US2940661A - Vacuum pumps - Google Patents

Description

June 14, 1960 A. LORENZ 2,940,661

VACUUM PUMPS Filed Jan. 14, 1957 5 Sheets-Sheet 1 FIG. 2

FIG. 2.

INVENTOR. ALBERT LORENZ A TTORNE VS June 14, 1950 A. LORENZ 2,940,661

VACUUM PUMPS Filed Jan. 14, 1957 5 Sheets-Sheet 2 FIG. 3.

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INVENTOR. ALBERT LORENZ ATTORNEYS June 14, 1960 5 Sheets-Sheet 3 Filed Jan. 14, 1957 INVENTOR. ALBERT LORENZ ATTORNEYS A. LORENZ 2,940,661

VACUUM PUMPS 5 Sheets-Sheet 5 June 14, 1960 Filed Jan. 14, 1957 .z W mm /r N 7 m w m u L A g 3 Y 3 (w 5 B QQ w 7! l, NE W m ll'l'l'l IIIVWMWM'HINWWWQ V W m I w! m g m m g v m m Vk\ v.3

lingual I v\\\\\\\\\\\\\\\\ v V w ATTORNEYS an external cooling coilon the motor housing;

Fig. 6 is a longitudinal sectional view of a motor impeller mounted on a hollow shaft in which there is disposed an electric motor for driving the impeller; V

Fig. 7 is a sectional .view taken on 'line 7-7 of Fig. 6; and a Fig. 8 is' a longitudinal sectional elevation of a Roots pump in-which a separate motor is provided at each end of one of the shaftsiand separate synchronizingand coupling means are provided at each end of the shafts. Referring to Figs. 1 and 2, a horizontal drive shaft 12 is 'journalled at opposite ends in separate roller bearings 14 mounted in respective'lopenings 16 in end walls 18 of a pump casing 19 having an inlet 20 and an outlet 22, the

' inlets and outlets being at diametrically opposed points in the central portion of the pump casing. The pump casing is of oval cross section, and the. inlet is somewhat larger than the outlet. 7 I

The left end (as viewed in Fig. 1) of the drive shaft extends outwardly from the pump casing and is surrounded by' a first vacuum tight housing 24 secured by a flange 25 to the left end wall of the pump casing. A rotor 26 of an electric motor 27 is attached to the left end of. the pump drive shaft and is coaxially disposed within a stator 28 of the motor. The motor is supplied power through electric leads (not shown) sealed through the wall of the first housing. Cooling fins 29 and a cooling jacket 30, which maybe supplied cooling waterby suitable conduits (not shown), surround the first housing. The first housing is adapted to be evacuated through a conduit 31 which leads to a suitable vacuum system (not shown). V

A second vacuum'tight housing 32 is disposed over the right hand end of the pump casing. The second housing is spaced from the right hand end of the pump'casing and casing outlet and inlet, respectively. .Thus, there is a space 37 between the intermediate portion'of the pump casing and thesecond housing, and between the right hand ends of the pump casing and second housing. A sump 38 is in the bottom of the right hand end of the second housing. A drive gear 39 is connected near the right hand end of the pump drive. shaft which extends beyond the end of 7 the pump casing. Gear 39 meshes with a driven gear 40 it then drains through a conduit 58 to return to the sump. Each of the four shaft bearings are supplied lubricant through conduits 60, and gears 39 and 40 are supplied lubricant through conduit 61.

Preferably, the lubricating oil has'a low vapor pressure to avoid adverse effects on the ultimate vacuum produced by the pump. 'Various'organic oils used in condensation vacuum pumps, for example, Apiezon oil, are suitable.

Each shaft opening in the casingend walls includes a pair of annular grooves 62 located between the casing interior and the'adjacent rollerbearing. Each groove receives the outer periphery of a respective disk or baffle 63 attached to the shafts. Thus, the grooves and baflles form labyrinth seals to impede the diffusion of gas between the pump casing interior and the spaces enclosed between housings.

The space between the pump casing and the second housing may be evacuated by providing a conduit 64 (see I Fig. 2) which connects the space with the housing outlet,

' the pump of Figs. 1 and 2 can be operated at extremely which in turn is connected 'to a fore pump (not shown) that maintains the pump outlet at'sub-atmospheric pressure. The space between the pump casing and the second housing may also be kept. under sub-atmospheric pressure through a conduit 65 which is adapted to be connected to a suitable vacuum pump (not shown), or the space may be connected to the inlet side of the pump through a conduit 66.

Both conduits 65 and 66 each have a valve 67 to permit. their optional operation.

As can be appreciated from the foregoing description,

high rotational speeds due to the absence of anysliding ,or friction seals around the shafts. The spaces within the two housings are evacuated to sufficiently low 'pres-. sures, so that gas within them flows by diifusion'rather than by pressure diiferential. Thus, there is little flow of gas through the shaft openings, and the flow of gas is further reduced by the presence of the labyrinth seal arrangement.

