Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~3~
HIGH HEAD CENTRIFUGAL SLICING SLURRY PUMP
This application is a division of Canadian
application Serial No~ 391S172, fil~d November 30
1981, for High Head Centrifugal Slicing Slurry Pump~
The present invention 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 slurryO
The pump of the present invention is of the
same general type as the "Centrifugal Chopping Slurry
Pump" disclosed in Vaughan U.SO patent No~ 3,~73~866,
issued August 10, 1976, which 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 pumps of hoth of those patents are designed
for pumping slurries containing chunks or lumps of
solid material~
In general~ each of the pxior pumps has an
upright drive shaft, the lower end portion of which
projects downward into a substantially cylindrical
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 vanes~ The bottom of the casing is closed
by an end plate having arcuate inlet apertures ~or
`'" J `~t ~
~3~1~3
intake of slurry in an axial clirection. The sharpened
lower edges of the impeller blades cooperate with the
leading edges of the inlet apertures for chopping
chunks or lumps of solid material in the slurry being
pumped4 The slurry is accelerated circumferentially
and outward to a generally tangential outlet conduitc
The pump disclosed in UOS~ patent NoO
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 ~nd plate~
Such propeller has generally radial blades with
somewhat sharpened leading edges for chopping chunks
or lumps in the slurry. In addition, the screw
propeller is stated to generate a positive current
flow of slurry through the end plate inlet apertures.
Another aspect of the pump of U.S. patent
No. 3 t 973,866 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 pumpi.ng impeller blades~ Such upper vanes are
in the form of volute r.ibs 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 paragxaph beginning at
column 2, line ~1.
The prior pumps are of relatively low head
and efficiency as compared to the pump o the present
invention~ In such pumps flow through the end plate
inlet apertures lnto the impeller-r~ceiving pump
casing and out of the casillg through the pump outlet
A !~
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~Ss patent
NoO 3,9731866 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 or
e~fecting smooth gradual acce~eration of slurry toward
the inlet apertures~ locating the inlet apertures
closer to the axis of rotatlon 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; xounding the entrances to fair the inlet
apertures for smooth flow into the pump casing;
enclosing the impeller in a semicylindrical,
semivolute 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 shaxpened lower edyes of the blades in
cooperation with sharpened forward edges of the inlet
ap~rtures; decreasing the thickness of the impeller
blades r~lative to the radial width of the inlet
apertures so as not to interfere with intake of slurry
through the inlet apertures, merging the impeller
blades into the shroud plate with fillets for smooth,
substantially nonturbulent acceleration of the slurry
circumferentially and outward ~oward the pump outlet;
cupping the lead.ing faces of the impeller blac~es to
--3--
ensure smooth change of direction of the slurry and
effective slicin~ of chunks or lumps of solid rnaterial
in the slurry; recessing the apertured end plate into
the pump casing to dispose its inner surface flush
with khe ad~oining surface of the pump outlet for
smoother flow of slurry into the pump outlet; and
arranging the upper "slinger'l rihs or vanes or
producing a slighk suction in the area of the drive
shaft seal for increasing the life of the seal and to
enable quick and accuxate detection oE seal failure~
The principal object of the present invention
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 paxt by
providing in a centrifugal pump, the improvement
comprising the combination of a rotatable drive shaft
defining an axisl an impeller fixed to said drive
shaft and having a generally radial shroud plate and
first and second sets of vanes projecting,
respectively, generally axially in opposite directions
from said shroud plate~ a pump casing including a bowl
encircli~g said impeller, said casing having an inlet
end adjacent to said first set of impeller vanes and a
second end adjacent to said second set of impeller
vanes, said s~cond end of said pump casing including
seal means encircling said drive shaft for sealing
said second end o the pump casing~ and a lubricant
reservoir outside khe pump casing and in communication
with the seal means, said first and second sets of
3~
impeller vanes being constructed and arranged
relatively so that during rotation of said impeller
suction toward the bowl is generated at the location
of said seal means tending to draw lubricant from said
reservoir to said seal means~
