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Aug. 9, 1938. C. S. HORNBERGER El' AL' 2,126,553 VAÓUUMIKPUMP ' Filed April 26, 1935' 6 Sheets-»Sheet 1 Aùg. 9, 1938. c. s. HORNBERGER Er AL. ì -2,125,553- VACUUM PUMP Filed April 26, 1955 » 6 Sheets-Sheet 2 M Aug. 9, 1938. » c. s. HQRNBERGER ET Al. v ' _ VACUUM « 2,126,553 PUMP Filed April _26, 1935 _ ' 6 Sheets-Sheet 5 ’ '.5 l/ Z5 '. ' Aug. 9, 1938, . cß s. HORNBÈRGER Er' AL 2,126,553 VACUUM PUMP Filed April 26, -1935 I 6 Sheets-Sheet 4 ,MUN $2271 Allg- 9, 1938~ , c. s. HoRNBl-:RGER Er AL 2,126,553 VACUUM PUMP Filed April 26, 1935 6 Sheets-Sheet 5 lily/enfans v CÉVÄ 5'. Ã’Or'zzâœ 5 l Aug. 9, 1938. 2,126,553 c. s. HORNBERGER Er AL VACUUM PUMP Filed Aprií 26, 1935 ' 6 Sheets-»Sheet 6 ,37250775 „u „f „E 42,126,553 PaantedvAug. 9,1938. UNITED STATES PATENT OFFICE n `'VACUUM PUMP Carl S. Bamberger, Glen Ellyn, and Marshall N. States, Evanston, IIL, assignors to Central Sci entiïlic Company, a corporation of Illinois Application April 26, 1935, Serial No. 18,364 15 Claims. (Cl. Mil-_207) cinc description are used for the purpose of dis This invention relates to apparatus for’pro ducing high vacua commonly called vacuum: closure because they conform to an embodiment pumps, and the principal object is to increase the degree of exhaustion, or the heightof the 5 vacuum and the speed of producing it. that has demonstrated its ñtness for the purpose, and they are not intended to indicate the limits of the invention, which is susceptible of other 5 _ Generally speaking, this is accomplished by connecting two eccentric pumps in series, the embodiments. first, or iinishing stage, being of large capacity main pump, or finishing stage is indicated at A, and the fore pump, or roughing stage, is indicated 10 at E. The pump A comprises a casing it having a cylindrical pump chamber Ill, having an intake port l2 and a vestibule chamber lli connected with the chamber il by an exhaust port it, the intake and exhaust being divided by a vane, or blade llt, sliding in the casing and cooperating with the and arranged to deliver past the other in the l0 initial operation, or until the pressure in the sys tem is materially reduced, and then to deliver to the other that serves as a roughing stage, or lore pump, and by protecting the large finishing pump with a complete oil seal, and making the rough 15 ingstage of sufûcient capacity to really out-gas the oil in the sealing and lubricating system of the ñnishing stage, and thus prevent the oil nec periphery of an eccentric rotor it that serves as a ' essary for lubrication and sealing from placing a piston. worir on the system to be exhausted with all its intatte port it, an exhaust port it, and between them is a vane, or blade 2l, sliding in the casing and cooperating with the periphery‘of an eccen tric rotor it. The pipe it leads from the vessel, or system, to be exhausted, and is connected with the pump casing by a fitting tti which, together with the adjacent portion of the casing, provides a copious inlet passage leading to the intake port li. The vestibule chamber it is provided with a 30 ball check valve (several in a row) tti, by which the vestibule chamber may be exhausted to an exhaust chamber tit open to the atmosphere at capacity. till.. tem is approached. ` At atmospheric pressure lubricating oil contains dissolved air, absorbed gases, and volatiles which are released at lower pressures, and even a small 25 quantity of gas released to the pump chamber at extremely low pressure expands greatly and when regularly supplied by the necessary feed of oil, it slows down the exhaust and eventually deter ‘ mines the limit of vacuum that the apparatus can 3d produce. By practically out-gassing all the oil that goes into the sealing and lubricating system of the :finishing stage that pump is lei't free to tion will appear as the disclosure proceeds and the description is read in connection with the accortin intake and theoiexhaust the pump portid»itis of indicated the pump by Ba istube shown connected with the exhaust chamber 2t by a panying drawings, in which Fig. l is a perspective of the apparatus with 4,0 part of the casing at the right and the inter mediate portion removed to reveal the interior; Fig. 2 is an end-elevation looking ’from the right in Fig. l, with parts out away _on the line , in these diagrammatic views it to it, the con 35 nection between the vestibule chamber and the Further objects and advantages ci the intenn tube it. .But this is for the purpose of simpliíy- ‘ ing thev illustrations, and the actual connections are quite different. ` ' A comparison of thesuccessive positions shown Fig. 3 is a plan section taken on the line t-At in Figs. l2 to lll indicates the operation of the two pumps as the driving motor turns the large rotor countercloclrwise and the other rotor clockwise. Figs. íi, 5, 6 and 'Z are sections taken on the lines in considering the diderence in capacities appar t-ii of Fig. 3; e of Fig. 2; til-«tt .li-_5, t-t and 'l-l, respectively, of Fig. 3; Fig. 8 is a section taken on the line 1li-«t ot Fig. 6; Fig. 9 is a section on the line t--t of Fig. 3; Figs. 10 and 1l are enlarged portions of Fig. "l'; Figs. l2, 13 and 14 are diagrammatic sectional views of the two pumps and their connections. 