Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION:
CUTTER SYSTEM FOR PUMP SUCTION
SPECIFICATION
BACKGROUND OF THE INVENTION
1. FIELD OF INVENTION
This invention relates generally to pumps for liquids, and more particularly,
to centrifugal
pump cutters for cutting solids suspended in the liquid.
2. DESCRIPTION OF RELATED ART
Pumps in both the manure slurry and municipal waste markets are subjcct to
clogging due to
the nature of stringy materials and other soft solids which tend to restrict
or block the impeller
passages in a centrifugal pump. This clogging can occur as often as every few
days.
One attempt to solve the clogging problem was provided by a drawing of an "A
Series Cutter
Assembly: Drawing #046897" to Homa. The Homa assembly is a crude welded device
with a single
slicer blade welded to a cutter plate, and two flat slicer blades welded
inside an impeller and leaving
a small opening therebetween. The Homa assembly has operational flaws,
including shortcomings
present in any welded device designed without thought to hydraulic impact of
the cutters. For
example, the Homa cutter and stator teeth block flow into the impeller,
causing substantial pressure
drop as flow enters the pump. This pressure drop will limit the amount of
"lift" that the pumps can
generate, limit the flow range of a pump, limit the size of a solid that can
flow through the pump, and
increase the amount of power that would be required to operate the pump. With
just one impeller
tooth the cutting force is skewed to one side causing life reducing unbalanced
loads. The cutter teeth
and impeller will have a reduced operational life because of the unbalance.
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The Boma mechanism is fabricated with the teeth welded into the impeller and
stator.
Welding the teeth adds problem on operation of the pump. For example, welds
can be attacked by
corrosion causing premature failure. Heating from the welds can damage the
impeller and stator.
That is, the heat could warp the teeth and change the base structure of the
underlying material. The
corrosion resistance near the weld can change because of the heat. In
addition, impact loads (from
cutting) are concentrated at the weld points leading to reduced
impeller/stator life. Further, the
welded on teeth are non-replaceable. This means that failure at the weld would
likely require a new
impeller or plate in order to make a repair that now requires a pump rebuild.
Even prior to failure, the
welded-on teeth are wear items and will need to be renewed on a regular basis.
Since pumps can go
several years without a major rebuild, the requirement that base parts
(impeller/stator) be replaced
with the teeth is an expensive time consuming problem for pump users.
In the related art described in U.S. Publication No. 2014/0064929 filed by the
same assignee,
a cutter device for a centrifugal pump includes an impeller, a cutter ring, a
wear ring and a stationary
cutter plate. The impeller is concentrically located in a volute of the
centrifugal pump. The volute
has a front wall with a front flange defining an inlet port. The impeller has
a rotational axis about
which the impeller rotates within the volute. Further, the impeller has an
inlet end that extends into
and sits concentrically within the front flange. The cutter ring is releasably
attached to the impeller,
with the cutter ring concentric with the impeller and including a first set of
teeth extending inwards
towards the rotational axis of the impeller. The wear ring is located about
the cutter ring between the
cutter ring and the volute. The stationary cutter plate is releasably attached
to the volute, concentric
with and adjacent to the cutter ring. The stationary cutter plate includes a
plate ring and a second set
of teeth extending inwards from the plate ring towards the rotational axis of
the impeller. The
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second set of teeth is in shearing communication with the first set of teeth
to shear apart solids in the
inlet port of the volute.
According to another example described in U.S. Publication No. 2014/0064929, a
centrifugal
pump includes a volute, an impeller, a cutter ring, a wear ring and a
stationary cutter plate. The
volute has a front wall with a front flange defining an inlet port. The
impeller is concentrically
located in the volute, with the impeller having a rotational axis about which
the impeller rotates
within the volute, and the impeller having an inlet end that extends into and
sits concentrically within
the front flange. The cutter ring is releasably attached to the impeller, with
the cutter ring concentric
with the impeller and including a first set of teeth extending inwards towards
the rotational axis of
the impeller. The wear ring is located about the cutter ring between the
cutter ring and the volute.
