U.S. patent application number 15/326663 was filed with the patent office on 2017-07-20 for vacuum pump.
The applicant listed for this patent is Edwards Limited. Invention is credited to Alan Ernest Kinnaird HOLBROOK, Jeon Seungho, Nomikos TRIKOILIS.
Application Number | 20170204859 15/326663 |
Document ID | / |
Family ID | 51494906 |
Filed Date | 2017-07-20 |
United States Patent
Application |
20170204859 |
Kind Code |
A1 |
HOLBROOK; Alan Ernest Kinnaird ;
et al. |
July 20, 2017 |
VACUUM PUMP
Abstract
The present invention relates to a multi-stage vacuum pump
comprising: first and second half-shell stator components and first
and second end stator components which when assembled define a
plurality of pumping chambers. The half-shell components are
assembled together along respective pairs of mutual engaging
longitudinal faces and the end stator components are assembled at
the ends of the half-shell components at respective pairs of mutual
engaging end faces. A longitudinal channel is counter-sunk in at
least one longitudinal face of each pair of mutual engaging
longitudinal faces for receiving respective longitudinal sealing
members for sealing between the half-shell components. Counter-sunk
in at least one longitudinal face of each pair of mutual engaging
longitudinal faces is a pocket extending transversely from the
longitudinal channel for receiving sealant and allowing sealant to
flow around a longitudinal sealing member received in the
longitudinal channel for preventing the formation of a leakage
path.
Inventors: |
HOLBROOK; Alan Ernest Kinnaird;
(Pulborough, West Sussex, GB) ; TRIKOILIS; Nomikos;
(Burgess Hill, GB) ; Seungho; Jeon; (Gyeonggi-do,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Edwards Limited |
Burgess Hill, West Sussex |
|
GB |
|
|
Family ID: |
51494906 |
Appl. No.: |
15/326663 |
Filed: |
July 17, 2015 |
PCT Filed: |
July 17, 2015 |
PCT NO: |
PCT/GB2015/052069 |
371 Date: |
January 17, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04C 27/02 20130101;
F01C 19/005 20130101; F04C 25/02 20130101; F04C 2240/10 20130101;
F04C 18/126 20130101; F01C 21/10 20130101; F04C 2220/10 20130101;
F04C 23/001 20130101 |
International
Class: |
F04C 27/02 20060101
F04C027/02; F04C 18/12 20060101 F04C018/12; F04C 25/02 20060101
F04C025/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 21, 2014 |
GB |
1412925.8 |
Claims
1. A multi-stage vacuum pump having a stator comprising: (a) first
and second half-shell stator components and first and second end
stator components which when assembled define a plurality of
pumping chambers; and (b) a longitudinal channel counter-sunk in at
least one longitudinal face of each pair of mutual engaging
longitudinal faces for receiving respective longitudinal sealing
members for sealing between the half-shell components; wherein the
half-shell components being assembled together along respective
pairs of mutual engaging longitudinal faces and the end stator
components being assembled at the ends of the half-shell components
at respective pairs of mutual engaging end faces; and, wherein
counter-sunk in said at least one longitudinal face of each pair of
mutual engaging longitudinal faces is a pocket extending
transversely from the longitudinal channel for receiving sealant
and allowing sealant to flow around a longitudinal sealing member
received in the longitudinal channel for preventing the formation
of a leakage path.
2. The multistage vacuum pump of claim 1, further comprising
shallow recesses counter-sunk at the end portions of the
longitudinal faces for receiving a sealant for sealing between the
stator components, the depth of the shallow recesses being less
than the depth of the longitudinal channels and each pocket
extending into a respective said shallow recess from the
longitudinal channel.
3. The multistage vacuum pump of claim 1, the pockets have a depth
approximately equal to the depth of the longitudinal channels.
4. The multistage vacuum pump of claim 1, wherein pockets extend
laterally from both sides of respective longitudinal channels.