55 \ The pump B comprises a casing il having a cylindrical pump chamber it, provided with an 20 limit on the finishing pump by releasing gas to 20 the chamber as the complete exhaust of the sys ‘ ’ In the diagrams, Figs. l2, 13 and 14, sheet 4, the But these drawings and the corresponding spe ent from these drawings, it will be seen that in the initial operation the fore pump B cannot handle all oi the gas delivered by the finishing pump A, and the pressure rises in the vestibule chamber lli until the check valve tti opens to discharge the contents directly into the chamber tti until the delivery or the finishing stage A comes within the capacity of the roughing stage B, 55 2,126,553 2 . when me valve 2| win close and thereafter uie pumps will work in series. . 'I‘he casing I8 is made in several parts, but in the main is composed of end pieces 88 and 8l (Fig. 6) and an intermediate body piece 82 containing the cylindrical bore ofthe main pump chamber II. 'I‘he end piece 88 has a bearing 88 for the shaft 84, driven by the pulley 45, and equipped with two stuiiing boxœ 88 and I1. 8| also has'a bearing (not shown) forl the shaft 84 and a stumng box 88, a portion ot which ap pears in Fig. 8. . The vane, or blade I5 runs in a slot 88 in the body member 82 of the casing and is urged to 15 wards the rotor I8 by springs 48,~ Fig. 1, con nected to the ends of a bar 4I (Fig. 6) on top . of the blade andy to the end pieces Il and 8| by screws 42, near the lower ends of spring bores 48. One wall 444 of the exhaust port I4 is inclined towards the blade Il (Fig. 1), and receives a tube 45, which serves as a valve cooperating with the inclined wall 44 and the adjacent surface oi the “ blade to close the exhaust passage against re entry of gas and the flow oi' oil from the vestibule chamber Il after the fashion disclosed in the pat ent to Dubrovin, No. 1,890,571 ofDecember'13, 1932, the ends of the tube beingslightly reduced externally to admit a small amount of oil for lubrication and sealing. ' In the ordinary operation of the pump there is no occasion for the valve 45 to open wider than in the position shown in Fig. 10, but when the pump has been standing for a long time and a large amount of oil has seeped into the pump chamber the ?rst revolution of the- rotor must discharge the bulk of that oil through the exhaust port. This makes it appropriate to vprovide for an emergency wide opening by permitting the valve to rise to the position shown in Fig. 1l. To achieve this the body member 82 of the casing is provided with a iiat seat 46, which con stitutes a retaining wall for the body of oil in the vestibule and upon which is secured angular keeper blocks 41 having spaces 48 (Fig. 6) be tween them to receive the teeth 48'on a bar 55 Yprovided with a plurality of holes 5I for screws that compress springs 58 against the bar 5|), and normally hold it in the position shown in Fig. 10, but upon being pressed from below by the valve 45, allow it to take the position shown in Fig. 11. The gas discharged from the iinishing pump passes through the spaces 48 into the vestibule. Likewise, oil in a thin layer ilows’over the seat or retaining wall 48 for supplying the cylinder I I with lubricant. The oil at a depth below the surface vcannot be entirely degassed because of hydrostatic pressure but the surface oil in the vestibule, being free of this pressure, is eil'ectively degassed at low pressure and since the oil sup plied to the cylinder is from the surface, the pump is not handicapped by the adsorbedvair contained in the oil and consequently, extreme low pressures have been obtained. 'I'he wide slot in the body member 52 necessary to admit this valve mechanism is partially closed by a grating 54, made fast by machine screws 55 (Fig. 7) and having copious openings 56 to es >tablish communication between the vestibule chamber I8 and the dome of an arched cover 51, secured to the top of the casing forming an 70 extension of said chamber and aiïording working space for the blade l5. l The vestibule chamber i8 has an upright wall 58 and a substantially horizontal wall' 59, the The opening movement of those valvesvis lim ited by a stopßl secured to the vertical wall 58 of the vestibule chamber (Fig. 3) by screws 62 passing through it and spacers G3. 