US2008098A - Boiling and condensing heat transfer apparatus - Google Patents

Description

C. FIELD .July 16,' 1935.

BOILING AND CONDENSING HEAT TRANSFER APPARATUS Filed July 25, 1952 5 Sheets-Sheet 1 ffm ...20

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July 16, 1935. c. FIELD BOILING ANDCONDENSING HEAT TRANSFER APPARATUS Filed July 25, 1932 5 Sheets-Sheet 2 wm E Judy 16, 1935.

C. FIELD BOILING AND CONDENSING HAT TRANSFER APPARATUS CONTROL PRESSURE 1 ATMOSPHERIC l5 LB 5 Sheets-Sheet 3 SUPPLY PRESSURE c ROASTER PRESSURE 0.004 LB.

l l I INVENTOR ATTORNEY Patented July 16, 1935 UNITED STATES PATENT oid-TCE BOILING AND CONDENSING HEAT TRANSFER APPARATUS My present invention relates to systems where-V in mercury is boiled to produce vapor, the Vapor is circulated through a suitable conduit circuit, including one or more roasters, driers or other devices which absorb the heatvfrom theY vapor to condense it, and from the latter the liquid mercury flows by gravity to theboiler. In such systems desired temperatures are maintained by suitably regulating the pressures toraise or lower the boiling and condensing points.

AccordingV to my present invention, kthe system may be operated at, above, cr below atmospheric pressures; and the system inoludes'devices for controlling the pressures of the vapor in various parts of the system so that the boiler may be operated at a suitable pressure and temperature for boiling, while one or more of the devices to be heated may be operated at any desired lower pressure and temperature; also different devices supplied by the same boiler may be operated Vat temperatures and pressures differing one from another.

Preferably, the boiler and vapor distributing part cf the system has a high Vacuum pump adapted for operating to reduce pressure below atmosphere; and rise of pressure is limited by an automatic relief valve whereby when a predetermined maximum internal pressure is exceeded, the vapor .is vented to a safety condenser. Preferably, the automatic relief valve is a mercury bubbler wherein a static head of liquid mercury is maintained at a normally constant level anda novel feature of the arrangement includes providing an overflow outlet for liquid mercury at a desired level, in combination with'a return conduit from the safety condenser whereby the condensate is first applied to replenish any liquid that may be blown out of the safety bubbler, excess liquid from the overflow being returned to the boiler. l

A valve device also depending on diierential depth pressures of liquid mercury,4 is employed for controlling the flow of vapor to the roaster or other device to be heated. In this device, the differential pressure required for depressingthe liquid mercury and `permitting escape of Ythe vapor to the roaster, is pressure much greater than that of the bubbler relief valve; and the valve construction may be accurately predetermined for a certain pressure differential between the boiler supply and roaster condenser; whereby the vapor will be supplied to the roaster at rates sufficient to maintain only its required lower internal pressure condition. This valve device has a predetermined overilow level to predetermine a minimum differential pressure of the liquid mercury, which must be exceeded bythe boiler pressure, before the valve can open; together with special means whereby condensate is automatically supplied to replenish overflow or evaporated mercury in said valve, and so? restore the desired normal depth pressures and liquid levels. This control valve diners from the bubbler inthat, during normal operatiornthe` depth pressure of the mercury may be increased or decreased by increase or decrease of gas or air pressure applied to the surface of the mercury in the overflow level part of the valve.' Air or gas admitted to. control the level of this overilow surface ofthe mercury is absolutely preeluded from entering the vapor system by providing U-trap tubes, one between the overflow and valve, and one in the drain pipe from the overflow, below the point of admission of said air or gas; both of these traps being of sufficient vertical height tomoreV than sustain full atmospheric pressure on their air or gas engaging surfaces, as against Va complete vacuum on their other surfaces.V

