Centrifugal pump

Abstract

The centrifugal pump for pumping liquids containing solid material comprises a diffuser member (5), forming an inlet section (2) and an outlet section (3) for the liquid, an impeller member (4) disposed inside the diffuser member (5), rotatable about a longitudinal axis (A). The impeller member (4) defines at least one outflow channel for the liquid between the inlet section (2) and the outlet section (3). The pump also comprises a wear plate (6), sealingly mounted on the diffuser member (5) and adapted to act as a seat for the impeller member (4).

Description

[0001] Description

[0002] CENTRIFUGAL PUMP

[0003] Technical field

[0004]

[0001] The present invention relates to a centrifugal pump, in particular a submersible electric pump for lifting wastewater.

[0005] Prior art

[0006]

[0002] The use of pumps, in particular submersible electric pumps, for lifting wastewater is known.

[0007] Such pumps are used, for example, for pumping from civil and industrial drains, in sewage lifting stations and purification plants.

[0008]

[0003] Such pumps convey in particular liquids that may have high concentrations of solid substances. These substances can clog the passage sections, causing the pump to stop, until functionality is restored. In some cases, clogging can cause damage to the operating members. To avoid this, such pumps usually integrate anti-clogging solutions.

[0009]

[0004] For example, patent EP 1 899 609 illustrates a pump for conveying contaminated liquids that may contain solid material. It comprises a body equipped with an impeller, mounted suspended on a motor shaft and provided with at least one room. The pump also comprises at least one seat for the impeller. The impeller and its respective seat are mounted in such a way that during the operation of the pump, they are axially movable with respect to each other. Furthermore, the impeller seat has at least one groove on its upper surface. This groove serves to guide the outflow of solid material that can be dragged by the pumped liquid.

[0010]

[0005] More precisely, the axial mobility between the impeller and the seat allows for generating, during operation, a useful space for the passage of solid material.

[0011]

[0006] The groove formed on the upper, operative surface of the seat can cooperate with this space, accommodating and guiding the outflow of the solid material. This provision allows for diverting solid material of considerable size towards the pump outlet, without clogging the impeller and without damaging it.

[0012]

[0007] The technical solutions proposed so far to ensure sufficient axial mobility between the impeller and its respective seat and, at the same time, effective pumping of the liquid, however, present considerable complexity, both from a structural and an assembly and maintenance point of view.

[0013]

[0008] For example, it is complicated to axially adjust the impeller when, to obtain said axial mobility, it is mounted floating on the pump shaft.

[0014]

[0009] A further example of a solution for axial mobility between an impeller and its respective seat is illustrated in application IT 202200026505 A1 in the name of the Applicant.

[0015]

[0010] Finally, application WO 2024 / 134699 A1 in the name of the Applicant illustrates a wear plate fixedly mounted on the diffuser member. Disclosure

[0016]

[0011] The task of the present invention is to solve the aforementioned problems by devising a centrifugal pump of simple and economical design that allows for reliable operation.

[0017]

[0012] Another object of the invention is to provide a centrifugal pump that allows for the safe avoidance of clogging when used for transporting liquids with high concentrations of solids.

[0018]

[0013] Within the scope of this task, a further object of the present invention is to provide a centrifugal pump with a simple and functional structure, equipped with certainly reliable operation and great flexibility of use.

[0019]

[0014] The cited objects are achieved, according to the present invention, by the centrifugal pump according to claim 1.

[0020]

[0015] The centrifugal pump according to the invention is intended for pumping liquids, in particular liquids containing solid material.

[0021]

[0016] The pump comprises a diffuser member, forming an inlet section and an outlet section for the liquid, and an impeller member disposed inside the diffuser member, rotatable about a longitudinal axis.

[0022]

[0017] The impeller member defines at least one outflow channel for the liquid between the inlet section and the outlet section.

[0023]

[0018] The pump also comprises a wear plate, sealingly mounted on the diffuser member and adapted to act as a seat for the impeller member.

