US2877946A

US2877946A - Vacuum pump

Info

Publication number: US2877946A
Application number: US546052A
Authority: US
Inventors: Victor C Garrison; Edward M Nakaji; Kenneth F Wessling
Original assignee: Central Scientific Co
Current assignee: Central Scientific Co
Priority date: 1955-11-10
Filing date: 1955-11-10
Publication date: 1959-03-17
Anticipated expiration: 1976-03-17
Also published as: DE1293385B

Description

March 17, 1959 v. c. GARRISON ET AL 7 ,9

VACUUM PUMP Filed Nov. 10, 1955 s Sheets-Sheet 1 BY 777M March 17, 1959 v. c. GARRISON ETAL 2,877,946

' .VACUUM PUMP Filed Nov. 10, 1955 e Sheets-Sheet 2 10 130 98 .l l/w ill/l1 mm.

March 17, 1959 v. c. GARRISON E'T AL 2,

. VACUUM PUMP Filed Nov. 10, 1955 a Sheets-Sheet s h xww March 17,1959 v. c. GARRISON ETAL v VACUUM PUMP 6 Sheets-Sheet 4 Filed NOV. 10, 1955 Margh 17, 1959 v. c. GARRISQN ET AL 2,877,

VACUUM PUMP Filed NOV. 10, 1955 BY k%,% ,M I

March 17, 1959 v. GARRIQDN ET AL 2,877,946

VACUUM PUMP- Filed Nov. 10, 1955 v 6 Sheets-sheaf; 6

Q 67mm: fir/ ai k lezce% 656% VACUUM PUMP Victor C. Garrison, Chicago, Ill., Edward M. Nakaji, Monterey Park, Calif., and Kenneth F. Wessling, Arlington Heights, 111., assignors to Central Scient1fic Company, Chicago, [1]., a corporation of Ilhnois Application November 10, 1955, Serial No. 546,052

8 Claims. (Cl. 230-153) Our invention relates to a vacuum pump, and more particularly, to a rotary, oil sealed, two stage, series connected pump utilizing the internal vane principle.

In recent years it has become increasingly desirable, from scientific and technological standpoints, to approach a perfect vacuum as closely as possible Where a high degree of evacuation is required. Most vacuum pumps are effective to produce varying degrees of vacuum, but as more and more air is evacuated from the space in which a vacuum is desired, further evacuation becomes more difiicult and time consuming. This is because the remaining gas within the space to be evacuated is in substantially molecular form and some means must be devised to efiiciently and rapidly draw out these gas molecules if a high degree of vacuum is to be obtained.

The principal object of the invention is to provide an improved pump which is capable of materially increasing the degree of exhaustion, or the height of the vacuum, and the speed of producing it.

A further object of the invention is to provide a pump in which the operating elements thereof are more efiectively sealed from air leak than pumps of prior practices.

Another object of the invention is to provide an oil sealed, two stage, vacuum pump having finishing and roughing stages in which the finishing stage is continually lubricated by completely degassed oil, and in which oil is continually circulated through the pump.

Still another object of the invention is to provide a vacuum pump which includes means for trapping gas molecules of highly evacuated systems in oil and which provides means for insuring that this oil is positively ejected from the pump.

Yet another object of the invention is to provide an oil sealed vacuum pump in which back up of the oil to the system being evacuated is prevented.

Generally speaking, this is accomplished by mounting the two stages of the pump on a center plate, which acts as the heart of the pump. The two stages, known in the art as the finishing or intake stage and the roughing or exhaust stage, have equal volumetric displacements, and consist of cylindrical chambers in which concentrically driven rotors are eccentrically and rotatably mounted in such a manner that contact is made with the top of the respective chambers. The intake and exhaust ports of each stage are placed on opposite sides of the contacting portions of the respective rotors and chambers. Vane means comprising two diametrically opposed vanes or blades are slidably fitted in slots formed in each rotor so that as the rotors are driven, a small volume of gas having access to each intake port is expanded, cut off, and compressed into the respective stage exhaust ports.

