U.S. patent application number 12/736847 was filed with the patent office on 2011-03-17 for apparatus for impeller sealing in centrifugal pumps.
Invention is credited to Uwe Wuerdig.
Application Number | 20110064566 12/736847 |
Document ID | / |
Family ID | 41017071 |
Filed Date | 2011-03-17 |
United States Patent
Application |
20110064566 |
Kind Code |
A1 |
Wuerdig; Uwe |
March 17, 2011 |
APPARATUS FOR IMPELLER SEALING IN CENTRIFUGAL PUMPS
Abstract
The invention relates to a device for impeller sealing in
centrifugal pumps for fluid media, by means of which the gap
between pump housing (1) and at least one impeller (2) is
completely sealed against a transport of material from the pressure
side (3) of impeller (2) to the suction side (4) thereof. According
to the invention, a sealing ring comprising a rigid pressure ring
(7) as well as an annular elastic sealing lip (8) joined with
pressure ring (7) is disposed in pump housing (1) between pressure
side (3) and suction side (4), whereby, when the centrifugal pump
is in operation, sealing lip (8) is applied in sliding manner over
the entire periphery of impeller (2) on a sliding surface (6)
formed on impeller (2) in the region of impeller intake (5). For
this purpose, the sealing ring is positioned in pump housing (1) by
means of an adjusting member (9) and its sealing lip (8) inclined
against said sliding surface (6) is pre-stressed.
Inventors: |
Wuerdig; Uwe; (Berlin,
DE) |
Family ID: |
41017071 |
Appl. No.: |
12/736847 |
Filed: |
May 15, 2009 |
PCT Filed: |
May 15, 2009 |
PCT NO: |
PCT/DE2009/050026 |
371 Date: |
November 15, 2010 |
Current U.S.
Class: |
415/174.2 |
Current CPC
Class: |
F04D 29/167
20130101 |
Class at
Publication: |
415/174.2 |
International
Class: |
F01D 11/00 20060101
F01D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 15, 2008 |
DE |
10 2008 001 814.7 |
Claims
1. A device for impeller sealing in centrifugal pumps for fluid
media, by means of which the axial or radial gap which is formed
between the pump housing and at least one motor shaft-driven
impeller of the centrifugal pump and which makes possible the
rotational movement of impeller in pump housing is sealed against a
transport of material from the pressure side of the at least one
impeller to the suction side thereof at the impeller intake is
hereby characterized in that a sealing ring is disposed in pump
housing between the pressure side and the suction side of the
respective impeller, this sealing ring being composed of a rigid
pressure ring and an annular elastic sealing lip joined with
pressure ring, this lip being joined to pressure ring in the region
of its inner diameter and being inclined against a sliding surface
formed on impeller at the peripheral contour in the region of the
impeller intake in a region projected on by pressure ring or/and
projecting over the diameter thereof, and that an adjusting member
mounted in pump housing acts on the sealing ring, by means of which
the sealing ring is positioned relative to sealing surface and its
sealing lip is pre-stressed in region in such a way that sealing
lip is applied to sliding surface by a radially outer end of its
region, when the centrifugal pump is operating, due to the pressure
difference existing between pressure side and suction side, and
completely seals the axial gap or the radial gap, whereby, due to
the deformability of region of sealing lip and the pre-stressing
produced in sealing lip by means of adjusting member, a permanent,
self-adjusting seal as well as a seal that equilibrates the radial
and axial oscillations occurring during operation of the pump is
provided.
2. The device according to claim 1, further characterized in that
sliding surface is part of a rigid wear ring attached to the
peripheral contour of impeller in the region of impeller
intake.
3. The device according to claim 1, further characterized in that
sealing lip comprises an elastomer and is joined to pressure ring
by vulcanization, whereby pressure ring comprises metal.
4. The device according to claim 3, further characterized in that a
reinforcing material is embedded in the elastomer of sealing
lip.
5. The device according to claim 4, further characterized in that a
metal wire mesh is embedded in the elastomer of sealing lip.
6. The device according to claim 3, further characterized in that a
metal washer is vulcanized in sealing lip.
