US2668655A - Vacuum pump - Google Patents

Description

9, 1954 H. G. BOWERING 2,668,655

VACUUM PUMP Filed May 19, 1951 6 Sheets-Sheet l Z'mventor Clamp,

Gttorneg Feb. 9, 1954 G. BOWERING 2,668,655

vzicuum PUMP Filed May 19, 1951 s Sheets-Sheet 2 1 i FiG.2

3nventor Hen-r5 G.Boweri.ng

attorney Feb. 9, 1954 Filed May 19, 1951 H. G. BOWERING 2,668,655

VACUUM PUMP 6 Sheets-Sheet 4 Feb. 9, 1954 Patented Feb. 9, 1954 VACUUM PUMP Henry G. Bowering, Needham, Mass., assignor to Kinney Manufacturing Company, Needham, Mass., a corporation of Massachusetts Application May 19, 1951, Serial No. 227,181

7 Claims.

This invention relates to vacuum pump units of the type consisting of first and second stage pumps combined in a single housing and driven by a common shaft with the inlet of the second stage pump being in communication with the outlet of and the oil reservoir for the first stage pump- Such compound vacuum pump units are wide- 1y used because of their pumping efiiciency in the region of high vacuum. The function of each pump of such a unit, in attaining that efficiency, is that the second stage pump serves as a roughing stage in which it functions to back-up the first stage pump and to de-gas its sealing oil while the first stage pump serves as a finishing stage. The second stage pump, however, has the heavier load since its discharge to atmosphere is through a spring loaded outlet valve. In practice, it maintains a low pressure, typically in the range of from to microns, on the outlet of the first stage pump and on the oil in its reservoir to remove dissolved or entrained air, or both, therefrom to condition it for sealing purposes. The first stage pump must be adapted to maintain a substantially lower pressure, .05 micron or less, on the chamber or system with which its inlet is in communication. The pressures referred to herein are based on MacLeod gauge readings.

, Leakage into a vacuum pump would, of course, make satisfactory performance impossible and care is exercised to provide suitable air-tight housings. The housings for compound vacuum pumps vary considerably in their specific forms but each commonly includes a pair of easing parts for the pump mechanisms, a center wall part separating them, and a head to close the other end of each casing part. The shaft extends through the head for the second stage end of the housing, through the center wall part and is supported by a bearing unit located in a blind recess in the head for the first stage pump. In some housings, each part is a separate casting while in other types, the center wall and casing parts are combined in a single casting.

While such housings suitably safeguard against air leakage into them, interstage leakage, when it occurs, impairs performance and is difficult to locate. There is a substantial pressure differential between the stages of a compound vacuum pump and even the slightest leak from the second stage pump to the first stage pump is serious because of the substantial volume to which gases expand at the low pressures maintained by the first stage pump.

There are two probable paths for interstage leakage. One of them is along the shaft and the second is through the center wall. Spongy cast iron commonly results when the casting is thick or where adjacent portions thereof differ in thickness. Even where it occurs, the surface or skin of the casting is usually sound. If the surface skin of the casting is machined away on only one side, the skin on the other side usually will prevent leakage therethrough. If opposite surfaces are machined, leakage through the metal between the machined faces will occur often enough to be a commercial problem.

The principal objective of the present invention is the provision of a compound or two stage rotary vacuum pump in which the probability of interstage leakage, both through the center wall and along the shaft, is virtually eliminated.

This result is attained by providing a rotary two stage vacuum pump the housing of which has two axially alined cylindrical working spaces isolated from each other by a partition. The partition isolates and forms the proximate end walls of the working spaces and includes within itself chambers, formed in the casting operation and retaining the casting skin. These chambers are directly interposed between the parallel machined surfaces which are the proximate end surfaces of the two working spaces and approximately surround a central hub which has a bore coaxial with both working spaces. Sealed in the bore is a plain bearing-bushing rotatably supporting the shaft which extends into the working spaces and operates the rotary displacing means of which there is one in each working space.

One of the chambers is the oil reservoir for the first stage pump and has ports opening through the machined surfaces to establish the outlet for the first stage pump and the inlet port for the second stage pump. formed with oil passages which are fed by an oil passageway leading from that oil reservoir. One such passage leads to the shaft and the other is arranged to deliver oil to the first stage pump for lubricating and sealing purposes without breaking the shaft lubricating oil film and thus destroying its effectiveness as a seal against interstage leakage along the shaft.

