U.S. patent application number 14/374771 was filed with the patent office on 2015-02-05 for pump.
The applicant listed for this patent is Edwards Limited. Invention is credited to Malcolm William Gray, Paul David Neller, Jack Raymond Tattersall, Neil Turner.
Application Number | 20150037187 14/374771 |
Document ID | / |
Family ID | 45876315 |
Filed Date | 2015-02-05 |
United States Patent
Application |
20150037187 |
Kind Code |
A1 |
Turner; Neil ; et
al. |
February 5, 2015 |
Pump
Abstract
The present invention relates to a multi-stage vacuum pump which
has a plurality of pumping stages. The pump comprises a stator
forming the pumping chambers of respective pumping stages and at
least one shaft, for supporting a plurality of rotors for rotation
in respective pumping chambers. The stator comprises: a stator
envelope which extends over an axial extent of a plurality of
stator stages thereby circumscribing said at least one shaft and
forming an internal profile of a plurality of stator stages: and a
plurality of transverse walls located on either axial side of the
stator stages to form respective said pumping chambers. At least
one of the transverse walls is an inter-stage between stator stages
and the stator envelope is configured to circumscribe the
inter-stage for location of said inter-stage radially inward of the
stator part.
Inventors: |
Turner; Neil; (Godalming,
GB) ; Tattersall; Jack Raymond; (Bonbeach, AU)
; Neller; Paul David; (Worthing, GB) ; Gray;
Malcolm William; (Crawley, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Edwards Limited |
Crawley, West Sussex |
|
GB |
|
|
Family ID: |
45876315 |
Appl. No.: |
14/374771 |
Filed: |
January 29, 2013 |
PCT Filed: |
January 29, 2013 |
PCT NO: |
PCT/GB2013/050188 |
371 Date: |
July 25, 2014 |
Current U.S.
Class: |
418/9 |
Current CPC
Class: |
F04C 2230/85 20130101;
F04C 2230/80 20130101; F01C 21/10 20130101; F04C 2240/805 20130101;
F01C 21/108 20130101; F04C 23/001 20130101; F04C 18/126 20130101;
F04C 25/02 20130101; F04C 18/123 20130101; F04C 2230/70 20130101;
F04C 23/003 20130101; F04C 2230/60 20130101 |
Class at
Publication: |
418/9 |
International
Class: |
F04C 23/00 20060101
F04C023/00; F04C 25/02 20060101 F04C025/02; F04C 18/12 20060101
F04C018/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 30, 2012 |
GB |
1201555.8 |
Claims
1. A multi-stage vacuum pump comprising: a stator forming a
plurality of pumping chambers and at least one shaft for supporting
a plurality of rotors for rotation in respective pumping chambers,
the stator comprising: a one piece stator envelope enclosing a
plurality of axially adjacent pumping chambers about the shaft and
at least one inter-stage transverse wall located radially inwardly
of the stator envelope and between axially adjacent pumping
chambers.
2. The multi-stage vacuum pump as claimed in claim 1, wherein the
stator envelope has an axially extending internal bore formed
therethrough which forms the profiles of the respective pumping
chambers.
3. The multi-stage vacuum pump as claimed in claim 1, wherein a
radial cross-section of the internal bore at each pumping chamber
is generally uniform in the axial direction.
4. The multi-stage vacuum pump as claimed in claim 1, wherein the
radial cross-section of at least one pumping chamber is different
from that of at least one other pumping chamber.
5. The multi-stage vacuum pump as claimed in claim 1, wherein at
least one end of the stator envelope is open to allow insertion of
said at least one inter-stage wall along said internal bore for
location between two pumping chambers.
6. The multi-stage vacuum pump as claimed in claim 1, wherein the
internal bore comprises a formation for locating an inter-stage
wall between two pumping chambers.
7. The multi-stage vacuum pump as claimed in claim 6, wherein the
formation comprises a stepped surface extending radially inwardly
into the internal cavity against which the transverse wall abuts
when correctly located between the pumping chambers.
8. The multi-stage vacuum pump as claimed in claim 6, wherein the
formation comprises at least one closed bore for receiving a
fastener for fixing the transverse wall in location.
9. The multi-stage vacuum pump as claimed in claim 1, wherein said
at least one inter-stage wall comprises a bore through which a
fastener can extend for fixing the inter-stage to the stator
envelope.