'I'he rush of the oil from the vestibule cham ber during the initial operation of the pump is likely to reduce the level in the system below what is desirable and it is automatically returned through a iloat valve mechanism, as shown par ticularly in Figs. 3, 'I and 9. This iioat valve 10. mechanism in like ymanner replenishes the oil gradually withdrawn from the vestibule chamber for lubricating and sealing the ports of the fin ishing pump. 'I'he wall 58 of the vestibule cham ber is drilled and tapped at 54 to receive a valve 15 ' plug 85, Fig. 9, having inlet openings 55 in a cen tral passageway 81 leading through a valve seat l 88 near the bottom. A lever 85 fulcrumed on a pin 1l in the forked end of the valve plug car ries a valve stem 1i through a pin 12, and the 20 lower end of the stem cooperates with the valve seat 58 to close the passageway when the lever is in the appropriate position, and open the pas-f sageway when the lever is raised above that“ position.V 'I'he control is by means of a float 18,at the free end of the lever, acted upon by the oil in the exhaust chamber, where vthe normal level is substantially as indicated in Fig. 9 by the line 14. In order to prevent the rush of oil from the adjacent valve displacing the iloat'13, the 30 valve stop 6| (Fig. 3) is equipped with an angu lar plate 15, which serves as a shield or baille. The exhaust chamber 2,6 is also provided with a baille 15 (Fig. 9) to prevent loss of oil through the exhaust outlet 21. ' 35 Incidentally, this baille 15 (Fig. 9) is so placed in the exhaust chamber as to provide two paths of unequal length leading from valves 25 to the exhaust outlet 21. These paths are so related to the exhaust impulse of the pump that the noise 40 is damped, that is, one path is longer than the other whereby the crest of the impulse going around one end of the 'baille will engage the trough, as it were, of that portion going around the otherV end whereby they tend to neutralize 45 each other thereby resulting in a quieter, smooth er, ilow of the exhaust air through the exhaust conduit 21, 'I'he right end piece 3i of the casing is cored out to form a chamber ‘18 (Figs. 3, 5 and 6) pro vided with a door 19 (Figs. 1 and 5) to afford ac cess to the shaft bearing, the stufling box 38 and screws 42. The end piece 3|,is also cored out to provide a chamber 80 (Figs. 4 and 5), the end Wall 8| of 55 which is provided with a large opening closed by the plate 85 to permit the fore pump B to be inserted as a unit. The pump B in this illustration is really two eccentric pumps in series, the casing of which in-" w cludes the end plate 82 (Fig. 6) < the cylinder rings 88 and 84, the intermediate plate 85, and the large end plate 85, the latter being bolted to the end wall 8l to secure the fore pump in place. Two stage eccentric pumps of this general char acter are well known on the market, and may be had somewhat in the form shown by the patents to Dubrovin, No. 1,890,572 of Dec. 13, 1932 and to _ Klopsteg, No. 1,890,614 of Dec. 13, 1932. l 'I'he main pump shaft 34 projects through the 70 end piece 3i and is equipped with a gear,81 (Fig. 1) meshing with a gear 88 on the shaft 89 of the latter equipped with valve seats 88 (Figs. 9, 12, Afore pump B. The gears are enclosed by a cover 75 13 and 14) to receive the ball valves 25.v 90 which also serves to enclose part of the pss 75 3 2,126,553 sageway from the vestibule chamber I3 to the ’ intake oi the fore pump. As shown, an opening 9| (Figs. 1 andv 2) through the end wall 3| puts the upper portion of the chamber 13 in communication with the inside of the cover 90, and an opening 98 (Figs. 2 and 6)., puts the lower portion of the chamber 1l in communication with the inside oi the cover 9|. » - ` 10. The intake port 92 of the fore pump is through ' the end plate 96. the exhaust port from the first stage and the intake for the second stage is a f bore 93 `through the intermediate plate 35, and the exhaust port 94 (Figs. 4 and 6) of the second stage leads into the chamber 90, which is in com munication with the exhaust chamber 26 through a cored passage 95. ` The end plates 30 and 3| are each provided with a groove 96 (Figs. 6 and 8) which has its upper end in communication with the dome of the cover 61, which is in communication with the vestibule chamber through the openings 56 (Fig. 7). 