US2378760A - Steam heating system and control valve therefor - Google Patents

Description

June 19, 1945. A

n w. T. FERGUSON STEAM HEATING SYSTEM AD CONTROL VALVE THEREFOR Filed April 25,l 1940 INVENTOR WARREN' 1' FERGUSON BY ATT RNEY duce a `W cost `of the cycle, referred becomes available, While `cycle may be considered as occurring at the time "f cessation `of operation `thecessation of the normal supplyof steam.

Patented June 19, `1945 STEAM HEATING SYSTEM AND f VALVE THEREFOR i `Warren T. Ferguson, Waban,` Mass., assignor to Anderson Products, Inc., Cambridge, Mass., a corporation of Massachusetts Application Atril 25, 1940, serial No. 331,506

CONTROL `2,2 claims. (ci. 237-9) This invention relates to heating systems, and includes both the apparatus andmethod.

'I'he invention relates particularly to steam heating systems and may be used in connection with both the `so-salled one pipe or `tvvo pipe systems. i

1 @ne of the objects of the `invention is to prosteam heating system which Will have the attributes of` proper distribution of heat and `economical operation. i Another object of the invention is to provide a steam heating system arranged to operate so that the rate of heat transfer from the steam to the radiators will the heating cycle, and further to provide means for controlling the heat output of the radiators whereby the temperature of the spaces to be heated "may be held more'nearlyuniform than heretofore. l i

A further object of the invention is to provide, in a steam heating system, allof the benets of the so-called `vacuum system, coupled with the additional benefits that may befderived from the use with avacuum system of a vacuumcontrol valve;

tIt is Well understood by those `skilled in the steam heating art that, in vacuum systems which toward the end of the "heating cycle have a rather `high vacuumtherein, it is desirable at the start of the next heating cycleto reduce the pressure in the system to atmospheric quickly so that the newly'created steamwill travel to the several radiators in accordance with the setting ofthe vent valves thereon.

`A heating cycle Vas used in connection `with this invention is intended `to mean one complete cycle comprising two parts; inst, the ring part to `hereinafter as the firing cycle; and secondly, the olf p art of the cycle,

referred to hereinafter as the off cycle.

f 1 The commencement fof theringcycle may be `considered as either the time heat is supsteam is generated,` while inthe second, steam will be supplied immediately.

For the purposes of this application, unless i otherwisenoted, reference to 4the commencement be relatively high during plied to the boiler in quantities suicient to pro duce steam thereafter or the time steam actually the `end of the firing of the heat source or In the ordinary situation, a room thermostat burner, an automatic stoker or other heating Isource, or the thermostat may cause theopening ofa valve connected to a steam source. In the first situation, there will be a lapse of afew minutes between the times heat is suppliedand of the firing cycle may be taken to mean the startv of operation of the heatV supplying source, whether or `,not time elapses` thereafter before steam becomes available. Q i Throughthe use ofl a vacuum control which operates automatically at or about the commencement of eachheating cycle, coupled with the use of adjustable venting valves on the radiators, it is Well `known that steam distribu` tion ,can bei, adequately controlled so that cold rooms willreceive greater quantities of heat than warm rooms, `all of which results in controlled heating of the building. i t

In the ordinary vacuum system, the vacuum that is formed during the off cycle is `dependent solely upon the degree :of tightness of the system and the time that elapses before theroom ther-` mostat calls for additional heat. In the average case, the negative pressurethat will develop in a` system after the discontinuance of the heat supply and prior to the commencement of the next cycle Will be substantial. C

, Experiments have shown that, as the vacuum ina system increases, the heat content `of a given `volume of steam decreases, with the result that the amount of heat that may be `transferred to radiators by vapors under a large negative pressurefis so small that the radiators practicallycease to have `any effect in maintaining the room temperature.

A further object of thevinvention, therefore,

`isto provide `means for and a method of `heating in which, as long as there is heat available from the heat source during'any cycle, the pressure in the system will be maintained at a point where the heat content of the steam will be such that` the radiators, during the off cycles, will give oif heat in sufficient quantities to ap preciably assist in the maintenance of room. temperaturet `AA further` object is to `provide in addition a relatively low cost vacuum `control valve which will operate automatically under the control of system `temperatures and pressures and which will come into operation to introduce atmospheric pressure to the system prior tothe distribution of steam to the radiators on the next cycle.