The structure forming the two stages is completely immersed in an oil bath. The is lubricated through conduit means having an entry port disposed closely adjacent the surface of the oil bath. The oil supplied to the finishing or intake stage passes from the roughing or exhaust stage through and is con- United States Patentroughing or exhaust stage' trolled by conduit means formed in the center plate,

2,877,946 Patented Mar. 17, 1959 this oil being degassed by the exhaust or roughing stage before it reaches the finishing or intake stage. The pump intake nipple and exhaust or venting structure are secured to the center plate of the pump, the center plate being formed with conduit means, respectively, connecting these elements to the intake side of the finishing stage and the exhaust side of the roughing stage.

The finishing and roughing stages are supported by the center plate, and a housing plate is secured about each stage, said housing plates being secured to the center plate, and including lower or fiat surfaces that are adapted to contact the pump supporting surface. The pump intake port leads to a large intake chamber adapted to receive a large quantity of oil in case back up starts drawing the oil from the pump. The housings contain the oil bath in which both stages are submerged and the intake chamber is formed in the center plate.- The oil serves a three fold purpose in insuring a vacuum-tight seal of the stages, acting as a coolant, and lubricating the moving parts through oiling holes and appropriate conduit means.

Oil has access to the pump stages through only one port, which is located near the surface of the oil bath. This protects the oil seal when the pump is running, but permits air to be drawn into the pump for ease in starting.

The roughing or exhaust stage is so arranged that a metered quantity of oil is admitted into the high pressure or compression side thereof on each revolution of the respective vanes. As a result, this metered oil is forced into the roughing stage discharge port and provides means by which the pump discharge valve is opened. The gas being pumped by the roughing stage is entrapped or absorbed by the oil in the high pressure or compression side of this stage, and is positively forced out of the roughing stage discharge port and valve by the movement of oil through said port and valve occasioned by each quantity of oil forced into the discharge port at the end of each compression stroke.

Other objects and advantages will be obvious or become apparent as the description, taken in conjunction with the accompanying drawings, proceeds.

In the drawings:

Figure l is a vertical cross sectional view of one embodiment of our pump, as viewed along line 1-1 of Figure 2;

Figure 2 is a vertical cross sectional view along line 2-2 of Figure 1;

Figure 3 is a vertical cross sectional view along line 3-3 of Figure 1, with parts broken away for clarity of illustration;

Figure 3a is a fragmental view of one of the pump ports shown in Figure 3;

Figure 4 is an enlarged view of the pump shaft and adjacent structure shown in Figure 1;

Figure 5 is an exploded perspective view of the various elements comprising the embodiment of the pump shown in Figure 1; t

Figure 6 is a diagrammatic perspective view of the main operating elements of the finishing stage of the pump, with parts broken away for clarity of illustration;

Figure 7 is a view similar to that of Figure 6, but h lustrating the main operating elements of the roughing stage of the pump; and

Figure 8 is a perspective view of our pump as applied to a suitable pump mounting along with a motor for actuating same.

But these drawings and the corresponding specific de scription are used for the purpose of disclosure because they conform to an embodiment that has demonstrated its fitness for the purpose, and they are not intended to indicate the limits of the invention, which is susceptible of other embodiments. 4

nested to suitable 'p'o'wer ine'ans,"actuat's the finishing stage 14 and the roughing stage 16 v The finishing or intake stage of the umpfto cemprises a stator 26 and 'an :endfpla'te ZS'fi'X'edtotlie center plate by bolts 30. A rotor 32, formedwith apair 'df fdiaine tiically opposed slots 34 see Figures 5 and '6' one of which is adapted to be aligned with a slot 36 inthe shaft 24, is keyed to 'thesh'aft 24 by'a suitable key interposed in the '"space'defined byaslot -34'al igned with the slot 36. The rotor 32 is generally cylin dric'al in configulation, and is eccentricallymou'rited ivithin the generally circular internal surface 38 dfstator to provide a generally crescent shaped pumping "chamber 37 (see Figure 6). In the presentemb'odiment. the "upper-inost'portion of thesurface 38 is formedwith a -''u'r ved surface 39 having "a radius of curvature eqiial to that of the periphery of the'r'otor 32, and the rotor is positioned in contactwith this surface. Surface "39 extends between points 4landf43 of Figure 5.

