US3438570A

US3438570A - Two stage vacuum pump

Info

Publication number: US3438570A
Application number: US662849A
Authority: US
Inventors: Helmut Bode; Bergisch Gladbach; Rudolf Brinkman
Original assignee: Leybold Heraeus GmbH
Current assignee: Balzers und Leybold Deutschland Holding AG
Priority date: 1966-08-20
Filing date: 1967-08-18
Publication date: 1969-04-15
Anticipated expiration: 1986-04-15
Also published as: DE1628313A1; FR1558930A

Description

TWO STAGE VACUUM PUMP Filed Aug. 18, 1967 Sheet of'4 HELMUT BODE RUDOLF BRINKMANN ATTORNEY April 15, 1969 H. 8055 ETAL 3,438,570

TWO STAGE VACUUM PUMP Filed Aug. 18, 1967 Sheet 9 of 4 FIGURE 3 HELMUT BODE RUDOLF BRINKMANN BY @375 )W ATTORNE Y April 15, 1969 BODE ErAL 3,438,570

TWO STAGE VACUUM PUMP Filed Aug. 18, 1967 Sheet 4 of 4 HELMUT BODE RUDOLF BRINKMANN BY fa ATTORNEY United States Patent 0 54, Int. Cl. F04c 23/00, 29/02 US. Cl. 230-158 9 Claims ABSTRACT OF THE DISCLOSURE A two stage vacuum pump includes an outer housing consisting of a cup-shaped member defining one end wall and the peripheral side Walls, and a closing end wall which may be integral with a driving motor housing. The two pump stages are side-by-side within the housing, each stage including a cylinder defining a cylindrical pumping chamber with suitable inlet and outlet ports, and a cylindrical rotor eccentrically mounted within the chamber and provided with three radial slots for accommodating sliding vanes. The stages are separated by a partition in the form of a circular plate which is sealed with respect to the housing side walls by a peripheral O-ring, defining two housing chambers. The rotors are mounted on a common shaft which passes through the partition; and a passage through the partition communiactes the two stages. Each of the stage cylinders is mounted within its respective housing chamber to define an annular space between the cylinder and the housing. The partition is provided with a passage communicating the second stage inlet with the annular space surrounding the first stage, whereby this space is maintained at the inlet pressure of the second stage defining a vacuum jacket chamber for the first stage. The peripheral space between the second stage cylinder and the housing wall defines an oil reservoir; and a controlled fiow passage in the cylinder provides for oil flow from the reservoir into the second stage pumping chamber. The opening of the jacket chamber passage is positioned in a second stage pumping chamber so that, when the pump is shut down without venting, the oil in the second stage chamber will flow through this passage into the jacket chamber rather than into the first stage pumping chamber; and this jacket chamber is large enough to accommodate all of the oil which might otherwise be sucked into the first stage resulting in undesirable contamination.

Background of the invention This invention relates to a two stage vacuum pump, and more particularly to a rotary, mechanical, oil-sealed series-connected pump.

For obtaining of near-perfect vacuum, two stage pumps are desirable; and the effective sealing of the pump structure to prevent leakage is an ever present problem. Another problem with pumps and pump systems, where an oil-sealed pump is employed, is to prevent back-up of oil into the first or low pressure stage or into the system being pumped, should the pump be shut down without venting. It is, of course, undesirable to have this oil flow back into the vacuum system, and it is also particularly undesirable to have the oil flow back into the first stage to contaminate this stage, since this necessitates considerable pumping down of the first stage before ultimate vacuum is obtained.

An object of this invention is to provide an improved structure for a twostage, oil-sealed vacuum pump.

3,438,570 Patented Apr. 15, 1969 A further object of the invention is to provide a two stage pump in which the operating elements thereof are more. effectively sealed against leakage than pumps of prior practices.

A'further object of this invention is to provide a two stage oil-sealed vacuum pump in which back-up of the oil into the low pressure stage is prevented.

Summary of the invention The above objects are accomplished by a pump structure including a housing having an internal partition defining two chambers. First and second pumping stages are mounted respectively in the two chambers, each of the stages being mounted to define an annular space between the outer walls of the pump stage cylinders and the housing wall. The annular space surrounding the second or high pressure stage defines an oil reservoir chamber; and a metering passage provides for flow of oil into the second stage pumping chamber. The annular space surrounding the first or low pressure stage is communicated, by a passage in the partition, with the second second stage inlet to define a vacuum jacket chamber for the first stage. The vacuum jacket chamber and communicating passage also serve as an oil trap chamber for receiving oil from the second pumping stage which seeks to flow back into the first stage when the pump is shut down.