10. The multi-stage vacuum pump as claimed in claim 1, wherein the
inter-stage is configured for selective fixing at more than one
location in the stator envelope.
11. The multi-stage vacuum pump as claimed in claim 1, comprising a
one or more fasteners for fastening one or more of said inter-stage
walls to the internal profile of the stator envelope.
12. The multi-stage vacuum pump as claimed in claim 11, wherein the
fastener is shaped such that in a first condition thereof the
inter-stage can pass through the internal bore of the stator
envelope and in a second condition thereof the fastener fastens the
inter-stage in location to the stator envelope.
13. The multi-stage vacuum pump as claimed in claim 1, wherein at
least one of an axial facing surface of the inter-stage wall or
axial facing surface of an adjacent rotor is coated with a friction
reducing material.
14. The multi-stage vacuum pump as claimed in claim 1, wherein the
inter-stage walls are not fixed at predetermined locations within
the stator envelope and are allowed to float between rotors.
15. A stator configured for the multi-stage vacuum pump as claimed
in claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a Section 371 National Stage Application
of International Application No. PCT/GB2013/050188, filed Jan. 29,
2013, which is incorporated by reference in its entirety and
published as WO 2013/114093 A2 on Aug. 8, 2013 and which claims
priority of British Application No. 1201555.8, filed Jan. 30,
2012.
BACKGROUND
[0002] The invention relates to a multi-stage vacuum pump and a
stator of such a pump.
[0003] A vacuum pump may be formed by positive displacement pumps
such as roots or claw pumps, having one or more pumping stages
connected in series. Multi-stage pumps are desirable because they
involve less manufacturing cost and assembly time compared to
multiple pumps in series.
[0004] Multi-stage roots or claw pumps are typically manufactured
and assembled in one of two common forms, that is, as a stator
stack or clamshell.
[0005] A pump 110 having a stator stack arrangement is shown in
FIG. 10. Pump 110 comprises a plurality of pumping stages, 112,
114, 116, 118. Each of the pumping stages comprises a rotor
arrangement (not shown) and a stator arrangement 120, 122, 124, 126
for pumping fluid from an inlet to an outlet of each stage. The
outlet of one pumping stage is in fluid communication with an inlet
of the adjacent downstream stage so that the compression achieved
by the pump is cumulative of each of the stages. Inter-stage
arrangements 128, 130, 132 interpose adjacent pumping stages. The
inter-stage arrangements separate the pumping chambers of adjacent
pumping stages and convey fluid from the outlet of an upstream
pumping stage to the inlet of a downstream pumping stage. Two head
plates 134, 136 are located at each end of the pumping stack. The
head plates separate the pumping chambers of the most upstream and
most downstream pumping stages, respectively, from other components
of the pump, such as gears and motor, and convey fluid into the
inlet of the first pumping stage and from the outlet of the final
pumping stage. Accordingly, the pump is manufactured from a
plurality of discrete layers which are laminated together to form
the pump. Lamination may suitably be achieved by one or more anchor
rods which pass through apertures in each of the layers and
fastened with fasteners such as bolts. Herein, the stator
arrangements will be referred to as stator slices and the
inter-stage arrangements simply as inter-stages.
[0006] A section through the pump 110 is shown in FIG. 11. The
rotor arrangement is shown in FIG. 11 and comprises a plurality of
rotor stages 138, 140, 142, 144 each comprising in this example a
pair of co-operating rotors A, B. Only the rotors in the first
rotor stage 138 are referenced A, B for the sake of not
over-populating the drawing with reference numerals. The rotors A
are supported for rotation by shaft 146 and the rotors B are
supported for rotation by shaft 148. On rotation the rotor stages
pump fluid from an inlet of the stage to an outlet of the stage
such that fluid is pumped through the stages from the pump inlet
(IN) to the pump outlet (OUT).
