Centrifugal pump with solids cutting action

A centrifugal pump has an impeller rotatable by means of a drive shaft. The impeller has a plurality of radially extending vanes connected to a hub and a partial back shroud with sharpened leading edges. The pump has a pump casing with a back plate adjacent to the back side of the impeller. Spiral grooves on the back plate interact with the sharpened edges on the back shroud to aid in protecting the area between the back plate and the impeller by cutting of solids and expulsion of solids through an output port. Cutting bars on the front plate of the casing project into the pump intake and interact with front edges of the vanes to cut incoming solids in a liquid mixture. A preferred form of impeller has vanes with sharpened leading edges that extend in a generally radial plane. These vanes sweep backwardly from their leading edges and each vane is given a double twist between the leading edge and its trailing edge. This form of impeller has both an effective slicing action and an efficient transmission of kinetic energy to the fluid.

BACKGROUND OF THE INVENTION
 The present invention relates to centrifugal pumps, and in particular,
 pumps of this type that have a chopping or cutting capability.
 A variety of centrifugal pumps are known currently which are capable of
 pumping liquids and slurries containing solid matter such as small pieces
 of garbage or other disposed items. These pumps have the capability of
 chopping or cutting solid matter in the liquid mixture permitting the
 output from the pump to be disposed of more readily.
 U.S. Pat. No. 3,155,046 issued Nov. 3, 1964 to James E. Vaughan describes a
 centrifugal pump for pumping a mixture of liquid and stringy solid
 material that includes a housing with a peripheral wall having a discharge
 aperture therein, a closed end, and an open end. The pump has an impeller
 secured on a shaft and the impeller has radially disposed impeller blades.
 Edges of these vanes adjacent to the pump inlet co-operate with sharpened
 edges of pump inlet apertures to cut solid material entering the pump.
 One pump known in the prior art is the ABS "Piranha" Grinder pump. This
 pump incorporates sharpened spiral cutting grooves on the inside of an
 intake plate of the pump. Front edges on the impeller vanes of the pump
 rotate against the grooves to produce a cutting action. The edges of the
 vanes are flat in profile. This pump design is susceptible to binding
 problems from material being wedged between the impeller edges and the
 intake plate.
 Another known pump is the Vaughan chopper pump disclosed in U.S. Pat. No.
 5,256,032 issued Oct. 26, 1993. Features to chop and expel material from
 behind the impeller of the pump are incorporated into the design. The pump
 incorporates elongated curved vanes of the impeller operating in close
 cutting relationship with axially protruding ribs on a back plate of the
 casing. The vanes of the pump produce a cutting action as they pass over
 the ribs on the back plate.
 Yet another known centrifugal pump is the screw centrifugal pump which
 utilizes spiral grooves in the rear face of the impeller of the pump and
 on the back plate of the casing of the pump. The rotating groove in the
 rear of the impeller operates against the stationary grooves in the casing
 backplate providing the function of discharging solids from the space
 between the backplate and impeller of the pump.
 A known Allis-Chalmers type "SSOR" pump designed especially for pumping
 paper stock in a paper mill employs an impeller that rotates in a pump
 casing having a frontal inlet and a side outlet. This known impeller has a
 partial back shroud and two vanes project forwardly from this back shroud.
 These vanes, which are twisted along their length, sweep backwardly from
 around a leading edge. This pump does not have any capability of chopping
 or cutting solids that enter the pump.
 An object of the present invention is to provide a novel and durable
 centrifugal pump effective for pumping a mixture including solids
 suspended in a liquid.
 A further object of the invention is to provide an efficient and reliable
 centrifugal pump having an improved impeller with radially extending
 vanes.
 Preferably the present pump is provided with a radial partial back shroud
 with sharpened leading shroud edges that cooperate with grooves formed on
 a back plate of the pump casing. The sharpened shroud edges and the
 grooves interact to cut solids that have entered the pump through the
 intake port.