Brief description of the drawings FIG. 1 is a sectional view of a two stage vacuum pump according to the invention, the section being taken in a vertical plane through the axis of the rotors;

FIG. 2 is a transverse sectional view through the first pumping stage, taken along the line 22 of FIG. 1 looking in the direction of the arrows;

FIG. 3 is a transverse sectional view through the second pumping stage, taken along the line 33 of FIG. 1 looking in the direction of the arrows; and

FIG. 4 is a fragmentary sectional view taken along the line 44 of FIG. 3 looking in the direction of the arrows.

Description of the preferred embodiment Referring to the drawings, a two stage vacuum pump according to the present invention includes a housing defined by a cup-shaped member defining one end wall 11 and a peripheral wall which will be referred to as the side wall or side walls 12. The cup-shaped member is secured, by any suitable means, to a plate member which defines the opposite end wall 13 of the pump housing, and which also may be the common end wall of an adjacent housing containing a motor for driving the pump. The end wall 13 includes an opening within which is mounted a bearing 15 for rotatably supporting a shaft 16, which extends through the end wall 13 and into the pump housing to a point adjacent the opposite end wall 11. This shaft 16 may be an extension of the drive shaft of a motor which is mounted on the opposite side of the end wall 13. A suitable rotary seal 17 may be provided to seal the shaft opening through the end wall 13.

The pump housing is provided with an intermediate partition 18, in the form of a circular disc or plate, which is disposed parallel to the two end walls. This partition is provided with a peripheral annular groove for retaining a resilient seal gasket such as a rubber O-ring 19. The housing side wall 12 is provided with an internal, integral annular rib 20 defining an annular shoulder facing toward the end wall 13. The inner diameter of the rib 20- is slightly larger than the outer diameter of the partition 18, so that the partition is relatively closely received within the rib 20; and the O-ring 19 bears against the shoulder 3 to provide the desired sealing between

chambers

21 and 22 in the pump housing defined by the partition 18 on the left and right sides thereof, respectively, as viewed in FIG. 1.

As best seen in FIGS. 1 and 2, the first stage of the vacuum pump is mounted within the chamber 21, and includes a stage housing or cylinder 25 supported within the chamber in a manner to define an annular space between the periphery of the stage cylinder and the housing side walls 12. The first stage cylinder 25 is a disc-like member having parallel end walls which are dimensioned for a close fit with the inner surface of the end Wall 11 and the confronting parallel surface of the partition 18. The rotor is provided with a transverse cylindrical bore 26, which defines, with the closing walls, a first stage pumping chamber; and a cylindrical rotor 27, of lesser diameter than the bore 26, is mounted on the shaft 16 for rotation therewith by means of a key 28. The rotor is positioned relative to the chamber so that the axis of rotation of the rotor is eccentric relative to the axis of the cylindrical chamber, and the rotor is tangent to the chamber at the upper periphery thereof as viewed in the drawings. The axial dimension of the rotor is substantially the same as the distance between the cylinder closing surfaces of the end wall 11 and partition 18, the tolerances being such as to provide effective sealing aided by a lubricating and sealing oil as will be described. The rotor 27 is provided with three radial slots, for accommodating sliding vanes 29 which seal against the cylindrical -wall and the end walls of the pumping chamber 26. The cylinder, rotor, and vanes then define three separate chambers around the periphery of the rotor which serve to pump the fluid from the intake port to the discharge port of the pumping chamber.

As best seen in FIGS. 1 and 3, the second or high pressure stage of the pump is mounted Within the chamber 22 between the partition 18 and the end wall 13. The structure of the second stage is generally identical to that of the first stage, the rotors and vanes being identical and interchangeable. The second stage also includes a stage housing or cylinder 31 which is a disc-like member having parallel end walls which are dimensioned to engage the confronting parallel surfaces of the partition 18 and end wall 13 in sealing relation; and this cylinder 31 is positioned within the chamber 22 to define an annular space between the periphery of the cylinder and the housing side Walls 12. The cylinder 31 is provided with a cylindrical bore 32 which defines, with the closing wall surfaces, the second stage pumping chamber. A cylindrical rotor 33 is mounted for rotation on the shaft 16 by means of a key 34; and this rotor is eccentrically mounted within the bore 32 in the same manner as the first stage rotor 27. The rotor 33- is also provided with equally spaced radial slots for accommodating sliding vanes 35 which are dimensioned to seal against the cylindrical and side walls of the second stage pumping chamber.

