US2443667A

US2443667A - Pump

Info

Publication number: US2443667A
Application number: US611415A
Authority: US
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1945-08-18
Filing date: 1945-08-18
Publication date: 1948-06-22
Anticipated expiration: 1965-06-22

Description

Patented June 22, 1948 FF! y PUMP y Frederieltw Stalhnann, deceased, late of Wile kinsbiirg, .Pa-5, `by 'Mary E. Bechtel, administra-.- trinf-Pittfsbnrgin;:Pa:1 assigner to `7i/'eatinghouse Electric Corporation, .East Pittsburgh.Pa., a corporation -of= Perrin'.ylyarria,y

Application'riug'ust I8, 1945,-Se1'ial No. '611,415

This'inventions-relates to vacuumI pumpsfor producing the high Va'cua which vare'need'ed 'for certain' types cf 'electronic-f discharge' apparatus, and'r in particular relates tevac-num :pumpsof-the diliision type; l While the principles are of broaderI application,` the Iinvention is fillustrated by an embodiment in Wl'iiclrthe"workingfluidl producing the diffused vapor comprises an oil or other-hydrocarbon.

A-diffusion pump of `this'general type is shown in Patent No. 2,361,245, granted-October 24, 1944, forVacuum pumps, and 'assigned to the Westing house Electric Corpo-ration, East Pittsburgh, Pennsylvania. The'oildiffusion pump shown inl that application comprises a plurality of stages in which oil vaporsissuefroma plurality of nozzles positioned "at different heights along the axis' of a vertical water-cooled containerthe jets of oil vapor issuing `from the nozzle exerting a'pumping'action on gases'present in the container by entraining and'imparting'a translatory velocity to them which carries them to a .backing'eup pump issuing to the atmosphere. I'1"l`1eoil vapors from each jet are, however, condensed on .the

cool walls of the containeigand. are then runA back'througha `suitable drainv to a boiler which' reeva'porates the oil.`

In' accordance with theprior art practice, asi'llustrated in the above-mentioned application, the boiler. is subdivided into `a number of. sections equal to the number. of stages of the pump.; the condensedr oilis drainedinto the boiler .section connected tothe highest pressure stage ofthe pump, is. then passed to the intermediate stage or stages. andends up in the sectionf the `boiler whichV supplies vapor to the lowestv pressure stage of the pump. Itlh'as been found,..h'owever., that in certain instances higher pumping. effectiveness is attained if the condensed oilfis drained. back into the lowest pressure stage.

It is also .prior practice.- to vsurround. the nozzles.

of. such diffusion pumps withwalls cooled articially with water ory the` like. It has been-discovered. .that better results-fare'obtained if the walls. immediately-adjacent the nozzles areat least partially.heat-insu1atedg thereby preventing too rapid condensation of. the working vaportoo close to. the orice of. the nozzle.

It-is,l accordingly,y an. object otthelinvention to provicl'e'a-.vacuum4 pump of the diffusion: type', employing a fluid hawingfay number.- of components ofdifferent vapor pressures,- wl'iich'shall` havehigher pumping'efliciencythan did *similar dimisionapumpszof the prior art'.V

It is another object of the invention to producef 2 v a structure for diffusionpumpsemploying aiuid made up of a number* of components ofdifferentf. vapor pressures which shal'l'be capable ofiproduc ing `a higher'vacuum' than was possible with diiliu-y sionipumps ofthe priorart'.

Itis a still? furtherobje'ct of the invention-:to produce a vstructure fdr-'oil :diffusion xpumps which sha-ll enablev themto pump against :a 'higher backing-'up pressure thanfpumps ofi the prior art.'

It' is a further object ofi the invention tocon. trol thev vapor condensationin the Vregion'offthe nozzle outlet.

Other objects of the invention'willbeccme =ap parent` upon readingthe `following' description,v

' taken in connection witnthe drawinggfiniwhlch:

Figure 1 showsxan elevation viewpartlyin sect tion of an embodiment of the invention'firrwhic'l'iv a single `stage'izaump.v has an upwardly directed nozzle whichVA is' surrounded by a heat-insulatedwall,y

Fig.-A 2 shows asimilar vievwcf an embodiment ofzfthe inventionwin whi'chwa-multstage pump with clownward'ly'directednozzles isi-surrounded bya similar wal1;` and'7 f Fig. 3'sh'ows'a `similar. view ofA an` embodimen of the invention nfwhich condensed `vapor-inA a multistage pump isf/returned to thel lowest pres-r sure stage.

