The invention relates to a chopper pump, that is to say, a pump suitable for conveying a fluid comprising a liquid part in which solid residues are dispersed.

The chopper pump according to the invention may be used for processing fluids such as livestock slurry, for example of bovine or suine origin, or in the transport and treatment of biomasses in systems which obtain energy from the latter.

Chopper pumps usually comprise a casing in which an impeller is rotatably mounted, the impeller being arranged to send a fluid from a suction zone to a delivery zone. Upstream of the impeller, there is a rotatable cutting element arranged to interact with a plurality of fixed knives so as to exert a cutting action on the solid residues contained in the fluid to be processed. The rotatable cutting element is coaxial with the impeller and rotates inside an infeed duct of the pump.

An example of a chopper pump of the above-mentioned type is disclosed in US 2013/0121811 , wherein the pump comprises a casing in which is housed the impeller and an annular body, fixed to the casing, in which the infeed duct is formed. The rotatable cutting element rotates inside the annular body. Two supporting blocks are fixed to an inner surface of the annular body. The supporting blocks are in turn fixed to respective fixed knives with which the rotatable cutting element interacts periodically to cut any solid residues contained in the fluid to be processed.

A drawback of the chopper pump disclosed in US 2013/0121811 is that the fixed knives and the respective supporting blocks project inside the infeed duct, which is consequently partly obstructed. More specifically, the supporting blocks protrude radially inside the infeed duct, whilst the fixed knives are entirely contained in the infeed duct. The latter therefore has a section whose area is reduced by the fixed knives and the relative supporting blocks, which occupy a not negligible percentage of the area. This reduces the efficiency of the chopper pump. Further, any solid or filamentary parts present in the fluid to be processed may be embedded in the fixed knives or in the relative supporting blocks. If this happens, the solid or filamentary parts remain stationary inside the pump, compromising its operation.

Other examples of prior art pumps are disclosed in JP 4-971924, KR 101672432, US 3417929, US 5456580.

Irrespective of the drawbacks described above with reference to the overall dimensions of the fixed knives and the relative supporting blocks, the existing pumps can be improved from the point of view of their ability to chop the solid parts present in the fluid to be processed.

An object of the invention is to improve the chopper pumps, that is to say, the pumps designed for processing a fluid which comprises a liquid in which solid parts can be dispersed, which are able to exert a cutting action on the solid parts.

Another object is to provide a chopper pump which is able to chop solid parts, even filamentary parts, with a high chopping efficiency.

A further object is to provide a chopper pump having a good efficiency.

Another object is to provide a chopper pump whose efficiency is not excessively penalized by the devices for cutting the solid parts with which the chopping pump is equipped.

A further object is to provide a chopper pump in which the risk of solid and/or filamentary parts contained in the processed liquid is minimised and can be stopped inside the pump, thus adversely affecting the operation.

According to the invention, there is provided a chopper pump for processing a fluid comprising a liquid part in which solid parts may be present, the chopper pump comprising a casing, an impeller for sending the fluid from an inlet zone towards an outlet zone, a rotatable cutting element which can rotate about an axis and is positioned upstream of the impeller and a plurality of stationary cutting elements intended to interact with the rotatable cutting element so as to apply a cutting action on the solid parts, wherein the stationary cutting elements are directly fixed to a common annular support which is fixed with respect to the casing.

Owing to the invention, it is possible to increase the efficiency of the chopper pump compared to prior art chopper pumps. In effect, by fixing the stationary cutting elements directly to a common annular support, it is possible to avoid using the fastening blocks of the prior art, which have a significant size, in a radial direction, such as to partly obstruct an inlet section of the pump.

The maintenance and repair operations are also simplified compared to prior art chopper pumps because, when the stationary cutting elements are worn, they can be quickly replaced with a single operation, removing the annular support to which all the stationary cutting elements are fixed. This avoids having to remove the individual stationary cutting elements one at a time, working on the chopper pump already installed and therefore in non-ideal operating conditions.

The stationary cutting elements may be mounted in such a way that only one of their cutting ends protrudes radially from the annular support inside an inlet section of the pump.

This makes it possible to further reduce the overall dimensions of the stationary cutting elements in the inlet section of the pump, compared with that of the prior art pumps wherein the stationary cutting elements were entirely positioned in the inlet section.