7. The device according to claim 1, further characterized in that
the thickness of annular sealing lip decreases in the direction of
its outer periphery.
8. The device according to claim 1, further characterized in that
the adjusting member is formed as a collar directly acting on the
sealing ring, the position of the collar being adjustable in pump
housing in the axial direction by means of two or more adjusting
screws arranged approximately equally distributed relative to the
periphery of collar, each of these screws being engaged with a
thread of pump housing and pressing on collar.
9. The device according to claim 8, further characterized in that
the threads for adjusting screws are formed in threaded bores,
which are guided through pump housing in the axial direction.
10. The device according to claim 8, further characterized in that
an additional housing ring which is applied to collar on the side
opposite to the sealing ring is inserted into pump housing and each
of the threads for adjusting screws is formed in part by circular
segment-shaped recesses disposed on the outer periphery of housing
ring and in part disposed in annular recesses of pump housing
corresponding to recesses of pump housing and enclosing together
with these a full circle in each case, wherein housing ring is
fixed in pump housing by adjusting screws engaged with the
threads.
11. The device according to claim 1, further characterized in that
the adjusting member is formed as a collar with an outer thread,
this collar acting directly on sealing ring, and the position of
this collar is adjustable in pump housing in the axial direction by
turning collar in an inner thread formed on an inner surface of
pump housing.
12. The device according to claim 8, further characterized in that
collar can be fixed in the axial position adjusted for it by means
of set screws.
13. The device according to claim 8, further characterized in that
the respective elements thereof are components of a kit for
retrofitting centrifugal pumps which have not previously been
equipped with a gap seal, and a drilling template or hole gauge for
the correct positional arrangement of threaded bores to be formed
is also included in the kit.
14. The device according to claim 11, further characterized in that
collar can be fixed in the axial position adjusted for it by means
of set screws.
Description
[0001] The invention relates to a device for impeller sealing in
centrifugal pumps for fluid media. The device serves for the
purpose of sealing the gap that is present between the impeller and
the pump housing--and that is due to the construction of
centrifugal pumps--against the transport of material from the
pressure side of the impeller to the suction side thereof at the
impeller intake. It can be used for the initial equipping of
generic pumps when they are manufactured, but also can be used for
retrofitting pumps which have not previously been provided with a
corresponding gap sealing.
[0002] Centrifugal pumps of different structural forms are used for
the transport of fluid media, particularly liquids in very large
amounts. The pumps comprise one or more impellers disposed on a
shaft, which, when driven by a motor, move in a corresponding free
space of a pump housing (also called a housing bore). Due to its
rotation, each impeller produces an underpressure on its intake
side, where the inflow for the fluid medium to be transported is
found. In this way, the medium is broken up at or in the impeller
and transported from it by the rotational motion to the impeller
outlet on the pressure side of the impeller. Thus, in order for the
impeller to be able to move in the pump housing, a gap between the
impeller and the inner wall of the pump housing is indispensable.
This gap is formed as an axial or radial gap depending on the form
of the housing and of the impeller.
[0003] A portion of the transported fluid, however, inevitably
flows back via the gap to the suction side of the impeller.
Hydraulic losses occur in this way. Pump manufacturers are thus
attempting to keep the gap dimensions as small as possible. On the
other hand, certain minimum gap measurements cannot be further
reduced, particularly due to tolerances of the components, since if
they were, there is the danger that an impeller that may be running
in a somewhat eccentric manner, might strike the inner wall of the
housing. This danger also increases over the course of the
operating time of a pump because deposits form on the impeller, and
these deposits can be added on to a gap dimension that is too
small, so that the pump finally"seizes up". Consequently, there
occurs a blocking of the impeller and damage to the machine, which
may end up in complete failure of the pump. In the individual case,
this causes expensive interruptions in operation. The named
problems are additionally increased due to other factors. For
instance, material damage to the housing and/or to the impeller
occurs over the course of pump operation due to cavitation, i.e.,
due to implosion predominantly of gas bubbles that arise in the
transported medium, and, apart from serious damage, such as the
breaking of component parts of the impeller, for example, this can
also unfavorably influence gap dimensions. In addition, a
particular problem occurs with the use of pumps for the transport
of wastewater. Due to the contaminants contained in the wastewater
in the form of solids and fibrous components, so-called braid
formation occurs on the impellers and as a consequence of this, the
gap is stopped up by these added formations, whereupon finally, the
impeller is also blocked. Due to the pressure difference between
the suction side and the pressure side, the gap between the pump
housing and the impeller is a particularly critical region, into
which the contaminants are actually pulled.