The rotor 32 is formed with a'pair ofrelatively Hee oppci'sed slots 40 in each of whichis positioned fa Vane "o'r blade '42. The varies '1- blads 42 are slidably nhuman within slots '40, prefer'ahly'withrelatively erase tgleranc'es both between 'thefsides -6t" these slots and the fa diacent surfaces of the end plate 28 and ccn'te'r'plate 12. Each of the blades 42a fanned with 'a rounded -"e'n'd '44 adapted to contact "the surf ces 38 and ;-39 "of stator '26; the other "end or each blade is formed with "a 'hole 46 (see Figures l 'an'd'4) -adaptedto "receive 'one end of a pin or small rod 48, a 'c'ompres'sidn "s'pring "5 0 "being interposed between thhe twp vanes or blades and icc'eived about the pin or rod "48. The 'pin or rod 48 and spring 50 pass through 'a hole SZ'fGrfiie d in the shaft 24 and holes 53 formed in the rotor 32. I

The stator 26 is formed with a -pair er 'holes'54 (see Figures 5 and 6) through w'hich bolts 56 pss'to fasten the Stator to the center plate 12, and a plurality of other holes 58 through which bolts 30 pass "fixing both end plate 28 and stator 26 to the centerplate. 'On dne'side o'ffthe rotor contacting surface 39 (see Figure 6), the -"stato'r is formed on bdth'flat'stirfacs 60 and 62"thcrecif with

identical'rounded slots

64 and 66 and a't'rarisversely I extending hole'or passage 68 positioned somewhat'above the space enclosed by the stator. On the othefsidc o'f the surface 39 thestat'or is fornrc'don both sidesthereof with

identical slots

70 and 72 that are flatter in configuration than the'slpts 64 and mane a hole drl'passage 74'similar to hole 68, it being noted that 'the'holes 68 and 74e ttend parallel to the axis of's'h'a ft 24.

The surface 73 of endlplate 28 of thefinishin'g'stage is machined fiat and is formed with a'circula'r recess 75 (seejFigure 4) for a purpose'hereinafter 'made "clear.

I fl hecente'r plate 12 -comprisesagenci'ally rectangular =body *77 having machined fiat "surfaces 76Tand78 on either side thereof, and a flat bottom "surface 80 which provides 'a base adapted to engage any desired support siirfa'ce for the pump. The centerplaite is formed with an intake port 82 leadingto -a char'nber'84 (see Figure :3 fanned inside of'the ce'fiter plate that has "assistant {sear-m win; animetp'assage 86 terminating i'n aprt 8 3 'o'nthe finishing s'tageside 'of plate 12. T1116 fiir plate 12'is'als'o farmed :vvi'th'anexhaust port 90 tliatleads extending transversel through the center plate. The

shaft 24 is rotatably moupted in a bearing surface 94 formed in the center plate: and holes 96, receiving the

bolts

30 and 56, and holes 98, receiving bolts securing the finishing stage housing plate 20, are formed in this center plate. The center plate also includes a transversely but diagonally extending passage 102 beginning in a port 104on the finishing stage side of the plate and terminating in a port 106 on the roughing stage 'side of theplate. This passage 102 is inclined with refs'pec't to the axis of shaft 24 but -:is substantially level horizontally. As shown in Figures Band 5, the center plate is preferably formed with transversely extending openings such as those indicated at 105, 107 and 108 so that the oil on each side of the' center plate will in efifect be a single bath of oil.

About the bearing surface 94 on the finishing stage side of the center .plate, it will be observed in Figures 3 and 5 that the plate is formed with a circular reccssllt) having communication with the passage 102 through aslot 112 for a purpose hereinafter made clear.

The roughing stage side of the pump is formed simii-larly "to the finishing stage side, and includes

similar holes

96 and 98 forreceiving

similar bolts

30, 56 and 100. On this side of the center plate, the surface 78 is formed with a curved recess 113 about bearing 'sur fa'cc The roughingor exhaust stage 16 of the pump 10 is generally similar to the finishing or intake stage 14 and comprises a stator 114 and an end plate 116 having a machined surface 117 fixed to the center plate by bolts 30. -A rotor 118, formed with 'a pair of diametrically opposed slots 119 either one of -whichis adapted to be aligned with a slot 120 formed'in'the shaft24,1is keyed to thefshaft 24-b'y a suitable ltey 121 interposed in the space defined by a slot 119 aligned with =th'efslotv 120. The rotor 118 is generally cylindrical in configuration,

and is eccen'tric'ally mounted within the generally circular internal surface 122 of stator 114 to provide a generally crescent shaped pumping chamber 123 .(sec Figure 7). As in the case of the finishing stage, the l'lppermostportion of the surface 114 is formed with a curved surface 124 having a radius of curvature equal to that of the periphery of the rotor 118, and the rotor is positioned in contact with this;s u'rface. Surface 124 eigtends between

points

125 and 127 "of Figure 2.