In the pump of Figs. 3 and 4, a pair of vertical and lat- V erally spaced shafts 70 are'journalled at their respective upper and lower ends on roller bearings 71 supported in the upper and lower end walls of upright pump casing 72, the lower end of which rests on an inwardly extending annular flange 73 of a base 74 which has an outwardly extending flange 75 and an upwardly opening concave central portion. A bell jar type 1housing.76 is disposed over the upper portion of the pump. casing and is secured by bolts 77 and nuts 78 to flange 75 of the base. The housing has an inlet 80 at its upper end and an outlet 81 in an intermediate portion. The upper, ends of the shafts project above the pump casing and arej each provided with a rotor 82 fo rmed integrally on their upper ends. Each rotor is coaxially disposed withina stator. 83 to form an electric motor 84 which is supplied power through suitable leads (not shown) sealed through the walls of a motor housing 85 disposed over each of the motorsvand which is mounted on the right hand end of a second shaft 7 42 journalledat opposite endsin bearings 43located in openings 44 of the pump casing end walls.

First and second Roots type impellers 46, 47am, re-

.spectively, mounted on the first and second pump shafts.

sealed to =the upper end of; the pump casing. A separate bevel gear 86 is attached to the lower end of each shaft beneath the casing, and engages'respective synchronizing gears 87 located at opposite ends of a rotatable horizontal Each impeller has a pair of longitudinal bores 49 to reduce the mass of the impellers, and thereby facilitate the operation'of the pump at high rotational speeds.

A .vertical lubricating pump 50 has its lower end im-- mersed in a pool of lubricant 51 in the sump. The pump is driven by .afirst bevel gear 52 located on the extreme right hand end of the shaft 12 and meshing with a horif through a conduit 56 to the interior of abore 57 in the left hand end of drive shaft 12. The fluid flows out conduit 56, and back out the: left'hand end of bore 57 where synchronizing shaft 88, supported in a bearing 89 attached to the bottom of the pump casing.

The pump casing'has an inlet 90 which opens into the space between the housing'and casing, and it has an outlet 91 which is sealed from the, space between the housing and pump casing and connected'to the housing outlet by a conduit 92. A separate Roots type impeller 93 is mounted on each'of the shafts. W 7 Thus, with-thepump of Figs.'3 and 4, the shafts'are driven 'by separate motors at auniform speed, which is insured by the synchronizing gears. -The pumped gas enters the inlet'at the upper end of the housing and passes into the pump through the pump casing'inlet. Theimpellers move the gas to the pump outlet where it is dis charged'from the housing outlet through conduit 92. As with the pump of Figs. 1 and2, the shafts rotate freely in the openings in the casing walls through which they .pass.

The pump shown .in .Fig. .5 vis similar to the pump shown in Figs. 1 and 2, except thatrhepump of FigQS has an outer housing 100 which completely surrounds the pump casing and a motor housing 102 rigidly attached to the lefthand end of the pump casing. All elements of the pump of Fig. whichare not described in detail and which have no referencenurnbers areidentical with corresponding'elements of the pump -showni-n Figs. 1 and 2.

A cooling coil 104 is soldered to the exterior of the cylindrical motor housing and cools the stator attached to the motor housing interior by the circulation of fluid from the lubricant pump, which supplies cooling fluid through conduit 106. The cooling fluid returns to the sump from the cooling coil through conduit 108. Conduit 110 supplies cooling fluid to the bore in the left hand end of the upper shaft through a conduit 112 in the left hand end of the motor housing. Fluid flows out of the bore and returns to the pump sump through conduit 114 in the lower portion of the left hand end of the motor housing and through the space between the pump casing and the surrounding housing 190.

In Figs. 6 and 7, a Roots type impeller 116 is mounted on a hollow and vertical (as viewed in Fig. 6) rotatable shaft 122. The impeller has a pair of longitudinal bores 120 to reduce the impeller mass.

A stationary hollow shaft 118 extends coaxially through the rotatable shaft and is supported at its upper end (as viewed in Fig. 6) by a support 124 in an end Wall 126 of a pump casing 128. The other end of the shaft is in a support 130 which is spaced from the other end casing wall 132.

The rotatable shaft is journalled at each end on the stationary shaft by bearings 134 which are located just inside each adjacent end wall of the pump casing.

An annular rotor 136 is rigidly attached to the inside of the rotatable shaft and is coaxially disposed around an annular stator 138 which is attached to the stationary shaft and which is supplied three phase alternating current through leads 149 sealed through the upper portion of the hollow stationary shaft.

A synchronizing bevel gear 142 is attached to hearing 134 at the lower end of the rotatable shaft and is jour' nalled on a bearing 144 in the pump casing end wall 132.