 SUMMARY OF THE INVENTION
 According to one aspect of the invention, a centrifugal chopper pump
 comprises a pump casing having a frontal intake port and a pump outlet in
 a side thereof and a rotatable drive shaft extending into the casing from
 a rear side of the casing. The drive shaft rotates about an axis of
 rotation in a preselected direction of rotation. An impeller is mounted on
 the drive shaft for rotation therewith. This impeller has a set of
 radially extending vanes and a generally radial back shroud joined to an
 elongate side edge of each vane. The vanes each have a sharpened leading
 edge that extends generally radially in relation to the axis of rotation.
 Each vane projects forwardly from the back shroud and sweeps backwardly
 from the leading edge relative to the direction of rotation to a trailing
 edge. Narrow elongate cross-sections of each vane taken in a series of
 consecutive axial planes as defined by the axis of rotation are rotated
 relative to one another from an initial cross-section near the leading
 edge that extends generally radially to a trailing cross-section adjacent
 the trailing edge which extends at a substantial angle to the initial
 cross-section. At least one cutter member is rigidly mounted on the pump
 casing and is located in the intake port. This cutting member has an inner
 edge that extends generally radially in relation to the axis of rotation.
 During operation of the pump, the leading edges of the vanes rotate
 closely past the at least one cutter member to cut incoming solid material
 caught between the leading edges of the vanes and the cutter member.
 Preferably the impeller includes a central hub through which the drive
 shaft extends and both an inner side edge of each vane and the back shroud
 are rigidly connected to this hub.
 According to another aspect of the invention, an impeller is provided for a
 centrifugal chopper pump having a frontal intake port formed in a casing
 of the pump and a drive shaft rotated about an axis of rotation. This
 impeller comprises a central hub connectible to the drive shaft for
 rotation in a predetermined direction and two or more similar vanes
 extending radially outwardly from the hub and connected thereto. Each vane
 has an elongate sharpened leading edge that extends generally radially in
 relation to the axis of rotation and each vane sweeps backwardly from this
 leading edge relative to the direction of rotation to a trailing edge.
 Each vane defines narrow, elongate vane cross-sections taken along various
 consecutive axial planes as defined by the axis of rotation. These
 consecutive cross-sections are rotated relative to each other from an
 initial elongate vane cross-section near the leading edge of the vane that
 extends generally radially to an elongate trailing cross-section adjacent
 the trailing edge. The latter cross-section extends at a substantial angle
 to the initial vane cross-section.
 In the preferred embodiment, the pump casing includes an intake plate that
 forms the intake port and at least a portion of the inner sidewall of this
 intake plate has spiral grooves which interact with sharpened edges of the
 vanes to provide further cutting of solids entering the pump.
 According to a further aspect of the invention, a centrifugal pump suitable
 for pumping a liquid mixture containing solids includes a rotatable drive
 shaft defining an axis of rotation, an impeller mounted on this drive
 shaft and a pump casing for forming a pump bowl that surrounds the
 impeller. The impeller has radially extending vanes and a back shroud
 located at rear edges of these vanes. The shroud has cutouts located
 between adjacent vanes and forming leading shroud edges adapted for
 cutting the solids. The casing also forms an intake port adjacent to a
 front side of the impeller and a pump outlet. A back plate of the casing
 is located adjacent the back shroud and has cutting edges that extend at a
 substantial angle to the leading shroud edges that are adapted for
 cutting. These leading shroud edges and the cutting edges on the back
 plate closely interact to cut solids that have entered into the pump bowl.
 Preferably the cutting edges on the back plate are formed by at least one
 spiral shaped groove formed on an inner surface of the back plate.
 In a preferred embodiment of the pump, a disintegrator is mounted on the
 end of the drive shaft to provide initial cutting of solids as they enter
 the pump through the intake port.
 Further features and advantages will become apparent from the following
 detailed description of a preferred embodiment, taken into conjunction
 with the accompanying drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
 FIGS. 1 and 2 of the drawings illustrate major parts of a centrifugal pump
 12 in perspective. Further parts and features of this pump, which is a
 form of chopper pump, can be seen in FIG. 7. The major components of the
 pump include a central, rotatable drive shaft 42 that defines an axis of
 rotation extending along its central longitudinal axis. An impeller 22 is
 fixedly mounted on this drive shaft and this impeller has a set of
 radially extending vanes 30 with the illustrated impeller having four such
 vanes, each of which is curved from its inner end to its outer end. The
 impeller also has a generally radial, partial back shroud 26 with
 sharpened, leading shroud edges 28. Preferably these shroud edges are also
 beveled and serrated as shown. In the preferred illustrated embodiment,
 seven or eight teeth having a generally triangular shape provide the
 serrations between each pair of adjacent vanes. The vanes project
 generally forwardly from the back shroud towards an intake port 29 of the
 pump 12.