Referringdndetail tofFi'g: 1, the main body of thef'pu-mp comprises a vvertical cylindrical casing I closed-'at its lower'end by'a fbasezhaving anv electricalA- heating'element 3F01 a type too Iwelliknow'n toneed? a-'detailed description in good thermal contact with the lfloor of the cylinder i. If. desired,'thef-elenients l and"2'l"may=be made' cf iron or steel, 'although'either may alternatively comprise aluminum'. The upper end of the container I isrprovidedE Witha'fiange- 4'=to which can" be boltedfa -vacuum tight connection to' a back-2' ing-upf `pressure (not: shown). At roughly one fth' the height ofthe yflange 4 above the l'base2,'`

pipe 5 leading to an intake for gases from'fthe piping system Which-'is tofbe evacuated' is foonnected-vacuumtightto the cylinder l`.

Thefbottom portionof the cylinder-UI'v contains the working Ifluid S'for the pump,.the latter being The wall of the cylinder I is cooled by some suitable means, such as the helical pipe ISA, maintained in good heat exchanging -relation therewith, and carrying a cooling fluid.

Aflixed to the inside Wall of the container I and supported above the outlet of the cylinder I IA is a cylinder IEA outwardly flared at both its upper and its lower end. The ared lower end is separated from the cylindrical wall I by an annular gap, and the cylinder ISA is so positioned that the cylinder IIA extends into the flared lower end to a distance not quite as high as its junction with the cylindrical wall of I5A. The flared upper end of member ISA makes contact with the wall of the cylinder I throughout the circumference of the latter except for a small gap at one point where a vertical lip IGA extends downward below the flared upper wall. The upper edge of the member I5A which lies adjacent to the wall portion is bevelled so as to form what may be termed an annular trough; and is likewise cut at a slight angle so that the highest portion of this trough lies diametrically opposite to the center of the lip IBA and the low-- est portion of the trough conducts any liquid which may find its way into said trough to the opening between the lip I6A and the wall I.

Spaced slightly away from the lower end and side wall of the lip IGA is a member I'IA which is attached to the wall IA, and forms therewith a small trough in which liquid conducted downward by the lip ISA may accumulate.

In the partition I2A, preferably directly beneath the lip ISA is positioned a funnelnshaped duct I8A positioned to conduct any liquid accumulating above the partition IZA downward into the fluid 9.

The member I5A preferably has its outwardly flared upper portion composed of some material such as the alloy comprising substantially 32% nickel, 18% cobalt and the remainder iron which is described and claimed in Scott Patent 1,942,- 261. Whether made of this alloy or not, the red upper portion of the member ISA is made as poor a conductor of heat as is feasible, and this objective may be assisted by making this flared portion as thin as is consistent with mechanical strength.

The arrangement of Fig. 1 is as follows: The fluid 9 is vaporized by heat from` the heater 3 and flowing out of the upper end of the cylinder IIA passes through the member ISA; comes in contact with the cooled wall of cylinder I above the top of member ISA and condenses there. By reason of the poor heat conductivity between the central and lower portions of the member I 5A and the portion of that member which is attached to the wall of cylinder I, the said central an-d lower portions soon become heated to such a temperature that the vapor issuing from cylinder IIA will not condense upon them,

The condensed liquid forming on the upper portion of the cylinder I ows down the wall thereof into the annular trough at the upper edge of member ISA; is conducted thereby through the lip IBA into the trough at I'IA. Here it soon accumulates in sufficient quantity to submerge the lower end of lip IEA and thereby seal the upper portion inside cylinder I above the member IEA from the region in that cylinder below the member I5A and above the partition I2A. When sufficient iiuid accumulates in the trough portion IIA, it overflows the upper edge thereof, falls down to the partition I2A and thence :sul

4 through the funnel IBA is returned to the uid 9.