The stationary cutter plate is releasably attached to the volute, concentric
with and adjacent to the
cutter ring, with the stationary cutter plate including a plate ring and a
second set of teeth extending
inwards from the plate ring towards the rotational axis of the impeller. The
second set of teeth is in
shearing communication with the first set of teeth to shear apart solids in
the inlet port of the volute.
The cutter device and centrifugal pump described in U.S. Publication No.
2014/0064929
shears apart solids in a centrifugal pump' s suction inlet to prevent
restriction or blockage in the
impeller passages. The shearing action is accomplished by the mechanical
interaction of a cutter ring
fastened to the rotating impeller and a cutter plate fastened to the
stationary volute of the centrifugal
pump. The action of the cutter mechanism disrupts the formation of the
clogging action and keeps
flow moving through the pump. Some elements of the cutter device may include:
profiled cutter
teeth to optimize flow and Net Positive Suction Head (NPSH) characteristics,
adjustable cutter
clearances to maintain optimal shearing action, keyed engagement that takes
impact away from the
fasteners on a rotating cutter ring and stationary cutter plate.
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The cutter device and centrifugal pump described in U.S. Publication No.
2014/0064929 has
been successful, especially in light to medium duty services. However, the
inventors have
recognized that heavier concentration of solids in these applications indicate
that the cuter assembly
may at some level still be susceptible to the heavier concentration of solids
filling in voids at the
center of the impeller and around the vane tips, which may restrict the
hydraulic flow. Accordingly,
the inventors have designed an improved cutter system.
BRIEF SUMMARY OF THE INVENTION
This summary is provided to introduce a selection of concepts in a simplified
form that are
further described below in the detailed description. This summary is not
intended to identify essential
features of the claimed subject matter, nor is it intended for use in
determining the scope of the
claimed subject matter.
According to an example of the invention, a cutter device for a centrifugal
pump includes an
impeller, a rotor, a wear ring and a stationary cutter plate. The impeller is
concentrically located in a
volute of the centrifugal pump. The volute defines a chamber and has a front
wall with a front flange
defining an inlet port. The impeller has a rotational axis about which the
impeller rotates within the
volute. The impeller further includes an impeller vane having an inlet angle.
The impeller also has
an inlet end that extends into and sits concentrically within the front
flange. The wear ring sits
adjacent the impeller between the impeller and the volute. The rotor is a
cutter auger releasably
attached to and concentric with the impeller. The rotor includes a central
section and an auger vane
extending away from the central section. The stationary cutter plate is
releasably attached to the
volute or a suction cover thereof, concentric with and adjacent to the cutter
auger. The stationary
cutter plate includes a plate ring and teeth extending inwards from the plate
ring towards the
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rotational axis of the impeller and cutter auger. The teeth are in shearing
communication with vanes
of the auger to shear apart solids in the inlet port of the volute.
According to another example of the invention, a centrifugal pump includes a
volute, an
impeller, a rotor, a wear ring and a stationary cutter plate. The volute
defines a chamber and has a
5 front wall with a front flange defining an inlet port. The impeller is
concentrically located in the
volute, with the impeller having a rotational axis about which the impeller
rotates within the volute,
and the impeller having an inlet end that extends into and sits concentrically
within the front flange.
The impeller further includes an impeller vane having an inlet angle. The wear
ring sits adjacent the
impeller between the impeller and the volute. The rotor is a cutter auger
releasably attached to and
concentric with the impeller. The rotor includes a central section and an
auger vane extending away
from the central section. The stationary cutter plate is releasably attached
to the volute or a suction
cover thereof, concentric with and adjacent to the cutter auger. The
stationary cutter plate includes a
plate ring and teeth extending inwards from the plate ring towards the
rotational axis of the impeller
and cutter auger. The teeth are in shearing communication with vanes of the
auger to shear apart
solids in the inlet port of the volute.