The normal overflow level of thevalve may be arranged a predetermined distance above the level of the vapor inlet to the valve, such that the valve cannot open at a pressure low enough to endanger the operation of the boiler; The external means for regulating air or gas pressure on the mercury within the overflow makes it possible to shut oifmercury vapor from the body of the roaster at willand to permitentrance of the mercury vapor whenever desired. As concerns'normal operation, the heightsof i the liquid columns in the valve chamber and in the overflow chamber are such as tol afford a normal-differential depth pressurewhereby the boiler and conduits leading to theroaster may be maintained at a comparatively high mercury vapor pressure, say, 6` lbs. per square inch absolute, while the pressure Vin the jacket ofy the roaster may be nearly a perfect vacuum, say 0.004 lb. per square inch. In such case, the difference in heights of the liquid columns in the valve, will be approximately l2 inches, as is necessary to sustain the desired pressure differential of 6 lbs.; and the valve surface of the mercury may then be depressed below or forced above the levelof the valve outlet. Wheneverthe internal pressure in the roaster falls-belowdesired normal, the sealing surface of the mercury in the valve supply outlet is depressed and the valve outlet is unsealed, thereby permitting vapor to flow freely into the `jacket of the roaster until the internal pressure in the latter is raised to normal. Similarly when thersealing surface of the mercury is forced upward, the valve is closed. rI'hus in normal operation, a temperature in the roaster corresponding to a low mercury vapor pressure may be obtained by intermittent opening and closing of the valve; or, what may be called a pu method of operation. rIhe alternate opening and closing of the valve permits successive injections of small quantities of hot mercury vapor at each operation. denly, producing the lower pressure and the desired lower temperature required for the roaster jacket.

An important utility of the above arrangement is that when the roaster is to be initially heated, the control pressure on the mercury surface of the valve overow may be reduced enough so that the 6 lb, boiler pressure will depress the sealing surface of the mercury in the Valve, thereby keeping the valve'open, thus freely supplying the roaster'with mercury vapor at boiler pressure and correspondingly high temperature, thus shortening time required for the'heating o the roaster to normal operating temperature.

From. the above,rit will be evident that both the bubbler safety valve and the automatic control valve give control of the mercury vapor without presenting any metallic surface, other thanliquid mercury, at the valve seat so that there is never l any necessity for replacing valves or valve seats,

and in case of accident whereby the liquid mercury is displaced so as to unseal the valve, it is automatically replaced by condensate which refills it'to its normal overflow level. An important practical feature of both valvesconsists in heavily insulating the conduit through which 'the hot vapor flows vertically downward to the mercury sealed outlet. Such insulation is of great practical advantage in minimising or preventing boiling of the liquid seal mercury which comes in contact with said conduit when the valve is sealed. j

The above and other features of Vmy invention may be more fully understood from the following description in Yconnection with the accompanying drawings, inwhich Fig. 1 is a more or less diagrammatic view ci the complete system embodying my invention;

` 'Fig.,2 is a characteristic vertical section showing the safety bubbler on a larger scale;

, Figs. V3, .4l and v5 are diagrammatic views of the control valve, on a large scale, showing char@ acteristic stages, warming up,fopen valve relations and closing valve relations, respectively;

and

Fig. 6 is a View of said valve on a muchlarger scale, showing details of construction more fully, showing the mercury level under extreme valve closed conditions, and graphically indicating characteristic depth differentials of the counterbalancingmercury columns at all of the characteristic stages of operation.

The showing of the system in Fig. l is necessarily diagrammatic to a certain extent, but in view of the fact that many of the more important features oi operation depend upon absolute and diierential depth pressures of the liquid mercury,

' an attempt has ,been made to make'the vertical This vaporexpands sud-V boiler A for supplying mercury vapor at desired high temperatures, as determined by the absolute pressure maintained in the boiler; one or more roasters or other jacketed containers or utensils to be heated by the vapor; a pressure operated mercury Vapor Valve C for controlling ow of the vapor to the roaster; an after condenserD preferably connected in shunt across the outlet from the roaster for condensing uncondensed vapor and collecting any non-condensible gases; together with suitable lead and return pipes, traps, sumps, etc. ln a shunt circuit across the vapor supply main and the liquid mercury return, is a vapor circuit through a safety bubbler E, controlling excess pressure by permitting escape or mercury vapor to a water-cooled safety condenser F, supply of water to which is through float controlled inlet valve V. From F the condensate iiows `back to the safety bubbler to maintain the depth pressure of liquid therein; thence through suitable sumps and traps, back to the boiler A.

The above elements and their functioning in the system may be more easily explained in connection with a speciiic illustrative case, as, for instance, Where the pressures are all less than atmosphere, the boiler operating at approximately 6 lbs. per square inch, absolute; safety bubbler at 81/2 lbs.; and roaster at (i084 lb.