By reducing the overall size of the stationary cutting elements in the inlet section of the pump, it is possible to minimise the risk that any solid or filamentary parts which enter the pumping device remain fixed among the components of the device.

In effect, it is difficult for the solid or filamentary parts to become entangled in the stationary cutting elements, which protrude a little way inside the inlet section.

Each stationary cutting element may have, in a plane positioned perpendicularly to the axis of the rotatable cutting element, a constant transversal cross-section in an axial direction. In an embodiment, the impeller comprises a central pin and a plurality of blades, for example helical blades, which project from the central pin.

The blades may have respective head surfaces which, by rotating, define an ideal cylindrical surface.

In this way, the head surfaces of the blades may be moved close to the stationary cutting elements, with which they act in conjunction to chop any solid residues, without the stationary cutting elements having to project excessively inside the annular support.

In an embodiment, the pump comprises a component having a hole, the component being arranged in a fixed position.

The component optionally has the shape of a disc.

The component having a hole surrounds the rotatable cutting element.

The component may be interposed between the impeller and the rotatable cutting element.

Each blade of the rotatable cutting element has a recess delimited by an axial or lateral surface arranged to make contact with the component having a hole in such a way as to perform a cutting action.

The recess is furthermore delimited by a front surface extending transversely to the axis of the rotatable cutting element and suitable for coming into contact with the component having a hole so as to perform a front cut.

This allows fine chopping of solid residues of relatively large dimensions or materials which are difficult to cut, such as pieces of ropes, wooden parts or plastic pieces.

This improves the effectiveness in the chopping action of the pump.

The invention can be better understood and implemented with reference to the accompanying drawings which illustrate non-limiting example versions thereof and in which:

Figure 1 is a side view showing a chopper pump;

Figure 2 is a view of the chopper pump of Figure 1 , taken from direction D of Figure 1 ; Figure 3 is a cross-section along the plane Ill-Ill of Figure 2;

Figure 4 is a scaled-up perspective view showing an inlet section of the pump of Figure 1 ;

Figure 5 is a perspective view similar to that of Figure 4, in which some parts have been removed for clarity of representation;

Figure 6 is a perspective view from below showing the components of the pump which appear in Figure 5;

Figure 7 is a schematic view of an inlet section of the chopper pump of Figure 1 , showing how a plurality of stationary cutting elements protrude inside the inlet section;

Figures 8 and 9 are schematic views like those of Figure 7, referred to alternative versions of the pump;

Figure 10 is a perspective view from below of a component shaped like a disc of the chopper pump of Figure 1 .

Figures 1 to 3 show a pumping device 1 for processing a fluid which may comprise a liquid in which solid parts are dispersed. More specifically, the pumping device 1 makes it possible to process sewage of livestock origin, in which small pieces of wood, straw, plastic parts such as wires or portions of mesh or the like are often present. The pumping device 1 may also be used in the treatment of biomasses.

The pumping device 1 may be designed to work in submerged conditions, for example inside a tank for collecting sewage, with any orientation, for example vertical or horizontal. Alternatively, the pumping device 1 may be designed to work in non-submerged conditions, that is to say, outside a tank or tank containing the fluid to be processed, to which the pumping device 1 may be connected by means of a duct. In this case, too, the orientation of the pumping device 1 may be any, optionally horizontal.

The pumping device 1 comprises a pump 5 designed for sending the fluid from an inlet zone 2 towards an outlet zone 3. The pump 5 is further designed to exert a cutting action on the solid parts present in the fluid to be processed, reducing the dimensions to prevent clogging. For this reason, the pump 5 may be considered as a chopper pump.

The pump 5 comprises a casing 4.

The pump 5 is of the centrifugal type. More specifically, the pump 5 comprises an impeller 7, rotatable about an axis A, housed in a lead nut part 8 of the casing 4.

The pumping device 1 also comprises a drive part 6 for driving the pump 5. As shown in Figure 3, the drive part 6 may comprise an electric motor 9 having a drive shaft 10 extending along the axis A.

The impeller 7 is coupled to the drive shaft 10 so that the electric motor 9, as it turns, sets the impeller 7 in rotation. The impeller 7 may be located at one end 12 of the drive shaft 10. The impeller 7 may be coupled to the drive shaft 10 by splining.