. In effect; therefore, `it is the object of thisr invention to `generally improve the quality of the results thatimay be obtained from steam heat- `The equipment involved does not Russian valve, y

uum control valve vused in connection with thisl system' and which brings about the indicated operation.

Referring to Fig. l, in which' is shown a typi- 'cal one pipe steam heating system, although it should be understood that the invention will work equally well in connection with a two pipe system, there is provided a steam boiler 2 and a source of heat 4, which in this case is shown as a typical gun type oil burner. However, any other automatically controlled steam source could be Aused. Extending from the boiler is the steam main, which branches-off in the risers 8 and Il) to connect withradiators l2 and I4 which are positioned inthe enclosed spaces to be heated.

.On the radiatorsl l2 and vI4 areventing Valves or Vents rI6 and I8 of the customary and wellknown vacuumy type. By that it is meant that the valves are of the type whichyent air from the radiators upon the entrance of steam to the latter, but which'automatically close through the operation of a vthermostatic element within the valve when thesteam arrives thereat and thereafter remain closed while a negative pressure prevails in the system. Furthermore, these valves are preferably adjustable so that the rate atfw-hich air is vented `from the radiators may be Varied. A Valve suitable for use in this connection is shownin the patent to Lasher et al., No.f2,163,909. The vacuum type Valves I6 and I8, above referred to, are customarily constructed to close under conditions of negative pressure that may develop following the'end of a heating cycle, whether or'not they'havebeen closed by heat during Vthe heating cycle. This feature is necessary because it sometimes happens that the controlling thermostatwill operate to cut oi the supply of steam befcre'all of the radiators have become heated.

`Positionedon main 6 is the vacuum control Valve which is shown'in detailiniFig. 2 and which will beirnore particularly described'hereinafter.

The particular location 'of vacuum control `Valve 20 is relatively'irnmaterial except that it should preferably be some place where steam supplied after commencement of the firing cycle will reach it indue course to cause it to close. In the ordinary case, the vacuum control Valve may be positioned at any convenient place on the main and may take theplace of a main vent.

The operation of oil burner 4 is under the control of a room thermostat 22 of the usual type,

which, -upon increase or decrease of room temperature beyond'predetermined limits, operates to stop or startthe oil burner." This is accomplished through the use of well-known electric circuits, and in this instance theoperation is shown diagrammatically through the use ofa relay 24'which operates: to open or close the circuit to they oil burner, depending upon the requirements called for by the thermostat 22.

`Referring-now to Fig.=2, the construction `of the vacuum control Valve 20 isas follows. The

f, 46 carried in turn by imposed upon it by The upper end of shell 34 is closed except for port .42, which is constructed so as to include a` valve seat at 44.

`Mounted within shell 34 is a thermostatic float an expansible bellows 48, which bellows is supported by a hollow stem 5U designed, through the mechanism disclosed generally at 52, for limited vertical adjustment.

On the top of oat 46` is mounted .a valve pin 54 which can make airand water-'tight engagement with' valve seat 44. -Thermostatic float46, containing a small quantity of volatile liquid such as alcohol, is shown in its contracted position in which the bottom 56 thereof is curved upwardly; Upon the application of sufficient heat to this float, the volatile `liquid will vaporize, forcing bottom 56 outwardly, which will result in upward movement of the float body and valve rpin 54 .to cause engagement of the latter with valve seat 44. If water should `fill theshell, the float 46, being buoyant,will rise to close port 42, preventing leakage. The oatis Vdirected in its movement by guidei51.

The expansible bellows 48, madev according to usual bellows construction and of a wall thickness great enough to give the` desired characteristics, is mounted on andsealed to a circular .base plate 58. Extending upwardly through the center of the base plate is the support which is fixed with respect to vbase plate 58 and extends upwardly la suitable distance so that the upper end-60 of bellows 48 may rest thereagainst. In this manner, support 50 acts as a stop to prevent further collapse of the bellows under the Aload thermostatic oat 4B. It will also be noted that support 50 is hollow, `as at 62,

the oriceprovided thereby extending from the atmosphere to the interior of the bellows. Be-

I cause'of this construction, the pressure within the bellows is at all times atmospheric. Support50, when initiallyadjusted within base plate 58, is set so that the upper end `6l) of the bellows presses thereon with greater or less vforca-.depending on the negative pressure within the Vacuum control valve at `which it is desired to cause initial expansion of the bellows.