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
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
Figu.re 3 but on a larger scale~
Figure 5 is a section taken on line 5--5 of
~igure 1 with parts broken away;
~5--
~ ;!`
~3~3
Figure 6 is a ~ragmentary section taken on
line 6--6 of 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 in Figure 1, the centrifugal
pump of the present invention includes an upright
drive shaft 1 received within an up.right housing 2
forming a reservoir for 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 opening cavity or
bowl 6 receiving the pump impeller 7. 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 projecting 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 encircling the drive shaft 1~ and
the bottom o~ the pump bowl is closed by an end plate
13 bolted to the bottom of the pump casing and having
inlet apertures 14 which, as best seen in Figure 2~
are arcuate and con~entric with the axis of rotation
of the drive shaft and the impellerO
A disintegrator or booster propelle.r 15
having generally rad.ially projecting, diametrally
--6--
13
opposed blades 16 and a streamlined~ convexly curved
bottom cap 17 i5 fixed to the bottom end of dr:ive
shaft 1~ Rotation of the drive shaft, such as by an
electxic ~otor, effects rotation of the booster
propeller fox 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 i5 connected to
a discharge conduit 19 for conveying the pumped slurry
to a desired location.
The slurry pumped can include mixtures of
~ater and, for exampl.e~ 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 solidl sometimes stringy material which, to be
pumped effectively, must be chopped or otherwise
comminuted into relatively small piecesO Commonly the
pump will be located near the bottom of a sump so that
the slurry must be pumped upward a substantial
distance. As a result~ the pressure of the slurry at
the pump outlet must be highl that is, the pump must
operate at a high head~
One factor that has been found to be
important in increasing the head of a centrifugal
slurry pump i5 the specific design of the
disintegratox or booster propeller 15l The preferred
design showrl in Figures 2~ 3 and 4 incorporates two
_, _
~993~3~3
generally radially extending, diametrally opposed
blades 16 whichl as shown in Figure 2~ are of
substantially uniform circumferential wldth from
their roots to their tips. As best seen in Figures 3
and 4I the leading edge 20 of each blade is thin for
chopping or comminuting chunks or lumps o solid
material in the slurry passing to the pump inlet~
While the root portions of the blades project
substantially radially from the propeller hub~ 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 inletO
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
sub~tantially linear~ preferably substantially parallel
to the axis of rotation. Also for any transversP
cross section, preferably a laterally extending
element of the lower side 22 of the blade is
substantially linear and lies in a plane substantially
pexpendicular to the propeller axis; and for any
transverse cross section preferably a laterally
extending element of the upper, slurry~propelling side
23 of the blade also is swbstantially linear or only
slightly concavely curved and is inc~ined upward from
the leading edge 20 of the blade to the upper edge 24
o~ the trailiny side 21. Accordingly, throu~hout at
~13~83
least the major portion of its radial extent the blade
is of generally triangular cross section t and, more
specificallyr of generally right triangular cross
sectionO
In side elevation, as shown in Figure 1 f
each klade 16 also is substantially triangulaL, the
lower edge of the blade, defined by its cutting 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
-l6 the angle of the upper surface 23 to a radial plane
is sharply acute. Progressing inward, the angle
increases uniformly to the root of the blade and,
since the blade is of substantially uniform
circumferential width throughout its length, the
propelliny force genexated 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 hlade~
While each feature of the booster propeller
is considered important~ experiments have shown that
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,
-9
~93~33
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-increas.ing 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 b~ formed as a recess in the
pump end plate 13 leading to the arcuate inlet
apertures 14~ The sides of the funnel flare outward
at an angle of about 45 degrees relative to the axis
of rotationl 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 di.ameter 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 the 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 heing
rounded to assure a smooth flow into the pump.
Similarly the ra~ially inner edges 27l of the inlet
apertures are xounded for smooth flow of slurry into
the pump.