In Fig. l, the boiler A is conventionally indicated as being of the depending-tube type in which liquid mercury flows down through an inner tube and is boiled in the annular space between it and the outer closed bottom tube, the latter being heated by afurnace, not shown. For present purposes, it is sufcient to note that the boiler Will bedesigned, and the heat of the -furnace'will` i be adjusted with reference to the normally required output of mercury vapor, atthe pressure selected for normal operation of the boiler; and when designed for operation at a given pressure, as, Vfor instance, 6 lbsyabsolute, it is undesirable to attempt operation at a much lower pressure, say, 2 lbs., because ofthe much greater volume of vapor that will be boiled ci by the same number of heat units, at the lower pressure. means for preventing toro great 'fall of boiler pressure during otherwise normal operation, will be more fully explained hereinafter.

The vapor from the boiler flowsthrough conduit I to down-take pipe 2 leading to control valve C of a roaster B. As indicated, the conduit i may be extended to down-take pipes supplyingV other control valves and roasters which may be supplied in parallel with the one shown in Fig. l, and which may have their control valves designed oradjusted for any other desired rcaster pressures and temperatures, within the limits perlnitted by the design or adjustment of the vapor supply circuit. l i v Frein conduit i there is a shunt circuit through pipe la, to the safety bubbler E, controlling vent oi vapor to safety condenser from which latter, the condensate flows to the bubbler, and excess passes back to the boiler.`

It will be understood that all pipes and as far as possible all valve parts are preferably of heavy seamlesstubing, all joints being carefully elec-Y trically welded so as to seal the entire system against 'inleak of air or outleak ci mercury vapor. The boiler part of the system is preferably supplied with a pressure indicating gauge e, the normal working pressure of the boiler being illustratively indicated on Fig. l as o ibs. to the square inch absolute, which corresponds to a boiling temperature of 591 F,

My novel Y A pump (not shown) capable of highly evacuating the system is connected with various parts of the system through independently operable valves, the vacuum line connection for the bubbler- E and condenser F being controlled by Valve'3;` that for the main -distributing conduit l, Vby valve 4; that for the after condenser and roaster jacket circuit, by valve 5; and that for the pressure con-` closed at the end by a welded quarter inch plate Il, and at the top by washer l2. In normal operation, the inner surface of the down-take pipe la is heated by mercury vapor at the working temperature (say, 51 F. at 6 lb. pressure), while its outer surface is in contact with a por-` tion of the sealing liquid. mercury which has a much lower boiling point because the pressure on it is 6 lbs. less So an important'feature is providing said down-take pipe la. with Very substantial heat insulation to retard boiling off of the sealing liquid. This insulation may conveniently take the form of a jacket tube I3 secured around tube la by weldedwashers as indicated. Preferably, the space between la and I3 is filled with a highly heat resistant insulating material such as magnesia or fire clay. i

f Casing Il] has an overflow outlet I4, the overiiow level of which is above the level of the open end of pipe la .by a distance corresponding to the desired relief pressurerat which the bubbler is intended to operate. In the illustrative case where the normal operating pressure ofthe system is supposed to be lbs., this vertical distance may be 19 inches, affording a differential depth pressure. Theoretically, this would Vent when the boiler pressure on the inner surface of the sealing liquidreaches' 9% lbs., as against the nearly zero pressure which is maintained on the surface of the outer counterbalancing column. However, the high temperature of the liquid mercury in the. valve increases itsv uidity and decreases its specific gravity to such an extent that vin practice, the measured differential of 19 inches, will permit relief at approximately the 81/2 lbs., above assumed as the desirable relief pressure. l

. Mercury escaping through overflow I4, passes into separator chamber l5, wherein any vapor .entrained in the liquid is separated therefrom and escapes upward through pipe lileading to safety condenser F, while the liquid part flows downward through pipe H, sump I8, trap i9 and return 2U to sump 2l, whence the liquid flows to the boiler through trap 22.

Vapor evaporated in the bubbler or blown through the same 'during relief operations, passing through pipe I6 is liquefied in condenser F and flows downward, primarily through pipe 23, sealing trap 24 and re-enters the valve at 25. It will be noted that the point of re-entry at 25 is substantially below theoveriiow level I4, and by this arrangement the sealing mercury in theV bubbler is always kept up to the overflow level. As it is not desirable to have large quantities of liquid mercury passing through the bubbler, there is a .by-pass 25, through which Vex'cesslrnercury mayfpass directly downward to sump I8 as, forinstahce, when greatly excessive pressure in the boiler causes large quantities of vapor to fiow thro-ugh the bubbler.

The structural parts of Vcontrol valve C are similar to those of the safety bubbler, as `concerns the use of seamless tubing, electrically welded closures, insulating jacket for vthe Vapor inlet pipe 2 but, as will be evident from the detail View Fig. 6, various features such as the functionally important vertical dimensions, manual and automatic pressure controls, etc., are specifically different, as is necessary to take care of the various special conditionsand functionings of said valve.