In order to adjust the normal clearance between lValve pin `54 and valve -seat 44, support 50 is made adjustable with respect to thebase -26 throughY the Vmechanismgenerally shown at 52, `which in .particular consistsv of :a sleeve .-.64 threaded externallysfor adjustable engagement with the base andk internally for adjustable engagement with support 50. Secured against the upper end of lsleeve- 64 is a `splitiwasher 66 held in position by the collar 68. Washer-66.V extends about support-50 and is located within-the .confines of the short circumferentiallyiextending groove fill.` It is obvious that. by thisarrange- .mentl support 50 may be screwed up, and ydown within sleeve y64 a limited amount. To prevent leakage suitable washers andra, glandnutare pro- H vided at 12.

Through Vthe provision' of theadjusting mech- I thevaive 'than would be A84 is mounted. For V86` in located position f 2,378,760' comprising the' valve pin VS4, thenmostaticflo t4`8 y bellows 48, may be adjustedvertically. It is apparent that port42 will be closed or opened` and by expansion' or .contractionfofthe Ioell'owsde-` pending upon` lthe relation vof e e the negative pressure ofthesystem to the adjustmentof the-valve. That is to say, if the valve is adjusted downward-l ly te increasethedistance betweenvalve pin `54 and seat 44, it will require a greater negative pres-y sure` to` elongate e bellows e 8N" suiliciently" to close the case ifyalve pinl 54 `vfvereadjusted toa lessopenposition. "'I'hisassumes, of course, that float `46 is 'inl contracted position atthe time.` e V 1 Mounted elsewhere on the base is a second shell 14 ordinarily of smaller size than shell"34. Both shells are, ofcourse, nipple 28 through a common connecting passageway, although itis to be understood that separate connections to the steam maincould be provided. The intent is that both shells shall be subject to whatever effects `may be present within the steam main.' i

,"'rhe` sneu 14, through a suitable washer 1s .and nut'IB, isheld in position in the same water`, air` and steam-tight manner asshell 34. A port 8U to theatmosphere atthe upper'endof shell I4 sconstructedto provide a valve seat`82.` Port e A80 isnormally closed through engagement of ai valve pin 84 `with valve seat 82, andthe parts are maintained in this condition through the use of a spring 86 which exerts a continuous upward pressureagainst aplug 88 on which valve pin the purpose of holding spring ment for the spring pressure, a `spring stem `90, with a spring supportingcup 92, is `in threaded engagement with baseY 26 and has its upper end extending a limited distanceinto the lower end of spring 8U. Stem `90 is, of course, in fluid-tight relation to` the base, andif necessary,a suitable packing arrangement of ordinary construction could be added to insure that no leakage could occur. Ordinarily, in the eld, stem 98 is soldered into place, eliminating further adjustment, as` a suitable maximum negative pressure at `which the valve is to bleed can be` generallydeltermined upon.

Affxed to and depending` from plug 88`is a shroud 94 in the form of a cylindrical tube open` at its lower end. Surrounding vshroud 94 is a guide 98 which assists in directing valve pin84 ,toward valve seat 82.

From the description set forth it `can be seen that the upward pressure `exerted againstivalve `pin 84 may be varied through adjustment of spring stem 90. It is contemplatedin this invention, however, `that no adjustment of. spring stem 90 will be madeby users, for after suitable `adjustment has been made at the factory, further adjustment would `ordinarilybe unnecessary `andinadvisable:` e I 1 In Fig. 2 the mechanism within shell 34 will hereinafterbe referred to as the thermostatic `pressure control, while `the mechanism within e shell 'I4 will be referred to as thebleeder. The general purpose of vacuum control `valve 28 is to provide means through the `mechanism within shell 34 of closing the system at tln'sipoint tothe atmosphere under conditions of suitable temperature through the expansion ofthermostatic iioat` 46, and` to thereaftermaintain` the system closed through' the cooperation of expansible bellows 48 after the temperature has dropped l e andfloat 46 has contracted and while a negative `7:5

directlyconnected with and providing an adjust- Will be set forth pressure greater than `a predetenninedudegreei prevails. The bleeder` mechanism within `shellf14 Y which operates to 'maintain port" 8|! normally i broad'epurposes; one, to close `the systemwunder temperature and4 to maintain it closed un'dercon;l ditions of negative pressure greater than 1a pref 1 determined degree, and two, toulimitithe. degree ofnegative pressure that maybedeveloped 'within the system. The particularuse of this unit in connection `with the follow`` ing description of t e operation oftheheating system with whicnit is employed. i