[0024]

[0019] According to a prerogative of the invention, in an assembled condition, the wear plate is movably connected in an axial fluctuation stroke with respect to the diffuser member by means of a fixing assembly, between a first position, of proximity, at which the plate is axially close to the impeller member, the action adapted to support the plate in said first proximity position in an active operating condition being exclusively hydraulic, and a second position, of opening, at which the plate is positioned ata certain maximum axial distance with respect to the impeller member, so as to axially define a free passage clearance between the plate and the impeller member, adapted to accommodate the solid material and allow its outflow towards the outlet section, by-passing the impeller member when the pump is in said active operating condition.

[0025]

[0020] Said axial fluctuation stroke can be considered a condition of free mobility of the plate with respect to the diffuser member, in particular in a rest condition of the pump, particularly an empty pump, without pumping liquid, except for contrasting actions deriving from the friction generated between the same members, for example by virtue of sealing means interposed between them.

[0026]

[0021] In particular, the fluctuation stroke of the wear plate is understood as not being counteracted and / or supported, during the operation of the pump, in the passage between the first position and the second position, by any active urging of the fixing assembly.

[0022] Said first position, during the operation of the pump, is not supported and / or counteracted by any force other than the hydraulic action or thrust exerted by the pumped fluid.

[0027]

[0023] In particular, said fixing assembly does not comprise elastic counteracting and / or supporting means for said fluctuation stroke, in particular of the type of a spring, for example a helical spring.

[0028]

[0024] Consequently, the fluctuation stroke of the wear plate is free, that is, it is not counteracted and / or supported by the action of elastic means, such as for example one or more springs, in particular when the pump is in an assembled condition at rest.

[0029]

[0025] Advantageously, during the operation of the pump, the fluctuation stroke of the wear plate occurs effectively and reliably, due to hydraulic action.

[0030]

[0026] Advantageously, the provided fixing assembly is very compact, has a reduced number of components and a simple assembly.

[0031]

[0027] Preferably, the first position corresponds to a lifted condition and the second position to a lowered condition for the plate.

[0032]

[0028] Preferably, the minimum distance of the wear plate from the impeller member, in the first proximity position, is preferably in a range between 0.30 mm and 0.50 mm, for example equal to 0.5 mm.

[0033]

[0029] The fluctuation stroke of the plate is preferably at least 3 mm, in particular not less than 5 mm, to allow the outflow of solid material, by-passing the impeller member in the active operating condition.

[0034]

[0030] The fixing assembly can comprise at least one fixing element and a locking element, mutually tightened so as to delimit the axial fluctuation stroke, in particular the first proximity position.

[0035]

[0031] The fixing element is preferably made of a threaded element and the locking element of at least one nut.

[0036]

[0032] The pump may comprise at least one adjustment element for adjusting, in an assembly phase, the axial fluctuation stroke, in particular the first position. For this purpose, the diffuser member preferably comprises a hole for the insertion of the adjustment element abutting the plate, accessible from the outside of the diffuser member.

[0037]

[0033] To allow for easy insertion of the fixing assembly, the diffuser member may have at least one through hole accessible from the outside of the pump and the plate may have at least one hole.

[0038]

[0034] The plate may have a groove made on a respective operative surface which, in use, is facing the impeller member, to guide the solid material from the inlet section towards the outlet section.

[0039]

[0035] The groove preferably develops in a volute shape from an inner edge towards a peripheral edge of the operative surface of the plate.

[0036] A method for the assembly of the centrifugal pump is also provided, comprising the steps of:

[0040] a) assembling a motor unit of the pump, associating a respective pump shaft with a respective electric motor member;

[0041] b) mounting the impeller member on the pump shaft, by means of axial and rotational locking;

[0042] c) pre-assembling the fixing assembly together with respective sealing means in the wear plate;

[0043] d) inserting the plate into the diffuser member, positioning the plate in the second opening position, abutting against an inner wall of the diffuser member;

[0044] e) assembling the motor unit to the diffuser member;

[0045] f) adjusting the positioning of the plate in the first proximity position, preferably by means of at least one adjustment element inserted through the diffuser member;

[0046] g) tightening the fixing assembly in the first position of the plate;

[0047] h) releasing the axial fluctuation stroke of the plate towards the second opening position, preferably by retracting the at least one adjustment element.