'I'he other end 91 of each groove 96 is in communication with the vestibule chamber at the> end of the valve cylinder 45. v f The grooves 36 at their lowermost portions are connected by a transverse bore 99 (Fig. 6) which also°commuhicates with vertical bores |00 and |9|, which establish communication with the spring bores 43 and.’ hence, with the vestibule chamber. is ample when geared down to drive vthe main shaft 34 at 450 R. P. M. which, with the ratio indi cated would drive the fore pump shaft at 375 R.. P. M. With such a pump vacuum, less than one hundredth oi’ a micron has been produced with ten microns in the vestibule chamber. The best mechanical pumps having similar vol ume heretofore available have reached a limit at 10 about one micron. It frequently happens in the use of this ap~ paratus'that it is shut down, without being re lieved, long enough for atmosphere to force oil from the exhaust chamber into the Dump cham bers of the roughing stage. Upon starting the 15 motor with the apparatus in this condition the load is unduly heavy, and to relieve it, a friction clutch |04 (Figs. 1 and 6) is introduced into the gear 99 to allow the finishing stage to operate with comparativefireedom while the oil in the 20 chambers of the roughing stage gradually works out through the restricted ports. As soon as the great Jresistance offered by the oil has been re lieved, the clutch engages and the roughing stage begins to operate. This delayed operation of the 25 roughing stage is no detriment to the efiiciency of the apparatus, for during the period that it is inactive, the finishing stage is working against comparatively high pressure, and is therefore de livering so much gas that the valves 25 are open 30 and the operation of the roughing stage would ’ The opening 9| (Figs.- l, 2 land 3)> through the end wall 3| of the end piece 3l allows oil in the system to enter the chamber formed by that end wall and the cover 90 enclosing the gearing, and -the normal oil level in this chamber is about as indicated by the line |02 (Figs. 1 and 10) and is the same as that of the oil in the vestibule cham ber I3 (Figs. l2, 13 and 14) . The baffle |03 shields the intake port 92 of the forepump and deter mines the maximum height of the oil level‘in the vestibule chamber I3 -and chamber 10. When the oil level rises abovethe upper end of the plate |03, the oil will flow over the baiile and will be drawn into the roughing pump andv discharged into the chamber` 90, which is in communication with the reservoir 26, on the discharge side of the rough/ing pump. The height of the oil in the chamber may be observed through the glass covered sight opening lll (Fig. 6). y These various passages and grooves put oil in every joint of the pump casing to seal it, and all of the oil in the system for lubrication and sealing is in communication with the vestibule 55 chamber and subject to the pressure in that chamber. The fore pump, having its intake con nected with the vestibule chamber in addition to ’I‘he stuiling boxes 36 and 31 are of the ring seal type shown and described in Dubrovin, No. 1,890,573, Dec. 13, 1932; and the box 31 is con 35 nected by a pipe |05 (Figs. 6 and 9) with the vestibule chamber 26 below the oil level. Hence, any leakage past the box is degassed oil. The ñtting 24 (Fig. 1) has a Wide flange |06 fitted to a machined face |01 on the body piece 40 32 of the pump casing I0; and the flange is pro vided with a sealing groove |08 connected by a drilled passage |09 (Fig. 8) through the body piece with sealing groove 96. As a result, any leakage, upon reaching the groove, passes to the 45 vestibule and is taken ofi by the fore pump. We claim as our inventionz- ’ l. In apparatus for producing high» vacua., a pump of large capacity having a pump chamber and an exhaust vestibule chamber, a check valve 50 permitting gas to iiow from the pump chamber to the vestibule, an oil seal for the pump charn ber connected with the vestibule and subject’to the pressure in the vestibule, a second pump having its inlet connected with the vestibule 55 chamber and of small capacity relative to the first pump, but of sufficient capacity to outgas exhausting it, serves to outgas all the oil in‘the the oil inthe seal and vestibule, a check valve exhaust from the vestibule when the system and, thereby prevent gas'reaching the permitting delivery of the first pump exceeds the capacity 60 ,the finishing stage, either as anl chamber Il of of the second pump, an exhaust chamber receiv incident to lubrication, or as seepage through the ing the exhaust from the vestibule chamber, a joints ci' the casing. The inlet ports i2 of the finishing stage and return passage connecting the exhaust -and the all passages leading to them are made very wide vestibule chamber, a valve controlling the return 65 as compared with their length to reduce the im pediment to rai'eñedv gas finding its Way into the chamber of` the finishing stage. The main pump chamber ii is ’7l/2 inches long and d inches inside diameter and the rotor it is (ii/2`inches outside diameter. 7 The cylindrical chambers of the fore pump are . 2%» inches inside 4_diameter and l inch long, and v the rotors are 2 inches in diameter. The gear' 31 has sixty teeth and the gear bt 75 seventy-two teeth, and 11/2 i-l. P. electric motor passage, a lever for operating the valve, and a 65 float for the lever. 