The auger may include vanes numbered preferably to match the number of vanes
on the
impeller. The radial profile of the auger preferably makes a continuous vane
with the impeller, and
prevents solids from hanging on the inlet vane tip or center void while
providing a smooth flow
transition into the impeller.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
The invention will be described in conjunction with the following drawings in
which like
reference numerals designate like elements and wherein:
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Fig. 1 is a perspective view of an exemplary cutter pump assembly in
accordance with the
preferred embodiments of the invention;
Fig. 2 is a front view of the cutter pump assembly of Fig. 1;
Fig. 3 is an axial sectional view of the cutter pump taken along line 3-3 of
Fig. 2;
Fig. 4 is an isometric exploded assembly view of the cutter pump of Fig. 1;
Fig. 5 is a perspective view of an exemplary cutter auger from the cutter pump
of Fig. 1;
Fig. 6 is a top view of the exemplary cutter auger from the cutter pump of
Fig. 5;
Fig. 7 is a side front view of the exemplary cutter auger of Fig. 6;
Fig. 8 is a side sectional view of the exemplary cutter auger of Fig. 6 taken
along line 8-8 of
Fig. 6;
Fig. 9 is a perspective view of an exemplary impeller, cutter auger and cutter
ring; and
Fig. 10 is an axial side sectional view of an exemplary cutter pump including
the cutter auger
and cutter ring of Fig. 9.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
1 5 An example of the improved system is shown in the additional figures
and includes an auger
or auger style part that is profiled radially to match the inlet geometry of
the impeller vanes while
extending along its central axis towards the pump suction. The auger is
preferably radially
concentric to the impeller. The auger includes vanes numbered preferably to
match the number of
vanes on the impeller. The auger depicted in the drawings is axially profiled,
top and bottom, at least
substantially parallel to the suction flange of the pump, the mating
stationary cutter, and the mating
surface on the impeller where it registers. The auger acts as a rotating
(rotor) cutter, which may
replace the toothed cutter from the invention described above. It is affixed
to the impeller, preferably
with a lockscrew threaded into the common pump shaft. The radial profile of
the auger essentially
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makes a continuous vane with the impeller, and prevents solids from hanging on
the inlet vane tip or
center void while providing a smooth flow transition into the impeller.
Accordingly, the profile of the exemplary auger design prevents solids from
accumulating in
at least these locations while also shearing the solids and guiding the flow
into the pump. For light
and medium applications, the invention described in U.S. Publication No.
2014/0064929 at least
achieves this purpose. The auger more efficiently handles heavier duty in more
severe applications
than prior art pumps, and preferably is retrofitable in common pumps. Further,
the auger can be in
integral part with the impeller or a replaceable part used with the impeller.
Shearing action is achieved by the interaction of the auger as the cutter
rotor and toothed
cutter stator. The auger design of the rotor is integral with the impeller and
preferably a replaceable
part. The cutter pump apparatus is useful especially in extreme service
conditions to prevent heavier
concentrations of solids from accumulating in the center of the impeller and
the leading edge of the
impeller vane while guiding the flow into the impeller. In addition, the
cutter auger rotor design
prevents solids from restricting or blocking the impeller inlet without
significant decrease of flow
throughput or significant increase in absorbed hydraulic horsepower.
The exemplary embodiments include cutter auger vanes and stator teeth that
minimize
clogging of the impeller passages into the pump. The size of the teeth is
large enough to interrupt
clogging, yet small enough to not restrict the original solids capacity of the
centrifugal pumps. For
example, the teeth project radially inwards preferably less than one-fourth of
the diameter of the inlet
to the impeller. The vanes are preferably structured with a hydraulic profile
that matches the inlet
angle of the impeller vanes. In this manner, each pump preferably has an auger
interacting with the
stator teeth to shear solids entering the cutter pump apparatus. Moreover, the
auger has vanes
designed to match the impeller inlet vane angles. That is, the teeth and vanes
are preferably
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hydraulically profiled to match the impeller. They may even be clocked at
installation ¨ oriented
such that the teeth minimize the interruption of the inlet flow path.
Accordingly, the exemplary
embodiments reduce the impact to suction lift and restricted flows experienced
by known designs.
The cutter assembly and cutter system is machined from a casting bolted in,
adjustable and
preferably symmetrical and retrofitable, leading to predictable mechanical and
hydraulic results. Cast
and machined parts are not subject to corrosion caused by welding. The
impeller and suction case are
machined to accept the rotor (e.g., cutter auger, cutter ring) and stator
(e.g., cutter plate). This
eliminates potential damage caused by welding on the parts. Further, the wear
parts are retrofitable.