 The pump further includes a pump casing 69 that forms a bowl encircling the
 impeller in a manner known per se and illustrated in FIG. 7. It is the
 casing 69 that forms the intake port 29 adjacent to a front side of the
 impeller 22. Major components of the casing which are illustrated in FIGS.
 1 and 2 are an intake plate 10 and a back plate 16, the latter being
 adjacent to the back shroud 26. The back plate is formed with spiral
 grooves 34 that face the back shroud. An important feature of the present
 pump is that the sharpened shroud edges 28 and the spiral grooves 34
 interact to cut solids that have entered the pump 12 through the intake
 port. Preferably the spiral grooves 34 are outward threaded in the
 direction of rotation of the impeller 22 and extend circumferentially at
 least several times around the drive shaft 42. As a result of the
 direction of rotation of the vanes on the impeller and the outward thread
 of the grooves, any solids in these grooves tend to be expelled or are
 expelled from the grooves by the shroud edges as they rotate over these
 grooves.
 The preferred form of intake plate 10 is shown in detail in FIGS. 3A and
 3B. The inner region of this plate forms an intake cone in order to funnel
 the incoming liquid into the pump. Extending radially outwardly from the
 generally circular inner edge 14 is an inner side wall 23 forming one side
 of the pump bowl. The sidewall 23 thus extends radially outwardly from the
 input port. The preferred intake plate has eight connecting ears 102 as
 shown in FIGS. 3A and 3B with each ear having a single bolt receiving
 notch 103. In the alternate construction shown in FIGS. 1 and 2, the
 intake plate has a generally circular perimeter with no connecting ears.
 Eight notches 20a are formed in the perimeter of this version. Preferably,
 spiral shaped grooves 36 are formed on the inner sidewall 23 and extend
 circumferentially about the intake port 29. The sharpened front edges of
 the vanes 30 pass closely over these spiral grooves in order to provide
 additional cutting of solids in the liquid mixture during operation of the
 pump. In addition, radially inwardly projecting anvil ribs or bars 38 are
 integrally formed on the intake plate 10 and extend substantially into the
 intake port. These ribs are also swept closely by the front edges of the
 vanes 30 during pump operation in order to cut the solids in the liquid
 mixture that enters through the intake port. The beveled and sharpened
 front edge of the anvil ribs is indicated at 115.
 In one embodiment of the pump 12, the intake plate 10 as shown in FIGS. 3A
 and 3B has an outer diameter of 11 inches and an internal diameter at
 inner edge 14 of 5.25 inches. The depth of this intake plate is 3.75
 inches. The radial cross-section of the spiral grooves 36 is illustrated
 in detail in FIG. 4. This cross-section is taken along an axial plane
 extending through the center axis of the drive shaft. The grooves 36 have
 opposing groove sides 60 and 62 and these are joined at the bottom of the
 groove by a sloping bottom 61. Thus, the side 62 is deeper than the
 radially outermost side 60. In one preferred embodiment, the side 60 has a
 depth of 0.13 inch while the side 62 has a depth of 0.23 inch.
 Turning now to the construction of the preferred back plate 16, the
 cross-section of this plate is shown in detail in FIG. 7 with an alternate
 possible version being illustrated in FIGS. 1 and 2. The preferred back
 plate includes a cylindrical outer wall section 18 and a cylindrical inner
 wall section 19. These two cylindrical wall sections are connected by a
 radially extending wall section 350. In the back plate of FIGS. 1 and 2,
 there is a radially outwardly extending connecting flange 352 in which are
 formed a number of bolt receiving notches 20b. In the back plate of FIG.