' Assume the rooms tote cold'. Roumthermostat 22 will call forheat, therebyclosing "relay 24 and putting oil burner`4` in operation. Steam', generated in boiler 2, commences to' flowialog main 6.` At thispoint,` port 42 'is' openan`d port is closed".` e Steam will enter shell 34`thr`ough nipple 28 to raisethe temperature oithermostatic iloat `36.` `When the necessary temperature is reached, iioat 48 will expand, `causing port42 `to be closed. `"This,condition will thereafter be continuously maintained uhtii ttfterjtiie steam supply has been discontinued.` Steam-will continue; to

flow alongmain 6, up risers 8 and IUto radiators I2 and I4, forcing ahead and out through vvents i6 and I8 such air as may be in the radiatorsy In duewcourse, whenthe radiators are `rllled I With steam, vents I6 'and e les `winl automatitauy close, and the room in which; thermostat 22i`s located Will be warmed sufficiently to indicate the discontinuance of heat, 'whereby'thermstat$22 wi11 be actuated, relay 24 wiii'b dpened'andf the oil burner Will stop. Thisresultsin the discon# tinuance 'ofthe generation of 'steam/the' radlagtors begin` to coolas they dissipatetheirheatto the surrounding air, and the steam,` Withinfthe system is rapid condensed, resultinginl the development of anegativepressure. `Vents'Iiifand I will remainjclosed I8, being of the vacuum type, under conditions of negative; pressure, `even though the temperature at the ventsf majfhave fallen belowthe closing temperature. `j ,l

Depending upon the tightness and fsize `ofthe system and other factors such asrate of'radiation, outdoor temperature, wind, insulation,"etc., the negative pressureewill develop more` or less rapidly. It is contemplated through the use "of vacuum control valve `20 that when thenegative pressure has reached a3 predetermined point,` say, for example, a negative pressure of, ten'inches of mercury, port80 will beopened automatically to admit atmospheric air to the system;" soon as suilicient air has been admitted to reduce the negative pressure toten inches Vor less, then port 80 `will be closed automatically. If, asmore steam condenses, the `negative pressure again increases beyond ten `inches ,of` mercury, then `port 80 will again open to-admit more atmosphericiair.' L Thus the bleeding mechanism Within shell 'I4 repeat-` I does not control cient elongationoifbellowsl x 42 closed. `This is accomplishied by constructing i of mercury,

awhile; :followed by gradual dissipation -due `generally to. slightleakagesin the system..

, vFollowing the discontinuance of the steam supply, the situation that prevails Within shell 341sI this. The temperature of the thermostatic. float 4G .gradually decreasesand at a predetermined degree 'bottom 56 willxsnapv upwardly,v thereby tending toopenport 42. However, such opening does' not take place because at .that time the difference between the atmosphericepressure against; the interior of the bellowsA and the negativesystem; pressure against the exteriorof the bellows isysuch `as to cause instant elongation of bellows 48.; The critical negative pressure at Whichopening and closing of port 42 takes place under *tbeinfluence ofthe bellows is set by adjustment of support v5|! at a pressure which is slightly less .negative than. at. which port 8U opens.` y

For example, if portail is arranged to open at theheretofore suggested `negative pressure of ten inchesgof mercury, bellows 48 might be adjustedf to elongate sufficiently to maintain port closed at negative pressures in excess oreight inchesffof mercury. .It has been found that, in practically all systems that are reasonably tight at `the timethermostatic float 46 collapses after the discontinuance oi steam, a negative pressure sufficient to elongatethe bellows` 48 Will be present. Hence port 42 remainscontinuously closed during the first-portion of the oiT cycle.