The rotor 118 is formed with a pair of opposed slots :12 6'in each of which is positioned a vane or blade 128.

The vanes or blades 128 are slidably mounted within slots 126,p re ferably withrelatively close tolerances as-in the case of the finishing stage blades or vanes. 'Each of the blades is formed witharounded end'130 adaptedtocontact the surfacesi1 22'and 124 of-stator11 4 and theother end of each blade is formed with a hole 132 adapted to receive apin or small rod 134 (see-Figure 1), a cot'n- .pression spring 136 being interposed between the two "vanes or blades 128 and received about the pin or red 1 4. The pin or rod 134 and the spring 136 extend through a hole 138 formed in the shaft 24 and holes 139 formed in thc rotor.

, The-statori1l14 is formed-with a pair of holes 54 through which bolts 56 pass to fasten this stator to the center plate 12, and a plurality of other holes58 through which bolts 30 pass fixing both end plate II G-and-stator '1-14 to the centerfplate. On one side (the intake side) of the contact surface 124 (seeFigures 2 'and 7), the stator isformed onboth flat surfaces 140 and 142 thereofwith slots 144 and 146, similar to slots '70'and 72 of the finish ing 'stage stator, and a transversely extending hole or {passage 148 positioned=somewhat above or away troin the space "enclosed by the V stator. )n the otlier side-the exhaust "side of the surface -1-24, the stator is formed 'with one or'm oresubstantially vertical passages 150 posiftiond so that they-are bisected by a vertical planep'asjsin'g 75 stator 114 is made Hat, and a germ re flap valve 154 ,(see Figure 2), comprising a thin strip 156 of spring steel secured to surface 152 by screw means 158, cooperates with the vertical passages 150. An angled valve limiter element 160 is mounted over the free end of strip 156 to limit the flapping action of this valve. The element 160 also deflects ejected oil away from the exhaust port 90, this being a particularly important function at the beginning of the pumping operation when large quantities of air are being passed through the pump.

The shaft 24 on the finishing side of the pump ter minates within the space enclosed by the stator 26, but on the roughing side of the pump, the shaft extends through and is mounted in a bearing surface 162 (see Figure 4) formed in the end plate 116. Shaft 24 is formed with two

annular grooves

164 and 166 which are positioned on either side of end plate 116. Thrust washers 168 are secured against the faces of end plate 116 by, for instance, crescent Truarc rings 170 made by the Waldes Kohinoor, Inc., the inner washer 168 and ring 170 being positioned within a round recess 172 formed on the flat inner surface 117 of the end plate, about the bearing surface 162.

The dished housing plates 20 secured to the center plate 12 about the finishing and roughing stages each comprise a dished shaped upper portion 176 (see Figure 1) having an outer flange 178 surrounding same in which the bolt holes 179 for bolts 100 are formed and which merges into a lower flat stand portion 180. Webs 181 may interconnect the

portions

176 and 180 for strengthening purposes. The flat surface 182 of the stand together with the fiat surface 86 of the center plate forms the pump stand that bears against the desired supporting surface for the pump. The dished housing plate 20 covering the finishing stage 14 is provided with a transparent window 184 comprising a round piece 186 of glass or plastic provided with an oil level line 187 mounted with in a suitable retaining frame 188 that is sealed Within the port 190 formed in the plate 20. A drain passage 192 is formed in the lower end of this plate 20, leading to a suitable drain cock 194. Plate 196 secured to the outer surface of this plate 20 is for trade mark indicia, directions for operating the pump, and the like.

The dished housing plate 20 covering the roughing stage is apertured at 198, with an O-ring seal 200 being mounted within this aperture. The seal 200 engages the cup 202 forming one part of a conventional shaft seal device 204 held in place by a thrust washer 206 bearing against the crescent Truarc ring 288 mounted in the annular recess 210 formed in shaft 24. The shaft 24 is provided with an elongate slot 212 adapted to receive a key 213 for keying a pulley to this end of the shaft.