Turning now to Fig. 2, it shows a two-stage pump embodying the principles of Fig. 1 but applied to jets issuing downwardly instead of upwardly from their off-take ducts. This pump comprises a vertical cylinder I provided with a bottom member 2 and heater 3 substantially similar to those of Fig. 1. The upper end of cylinder I is provided with a flange 4 for connection to a piping system to be evacuated, and roughly 1/5 the height of flange 4 above base 2, is provided with an offtake pipe 5 leading to a backing pump not shown, The bottom portion of the cylinder I contains the working iiuid 9 for the pump, the latter being heated by the electrical heater 3 to a suilicient temperature to cause a copious offflow of vapor,

Centrally positioned in the cylinder I is a cylindrical vertical pipe II which may, if desired, be of the same material as the cylinder I, and which is preferably flared outward at its lower end to rest on the base 2. The cylinder II is likewise provided with an outwardly flared portion at its upper end as will be described in more detail below. A tie rod I2 may be positioned in the central axis of the cylinder II, its lower end screwing into the base 2.

Upon the upper end of the cylinder II is supported, preferably by means of three small spacn ing pieces I3 overlapping its edges, a cap ld roughly in the form of a truncated cone. The precise form of the cap will be discussed in detail below. The cap I4 is held iirmly against the spacers `I3 by a nut threaded on the end of the tie rod I2.

It will be evident that the upper portion of the cylinder II together with the cap I4 constitutes what may be termed an annular nozzle or orifice from which vapor emitted by a central part of thc liquid 5i and iiowing through the cylinder II is discharged into the annular space between the walls of the cylinder II and the cylindrical container I. The diameter of the inner cylinder I I is made roughly of the order of one-fourth of that of the cylinder I in order to provide a suitably large volume for the annular space into which the vapor issues from the above-mentioned annular orice. While it might be possible to make the cylinder II of a diameter smaller than that just mentioned, such reduction in diameter would not greatly add to the .available annular space surrounding the cylinder I I but would materially reduce the pressure of the vapor at the inlet side of the above-mentioned annular oriiice. Beyond these general limitations the diameter of the cylinder II is not a critical dimension but failure tor realize the importance of even these general limitations has resulted in inefficiency in many pumps of the prior art.

Ahood or umbrella I5 of conical form is fastened to the cylinder II at a distance below the lower end of the cap I4 which is roughly equal to the mean free path of the molecules of the vapor issuing from the upper end of cylinder II.

Surrounding the cylinder II is a second and shorter cylinder I6 which may be of the same material as cylinder I I and the lower end of which rests on the base 2. The diameter of the cylinder I@ should be in the neighborhood of two-thirds that of the cylinder I, the principal limitation on this dimension being that, if too small, it will reduce the vapor pressure at the orice issuing from its upper end, and that if too large it will leave too little space for gases to flow from the space above the umbrella I5 to the offtake conduit 5.

Vbelowthe surface-of the 'oi'l'therein The vupper end ofi the* fcylinder fIlBl is\:bevelled and spaced slightly away. from 'the :umbrella- 1I`5 to'l fprovidean annularorifl'ce. from# .fwhich lvap'ors rising from-they sindaceroi-k they li'q-uidffil` into. the space between the cylinders-III andclican eject'cdfinto/the annule/hspace intervening be tween the cylinders :Iland vI.-

Approximately onetenth-iofrthelength ot' the cylinder i vabo-ve the base/Eis providedfahori tA tal-1 partitionvv il' which may` convenientlyfbe lscrewed into threads cut on the-interior -wal-luoi' theylind'er I. and which' covers thespace between thelcylinder rIii-and'. the outer wall; of the cylinder This 'partition vI l' isxprovidedwitli. 'a 'grooveini itsf lower face'y which nts' the upper end portion: ot a'liner li'for the interior wall ofthe lower `por'- tion of;` cylinder 1I.'-

The. partition-VI.' is likewise'pi-ovi'd'ed-r -w-itlt a bevelled hole 2l issuing-into a-smalfl-y du'ct'lZAI-b which connectsi withla vhole inthe cylinder. 1:6 By this arrangement, tliecond'ensed 'oil is retulnedito' the portion" of.' the boile; irrmriediately''below,y .and whichY issues-vapor inf-tc.,t the;'interiory of: the cyl# inder. It This vapor issuing througliiithe-oriii'ce atf-the' upper endA of thea cylinderf '.l-S constitutes the-intermediate stage of'thelpump;

Atfben't -zcylinder or nozzle 2 IfA is. removablyin" sertedrinthe disc y'I'l and-.extends-to eject'vapor irrtooit-takev 5. i

The exterior'wall tof-th'e casing lf and-5 is surrounded by a he1ical-pi-p'e-"I'A4 through' which water-or-otl-"ier cooling fluid flows to maintain the temperaturaof suchwalls at 'av suiliciently low temperature to condense thev vapor owing 2from the orifices and nozzles already described.