5. The multi-stage vacuum pump of claim 1, further comprising an
annular channel counter-sunk in at least one end face of each pair
of mutual engaging end faces for receiving respective sealing
members for sealing between the half-shell components and the end
stator components.
6. The multistage vacuum pump of claim 5, wherein the deep pockets
are spaced from the annular channels so that the spacing between
the half shell stator components at the annular channels is defined
by the depth of the shallow recesses for resisting protrusion of
annular sealing members received in the annular channels protruding
between the half shell stator components.
7. The multistage vacuum pump of claim 5, further comprising
supports for supporting the annular sealing members at the recesses
when the annular sealing members are received in the annular
channels to resist protrusion of the annular sealing members into
the recesses when compressed between mutually engaging end
faces.
8. The multistage vacuum pump of claim 7, wherein the supports
extend across respective recesses transverse to a plane of the
longitudinal faces.
9. The multistage vacuum pump of claim 7, wherein the supports are
formed by wails extending from the counter sunk surfaces of
respective the recesses in alignment with the annular channels.
10. The multistage vacuum pump of claim 7, wherein the annular
channels have a channel width for receiving the annular sealing
members and the supports have a support width which is less than
the channel width to allow sealant in the recesses to contact the
annular sealing members.
11. The multistage vacuum pump of claim 10, wherein on both sides
of each support a space is provided between the support and the end
face so that sealant can flow and directly contact and seal against
an annular sealing member in the annular channel on both sides of
the support.
Description
[0001] This application is a national stage entry under 35 U.S.C.
.sctn.371 of International Application No. PCT/GB2015/052069, filed
Jul. 17, 2015, the entire content of which is incorporated herein
by reference.
TECHNICAL FIELD OF THE INVENTION
[0002] The invention relates to a vacuum pump, in particular a
multi-stage vacuum pump and a stator of such a pump.
BACKGROUND TO THE INVENTION
[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 single stage pumps in series.
[0004] Multi-stage roots or claw pumps may be manufactured and
assembled in the form of a clamshell. As shown in FIG. 1, the
stator 100 of such a pump comprises first and second half-shell
stator components 102, 104 which together define a plurality of
pumping chambers 106, 108, 110, 112, 114, 116. Each of the
half-shells has first and second longitudinally extending faces
which mutually engage with the respective longitudinally extending
faces of the other half-shell when the half-shells are fitted
together. Only the two longitudinally extending faces 118, 120 of
half-shell 102 are visible in the Figure. During assembly the two
half shells are brought together in a generally radial direction
shown by the arrows R.
[0005] The stator 100 further comprises first and second end stator
components 122, 124, also known as head plates. When the
half-shells have been fitted together, the first and second end
components are fitted to respective end faces 126, 128 of the
joined half-shells in a generally axial, or longitudinal, direction
shown by arrows L. The inner faces 130, 132 of the end components
mutually engage with respective end faces 126, 128 of the
half-shells.
[0006] Each of the pumping chambers 106-116 is fanned between
transverse walls 134 of the half-shells. Only the transverse walls
of half-shell 102 can be seen in FIG. 1. When the half-shells are
assembled the transverse walls provide axial separation between one
pumping chamber and an adjacent pumping chamber, or between the end
pumping chambers 106, 116 and the end stator components. The
present example shows a typical stator arrangement for a roots or
claw pump having two longitudinally extending shafts (not shown)
which are located in the apertures 136 formed in the transverse
walls 134 when the half-shells are fitted together. Prior to
assembly, rotors (not shown) are fitted to the shafts so that two
rotors are located in each pumping chamber. Although not shown in
this simplified drawing, the end components each have two apertures
through which the shafts extend. The shafts are supported by
bearings in the end components and driven by a motor and gear
mechanism.
[0007] The multi-stage vacuum pump operates at pressures within the
pumping chamber less than atmosphere and potentially as low as
10.sup.-3 mbar. Accordingly, there will be a pressure differential
between atmosphere and the inside of the pump. Leakage of
surrounding gas into the pump must therefore be prevented at the
joints between the stator components, which are formed between the
longitudinally extending surfaces 118, 120 of the half-shells and
between the end faces 126, 128 of the half-shells and the inner
faces 130, 132 of the end components.