, Duringtheoff cycle it port `4,2 shall remain. closed'until the negative system pressure has become less negative than a predetermined degree, as, for example, the eight inches of mercury previously referred to. The temperature ofthe system during the ofi cycle the reopening of port 42. That is to say, even thloughthe system temperature may fall suicientlytocause float 45 tocontract, vstill .port 42 Will not be opened, because atthat time the negativepressure in "the system Willfbe adequate to maintain bellows 48 elongated. At .the Icommencement oi the ofi cycle,` theternperature at the vacuum control, valve willcommence'to dropv andat the same time the negaytivepres'sure will begin'tofbu'ild up. 'It is necessary that the' Valve be so adjusted vthat the negative pressure `created by the'time the temfloat 46` has dropped enough to'cause thereoiuis adequate to cause suffi- 4-8 to maintainport perature lat contraction thermostatic float v4'5 to operate a't ajrelatively l 'lowjtemperature of 130 to`l l0 F.- ihat :is to say, ,a temperature considerably'below the tem- 'per'ature at which the u thermostatic Floats in the radiator lair valves l5 and i8 operate; In fthis Way' port 42 VWill be maintained Closedfbyiloat 46 for a period Vlong enough to permit the 1de- Yvelopment of a negative pressure Iat least equal to the predetermined degree of, say', eightinches u which is necessary vto-cause suicient elongation oi bellows 48 to maintains-port `42 closed vfollowing collapse of iloa't 46.

AItshould be pointed out that the-vacuumvalves 'I6 and l81diiier materially from vacuum control valve `2l) Ainrthat they are-constructed to. .close at high temperatures-175 vlf-or '-higher-Lsand to be maintained closed by low #negative pressures; in the neighborhood of one incl-roi mercury orless.

Asv heat is dissipatdj'iurtherfeondensation takes placel tending' to-increaseithe inegatiyefpressure, *but this Ais the negative pressure limited by the operation Aofxthe.-

isv contemplated that f In the meanwhile the bleedingmechanism. Finally there comes. a time when `further u development oi vacuum bec'omkes impossible, at which time the .negative .pressure within thesy'stem beginsto inchesoi mercury, due usually to slight leakage. Obviously the negative pressure Will reachjinA due time, eight. inches of mercury. Since thisis .the degree of Anegative pressure necessary tomamtain bellows ,48, elongated, a further decrease in pres# sure beloW that point willresu-lt in afcollapse of bellows 4.8.and consequent reopening'o'f port 42. Uponthishappening, the entire systemwill be charged. with air and the pressure Vautomati'cally reduced to atmospheric.

l temperature Vof the room in which thermostat 22 is locatedhas been vgradually decreasing.,` later the thermostat again calls for heat, putting burner 4 in operation.` When this happens, vsteam is againl generated andthe cycle heretoforendescribed is repeated.

However, under. certain conditions of' radiation thermostat 22 may call for heat before/port 42 has reopened .under normal dissipation of negai tive pressure from the system. When this occurs, theboilerA Will go into operation while the negatiye pressure Within the system is at some point between eight inchesv andteninches of mercury. This fact, nevertheless, in no Way" adversely affects the operation, becauseas lowpressure vapor' is generated, the negative pressure will be dissipated lvery quickly to the extent of two inches of mercu-rgnwhich Willbring the negative pressure `below eight inches, to` resultin 'the reopeningcf. port 42. A11 this will always tak-e piace before any `steam reachesany of the radiators, andthe nrush oi atmospheric air will at once 'condense the developing low pressure vapors so that the` generation of steam boiler water has been brought up'ito 212 F.

, The reason for recharging the system on'each cycle is to provide an' air buier ahead ci, the

steam, which air must Lbe forced from the radiators by the oncoming steam before Vents" I B 4and ifcan be closed. Since vents IBand lfhave been adjusted to control the rate of air escape, it .is obvious that steam will reach radiators |2` and I4 in accordance with the rate of escapeof air 4from the respective'radiators Discharge of air .throughv the vents -oi the radiators, Whichjisnecessary-for controlled distribution of stearm` can only come into .operation if the system re-` charged on each cycle.