This will be an incredible benefit to scores of municipal wastewater pump
stations that have flow
interruptions because of clogging and will be able to quickly add cutters
without changing pumps or
increasing motor size. When the parts have worn and need to be renewed the
impeller and suction
piece will be undamaged. The customer will be able to quickly change out the
rotor and stator
without replacing a damaged impeller or suction piece.
Referring now in greater detail to the various figures of the application,
wherein like-
referenced characters refer to like parts, a general communication environment
including an
exemplary cutter pump assembly 10 of the invention is illustrated in Fig. 1.
Fig. 2 depicts the cutter
pump device or assembly 10 in front view, Fig. 3 depicts the cutter pump
assembly in axial cross
view, and Fig. 4 depicts the cutter pump assembly in exploded view. With
reference to Figs. 1-4,
shown therein in perspective view is a pump volute 12 having a front cover 14,
a backplate 16 and a
housing 18. The volute 12 defines a chamber 17 within scrolling out to a
discharge flange 19.
Typically the volute is made of iron, however, various other metals know in
the art for increased
hardness or corrosion resistances are acceptable as well. The volute is
preferably cast and thus not
subjcct to corrosion caused by welding.
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The front cover 14 has a front annular flange 20 partly defining an inlet port
22, and is cast as
a separate suction cover that is attached to the volute 12, preferably via
front cover bolts 24 threaded
into matching bores 26 (Fig. 4) in a forward facing annular flange 28 of the
volute housing 1 8. Thus
the front cover is an exemplary detachable front wall of the volute 12. It
should be noted that the
front wall of the volute 12 is not limited to a detachable front wall, as the
volute may include a front
wall permanently integral with the housing 18.
Now referring to Figs. 3 and 4, the backplate 16 is secured to a rearward
facing annular
flange 30 of the volute housing 18 where it may be compressed between the
volute housing and a
motor 32. The backplate 16 has an outward extending center section 34 with an
annular recess cavity
36 into which a drive shaft 38 of the motor 32 extends. The backplate 16 is
preferably secured to the
volute housing via bolts 40 threaded into matching bores (not shown) located
in the rearward facing
annular flange 30. While not being limited to a particular theory, the
backplate 16 also includes an
annular extension 44 that in Fig. 3 abuts a spacer bracket 46 fixed between
the motor 32 and the
backplate, and about the drive shaft 38 to provide stability to the pump.
Other examples of the cutter
pump assembly 10 may encompass a wide range of different volute styles and
shapes, as many
aspects of the invention are not limited to use on centrifugal pumps.
An impeller 48 concentrically sits in the volute 12 rotatable between the
backplate 28 and
front cover 14. A back wall 50 of the impeller 48 extends radially inwards
into an annular collar 52
that defines a bore 54 for attachment to the drive shaft 38 of the motor 32.
The drive shaft 38 is
fixed to the impeller 48; preferably via a lockscrew 56 threaded into a
matching bore 58 axially
located in the driveshaft 38, as will also be described in greater detail
below. While not being limited
to a particular theory, the impeller 48 is preferably closed vane as it
consumes much less energy than
open vane impellers. The impeller 48 also includes a front wall 60 and vanes
62 between the front
1_0
wall and the back wall 50. The front wall 60 is turned towards an inlet end 64
that extends into and
sits concentrically within and spaced from the front cover 14 by a wear ring
66 therebetween. The
impeller 48 is preferably machined from metal or a solid composition including
metal. In use, the
impeller 48 is rotated by the pump motor 32 to induce a pumping action as
understood by a skilled
artisan. The pumping action pulls slurry or pumpage into the inlet end 64,
through the impeller 34
and out the volute flange 27.
Referring to Fig. 3, a seal structure 42 exposed to the chamber 17 seals the
drive shaft 38
and volute 12. This seal structure includes a stationery seal 41 and a rotary
seal 43 which rotates
with the drive shaft. An urging member, such as a compression spring 45, urges
the rotary seal 43
against the stationery seal 41. With the construction described, liquid within
the chamber 17 is
prevented from leaking outwardly past the backplate 16 of the volute 12. The
example depicted in
Fig. 3 shows the backplate 16 and impeller 48 having surfaces facing each
other that are relatively
smooth. It is understood that the invention is not so limited, as the mutually
facing surfaces may also
have a vane construction distributed circumferentially of the drive shaft 38
effective to produce a
circulating action in pumpage moved between the mutually facing surfaces which
results in debris
leaving the seal structure adjacent the annular collar 52 to move radially
outwards to a larger
diameter end of the backplate adjacent the rearward facing annular flange 30
and thence out into the
main discharge stream of the pump as described in greater detail in U.S.
