OPEN ROTOR FOR SUBMERSIBLE PUMP CONFIGURED TO PUMP LIQUID CONTAINING ABRASIVE MATTER
Patent Information
- Authority / Receiving Office
- MX · MX
- Patent Type
- Patents
- Current Assignee / Owner
- XYLEM EURO GMBH
- Filing Date
- 2023-03-15
- Publication Date
- 2026-06-12
Smart Images
Figure MX434816B0
Abstract
Description
OPEN ROTOR FOR SUBMERSIBLE PUMP CONFIGURED FOR PUMPING LIQUID CONTAINING ABRASIVE MATTER cu nenn / eznz / E / YiAi Field of Invention The present invention relates generally to the field of pumps configured to pump liquids comprising solid / abrasive material. Furthermore, the present invention relates specifically to the field of submersible pumps, such as sewage pumps and drainage pumps specially configured to pump liquids comprising sand and stone material, such as wastewater, drilling water in mining / tunneling applications, surface water at construction sites, etc., i.e., conveying and drainage functions. The present invention relates specifically to an open rotor suitable for such pumps and functions, and to a submersible pump comprising such an open rotor. The open rotor comprises a cover plate, a centrally located hub, and at least two spirally extending blades connected to the cover plate and the hub, each blade comprising a leading edge adjacent to the hub, a trailing edge at the rotor periphery, and a lower edge, the lower edge extending from the leading edge to the trailing edge. Ref. 343537 and separates a suction side of the vane from a pressure side of the vane, and the lower edge being configured to be oriented and located opposite a wear plate of the submersible pump, at least one vane comprising a fin on the lower edge, wherein the fin connects and projects from the suction side of the at least one vane. Background of the Invention In mines, tunnel construction, quarries, and similar construction sites, there is almost always a need to remove unwanted water to ensure a sufficiently dry environment at the work site. In mining, tunneling, and quarrying applications, a significant amount of drilling water is used when preparing for loading before blasting. Water is also used to prevent dust from spreading after blasting. If this produced water is not removed, at least the blast site and the lower parts of the mine will be flooded. Surface water and groundwater will also contribute to the accumulation of unwanted water that must be removed.It is customary to use drainage / dewatering pumps to lift water out of the mine to a settling basin located above ground. The water is then pumped in stages from the lower parts of the mine to different basins / pits located at varying depths. Each stage / lift can be found, for example, at intervals of 25–50 meters vertically, and the length of the outlet pipe, i.e., the transport distance, at each stage / lift can be, for example, at intervals of 100–300 meters. In mining applications, a considerable amount of sand and stone material is suspended in the water, in some applications up to 10%. Wastewater pumping stations, in addition to sewage, also contain sand, stones, and other abrasive materials, especially those originating from surface water. Therefore, there are several applications where the pumped media are highly abrasive, including sand, stones, etc. The applications considered for this patent application are not so-called vortex pumps—that is, pumps with a large distance between the rotor and the volute wear plate—but rather pumps with only a small axial gap between the lower edge of the rotor vanes and the upper surface of the volute wear plate (pump casing). This gap is conventionally less than 1 millimeter. The gap in vortex pumps is several centimeters, and these pumps are not subject to the problems addressed by the present invention. In all pumping applications, there is a pressure difference between the suction side (inner radial side) and the pressure side (outer radial side) of the vane, due to the rotor design and rotation. Most dewatering pumps are so-called high-pressure pumps, in which the pressure difference across the vane can be very high. This pressure difference across the vane, or the differential pressure across the lower edge gap, results in a jet of media flow—i.e., liquid and abrasive material—from the pressure side to the suction side through the narrow space between the lower edge of the vane and the wear plate.The jet of flow from the pumped media through the gap will wear down the lower edge of the vane, and the resulting increase in gap distance will result in a rapid decrease in performance and efficiency, i.e., a decrease in head, less pumped flow rate, and higher energy consumption. Prior art pumps are known that have so-called fins on the lower edges of the rotor blades and a small axial gap between the rotor and the wear plate, for example, in US7037069, in order to increase the length (cu nenn / eznz / E / YiAi) of the gap between the lower edge of the blade and the wear plate / suction cover of the pump volute. The document describes an acute angle between the fin and the rotor's central axis, and the fin is located on the pressure side of the blade. Other known rotors have the fin located on the suction side of the blade, for example, in GB2175963, but these describe a vortex pump / rotor. Prior art solutions describe the use of a fin up to the lower edge of the blade, i.e., from the hub to the periphery, and according to document US7037069, the width of the fin should decrease towards the periphery of the rotor. The inventor of the present invention has identified serious problems with known vane solutions, namely, the increased wetted area between the lower edge of the rotor and the wear plate due to large vanes leads to increased energy consumption. There is a general challenge within the technical field of pumps to reduce energy consumption. Therefore, the inventor realized that using vanes across the entire distance from the leading edge to the trailing edge of the vane will result in an unnecessarily large wetted area between the rotor and the wear plate—that is, the gap