Referring to Fig. 6, vapor downflow lconduit 2 is shown as surrounded by insulating jacket 33 and the external valve casing 30 is cl-osed at the bottom 3| and `top32, but the outlet 34 to the condensing roaster jacket, is much higher above the valving level c, than inthe bubbler; Vand the top 32 is preferably inclined at an angle of 45"., so as to defiect away from outlet 34, any liquid mercury that may be projected upward by the incoming vapor, at times of opening and closing yof the valve seal. The overflow outlet 35, which determines a normal datum level Vfor the liquid niercury in the valve leads from a chamber 36, instead of `directly from the valve casing, and it discharges into a separating` chamber 3l, whence liquidY mercury iows downward in pipe 38 to the liquid return conduit and the boiler sump, througha trap 4! a. Preferably, this trap affords a differential depth pressure of mercury sufficient to withstand greater-than-atmosphere pressure differentials both from and toward the overflow. The chamber 36 is connected with the bottom 3l of the valve chamber 30 through a U-tube affording counterbalancing liquid mercury columns in the legs 39, 4D. Preferably, each of these columns 39, d is of a height substantially greater than the 30' or 32 inches which wouldA be necessary to sustain a full atmosphere-vacuum differential of 15 pOlll'ldS. j

Having the overflow thus arranged in a separate chamber cut off from the valve by the U-tube 39 and from the liquid return system by trap 4 la, each capable of sealing against atmospheric-vacuum differentials, in both directions, makes it safe, as well as possible, to apply control pressures to the upper overflow surfaces of the liquid, inde# pendently of the boiler-valve-roaster circuit, and as before stated, this control is operated by opening valve 6 to the vacuumizing'pump when the pressure is relieved or to a pressure source which may be either by air leak through Valve 6, which is ordinarily used for vacuumizing; or it may be by inlet throughvalve l, of air or gas,'preferably nitrogen or carbon dioxide.

Pro-Vision is made for supplying condensed mercury to the overflow chamber and to the Valve by i means of an uninsulated condenser Vbranch pipe 4l leading from the low pressure conduit 34 which supplies the roaster. This `condenser supplies the replenishing condensate to the valve `system through pipeftVwhich is preferably of smaller diameter and delivers the condensate at the bottom of the U-tube, 39, 40.

In Fig. 6, `the liquid is shown ;at the highest levels attained in the valve and overflow after the valve has been fully closed by application of a full atmospheric lli-lb. control pressure through valve l; `and after the condenser 4l has had time to fully restore the liquid level in overow chamber 3G, which will have been depressed by "said mum control pressure of l lbs. applied tothe. overflow surface, and that it is applied as against 6 lbs. supply pressure, and 0.004 roaster pressure. The legends also indicate in inches, the theoretical vertical distances between characteristic levels corresponding to all characteristic stages oi operation of the valve, said theoretical Vdistances being subject to slight correction for the working temperature of the liquid mercury in any given case. These vertical distances may be more fully explained, in logical sequence.

The system isevacuated by operating the pump with valve l vclosed and valves 3, rl, 5, El and 8 open.

When it shall have been determined that the system is tight and down to approximately 0.004 lb. per square inch absolute pressure (approxin mately 0.2 mm.) then valves 3, d, 5 and are closed, thus separating the system from the vacuum pump which still continues to operate, however, on valve 5.

The boiler is then nred and slowly brought up to temperature.r At the very low absolute pressure Vof about 0.004 lb. per square inch (0.2 nun), the vapor begins to travel through the Vapor llows through empty safety bubbler and condenses in the tu e it and condenser F. Condensate from the latter ilows through pipe until it has reached a level that balances the pressure oi the vapor in pipe id. At this point f the bubbler seals andiurther vapor prel Should the Vamount' of mercury vapor be too great,

as in case of very high pressure, then the mercury will rise to a point Where' any additional liquid mercury will flow over into separating chamber I5, through pipe El, sump I8, and trap i5, sump 2i, and thence to the boiler. When the pressure in la becomes less than that due to the diierential liquid pressure of the cylindrical column in lo and the annular column in i0, then the bubbler will reseal. As the pressure reduces to normal and as further condensate flows down through 23,' l5 or Iminto casing iti, the height of mercury in the latterwill increase until it overflows at ill, and returns through pipes l5, il', sump lil, etc.7 to the boiler.

