Note: Descriptions are shown in the official language in which they were submitted.
HIGH HEAI:) CENTRIFUGAL 5L:I[CIN(; SLURRY PUMP
This application ic; a division of Canadian
application Serial No. 391,172, filed November 30,
1981, for High Head Centrifugal Slicing Slurry PumpO
The present inventlon relates to centrifugal
pumps and particularly to centrifugal pumps effective
for pumping slurries of liquid, usually water, and
suspended solids constituting up to about 25 percent
by weight of such slurries. Usually, the slurries
have chunks or lumps of solid material that could clog
or otherwise reduce the efficiency of a centrifugal
pump so that such slurry pumps must have mechanism for
comminuting the lumps or chunks to ensure effective
and consistent pumping of the slurry.
The pump of the present invention is of the
same general type as the "Centrifusal Chopping Slurry
Pump" disclosed in Vaughan UOSO patent No. 3,973,866,
issued August 10, 1976, whi.ch is stated to be an
improvement on the general type of pump disclosed in
Vaughan U.S. patent No. 3~155,046, issued November 3,
1964~ The pllmps of both of those patents are designed
for pumping slurries containing chunks or lumps of
solid material.
In general~ each of the prior pumps has an
upright drive shaft, the lower end portion o~ which
projects downward into a substantially cylindr.ical
pump casing~ The impeller fixed to the drive shaft
within the casing has a radial shroud disc or plate
with downward projecting~ generally radially extending
blades or vanesO The bottom of the casing is closed
by an end plate havi.ng arcuate inlet apertuxes for
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intake of slurry in an axial direction~ The sharpened
lower edges of the impeller blades cooperate with the
leading edges o the inlet apertures for chopping
chunks or lumps of solid material in the slurry being
pumped. The slurry is accelerated circumferentially
and outward to a generally tangential outlet conduitD
The pump disclosed in U~S. patent No,
3,973~866 also includes a screw propeller cantilevered
from the pump drive shaft outside the pump casing and
adjacent to the inlet apertures in the end plate.
Such propeller has generally radial blades with
somewhat sharpened leading edges for choppin~ chunks
or lumps in th~ slurry~ In addition, the screw
propeller i5 stated to generate a positive current
flow of slurry through the end plate inlet apertures~
Another aspect of the pump of tloS~ patent
No. 3~973,~66 that is pertinent to the present
invention is the use of elongated "slinger" ribs or
vanes of small axial height projecting from the side
of the impeller shroud plate opposite the lower
primary pumping impeller blades. Such upper vanes are
in the form of volute ribs for slinging away from the
drive shaft bearing structure the solid material
component of slurry which may work its way past the
edge of the shroud plate so as to reduce wear of such
bearing structure See the paragraph beginning at
column ~, line 21O
The prior pumps are of relatively low head
and efficiency as compared to the pump of the present
inventionO In such pumps flow through the end plate
inlet apertures into the impeller-receiving pump
casing and out of the casing through the pump outlet
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is much more turbulent than in the pump of the present
invention.
In accordance with the present invention,
improvements made to the pump disclosed in U.S. patent
No~ 3,973,866 include: changing the design of the
bottom booster propeller so as to increase the head of
the pump without decreasing the chopping effectiveness
of such propeller; locating the booster propeller at
the entrance to a downwardly flared funnel for
effecting smooth gradual acceleration of slurry toward
the inlet apertures; locating the inlet apertures
closer to the axis of rotation of the impeller so as
to eliminate or greatly reduce backflow of
high-pressure slurry in the radially outer portion of
the pump casing and increase the effectiveness of the
impeller vanes to accelerate outward movement of the
slurry; rounding the entrances to fair the inlet
apertures for smooth flow into the pump casing;
enclosixlg the impeller in a semicylindrical,
semivolut~ casing, the volute portion being located
immediately rearward of the pump outlet; sweeping back
the impeller blades for providing an improved slicing
action of the sharpened lower edges of the blades in
cooperation with sharpened forward edges of the inlet
apertures; decreasing the thickness of the impeller
blades relative to the radial width of the inlet
apertures so as not to interfere with intake o slurry
through the inlet apertures; merging the imp~ller
blades into the shroud plate with fillets for smooth,
substantially nontuxbulent acceleration of the slurry
circumferentially and outward toward the pump outlet;
cupping the leadin~ faces o-f the in~pel:ler blade~s to
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ensure smooth change of di.rection of the slurry and
effective slicing of chunks or lumps of solid material
in the slurry; recessing the apertured end plate into
the pump casing to dispose its inner surface flush
with the adjoining surface of the pump outlet for
smoother flow of slurry into the pump outlet; and
arranging the upper l'slinger" ribs or vanes for
producing a slight suction in the area of the drive
shaft seal for increasing the life of the seal and to
enable quick and accurate detection of seal failure~
The principal object of the present invsntion
is to provide an efficient, durable centrifugal pump
having a high head characteristic and adapted to
consistently pump slurry containing solid chunks or
lumps.