While it is preferred that the propeller be
located at the entrance to or substantially within the
end plate funnel 28l it also is preferred that the
propeller be spaced downward from the inlet apertures
- 1 0 -
~3~3
a distance sufficient that .i~ will not interfere with
the slicing effectiveness of the impeller blades 10
and entry of slurry and sma:Ll 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 edges 27' of the
inlet apertures 14~
For assuring a compact design, the apertured
end plate 13 is received within the pump bowl and has
a bottom annular flanye 29 enahling 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 is integral with the pump
casing 5. In prior pumps, such as the pump of U.S~
patent No~ 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 area of the entrance to such
conduit 5
To minimize backflGw of high-pressure slurry
in the pump casing 5 out the inlet apertures 14~ such
apertures are located as close to the center of the
impeller as possible. The .radially outer edges of the
inlet apertures are positioned approximately midway
- 1 1 -
between the axis of rotation and the radially outer
tips of the primary pumping impeller blades 10o
Preferably at least khe 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
assurPs a high head and effective slicing action of
chunks or lumps of solid matexial in the slurry being
10 pumped, As best seen in Figures 5 t 6 and 7~ three
primary pumping blades 10 are provided projecting
downward 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
r~arward in the plane of rotation. As best seen in
Figure 7, the low~r 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 purpos~ the leading arcuate sides 34 of the end
plate inlet ap~r~ures are beveled to a xearward facing
sharpened edge 34l for close slicing contact with the
leading sharpened edges 33 of the blades~
Whereas prior centrifugal slurry pumps
having used blades that project generally radially in
the area of the inlet apertures for abrupt chopping of
chunks or lumps of solid material in the slurry, the
blades of the present invention are angled rearward in
the area of the inlet apertures at a substantial angle
relative to a radius, preferably at least 45. As
best seen in FicJure 2, the apparent movement of a
-12~
39~
blade as it approaches a sharpened leading edge 34l of
an inlet aperture 14 i~ both forward and radially
outward for effecting an angular slicing action, as
opposed to an abrupt chopping action, of chunks or
lumps of solid material in the slurry~
So that the primary impeller vanes 10 do not
themselves interfere with entrance of slurry through
the inlet apertures~ it is preferred that the
circumferential width of the blades be as small as
possible at their lower sides 35, preferably no
greater than one-half the radial width oE the inlet
apertures. As best seen in Figure 7, however, the
upper portions of the leading sides 32 and the
trailing sides 36 of hlades should ~e 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 of
rotation~ As a result of the fairing, the blades are
tap~red in circumferential width from their roots to
their tips such that the circum~erential width of each
blade at its tip is no greater than about one-half the
¢ircumferential width of the bl~de 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 blade leading to the
sharpened cutting edge 33 forms a substantial forward
opening cup that is swept spirally rearward in the
plane of rotation for effective but smooth
acceleratlon of th~ slurry circumferentially forward
and outward toward the pump outlet. As shown in
Figure 7~ the Eairing of the trailing side 36 of the
13~
~391 Z~
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 curvatuxe o:E the ~illet formed at
the upper portion of the trailing side is greater than
the radius of curvature of the fillet formed at the
upper po.rtion 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 slurryl Such vanes axe substantially
shorter than the primary pumping vanes 10 t and more
upper vanes 11 are prcvided at closer spacingS Rather
than being volute or curved rearward in the plane of
rotation, such upper vanes 1'1 are substantially
stxaight 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 7.
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 is some suction above the plate away
from the seal 12~ Accordingly, lubri~ant from the
reservoir in housing 2 tends to be drawn through the
bearings 3, the seal 4 and the seal 12, assuring
longer life than if a positive pressure were exerted
abuve the shroud plate toward the seals which could
force slurry through the seals and bearin~s into the
lubri.cant housing. In addition~ seal fa:ilure is
-14-
~3~E~3
quickly and accurately detected by a .rapid decrease in
the level of lubricant in the reservoir formed by the
housing.
A final factor affecting 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 casing
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 fox the final one-half of its circumference
the casing closely encircles the shroud plate
providing a semicylindrical zoneJ 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 th~
pump is substantially increasedu
-15-