In the example shown, the drive part 6 is connected to the pump 5 on the side of the pump 5 opposite the inlet zone 2.

The pump 5 also comprises a rotatable cutting element 11 coaxial with the impeller 7, in particular mounted at the end 12 of the drive shaft 10 on which the impeller 7 is mounted. The rotatable cutting element 11 can thus be driven in rotation about the axis A together with the impeller 7. The rotatable cutting element 11 may be coupled to the drive shaft 10 by keying.

The rotatable cutting element 11 is mounted upstream of the impeller 7, that is to say, closer to the inlet zone 2 relative to the impeller 7.

The impeller 7 is interposed between the electric motor 9 and the rotatable cutting element 11 .

The pump 5 comprises a plurality of stationary cutting elements 13, positioned in a fixed position relative to the casing 4 in such a way that the rotatable cutting element 11 , rotating about the axis A, periodically interacts with the stationary cutting elements 13 to apply a cutting action on the solid parts dispersed in the fluid to be processed.

The stationary cutting elements 13 may be fixed to a common annular support 14, for example by screws not, illustrated. The annular support 14 may in turn be removably fixed to the casing 4. In the example shown, the annular support 14 is fixed, by screws 15, to an annular flange 26 forming part of the casing 4 and in turn fixed to the lead nut part 8.

The stationary cutting elements 13 are positioned along the annular support 14, for example at a constant angular distance from each other. In the example shown, there are four stationary cutting elements 13, separated by an angular distance of 90° from each other. However, it is also possible to provide a number of stationary cutting elements 13 that is different from four, for example smaller or greater than four.

The stationary cutting elements 13 are fixed at the front of the annular support 14, that is to say, they project parallel to the axis A from a face of the annular support 14. The stationary cutting elements 13 project towards outwards of the pump 5. The face of the annular support 14 to which the stationary cutting elements 13 are fixed is opposite a further face of the annular support 14 facing towards the impeller 7.

Each stationary cutting element 13 has a body 18 from which a cutting end 17 projects. The body 18 is designed to be fixed to the annular support 14, for example by at least one fixing hole 33 in which can engage a corresponding screw not illustrated.

The cutting end 17 may be delimited by a face 19, which may be a flat face extending parallel to the axis A. The face 19 may be, for example, inclined at 45° to an adjacent face of the body 18. Each stationary cutting element 13 may have a transversal cross-section which remains constant moving parallel to the axis A.

This makes the stationary cutting elements 13 easy to produce.

The rotatable cutting element 11 comprises a central portion 20, for example cylindrical in shape, which may be equipped with an axial hole in which the end 12 of the drive shaft 10 passes. A plurality of blades 21 project from the central portion 20, which in the example shown there are three in number. However, it is also possible to use a number of blades other than three, for example greater or less than three. The number of blades 21 may be less than the number of stationary cutting elements 13.

In the example shown, the blades 21 have a helical shape, that is to say, they are wound on the central portion 20 about the axis A as portions of turns of a spiral. The winding direction of the blades 21 on the central portion 20 is such that the blades 21 convey the fluid to be processed towards the impeller 7. For this reason, the rotatable cutting element 13 may also be defined as a conveyor.

The blades 21 are delimited by respective head surfaces 22 which, as shown in Figure 2, can optionally lie on a common cylinder.

In other words, during rotation of the rotatable cutting element 11 about the axis A, the head surfaces 22 of the blades 21 form an ideal cylindrical surface, at least in a portion further from the impeller 7.

Each stationary cutting element 13 has a cutting edge 34, which may delimit the corresponding face 19 in a position proximal to the axis A. The cutting edge 34 is designed to interact with the head surface 22 of the blades 21 to cut any solid or filamentary parts present in the fluid processed by the pumping device 1 .

The cutting edge 34 may be a straight cutting edge extending parallel to the axis A.

The annular support 14 has a central opening or hole which defines an inlet section 16 of the pump 5. The inlet section 16 is a transit section through which the fluid to be processed can enter the pump 5.