It will be noted that the end plate 116 and the vanes or blades 128 of the roughing stage differ from the like elements of the finishing stage. The end plate 116 is formed with a passage 214 (see Figures 1, 4, 5, and 7) extending radially from a port 215 at the top of the plate toward a cross passage 216 positioned adjacent the bearing surface 162. The passage 216 terminates in a port 218 in the recess 172 formed in the inner surface of this end plate. Passage 216 in the present embodiment was formed by boring a hole through the plate at this point, and inserting a plug 220 in the outer end thereof.

Both of the

rotors

32 and 118 are formed in their inner surfaces (the surfaces adjacent the center plate 12) with radially extending slots or grooves 222. Also, both the inner and outer surfaces of these rotors are formed with annular grooves 223. As shown in Figure ,2, one edge 225 of the outer sides of blades or vanes 128, that is, the sides adjacent surface 117 of end plate 116, are chamfered or beveled at 227 a part of their respective lengths. These edges are chamfered sufficiently far enough from the inner end 224 of the blades so that the passages provided by them, as further defined by the adjacent portions of the rotor and the end plate 116, respectively, will momentarily communicate with the pumping chamber 123 between the rotor 116 and the stator 114 when the respective blades are at their fully extended position shown in Figure 2.

A coupling hose nipple 226 may be mounted in the inlet port 82 and a suitable exhaust or venting device 228 may be mounted in the exhaust port 90. The nipple 226 is adapted to be connected to the tube 230 (see Figure 1) leading to the space or system to be evacuated. A tubular intake screen 229 preferably extends through nipple 226 down into and through the intake chamber (see'Figure 3). As shown in Figure 8, we prefer to mount the pump 10 on a stand 232 together with a suitable motor 234 for powering the pump through a pulley belt 236 engaging suitable pulleys, one of which is powered by the motor 234 and the other which is keyed to the end of shaft 24 by key 213.

A suitable sealing compound may be applied between the abutting portions of the center plate 12 and the re- 7 spective housing plates 20 to insure a perfect seal.

' Operation The pump is filled with a such as Cenco Hyvac Company of Chicago,

good grade of machine oil, oil, sold by the Central Scientific Illinois, through the exhaust port after removing the venting device 228. The surface 22 of the oil should be aligned with the oil level line 187 in the window 184 and during operation of the pump the oil should be maintained at or near this level.

The pump 10 is connected to the space to be evacuated by any conventional means, such as the tube 230 (see Figure 1). Care should be taken, however, to eliminate all leakage. All connections should be as short as possible, and of large diameter to reduce molecular friction. If an unmounted pump is obtained, it should be mounted on a fiat, rigid steel or cast-iron base, such as the stand 232 of Figure 8. The motor connection to the pump should be made so that the pump pullev rotates clockwise when viewed from the pulley side of the pump. This will be clockwise as viewed in Figures 2 and 7 and counterclockwise as viewed in Figures 5, 6 and 8.

The flow of oil and gas, such as air, through the pump 10 when the motor is in operation is indicated in the drawings by the unwavy and wavy lines, respectively. That is, the wavy lines, whether in broken or full lines, indicate the progress of air through the pump, while the unwavy arrows, whether in broken or full lines, indicate the path of oil through the pump.

When the motor is running, oil enters the port 215 of end plate 116 (see Figures 1 and 4) and travels downwardly through the passage 214 to passage 216 and thence through port 218 into the space 238 defined by the recess 172 formed in the end plate 116 and the adjacent face of the rotor 118, including the recess 223 therein. Oil from this space spreads to and between the abutting sides rotor 118 and end plate 116 and enters the space 240 defined by the extra recess 119 formed in rotor 118 (see Figure 2), passing through space 240 into the space 242 defined by the inner face of rotor 118 including its of the center plate together with the curved recess 113 formed therein about the bearing surface 94. The oil then passes through the spaces defined by grooves 222 into the space 243 between the radially inward ends of vanes 128 and the inner ends of slots 126 and thence to the holes 139 of the rotor leading to the radially inward portions of the vanes 128. The oil also passes into the space defined by the chamfered edge 225 of vanes 128, face 117 of end plate 116 and the adjacent portions of rotor 118, as hereinafter more particularly described.