[0004] Therefore, in pump manufacture, structural measures are
sought, by means of which the gap dimensions are kept small or
optimized, but in addition, can be kept constant as much as
possible over the long-term operation of the pump. Thus, a device
is described in DE 199 60 160 A1, for example, for optimizing the
gap width in centrifugal pumps. According to the described
solution, a beading is formed on the outer periphery of the free
end of a pump impeller. When the impeller is inserted into the pump
housing, this beading is introduced behind a sealing collar, which
is formed on a gap ring disposed in the housing. A very small gap
dimension is achieved in this way. Since the sealing collar
involves a rigid element according to this solution, however, there
is the danger that, since depositions are formed on it, it may run
into the impeller above the beading formed on the impeller. Also,
due to the remaining small gap, a transport of material from the
pressure side to the suction side is not prevented, so that the
danger of braid formation and finally the blocking of the gap is
also not eliminated.
[0005] A solution for reducing the width of a radial sealing gap,
by means of which an undesired widening of the gap with increasing
operating time of the pump will also be prevented to the greatest
extent, is described in EP 1 808 603 A1. For this purpose, a rigid
wear ring and an elastic ring are introduced into the radial gap
between the pump housing and the outer contour of the impeller.
Whereas the wear ring, which comprises, for example, hardened cast
steel or a ceramic material, surrounds the impeller with a small
residual gap remaining, the elastic ring is disposed around the
wear ring and is attached to the inner contour of the pump housing.
In this way, a type of elastic suspension is formed for the wear
ring acting as the gap ring. Oscillations of the impeller, as they
occur primarily when the pump is started up, are especially
intercepted by means of this elastic suspension, and thus a
damaging of the gap ring or of the outer contour of the impeller is
prevented. Further, the gap ring and the inner contour of the pump
housing are thermally decoupled from each other in this way. An
optimizing of the gap is provided by this solution, which makes it
possible to constantly maintain the gap dimension, even over a
rather long operating time of the pump with compensation of
dimension tolerances of the pump parts and of oscillations that
occur in the operation of the pump. In each case, however, in this
solution, a residual gap also remains, in which there additionally
exists the danger of a braid formation or tressing, in particular,
with the use of the pump for transporting wastewater. Therefore,
pumps designed corresponding to this solution are suitable for use
as wastewater pumps only under certain conditions.
[0006] A solution in which a nearly complete sealing of the gap is
achieved by means of several elastic elements that are pressed by
screws and springs to contour segments of the impeller is described
in U.S. Pat. No. 2,109,679 A. The arrangement, however, is
relatively complicated, and since it is not self-sealing without
further measures, due to a friction wear occurring on the elastic
elements during the operation of the pump, the remaining minimum
residual gap would be enlarged very rapidly. Also, the regions in
which the springs are disposed are themselves not sealed. In this
way, deposits may be formed on the springs and block them, in
particular, when the pump is used with wastewater, so that they no
longer can exercise the pressure necessary for extensively sealing
the gap on the elements pressing against the impeller. Further,
there is the danger of a contraction of the elastic elements that
are applied to the impeller and in part have somewhat large surface
regions into the corresponding bearing surfaces, whereby it is also
expected that the sealing will become ineffective after a
relatively short operating time of the pump. Finally, radial and
axial oscillations of the impeller, as they always occur when the
pump is operating, are not equilibrated by the sealing system. As a
consequence of this, in general, the gap could in fact almost be
sealed, but in each case, particularly with axial oscillations of
the impeller, the gap could ocasionally be opened further. In the
case of a repeated brief opening of the gap, however, deposits are
unavoidably formed in the gap region, particularly when the pump is
used for transporting wastewater, which, over the course of time,
lead to the braid formation, which has already been mentioned, and
finally to the blockage of or even damage to the pump.