[0007] In assembly, the individual components of the pump are
stacked together in order. A first head plate 134 and shafts 146,
148 are assembled. The stator stage 120 is positioned in location
against the head plate 134 typically with dowels. One or both of
the head plate and stator stage may comprise annular grooves which
receive an O-ring for sealing the interface between the head plate
and the stator stage. The rotors 112 are fitted on the shafts and
may have a keyed arrangement for locating the rotors in the correct
position. The inter-stage 128 is then fitted against the stator
stage 120, again typically with the use of dowels and having a
O-ring for sealing between the interface. The remainder of the pump
stack is assembled in similar fashion and the stack may be clamped
to resist movement in the axial direction between components. In
some arrangements each inter-stage is integral with an adjacent
stator stage and this integrated component is assembled similarly
as described above. It will also be apparent that the pump may be
assembled in a different order, for example, the head plates may be
fitted last.
[0008] In an alternative arrangement, a stator component may
comprise two of the previously mentioned stator components, for
example parts 122 and 130 may be integral, provided such integrated
components form no more than one inter-stage.
[0009] The axial spacings, or clearances, between the rotors and
the inter-stages or head plates must be controlled accurately
because otherwise pumped fluid may leak from a low vacuum region of
the pumping chamber to a high vacuum region through the axial
clearances. Whilst the components are machined accurately, there
are inevitably variations in the component configurations which
require tolerances to be imposed on pump design that potential
increase axial clearances between the rotors and the inter-stage or
head plate. The pump stack suffers from an accumulation of
tolerances provided by each of the many interfaces between
components. In the illustrated pump there are eight such
interfaces. It will be seen therefore that relative location of the
rotors and the inter-stages or head plates cannot be controlled
accurately, which either leads to leakage of pumped fluid or
contact between the rotors and inter-stages or head plates.
[0010] Variation in component sizes can result in excessive
clearance or inadequate clearance leading to seizure. To eliminate
the possibility of seizure, the nominal clearances will be
increased, leading to an increased likelihood of excessive
clearance and impaired vacuum performance. In turn this may result
in a need for additional pumping stages, with the associated
increase in complexity and cost.
[0011] Additionally, as each interface requires sealing, a large
number of interfaces requires a large number of seals, each of
which is potential source of leakage. The seals may not be
assembled correctly; the O-rings degrade over time by chemical
erosion; and imperfect sealing faces abutting the O-rings all
contribute amongst other things to reduced sealing.
[0012] The requirement for O-rings increases the cost of the pump
and adds additional machining for the O-ring grooves. The dowels
and dowel holes also contribute to the cost of manufacture.
[0013] A modified stator stack arrangement is disclosed in
EP0480629. This document discloses a stack of stator parts 16 which
are joined together end of end. Inter-stages 17 are located
radially inside respective stator parts. The outer perimeter of the
inter-stages and the axial interface between stator parts are
sealed with O-rings. This arrangement suffers from many of the
disadvantages of the stator arrangement described in more detail
above. The interfaces between stator parts require sealing and
fastening together to prevent pumped fluid from escaping from the
pump. There is also inevitably an accumulation of axial tolerances
which restricts the ability to design an accurate pump.
[0014] An alternative pump arrangement comprises a so-called
clamshell as illustrated in FIG. 12. The pump 150 comprises two
stator parts, or shells 152, 154. The stator part 154 is shown from
the drawings perspective in more detail and the stator part 152 has
a corresponding configuration. The stator part 154 comprises head
plate portions 164, 166 and inter-stages 168, 170, 172, 174, 176
which together with part 152 form stator stages 155, 156, 157, 158,
159, 160. The head plates and the inter-stages have recesses 178,
which when assembled receive two shafts on which the rotors are
supported.
[0015] In assembly, the rotors and shafts (not shown) are brought
together as shown by the arrows in FIG. 12 and located in place by
dowels, then sealed and clamped to form the pump. The interfaces
174 between the first and second stator parts are typically sealed
with a gasket or sealant, which is inherently less resistant to
leakage than the previously discussed O-rings.
[0016] The radial spacing or tolerances between the rotors and the
stator stages is required to be tightly controlled so that the
rotors may efficiently sweep the internal surface of the pumping
chambers during rotation and resist the leakage of fluid past the
rotors. In a clam shell stator, the radial tolerances are larger
because the stator profile cannot be machined as easily or
accurately as the bore of a stator stack. Additionally axial
tolerances are required in case of potential misalignment between
two stator halves.
[0017] The discussion above is merely provided for general
background information and is not intended to be used as an aid in
determining the scope of the claimed subject matter. The claimed
subject matter is not limited to implementations that solve any or
all disadvantages noted in the background.