[0008] A known alternative sealing arrangement is disclosed in
US2002155014 providing a one piece sealing member comprising two
longitudinal portions and two annular portions. The sealing member
is however generally quite intricate to fit in place and expensive
to manufacture.
SUMMARY OF THE INVENTION
[0009] The present invention provides in the embodiments an
improved seal arrangement for sealing a clam shell pump.
[0010] The present invention also provides multi-stage vacuum pump
comprising a stator comprising: first and second half-shell stator
components and first and second end stator components which when
assembled define a plurality of pumping chambers; the half-shell
components being assembled together along respective pairs of
mutual engaging longitudinal faces and the end stator components
being assembled at the ends of the half-shell components at
respective pairs of mutual engaging end faces; a longitudinal
channel counter-sunk in at least one longitudinal face of each pair
of mutual engaging longitudinal faces for receiving respective
longitudinal sealing members for sealing between the half-shell
components; wherein counter-sunk in said at least one longitudinal
face of each pair of mutual engaging longitudinal faces is a pocket
extending transversely from the longitudinal channel for receiving
sealant and allowing sealant to flow around a longitudinal sealing
member received in the longitudinal channel for preventing the
formation of a leakage path.
[0011] An annular channel may be counter-sunk in at least one end
face of each pair of mutual engaging end faces for receiving
respective sealing members for sealing between the half-shell
components and the end stator components and supports may be
provided for supporting the sealing members across a gap between
the half-shell stator components to avoid kinking of the members
when compressed between the end faces.
[0012] Other preferred and/or optional features of the invention
are defined in the accompanying claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] In order that the present invention may be well understood,
two embodiments thereof, which are given by way of example only,
will now be described in more detail, with reference to the
accompanying drawings, in which:
[0014] FIG. 1 shows generally the components of a clam shell
stator;
[0015] FIG. 2 shows a plan view and section of part of a half shell
stator component without adequate sealing and the formation of a
leakage path;
[0016] FIG. 3 shows one example of a half shell stator component
with adequate sealing;
[0017] FIG. 4 is an enlarged view of an end portion of the half
shell stator component shown in FIG. 3;
[0018] FIG. 5 is a section taken through a recess at the end
portion shown in FIG. 4;
[0019] FIG. 6 is a plan view of a longitudinal face of another
example of a half shell stator component with adequate sealing;
[0020] FIG. 7 is an enlarged view of an end portion of the half
shell stator component shown in FIG. 6; and
[0021] FIG. 8 is a section taken through a recess and deep pockets
at the end portion shown in FIG. 7.
DETAILED DESCRIPTION OF THE INVENTION
[0022] By way of background to the invention, US2002155014
discusses the problem of sealing a clam shell stator. In
particular, it indicates that leakage lines exist between a
longitudinal gasket providing peripheral radial sealing and O-rings
providing axial sealing at the ends, which results in
unsatisfactory sealing. As a consequence the patent proposes a
one-piece three-dimensional sealing member as discussed above. This
three-dimensional sealing member is expensive to manufacture and
intricate to fit in place.
[0023] Previous patent applications of the present applicant have
proposed the use of four separate sealing components, namely two
longitudinal sealing members, or gaskets, for sealing between the
half-shell components 102, 104 in FIG. 1 and two annular sealing
members, or O-rings, for sealing between the end faces of the
half-shell components and the end stator components 122, 124.