[0007] A more favorable solution, particularly due to its simple
construction, is described by DE 196 13 486 C2. According to this
solution, when the pump is operating, an elastic sealing ring held
in recesses of the pump housing in the gap region thereof slides
along a front cover plate of the impeller. However, as is even
mentioned in the document, the device does not lead to a sealing of
the gap, but rather to an extremely small gap dimension, whereby
this dimension would increase in a relatively short time due to
abrasion and a wear of the sealing ring that is caused thereby.
With respect to the fact that radial and axial oscillations of the
impeller also cannot be equilibrated in this solution due to the
type of arrangement of the sealing ring in the pump housing, the
described arrangement is also not suitable for application in
wastewater pumps. There also exists here the danger of a rapid
deposition of solids or fibrous contamination in the region of the
sealing ring and of its edge resting on the impeller, together with
the danger of braid formation in the gap region.
[0008] The object of the invention is thus to create a device for
impeller sealing in centrifugal pumps, by means of which the
transport of material between the pressure side of the impeller of
a centrifugal pump and its impeller intake is reliably and
permanently prevented with a very simple construction of the
device, but an unhindered rotational movement of the impeller or
impellers in the pump housing is made possible. This type of
transport of material and thus braid formation in the gap region,
particularly in the case of application in wastewater pumps, will
be prevented by the device to be created. In addition, the device
will make possible the equipping of pumps in the factory as well as
retrofitting pumps already produced.
[0009] The object is accomplished by a device with the features of
the principal claim. Advantageous embodiments or enhancements are
given by the subclaims.
[0010] As has already been mentioned initially, the device
according to the invention can be used both in centrifugal pumps
with an axial gap as well as in those with a radial gap, depending
on the geometry of their elements and of their structural
arrangement in the pump. Further, both one-stage as well as
multi-stage centrifugal pumps, i.e., centrifugal pumps with more
than one impeller, can be equipped with the device according to the
invention either in the factory or as the object of a
retrofitting.
[0011] In order to accomplish the object according to the
invention, a sealing ring is disposed between the pressure side and
the suction side of the at least one impeller in the pump housing
of a centrifugal pump, which is either equipped in the factory or
retrofitted with this device, this sealing ring being composed of a
rigid pressure ring and an annular elastic sealing lip joined with
the pressure ring. The sealing lip is joined with the pressure ring
in the region of its inner diameter. In a region projected on by
the pressure ring or/and projecting over the pressure ring, with
respect to its diameter, the sealing lip is inclined against a
sliding surface formed on the impeller at its peripheral contour in
the region of the impeller intake. According to the invention, an
adjusting member on the pump housing acts on the sealing ring
formed as described above. The sealing ring is positioned relative
to the sliding surface by this adjusting member, and at the same
time, its sealing lip is pre-stressed against the sliding surface
of the impeller in the region projected on by the pressure ring
or/and projecting over the diameter of the pressure ring. The
sealing ring is thus positioned in such a way and its sealing lip
is pre-stressed such that it is applied to the sliding surface by a
radially outer end of the above-named region when the pump is in
operation. The adjustment to be carried out at the adjusting member
can be such that the sealing lip is applied only slightly (very
small pre-stressing) to the corresponding sliding surface of the
impeller when the pump is in its resting state, while the
application of the radially outer end of the sealing lip to the
sliding surface is reliably assured by the pressure difference
existing additionally between its pressure side and the suction
side when the pump is in operation. The sealing device is thus
configured such that, due to the deformability in a length
sufficient for this purpose of the region of the sealing lip
projected on by the pressure ring or/and projecting over it to a
sufficient extent relative to its diameter, and based on the
pre-stressing produced in the sealing lip by means of the adjusting
member, a permanent as well as a self-adjusting complete sealing of
the gap is provided. In an advantageous manner, due to the possible
large-scale deformation of the elastic region projecting over the
pressure ring or/and projected on by it, the radial and axial
oscillations occurring during pump operation are also equilibrated
so that they do not lead even to only a brief opening of the gap.