SUMMARY
[0018] The present invention provides an improved vacuum pump.
[0019] The present invention provides a multi-stage vacuum pump
comprising: a stator forming a plurality of pumping chambers and at
least one shaft for supporting a plurality of rotors for rotation
in respective pumping chambers, the stator comprising: a one piece
stator envelope enclosing a plurality of axially adjacent pumping
chambers about the shaft and at least one inter-stage transverse
wall located radially inwardly of the stator envelope and between
axially adjacent pumping chambers.
[0020] The invention also provides a stator for the multi-stage
pump.
[0021] The Summary is provided to introduce a selection of concepts
in a simplified form that are further described in the Detail
Description. This Summary is not intended to identify key features
or essential features of the claimed subject matter, nor is it
intended to be used as an aid in determining the scope of the
claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] In order that the invention may be well understood, some
embodiments thereof, which are given by way of example only, will
now be described with reference to the drawings in which:
[0023] FIG. 1 shows schematically a cross-section through a
multi-stage vacuum pump;
[0024] FIG. 2 shows a radial cross-section taken along line II-II
in FIG. 1;
[0025] FIG. 3 is a simplified view of the stator part shown in FIG.
1;
[0026] FIGS. 4a, 4b, and 4c show a modified stator part together
with rotors and transverse walls during assembly; and
[0027] FIG. 5 shows another modified stator part and transverse
walls;
[0028] FIGS. 6a to 6d show fastening of a transverse wall to the
stator part;
[0029] FIG. 7 shows another was of fastening a transverse wall to
the stator part;
[0030] FIG. 8 shows an inter-stage transverse wall in more
detail;
[0031] FIG. 9A is a cross-section through a modified pump and FIG.
9B is an enlarged view of a fixing arrangement;
[0032] FIG. 10 shows a vacuum pump having a stator stack
arrangement;
[0033] FIG. 11 shows a cross-section taken through the vacuum pump
shown in FIG. 10; and
[0034] FIG. 12 shows a perspective view of a clamshell type vacuum
pump.
DETAILED DESCRIPTION
[0035] Referring to FIG. 1, a multi-stage vacuum pump 10 is shown
having a plurality of pumping stages 12, 14, 16, 18. In this
example, four pumping stages are provided but there may be two,
three or more than four pumping stages depending on requirements.
The pump comprises a stator comprising components 20, 22, 24, 26,
28, 30 forming the pumping chambers 32, 34, 36, 38 of respective
pumping stages. FIG. 1 shows a roots or claw type pump in which
there are two shafts 40, 42 that support a plurality of
intermeshing rotor pairs 44a, 44b; 46a, 46b; 48a, 48b; 50a, 50b for
rotation in respective pumping chambers 32, 34, 36, 38. Other types
of pumping mechanisms fall within the scope of the present
invention, such as a rotary vane pump having a single shaft
supporting a single rotor in each pumping chamber.
[0036] As shown in FIG. 1, the stator comprises a one-piece stator
part, or envelope, 20 which circumscribes the axial shafts and
forms an internal profile 52 of a plurality of stator stages. This
arrangement is to be distinguished from the known stator stack
arrangement in which a stator part circumscribes the shafts but
defines the internal profile of one stator stage only. Likewise,
the present arrangement is to be distinguished from the known
clam-shell arrangement in which a stator part only partly extends
around the shaft and has an internal profile which forms part of
the stator stages of a plurality of pumping chambers.
[0037] Reference is also made to FIG. 2 which shows a radial
cross-section taken through the pump in FIG. 1 along line II-II
through pumping stage 16. It will be appreciated that the pumping
stages 12, 14 and 18 have similar cross-sections. The stator part
20 forms the internal profile 52 of each of the four stator stages.
In use, the internal profile 52 of the stator stages are swept by
the rotors 44 to 50 during rotation. A small clearance between the
radial extremity of the rotors and the internal profile 52 is
maintained to allow for expansion during use. The outer profile 54
of the stator part 20 may be any suitable shape such as a block.
Preferably however the outer profile is relatively thin to allow
heat transfer away from the pumping chambers and in this case the
outer profile 54 may be approximately the same shape as the
internal profile.