2. A pump comprising a casing having a pump chamber, a vestibule chamber normally at sub atmospherlc pressure and an exhaust chamber having sealing oil therein, a rotor in the pump 70 chamber, a check valve between the pump cham ber and the vestibule chamber, another check valve between the vestibule chamber and the exhaust chamber, a. second pump chamber, an intake passage for said second pump chamber in 75 4 2,126,553 communication with said vestibule chamber, an oil seal for the first pump supplied solely from the vestibule chamber and means including valve mechanism to return oil to the _vestibule chamber when oil in the exhaust chamber reaches a selected level. 3. A pump comprising a casing having a pump chamber, a vestibule chamber and an exhaust chamber, a rotor in the pump chamber, a check 10 valve between the pump chamber and the ves tibule chamber, another check valve between the vestibule chamber and the exhaust chamber, an oil seal for the pump supplied from the vestibule chamber, means including valve mechanism for 15 returning oil to the vestibule chamber when oil in the exhaust chamber reaches a selected level, a> second pump having an intake connected with the vestibule chamber and an exhaust connected with the exhaust chamber. A 4. In a vacuum pump mechanism, a ñnishing pump having a rotary piston and intake and discharge passages, a two-stage roughing pump, a chamber for containing oil for supplying the same to said finishing pump only, for sealing and lubricating the same, a shallow mass of oil in said chamber, oneY of said passages being in com munication with said chamber beneath, but ad jacent to, the surface of said oil, the intake pas sage of said roughing pump being in communica tion with said chamber above the level of said oil whereby said oil will be degassed prior to the entry into said finishing pump, a reservoir in the dis charge passage of said roughing pump for col-~ lecting oil contained in the discharge gases of 35 said pump, and float controlled valve means for supplying oil from said discharge passage to said chamber when the oil in said last-named passage rises above a predetermined level. 5. In a vacuum pump, a cylinder, a piston for 40 for said cylinder and an exhaust vestibule for containing oil for lubricating said cylinder and into which said' pump exhausts, a check valve in said vestibule at the level of said oil, said valve arranged for admitting oil to said cylinder from y the surface only of said oil in a thin layer for lubricating the cylinder. a roughing pump, and a passage connecting the intake of the roughing pump with said vestibule above the level of the oil therein whereby the amount of oil supplied to said cylinder is degassed. 9. An apparatus for producing high vacua com prising a ñnlshing pump having a cylinder, -an intake for said cylinder, a piston movable in said cylinder and an exhaust vestibule for containing oil for lubricating said cylinder and into which said pump exhausts, a check valve in said vesti bule, a valve seat for said check valve, a retainer wall associated with said seat, 'said wall con stituting retaining means for said oil whereby 20 oil supplied to said cylinder fiows over said wall from the surface of the oil ln said vestibule, a two stage roughing pump in series having intake and discharge passages, and a passage connect ing the intake of said roughing pump with said 25 vestibule above the level of the oil therein, where by the oil in said vestibule will be under partial vacuum for degassing the oil supplied to said cylinder. 10. An apparatus for producing high vacua 30 comprising a finishing pump having a cylinder, intake and discharge passages for said cylinder, a piston movable in said cylinder, a roughing pump in series with said finishing pump and having intake and discharge passages, a reser 35 voir for containing'a mass of oil for lubricating s_aid cylinder, means for maintaining the oil in said reservoir at a pressure not substantially above that of the intake of said roughing pump said cylinder, intake and discharge passages .for for degassing said oil, and a passage in communi the pump, valves in the discharge passage, and cation with said reservoir at substantially the a baille in the discharge passage so positioned rel ative to said valves as to cause the discharge gas to strike said baiiie at right angles thereto closer to one end of said baille than to the other whereby said gas is caused to take two paths of unequal lengths, whereby the noise incident to the opera tion of said pump will be reduced to a minimum. 