In new pumps equipped with a corresponding gap seal or in pumps
freshly retrofitted with the corresponding gap seal, the sealing
ring is thus adjusted by means of the adjusting member with respect
to its position and the pre-stressing of its sealing lip in such a
way that the radial outer end of the sealing lip very reliably
contacts the wear ring with pre-stressing that is as small as
possible.
[0012] According to one possible embodiment of the invention, the
sliding surface is part of a rigid wear ring attached in the region
of the impeller intake on the peripheral contour of the impeller.
Said wear ring can thus be disposed on the impeller in a pump
equipped with the device according to the invention at the factory
or it can be attached later by a corresponding reworking of the
impeller as the object of a retrofitting. The wear ring comprises a
particularly wear-resistant material, such as stainless steel/cast
iron, ceramic or a special composite material, or it is provided at
least with a special wear-resistant coating. It is also
conceivable, of course, to configure at least the sliding surface
of the impeller in a particularly wear-resistant manner by a
suitable surface treatment or coating of the material or to form
the impeller overall from a corresponding wear-resistant material,
but this optionally leads to increased costs. Particularly in
connection with retrofitting, however, in practice, the
wear-resistant sliding surface is to be realized preferably by
introducing a wear ring onto the impeller in the region of the
impeller intake.
[0013] As already mentioned, the sealing ring is realized by a
rigid pressure ring and an elastic sealing lip joined to it,
whereby the pressure ring also is composed of a wear-resistant
material, preferably metal. In the case of a metal pressure ring,
according to a preferred embodiment of the invention, the sealing
lip is composed of an elastomer and is joined with the pressure
ring by vulcanization. In this way, the invention can be enhanced
advantageously still further due to the fact that a reinforcing
material, preferably a metal wire mesh, is embedded in the
elastomer for mechanical stabilizing. It is also possible to
vulcanize a metal washer in the elastomer for stabilization.
[0014] The geometry of the elastic sealing lip, preferably composed
of an elastomer or of rubber is advantageously configured such that
its thickness decreases radially toward the outside. This
configuration of the geometry of the sealing lip and the measures
for its mechanical stabilization, which have been explained above,
serve for the purpose that the sealing lip is applied in a sliding
manner to the wear ring or to the sliding surface, respectively,
only by its radial outermost region according to the basic concept
of the invention, even when there are large pressure differences
between the pressure side and the impeller intake side. It has been
shown that without appropriate measures, due to the high pressure
acting on the sealing lip, the danger exists that the sealing lip
will be bent or snapped off and in this way would come to rest with
a large surface region on the wear ring, whereupon the danger is
increased that the sealing lip would enter further into the sliding
surface over the course of time or would work into the wear ring.
Due to the pressure difference that exists between the pressure
side and the impeller intake on the suction side, however, it is
nevertheless assured that the sealing lip will be applied by
sliding on the sliding surface of the impeller associated with it
as well as completely sealing the gap, at least when the
centrifugal pump is in operation.
[0015] As has already been mentioned, due to the pre-stressing of
the elastic sealing lip against the sliding surface, the gap seal,
insofar as it is self-adjusting, is continually applied more
closely to the sliding surface as the sealing lip, even if it is
gradually abraded over the course of operation, due to the pressure
difference between the pressure side and the suction side provided
during operation, up to a certain extent of wear, when the pump is
in operation. A complete sealing of the gap during the operation of
the pump, by means of which a deposition of solids and/or of
fibrous components contained in the transported medium in the gap
region and thus a blockage due to braid formation when it is
applied in wastewater is effectively prevented, can then also be
provided in this case, if, when the pump is turned off, the sealing
lip is no longer applied to the sliding surface, due to the wear of
material that has occurred.
[0016] According to the basic concept of the solution, the
pre-stressing in the elastic sealing lip of the sealing ring is
achieved by suitable positioning of the sealing ring in the pump
housing or positioning relative to the sliding surface, whereby the
sealing ring is supported on an abutment present inside the pump
housing so that a certain pressure is exercised on its sealing lip.