The oil passes in a thin film between the shaft 24 and the bearing surface 94 to the space 244 defined by the recess 223 and the face 78 asst-sis 3 110 in the center ipl'ate face '76 "and the adjacent race of rotor 32 togetherwith the grooves 222 and the curved annular recess 223 formed in this face of the rotor. Oil passes from'thisspace 244 through the "space 246 (see Figure '6) defined by the extra "slot34 and the surface of the shaft 24 to the space 248 defined by recess 75 ofend plate 28 and the adjacentor outer face of rotor 32 including its recess 223. Oil passes into the space 245 between the radially inward ends of vanes 42 and the inner'ends'of slots 40 from the

spaces

244 and 248 and inwardly therefrom through the holes 53 to the radially inward ends of blades 42. Oil in the

spaces

244 and 248 at either side of thisrotor lubricates the sides'of the rotor and blades.

The arrows in Figures 1 and 4 indicate the path the oil follows as it passes through the center of the pump. The

spaces

238, 242, '244 and 248 act as oil collecting wells for maintaining pools of oil adjacent surfaces that require maximum lubrication.

"Referring to Figure 6, the gas, such as air, enters the pump through the port 82 and passes through the inlet chamber 84 and passage 86 to the space defined by the slot 66 formed in the face 62 of stator 26 through the port"8 8. As the vanes or blades 42 are rotated counterclockwise (as viewed in Figure 6), the air is drawn by, for instance, one ofthe blades '42, downwardly through this slot 66 as well as through the passage 68 and the slot 64 formed in face of the stator 2 6into the pumping'chamber 37. The following blade forces the air from the pumping chamber 37 through the slot :70 formed in face 60 and pa'ssage 74 as well as the slot 72 (see Figure 6) formed in the face 62 into passage finishing stage "rotor a'ndvan'e or blade surfaces is :fed into the passage 102 through the "p'ort 104. This is he'causethe bottom of the 'pas's'age 102 at ort 104is rower than then-pi er end ofslot 112 that is "formed in "the face 76 or theccnter plate. This is clearly shown in Figure 321 wherein it will be seen that the upper end of slot 112 merges into port 104 at a point somewhat above the bottom periphery of passage 102.

Referring to Figure 7, the oil and air are drawn from the passage 102 through port 106 into the space defined by the slot 146 formed in the face 142 of stator 114 by the action of a blade or vane 128 rotatingin a clockwise direction (as seen in Figure 7) from the contact surface 124. This action of the blade also draws part of the oil and air through pass'age 148 and the "slot 144 formed in v.

the face 140 of stator 114. Thefollowin'g blade 128 then forces the oil and air through the pumping chamber 123 arid-into one or both of thepassage's 1'50.

A'seach blade'orvane 128 approaches its lower substantially vertical position in the present embodiment,

the deepest portion of the pumping chamber 123 is reached. As the-instantaneous pressureadjacent the leading face of each blade or vane at this position is quite low, and each blade or vane has moved outwardly of the rotor far enough to bring the passage provided by champfering or beveling the edge 225 of 'the vane or blade intomomen'tary communication with the pumping chamber 12 3, a metered amount of oil is drawn into the chamber. This extra oil drawn into the pumping chamber 123 is likewise forced into the passages 150. The result is that the oil tends to fill up these passages, so that each time a quantity of oil and air is forced into'thepassages, the strip 156 of valve 154 is lifted somewhat, to free the mixture of oil and air at the top of these passages.

As the amount of air passing throughthe pump becomes less and less 'du'etothe increasing vacuum in the :spaeebein evacuated, the "air molecules tend to become entrapped or absorbed by the "oil "that is drawn into the roughing stage from the finishing stage. By inserting a 'quantityof oil "at the beginning of the 'com 'lressi'on -=nsre in the chamber "123, the passages "1'50 become filled with oil, insiirl'n'gtliat some of the 'bil "With'the molecules entrapped or absorbed therein is fo'r'ce'd out of 'thesedischarge ports each time oil is forced into them. A result of the relatively lon path the oil travels to the cham fered edges 275 is thatthe oil has 'sufiicient time 'to become outgassed before entering exhaust chamber 123.

After the oil and air is forced from the valve 154, the air molecules move to the surface of the oil bath and pass from the pump through port and the venting device 228.

It will be noted that the finishing stage of thepump is lubricated by oil passing from the roughing stage, and further, that the oil passing to the finishing stage is degassed before it reaches it. The slot 112 connecting the recess and space 244 with the port 104 and passage 102 serves this function.