Patent No. 5,489,187.
The wear ring 66 is disposed concentrically about the front wall 60 of the
impeller 48, and is
supported between adjacent surfaces of the front wall and the front cover 14
where the wear ring can
minimize friction and wear between the rotating impeller and the stationary
volute 12. In cross
section, the wear ring 66 can be seen as generally rectangular. However, the
shape of the wear ring is
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not limited thereto. For example, the wear ring may be L-shaped with a
longitudinally extending
portion and a radially extending portion located at a front side of the front
wall between the impeller
48 and the volute 12. The wear ring 66 may be a single piece of machined metal
or other alloy
composition. It is also understood that the wear ring 66 may be a bushing or
other multi-piece
annular unit.
The impeller 48 and front annular flange 20 define a generally conical shaped
interior
chamber 68 extending outwards through the inlet port 22. Within the interior
chamber 68 resides a
cutter assembly 70 supported at least by the volute 12 and the impeller 48. As
can be seen in Figs. 3-
8, the cutter assembly 70 includes a rotor (e.g., rotating cutter auger 72)
and a stator (e.g., cutter plate
74). The cutter auger 72 is preferably machined from a metal casting, and is
retrofitably (e.g.,
releasably) attached to the back wall 50 the impeller 48 preferably by the
lockscrew 56. For
example, the cutter auger 72 includes a central section of a base portion 76
fixed concentrically
against the impeller 48 that extends axially towards the inlet port 22 into a
tubular portion 78 ending
at a front surface 80 thereof. The base portion 76 and tubular portion 78
define an axial bore 82 (Fig.
8). As can best be seen in Fig. 3, the lockscrew 56 abuts the front surface 80
and extends through the
tubular and base portions, and finally through an aperture 84 in the back wall
50 into threaded
engagement with the matching bore 58 of the driveshaft 38 to fix the cutter
auger, impeller and
driveshaft together. Of course the auger 72 can be fixed to the impeller via
other ways as readily
understood by a skilled artisan, for example, via screws extending through
offsetting longitudinal
bores in the base portion that attach to matching threaded bores in the
impeller 48.
Figs. 5-8 depict an exemplary cutter auger 72 in various views. The cutter
auger 72 includes a
plurality of vanes 86 that extend outwards spirally from the base and tubular
portions 76, 78 of the
cutter auger. Preferably each vane 86 has a top spiraled surface 88 having a
sharp edge 90 for
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interacting with the cutter plate 74 to shred solids entering the inlet port
22, as will be described in
greater detail below. Each vane 86 also spirals from the base and tubular
portions 76, 78 to an outer
edge 92. The vanes 86 arc preferably numbered and structured with a hydraulic
profile that matches
the inlet angle of the impeller vanes 62. Moreover, the auger vanes 86
preferably intentionally match
the impeller inlet vane angles. In this manner, the cutter auger vanes 86
remove solids from
restricting or blocking the interior chamber 68 before the impeller vanes
efficiently without
significant decrease of flow throughput. While there is no limitation on the
number of auger vanes
86, it is preferred that the auger 72 has at least two vanes 86 equidistantly
spaced radially about the
base and tubular portions 76, 78 to balance the impact load with the solids or
slurry flowing into the
impeller 48, which leads to a longer service life of the rotating cutter auger
and the impeller. Further,
while the front surface 80 of the tubular portion 78 and the tip spiraled
surface 88 of the vanes 86 are
shown on two different planes in this example, it is understood that the
invention does not limit the
planar relationship between the surfaces.