In the meantime, vapor has been iiowlng through l into control valve C, where some oi it condenses; also through roaster jacket circuit where more of its condenses, thus accumu-V lating some mercury in the valve and in the low level sumps and traps leading to the mercury boiler; but the safety bubbler being sealed for the then pressures, attention may be directed to the control valve. Y

Fig. 3 indicates a stage where thel increasing amount of liquid in the bubbler is causing'the pressure to increase from minimum which may be 2 lbs. to normal which may be 6 lbs. absolute. During this period, the valve is of course wide open and the vapor is passing freely to the roaster at a pressure correspondingly 'increasing from 2 lbs. to 6 lbs.

The operation of condensing vapor in 4i. to seal the valve may be greatly accelerated by opening valve 5l to spray water on said cone denser. Condensed mercury ,falls through Vthe pipe 5.2 to the bottom of the Utube andthe level of the liquid gradually rises until. at some pressure, say about 3 lbs., the levels in te and Q2 which are under boiler pressure, will be asshcwn in Fig. 3, while the level in control chamber 36 pressure difierential.

will be substantially higher because its surface is still exposed to the original approximate vacuum of 0.004 lb. The levels continue to rise in this way until the liquid in 39, 36, reaches, the

overilow and, as shown in Fig. 4, at this time the boiler pressure and drier pressure will have risen to 6 lbs. while the control pressure remains a substantial vacuumas before. At this time, the sprayer 5l will betulned oit and. will not be used until it is necessary to again fill the valve. During normal operation, replenishment of liquid will be provided byordinary Vcondensation in pipes 4|, 42, and by entrained liquid, if any, from pipes I and 2. At this time, the differences of level will be approximately 12 inches as indicated in Fig. 4, this corresponding to 6 lbs. This is the condition of normal operation during open-valve periods.

The vacuumizing of the overflow through valveY 6 may be discontinued and inleak of air or nitrogen through 6 or l may be permitted to raise the pressure on the overflow surface to full atmospheric of 15 lbs. asindicated in Fig. 5. Thereupon the mercury level willbe depressed in the control chamber forcing upward theY liquid in the valve chamber until a 9 lb. differential (l5 lb. minus G lb.) is established by 18 inches of differential head. The valve 5, connecting the roaster jacket and condenser with the vacuum pump, will then be opened enough to reduce the working pressure in the roaster jacket to the normal Working pressure, which iri this case is sup-posed to be 0.004.

Whilethis reduction in roaster jacket pressure being eiected, condensation in the down pipe 2 and in condenser Mwill operate as shown in lig. 6, to replenish liquid in the control chamber and in the valve until, as shown in Fig. 6, the level in the controlchamber will rea-ch the level d Whichris that of the overflow 35; then the level .in 2 which Yis at 6 lbs. pressure will reach the level e, which affords an 18 inch differential which equals 9 lbs. oi ressure, and the surface of the mercury in 30will reach the level f which is l2 inches higher than e, representing the 6 lb. boiler pressure balanced against the practical vacuumin the roaster. The total vdiiferential. d-f remains 30 inches, representing the full differential between control surface 35,

which is at the l5 lb. pressure, and the annular A surface in 30, which is practically complete vacuum.

Preferably, the vacuiunizing valve 5 controlling roaster `pressure is run slightly open at all times when noncondensible gases are present,

so that the absolute value of the vacuum prese' v sure will be practically constant. As we have seen, the safety bubbler prevents the supply pressure in 2 fromrising more than about 21/2 lbs. above the normal 6 lbs. optimum pressure for theboiler; while lowering of boiler `pressures below 2 or 3 pounds is prevented, by reason of the normal predetermined diffe-rence of level c--d, between the sealed outlet of pipe 2 and the overilow level of the control surface at 35; In normal operation, opening or sealing of the valve at level c may be eilected by hand in acY cordance with indications of thermometers whichmay be installed at .r in the top of the reas-ter jacket, or .r in the roaster jacket, or :r2 through the roaster jacket into the material which is being treated inthe roaster. In'most practical cases, such thermometers will be there mostatic controllers Vwhich will automatically govern pressure in control chamber 36, to open `that of the vapor outlet of the valve C, at c.