[0048]

[0037] In this way, in an assembled rest condition of the pump, the wear plate is freely movable between the first position and the second position.

[0049]

[0038] By "freely movable" is meant a condition of free motion, except for friction, in particular generated by sealing means interposed in the fixing between the wear plate and the diffuser member.

[0050]

[0039] Furthermore, by "freely movable" is meant a condition of motion not counteracted and / or supported by active forces exerted by the fixing assembly, except for friction.

[0051]

[0040] Preferably, said axial fluctuation stroke is at least 3 mm, in particular not less than 5 mm.

[0052] Description of the drawings

[0053]

[0041] The particulars of the invention will become more evident from the detailed description of a preferred embodiment of the centrifugal pump according to the invention, illustrated by way of non-limiting example in the accompanying drawings, in which:

[0054] figures 1a and 1b respectively show an axial sectional view of the centrifugal pump according to the invention in different conditions;

[0055] figure 2 shows a bottom view of the same centrifugal pump;

[0056] figures 3 and 4 respectively show an axial sectional view of a portion, more precisely the hydraulic part, of the pump arranged in the condition illustrated in figure 1a, according to the axial trace planes Ill-Ill and IV-IV indicated in figure 2;

[0057] figure 4a shows an enlargement of a detail of the centrifugal pump according to the invention, indicated in figure 4;

[0058] figures 5 and 6 respectively show a perspective view from opposite viewpoints, from above and from below, of a component used in the centrifugal pump according to the invention.

[0059] Description of embodiments of the invention

[0060]

[0042] With particular reference to these figures, 1 indicates as a whole a centrifugal pump, in particular a submersible electric pump.

[0061]

[0043] The pump is adapted to pump a liquid that may contain solid material, for example wastewater, from an inlet section 2 or suction to an outlet section 3 or delivery, through one or more pumping stages. More precisely, the pump 1 comprises a hydraulic part 10 and a motor unit 20, intended to be reciprocally coupled. In the illustrated case by way of example, the pump 1 is single-stage.

[0062]

[0044] The hydraulic part 10 comprises an impeller member 4 and a diffuser member 5, inside which the impeller member 4 is placed, rotatable about a longitudinal axis A (see figures 1a, 1b and 3).

[0063]

[0045] The motor unit 20 comprises a pump shaft 21 driven by an electric motor member 22. More precisely, the impeller member 4 is keyed onto the pump shaft 21 to be moved in rotation about the longitudinal axis A by the actuation of the motor member 22 (see figures 1 a and 1 b). For fixing the impeller member 4 on the pump shaft 21 , threaded connecting means 23 and, preferably, anti-rotation means 24, such as for example a mechanical key (see figure 1b), can be used.

[0064]

[0046] The impeller member 4 comprises at least one blade 40, for example a plurality of blades 40, with a volute-like path from the center to the periphery, to define respective passage channels for the pumped liquid. In particular, each blade 40 has a border 41 adapted to establish at least one operating condition in proximity to the fixed body of the pump, as described in detail below.

[0065]

[0047] Advantageously, the diffuser member 5 axially forms an inlet opening 50 adapted to define said inlet section 2 for the liquid to be pumped (see figure 3).

[0066]

[0048] The pump 1 also comprises a wear plate 6, sealingly mounted on the diffuser member 5, adapted to act as a seat for the impeller member 4.

[0067]

[0049] The plate 6 is mounted around the axis A of the pump, substantially at the inlet section 2, to cooperate with the impeller member 4 to delimit said passage channels for the liquid to be pumped.

[0068]

[0050] More precisely, the plate 6 forms a tubular inlet portion 6a, connected to a discoidal portion 6b, of annular shape.

[0069]

[0051] The tubular portion 6a is adapted to be inserted axially at the opening 50 of the diffuser member 5, with the interposition of known-type sealing means 7 (see figure 4a).

[0070]

[0052] The discoidal portion 6b is preferably adapted to be applied on an inner wall 51 of the diffuser member 5, adjacent to the opening 50 and opposite the impeller member 4 (see figure 3).

[0053] The discoidal portion 6b, in particular, has an operative surface 6c facing, in use, towards the impeller member 4, and a rear surface 6d, facing instead towards the inner wall 51 of the diffuser member 5 (see figures 5 and 6).