As can best be seen in Figs. 1, 2 and 4, the cutter plate 74 is preferably
annular, stationary and
retrofitably (e.g., releasably) attached to the front annular flange 20 of the
volute 12 by cutter plate
cap screws 94 threaded through bore walls 96 (Fig. 4) of the cutter plate into
screw fixing bores 98
(Fig. 4) of the front annular flange 20. The stationary cutter plate 74 is
preferably machined from a
metal casting with three integrally formed stationary teeth 104 provided to
engage with the sharp
edges 90 of the auger vanes 86 for cutting or shearing solids flowing into the
inlet port 22 of the
volute 12. The teeth 104 are machined from a casting with a profile that
allows entry of solids/slurry
into the chamber 68 while extending into the inlet port 22 far enough to match
against the sharp
edges 90 of the top spiraled surface 88 for shearing action. The stationary
teeth 104 each have a
sharp edge closest to an approaching sharp edge 90 to maximize the cutting and
shearing action there
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between. While there is no limitation on the number of stationary teeth 104,
it is preferred that the
cutter auger 72 has one more or less vane in comparison to the number of
teeth. The stationary teeth
104 are equidistantly spaced about the stationary cutter plate 74 to balance
the impact load with the
solids or slurry flowing into the impeller 48 and to balance the shearing
action between the stationary
teeth and the auger vanes, which leads to a longer service life of the
stationary cutter plate and the
rotating cutter auger 72.
Sct screws 100 are threadingly disposed through the cutter plate 74 to adjust
a clearance 102
between the top spiraled surface 88 of the auger 72 and the cutter plate 74.
In particular, the set
screws 100 are threaded through threaded bores 106 (Fig. 4) in the cutter
plate 74 and into abutment
against a recessed annular face 108 (Fig. 4) of the front cover 14 to
spatially set the cutter plate at a
distance from the recessed annular face as the cutter plate is attached to the
front annular flange 20
via the cap screws 94 threaded into the screw fixing bores 98. The set screws
100 are designed to set
the distance between the cutter plate 74 and the recessed annular face 108 to
provide the clearance
102 between the stationary teeth 104 and the top spiraled surface 88 of the
rotating cutter auger 72 to
allow a shearing interaction in use therebetween when the auger vanes 86 are
rotated adjacent the
stationary teeth. Preferably this clearance is set to bctween 0.01 and 0.02
inches. While the
exemplary embodiment shows four set screws 100, it is understood that the
invention is not limited
thereto and that any number of set screws is within the scope of the
invention. Preferably the number
of set screws is plural and spaced equidistantly about the stationary cutter
plate 74 to provide equal
clearance between the stator teeth 104 and the sharp edges 90.
As discussed above, the rotating cutter auger 72 and the stationary cutter
plate 74 are
retrofitable. For example, the cutter auger 72 and cutter plate 74 are
releasable with the impeller 48
and front cover 14, respectively, here via the lock screw 56 and the cap
screws 94 (Fig. 4). This is
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beneficial since both of these members include wear parts (e.g., vanes, teeth)
that wear out over time
and generally quicker than the other parts of the cutter pump assembly 10. As
the sharp edges 90 of
the cutter auger 72 and teeth of the stationary cutter plate 74 become dull,
break, or wear down, the
members can be removed and replaced with a new or refurbished auger or plate
having sharp edges
and teeth effective for shearing the slurry. This extends the life of, for
example, the impeller 48 and
volute 12, which have a longer service live than the auger 72 and cutter plate
74, because a plurality
of augers and cutter plates may be retrofitted and used. This also adds
flexibility to the cutter pump
assembly 10 as differently configured augers and cutter plates can be used
with the assembly based
on which configuration (e.g., number of vanes/teeth, angle of teeth blades,
size of teeth, shape of
vanes) may be preferred for a specific slurry, suction level, or output.
As can best be seen in Fig. 3, during pump operation, the slurry or pumpage,
including
suspended solids and stringy materials, enters thru the inlet port 22 of the
pump volute 12. The
slurry then is drawn into the cutter assembly 70 by the pumping action of the
impeller 48. The slurry
passes between the stationary cutter plate 74 and the rotating cutter auger
72, at which point the
suspended solids are sheared into smaller segments and pulled into the auger.
The sheared pumpage
then flows through the impeller 48, is discharged out into the volute chamber
25 and exits the volute
12 through the discharge flange 27.
It should be noted that in the examples of the cutter assembly may also
include a toothed
cuter ring similar to the cutter ring disclosed in U.S. Publication No.