and close the outlet at c according as the roaster temperature varies up or down from the normal desired temperature. l Y i In the present case, it is assumed that theboiler is designed for satisfactory operation at 6 1b. absolute, and *should not operate at a pressure less than2 lbs;` absolute, whichv corresponds to a ,il inch mercury head. This is provided for by making the overflow level at least 4 inches above It will be understood,v however, that this differential level may be' inches fora minimumV 3 lb.'opening pressure; or may be otherwise varied to suit conditions; also that this static differential may be interfered With and controlled by imposing a vconstant minimumY and/or maximum for the operating Variations of the control pressure as applied to the surface of the mercury in overflow chamber 36. Also adenite control pressure constantly or variably applied can Ybe made to take care of widely different values of pressure that may be desired for boiler operationsas against widely different pressures that may be required for roaster operations' in special cases. In gen-V eral, however, anormal predetermined static head and a desired set f ofV static differentials Y'should be embodied inthe valve -to suit special conditions and special kinds of workfto be performed in the apparatus. i 2

As before explained, the supply line I, may have Vany desired number of roasters or the Vlike operating in parallel with roaster B, and the control valves for the other'roasters may be designed or operatedfor roaster-jacketpressures and ternperatures entirely different from: those illustratively described in connection with roaster B.

While the primary function` of the after condenser D is to act as asafety device to prevent the mercury vapor in the jacket of the roaster from getting too hot, and to equalize pressures on ends of the roaster, lthese primary functions are' sup- -plemented by a valuable secondaryl function,v

condensedtherein'and is returned tothe boiler. Under certain conditions vit maybe `found advantageous torun with valve 5 always cracked slightly, but VinY general thisV Will bev found unnecessary after the system has been in operation- 'A for a fairly long',A periodwith intermittent cracking ofthe valve as above described.

1W here more than one `ro'aster 4is proper division of loads tolsuit the requirements o f each, by suitable"adjustmentsy of the respec- `tive valves 5; of the several roastersi' If it becomes necessaryto shut down the equipadmitted to thel vapu` system 'tends' to create trouble." lv" 7 "i f `mill scale and sludge.

. indicate actual liquid level in the boiler.

l v Aoperated' on v Ythe same supply, l, itis possible to arrange for The sumps are useful topermit cleaningout They should be cleaned out frequently when the equipment is first put into operation, but it Will be found that the amount of mill scale obtainable from `the sumps will diminish greatly, and when this has reached its minimum further cleaning out Will be unnecessary.

vAfter operation, as described above, the system may be shut down, leaving mercury in the safety bubbler and in the valve. The levels in the valve C Will then be found to remainin a position near or slightly below Vthe line d, Fig. 6. It is preferable that the vacuum remain on the system during intermissions of operation, so that re-cvacua-` tion will be unnecessary. Even so, at restarting, it will be found good practice to putthe vacuum pump on the system by opening valves 3, 4, 5 and 8, keeping 1 open and 6 closed, but not thecontrol valve, until it is certain that the system is completely evacuated. The mercury boiler is then red and operated with the valve C closed, as inrFig. 5, while the line pressure is gradually brought upY to a minimum of13 lbs. per square of these sumps inch, `whereupon normal `operation of said valve may be resumed, las 'above described.

It may be noted that the boiler shown in Fig. 1 has a. diagrammatically indicated mercury level indicator, comprising an inverted U-tube the,

ment'in which mercury is maintained at a. higher level; 'in this ,case 8- incheshigher, by. condensation `'through ai pipe connected with the vapor cavity of 'the boiler, above the` liquidlevel, The height of the mercury in this trap being constant, variations in the leveLof the-otherwill As before stated, howeven'the boiler and the level indicator are not essential features of my present y ential depth pressure against the boiler pressure;

and conduit means for returning condensate from the condensing element to the valve to replenish sealing liquid that, is evaporated, entrained or forced out duringvnormal operation.` v

2,. A mercury vapor-'heating system including mercury boiling means, mercury condensing ymeans and intermediate mercury liquid-sealed, i pressure-operated Valve meansembodying col-r umns of liquid mercury having their surfaces `exposed to inlet and outlet pressures respectively,`

in counterbalancing U-relation and each of vertical height sufficient to afford a desired differential depth pressure `against the boiler pressure; a

liquid overflow outlet determining a normal datum level for the liquid columns; and conduit means for returning condensate from the condensing element to the valve to replenish the sealingliquid evaporated, entrained or forced out during normal operation. Y n