Only the cutting end 17 of each stationary cutting element 13 protrudes in the inlet section 16. More precisely, if a view of the inlet section 16 is considered on a plane perpendicular to the axis A, as shown in Figure 7, only the cutting end 17 of each stationary cutting element 13 is inside the inlet section 16, whilst the remaining body 18, that is to say, a larger portion of the stationary cutting element 13, is outside the inlet section 16. In other words, in an assembled condition of the pumping device 1 , the cutting end 17 is at a distance from the axis A less than the radius of the inlet section 16, while the body 18, which constitutes a larger portion of the stationary cutting element 13, is outside the inlet section 16.

In this way it is possible to minimise the dimensions of the stationary cutting elements 13 inside the inlet section 16.

In more detail, the cutting end 17 has, in a plan view (that is, on a plane perpendicular to the axis A), a pointed shape, in particular triangular, thanks to which the cutting end 17 protrudes in the inlet section 16 by a limited quantity.

In other words, the cutting end 17 is tapered in a direction directed from the periphery towards the axis A, that is to say, moving towards the axis A. A plan view is now considered, that is to say, in a plane perpendicular to the axis A, of the stationary cutting elements 13 and of the inlet section 16, as shown in Figure 7. It is possible to calculate the total occlusion area Atot of the inlet section 16 by the stationary cutting elements 13, meaning the sum of the area Ai which each stationary cutting element 13 projects into the inlet section 16. Each area A has is in black in Figure 7.

In the example shown in Figure 7, the total occlusion area Atot of the inlet section 16 by the stationary cutting elements 13, in a plane perpendicular to the axis A, is equal to 0.9% of the area of the inlet section 16. The area of the inlet section 16 is meant as an area of a circle having a radius equal to the radius of the central opening or hole of the annular support 14, which defines the inlet section 16.

More in general, the area of the inlet section 16 is understood as the area of the opening through which the fluid to be processed can enter the pump 5, taken in a plane perpendicular to the axis A.

In an alternative version, shown in Figure 8, in which there are four stationary cutting elements 13 and wherein the inlet section 16 has dimensions greater than as shown in Figure 7, the total occlusion area Atot is equal to 0.7% of the area of the inlet section 16.

In another alternative version, shown in Figure 9, in which there are five stationary cutting elements 13 and wherein the diameter of the inlet section 16 is greater than that shown in Figure 8, the total occlusion area Atot is equal to 0.4% of the area of the inlet section 16.

In general, the total occlusion area of the inlet section 16 by the stationary cutting elements 13, calculated in a plane perpendicular to the axis A, is less than 5%, for example less than 2%, in particular less than 1%, of the area of the inlet section 16. The stationary cutting elements 13 consequently have a small size in the inlet section 16. Thus, the stationary cutting elements 13 do not excessively disturb the flow of the fluid towards the impeller 7, which makes it possible to maintain a good efficiency of the pump 5.

The above-mentioned ratios between the total occlusion area Atot and the area of the inlet section 16 are optional. The small size of the stationary cutting elements 13 in the inlet section 6 is made possible because the stationary cutting elements 13 are mounted on a single annular support 14, without using intermediate blocks which would be quite bulky.

This type of assembly of the stationary cutting elements 13 allows easy replacement of the worn stationary cutting elements 13, which can all be removed together by removing the annular support 14 from the casing 4. The stationary cutting elements 13 are mounted on the annular support 14 with a predetermined orientation relative to the axis A, and normally do not require complicated adjustments after being installed on the pumping device 1 .

In assembly devices according to the prior art, when the stationary cutting elements were worn, the device had to be stopped and the position of each stationary cutting element had to be adjusted to make it suitable for working further. On the other hand, in the cutting device 1 , the stationary cutting elements 13 may remain installed in a fixed position until they are completely worn, after which they can be replaced all together by removing the annular support 14. It is therefore possible to avoid adjustments during the life of the stationary cutting elements 13.

This is mainly due to the operating modes of the stationary cutting elements 13 which, as described in more detail below, interact with the blades 21 to make a scissor-type cut, which allows a good cutting efficiency to be maintained for the entire life of the stationary cutting elements 13. Further, since the rotatable cutting element 11 , when rotating, defines a cylinder, it is not necessary to move the stationary cutting elements 13 very close to the axis A, as would happen if the rotatable cutting element 11 has a frustoconical geometry.