[0038] Referring again to FIG. 1, a plurality of transverse walls
22, 24, 26, 28, 30 are located on either axial side of the stator
stages to form the pumping chambers 32, 34, 36, 38. Transverse
walls 22, 24 are so-called head plates located at axial ends of the
stator part. One of the head plates may if required be formed
integrally with the stator part 20. The transverse walls 26, 28, 30
are so-called inter-stages as they are located between two adjacent
stator stages. The stator part 20 is configured to circumscribe the
transverse walls 26, 28, 30 for location of the transverse walls
radially inward of the stator part. Fixing means 56 fix the
inter-stages in location. The present invention relates to a
multi-stage pump having two or more stages and in a pump having
only two stages only one inter-stage need be located radially
inwardly of the stator part 20.
[0039] The stator part encloses the axis or axes of the pump and
extends through 360.degree., unlike the previously discussed
clamshell arrangement in which each stator part extends about the
axis or axis only about 180.degree.. Additionally, the stator part
defines a plurality of stator stages which together with one or
more inter-stages forms a plurality of pumping chambers. This
arrangement is unlike the previously discussed stator stack
arrangement in which a stator part encloses the axes of the pump
and extends through 360.degree. but each stator part defines only a
single stator stage.
[0040] Accordingly, the stator part or enclosure has a
longitudinally, or axially, extending internal cavity, that extends
partially or fully through the enclosure. FIG. 3 shows the cavity
64 of the stator part 20 without other parts of the pump for
clarity. The locations 60 of the head plates and the locations 62
of the inter-stages are shown by broken lines. Formations 58 are
shown at which the inter-stages can be fixed in location and are
described in greater detail below. As shown in FIG. 3, the
cross-section through each of the stator stages is generally
uniform and the cross-section from one stage to the next is also
uniform. The inter-stages are generally therefore of similar size
and shape.
[0041] In an alternative arrangement shown in FIG. 4, the cross
sections of each stage may be uniform but vary from one stage to
the next. The stator stages have greater volume towards the right
in the diagram which are typically the upstream pumping stages of
the pump. FIG. 4 shows schematically three manufacturing phases of
the pump. In FIG. 4a, the stator part 20 is shown together with two
inter-stages 26, 28 in an unassembled condition. In a partially
assembled condition in FIG. 4b, a first rotor or rotors 44 are
inserted through the internal cavity 64 and located in position on
one or more shafts (not shown). A first inter-stage 26 is then
inserted through the cavity and locked in position. Subsequently, a
second rotor or rotors 46 are located in position on the shafts and
the second inter-stage 28 is inserted through the cavity 64 and
locked in position. In a fully assembled condition in FIG. 4c, a
third rotor or rotors 48 are locked in place on the shaft or shafts
and head plates 22, 24 are fixed in position at axial ends of the
stator part 20.
[0042] In a still further alternative, the axial spacing A.sup.1,
A.sup.2, A.sup.3, A.sup.4, A.sup.5 (FIG. 5) between adjacent
transverse walls may vary from one stator stage to the next
according to pumping requirements. In one example, the inter-stages
may be located at predefined formations of the stator part, as
previously discussed. In this regard, the fixing means are
configured for locating and fixing at least one and preferably all
of the inter-stages at any selected location along the axial extent
of the stator part. The inter-stages may be interference fitted
inside the stator 20 and may have a radial outer perimeter which
comprises a sealing material for sealing against the inner surface
of the stator 20.
[0043] In another example as shown in FIG. 5, the location of the
inter-stages in the stator part is not predefined and can be
selected in situ by the operative assembling the pump. In selecting
the interstage location at the time of assembly, it is possible to
eliminate from the clearance some of the allowance for
manufacturing variation in the rotor and stator components, thus
improving the machine's performance without increasing
manufacturing cost. In this regard, one or more inter-stage may be
arranged to float between adjacent rotors. A floating inter-stage
is not fixed to the stator and is free to move in the axial
direction. Angular movement of the inter-stage is prevented by
virtue of the complementary shape of the inter-stage and the inner
surface of the stator. Axial movement is restrained by the axial
ends of the rotors adjacent the floating inter-stage. Preferably,
the inter-stage and the axial ends of the rotors are coated with a
friction reducing material to reduce resistance to rotation of the
rotors and to reduce frictional heating. This arrangement allows a
further reduction in the total axial clearance required since the
floating inter-stages will be located in position by the adjacent
rotors rather than by fixing to the stator envelope and because
much of the allowance for thermal expansion can be removed from the
pump clearance.