 7, there is no substantial connecting flange 352 but only a short annular
 outward projection which is received in a suitable annular recess formed
 about the bowl casing. The aforementioned spiral grooves 34 are formed on
 the inner surface of the wall section 350 and these grooves can have the
 same cross-section as the above described grooves 36. The grooves 34
 provide cutting edges that extend at a substantial angle to the leading
 shroud edges 28 that are adapted for cutting. The cutting edges of the
 back plate extend in a generally circumferential direction around the back
 plate 16. It will also be noted that the inner wall section 19 forms a
 round aperture 41 for the drive shaft 42. The shaft extends through this
 aperture and through a round aperture 46 formed in the hub 44 of the
 impeller. A key 360 can be used to secure the impeller on the shaft,
 thereby preventing relative rotation.
 Referring now to FIGS. 7 and 8 which illustrate a version of the
 centrifugal chopper pump, an output port 72 is provided for the pump on a
 top side thereof. It will be noted that a horizontal version of the
 chopper pump is illustrated but it is also possible for the pump to be
 constructed as a vertical pump wherein the drive shaft extends vertically.
 The pump bowl or chamber is indicated at 68 and this bowl is formed about
 its periphery by the pump casing 69 connected to both the intake plate 10
 and the back plate 16. The bowl and its casing extend completely around
 the circumference of the impeller 22. Bolts 76 and nuts 77 are used to
 secure the intake plate 10 to the pump casing 69 by means of the
 aforementioned ears 102. There can also be attached to the front of the
 intake plate by means of the same bolts and nuts a short intake pipe 84
 having a cylindrical intake passageway 82. The intake pipe 84 can be
 provided with a branch port 86 which is sealed by a removable cover 88 and
 is provided for suction inspection. The cover 88 can be held in place by
 two bolts 90 positioned at opposite ends thereof.
 It will be understood that after the liquid mixture enters through the
 intake port 29, the liquid mixture is driven by the impeller 22 around the
 bowl 68 and out through the output port 72. A suitable discharge pipe can
 be connected to the port 72 if desired.
 Attached to the rear side of the bowl casing is a relatively large oil
 reservoir and bearing support casing 310 on which is formed a connecting
 flange or connecting ears 75 at one end of the casing. Connecting bolts 74
 and cooperating nuts (one of which is shown in FIG. 7) are used to secure
 the casing 310 to the bowl casing 69. By connecting the casing in this
 manner, the preferred back plate 16 is held in place by being clamped in a
 recess formed about the bowl casing. The liquid mixture which enters the
 pump in the flow direction indicated by the arrow F will not leak past the
 back plate because of an O-ring seal 92 that extends about the
 circumference of the back plate. The main function of the casing 310 is to
 support a pair of spaced apart bearings 202 and 204 that rotatably support
 the shaft in the casing. The outer bearings 202 are mounted in a bearing
 housing or sleeve 213 which is detachably connected to the casing 310 by
 bolts 210, one of which is shown. At the outer end of the housing 213 is a
 bearing cap 207 which is attached to the housing 213 by suitable bolts
 208. Located on the opposite side of the large cavity 231, which can be
 filled with lubricating oil, is the roller bearing 204. The two bearings
 204 and 206 can either be lubricated with the oil in cavity 231 or by
 means of grease which can be supplied to the bearing 202 by means of
 grease nipple 228 and which can be supplied to the bearing 204 by means of
 grease nipple 230. As will be seen in FIG. 7, the shaft section 98 which
 extends between the two bearings is enlarged and this helps to hold the
 bearings in place.
 A shaft extension 200 extends outside of the casing 310 and this extension
 can be connected to a pump motor (not shown). Surrounding the base of the
 shaft extension 200 is a lip seal 201. The rear side of the bearing 202 is
 held in place by means of a bearing lock nut 362. Located on the pump side
 of the bearing 204 is a lip seal 364 which is covered by a V-ring 234 that
 is mounted on the shaft. Also mounted around the shaft and within the back
 plate structure are packing rings 205 of which there can be several.