Insofar as the solution according to the invention can also be
realized optionally by a gap ring that is already present and fixed
in the pump housing acting as an abutment, as is usual for the
adjustment of a pre-determined gap width in pumps of the prior art,
after an appropriate retrofitting according to the invention, this
gap ring is joined by mechanical fastening or vulcanization with a
sealing lip inclined against a wear ring of the impeller or the
sliding surface thereof, which has also been retrofitted.
[0017] According to a practical embodiment of the invention,
preferably and particularly provided for use in one-stage
centrifugal pumps with an axial gap, the adjusting member acting on
the sealing ring is formed as a collar that can be adjusted in the
axial direction with respect to its position, and it acts directly
on the sealing ring. In this embodiment, at least when the
centrifugal pump is operating, the sealing lip is applied in a
sliding manner to an outer surface of the wear ring, which is
disposed preferably orthogonal to the axial direction or pump axis,
whereby the axial direction is given by the direction of the
lengthwise extension of the motor shaft driving one impeller or
optionally several impellers. Corresponding to one configuration of
this embodiment that is provided, the position of the collar can be
adjusted by means of two or more adjusting screws disposed
approximately equally distributed relative to the periphery of the
collar, and each of these screws is engaged with a thread extending
in the pump housing in the axial direction. The threads for the
adjusting screws are thus preferably formed in threaded bores,
which are guided through the pump housing in the axial
direction.
[0018] In particular, when pumps are retrofitted with the gap seal
according to the invention, however, it may be necessary to insert
into the pump housing an additional housing ring applied to the
collar on the side opposite to the sealing ring. This is the case
particularly in pumps which have a relatively large housing bore or
housing chamber, respectively, on the intake side of the impeller.
In these pumps, it is not possible, without the placement of the
additional housing ring, to position the adjusting screws in such a
way that the collar acts on the sealing ring at an appropriate
place, namely, in particular, in the region of the sealing lip
projecting over the rigid pressure ring of the sealing ring or/and
the region projected on by it. In order to make this possible, said
housing ring, which has several circular segment-shaped recesses on
its periphery, is inserted. Each of the threads for the adjusting
screws of the adjusting member here are in part formed in the
circular segment-shaped recesses disposed on the outer periphery of
the housing ring and in part in annular recesses of the pump
housing disposed corresponding to these first recesses of the
housing ring and preferably enclosing together with these a full
circle in each case. The housing ring is simultaneously fixed in
the pump housing by the adjusting screws engaged with the
threads.
[0019] In a particularly advantageous embodiment of the invention,
the collar has an outer thread and is engaged with an inner thread
of the pump housing that is correspondingly disposed for this
purpose. The axial position of the collar can thus be adjusted
inside the centrifugal pump by turning the collar in the inner
thread of the pump housing. Independently of which of the
above-described embodiments are used for the collar and/or the
means serving for the positioning thereof or for establishing the
contact force acting on the sealing ring, according to an
advantageous enhancement, the device according to the invention has
set screws, by means of which the collar can be fixed in the place
and position adjusted for it each time.
[0020] As has already been mentioned several times, the device
according to the invention is suitable for both equipping
centrifugal pumps in the factory as well as for retrofitting them.
Therefore, the device according to one embodiment provided for
retrofitting is designed in such a way that its respective elements
are components of a kit, in which is also included a drilling
template or a hole gauge for correct positional arrangement of the
threaded bores to be formed for the adjusting screws and optionally
for the set screws.
[0021] The invention will be explained in more detail below on the
basis of embodiment examples. In this case, the explained examples
concern variants that are particularly suitable for retrofitting
pumps that have not been provided previously with a corresponding
device. The following are shown in the appended drawings:
[0022] FIG. 1: a centrifugal pump retrofitted with a device
according to the invention corresponding to one possible embodiment
of this device,
[0023] FIG. 2: an enlarged excerpt of the pump according to FIG. 1
with the device for impeller sealing,
[0024] FIGS. 3a, 3b: the housing ring additionally inserted into
the pump housing according to the embodiment according to FIG. 1
and FIG. 2,
[0025] FIG. 4: another basic embodiment of the invention, with a
specially configured collar.