This object can be accomplished in part by
providing in a centrifugal pump including an impeller
rotatable about an axis and a pump casing including a
bowl receiving the impeller and a generally
ZO circumferential outlet, the improvement comprising the
bowl including a cylindrical portion, coaxial with the
impeller, forming a wall closely encircling no greater
than approximately one-half of the circumference of the
impeller and a volute portion foxming a wall spiraled
outward from said cylindrical portion in the direction
of impeller rotation~
This object also can be accomplished in part
by providing in a centrifugal pump including an
impeller rotatable about an axis t a pump casing
including a bowl encircling the impeller and an outlet
conduit extending substantially tangentially from the
bowl, the improvement compxising the pump bowl being o~
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substantially semicylindrical and semivolute cross
section, the semicy1indrical portion of the bowl being
coaxial with the impeller, forming a wall closely
encircling the impeller for appro~imately on~-half thQ
circumference of the impeller and located forward of
the outlet with reference to the direction of impeller
rotation to form a pressure increasing zone, and the
semivolute portion of the bowl forming a wall spiraled
outward from the wall of the cylindrical portion to the
radially outer side of the outlet conduit and
encircling about one-half the circumference of the
impeller.
In drawings which illustrate an embodiment
of the invention:
Figure 1 is a side elevation of a
centrifugal slicing slurry pump in accordance with the
present invention with parts broken away and parts
shown in section;
Figure 2 is a bottom plan of the pump of
Figure 1;
Figure 3 is a somewhat diagrammatic;
fragmentary, top perspective of a component of the
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pump of Figure 1, namely, the disintegrator or booster
propeller, showing its mounting structure in phantom;
Figure 4 is a section taken on line 4--4 of
Figure 3 but on a larger scale;
Figure 5 is a section taken on line 5--5 of
Figure 1 with parts broken away;
Figure 6 is a fragmentary section taken on
line 6--6 o Figure 5; and
Figure 7 is a fragmentary, detail section
taken on line 7--7 of Figure 5 on a larger scale with
parts in different positions.
As indicated ~n Figure 1, the centrifugal
pump of the present invention includes an upright
drive shaft 1 received within an upright housing 2
forming a reservoir or oil or other lubricant. The
bottom of the reservoir is closed by conventional
antifriction bearings 3 for the drive shaft and a
conventional seal 4~
The bottom portion of housing 2 is bolted to
a pump casing 5 having a downward openirlg cavity or
bowl 6 receiving the pump impeller 7O Such impeller
consists of~ a cylindrical shroud disc or plate 8
projecting radially from the impeller hub 9 fixed to
the drive shaft; the primary pumping vanes or blades
10 projecting downward from the shroud plate; and
vanes or ribs 11 projectin~ upward from the upper face
of the shroud plate opposite the primary pumping
blades 10.