6. In a vacuum pump, a finishing pump, a 50 roughing stage pump, a chamber for containing a small amount of oil for lubricating said pumps, an exhaust port for said finishing pump opening into said chamber and constituting the principal means for conducting oil from said reservoir to 55 said finishing pump for lubricating the same, an intake passage for said roughing pump in com munication with said chamber above the level of the oil therein, a discharge passage for said roughing pump, a reservoir in said discharge pas sage, a passage between said chamber and reser- . voir, and a float valve for controlling the passage , of oil from said reservoir into said chamber. 7. In a vacuum pump, a casing having a finish ing pump therein, an oil chamber for receiving the 65 discharge from said pump, an end piece for said casing, said end piece having a chamber therein, the outer wall of said chamber having an open ing therethough, a closure plate for said opening, a roughing pump secured to said closure and in 70 sertable through said opening, and an intake for said roughing pump in communication with said oil chamber. 8. An apparatus for producing high vacua com prising a finishing pump having a cylinder, a pis 76 ton movable in said cylinder, an intake passage 40 oil level therein for conducting degassed oil from the surface of said mass to said cylinder for lubricating the same. ’ il. An apparatus for producing high vacua comprising a finishing pump of large capacity, a roughing pump of small capacity, a discharge passage comprising a vestibule containing oil for said finishing pump in communication with the intake of said roughing pump, an oil sealed relief check valve in a Wall of said vestibule for permitting the escape of the exhaust through said passage from said finishing pump only when the delivery of the finishing pump exceeds the capacity of said roughing pump. l2. In apparatus for producing high vacua, a pump of large capacity having a pump chamber, an intake passage for said chamber, and an ex haust vestibule, said vestibule being adapted to contain oil for lubricating said pump, a check 60 valve permitting gas to flow from the pump chamber to the vestibule, an oil seal for the pump chamber connected with the vestibule and subject to the pressure in the vestibule, a sec ond pump having intake and discharge passages, 65 said last-named intake passage connected with the vestibule above the level of the oil therein and of small capacity relative to the first pump, but of sufiicient capacity to outgas the oil in the seal and vestibule. a check valve permitting 70 exhaust to be discharged from the vestibule in dependently oi’ the second pump when the de livery of the first pump exceeds the capacity of the second pump, and an oil seal for said last named valve. ‘ 75 2,126,553 5 , 13. A high vacuum pump comprising a ñnish ing pump, an intake and a discharge port for said ñnishing pump, an oil reservoir for receiv intake passage for said roughing pump being in communication with said chamber above the level of the oil therein for outgassing the oil ing the discharge from the discharge port of said ñnishing pump, a valve for said port, oil within said reservoir at substantially the level of said valve and arranged to escape from the surface thereof past said valve into the discharge side only of said iinishing pump for lubricating 10 the latter, a roughing stage pump provided with in said chamber, a reservoir in the discharge pas sage of said roughing pump, a passage between said chamber and reservoir, and a float valve for controlling the passage of oil'from said reser voir into said chamber. 15. In a high vacuum pump, a rotary ñnishing pump of large capacity, a rotary two-stage rough an intake passage and a discharge passage and ing pump of smaller capacity arranged in series, having its intake passage in communication with said reservoir above the oil level therein whereby oil supplied to said finishing pump will be out a vestibule chamber for receiving the discharge from said iinishing pump, an oil retaining wall in said vestibule'for forming a chamber for con-t 15 gassed by said roughing pump. 14. In a vacuum pump, a finishing pump„a taining oil for lubricating said finishing pump by supplying the same directly to the discharge roughing stage pump, intake and discharge pas sages foi' said pumps, a chamber having its major portion above said finishing pump for contain 20 ing a shallow body of oil for lubricating said fin ishing pump by gravity, the discharge passage for said iinishing pump opening into said cham ber through which finishing pump discharge passage oil is supplied to the ilnishing pump, the side of said ñnishing pump in a thin layer over said wall, and means for connecting the intake of said roughing pump to said chamber above said wall andthe level of the oil in' said chamber _ for degassing all of the oil supplied to the dis charge side of the finishing pump. CARL S. HORN'BERGER. MARSHALL N. STATES.