Considerable difficulty was encountered when sealing at the
interfaces between the longitudinal sealing members and the annular
sealing members and the applicant's previous applications address a
number of solutions to the difficulties. The present application
differs from the previous applications in that rather than sealing
the interfaces between the sealing members the present embodiments
apply a sealant (which may be liquid or gel prior to curing to
solid) to seal between the longitudinal sealing members and the
half-shell components and between the annular sealing members and
both the half-shell and end stator components. Therefore, the
present embodiments do not have direct interfaces between sealing
members. However, even without these interfaces, sealing is
problematic particularly given that the differential pressure
across the seal can be both positive and negative and vary by
several bar. Early experiments conducted by the applicant and the
attendant problems which arose are now described with reference to
FIG. 2. FIG. 2 shows an end portion of longitudinal face 120 of a
half shell component 102 and a portion of the end face 128. In this
early arrangement, a longitudinal sealing member 140 is received in
a counter sunk deep channel 142 which extends over the length of
the longitudinal face leaving a space between the end of the
longitudinal member, or channel, and an annular sealing member 146.
The annular sealing member 146 is received in an annular channel
150 counter sunk in the end face 128. A shallow recess 144 is
counter sunk in the longitudinal face surrounding the end of the
deep channel 142 and in the space between this channel and annular
channel 150. Sealant 152 is applied in the shallow recess for
sealing between the longitudinal member 140 and the annular member
146. In this way, there is no direct interface between the
longitudinal sealing member and the annular sealing member.
[0024] It was found however as shown in section A-A that the
sealant 152 did not penetrate sufficiently into the channel 142 to
provide an adequate seal between the longitudinal sealing member
140 and the half shell components. Spaces 154 in channel 142 are
foamed and as shown in the plan view in FIG. 2 a leakage path 156
allows the flow of gas from atmosphere along one side of the
sealing member around its tip and along the other side of the
sealing member into the pump.
[0025] In order to increase penetration of the sealant around the
longitudinal sealing member the depth of the recess 144 was
increased so that it was approximately equal to the depth of the
longitudinal channel 142. This arrangement provided adequate
sealing about the longitudinal sealing member 140 but resulted in
less than adequate sealing at the annular sealing member 146. In
this regard, the sealant is fluid when applied until allowed to
cure, and when the annular sealing member is compressed between the
end faces of the half shell components and the internal face of the
end components a kink is formed in the annular sealing member where
it protrudes into the deep recess between the half shell components
and displaces sealant which in its fluid state cannot provide
sufficient resistance to kinking. Whereas the shallow recess shown
in FIG. 2 provided sufficient support for the annular sealing
member to avoid significant kinking, by deepening the recess and
solving the sealing problem around the longitudinal sealing member
it created a different problem around the annular sealing
member.
[0026] A first embodiment of the invention is described with
reference to FIGS. 6 to 8. FIG. 6 shows one of the longitudinal
faces 12 of one of the half shell stator components 102, 104. The
stator components 102, 104, 122, 124 have been described generally
with reference to FIG. 1 and will not be described again.
[0027] A longitudinal channel 40 is counter-sunk in at least one
longitudinal face 12, and typically both faces, of each pair of
mutual engaging longitudinal faces for receiving respective
longitudinal sealing members 34 for sealing between the half-shell
components. The sealing members 34 are located in the position with
a small amount of tension between pinch points 28. End portions of
the sealing members extend beyond the pinch points towards the end
faces of the half shell stator components. Shallow recesses 36 are
counter-sunk at the end portions of the longitudinal faces for
receiving a sealant for sealing between the stator components and
to the end portions of the sealing members 34. The depth of the
shallow recesses is less than the depth of the longitudinal
channels and counter-sunk into each recess is at least one deep
pocket 38 extending from the longitudinal channel for allowing
sealant to flow around the longitudinal sealing member in the
longitudinal channel for preventing the formation of a leakage
path.
[0028] The first embodiment therefore solves the problem of sealing
between the sealant and the longitudinal sealing member when the
recess is shallow. The reduced depth of the shallow recess reduces
kinking of the annular sealing members since there is less space
between the half shell stator components into which the annular
sealing members can protrude when compressed. The second embodiment
described below reduces kinking when the recess is deep. A deep
recess allows greater penetration of sealant around the
longitudinal sealing member to reduce leakage.