The top of the pump bowl 6 is closed by a
conventional seal 12 encirc:Ling the drive shaft 1~ and
the botto~ of the pump bowl i~ closed by an end plate
13 bolted to the bottom of the pump casing and having
inlet apPrtures 14 which, as best seen in Figure 2,
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are arcuate and concentric with the axis of rotation
of the drive shaft and the impellerO
A disintegrator or booster propeller 15
having generally radially projecting, diametrally
opposed blades 16 and a streamlined~ convexly curved
bottom cap 17 is fixed to the bottom end of drive
shaft 1. Rotation of the drive shaftt such as by an
electric motor~ ef~ects rotation of the booster
propeller for propelling a slurry of liquid, usually
water, and suspended solids constituting up to about
25 percent by weight of the slurry upward into the
pump bowl through the arcuate inlet apertures 14 where
the slurry is accelerated circumferentially and
outward to the pump outlet conduit 18. Such outlet
conduit extends generally tangentially from the
impeller in its plane of rotation and is connected to
a discharge conduit 19 for conveying the pumped slurry
to a desired location~
The slurry pumped can include mixtures of
water and, for exampler earth or vegetable pulp~ but
the pUMp iS particularly useful for pumping mixtures
of water and animal waste such as manure. Such sewage
slurries usually contain fairly large chunks or lumps
of solid, sometimes stringy material whichl to be
pumped effectivelyt must be chopped or otherwise
comminuted into relatively small pieces. Commonly the
pump will be located near th~ bottom of a sump so that
~he slurry must be pumped upward a substantial
distance. As a result, the pressure of the slurry at
the pump outlet must be high, that is, the pump must
operate at a high headD
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One factor that has been found to be
important in increasing the head of a centrifugal
slurry pump is the specific design of the
disintegrator or booster propeller 15. The preferred
design shown in Figures 2 t 3 and 4 incorporates two
generally radially extending, diametrally opposed
blades 16 which, as shown in Figure 2~ are of
substantially uniform circumferential width from
their roots to their tips. As best seen in Figures 3
and 4/ the leading edge 20 of each blade is thin for
chopping or comminuting chunks or lumps of solid
material in the slurry passing to the pump inlet.
While the root portions of the blades project
substantially radially from the propeller hubr the
outer end portions of the blades are curved slightly
rearward in the plane of rotation so that hard chunks
or lumps of solid material will be impelled outward so
as not to clog the pump inlet.
The transverse section of Figure 4
illustrates the preferred cross-sectional shape for
each propeller blade 16 throughout at least the major
portion of its length. Its trailing side 21 is
concave generally about an axis substantially parallel
to the axis of rotation. For any transverse cross
section an upright element of the trailing side 21 is
substantially linear~ preferably substantially parallel
to the axis of rotation~ Also for any transverse
cross section, preferably a laterally extending
element of the lower side 22 of the blade is
substantially linear and lies in a plane substantially
perpendicular to the propeller axis~ and for any
transverse cross section preferably a laterally
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extending element of the upperS slurry-propelling side
23 of the blade also is subst:antially linear or only
slightly concavely curved ancl is inclined upward from
the leading edge 20 of the b].ade to the upper edg~ 24
of the trailing side 21. Accordinglyr throughout at
least the major portion of it:s radial extent the blade
is of generally triangular cross section, and, more
specifically, of generally right triangular cross
section.
In side elevation, as shown in Figure 1,
each blade 16 also is substan~ially triangular, the
lower edge of the blade, defined by its cut.ting edge
20, appearing substantially linear and inclined upward
from the root of the blade to its tip, and the upper
edge 24 of the blade, defined by the junction of the
trailing side 21 and the upper surface 23, appearing
substantially linear and lying in a plane
substantially perpendicular to the axis of rotation.
Accordingly, each blade .is tapered in axial extent
substantially uniformly from its root to its tip.
As seen in Figure 3, at the tip of a blade
16 the angle of the upper surface 23 to a radial plane
is sharply acute. Progressing inward, the angle
increases uniformly to the roo~ of the blade and,
since the blade is of substantially uniform
circumferential width throughout its length, the
propelling force generated by a rotating propeller
blade is substantially uniform from the tip of the
blade to its root because of the greater tip speed of
the bladeO
While each .Eaature of the booster propeller
is considered important, experiments have shown that
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of almost primary importance is that the blade be
tapered in thickness from its trailing side 21 to its
leading edge 20 and that the upright elements of the
blade trailing side be substantially linear and r
preferably, substantially parallel to the axis of
rotation. Propellers substantially identical to the
propeller shown in the drawings but having blades with
convexly rounded trailing sides were much less
effective in boosting the head of a centrifugal pump.