With the exception of the machined surfaces which serve as the proximate end surfaces of the Working spaces and the axial bore for the bearing-bushin all other surfaces of the partition have an unbroken'casting skin which serves as an effective barrier against leakage. Those portions of the machined surfaces which are The bearing-bushing is the other walls. Thus sponginess throughout the casting is minimized and even should it occur, the skin of the casting is eifective to prevent leakage. V g These features of the invention make po: b 1e adequate protection against interstage leakage in compound vacuum pumps and. enable ether; changes to be made in the construction of the first stage pump that also contribute to economy in production and improved efficiency both in operation andv in relation to weight. and horse power requirementsas will be apparent fromthe accompanying drawingsshowing these and other features in an illustrative embodiment of the invention.

In the drawings:

Fig. 1 is aside View ofa compound vacuum pump in accordance with the invention with its oil trap partly sectioned.

Fig.2 is .a side view of that pump as viewed from its second stage end.

Fig. 3 isa section through the pump on a plane indicated by the lines 3-3 of Fig. 2.

Figs. 4, 5-; and 6 are sections through the pum on planes indicated by the lines fi; 5-5, and 8-5 respectively, 7 of Fig;

Fig. '7 is an end elevation of the main shaft bearing-bushing carriedby the center wall lookihg at its first stage end.

Fig. 8 is a longitudinal section of that bearing-bushing.

Fig. 9 is a Side elevation of the main shaft bearing-bushing carried by the second stage head, a part being broken away to expose an oil pas- Fig. "10 is viewor that bushing as viewed from its outer end. j V V N Fig. 11 is an end view of theeccentrieof the first stage. That for the second stage is 'i'dehti cal, and

Fig. 12 is a section along the, lines c n or Fig. '5.

in the embodiment or nie'iiiventieii illllstftd in the r lrawings (see particularly Fig 1) there is illustrated a two stage acuum pump housin comprising a center wall member generally in- (heated at It and supported by apedestal n, heads l8 and I9, and pump casing pails L'Zilgahd 2| each clamped between a corresponding head and the center wall.

Machine screws 22 eirtend through the head l8, the flanges 23 of the casing part 'd are threaded into the center wall It. The resulting assembly is the housingo'f the first stage pump and is generally indi'catedby the numeral 25. Machine screws 25 extend through the head is, the flanges 26 ofthe casing partzl and fare threaded into the center wall l5 thus proi'lidi'ng the housing of the second stage pump, indicated generally by the numeral 21. In practise, each face of the center wall I6 is provided with locating pins to ensure correct assembly.

The contacting faces of the castings are preci'sely machined to ensure surfaces that can be tightly sealed together to render the joints air tight. No gaskets are used between such faces.

As the heads l8 and I9 have only their inner surfaces machined and casing parts and 2| have only their inner and end surfaces machined, they 5 present no serious leakage problem.

As best shown in Figs. 3, 5 and 12, the center wall member 16 has, between its machined faces a first chamber or cavity 23 and a secondchamber or cavity 29. The chambers are produced in the casting operation, by coring or otherwise. These cavities are located and dimensioned to provide an external shell 36 and a partition 3| in the form of a web having a hub portion 32. Thehuh may be cored and in any case is bored at 33 to permit the bearing-bushing 42 (hereinafter described) to be pressed into position.

The first cavity gs extends from a point below the hub portion 32 to a point well above it and has; adjacent its upper end, a cored port 35 opening through one face of the center wall It and a cored port 35 opening through the other face thereof (see Fig. 12). These ports are laterally ofiset with respect to each other and constitute; respectively, the outlet port of the first stage pump and the inlet port of the second stage pump.

The cavity 28 serves as an oil reservoir for the first stage pump and has a drilled passageway 37 in communication with the bushing receiving bore 33. The center wall It a removable drainage plug 38. At 39, there is a pmg can y; ing a stem 48 which extends into the passageway 3'1 to provide interchangeable means for r ga; lating the rate of oil "flow thr'ethrough Both plugs seat against toric; riihber -like gaskets ll As no surface of the cavities is machined-the casting skin of those surfaces is effective to k the machined surfaces, ensuring against lea g'e. While not all portions of the machined faces "f the center wall 16 are sq kedth iiiba jl efd portions are suitably separated; The hub 3L2 is or substantial ag'iial length, a's w'ill be aiil arent from Fig. 3, but the gesigii of thjepjcente p'errriit's such uniformity of m' etal sections a s will ensure sound castings. Where, additionally; the hubis cored, it is unlikely to befspongy, T e