The stationary cutting elements 13 and the rotatable cutting element 11 are shaped in such a way that there is no more than one stationary cutting element 13 engaged with a blade 21. This allows the entire twisting moment supplied by the electric motor 9 to be concentrated on a single stationary cutting element 13, thereby improving the cutting efficiency.

Thanks to the helical shape of the blades 21 and to the rectilinear geometry of the cutting edges 34, at a predetermined instant, only a pointshaped zone of a cutting edge 34 interacts with the top surface 22 of a blade 21. In other words, the stationary cutting elements 13 do not simultaneously work along the entire cutting edge 34, but only along a part of the cutting edge 34 which, in the instant considered, is interacting with the head surface 22 of a blade 21. The portion of the cutting edge 34 which interacts with the top surface 22 varies during rotation of the rotatable cutting element 11 , and hence of the blade 21 , about the axis A.

This allows a scissor-type cut to be made which is very effective in chopping the solid and filamentary parts contained in the fluid which enters the pumping device 1 .

In other words, at a predetermined instant, a portion of the blade 21 whose length is shorter than the entire length of the blade 21 along the axis A interacts with a further portion of the cutting edge 34 whose length is less than the full length of the cutting edge 34 along the axis A. The portion of the blade 21 and the further portion of the cutting edge 34 along which the blade 21 and the cutting edge 34 interact with each other vary while the rotatable cutting element 11 rotates about the axis A, so as to make a scissor-type cut.

As shown in Figure 1 , the rotatable cutting element 11 and the stationary cutting elements 13 protrude axially from the casing 4 outwards of the pump 5.

The inlet section 16 opens directly outside the pump 5.

This makes it possible to limit the risks of clogging of the pump 5 even if solid filamentary or large parts enter the inlet section 16.

In effect, if the stationary cutting elements 13 and the rotatable cutting element 11 , instead of being free of lateral containment walls, were surrounded by a tubular element, any solid filamentary or large parts could fit between the tubular element and the cutting elements 11 , 13, with the consequent need to stop the pumping device 1 to remove the jammed solid parts.

As shown in Figure 4, the rotatable cutting element 11 has, close to the rotor 7, a discontinuity in the outside diameter, with consequent reduction in diameter.

In this way, in each blade 21 it is possible to identify a recess, delimited by a front surface 23, which may extend in a plane perpendicular to the axis A, and by a lateral surface 24. The lateral surface 24 may extend in a direction parallel to the axis A and may therefore be an axial surface.

The lateral surface 24 is arranged transversely, for example but not necessarily perpendicularly, to the front surface 23.

The front surface 23 and the lateral surface 24 act as cutting surfaces, as described in more detail below.

Owing to the recess on the blades 21 delimited by the front surface 23 and by the lateral surface 24, during rotation about the axis A, the blades 21 describe a cylindrical surface with a smaller radius at the recess, and a cylindrical surface with a larger radius in the portion where the recess is not present.

As shown in Figure 5, wherein the annular support 14 and the casing 4 have been removed for clarity of representation, the pump 5 comprises a component, which in the example shown is shaped like a disc 25 delimited by a first face 27 and by a second face 28. The first face 27 faces towards the annular support 14 and the stationary cutting elements 13, whilst the second face 28 faces towards the impeller 7. The disc 25 is in a fixed position in the pump 5.

The disc 25 has a central opening 29 for receiving the rotatable cutting element 11. The central opening 29 is not circular in shape. Along a border of the central opening 29, there is a plurality of protrusions 30 projecting towards the axis A. Between two consecutive protrusions 30 there is a recess 31 , as shown in more detail in Figure 10.

The protrusions 30 are positioned to engage with the front surface 23 and with the lateral surface 24 of the rotatable cutting element 11 , so as to chop any solid parts which have penetrated inside the inlet section 16.

More specifically, the front surface 23 and the lateral surface 24 do not work when, during rotation of the rotatable cutting element 11 about the axis A, the corresponding blade 21 is positioned close to a recess 31. When this occurs, the front surface 23 and the lateral surface 24 are in effect spaced from the disc 25.

When, on the other hand, the blade 21 passes through a protrusion 30, the front surface 23 engages the surface which delimits the first face 27, for example sliding on the surface, while the lateral surface 24 engages with a further lateral surface 35 of the protrusion 30, which delimits the protrusion 30, for example parallel to the axis A.