The head-increasing tendency of the
propeller also is aided by locating it at the entrance
to or substantially within an outwardly flared funnel
28 which can conveniently be formed as a recess in the
pump end plate 13 leading to the arcuate inlet
apertures 14O The sides of the funrel flare outward
at an angle of about 45 degrees relative to the axis
of rotation, and the axial depth of the funnel should
be at least equal to the maximum axial extent of a
blade 16 of the booster propeller 15. Such depth is
about 10~ to 15% of the diameter of the end plate. The
maximum radius of the funnel should be at least about
one and one-half times the radial extent of a blade
16. Slurry at the radially outer margin of the end
plate is accelerated smoothly through ~he funnel
toward the current generated by the booster propeller.
Preferably the tips of the propeller blades extend to
or slightly beyond the radially outer edges 27 of the
arcuate inlet apertures which are faired by bPing
rounded to assure a smooth flow into the pump.
Similarly the radially inner ~dges 27' of the inlet
apertures ~re rounded for smooth flow of slurry into
the pump~
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While it is preferred that the propeller be
located at the entrance to or substantially within the
end plate funnel 28~ it also is preferred that the
propeller be spaced downwarcl from the inlet apertures
a distance sufficient that i.t will not interfere with
the slici.ng effectiveness of the impeller blades 10
and entry of slurry and small particles into the pump
casing past the propeller. In the embodiment shown in
the drawings, a cylindrical spacer 25 spaces the
propeller downward from the flat inner portion of the
end plate a distance only slightly less than the
radial width of an inlet aperture. The lower portion
of such spacer has a bevel 26 guiding the slurry
toward the rounded radially inner edge$ 27' of the
inlet apertures 14~
For assuring a compact design, the apertured
end plate 13 is xeceived within the pump bowl and has
a bottom annular flange 29 enabling the end plate to
be bolted to the upright sides of the pump casing 5.
As shown in Figure 6~ the primary advantage of
recessing the end plate into the pump bowl is that the
planar upper surface 30 of the end plate can be
located flush with the lower side 31 of the pump
outlet conduit 18 which i.s integral with the pump
casing 5. In prior pumps, such as the pump of U.S.
patent NoO 3~973,866~ an end plate extends across the
lower edge of a pump casing having an integral outlet
conduit, so that a substantial turbulence-promoting
step occurs in the are.a of the entrance to such
conduit.
To minimize backflow of high-pressure slurry
in the pump cas.ing 5 out the inlet apertures 14, such
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apertures are located as close to the center of the
impeller as possibleO The radially outer edges of the
inlet apertures are posi.tioned approximately midway
between the axis of rotation and the radially outer
tips of the primary pumping impeller blades 10.
Preferably at least the major portion of the inlet
aperture area is located within a circle having a
radius one-half the radius of the circle defined by
the rotating impeller blades.