[0071]

[0054] The plate 6 is assembled to the diffuser member 5 so as to be fluctuating between a first position 6', at which the operative surface 6c of the plate 6 is positioned in proximity to the border 41 of the blades 40 of the impeller member 4, and a second position 6", at which the operative surface 6c of the plate 6 is distant by a certain maximum axial play from said border 41 (see figures 1a and 1b).

[0072]

[0055] This fluctuation of the plate 6 can be considered free, that is, not counteracted, in a rest condition of the pump, other than by the action of friction, for example generated by the sealing means 7 interposed between the plate 6 and the diffuser member 5.

[0073]

[0056] The aforementioned first position 6' corresponds to an operating condition in which the liquid is pumped and there are no solid bodies that may tend to separate the plate 6 from the blades 40 of the impeller member 4 (see figure 1a).

[0074]

[0057] The aforementioned second position 6" can correspond to a rest condition of the pump 1 or to an operating condition of the same, in which solid bodies are interposed between the border 41 of the blades 40 and the plate 6 and push the plate 6 itself towards the inner wall 51 of the diffuser member 5, in particular downwards, as described in detail below (see figure 1b).

[0075]

[0058] The plate 6 is therefore adapted to fluctuate freely, except for friction, between the first position 6' and the second position 6", eventually settling, at least temporarily, in one of the intermediate positions.

[0076]

[0059] In particular, the free axial fluctuation motion of the plate 6, in the sense of a lowering towards the inner wall 51 of the diffuser member 5, generates a passage clearance L between the plate 6 and the impeller member 4, which serves to facilitate the deviation of any solid material dragged by the liquid to be pumped, directly from the inlet section 2 to the outlet section 3. This passage clearance L represents an "escape route" for this material and is therefore aimed at preserving the pump from clogging of the impeller member 4.

[0077]

[0060] For this purpose, moreover, the plate 6 preferably has a groove 60 made on the operative surface 6c. The groove 60 serves to guide the outflow of any solid material towards the outlet section 3, as described in detail below.

[0078]

[0061] The groove 60 preferably develops in a volute shape, from an inner edge towards a peripheral edge of the operative surface 6c, to guide the solid material subject to the centrifugal action generated on the pumped liquid and on its solid content by the rotation of the impeller member 4 (see figure 5).

[0079]

[0062] The plate 6 is associated with the diffuser member 5 of the pump by the interposition of at least one fixing assembly 8, so as to realize said free axial fluctuation motion in a range comprised between the first position 6', at which the plate 6 is close to the borders 41 of the blades 40 of the impeller member 4, at a maximum axial distance from the inner wall 51 of the diffuser member 5, and the second position 6", of opening, at which the plate 6 is spaced from the borders 41 of the blades 40 of the impeller member 4, at a minimum axial distance from the same inner wall 51 of the diffuser member 5, for example in a condition of abutment against it.

[0080]

[0063] In practice, according to said free fluctuation motion, the plate 6 can be fluctuating between a lifted condition in proximity to the impeller member 4, in the absence of solid material to be diverted towards the outlet section 3, in said first proximity position 6', and a lowered condition down to the inner wall 51 of the diffuser member 5, in the presence of solid material to be diverted, down to said second position 6" of maximum opening.

[0081]

[0064] In the presence of solid material in the liquid to be pumped, the same solid material pushes the plate 6 towards the second position 6", of opening, moving it away from the impeller member 4, thus insinuating itself into the passage clearance L which diverts the material itself from a path through the channels of the impeller member 4. In particular, in this circumstance, the solid material eventually dragged through the inlet section 2 can be guided along the groove 60, interposing itself between the plate 6 and the impeller member 4, to then be diverted directly towards the outlet section 3.

[0082]

[0065] Said free fluctuation motion of the plate 6 is realized by means of the fixing assembly 8 that connects the plate 6 to the diffuser member 5.

[0083]

[0066] Preferably, the fixing assembly 8 comprises at least one fixing element 81 , for example a threaded element, by means of which the plate 6 is fixed to the diffuser member 5. In the illustrated example, the fixing element 81 is a threaded pin.