 Located between a forward packing ring 205A and several other packing
 rings is a lantern ring 203 and located above this ring is a flush
 connection or passageway 215. When not being used for flushing, the
 passageway 215 can be closed at its outer end by a suitable plug. The
 lantern ring, in a known manner, has a number of holes for the purpose of
 providing water lubrication in the region of the packing ring by water
 entering through the connection 215. Mounted next to the rear packing
 rings are a gland follower 209 and a gland plate 211, these being
 connected to the inner cylindrical wall of the back plate by means of
 bolts 311, one of which is shown. Also shown in FIG. 7 is an optional
 impeller flush connection 95 formed in the back plate structure. This
 passageway is normally closed by means of a plug at 97 when not being used
 for flushing purposes.
 An open space or region 222 surrounds a central section of the shaft 42.
 Extending across the top of this region is a connecting bar 365 which can
 act as a handle for the pump. Extending across the bottom of the region
 222 is a connecting plate 366 which can be rounded about the bottom side
 of the shaft to form a dish or trap to catch any liquids in this region.
 These liquids can drain through a drain 224 connected to the plate 366.
 It will be understood that if the cavity 231 is filled with lubricating
 oil, then grease is not required to lubricate the bearings 204 and 202 and
 the illustrated grease nipples 228 and 230 are not required. This
 lubricating oil can be drained from the cavity through a hole in the
 bottom thereof by removing a drain plug 233. On the opposite side of the
 cavity 231 is a vent plug 370.
 The illustrated horizontal chopper pump can rest on a suitable horizontal
 surface by means of feet provided at 79 and 220. Two integral feet 79 can
 be provided at the front end of the pump on opposite sides of the bowl
 casing 69. The rear portion of the pump can be supported by the foot 220
 which is detachably connected to the bottom of the casing 310. An
 adjusting bolt 218 can be used to adjust the relative height of this foot
 while a bolt or bolts 216 is used to connect the foot to the casing.
 A disintegrator 52 can be optionally mounted on the front end of the drive
 shaft 42. This disintegrator is formed with a hub 320 having a central
 aperture 53. The preferred disintegrator has two generally radially
 projecting, diametrically opposed blades 56. The two blades are
 illustrated in FIGS. 1 and 2. These blades have edges 58 so that the
 disintegrator is able to cut solids in the incoming liquid mixture. The
 disintegrator can be attached to the front end of the shaft by means of a
 bolt 50 that extends through the aperture 53 and into a threaded hole
 formed in the front end section of the shaft. The disintegrator is located
 in the intake port 29, a short distance in front of the impeller.
 It will thus be seen that the pump 12 described above is constructed so as
 to prevent the undesirable build up of dirt and contaminants in the space
 between the back shroud of the impeller and the back plate. In the past,
 dirt and contaminants have built up behind the back shroud of the pump
 causing damage and degradation to the shaft seals and the packing. This
 problem is reduced or eliminated with the described pump of this invention
 due to the cutting of solids in this region by the interaction between the
 spiral grooves 34 and the sharpened edges formed on the partial back
 shroud. Preferably the leading shroud edges are beveled and serrated for
 at least a substantial portion of their respective lengths resulting in a
 very good cutting action as these leading edges sweep over the spiral
 grooves.
 Illustrated in FIG. 9 is an improved, more efficient form of impeller 375
 that can be used in the centrifugal chopper pump 12 of the invention. As
 with the first impeller, this impeller has a central hub 376 that is
 connectible to the above described drive shaft 42 for rotation in a
 predetermined direction indicated by the arrow X in FIG. 9. Unlike
 impeller 22, this more efficient impeller as illustrated has two vanes 378
 which preferably are identical in their construction and layout. It will
 be appreciated, however, that this impeller also can have more than two
 vanes if desired and could, for example, have four vanes like the first
 impeller. Each vane has an elongate, sharpened leading edge 380 that
 extends generally radially in relation to the axis of rotation indicated
 by the dashed line A. In the illustrated preferred embodiment, the leading
 edges 380 are straight and disposed in a radial plane that is
 perpendicular to the axis of rotation. It is also possible for the leading
 edges 380 to be curved in the radial plane, for example, convexly curved
 so as to curve backwardly relative to the direction of rotation. Each vane
 378 sweeps backwardly from the leading edge 380 relative to the direction
 of rotation to a flattened trailing edge 382. As indicated in more detail
 below, these preferred vanes are bent or twisted in two direction
 resulting in a pump having a higher hydraulic efficiency (reduced power
 consumption during operation) and improved suction conditions (lower NPSH,
 reduced cavitation).