3. A mercury vapor hea 'ng system including mercuryboiling means, mercury condensing. means and intermediate mercury liquid-sealed,pressurei operated valve means; embodying columnsof iliquid mercury having their surfaces exposed to inlet and outlet 'pressures' re's-pectively, in counterbalancingl U'-1"elatiion.and&each of 'vertical height suflicient'to aiforda desiredidifferentialdep th' pressure against the boiler pressure; a liquid overiiow out- ,let`l deterrr'iini'ng: a normal. daturnvv level. forV said columns; and conduit means for supplyingi liquid.

to restore the` normal levely after losses, as by evaporation, entrainmcnt or overilow.

mercury vapor kheating system including mercury boiling" means', mercuryV condensing means and intermediate mercury liquid-sealed, pressure-operated valve means, embodying col- YVumns of liquid mercury having their surfaces ex-A mercury boiling means, mercury condensing means and'intermediate* mercury liquid-sealed,

pressure-operated valve-'.means, embodying col-- umns of liquid mercury having their surfaces ex- Yposed to inlet and outlet pressures respectively, Iin counterbalancing U-relation, and each oi vertical height suilicient 1to1 afford a desired diierential depth pressure against the boilerl pressure;

a liquid overflow outlet a predetermineddistance above, the vapor in letgpredetermining a Ydesired pressuredifferential at whichthe inlet will bej come unsealed; and conduit means for supplying vliquid to restore the normal level after losses, as

by evaporation,` entrainment or overflow; said overflow beingin a separate chamber communi- `eating witlivsaid valve means through a U-trap affording a permanent-differential depth-pressure of liquid as against maximum gaseous pressure Vdilleren'tials either toward or away from the valve.V

I 6. Af mercury Vapor heating system including mercury boiling means, 'mercury condensing l means and intermediate mercury liquid-sealed,

pressure-operated'valve means, embodying columns ofr liquid mercury having their surfaces exposed to inlet and. outlet Vpressures respectively, in counterbalancing U-relation, and Yeach oi Vertical height suflicient to afford a desired diierential depth pressure against the boiler pressure;

Y a liquid overflow outlet'a predetermined distance above the vapor inlet, predetermining a desired pressure differential at which the inletl will become unsealed; and conduit mea-ns for supplying liquid torrestore the normal level after losses, as by evaporation, entrainment or overflow; said overflow` being in a separate chamber communieating with-said valyermeans through a U-trap Y affording a permanent-differential depth-pressure of liquid as against maximum gaseous pressure diierentials either toward ory away from the valve; and discharging its overflow through a similar U-trap affording depth pressure seal l againstl maximum gaseous pressure differentials; ytogether withmeans for applying Variableriluid pressures to the surface of the overiiow column between said traps, to open or close said valve vindependently of the diierential static pressures of. the liquid columns.

7.V A primarily evacuatedheating-system serially including` a, mercury boiler, a supply conduit for the mercury vapor, mercury yaporV condensing means, a mercury condensate return conduit, a trapfor said-V mercury condensateV return. 'conduit embodying columnsof liquid mercury in counterbalancing til-relation, and; of suflicient vvertical Yheight to' seal said mercury condensing means against maximum working boilerV pressures; and

8. A primarilycvacuated heating system serially Y including a mercury boiler, a supply conduit for the mercu-ry vapor,V mercury vapor condensing Ymeans, a mercury condensate return conduit, a trap for said mercury condensate return conduit,

embodying columns of liquid mercury ,in counterbalancing U-relation," and of sufficient vertical height to seal said mercury condensing means` against maximum Working'boiler pressures; and

Va valve formaintaining a desired pressure drop between the lead conduit and the condensing means, said valve including a downwardly extending vapor inlet conduit enclosed by a valve casing of substantially larger diameter thereby enclosing and defining inner and outer columns of condensate in counterbalancing vU-relation, said valve having a liquid overflowoutlet a predetermined distance above the level of the Vapor inlet and a condenser connection for supplying condensed mercury to replace that lost in operation of the device. l,

' 9. A primarily evacuated heating system serially including a mercury boiler, a supply conduit for the mercury vapor, mercury vapor condensing means, a mercury condensate return conduit, a,

trap for said mercury condensate return conduit, embodying columns of liquid mercury in counterbalancing U-relation, and of sufficient Vertical height to seal said mercury condensing means against maximum working boiler pressures; and a valve for maintaining a desired pressure drop between the lead conduit and the condensing means, said valve including a heat insulated' downwardly extending vapor inlet conduit enclosedby a valve casing-of substantially larger diameter thereby enclosing and defining inner and outer columns of condensate in counterbalancing U-relation. v l

