Dual inlet vacuum pumps

Details Dual inlet vacuum pumps Dual inlet vacuum pumps

1999-02-02

2001-02-27

Look, Edward K. (Department: 3745)

Rotary kinetic fluid motors or pumps

Smooth runner surface for working fluid frictional contact

C415S199500, C415S143000, C417S250000

Reexamination Certificate

active

06193461

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to high-vacuum pumps used for evacuating vacuum enclosures and, more particularly, to dual inlet high-vacuum pumps which may be used for evacuating different chambers of a vacuum enclosure. The invention may be implemented in turbomolecular vacuum pumps and diffusion pumps, but is not limited to these types of vacuum pumps.
BACKGROUND OF THE INVENTION
Conventional turbomolecular vacuum pumps include a housing having an inlet port, an interior chamber containing a plurality of axial flow pumping stages and an exhaust port. The exhaust port is typically attached to a roughing vacuum pump. Each axial flow pumping stage includes a stator having inclined blades and a rotor having inclined blades. The rotor and stator blades are inclined in opposite directions. The rotor blades are rotated at high speed to provide pumping of gases between the inlet port and the exhaust port. A typical turbomolecular vacuum pump may include nine to twelve axial flow pumping stages.
Variations of the conventional turbomolecular vacuum pump are known in the prior art. In one prior art configuration, one or more of the axial flow pumping stages are replaced with disks which rotate at high speed and which function as molecular drag stages. This configuration is disclosed in U.S. Pat. No. 5,238,362 issued Aug. 24, 1993 to Casaro et al. A turbomolecular vacuum pump including an axial turbomolecular compressor and a molecular drag compressor in a common housing is sold by Varian Associates, Inc. under Model No. 969-9007. Turbomolecular vacuum pumps utilizing molecular drag disks and regenerative impellers are disclosed in German Patent No. 3,919,529 published Jan. 18, 1990.
Molecular drag compressors include a rotating disk and a stator. The stator defines a tangential flow channel, and an inlet and an outlet for the tangential flow channel. A stationary baffle, often called a stripper, disposed in the tangential flow channel separates the inlet and the outlet. As is known in the art, the momentum of the rotating disk is transferred to gas molecules within the tangential flow channel, thereby directing the molecules toward the outlet and pumping the gas.
Some instruments and processing systems have two or more vacuum chambers which it is desirable to operate at different pressure levels. The chambers may be connected through one or more orifices that are small enough to permit establishment of different pressure levels. Examples include mass spectrometers, molecular beam systems and ion beam systems. One approach is to connect a separate vacuum pump to each of the vacuum chambers. Another approach, which is typically more economical, is to utilize a single vacuum pump having two or more inlets which are connected to different points in a single vacuum pump. The inlets are connected to different vacuum chambers.
An example of a prior art dual inlet turbomolecular vacuum pump
10
is shown in FIG.
4
. The turbomolecular vacuum pump (turbopump)
10
includes a first pumping section
12
, a second pumping section
14
and an interstage region
16
between pumping sections
12
and
14
. First pumping section
12
includes axial flow pumping stages
20
,
22
, etc., and second pumping section
14
includes axial flow pumping stages
30
,
32
, etc. A housing
40
has a first inlet port
42
coupled to an inlet of first vacuum pumping section
12
, a second inlet port
44
coupled through a conduit
46
to interstage region
16
, and an exhaust port
48
coupled to an outlet
50
of second vacuum pumping section
14
. Each of the axial pumping stages
20
,
22
,
30
,
32
, etc. includes a stator having inclined blades and a rotor having inclined blades. The rotor of each axial pumping stage is connected by a shaft
52
to a motor
54
.
In use, first inlet port
42
is connected to a first vacuum chamber (not shown) at a relatively low pressure and second inlet port is connected to a second vacuum chamber (not shown) at a higher pressure level. The first and second chambers are evacuated simultaneously by turbopump
10
.
The turbopump configuration shown in
FIG. 4
provides generally satisfactory performance, but has certain disadvantages. The interstage region
16
has a relatively large axial dimension parallel to shaft
52
in order to provide adequate gas conductance between second inlet port
44
and second pumping section
14
. This requires a lengthening of shaft
52
in order to provide the same performance as an equivalent single inlet turbopump. This results in increased size and cost of the turbopump. In addition, since the shaft and rotors are typically cantilevered from the motor end of the turbopump, the increased shaft length may give rise to problems in balancing the turbopump for high speed operation and in reduction of bearing life.
Accordingly, it is desirable to provide vacuum pump configurations which overcome one or more of the above disadvantages.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, a vacuum pump is provided. The vacuum pump comprises a first vacuum pump section and a second vacuum pump section coupled in series and having an interstage region between them. The vacuum pump further comprises a housing containing the first and second vacuum pump sections. The housing includes a high conductance peripheral duct surrounding all or part of the interstage region and coupled to the interstage region. The housing defines a first inlet port coupled to an inlet of the first vacuum pump section, a second inlet port coupled to the peripheral duct and an exhaust port coupled to an outlet of the second vacuum pump section.
In a first embodiment, the vacuum pump comprises a turbomolecular vacuum pump. In a second embodiment, the vacuum pump comprises a diffusion pump. In a third embodiment, the vacuum pump comprises a mixed vacuum pump including both axial flow stages and molecular drag stages.
According to a second aspect of the invention, a vacuum pump comprises two or more axial flow stages coupled in series, a motor, a shaft and a housing containing the axial flow stages. The axial flow stages are divided into a first pump section and a second pump section separated from the first pump section by an interstage region. Each of the axial flow stages comprises a rotor and stator. The shaft is coupled between the motor and the rotor of each of the axial flow stages. The housing includes a high conductance peripheral duct surrounding all or part of the interstage region and coupled to the interstage region. The housing defines a first inlet port coupled to an inlet of the first pump section, a second inlet port coupled to the peripheral duct, and an exhaust port coupled to an outlet of the second pump section. The second pump section may optionally include one or more molecular drag stages.
According to a third aspect of the invention, a diffusion pump comprises two or more vapor jet stages coupled in series, a vapor source for supplying a vapor to the vapor jet stages and a housing containing the vapor jet stages. The vapor jet stages are divided into a first pump section and a second pump section having an interstage region between them. The housing includes a high conductance peripheral duct surrounding all or part of the interstage region and coupled to the interstage region. The housing defines a first inlet port coupled to an inlet of the first pump section, a second inlet port coupled to the peripheral duct, and an exhaust port coupled to an outlet of the second pump section.
In each embodiment, the housing may comprise a generally cylindrical wall having an annular gap adjacent to the interstage region. The peripheral duct may surround the annular gap and may be coupled through the annular gap to the interstage region.


REFERENCES:
patent: 5238362 (1993-08-01), Casaro et al.
patent: 5611660 (1997-03-01), Wong et al.
patent: 5733104 (1998-03-01), Conrad et al.
patent: 6030189 (2000-02-01), Bohm et al.
patent: 3919529 (1990-01-01), None
patent: 295 16 599 U (1995-12-01), None
patent: 0 072 892 (1983-03-01), None
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