The specific design of the impeller also
assures a high head and effective slicing action of
chunks or lumps of solid material in the slurry being
pumped. As best seen in Figures 5, 6 and 7, three
primary pumping blades 10 are provided projecting
downwaxd from the shroud plate 8, each of
substantially constant circumferential width
throughout its length. Each blade is at least several
times longer than its axial height and projects first
generally tangentially from the impeller hub 9 and
then is curved spirally rearward in the plane of
rotation~ As best seen in Figure 7, the lower leading
edge 33 of eAch blade is sharpened and is in close
slicing relationship to the upper side 30 of the pump
casing end plate 13. For this purpose the leading
axcuate sides 34 of the end plate inlet apertures are
beveled to a rearward facing sharpened edge 34' ~or
close slicing contact with the leadi.ng sharpened edges
33 of the bladesO
Whereas prior centrifugal slurry pumps
having used blades that project generally radially in
the area of the inlet apertures for abrupt choppin~ of
chunks or lumps of solid material iII the slurry, the
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blades of the present invention are angled rearward in
the area of the inlet aperture,s at a substantial angle
relative to a radius, preferably at least 45O As
best seen in Figure 2, the apparent movement of a
blade as it approaches a sharpened lead.ing edge 34' of
an inlet aperture 14 is both forward and radially
outward for effecting an angular slicing action, as
opposed to an abrupt chopping action 9 of chunks or
lumps of solid material in the slurry~
So that the primary impeller vanes 10 do not
themselves interf~re with entrance of slurry through
the inlet apextures, it is preferred that the
circumferential width of the blades be as small as
possible at their lower sides 3S, preferably no
greater than one-half the radial width of the inlet
apertures~ As best seen in Figure 7, however~ the
upper portions of the leading sides 32 and the
txailing sides 36 of blades should be faired gently
into the shroud plate by fillets extending from about
the axial center of each blade for smooth change of
flow direction of the slurry from a generally axial
direction to accelerated movement in the plane oE
rotation. As a result of the ~airing, the blades are
tapered in circumferential width from their roots to
their tips suGh that the circumferential width of each
blade at its tip is no greater than about one-half the
circumferential width of the blade at its root~ In
combination with the fairing of the leading side 32 of
the blade into the shroud plate, the forward curved
lower tip portion of the hlade leading to the
sharpened cutting edge 33 forms a substantial forward
openi.ng cup that is swep~ spirally reaxward in the
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plane of rotation for ef.Eect.ive but smooth
acceleration of the sl.urry circumferentially forward
and outward toward the pump outletO As shown in
Figure 7, the fairing of the trailing side 36 of the
blade into the shroud plate 8 is more gradual than the
fairing of the leading side 32 into such plate, that
is, the radius of curvature of the fillet formed at
the upper portion of the trailing side is greater than
the radius of curvature of the fillet formed at the
upper portion of the leading side.
The axially short ribs or vanes 11
projecting upward from the shroud plate are provided
primarily to protect the seal 12 rather than to assist
in pumping the slurry~ Such vanes are substantially
shorter than the primary pumping vanes 10, and more
upper vanes 11 are provided at closer spacing. Rather
than being volute or curved rearward in the plane of
rotation, such upper vanes 11 are substantially
straisht though angled rearward as to be generally
tangential to the periphery of the drive shaft 1~ As
with the lower primary pumping blades 10, such upper
vanes 11 are faired into the shroud plate by fillets
extending from at least about their axial centers as
shown in Figure 7O
The overall design of the upper vanes 11
results in development of higher pressure at the
periphery and above the shroud plate 8 than below it
so that there i.s some suction above the plate away
from the seal 12r Accordingly, lubricant from the
reservoir in housing 2 tends to be drawn through the
bearings 3, the seal 4 and the seal 12~ assuring
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longer life than if a positive pressure we.re exerted
above the shroud plate towa:rd the seals which could
force slurry through the seals and bearings into the
lubricant housing. In addition, seal failure is
quickly and accurately detected by a rapid decrease in
the level of lubricant in the reservoir formed by the
housing.
A final fa~tor af-fecting the head of the
pump is the design of the pump casing 5. As shown in
Figure 5, rather than being spiraled or volute
throughout its circumference, that is, rather than
having a progressively increasing radial extent
between the casing and the radially outer ends of the
pump blades in the direction of rotation, such casiny
is semicylindrical and semivolute. Beginning at the
outlet conduit 18 and moving opposite the direction of
rotation, for about one-half the circumference of the
impeller, the casing spirals inward toward the shroud
plate, and for the final one-half of its circumference
the casing closely encircles the shroud plate
providing a semicylindrical zone. Since slurry cannot
escape outward in the semicylindrical zone, pressure
of the slurry increases substantially in this zone
before the slurry can escape circumferentially toward
the outlet conduit and, as a result, the head of the
pump is substantially increased~
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