 The preferred impeller 375 has a back shroud 384 and, as in the first
 impeller, this shroud is preferably a partial shroud that is connected
 both to the hub 376 and to the vanes 378. The two vanes project forwardly
 from the back shroud and they can be integrally formed with the back
 shroud when the impeller is cast. The shroud 384 has sharpened
 circumferential edges at 386. As shown in FIG. 11, the back shroud extends
 completely around the central hub. Preferably the circumferentially
 extending edges of the back shroud are beveled and serrated with the
 serrations being provided on opposite sides of the hub at 390.
 Returning to the configuration of the leading edge of each vane, the
 preferred straight leading edge of each vane is angled backwardly by an
 angle "b" that is about 30 degrees, from an axial plane indicated at 392
 that extends through a meeting point 394 where the leading edge 380 of the
 respective vane meets the central hub. The indicated angle "b" is
 preferably a substantial acute angle but can be more or less than 30
 degrees. Each leading edge 380 is formed by two flat surfaces 396 and 398
 and these flat surfaces meet at a constant angle equal to 90 degrees minus
 angle "a", that in the preferred illustrated impeller is about 45 degrees.
 This sharp leading edge 380 is constructed to produce an excellent
 chopping and cutting action when it is rotated in close proximity past the
 two cutter bars or cutter members 38.
 The unique design of the vanes 378 assures an effective slicing cutting
 action (by means of the sharp leading edges on the vanes) and efficient
 transmission of kinetic energy to the fluid and to the chopped material.
 As illustrated in FIGS. 9 and 10, each vane 378 is generally thin
 throughout its length and width. As a result, cross-sections of each vane
 taken along a series of axial planes as defined by the axis of rotation A
 are generally narrow and elongate. Although the preferred illustrated
 vanes have narrow cross-sections which are substantially straight, it is
 also possible for the vanes 378 of the invention to have elongate
 cross-sections which are curved from the front to the back of the
 impeller. For the purpose of defining the twist in each vane, one can
 consider the position of an initial cross-section located along the line
 400 shown in FIG. 9, this initial cross-section being taken near the
 leading edge 380 of the vane. This cross-section extends in a generally
 radial direction. Because of the twist in the vane, a trailing
 cross-section taken along the line 402 is rotated substantially relative
 to the cross-section taken at 400. The trailing cross-section 402 is
 adjacent the trailing edge 382 and it extends at a substantial angle not
 normally exceeding about 90 degrees to the initial cross-section.
 Furthermore, if one considers a number or series of intermediate
 cross-sections of the vane such as ones taken at points C2, C3, C4 and C5
 indicated in FIG. 10, it will be apparent that there is a gradual rotation
 of the elongate consecutive cross-sections of the vane from a location
 near the leading edge to the trailing edge 382. It is the shaping of the
 impeller vanes in this manner that increases the performance of a chopper
 pump made with this type of impeller.
 The impeller 375 can be manufactured using standard manufacturing
 techniques for pump impellers. The impeller can be made by casting and the
 sharpened edges can be made by standard machining processes.
 It should be noted that not only is the leading edge 380 of each vane
 sharpened but also each vane has an elongate sharpened side edge at 406
 that extends backwardly from the leading edge of the vane. It will be
 appreciated that this side edge lies closely adjacent the spiral grooves
 36 formed on the inner sidewall of the intake cover. The sharpened side
 edge cooperates with these spiral grooves to provide additional solids
 cutting action similar to that provided with the first impeller.
 Also, in the preferred illustrated vanes 378, the trailing edge 382 is
 elongate and substantially straight. It is also possible for the vane 378
 to have a trailing edge which is curved from the front of the impeller to
 the back. As it will be apparent from FIG. 9, this trailing edge extends
 in a direction generally parallel to the axis of rotation A.
 Various modifications and changes to the preferred centrifugal pump
 described herein will be apparent to those skilled in the art of making
 centrifugal pumps. Accordingly, all such modifications and changes as fall
 within the scope of the appended claims are intended to be part of this
 invention.