. `Having noW described the general operation 'oi the system,. theparticu1ar advantages of limiting the `negativepressure that may be developed 'and thevreasonsior reopeningfthe system to theair at: a decreasing negative lpressure only a small amount belowthe maximum limit determined by the bleederwill be pointed out. `In providing uniformity of .heating in a Vroom l or building using a steam heating system of vthe vmentor a minimumva'riations in temperature may be secured by providing mini-- mumk variations in the heat supplied through the radiators. That is to say, if heat couldbesupplied .at ,a rate exactly equal Vto the rateoifradiation ofthe room, the temperature would `remain constant. v,Thus the smaller the vrange'of"temperature fof agiyen radiator from the commenceheating kcycle to the end ofthe time at which appreciableheat is given off 'by thegradiator, .the lesswillbe the fluctuation in room tem-v peratureduring` thfal. .periocl.r f i I c By the present inyentionin which the negative decrease be'lovilf` ten with the result that sooner or' `will be delayed until tnee 2,328,260, pressure thatmay developin` thesystem'is lim-1` ited throughV the usesof fthe.'` bleeder yalvel, it' follows: that `the .temperature of the radiators` will be maintained 'atsubstantiallya constanttemperature following the arrival of the system .pressure 'at .thepredetermined limited negative 'de-` sufficient heat` available of steam at lowing the iiring `cycle drops rapidly over the rst 1 portion ofthe-off cycle, andiduring thistimesub# stantial quantities of additional `vapors are given off whjchimay be utilized temperature Aof the radiators. i `If the Vacuumrthat immediately develops after the firing ;cycle, is unlimitedyand `reaches a high degree,` f say, `for example, `twenty-five inches of mercury or more, the available heatfromthe boiler isrnot` effectively transferred to the radiators .because asv given 'volume of steam at*` that pressurerweighs only a third asfmuch asthesame Volume .of fsteam at atmospheric pressure and likewise has ,arB.` t: content `of about one third. ,Hencerthe `B.t..u.fs transferable to the radiators whilethis high negativepressure'prevails is about one-third of steam at atmospheric-pressure, and [the1 temperature of" theradiators willv drop rapidlyttol -a 3 point far below the temperature` that prevailsduringthe ring cycle.` i i e; If, howeverethe negative pressure is limited to ten inches of mercury, for example, f'more heat "willbetransferred tothe radiators' than if the nega-tive pressure were greater, e as, Vfor example, ,twentyfveinches of mercury.; g .Thus, by limiting ,the negative pressure, theheat output of the ra- 1liators` will be `.greater and theiroom temperature `will decrease more` slowly than would be the case ThroughA the vacuumfcontrol Avalve 2li, prede- 1 terminedrupper and 'lower limits of negative pres sure may be selectedrthe vupper limit being chosen r t providef a satisfactory*` radiatoritemperature when the system Ais `sealed during. the off cycle iand the; lower limit beingfchosen toprovide positive recharging with airfbefore the' advent of lsteamonthenextfiringcycle.`

'wAfterthe .temperatureof` the boiler water has :dropped 'to a point where itcan `no longer supplyr isteamyat the limited f' negative pressure, `then the radiator- -temperatures will ,.drop rapidly to approach` room temperature', as no further heat will Vbe available. This brings about two situations;

diret, `the roomrtemperature will bee-accelerated `downwardly to operatethe thermostat to again bring the heat supply into operation; and secondly, it will `cause reopening of thesystem tothe 1 atmosphere as: soon `iasthe negative pressure has wbeen dissipated tof'the .predetermined minimum .of `eight'inches of mercury, for example, through leakage or througharrisingboiler water tempera ture;` That is; the valve, through thecontraction `of bellows 48 uponreduction of the negative presusure of the system,` reopens to `l'loool the system `with air at atmospheric pressure. This procedn `urein turn resetslthe system forthe oncoming `steam supplyfso'A that therewill be proper steam distribution. l f

- `Whether the 'maximum negative pressure should be ten inches of mercury and the reopening presisurefeight' inches 'may be `found by test on 'any givenA system. Teninches, however, is a good maximumi'lgure, as it `provides reasonably good heatfoutput froml theradiator, since the heat `confor maintaining the tent of a given volume of4 steam atthat pressure is only about one-third less than the heat content at atmospheric. `At the same time, ten `inches of negativepressure is suilicient to` cause vapors to be given olf by the boiler` `water in such quantity `that thevapors will travel readily to the several radiators. ten inches,

That is to say, a negative pressure of which will be quickly reachedl as compared with the .fall` in temperature of the boiler lo ered in relation to water, will insure the continued transfer of a sub.

stantial amount of heat fromthe boiler to the radiators after the commencement of `the off cycle. The minimumpressure maybe somewhat more than two inches less than the maximum, l

but it should be close enough so that if vacuum control valve 20 has not already opened at the start of the next firing cycle, it will open promptly thereafter so that the system with air before steam is supplied;` e