[0084]

[0067] The fixing assembly 8 may also comprise a locking element 82, coupled to the fixing element 81 , to fix the first position 6', of end-of-stroke for the plate 6, of said free fluctuation motion. For example, this locking element 82 is made by at least one clamping nut.

[0085]

[0068] Furthermore, the fixing assembly 8 can be usefully mounted on the diffuser member 5 with the interposition of known-type sealing means 7, to prevent the escape of the pumped liquid.

[0086]

[0069] To allow the assembly of the fixing assembly 8, the plate 6 may provide at least one hole 61 , preferably blind, open on said rear surface 6d, for the insertion of the fixing element 81. For example, as in the illustrated case, three holes 61 can be provided, preferably distributed in an angularly uniform manner on the periphery of the plate 6, for the housing of as many fixing elements 81.

[0087]

[0070] The diffuser member 5 may in turn comprise at least one through hole 52 to allow the insertion of a respective fixing element 81. Preferably, the diffuser member 5 comprises a plurality of through holes 52, provided for this purpose and corresponding to the holes 61 made on the plate 6. The through holes 52, in particular, advantageously allow for easy adjustment of the tightening of the fixing element 81 , from the outside of the diffuser member 5.

[0088]

[0071] Preferably, the fixing assembly 8 also comprises one or more adjustment elements 83, for adjusting, in an assembly phase, said first position 6' in the connection between the diffuser member 5 and the plate 6.

[0089]

[0072] The adjustment element 83 is preferably realized by a threaded grub screw.

[0090]

[0073] It preferably comprises a maneuvering portion 84, to allow axial adjustment, when it is inserted through a respective adjustment hole 53 of the diffuser member 5. In particular, the maneuvering portion 84 can form a recess of suitable section, for example hexagonal, positioned at the head of the adjustment element 83, so as to allow the coupling of a known- type tightening tool.

[0091]

[0074] The adjustment element 83 preferably also integrates a spacer portion 85, at an opposite end with respect to the maneuvering portion 84, intended to contact the rear surface 6d of the plate 6 in said assembly phase.

[0092]

[0075] Correspondingly, the plate 6 may comprise, for example next to each locking hole 61, an abutment zone 62, for example a preferably circular flat spot, adapted to precisely contact the top of the spacer portion 85 of the adjustment element 83.

[0093]

[0076] In other words, the adjustment element 83 can define the distance between the wall 51 of the diffuser member 5 and the plate 6, and consequently between the border 41 of the blades 40 and the operative surface 6c of the plate 6, by means of the controlled contact against the rear surface 6d.

[0094]

[0077] The operation of the pump according to the invention is easily understandable from the preceding description.

[0095]

[0078] In the assembly phase, the motor unit 20 is assembled, associating the pump shaft 21 with the electric motor member 22.

[0096]

[0079] The impeller member 4 is then mounted on the pump shaft 21 , being axially locked by the threaded connection 23 and being locked against rotation by the key 24.

[0097]

[0080] The fixing elements 81 with the relative sealing means 7 are pre-assembled in the holes 61 of the plate 6.

[0098]

[0081] Subsequently, the plate 6 is inserted into the diffuser member 5. More precisely, the plate 6 is superimposed on the diffuser member 5, centering the fixing elements 81 on the through holes 52 of the diffuser member 5.

[0099]

[0082] In this assembly phase, the plate 6 is arranged in the second position 6", of maximum opening, illustrated in figure 1 b, abutting against the inner wall 51 of the diffuser member 5.

[0100]

[0083] The motor unit 20 is then assembled to the diffuser member 5.

[0101]

[0084] Then the excursion of the free fluctuation motion of the plate 6 is adjusted.

[0102]

[0085] More precisely, each adjustment element 83 is mounted on the diffuser member 5, adjusting the positioning of the plate 6 at the minimum axial distance from the impeller member 4, preferably in a range between 0.30 mm and 0.50 mm, for example equal to 0.5 mm, in the first proximity position 6'.

[0103]

[0086] Each fixing element 81 is then tightened by means of the respective locking element 82 in said first position 6' of the plate 6 (see figure 1a), adjusted by means of the adjustment elements 83.