[0029] Referring again to FIGS. 6 to 8, the shallow recess 36 is
positioned between the deep channels 40 of the mutually engaging
longitudinal faces 12 of the half shell stator components 102, 104
and annular channels 22 in the end face of the half shell
components. The annular channels are arranged to receive an annular
sealing member 42 as shown in FIGS. 6 to 8, or alternatively
additional sealant, for sealing between the mutually engaging end
faces of the stator components.
[0030] The shallow recess has insufficient depth in itself to allow
penetration of the sealant 32 into the deep channel and around the
end portions of the longitudinal sealing members for effective
sealing. However, in this embodiment, deep pockets 38 extend
outwardly from the deep channels for receiving a sealant so that it
can penetrate more deeply into channels. In the Figures, the deep
pockets are located at each of the longitudinal ends of the deep
channels and extend transversely on both sides of the channels and
generally perpendicularly to the deep channel into the shallow
recess 36. Alternatively, there may be a single deep pocket.
[0031] The longitudinal sealing members may have any suitable
cross-section, such as circular, oval, polygonal or planar and it
is preferable that the deep pockets are shaped to allow sealant to
flow most readily around the particular cross-sectional shape
selected.
[0032] The shallowness of the recess 36 means that the annular
sealing member 42 may not require support across the gap between
the half shell stator components 102, 104 to prevent significant
kinking of the annular sealing member. Nevertheless, a support such
as a wall 25 shown schematically may be provided upstanding from
the counter sunk surface of the shallow recess to give additional
support to the annular sealing members across the space between the
half-shell components, similarly to wall 24 described in more
detail with reference to the second embodiment.
[0033] In another example, the recesses 36 may be omitted from the
half-shell stator components so that the end portions of the
longitudinal faces are planar. In this example the gap between the
half-shell components is minimal and only so much as is defined by
the manufacturing tolerances of the mating planar surfaces of the
half-shell components and any sealant between the planar surfaces.
Under these conditions there is no requirement for a support
extending across the half-shell components, such as wall 25.
However the provision of the deep pockets counter-sunk into the
planar surfaces becomes of greater importance to allow sealant to
flow around the longitudinal sealing member and to prevent back
leakage.
[0034] In assembly, the longitudinal sealing members 34 are
positioned in the deep channels 40 and secured in tension between
the pinch points 28. The two half shell stator components 182, 104
are brought together along their respective mutually engaging
longitudinal faces 12 compressing the longitudinal sealing member
and providing sealing along the length of the stator. Sealant 32
may be applied prior to assembling the half shell stator components
or injected following assembly. If applied prior to assembly the
overflow channels 30 allow excess sealant to escape or in the
alternative the side channels 26 can be used to inject sealant
under pressure into the assembled components. The deep pockets 38
allow sealant to flow from the shallow recesses 36 around the
cross-section of the end portions of the longitudinal sealing
members to provide adequate sealing as shown in FIG. 8.
[0035] When the half shell stator components are assembled together
they define the annular channels 22 at each end of the assembly and
following assembly the annular sealing members 42 are positioned in
the annular channels. Assembly of the end stator components 122,
124 at the end faces of the assembled half shell components
compresses the annular sealing members. This compression applies an
axial force to the annular sealing members but as the gap between
the half shell stator components is reduced by the shallow recess
36 the annular sealing members do not protrude into the recesses to
affect adequate sealing, particularly if a supporting wall is
provided.
[0036] A second embodiment of the invention is described with
reference to FIGS. 3 and 4.
[0037] FIG. 3 shows a half shell stator component 10 similar in
general structure to component 102 in FIG. 1 having two
longitudinal faces 12 located on either side of a series of pumping
chambers shown generally at 14. FIG. 4 is an enlarged view of an
end portion of one of the longitudinal faces. In the embodiments,
one or both of the half shell stator components may be structured
as shown. In this regard, FIGS. 3 and 4 show one half shell
component and the other half shell component may correspond
generally in structure or alternatively the other half shell
component may comprise a planar longitudinal face for cooperating
with the half shell component shown for sealing the pump.