The adjustments prvidedenable both the ma):` imum negative pressure and the minimum reopening pressure to be accurately controlled. l

In the specification and` claims,`when refer`` ence is made to negative pressuresit is to be understood that `the negative pressures` are consid- `zero or` atmospheric pressure.` Thatis to say,.a negative `pressure of ten inches of mercury is a greater negative pressure .than :tive inches ofmercury. Putting it in different words,"the greater the degree ofyacuum, .the greater isthe negative pressure. When reference is made herein to the `valvesin the control unit 20 being in parallel, it is intended only to incli-` cate that the valves areparalle1.functionally,

and itis not intended asaflimitationto any pare ticular geometrical relation of the valves.

Iclairn: s" Y y 1. A` method` of heating ,bysteam,utilizing a system ,comprising a pluralityof `radiators with vents thereon `and an intermittentlyoperating source of steam, in which each cycle comprises the following steps: setting the `source. of steam in operation; supplying radiators; with steam;v `sealp ing the system before or about the time the steam i source ceases operation; discontinuing thesupply of steam; thenallowing the` steam to condense to `create a substantial negative pressure;

maintaining saidnegative pressureat asubstantially uniform predetermined` degree;` and finally opening said `system tothe atmosphere prior to distribution of steam to the radiators on the `next `heatingzcycle.` 1

2. A method ofheatingby steamas set `forth in claim; 1,` in which the negative pressure `thatis Ucreated `isesubstantial, butV is not` in excess `of twelve inches of` mercury. C .i V i 3. A methodzofheating by steam `as set forth in claim lyin which themaximum negative pressure that is; allowedvtordevelop after thediscontinuance of steam is between six inches and `twelve inches of-mercury. i .e

4. A method of heating by steamV as set forth in claim l, in which the opening of saidsystem to` the atmosphere takes place when the negative pressure `has decreased not more thanfour inches i of mercury from the maximum negative pressure Y that is permitted to develop.

5. A` method of heating `by steam utilizing a .system comprising a plurality of radiators with 7 0.

vents thereon and anwintermittently operating source of steam,in whicheach cycle comprises the following steps: setting the source of steam in operation; i supplyingthe `radiators with steam; sealingthe system before or at vabout the time the `Steam source'ceases operation; discontinuing the will be recharged tween said maximum'and in operation; supplying thesystem 'sealed until the yventing valves close,

negative pressure in c terior of said unit, means supply of steam; then allowing the'steam Ato con-v dense to create a substantial rnegative pressure; bleeding limited amounts oi airinto the system when the negative pressure exceeds ra predetermined maximum, to` reduce the negative pressure thereblow; and nally opening said system to the atmosphere when the negative pressure has decreased to la predetermined minimum, the system being sealed whenthe negative pressure is betweensaid maximum and minimum.

6. A method of heating by steamas set forth in claimt, vin which the difference' in pressure beminimum does not exceed ve inches of mercury.

7. A method of heating by steam utilizinga system comprising a pluralityof radiators with vents thereon and an intermittently operating source of steam, in which each cycle comprises the following steps: .supplying radiators with steam; `sealing'the system before or about the time the steamsource ceases operation; discon tinuing the' supply of steam; then allowing the steam to condense to` creartev a substantial negative pressure; limiting the development of negative pressure beyond apredetermined ting the source of steam in operation; generating sufficient steam to reduce the negative pressure of the systeml to a predetermined minimum; and then opening said system'to the atmosphere.

8. A method of heatingby steam utilizing a system comprising aplurality of vradiators with -vents thereon andan intermittently'operating source of steam, in which each cycle comprises the following steps; setting'the source of steam radiators with steam; sealing the system before or about the time the steam source ceases operation; discontinuing the supply of steam; then allowing the steam to condense to create'a substantial Ynegative pressure; limiting thel developmentof negative pressure beyond a lpredetermined maximum; maintaining ngative pressure beenreduced to, a predetermined therein has minimum; and then opening rsaid systein'to the 9. A steam heating system comprising a source of steam,` a pluralityof radiators and connecting piping therebetween; vacuum`type'venting valves on the radiators, each of said ventingvalves having' thermostatically and negative `pressure operated means for closing said valve, a single vacuum control unit connectedto the piping", said having a first valve with vacuum control `unit thermostatically operated means for closing said rst valve, and negative pressureoperated means Vfor' .maintaining said rst valve closed between certain. negative pressure limits; the temperature at whichsaid first valve 4cl oses' bei'r ig substantially ,less than the temperature at which v'said the minimum negative pres sure necessary `to maintain said 'first valve closed *being substantially greater than the negative pressure necessary to maintain' saidfventing valves closed, and said'control unit includingv a second valve having means for. causing 'the temporary opening thereof to the atmosphere when the the system exceeds the said ,minimum pressureby at least two inches of mercury. V