Attached tothe' vinner wall oiA the cylinder l is a member of similar typeto and performing similar functions to the member-i5A` already described in Fig. 1. The member 2f: is... however, located so that the junction. between its dared upper portion and its straight cylindricalrmid?" portion are. approximatelyat: the: lower 'edge of the cap M'. It shouldbe' notedyhowever, that the member mifdiiers from themeinber lA-inFg' 1, irrthat` the' lip iA together with the bcvelle'd trough is omitted from the upper edge.

A second member performing the same function relative to the annular orifice about the upper end of cylinder I3 as the member 2d performs in connection with the annular orice about the upper edge of cylinder I l is connected to the wall of cylinder l with the junction between its flared upper portion and its cylindrical central portion approximately at the level of the lower edge of umbrella I5. The upper edge of the member 25 is, however, provided with a bevelled portion forming an annular trough similar to the bevelled upper edge of the member I5A in Fig. 1. The member 25 is likewise provided with a lip portion (not shown) capable of conducting condensed uid to a trough (not shown) substantially similar to the lip 16A and trough I'IA shown in Fig. 1-

The general mode of operation of the abovedescribed pump structure is as follows: The fluid 9, which may be any suitable material described in the art as usable in diiusion pumps, but for which is preferably employed a hydrocarbon of the ring-compound type, is heated and the resulting vapor flows up from its surface through the respective cylinders II, I5 and 2IA.

It will be evident from the foregoing that the vapor jets owing respectively from the upper end of cylinders I I, I6 and 2 IA constitute various stages of a pump for evacuating any containers r fax.

LTI

6. connected ytor-the flange 4' that-y the streainrowfingfr'om cylinder I I constitutes-the rsuv'crllowe est:v pressure, or highest! vacuum"'stag'e offfthis pumping system? thatth'e vapor vflowing from the upperendy of cylinder I 6'- constitutes an intermediete stage-' and that the vapor flowing-f fromnthe upper endof-'cylind'er- 2 IAfconstitutes the highest pressure or lowest vacuum stage.

The member 241 'and the-'memberV 25 wille-be seen .'fromthedescriptionfof Fig'. 1 to prevent condensation; ofthe vapor-issuing 4from the respecti'v'e' stages of the-pump until Atlfii's'vapor` has left the immediate vicinity otthemembers '2 45 and 25 and-the vWalls-of cylinder" I- immediately 4surrounding them, and has struck against the cooled portion-of the-walls--o-'cylinder I below thelower edges of themembers 2li-'and 25. Thevaporcon-J ld'ensingf-cn the wallsfof-cylinder'l above' member 25 will ow down into the annular troughformed bytlieupper edge thereof and fbeconducted -by the Jip and? .trough '(not shown) :associated-'With member 25 into the: annular spacel below vmemh4 ber 25 and-above' partitionv Hl.' The condensed tluid' froml bothfstages of the pump will,l yaccordingly, be conducted by duct 2th to the i-ntermeh diate' stage' off' vthe boiler between vcylinder II and cylinderv I6.

In lactual practice; it vis'foundimpossible to obtain pumping fluitlsA which are" literally and ab# solutely devoid of impuritiesand in` particular, whilethe-*hydrocarbon* ui'ds such'as'are proposed herein for use having nearly unifo'rmcon# struction, they are nevertheless'foundto vhave components ofsliglitly ,differentl vapor pressures at any given temperature.l The result of' this is that the componentsha'vin'g higher vaporpres sures tend to boil away rst and leave the com# ponents of lower, vapor pressure behind. With thisiin; mind, 'the cylinder'r I6' is arranged to have anopening in itsl lower wall-laeneath. the levelof the liquid'v 9 lat-'one side ot, the pump,;and. the cylindery II tolhave asimilar opening at a different point. The duct 2lb and-the two. openings justimentioned may,l for installed-.be positioned- 12,0,degrees.apart.about-axial-r rod I2. Inl this way any liquid flowing down the walls of cylinder I to duct 2lb must first ovv into the space within cylinder I6 and be heated there before it can ow through the respective openings into the interior of cylinder I I and into the annular space communicating with nozzle 2IA.