[0104]

[0087] Subsequently, each adjustment element 83 is retracted and locked in the retracted position with suitable locking means, for example a nut, so as to release the fluctuation stroke of the plate 6 towards the second position 6", for example downwards (see figure 1b).

[0105]

[0088] The fluctuation stroke of the plate 6 is preferably at least 3 mm, in particular not less than 5 mm.

[0106]

[0089] Once assembled, the pump is for example arranged immersed in a tank containing the liquid to be pumped. In particular, the outlet section 3 is connected to suitable connection means, for example a specific pipe, to convey the pumped liquid.

[0107]

[0090] When the pump is actuated, the impeller member 4 is brought into rotation about the longitudinal axis A and the liquid is suctioned from the inlet section 2 to the outlet section 3.

[0108]

[0091] As soon as the pump 1 is put into operation, the pumping liquid flows from the inlet section 2 to the delivery section 3 through the passage channels defined by the blades 40 of the impeller member 4. Through the centrifugal action generated by the outflow through the impeller member 4, the pressure of the pumping liquid increases from a suction value to a delivery value, greater than the suction value.

[0109]

[0092] Furthermore, part of the outgoing pumped liquid, at delivery pressure, flows into the gap defined between the inner wall 51 of the diffuser member 5 and the rear surface 6d of the plate 6. This outflow determines on said rear surface 6d an axial lifting thrust, greater than the opposite axial lowering thrust, exerted by the fluid flow which, dragged by the rotary motion of the impeller member 4 about the longitudinal axis A, comes from the tubular portion 6a and laps the operative surface 6c of the plate 6.

[0110]

[0093] While the actions that determine said opposite axial lowering thrust are on average lower than the delivery pressure, in particular increasing from the suction value to the delivery value, the actions that instead determine the aforementioned hydraulic lifting thrust are at the higher and constant delivery value.

[0111]

[0094] Therefore, upon actuation of the pump 1, as soon as the pumping liquid flows through the impeller member 4, the plate 6 is supported by said axial hydraulic lifting thrust in the first position 6', of proximity with respect to the borders 41 of the blades 40 of the impeller member 4.

[0112]

[0095] Likewise, during the normal operation of the pump 1, the outflow of the pumped liquid supports the plate 6 in said first lifted position 6'.

[0096] During operation, it may happen that solid material of even considerable size is dragged by the liquid to be pumped up to the inlet section 2, passing through the opening 50 of the diffuser member 5 and the tubular portion 6a of the plate 6.

[0113]

[0097] After passing the tubular portion 6a, the solid material is preferably intercepted by the groove 60, aimed at by-passing it towards the outlet section 3. In particular, if the solid material has a thickness greater than the depth of the groove 60 itself, the material, pushed by the centrifugal action, in turn exerts a thrust on the plate 6, actuating it downwards in said free axial fluctuation motion. More precisely, this thrust axially moves the plate 6 towards the second opening position 6" or in an intermediate position, until it allows the passage of the solid material towards the outlet section 3. This thrust therefore overcomes the hydraulic thrust generated by the different pressures acting on the plate 6, in particular on the operative surface 6c and on the rear surface 6d.

[0114]

[0098] The solid material finally exits through the outlet section 3.

[0115]

[0099] In the absence of interposed solid material, the plate 6 returns to the first position 6', in particular lifted, by virtue of the resulting hydraulic thrust acting on it, exerted by the different pressures acting in opposite directions on the operative surface 6c and on the rear surface 6d of the plate 6.

[0116]

[0100] The centrifugal pump according to the invention thus achieves the object of ensuring reliable operation in all conditions.

[0117]

[0101] In the practical implementation of the invention, the materials used, as well as the shape and dimensions, may be any according to the requirements.

[0118]

[0102] Where the technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs have no limiting effect on the scope of each element identified by way of example by such reference signs.