ingfighas an encircliri'g annular groove ll 'jnt mediate its ends, positioned to receive oil d ,5 charged through the supply passageway-s1; A radial port, leads from this to the. joi r yr the sha'ftf34, and to. the passage which leads to the first stage ens-iii the bushing l As best shown in nigsgs nd 4. the casing ztferi closes anfop'en, right circularcylindri cal "ch her 48, the ends of which are closed p ane" surfaces of the parts li and [8. 'lfhisisthefirst stage working space. .Ca singj'ZG also, includes an ri cha er Q I e n'ection is and a cylindrical seat 49, ea roir tri ev i V0 guide b16 5 T 5 3311 e tq sp a ri ht circular cylinder equalin length with the chain-'- ber :46. The casing part i fi'falso has anfo 8 ill extending from end to end thereof aria s v ing as an outlet'chamber' communication with the reservoir port 35 In 'tIfecn ter wan "l6. 751 outlet port 52 opens into the workin 'space E6 adjacent to and through the lower extremity of the cylindrical guide seat 50 and extends upwardly to open into the outlet chamber 5| over a dam or rim extending above the bottom thereof. This dam (see Fig. 4) serves to cause retentionof a limited column of sealing oil in the lower part of the port 52 by controlling discharge of excess oil.

The displacing abutment comprises an eccentric 53 keyed to the shaft 34 and rotatable in the cylindrical sleeve 54 which has a radial hollow, open-ended, plate-like arm 55 extending into the inlet chamber 41. Arm 55 fills the interval between the guide blocks 56 and is guided thereby. The eccentric 53, the sleeve 54, the arm 55, and the guide blocks 56 are all of the same length as the casing part 20. The arm 55 has a port 51 shown in Fig. 4 as closed by one of the guide blocks 56 when the sleeve 54 sweeps past the outlet port 52. It remains closed until the plunger has again started its sweep of the working space 46. The sleeve 54 does not engage the cylindrical wall of its working space, but requires for effective pumping action an oil seal.

Each end of the eccentric 53 is beveled at its outer edge as shown at 58 in Figs. 3 and 11, to establish with the sleeve 53 an annular groove with which a radial groove 59 in each end of the eccentric is in communication. On each rotation of the eccentric 53 the radial groove 59 adjacent the center wall I6 receives oil from the bearin passageway 45 (see Figs. 3 and S) This oil fiows outwardly to the groove 58. Sealing oil may also fiow through the running clearances between the eccentric and its sleeve to the opposite end of the sleeve where it is distributed in a similar manner to establish an oil seal at that end of the working space.

The second stage pump 21 is essentially similar to the first stage pump and, as best shown in Fig. 6, has its casing part 2| formed with an opening extending from end to end thereof. The opening affords a right circular cylindrical working space 60 axially alined with the similar working space 46, an inlet chamber 6| with which the center wall port 36 communicates, and a seal 62, 63 for the guide blocks. 15. The casing part 2| also encloses cavity 64 which, when the gasketed window 65 and frame part 66 are in place, serves as an oil reservoir for the second stage pump. The outlet 61 of this pump opens into the working space 60 adjacent to and through the lower part of the seat 63. The outlet 61 is controlled by a lightly loaded check valve (see Fig. 6) consisting of a facing element 60 and a valve block 69 freely guided by the bolts 10. Springs 1I tend to seat the valve. The window makes it possible to check the quantity and condition of the oil and the operation of the valve.

The pumping mechanism of the second stage pump includes an eccentric 12 keyed to the shaft 34 and rotatable in the sleeve 13. This has a hollow, open-ended, plate-like arm 14 extending into the inlet chamber H and slidably guided between the guide blocks 15. These are segments of the same cylinder as the seats 62 and 63. The arm 14 has a port 16 which is closed by one of the guide blocks 15 when the plunger 13 sweeps past the outlet 61. Like the corresponding parts of the first stage pump, the eccentric 12, the sleeve 13, the arm 14, and the guide blocks 15 are of the same length as the cylindrical working space 60 and at each end of the eccentric 12 are oil grooves identical to the grooves 58 and 59 of the first stage pumping mechanism.

The reservoir 64 has an outlet 11 provided with an oil trap, generally indicated at 18, which is employed to conserve oil and to prevent damage by the discharge of oil in the vicinity ofthe pump. I have shown the oil trap 18, in Fig. 1, as having a cylindrical body 19 through the center of the bottom of which extends an inlet pipe 80. The upper end of the pipe extends a substantial distance above the bottom of the body 19 to provide a sump out of the path of gas flow. The pipe 80 has a lateral oil return port 8|.

Above the upper end of the pipe 80 is a disc batlie 82 supported by brackets 83 while above the bafile 82 is an annular second baflie84 of frustroconic section. This establishes a gutter. which is slightly inclined to direct oil collecting therein towards the conduit 85, extending into the sump. The body 19 has outlets 86 adjacent its upper end overhung by a cap 81 having a downturned flange 8B spaced outwardly from the outlets 86. The cap 81 has a pendant annular baflie 89 located above the middle. part of the .bafile 84 so that oil dripping therefrom is caught and returned to the sump.