As shown in Fig. 7, the rotor or armature has sheet laminations 146 and electromagnetic eddy current ribs 148. The sheet laminations of the rotors of the various electric motors shown in the accompanying drawings are similar to conventional laminations, except that they are not impregnated with materials which liberate gas.

The structure shown in Figs. 6 and 7 has the advantage that the pump requires less space and operates quietly and with a minimum amount of vibration or oscillation due to the symmetrical construction of the motor. No uneven stresses are exerted on the pump housing or rotatabe shaft, thus assuring the vacuum tightness of the housing and smooth shaft operation. Such an arrangement is particularly suited for large pumps with large pumping capacity and power requirements.

The impeller of Figs. 6 and 7 may be coupled through bevel gear 142 to drive another impeller, if the other impeller does not have any drive of its own, or the bevel ear may be used merely as a synchronizing gear to synchronize the rotation of the impeller shown in Figs.

6 and 7 with a second similarly constructed impeller.

Referring to Fig. 8, a Roots type upper impeller 150 is mounted on an upper rotatable and horizontal shaft 152 journalled at each end in bearings 1-54 supported in end walls 156 of a casing 158 of :1 Roots type pump 160. A Roots type lower impeller 162 is mounted on a rotatable shaft 163 supported in the end walls as described for the upper shaft. Each of the shafts project outwardly from the end walls.

'6 A separatefdrivifig nidtor 164 is provided for each end of the upper shaft, and each motorisjenclosed in a separate respective end housing 166. An armature 168 of each motoris rig'idly' attached to ares'pective end of the upper shaft, and is coaxially disposed within its respective annular. stator 170, which is rigidly attached to the interior ofits respective end housing.

A separate-upper synchronizing .bevel gear 17 is mount ed on the upper shaft just outboasd' of the shaft bearings intea ch end wall. Each upper synchronizing beariug. engages .a separate second bevel gear 174 mounted on the upper end of 'a vertical rotatable-shaft 176 journalled in an outwardly extending projection 178 on each respective end wall of the pump casing. A separate third bevel gear 180 on the lower end of each vertical shaft 176 meshes with a respective lower synchronizing bevel gear at each end of the lower shaft.

Thus, with the arrangement of Fig. 8, the relatively long upper shaft is driven by a separate motor at each end, and the correspondingly long lower shaft is coupled and synchronized with the upper shaft through synchronizing gears at each end of the shafts. This arrangement reduces vibration and oscillation of shafts and impellers of relatively large pumps when operated at high rotational speeds.

With the improved driving means of this invention, Roots type pumps can be driven at high rotational speeds to permit their operation as mechanical high vacuum pumps, which operate without using a pumping vapor, such as is required in diffusion and ejector typ'e pumps.

I claim:

1. A mechanical vacuum pump of the Rootstype for operation at absolute pressure below 50 mm. Hg, the pump comprising a pump casing having an inlet and an outlet, a pair of rotatable shafts disposed within the casing, one of the rotatable shafts being hollow, a separate and balanced Root-type impeller mounted on each shaft, the impellers being adapted to mesh when the shafts are rotated to drive gas from the casing inlet toward the outlet, an annular electric motor armature mounted to the inner surface of the hollow shaft, a stationary shaft extending through the hollow shaft and disposed concentrically therewith, one end of the stationary shaft being secured to the casing, and an electric motor stator mounted on the stationary shaft and disposed within the annular armature.

2. A mechanical vacuum pump of the Roots-type for operation at absolute pressure below 50 mm. Hg, the pump comprising a pump casing having an inlet and an outlet, a pair of rotatable shafts disposed within the casing, one of the rotatable shafts being hollow, a separate and balanced Roots-type impeller mounted on each rotatable shaft, the impellers being adapted to mesh when the shafts are rotated to drive gas from the casing inlet toward the outlet, an annular electric motor armature mounted to the inner surface of the hollow shaft, a stationary shaft disposed concentrically within the hollow shaft, each end of the stationary shaft being disposed outside of the hollow shaft, one end of the stationary shaft being secured to the casing, an electric motor stator mounted on the stationary shaft and disposed within the armature and a gear train including a plurality of gears connected to the rotatable shafts for synchronizing the rotation of the impellers, one of the gears being secured to the hollow shaft adjacent the other end of the stationary shaft and having an axial opening therein through which the stationary shaft extends.

References Cited in the, file of this patent UNITED STATES PATENTS Re. 21,189 Price Aug. 29, 1939 1,038,075 Berrenberg Sept. 10, 1912 1,315,233 Needham Sept. 9, 1919 (Other references on following page) UNITED STATES PATENT ()FFICE CERTIFICATE OF CORRECTION Patent N00 2 940 66l June 14 1960 Albert Lorenz It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column l line 28 for "65" read 641 column 5, line 58 for 'rotataloe" read rotatable Signed and sealed this 15th day of November 1960,

(SEAL) Amer f KARL HQ AXLINE ROBERT c. WA-TsoN Attesting Ufiicer Commissioner of Patents

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