[0044] FIG. 6 shows in more detail an arrangement of the fixing
means 56 shown in FIG. 1. FIG. 6a shows an enlarged section of
portion VI shown in FIG. 1 looking in a tangential direction,
whilst FIG. 6b shows the same portion looking in an axial
direction. FIGS. 6c and 6d show a fastener 58 prior to fitting.
[0045] A fastener 58 comprises a fixing part 66 which in a first
condition allows an inter-stage 26 to be inserted through the
stator part 20 and in a second condition allows the inter-stage to
be fixed in location. A head part 68 is operable for transferring
the fixing part between first and second conditions. The fixing
part comprises a partially arcuate flange preferably having a
thickness which tapers. The stator part 20 has an undercut groove
70 formed in the internal profile 52 for receiving the fixing part
in the second condition. The inter-stage 26 has a cavity 72 for
receiving the fastener. The cavity opens radially outwardly to
allow the arcuate flange to project from the inter-stage when the
flange is in the second condition and opens axially to allow an
operative to insert a tool into the head part for operation. The
head part is shaped to receive a complementarily shaped tool for
rotating the fixing part between conditions.
[0046] Preferably, at least three fasteners 58 are provided around
the periphery of the inter-stage for fixing the inter-stage to the
stator part.
[0047] In use, the inter-stage 26 is inserted through the stator
part whilst the fixing part 66 is in the first condition. A lip 78
extending radially inwardly from the inner profile 52 of the stator
part may be provided for locating the inter-stage. When at the
correct location, the tool is used to rotate the flange of the or
each fastener 58 so that it projects into the undercut groove 70 of
the stator part 20. The thinnest part of the flange enters the
groove first and continued rotation causes a thicker part of the
flange to engage with axial faces 74, 76 of the groove for
accurately locating and locking the inter-stage in position.
[0048] In an alternative fixing arrangement shown in FIG. 7, a
closed bore 80 is formed at an oblique angle in the internal
profile 52 of the stator part 20. A through bore 82 is formed in
the inter-stage extending from an axial end face obliquely through
to a radial periphery of the inter-stage. The fastener is inserted
through aligned bores 80, 82 to fix the inter-stage in location.
One or both of the bores 80, 82 may be threaded to receive a
threaded fastener 58. The fastening of the fastener in the threaded
bore may be arranged to expand the inter-stage to a small extent
against the inner wall of the stator to improve sealing.
[0049] In a still further arrangement, the inter-stages may be
interference fitted to fix them in position in the stator envelope.
In this case, the stator envelope need not be provided with fixing
formations and may have a smooth inner surface. Alternatively, the
inner surface may be provided with annular lips for locating the
inter-stages in position prior to fixing. In assembly, an
inter-stage is made of a material which undergoes thermal
expansion, such as a metal or metal alloy. Prior to insertion in
the stator envelope, an inter-stage is cooled by any suitable means
so that it contracts. Preferably, it is contracted so that its
outer profile just fits within the stator envelope and therefore
can be inserted along the envelope until it abuts an annular lip.
The inter-stage is then allowed to warm under ambient temperature
conditions so that it undergoes thermal expansion and is
interference fitted in position. In an alternative, the stator
envelope may be heated so that it undergoes thermal expansion to
allow the inter-stage to be inserted and then allowed to cool to
produce the interference fit.
[0050] An exemplary inter-stage transverse wall 26 is shown in FIG.
8 for a claw type pump. The external profile 84 of the inter-stage
is shaped to correspond with the internal profile 52 of the stator
part so that the inter-stage can pass in an axial direction through
the internal cavity 64 of the stator part during assembly. The
inter-stage 26 comprises two bores 86, 88 for receiving shafts 40,
42 (shown in FIG. 1). One of the bores 88 is configured to provide
an outlet from an upstream pumping chamber to an inlet of a
downstream pumping chamber. The profile 84 in this example is
suited for a roots or claw type pumping arrangement in which the
rotors rotate generally in respective pumping chamber portions and
left and right hand lobes of the inter-stage as shown in the Figure
are configured complementarily with the respective pumping chamber
portions. In an alternative arrangement, particularly if the rotor
and inter-stage sub-assembly is assembled prior to insertion in the
stator envelope the inter-stages may be formed by two parts in
order to be fitted to rotor and drive shaft.