Claims

1. Claims1. A centrifugal pump for pumping liquids, in particular liquids containing solid material, comprising a diffuser member (5), forming an inlet section (2) and an outlet section (3) for said liquid, an impeller member (4) disposed inside said diffuser member (5), rotatable about a longitudinal axis (A), said impeller member (4) defining at least one outflow channel for said liquid between said inlet section (2) and said outlet section (3), and a wear plate (6), sealingly mounted on said diffuser member (5) and adapted to act as a seat for said impeller member (4), characterized in that in an assembled condition said plate (6) is movably connected in an axial fluctuation stroke with respect to said diffuser member (5) by means of a fixing assembly (8), between a first position (6'), of proximity, at which said plate (6) is axially close to said impeller member (4), the action adapted to support said plate (6) in said first proximity position (6') in an active operating condition being exclusively hydraulic, and a second position (6"), of opening, at which said plate (6) is positioned at a certain maximum axial distance with respect to said impeller member (4), so as to axially define a free passage clearance (L) between said plate (6) and said impeller member (4), adapted to accommodate said solid material and allow its outflow towards said outlet section (3), bypassing said impeller member (4) when said pump (1 ) is in said active operating condition, said axial fluctuation stroke of said plate (6) with respect to said diffuser member (5), between said first position (6') and said second position (6"), being, in an assembled rest condition of the pump, a free fluctuation motion, except for friction.

2. The pump of claim 1, wherein said first position (6') corresponds to a lifted condition and said second position (6") to a lowered condition for said plate (6).

3. The pump of claim 1 or 2, wherein said fixing assembly (8) does not comprise elastic counteracting and / or supporting means for said fluctuation stroke, in particular of the type of a spring, for example.

4. The pump of any one of the preceding claims, wherein in said first proximity position (6'), said plate (6) is close to said impeller member (4) by a minimum axial distance comprised between 0.30 mm and 0.50 mm, in particular equal to 0.50 mm.

5. The pump of any one of the preceding claims, wherein said fixing assembly (8) comprises at least one fixing element (81) and one locking element (82), mutually tightened so as to delimit said axial fluctuation stroke, in particular said first proximity position (6').

6. The pump of claim 5, wherein said fixing element (81) is made of a threaded element and said locking element (82) of at least one nut.

7. The pump of any one of the preceding claims, wherein it comprises at least one adjustment element (83) for adjusting said axial fluctuation stroke, in particular said first position (6'), said diffuser member (5) comprising a hole (53) for the insertion of said adjustment element (83) abutting said plate (6), accessible from the outside of said diffuser member (5).

8. The pump of any one of the preceding claims, wherein said diffuser member (5) has at least one through hole (52) accessible from the outside of said pump and said plate (6) has at least one hole (61 ), for the insertion of said fixing assembly (8).

9. The pump of any one of the preceding claims, wherein said plate (6) has a groove (60) made on a respective operative surface (6c) which, in use, is facing said impeller member (4), to guide said solid material from said inlet section (2) towards said outlet section (3).

10. The pump of claim 9, wherein said groove (60) develops in a volute shape from an inner edge towards a peripheral edge of said operative surface (6c) of said plate (6).

11. A method for assembling a centrifugal pump according to claim 1 , comprising the steps of:12.a) assembling a motor unit (20) of said pump (1 ), associating a respective pump shaft (21 ) with a respective electric motor member (22);13.b) mounting said impeller member (4) on said pump shaft (21), by means of axial and rotational locking;14.c) pre-assembling in said wear plate (6) said fixing assembly (8) together with respective sealing means (7);15.d) inserting said plate (6) into said diffuser member (5), positioning said plate (6) in said second opening position (6"), abutting against an inner wall (51 ) of said diffuser member e) assembling said motor unit (20) to said diffuser member (5);16.f) adjusting the positioning of said plate (6) in said first proximity position (6'), preferably by means of at least one adjustment element (83) inserted through said diffuser member (5);17.g) tightening said fixing assembly (8) in said first position (6') of said plate (6);18.h) releasing the axial fluctuation stroke of said plate (6) towards said second opening position (6"), preferably by retracting said at least one adjustment element (83), so that in an assembled rest condition of the pump, said plate (6) is freely movable between said first position (6') and said second position (6"), in particular except for friction.

12. The method of claim 11 , wherein said axial fluctuation stroke is at least 3 mm, in particular not less than 5 mm.

Images