[0026] FIG. 1 shows by way of example a centrifugal pump
retrofitted with the device according to the invention, wherein the
pump is shown with a cut-out in a pump housing 1 for better
illustration. The example shown relates to the retrofitting of a
centrifugal pump, in which an impeller 2 is designed in the form of
a channel impeller. This embodiment as well as the other embodiment
explained in connection with the drawings refers to a design, in
which the annular elastic sealing lip 8 joined to pressure ring 7
and forming the sealing ring together with this is pre-stressed by
means of a collar 9 acting on the sealing ring, and sliding surface
6' is formed on a wear ring 6 attached to impeller 2.
[0027] The pump is composed of pump housing 1 in which impeller 2
or the channel impeller, which is disposed on a motor shaft that is
not shown here, moves in the peripheral direction u when the pump
is in operation. The motor, which is also not shown here, is
flange-mounted onto pump housing 1 on the right side of the pump in
the drawing, so that the motor shaft extends in the axial direction
a. The gap which is to be sealed is formed between pump housing 1
and impeller 2, and this gap involves an axial gap based on the
structural form of the pump shown in the example. This gap is
completely sealed by means of the device according to the
invention, which is still better illustrated in the enlarged
excerpt according to FIG. 2, against transport of material between
the pressure side 3 of the pump and the impeller intake 5 on the
suction side 4 of the pump.
[0028] FIG. 2 shows an enlarged excerpt of the centrifugal pump
according to FIG. 1, which has been retrofitted with the device for
impeller sealing according to the invention, in a sectional view. A
shoulder has been formed for the retrofitting by working the outer
contour of impeller 2. A highly wear-resistant wear ring 6 provided
with a complementary step has been applied to this shoulder and
attached by means of several screws to impeller 2. For this
purpose, threaded bores corresponding to the counter-bores of wear
ring 6 are introduced into impeller 2, distributed on the
periphery. In order to reduce the relatively large diameter of the
housing bore for the pump shown in the example on the side of
impeller intake 5, a preferably metal housing ring 11 has been
inserted additionally into pump housing 1 of this pump, and the
design of this housing ring is illustrated in FIGS. 3a and 3b.
Housing ring 11 has several annular recesses 12, each of which is
provided with a first part of a thread and, together with the
corresponding recesses worked into pump housing 1 and provided with
the respective second part of the thread, each enclose a full
circle or circular cylinder. Each of adjusting screws 10 is engaged
with the inner threads formed in part in recesses 12 of housing
ring 11 and in part in the recesses of pump housing 1. Collar 9 can
be moved in the axial direction a by means of adjusting screws 10
that can be adjusted with an Allen wrench. Adjusting screws 10 in
this case serve simultaneously for fastening housing ring 11 in
pump housing 1. Collar 9, which is provided with shoulders, presses
against the flexible region 8' of sealing lip 8 of the sealing ring
disposed between collar 9 and wear ring 6, whereby the compressive
force by which sealing lip 8 is pressed against wear ring 6, is
dependent on the position of collar 9, which can be adjusted by
means of adjusting screws 10. The position of collar 9 that is
adjusted each time, and that can be re-adjusted if necessary, is
fixed by means of set screws 15, which are formed in the present
case as tension screws, and which are guided through an inner bore
of adjusting screws 10 and engaged each time with a threaded bore
in collar 9. In this way, the heads of set screws 15 that are
disposed in captive manner come to rest on a shoulder of the inner
bore of the respective adjusting screw 10.
