circuit the fluid; heated therein,I and means constantly and directly responsive to variations in the flow of fluid to said heater' for causing circulating duid from isaid'circult 'to flow through said fluid heater to` maintain ilow of fluid throughsaid fluid heater upon variations of the delivery of the fluid to be heated therein.-

10. Steam generatingv plant comprising a steam orated is positively circulated, a feed water preheater connected to discharge into said circuit the feed water after passing .through said pre-- heater, and means `constantly and directly iactuatedin accordance with variations in the vilow of the feed water for causing water from said circuit to flow through said preheater when dow of the feed water through said preheater is reduced to a predetermined point.

11. In a steam generating plant comprising a steam generating circuit in which the water bef generating circuit in which the water being evapv 'lov connection for by-passing water from vthe discharge side of said circulating means to the inlet side of said preheater anda ,check valve o f said preheater, whereby water from the circulating means is by-passed to the preheater only when the feed water back pressure on said valve is less than the pressure causedby said circulating means.

12. In a steam generating plant comprising a steam generating circuit in which the water being evaporated is circulated by a positively acting circulating means, a feed water preheater connected to discharge into said circuit the feed water after being heated in said preheater, a connection for by-passing water from the discharge side of said circulating means -to the inlet side of said preheater, a check valve in said by-pass opening toward said inlet side lof said preheater, whereby water from the circulating means is by-passed to the preheater only when the feed water back pressure on said valve is less than the pressure caused by said circulating means, and throttling means in said connec- 4 in said by-pass opening toward said inlet side tion for lcreating the desired pressure relations at saidcheckvalve.

13. In a steam generating plant comprising a steam generating circuit in which the water being evaporated is circulated by va positively acting circulating means, a feed water Vpreheater connected to discharge into said circuit the feed water after being heated in said preheater, a

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