It may be stated, so far as assembly of the pump is concerned, that the above-described second pumping stage, partition 18, and first pumping stage might be assembled to the end wall 13, with suitable dowels 38 to assure proper alignment of the parts. The housing member defining the end wall 11 and side walls 12 might then be suitably secured to the end plate 13.

As best shown in FIG. 1, the end wall 11 is provided with a chamber 41 which defines an intake chamber for the pump and which may be connected to the system to be evacuated by suitable tub-ulation not shown. The end wall 11 also includes an inlet passage 42 which communicates with an inlet passage 43 in the first stage cylinder 25. An inlet port 44 in the first stage cylinder communicates the inlet passage 43 with the first stage pumping chamber 26; and the fluid withdrawn from these passages by the first stage rotor 27 is pumped through the chamber to the first stage discharge passage 45, the

4 rotor being driven in a clockwise direction as viewed in FIG. 2.

The first stage discharge passage 45 is communicated with the second stage inlet passage 47 by means of a transfer passage 46 in the partition 18. The inlet passage 47, in the second stage cylinder 31, as best seen in FIG. 3, communicates with the second stage pumping chamber 32 through an inlet port 48; and the fluid withdrawn from the inlet port is pumped around the rotor 33 to the second stage discharge passage 49 in the cylinder 31, the rotor 33 also being driven in a clockwise direction as viewed in FIG. 3.

The discharge passage 49, opens to a recess 51 in the cylinder 31, and terminates in a valve seat 52 for a discharge check valve 53 of any suitable design. An elbow structure '54 is mounted on the top of the second stage cylinder 31 defining a transfer passage 55 communicating the recess 51 with a discharge passage 56 in the end wall 13, the joint between the elbow 54 and the end wall 13 being sealed by a suitable O-ring. The elbow structure 54 may include a web for supporting a bumper 57 pro vided for limiting the opening movement of the discharge valve 53. The discharge passage 56 opens to the upper periphery of the end wall 13; and communicates with a discharge housing 58 which may include an oil filtering device for the air discharge from the pump.

As indicated above, the described pump is an oil-sealed pump; and the annular space 22 surrounding the second stage cylinder 31 defines an oil reservoir, the housing being provided with a suitable filler opening not shown. A quantity of oil is maintained in this reservoir at a level, indicated in FIG. 3, such as to completely immerse the second stage cylinder 31 to assist in preventing leakage of atmospheric air into the second stage pumping chamber. This oil reservoir chamber 22 is subject to atmospheric pressure; and, as best seen in FIG. 3, a controlled flow passage 61 is provided in the cylinder 31 communieating the oil reservoir with the pumping chamber 32 adjacent to the discharge passage 39. A controlled quantity of oil flows from the reservoir into the pumping chamber in response to differential pressure across the passage 61. It will be seen that as each vane 35 passes the oil passage 61, this passage will be communicated With the chamber defined between this vane and the immediately following vane which is at a pressure lower than atmospheric. Since the pressure Within the oil reservoir chamber is atmospheric, a certain quantity of oil will be forced into the pumping chamber. Some of this oil will mix with the air; and this oil/ air mixture will be immediately forced out of the pumping chamber through the discharge valve 53 and be discharged to atmosphere.

As mentioned above, the discharge housing 58 may include a filter for removing this oil from the discharged air; and the pump may further include a drainage line for draining the removed oil back to the reservoir chamber 22. A portion of the oil will coat the surfaces of the rotor, vanes and cylinder bore of the second stage to perform lubricating and scaling functions; and a portion of this oil will migrate back to the first stage, to similarly lubricate and seal the parts for the first pumping stage.

As best seen in FIGS. 3 and 4, an inclined passage 62 is provided in the partition 18, the lower end of this passage defining a port 63 opening to the annular space 21 and the upper end of this passage defining a port 64 opening to the second stage pumping chamber 32. As seen in FIG. 3, the port 32 is adjacent to the second stage inlet port 48 but below the passage 47. This passage 62 communicates the annular space 21 with the second stage inlet whereby, during operation of the pump, the annular space 21 is evacuated to the pressure of the second stage inlet (or first stage discharge) to define a vacuum jacket chamber for the first pumping stage, this chamber being maintained at a pressure between the ultimate pressure of the first stage and atmospheric. This, of course, results in a reduced leakage of air into the first stage, resulting in better pump performance in terms of the ultimate degree of vacuum obtainable.