[0029] The sealing ring is composed of a rigid metal pressure ring
7 to which is screwed the annular sealing lip 8 comprised of rubber
in the example shown. However, a joining of rigid pressure ring 7
with sealing lip 8 by vulcanization is more advantageous. Sealing
lip 8 is subjected to a pre-stressing by collar 9 in such a way
that it is applied to wear ring 6 only by the outer end 8'
(relative to its periphery) of its flexible region 8' projecting
over pressure ring 7, as can be seen from the figure, when the pump
is turned off. When the pump is operating, sealing lip 8 is pressed
more intensely on wear ring 6 with complete sealing of the axial
gap based on the pressure difference existing between pressure side
3 of the pump and the impeller intake 5 of suction side 4. Based on
its elasticity, sealing lip 8, however, is applied only in sliding
manner on wear ring 6 by outer end 8' of region 8', so that the
rotational movement of impeller 2 of the pump is additionally made
possible. Based on the pre-stressing introduced on sealing lip 8,
its sliding contact with sliding surface 6 continually remains,
even with axial and/or radial oscillations of impeller 2 that occur
and are caused by pump operation. Therefore, a reliable and above
all permanent, self-adjusting, complete seal of the gap between
pump housing 1 and suction side 4 of impeller 2 or impeller intake
5 is provided despite possible oscillations. With the application
of a centrifugal pump furnished with the device according to the
invention as a wastewater pump, a braid formation in the gap region
and thus a later blockage of the pump are reliably prevented in
this way.
[0030] As long as the inner diameter of pump housing 1 is not too
large, differing from the previously explained example of
embodiment, collar 9 can also be inserted directly into pump
housing 1 without an additional housing ring 11. Adjusting screws
10 are guided through axially running threaded bores in pump
housing 1. In this way, in the case of equipping centrifugal pumps
with the device according to the invention carried out in the
factory, the embodiment without additional housing ring 11 is
preferred, of course. The representation of the embodiment shown in
FIG. 1 to 3a or 3b, respectively, however, will serve for the
purpose of showing that even pumps already in use can be well
retrofitted with the device according to the invention.
[0031] Another embodiment of the device according to the invention
is shown in FIG. 4 in a representation comparable to FIG. 2. In
this embodiment, collar 9 and thus the sealing ring are positioned,
and the contact force acting on the sealing ring made of pressure
ring 7 and sealing lip 8 is established by means of an outer thread
13 disposed on the front side of collar 9. This thread engages in a
corresponding inner thread 14 formed in pump housing 1 (optionally.
i.e., in the case of retrofitting, by a corresponding re-working of
pump housing 1). By turning in inner thread 14, the axial position
of collar 9 can be adjusted corresponding to the requirements,
i.e., application of the radially outer end 8' of the region 8' of
sealing lip 8 projected on by pressure ring 7, with pre-stressing
on wear ring 6 as small as possible. In the corresponding set
position, collar 9 can be attached by means of set screws 15 (one
or more set screws 15 is or are disposed in the outer region of the
collar), and these screws act as clamping screws and brace the
sides of threads 13, 14 of collar 9 and of pump housing 1 against
one another. For sealing, an O-ring 16 made of rubber is disposed
between pump housing 1 and collar 9.
[0032] By means of the device according to the invention, a clear
increase in efficiency is achieved for appropriately equipped
centrifugal pumps, due to the complete prevention of backflow,
i.e., backflow from pressure side 3 to suction side 4 in impeller
2, and by the elimination of cross-current losses. Suction-side
blockages are effectively prevented, particularly in wastewater
pumps with one or more channel impellers. The operating, energy and
repair costs with the use of centrifugal pumps are reduced thereby.
The device is also characterized by a simple construction and can
be well retrofitted in pumps already in use. Due to the automatic
equilibration of the structural tolerances of the components and/or
those occurring as a consequence of wear, the proposed solution is
also advantageously self-adjusting and thus permanently
self-sealing.
LIST OF REFERENCE NUMBERS
[0033] 1 Pump housing [0034] 2 Impeller [0035] 3 Pressure side
[0036] 4 Suction side [0037] 5 Impeller intake [0038] 6 Wear ring
[0039] 7 Pressure ring [0040] 8 Sealing lip [0041] 8' Region of the
sealing lip [0042] 8'' End (radial outer end of the sealing lip)
[0043] 9 Adjusting member, for example, collar [0044] 10 Adjusting
screw [0045] 11 Housing ring [0046] 12 Recess [0047] 13 Outer
thread [0048] 14 Inner thread [0049] 15 Set screw [0050] 16 O-ring
[0051] a Axial direction [0052] u Peripheral direction
* * * * *