Moreover, since a quantity of oil passes from the finishing stage to the roughing stage through passage 102 on each revolution of the pump, a fresh supply of oil is provided for sealing the roughing stage of the pump on each revolution. This action of the pump provides a continual circulation of the oil from the port 215, through the pump and back into the oil bath. Thus, the oil in thefinishingstage is continually being changed. The port 215 is the only place where any substantial quantity of oil enters the space defined by the stators and their end plates. "Very little oil, it any, passes from the oil bath through the thrust washer 168. I

One of the problems in operating vane pumps of the illustrated typehas been difficulty in starting due to the fact that the pump chambers fill with oil during a .period of idleness. In accordance with our invention, the oil inlet port 215 is positioned quite close to the operating level of the oil bath. When the pump is stopped, "the surface of oil drops to the port 215 asoil flows intothe exhaust chamber, and then air will be sucked into the pump chambers. Also, some air will be sucked into the pump when the pump is started. Since air can be compressed, starting with some air in the pump chambers is much easier. Moreover, the passage 102 connecting the two stages and the provision of two exhaust ports make for easier starting. With our arrangement, therefore, it is not necessary to provide some form of unloading device to start the pump.

A significant feature of this pump is that

slots

70, 72, 144 and 146 formed in the stators provide more operating space for pumping of the oil. This materially facilitates the starting of the pump and it has been found that this helps smaller models of the pump to evacuate faster.

Both stages of the pump are completely submerged in oil, and as noted above, both stages are substantially sealed oiffrom even the oil bath, except for theport215 and the passages it leads to. It will thus be seen that an extremely elfective seal is provided.

The relatively large intake chamber 84 is provided so that oil from the finishing stage will not back up into the space being evacuated if the pump is stopped and left connected to this space for a relatively long period of time. The oil as it is drawn from the finishing stage thus has a considerable space to fill before it can be drawn outwardly of the intake port 82.

The embodiment of our invention illustrated and described herein will produce a vacuum of 0.0001 mm. Hg or 0.1 micron.

The foregoing description and the drawings are given merely to explain and illustrate our invention, and the manner in which itmay be performed, and the invention is not-to be limited thereto, except insofar as the appended claims are so limited since those skilled in the art who have our disclosure before them will be able to make rnudificanens and variations therein without departing from the scope of the invention.

We claim:

1. A vacuum pump comprising an upright plate, .ra stator secured to one side of said plate, a rotor rotatably garnets and eccentrically mounted in said said stator, vane means carried by said rotor, means for rotating said rotor, a pump inlet passage formed in said plate, said passage leading to the intake side of said stator, an exhaust passage formed in said plate leading from the exhaust side of said stator, said inlet and exhaust passages terminating and commencing, respectively, at ports formed in said plate outwardly of the space enclosed by said stator, said ports being disposed adjacent the face of said stator in contact with said plate, said stator being formed with crosswise passages on the intake and exhaust sides thereof, said intake and exhaust passages being disposed in communication with said ports, respectively, and extending between said one face of said stator to the other face thereof, said one face and said other face of said stator being formed with conduit means for placing the ends of said crosswise passages in communication with the space enclosed by said stator, and an end plate fixed to said other face of said stator.

2. A two-stage rotary vacuum pump comprising a center plate, a stator fixed to each side of said center plate, said stators each being formed with an internal rounded surface, a rotor eccentrically mounted within each stator and in contact with the respective rounded surfaces to provide a crescent shaped pumping chamber within each stator, said stators each being formed with inlet conduit means on the intake side thereof and outlet conduit means on the exhaust side thereof, a pump inlet port formed in said center plate, a pump intake passage formed in said center plate and extending between said pump inlet port and said inlet conduit means of one of said stators, said one stator and its rotor comprising the pump finishing stage, a pump outlet port formed in said center plate, conduit means forming a pump outlet passage extending between said pump outlet port and said outlet conduit means of said other stator, said other stator and its rotor comprising the roughing stage of the pump, said center plate being formed with a crosswise passage connecting said outlet conduit means of said finishing stage stator with said inlet conduit means of said roughing stage stator, vane means carried by each or" said rotors, said vane means comprising a plurality of outwardly biased sliding blades having the outer ends thereof in contact with the respective internal surfaces of said stators, a shaft journalled in said center plate and extending outwardly of either side thereof, said rotors being keyed to said shaft, each of said stators having an end plate secured to the outwardly facing side thereof, a dished housing plate fixed to each side of said center plate, said housing plates enclosing said stators and the respective end plates fixed thereto, said shaft extending outwardly of one of said end plates and its enclosing housing plate, sealing means being interposed between said shaft and the last mentioned housing plate, said center plate being formed with at least one opening through the lower portion thereof that is enclosed by said housing plates, with the space within said housing plates being substantially filled with lubricant, whereby the lubricant comprises a single lubricant sealing bath for both stages of the pump.