2014/0064929. Figs. 9 and 10
depict an example with such a cutter ring integrated into the cutter pump
assembly 10 between the
cutter auger 72 and the cutter plate 74. While not being limited to a
particular number, a rotating
cutter ring 110 includes two integrally fon-ned profiled teeth 112 for cutting
or shearing solids and
two projections 114 designed to provide a keyed engagement with the impeller
48 as discussed in
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greater detail below. The profiled teeth 112 are machined from a casting with
a hydraulic profile that
preferably matches an inlet angle of the impeller vanes 62 and the auger vanes
86. For example, the
profiled teeth 112 have a cutting edge 116 and a blade 118 angled rearward
from the cutting edge
towards the impeller back wall 50 at an angle that matches the inlet angle of
the impeller and auger
5 vanes. This matching hydraulic profile minimizes any impact to suction
lift and restriction flow and
minimizes pump efficiency loss. The profiled teeth 112 may be oriented with
the auger vanes 86 to
minimize the interruption of solids and slurry into the inlet flow path partly
defined by the inlet port
22 and the chamber 68.
While there is no limitation on the number o f pro file teeth 112, it is
preferred that the rotating
10 cutter ring 110 has at least two profiled teeth 112 equidistantly spaced
about the cutter ring and
aligned with the auger vanes 86 to balance the impact load with the solids or
slurry flowing through
the impeller 48, which leads to a longer service life of the rotating cutter
ring and the impeller. Like
the cutter auger 72 and the cutter plate 74, the cutter ring 110 is preferably
retrofitable, as it is
releasably coupled to the impeller 48, for example, via cap screws 122 that
extend through apertures
15 126 in the cutter ring into threaded engagement with bolt fixing bores
124 in the impeller. This
prolongs the service life of the impeller 48, as a plurality of cutter rings
110 can be used with the
same impeller 48.
As can best be seen in Fig. 9, the projections 114 of the rotating cutter ring
110 are machined
to fit into notches 120 at the inlet end 64 of the impeller 48. The
projections 114 are sized to fit
snuggly into the notches 120 in a keyed engagement and take impact away from
the fasteners (e.g.,
cap screws 122) attaching the rotating cutter ring 110 the impeller 48.
Preferably the projections 114
and the notches 120 are squared to permit a snug fit and maximize the impact
transfer, here from the
cap screws 122 and bolt fixing bores 124 of the impeller 48, to the
projections and notches, which
CA 02863245 2014-09-12
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minimizes impact damage and wear at the cap screws and bolt fixing bores.
While the exemplary
embodiment shows two sets of matching notches 120 and projections 114, it is
understood that the
invention is not limited thereto and that any appropriate number of sets of
matching notches and
projections is within the scope of the invention. Preferably the number of
sets is plural and spaced
equidistantly about the impeller 48 and rotating cutter ring 110 to equally
distribute the impacts.
Fig. 10 also shows that the wear ring 66 may be set between the cutter ring
110 and the
impeller 48 to reduce wear there between. Here, the wear ring 66 is disposed
concentrically about the
cutter ring 110, and supported between abutting surfaces of the cutter ring
and the front cover 14,
where the wear ring can minimize friction and wear between the rotating cutter
ring and the
stationary volute 12. As noted above, the wear ring 66 may be a single piece
of machined metal or
other alloy composition. It is also understood that the wear ring 48 may be a
bushing or other multi-
piece or shaped annular unit.
It is understood that the cutter apparatus for a centrifugal pump and thc
cutter system
described and shown are exemplary indications of preferred embodiments of the
invention, and are
given by way of illustration only. In other words, the concept of the present
invention may be readily
applied to a variety of preferred embodiments, including those disclosed
herein. While the invention
has been described in detail and with reference to specific examples thereof,
it will bc apparent to
one skilled in the art that various changes and modifications can be made
therein without departing
from the spirit and scope thereof. For example, the number, location and shape
of the vanes, teeth,
projections, notches and channels described may be altered without departing
from the scope of the
invention. Without further elaboration the foregoing will so fully illustrate
the invention that others
may, by applying current or future knowledge, readily adapt the same for use
under various
conditions of service.