The vacuum jacket chamber 21 and the passage 62 provide an additional function, namely to provide a chamber for receiving oil from the second stage pumping chamber which might otherwise back up into the first pumping stage or into the system being pumped when the vacuum pump is shut down. As already mentioned, it is not desirable that any significant amount of oil be permitted to contaminate the first or low pressure stage of the pump, particularly when the oil contains entrained air or moisture. In this regard, the location of the port 64 for the passage 62 is important. When the pump is shut down, without the system being first vented to atmosphere, a pressure differential may exist between the oil reservoir and the pump chamber between adjacent vanes c and a of the second stage rotor (as indicated in FIG. 3) which is in communication with the oil passage 61 when the rotor stops. Because of the pressure differential, oil

will be forced through the passage 61 into this chamber;

and the second stage rotor 33 may then act as a motor being rotated in a counterclockwise direction. Without any provision for taking care of this oil carried in the chamber between the vanes c and a, this oil would be communicated with the second stage inlet passage 47 when the vanes a passes the inlet port 48; and the lower pressure within the inlet passage would have the effect of sucking the oil out of the chamber between the vanes c and a and into the first stage pumping chamber. It will be seen that this cannot occur, since the port 62 will be uncovered by the vane a, well before the oil is raised to the level of the inlet passage 47, to communicate with the chamber between the vanes c and a. The lesser pressure within the vacuum jacket chamber 21 will result in a sucking of this oil into the vacuum jacket chamber; and volume of the vacuum jacket chamber 21 is sufificient to accommodate all of the oil that may be pumped back in this manner until the pressures are equalized.

Operation of the preferred embodiment In the above described pump structure, no special sealing agents or structures are used to seal the end surfaces of the stage cylinders and 31 to the respective closing surfaces defined by the Walls 11 and 13 and the partition 18; and the problems associated with such sealing agents or structures are eliminated. Despite the lack of such sealing means, leakage into the first stage is held to a minimum by the fact that the annular chamber 21 surrounding the cylinder 25 is a vacuum jacket chamber maintained at the discharge pressure of the first stage. Similarly, the annular chamber 22 surrounding the second stage cylinder 31 is filled with oil to a level to completely enclose the cylinder, thereby reducing leakage of air into the second stage pumping chamber. Such oil that may leak into the pumping chamber along the surface of the end wall 13 and partition 18, is immediately pumped out by the rotor 33. The seal between the two

chambers

22 and 21 is maintained by the pressure differential act-' ing on the O-ring 19. The atmospheric pressure existent in the oil reservoir chamber 22 acts laterally on the O- ring 19 urging the O-ring against the shoulder defined by the annular rib 20, to maintain an effective seal between the

chambers

22 and 21. Should any oil leak into the chamber 21, this oil will immediately be pumped out through the passage 62.

While in the above described preferred embodiment of the invention the pumping stages are rotary vane type pumping units, it will be understood that this particular type of pumping unit is not an essential to practice the invention and that other embodiments of the invention may employ other types of pumps such as eccentric piston type pumps. In the appended claims, reference is made to pumping stages including a cylinder defining a pumping chamber and a rotor; and it will be understood that these terms as used in the claims are intended to include pumping stages of the rotary vane type, of the rotary 6 or eccentric piston type and of other equivalent pumping units.

In operation, the pump rotors are driven in a clockwise direction by the shaft 16, as viewed in FIGS. 2 and 3. The intake chamber 41 of the pump is connected to the system to be evacuated by suitable tubulation, and air is withdrawn from the system by the first or low pressure pump stage through the

passages

42, 43, and 44. The air so withdrawn is pumped by the several chambers defined by the first stage cylinder 25, rotor 27, and vanes 29 to the first stage discharge passage 45 at higher pressure. This discharge air is then withdrawn by the second pumping stage through the

passages

45, 46, 47, and 48, the air being pumped by the chambers defined by the second stage cylinder 31, rotor 33, and vanes 35, and discharged into the second stage discharge passage 49 at still higher pressure. This air is then discharged through the discharge check valve 53 when sufficient pressure has been built up to lift the valve, whence the air is discharged to atmosphere through the recess 51,

passages

55 and 56 and discharge housing 58.

Some of the oil which is admitted to the second pumping chamber through the oil passage 61 is discharged with the air; and some of the oil coats the internal parts of the second pumping stage to lubricate and seal the relatively movable parts. Some of this oil migrates back into the first pumping stage to lubricate and seal the relatively movable parts of this stage.

Since the annular jacket chamber 21 is communicated with the second stage inlet port 48 by means of the passage 62, the pressure maintained in the jacket chamber during operation of the pump is the same as the inlet pressure for the second pumping stage or the discharge pressure for the first pumping stage. The space 21 then provides an insulation space between the low pressure at the first stage inlet and the ambient atmospheric pressure at the exterior of the pump housing. This, of course, reduces the leakage of air into the first stage pumping chamber to provide for a lower ultimate pressure which can be achieved by the pump.