[0051] A modification of the FIG. 1 embodiment is shown in FIGS. 9A
and 9B. Like features of the two embodiments will be given like
reference numerals and the description of FIG. 9 will omit any
aspects already covered above.
[0052] In FIG. 9, the way in which the inter-stages are fastened to
the one-piece stator part is different from the FIG. 1 arrangement.
In more detail, a one-piece stator component 90 comprises a
plurality of through bores 94 aligned with the inter-stages 91, 92,
93. A fastener 95 is configured for extending partially through
each of the through bores and engaging with a closed bore 96 of an
inter-stage. The through bores 94 have countersunk shoulders 97 for
locating the fasteners in the radial direction. FIG. 9A shows six
such fastening arrangements and FIG. 9B shows an enlarged view of
one such arrangement as marked by the circle IXB in FIG. 9A.
[0053] The pump shown in FIG. 9A may be assembled by first
assembling a rotor and inter-stage sub-assembly. The sub-assembly
may then be inserted into the stator component 90. When in place
the sub-assembly is fastened in position by fastening each of the
inter-stages 91, 92, 93 to stator component 90 with fasteners 95.
After fastening the through bore 94 is preferably closed with a
closure member 98 and sealed with sealant. In this way, the rotors
can be fixed relative to the shafts 40, 42 prior to insertion in
the stator envelope 90 and therefore the angular alignment of the
multiple rotors can be more accurately controlled. In a further
modification, the rotors may be manufactured integrally with the
shafts. However, if this is the case, each of the inter-stages must
be made from at least two components which can be assembled
together in between the rotors. Whilst the modified arrangements
may be more susceptible to leakage than the FIG. 1 arrangement they
benefit from increased rotor alignment. Depending on the particular
pumping requirement, accurate rotor alignment may be desirable even
if leakage may increase.
[0054] In a modification of the FIG. 9 arrangement, the fixings may
be similar to those described in relation to FIG. 6. The fastener
with arcuate flange may be located in the stator envelope and
accessible through a bore by in the envelope for rotating the
fastener with a tool so that it engages and locks the inter-stage
in position.
[0055] In accordance with the discussed embodiments, the rotors and
inter-stages can be alternatively assembled within the stator. When
an inter-stage is positioned within the stator 20 it can then be
locked in position. This arrangement means that there is a reduced
requirement for sealing since pumped fluid is always maintained
within the stator envelope. The arrangement can be contrasted with
the known designs in which the stator parts must not only be
fastened together, typically with bolts, but seals must be provided
to prevent fluid escaping from the pump between stator parts. In
the present arrangement, such seals and fasteners are not required
and therefore the stator body may be made thinner since it does not
have to accommodate seals or fasteners. A thinner stator is more
suitable for dissipating heat from the pumping chambers. Further
cooling means, such as jackets may be located closer to the source
of thermal increase. Since heat can readily be dissipated, the
thermal characteristics of inter-stages is less important so that
the inter-stage material can be primarily selected for other
characteristics such as anti-corrosion.
[0056] The reduced functional and mechanical requirements of the
inter-stages means that the choice of materials from which they may
be made is increased such that more exotic materials can be
considered. Less material also means more expensive materials can
be considered such as Nickel enriched iron, stainless steel, PTFE,
composites, or Ceramics.
[0057] Since there are fewer parts connected together in axial
sequence there are fewer required axial tolerances at interfaces
and therefore the pump as a whole may be configured more
accurately.
[0058] The internal longitudinal cavity of the stator 20 may be
manufactured by machining relatively easily and accurately.
[0059] Modifications to the above described embodiments are
possible whilst still falling within the scope of the claims. For
example, the stator 20 is a one piece component defining each of
the stator stages. However, certain advantages of the invention may
still be gained by adopting two stator parts for example whereby
each stator part has an internal profile which defines more than
one stator stage. Accordingly, there will again be fewer axial
interfaces between stator parts.
[0060] Although the subject matter has been described in language
specific to structural features and/or methodological acts, it is
to be understood that the subject matter defined in the appended
claims is not necessarily limited to the specific features or acts
described above. Rather, the specific features and acts described
above are disclosed as example forms of implementing the
claims.
* * * * *