10. A primarily evacuated heating-system serlally including a mercury boiler, a supply conduit for the mercury vapor, mercury vapor condensing means, a mercurycondensate return conduit, a trap for said mercury condensate return conduit, embodying columns of liquid mercury in counterbalancing U-relation, 'and ofl sucient vertical height to seal said mercury condensing means against maximum working boiler pressures; and a Valve for kmaintaining a desired pressure drop-between the lead conduit and the condensing means,

said 4valve including a heat insulated downwardly extending vapor inlet conduit enclosed by a, valve casing of substantially larger diameter thereby` Y enclosing and defining inner and outer columns of' condensate in counterbalancing U-relatiom said valve having a liquid overow outlet a predetermined distance above the level ofthe vapor'inlet and a condenserV connection for supplying con-V densed mercury to replace that st in operation of the device.

ll. A primarily evacuated heating system serially including a mercury boiler, a supply conduit for the mercury vapor, mercury vapor condensing means, a mercury condensate return conduit, a trap for said mercury condensate return conduit, embodying columns of liquid mercury in counterbalancing U-reletion, and of suicient vertical height to seal said mercury condensing means against maximum working boiler pressures; and a valve for maintaining a desired pressure drop between the lead conduit and the condensing means, said valve including a downwardly extending vapor inlet conduit enclosed by a valve casing of substantially larger diameter thereby enclosing and dening inner and outer columns of condensate in counterbalancing U-relation designed to sustain a desired maximum differential depth pressure against the boiler pressure.

l2. A primarily evacuated heating system serially including a mercury boiler, a supply conduit for the mercury vapor, mercury vapor condensing means, a mercury condensate return conduit, a trap for said mercury condensate return conduit, embodying columns of liquid Vmercury in counterbalancing lJ-relation, and of sufcient vertical height to seal said mercury condensing means against maximum working boiler pressures; and

a valve for maintaining a desired pressure drop` between the lead conduit and the condensing means, said valve including a heat insulated downwardly extending vapor inlet conduit enclosed by a valve casing civ substantially larger diameter thereby enclosing and defining inner and outer columns of condensate in counterbalancing U-relation, said valve having a lateral vapor offtake to the condensing means above the maximum; high level of the mercury in the cuter leg.

13. A primarily evacuated heating system scrially including a mercury boiler, a supply conduit for the mercury vapor, mercury vapor conde. sing means, a mercury condensate return conduit, a trap for said mercury condensate return conduit, embodying columns of liquid mercury in counterbalancing U-relation, and of suiicient vertical height to seal said mercury condensing means against maximum working sures; and a valve for maintaining a desired pressure drop between the lead conduit and the condensing means, said valve including a downwardly extending vapor inlet conduit enclosed by a valve casing of substantially larger diameter boiler preslll. A primarily evacuated heating system seri-v ally/'including a mercury boiler, a supply conduit for the mercury vapor, mercury vapor condensing means, a mercury condensate return conduit, a trap for said mercury condensate return conduit, embodying columns of liquid mercury in counterbalancing U-relation, and of suiiicient vertical height to seal said mercury condensing means against maximum. Working boiler pressures; and a valve for maintaining a desired pressure drop between the lead conduit and the condensing means, said valve including a heat insulated downwardly extending vapor inlet conduit enclosed by a valve casing of substantially larger diameter thereby enclosing and dening inner and outer columns of condensate in counterbalancing U-relation, said valve having a lateral vapor oiltake to the condensing means above the maximum high level of the mercury in the outer leg, and having its top a substantial distance above said oitake to permit free upward projection of liquid mercury globules past the oitake.

l5. A primarily evacuated heating system serially including a mercury boiler, a supply conduit .for the mercury vapor, mercury vapor condensing means, a mercury condensate return conduit, a trap for said mercury condensate return conduit,y embodying columns of liquidv mercury in counterbalancing U-relation, and of suflicient vertical height to seal said mercury condensing means against maximum working boiler pressures; and a valve for maintaining a desired pressure drop between the lead conduit and the condensing means, said valve including a heat insulated downwardly extending vapor inlet conduit enclosed by a valve casing of substantially larger diameter thereby enclosing and dcning inner and outer columns of condensate in counterbalancing U-relation, said valve having a lateral vapor offtake to the condensing means above the maximum high level of the mercury in the outer leg, and having its top a substantial distance above said offtake to permit free upward projection of liquid mercury globules past the oitake, and the top of said valve being inclined in a direction to deiiect such mercury to the side ofV the valve opposite the offtake.

CROSBY FIELD.

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