[0038] Stator component 10 comprises a deep longitudinal channel 16
extending along a length of each of the longitudinal faces 12 for
receiving a longitudinal sealing member (not shown in these Figures
but see FIG. 6). The ends of the deep channel are separated from
the end face 18 of the half shell component by a deep recess 20.
When the half shell components are assembled together they form an
annular channel 22 which extends around the circumference of the
pumping chambers 14 for sealing the end faces.
[0039] As previously discussed, a problem with such a deep recess
as shown in FIG. 3 is that it results in kinking of the annular
sealing member received in channel 22. In the present arrangement,
the annular sealing member is supported across the deep recess. In
this way, sealant applied in the recess sufficiently seals around
the longitudinal sealing member and also can seal adequately
against the annular sealing member without kinking.
[0040] In more detail, a support 24 upstands from the counter sunk
surface of recess 20 at the end face 18 for supporting the annular
sealing member. As shown, the support is formed by a wall which is
generally in line with the counter sunk surface of the annular
channel 22. The annular channel has a width for receiving and
locating the annular sealing member and the wall extends only
partially over the width of the annular channel. On at least one
side, and preferably on both sides as shown in FIG. 4, is a space
26 between the wall and the end face so that sealant can flow and
directly contact and seal against the annular sealing member in the
annular channel. In this way, the arrangement supports the annular
sealing member whilst also permitting adequate sealing between the
sealant and the annular sealing member. In another example, the
support 24 may extend from the opposing half-shell stator component
with its end abutting or closely adjacent the counter-sunk surface
of recess 20.
[0041] During assembly, a longitudinal sealing member is inserted
in each of the longitudinal channels 16 shown in FIG. 3. In order
to locate the sealing member and provide a small tensile force the
longitudinal channel has two pinch points 28 referenced in FIG. 4
for applying pressure at respective end portions of the sealing
member. Following location of the longitudinal sealing members in
both channels 16, sealant is applied to the channels and recesses
20 prior to assembling the half shell components together or
injected after the components are assembled together. At least one
overflow path, or channel, 30 is provided at each end portion to
allow sealant to escape either under compression of the half shell
components together or following pressure from sealant
injection.
[0042] The deep recess 20 is of comparable depth to that of the
deep channel 16. Therefore, the sealant when applied can penetrate
around the longitudinal sealing member when it is positioned in the
longitudinal channel. FIG. 5 shows a section through one of the
deep recesses 20 counter sunk from longitudinal face 12. In FIG. 5,
the sealant 32 is shown penetrating and surrounding the end portion
of one longitudinal member 34 thereby providing an effective seal.
The depth of the recess allows the sealant to prevent the formation
of a leakage path around the longitudinal sealing member. As shown
in FIG. 4, the supporting wall 24 supports the annular sealing
member to resist kinking whilst allowing sealant to flow on either
side of the wall to contact and seal against the annular sealing
member. Therefore, the arrangement shown in FIGS. 3 to 5 provides
adequate sealing between the sealant and the longitudinal sealing
members and between the sealant and the annular sealing members to
provide effective sealing of the pump.
[0043] In both embodiments, bores 44 are provided in the half shell
stator components for receiving fastening members such as bolts for
fastening the components together.
[0044] The present description uses the terms `deep` and `shallow`.
In the context of this description, `deep` refers to the depth
substantially equal to that of the longitudinal channels counter
sunk into the end faces 12 for the longitudinal sealing members.
The depth is required for receiving the longitudinal sealing
members and to allow sealant to seal around the end portions of the
longitudinal sealing members to prevent leakage. `Shallow` refers
to a depth counter sunk into the end faces 12 which is less than
`deep`, preferably less than half of the depth and more preferably
less than a quarter of the depth, and which in insufficient to
allow sealant to penetrate around the longitudinal sealing members.
The exact measurements of deep and shallow depend on the overall
measurements of the stator and pump, however typically `deep` may
be 2 mm or more, and `shallow` may be 1 mm or less or preferably
0.5 mm or less.
* * * * *