In this way, a chopping action is generated between the disc 25 and the rotatable cutting element 13, which applies both frontally, that is to say, between the front surface 23 and the first face 27, and laterally, for example axially, that is to say, between the lateral surface 24 and the further lateral surface 35 of the protrusion 30. This double chopping action allows fine chopping of the solid parts present in the fluid.

Further, the front surface 23 exerts a brushing action on the first face 27 of the disc 25. This action makes it possible to remove from the first face 27 any solid parts present in the fluid which, for whatever reason, have been stopped or retained close to the first face 27.

On the second face 28 of the disc 25 there is a plurality of channels 32 which may extend in an approximately radial direction (or alternatively in a non-radial direction) from the central opening 29 towards the outside of the disc 25. The width of the channels 32 may increase as it moves from the centre towards the periphery of the disc 25.

The channels 32 penetrate into the thickness of the disc 25 by a quantity which can be constant.

The channels 32 define respective interruptions in the contact between the impeller 7 and the second face 28 of the disc 25. These interruptions operate as cleaning ducts to allow the discharge of the solid chopped parts, preventing them from remaining trapped between the impeller 7 and the disc 25, which would make it necessary to stop the pump 5.

As shown in Figure 10, each channel 32 has an inner end 36 closest to the axis A and an outer end 37 furthest from the axis A. The inner end 36 opens into a recess 31 , i.e., it is interposed between two consecutive protrusions 30.

This arrangement easily allows the chopped solid parts to be easily moved away from the rotatable cutting element 11 and from the impeller 7.

The impeller 7 is in contact, or almost, with the second face 28 of the disc 25, in such a way that, during rotation of the impeller 7 about the axis A, there is a chopping action also between the second face 28 of the disc 25 and the impeller 7.

During operation, the rotatable cutting element 11 and the impeller 7 are rotated about the axis A. The fluid present in the environment in which the pumping device 1 is inserted enters the casing 4 through the inlet section 16.

During the rotation of the rotatable cutting element 11 about the axis A, each blade 21 is moved periodically close to each stationary cutting element 13 and interacts with it to chop any solid residues interposed between the blade 21 and the stationary cutting element 13. A first cutting step of the pumping device 1 is thus defined.

The rotatable cutting element 11 , as it rotates, conveys the fluid towards the impeller 7.

The solid parts present in the fluid are further chopped during the interaction between the front surface 23 of the rotatable cutting element 11 and the first face 27 of the disc 25 (second cutting step), as well as during the interaction between the lateral surface 24 of the rotatable cutting element 11 and the further lateral surface 35 of the disc 25, which delimits the central opening 29 of the disc 25 about the axis A (third cutting stage).

The impeller 7 also has a chopping action on the solid parts present in the fluid, engaging with the second surface 28 of the disc 25 (fourth cutting step).

To sum up, the pumping device 1 described above makes it possible to effectively cut the solid parts present in the fluid to be processed, thanks to the presence of four different cutting steps, three of which involve the rotatable cutting element 11 .

The shape and arrangement of the stationary cutting elements 13 is designed so that the stationary cutting elements 13 occupy a little part of the inlet section 16, which guarantees that the pump 5 delivers a good performance.

The pumping device 1 can be installed in a plurality of operating configurations different to each other.

For example, in a first operating version, the pumping device 1 may be installed on the bottom of a tank or container in such a way as to work under submerged conditions. Both the pump 5 and the electric motor 9 may in this case be normally below the level of the fluid to be processed. Axis A can be vertical.

In a second operating version, the pumping device 1 may be installed in a tank or container in such a way that only the pump 5 works in submerged conditions, whilst the electric motor 9 is positioned outside the fluid to be processed. In this case, the axis A may be vertical and the electric motor 9 may be connected to the pump 5 by a shaft having a sufficient length to ensure that the electric motor 9 is at a height greater than the level of the fluid to be processed. In a third operating version, the pumping device 1 may be positioned outside a tank or container containing the fluid to be processed. In this case, the inlet zone 2 of the pump 5 may be in fluid communication with the tank or container through a duct connected to the inlet zone 2, in such a way that the fluid contained in the tank or container can be conveyed into the inlet zone 2. Axis A can be horizontal.