Fluid vaporized from the boiler outside the conlnes of cylinder I6 ows through the member 2 IA into Contact with the cooled walls of the 01T- take pipe 5 and assists in carrying away any gas which has been transported by the vapor jets constituting the pump stages from the intake space above flange 4 to the annular space below member 25,

Referring in detail to Fig. 3, it will sometimes be found that the primary feature desired of the pump is ability to rapidly pump against a relatively high back pressure in the oitake duct 5. In such cases, it has been found desirable to employ the arrangement of Fig. 3, in which a pump otherwise substantially similar to that described in the patent above-mentioned is arranged to return condensed vapor to the lowest pressure stage of the boiler rather than to a higher pressure stage. Since the members I, 2, 3, 4, 5, 9, Il, I2, I3, I3a, I4, I5 and |6111 Fig. 1 and I1, I8 and 2 Ia in Fig. 3 are precisely similar to those already described in connectionwith Fig. 2, they need no separate description here. However, the duct 2 IC which conducts uid from the annular region surrounding cylinder I6 to the fluid 9. passes through the lower portion of cylinder I6 and enters through a hole in the walls of the lower portion of cylinder Il, thus -replacing the arrangement of the duct 2lb in Fig. 2. Condensed fluid is accordingly returned directly to the lowest pressure stage at the pump inside the cylinder l l. Suitable apertures in the lower portions of cylinders Il and I6 permit the fluid introduced into the interior of cylinder H to pass outward successively into the intermediate pressure stage of the pump between cylinders Il and I6 and to the higher pressure stage of the pump outside cylinder I6. s

A pump of the type shown inFig. 3 is found to have the following characteristics:

1. A high ultimate vacuum such as 10-6 mm. of mercury.

2. A substantially flat pumping characteristic, i. e., the pumping speed does not decrease between a relatively low vacuum and a fairly high vacuum in the biasing system being evacuate-d.

3. Ability to work rapidly when the pressure in the oftake duct 5 is by no means low.

4. The possibility of collecting highly volatile materials undergoing fractional distillation in the pump, whereas in prior art types of pumps they are exhausted Iby the last stage,

5. The use of mixtures of oils, one of a `lower boiling point but lower vapor pressure at conn densation temperature and the other of a high boiling point but higher vapor pressure at the condensing temperature. The use of such composite oils permits the attainment of high vacuum even with a high backing Apressure in the oitake 5.

What is claimed is:

1. In a. diffusion pump, a. boiler, a duct leading vapor therefrom to a chamber enclosing a region surrounded by a relatively cooled Wall, and a wall surrounding the outlet of said duct and spaced away from said cooled wall portion, means for supporting said wall from said cooled wall portion by a relatively poor heat conducting material, and an inlet passage to said chamber and an outlet passage from said chamber for said pump on opposite sides of said outlet.

2. In a diffusion pump, a boiler, a duct leading vapor therefrom to a chamber enclosing a region surrounded by a relatively cooled wall, a member comprising two outwardly and oppositely :ared walls surrounding the outlet of said duct, the upper flared portion being supported against said cooled wall portion, an oiltake channel extending from the upper edge of said upper flared portion below the lower face of said upper flared portion, a trough cooperating with said cooled wall portion to seal the lower end of said channel, means for returning fluid overflowing said trough to said boiler, and an inlet passage to said chamber and an outlet passage from said chamber for said pump on opposite sides of said outlet.

3. In a diffusion pump, a boiler and a heater therefor, a central duct for conveying vapor from the central portion of said boiler to an annular orifice, a chamber having a cooled wall surrounding said orice, an annular duct for conducting vapor from the annular spac'e surrounding said central portion of said boiler to a second annular orifice, a partition separating the space above said boiler from the space within said cooled wall portion, and a duct for Conveying liquid from the last mentioned space to the central portion of said boiler, an inlet passage for said pump to said chamber and an outlet passage from said chamber for said pump on opposite sides of said two orifices.

MARY E. BECHTEL, Administratrix of the Estate 'of Frederick W.

Stallmann, Deceased.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,237,806 Bancroft et a1. Apr. 8, 1941 2,249,450 Bancroft et al July 15, 1941 2,361,245 Stallmann Oct. 24, 1944 2,390,814 Stallmann Dec.'11, 1945