3. The vacuum pump set forth in claim 2 wherein said roughing stage is formed with lubricant conduit means extending between a port adjacent but underneath the surface of the lubricant bath and the pumping chamber of said roughing stage, said lubricant conduit means forming the only inlet for lubricant to both of said stages.

4. The vacuum pump set forth in claim 2 wherein said pump intake passage has a relatively large volume to accept a substantial quantity of lubricant backfiow through the pump when the pump remains idle a substantial period of time while connected to the space evacuated.

5. A two-stage vacuum pump comprising a center plate, finishing stage pump means secured to one side of said center plate, roughing stage pump means secured to the other side of said center plate, a dished housing plate fixed toeach side. of, center plate, said housing plates enclosing the respective pump means and the space within said housing platesbeing substantially filled with lubricant, said center plate being formed with at least one relatively large opening that extends between each side thereof, whereby the lubricant forms a single lubricant sealing bath for both stages of the pump.

6. A vacuum pump comprising a center plate having a stator fixed to each side thereof, said stators each being formed with an internal rounded surface, a rotor eccentrically mounted within each stator and in contact with the respective rounded surfaces to provide a crescent shaped pumping chamber within each stator, said stators being formed with inlet conduit means on the intake side thereof and outlet conduit means on the exhaust side thereof, a pump inlet passage formed in said center plate and leading to said inlet conduit means of one of said stators, said one stator and its rotor comprising the pump finishing stage, a pump outlet passage formed in said center plate leading from the outlet conduit means of the other of said stators, said other stator and its rotor comprising the roughing stage of the pump, said center plate being formed with a crosswise passage connecting said outlet conduit means of said finishing stage stator with said inlet conduit means of said roughing stage stator, vane means carried by each of said rotors, said vane means comprising a pair of diametrically opposed outwardly biased, sliding blades having the outer ends thereof in contact with the respective internal surfaces of said stators, each of said stators having an end plate secured to the outwardly facing side thereof, said end plate of said roughing stage being formed with conduit means for supplying lubricant to the roughing stage pumping chamber, said roughing stage end plate conduit means being in communication with a source of lubricant, said roughing stage outlet conduit means being substantially vertically disposed, flap valve means separating said roughing stage outlet conduit means and said pump outlet passage, said vane means of said roughing stage sweeping the lubricant and gases drawn into the roughing stage pumping chamber into said roughing stage outlet conduit means to substantially fill said roughing stage outlet conduit means, whereby subsequent lubricant and gas forced into said roughing stage outlet conduit means by said roughing stage vane means lifts said flap valve means and forces a quantity of lubricant and gas toward said pump outlet passage, said center plate being formed with conduit means extending between said rotors, said finishing stage rotor being lubricated through the last mentioned conduit means, said center plate last mentioned conduit means being in communication with said crosswise passage, said pump further comprising a dished housing plate t fixed to each side of said center plate, said housing plates enclosing said stators and the respective end plates fixed thereto, with the space within said housing plates being substantially filled with lubricant and comprising said source of lubricant.

7. The vacuum pump set forth in claim 6 wherein a shaft is rotatably mounted in said center plate, said rotors being keyed to said shaft, said shaft being mounted in a bearing aperture formed in said center plate, said bearing aperture and said shaft defining the portion of said center plate last mentioned conduit means that lubricates said finishing stage, and including conduit means extending between said bearing aperture and said crosswise passage for degassing lubricant passing through said center plate last mentioned conduit means.

8. The vacuum pump set forth in claim 7 wherein the conduit means extending between said bearing aperture and said crosswise passage comprises an open slot in the finishing stage side of said center plate, said slot intersecting said crosswise passage above the bottom portion of said crosswise passage.

(References on following page) 'Osterhus Nov. 15,1949

Vdznic'a "Mar. 31, 1953 Auwarter Aug. '21, 1956