As already explained, should the pump be shut down without first venting to atmosphere, any oil in the system which may be transported to the second stage inlet passage 48, whereby it could be sucked back to the first vacuum stage, is sucked into the jacket chamber 21 through the passage 62 becaue of the lower pressure existing in the chamber 21. When pump operation is resumed, this oil is sucked out of the chamber 21 through the same passage 62 and carried by the second stage rotor to the discharge passage 49.

What is claimed is:

1. A two stage oil-sealed vacuum pump comprising:

a housing defining first and second chambers;

a first low pressure pumping stage including a cylinder defining a pumping chamber and a rotor; said first stage cylinder being mounted in said first chamber to. define an annular space surrounding said cylinder;

a second high pressure pumping stage including a cylinder defining a pumping chamber and a rotor; said second stage cylinder being mounted in said second chamber to define an annular space surrounding said cylinder; said second chamber annular space defining an oil reservoir; a controlled fiow passage communicating said oil reservoir with said second stage pumping chamber;

passage means communicating the discharge port for said first pumping stage to the inlet port for said second pumping stage;

passage means communicating said first chamber annular space with said second stage pumping chamber whereby said annular space defines a vacuum jacket chamber for said first pumping stage; and said last-named passage means opening to said second stage pumping chamber at a port positioned to intercept oil flowing toward said second stage inlet port,

whereby said oil is withdrawn into said first chamber annular space to prevent contamination of said first stage pumping chamber.

2. The invention set forth in claim 1:

wherein said port for said last-named passage opening to said second stage pumping chamber is below said passage means communicating the inlet port for said second pumping stage with the discharge port for said first pumping stage, whereby oil being carried toward said first-named passage mean will be intercepted by said second-named passage means.

3. The invention set forth in claim 1:

including an internal partition in said housing defining said first and second chambers; said partition comprising a circular plate member having a peripheral annular groove; an annular resilient sealing member disposed in said annular groove; said housing having an internal annular rib having an internal diameter only slightly larger than the diameter of said plate and defining a lateral shoulder adapted to be engaged by said resilient sealing member to provide a seal between the first and second chambers.

4. The invention set forth in claim 3:

wherein said housing comprises a cup-shaped member defining a first end wall thereof and peripheral side walls thereof, and a plate member defining the second end wall thereof; said annular rib being integral with the housing side walls and disposed in a plane parallel to the housing end walls; said annular rib shoulder facing said second end wall;

said first chamber being defined by first end wall and said partition; and said second chamber being defined by said partition and said second end wall.

5. The invention set forth in claim 4:

wherein said first mentioned passage means communi cating said pumping stages includes a passage through said partition; and said last mentioned passage means communicating said vacuum jacket chamber and said second pumping stage comprising a passage through said partition.

6. The invention set forth in claim 4:

wherein said housing and walls define confronting parallel surfaces, and said partition defines opposing surfaces parallel to said end walls surfaces;

said first pumping stage including a cylinder and rotor having parallel end walls which are dimensioned to be closely received within said first chamber in sealing relation with the parallel wall surfaces thereof; and the second pumping stage having a cylinder and rotor with parallel walls dimensioned to be closely received within said second chamber in sealing relation with the parallel wall surfaces thereof.

7. The invention set forth in claim 6:

wherein said first and second stage rotors are mounted on a common shaft passing through said partition.

8. The invention set forth in claim 1:

wherein said pumping chambers are cylindrical; wherein said rotor are cylindrical and mounted eccentrical- 1y relative to the respective pumping chambers to define a tangential seal line; and said rotors including a plurality of radial slots accommodating sliding vanes for sealing engagement with the walls of the respective pumping chamber.

9. The invention set forth in claim 1:

wherein the rotors for said pumping stages are identical and interchangeable.

References Cited UNITED STATES PATENTS 1,056,859 3/1913 Vernon 230152 2,126,247 8/1938 Eppers 230l58 2,147,194 2/1939 Ells 230-152 X 2,150,122 3/1939 Kollberg et al. 230152 2,824,687 2/1958 Osterkamp 230158 2,877,947 3/1959 Wessling et al. 230-158 X 2,902,210 9/1959 Power 230158 X 3,081,936 3/1963 Wessling 230-207 X 3,371,857 3/1968 Le Blanc 230152 FOREIGN PATENTS 809,443 2/ 1959 Great Britain. 1,236,343 6/1960 France.

938,559 10/1963 Great Britain.

DONLEY J. STOCKING, Primary Examiner.

W. J. KRAUSS, Assistant Examiner.

U.S. Cl. X.R.