The shaft 34 extends through the head I9 which includes a hub 90 and is bored to receive the shaft supporting plain bearing-bushing 9I. The hub 90 is counterbored to receive the ring 92 which carries a seal 93 of the toric type sealing against leakage between the ring 92 and the hub 90. A second counterbore 94 provides a chamber for the rotary shaft seal. The rotary shaft seal is shown as including a running ring 95 seated against the ring 92 and to which is attached the larger end of the corrugated resilient. sleeve 96. At its outer end, the sleeve 96 is con-- fined by a ring 91 connected to a sleeve compressing holder 98 which is under the influence of a spring 99. This spring is sustained by the: cap I00 locked to the shaft 34 by the retainer I0 I By these or equivalent means, leakage into the second stage pump 21 along the shaft 34 is pre-- vented.

In order to return the sealing oil to the sec-- 0nd stage pump 21 from its reservoir, there is: provided a reservoir outlet port I02 which regis-- ters with a bore I03 in the head I9.- The bore I03 intersects a passageway I04 opening into the bushing supporting bore in the head I 9. I Thepassageway I04 is sealed by a threaded plug: whose head I05 is seated against a toric gasket.

I06. The plug carries a stem I01 restricting the.-

The bearing 9| has a beveled outer'end I08 which defines with the seal ring 92 an annular groove. The beveled end I08 feeds a radial slot I09 which communicates with one end of a channel IIO extending from end to end of the bearing along its inner surface. The outer surface of the bushing 9| is provided with a longitudinal channel III, slightly larger than the channel H0 and circumferentially displaced therefrom. By this construction, oil is fed into the second stage pump along both surfaces of the bushing 9I, while oil is also supplied to lubricate the wear ring 95.

From the foregoing, it will be appreciated that the invention provides a novel center wall and a novel interstage shaft seal. These, when combined, solve the problems of interstage leakage and in addition make possible further improvements in the first stage pump. By the use of eluding a central hub approximately surrounded by said chambers and formed with a bore coaxial with both working spaces, said housing further including enclosing means, one for each of said working spaces, pump assembly bolts extending through each such enclosing means and into the shell wall which the chambers establish to seal each enclosing means and each sealed to a respective one of said mounting seats; a shaft extending through said hub bore and into said working spaces; and rotary displacing means arranged to be operated by said shaft, one in each of said working spaces.

6. A rotary two stage vacuum pump, comprising a housing enclosing first and second axially alined right cylindrical working spaces isolated from each other and each having an inlet and an outlet, said housing including a cast partition which isolates and forms the proximate end walls of said working spaces, and includes within itself chambers formed in the operation of casting the partition and retaining the casting skin, said chambers being directly interposed between said working spaces and between parallel machined surfaces which are the proximate end walls of said working spaces, one of said chambers serving as an oil reservoir open to the outlet of said first Working space and the inlet of said second working space, said partition including a central hub approximately surrounded by said chambers and formed with a bore coaxial with both working spaces, said housing further including enclosing means, one for each of said working spaces, the enclosing means for the second working space having a bore coaxial with said hub bore, a bearing in each of said bores, the hearing in said bore being a plain hub bearingbushing sealed therein and extending from end to end thereof; said hub having a passage effecting communication between said reservoir and an intermediate part of said bearing-bushing and said bearing-bushing having a passage fed by said hub passage and opening into said first workbearings and extending through the second and into the first working space; and rotary displacing means arranged to be operated by said shaft, one in each of said working spaces, whereby the rotary displacing means in the first working space is overhung as to the shaft bearings.

7. A rotary two stage vacuum pump comprising a housing enclosing first and second axially alined, cylindrical working spaces isolated from each other, each working space having an inlet and an outlet, said housing including a partition which isolates said working spaces and has opposite machined faces which are the proximate end boundary surfaces of the working spaces and includes Within itself chambers isolated from each other and directly interposed between said machined faces and establishing end walls and a hub having a bore coaxial with both working spaces; a shaft extending through said hub bore and into said working spaces; and rotary displacing means arranged to be operated by said shaft, one in each working space; one such chamber constituting an oil reservoir and having two ports adjacent its upper end, one opening through each end wall, one such port constituting a part of the outlet of the first stage and the other port constituting a part of the second stage inlet, said chambers and said ports being formed in the operation of casting the partition and including the casting skin, said pump having oil delivery means in communication with said reservoir and the first stage working space at the partition end thereof.

HENRY G. BOWERING.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,787,708 Teesdale Jan. 6, 1931 1,867,719 Van Deventer July 19, 1932 2,208,273 Karasick July 16, 1940

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