10. A device of the type described for use in a steam heating system; f omprising a single unit forming a closed casingv and including two valves the interior tothe eX- for connecting said unit in parallel leadingv from to said system whereby maximum; setboth valves may be inaggrave-oi fluenced simultaneously within the system,

beingnormally operi,` means for closing said first valve comprising a thermostatic element operable to Aclosed position: under the influence of heat in excess lof a predetermined' to move said first valve degree, and a pressure operated element subject tothe system pressure and operable v'to move said rst valve to closed position when saidisystenr pressure reaches a determinable negative l degree, the second of lsaidjtwo valvesbeing normally closed, and means operable `to opensai'd second valve when the pressure within said unitbecomes less negativethan apredetermined degree.A ff] f l1. A device of the type set forth i'n "claim 10,' and having means for afljustiigl saidfirst valve to vary the negative pressure at which said first valve will open and :close without affectingv the temperatureat which said -rst 'valve will open and` close.

12. A device of the type set forth Vin" claim- 10, and having means for adjustingy said first valve to vary the negative pressure at' which's'aid 'r'st valve will open and closeunder the influence "of said pressure operatedv element alone without aff'-` fecting the temperature at whichsaid fir'stvalve will open and close under the influence of"said thermostatic element alone@ 13.' A device of vtl'ieftype set lforth in claim lll", and having means for adjusting said secndfvalve opening means whereby the negative pressure at which said secondvalve 'opens may be varied independently of said first valve. y `i 14. A device of the type setforth in -iaimfid and having means foradjusting said first jvalve to vary the negative pressure at which said vaive will openand close without affecting uit temperature at which 'saidrst 'valve willfopen and close, and means foradjusti'ng said. second valve opening means whereby the negative pressure at which said second valve opensinaiy be varied independently' of said first valve.'V l5. A device of the typ setfforth in claim"y 1'0, in which said thermostatic Velement is combined with a buoyant element'adapted to 'close said first valve when liquid has risen to a predetermined point within said casing. 1. I i 16. A device of the type set forthin claim l10, in which said thermostatic element is" combined with a hollow sealed element' to form -a`buoyant member for closing said first valveV whendq'uid has risen to a predetermined pointin-'saidcas'ing 17. A device lof ther type set forth in cl'aim'lO,

`in which said pressure operated Aelement is'positioned so as to be exposed to the interior `r casing pressure on one side and' atmospheric" pressure ontheother. L T" 18. A ydevice ofthe second valve isa loaded springsubject to operiing movement when the pressure within said casing decreases to a predetermined negative degree to permit the entrance of 'air intofsaidcasingf 19, A device of the type set forth infclaimv 410, in which the pressure operated element for closing saidrst valve under conditions of negative pressure within said casing in excess oa predetermined degree comprises a'bellows positioned so as to be exposedv on one side tothe -interior casing pressure and on the other side to` tlieatmosphere. f

20. A device of the type set forthy in'claimll,

in `which the thermostatic ,elementl vforA closing saidiirstl valve isY included as part of a sealed float, and in which the pressure operatedelement by conditions existing the vii'rstfof said `two valves? type set forth in claim* l0, 1n` which the means permitting opening' `of said V in which thepressure air into said casing.

21. A device of the type set forth in claim 10,

operated element for closingsaid first valve comprises a Ibellows mounted on a hollow adjustable stem and open on one side to the atmosphere,` and said thermostatic element is mounted above said bellows, and said valve closingmeans is mounted on said thermostatic element, and the second of said two valves tive pressure within said casing falls to a predetermined negative degree.

22. A steam heating system comprising a source of steam, a plurality of radiators and connecting therebetween, vacuum type venting valves on the radiators, each of said venting valves having thermostatically and negative pressure operated pressure by a amount;

WARREN T. FERGUSON.

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