area perpendicular to the axial distance between the rotor and the wear plate—which increases the pump's energy consumption.Furthermore, the flow area of the rotor channels and the effective blade height will also decrease on the inner radial portion of the blade when a fin extending the entire distance from the leading edge to the trailing edge of the blade is used. A decrease in flow area and a decrease in effective blade height on the inner radial portion of the blade will negatively affect the rotor's efficiency. Therefore, considering the aforementioned drawbacks and based on the knowledge that rotor blade wear is worse with increasing rotor diameter due to the increased differential pressure and the increased relative speed between the blade and the wear plate, the inventor has arrived at the present invention. Object of the Invention The present invention aims to overcome the aforementioned disadvantages and shortcomings of previously known rotors and pumps, and to provide an improved rotor and pump. A primary object of the present invention is to provide an improved rotor of the initially defined type comprising vanes configured to prevent wear on the lower edge of the vanes and, therefore, less crossflow over the vane and efficiency retained thereon; i.e., the positive effects of using a vane are increased, while at the same time the known negative effects of known vanes are reduced and minimized. Brief Description of the Invention According to the invention, at least the primary objective is achieved by means of the initially defined open rotor and the submersible pump having the characteristics defined in the independent claims. Preferred embodiments of the present invention are defined in more detail in the dependent claims. According to a first aspect of the present invention, an open rotor of the initially defined type is provided, characterized in that the vane is located radially to the outside of an inner radius (r_interior) of the rotor and extends in the circumferential direction to the trailing edge on the suction side of the vane located at a maximum radius (r_max) of the rotor, wherein this vane has a lower wear surface configured to be oriented and located opposite the wear plate of the submersible pump, wherein the inner radius (r_interior) is equal to the larger of: the maximum radius (r max) of the rotor multiplied by 0.6, and - an inlet radius (r_inlet) of the rotor multiplied by 1.2, where the inlet radius (r_inlet) is taken at the interface between the leading edge of the blade and the trailing edge of the blade on the suction side of the blade. According to a second aspect of the present invention, a submersible pump comprising such an open rotor is provided. Therefore, the present invention is based on the intuition that the vane should not begin at the leading edge of the vane, i.e., at the pump volute inlet, to avoid negatively impacting the flow of the pumped liquid within the rotor channels. It is also based on the intuition that wear is greater with increasing rotor diameter, thus increasing the need for a fin. Simultaneously, the wetted area of the gap should be minimized to reduce energy consumption. A longer gap where the differential pressure is highest will result in less crossflow and less wear. According to several embodiments of the present invention, the width (W) of the lower wear surface of the fin, measured along the rotor radius, increases from zero at the inner radius (rinner) to a maximum width (Wmax) at the trailing edge on the suction side of the blade. In this way, the gap width added by the fin, in addition to the original gap width at the lower edge of the blade, increases with the increase in radius, thereby minimizing crossflow and wear where the differential pressure is greatest. According to several embodiments of the present invention, the rotor blade has a height (H) at the maximum width (W_max) of the fin, wherein the ratio between the maximum width (W_max) of the lower wear surface of the fin and the height (H) of the blade is equal to or greater than 0.4 and equal to or less than 0.6, when the height (H) is greater than 50 mm, and is equal to or greater than 0.5 and equal to or less than 0.8, when the height (H) is equal to or less than 50 mm. In this way, the width of the fin is adapted to the differential pressures for which the different rotors are configured to handle, that is, rotors configured to deliver higher pressure / height, i.e., with a less effective blade height and a higher differential pressure, have wider fins than rotors configured to deliver lower pressure / height, i.e., with a greater effective blade height and a lower differential pressure. According to several embodiments of the present invention, the fin thickness (T) is equal to or greater than 2.5 mm and equal to or less than 7 mm. In several embodiments of the present invention, the fin thickness (T) is at its maximum at the maximum width (W_max) of the fin's lower wear surface. Therefore, most of the fin material is added where wear is greatest and where the rotor channel has the largest flow area, i.e., it has the least effect on the channel's flow area. Other advantages and features of the invention will be evident from the other dependent claims, as well as from the following detailed description of the preferred embodiments. Brief Description of the Figures A more complete understanding of the features and advantages mentioned above and others of the present invention will become evident from the following detailed description of preferred embodiments in conjunction with the accompanying figures, in which: Figure 1 is a schematic side elevation view of the cross-section of the hydraulic unit of an inventive submersible pump, i.e., a drainage pump, comprising an inventive open rotor, Figure 2 is a schematic perspective view from below of an open rotor having two blades, wherein the rotor is an example of a rotor for a sewage pump configured for lower pressure and higher volume, Figure 3 is a schematic view from below of the rotor in accordance with Figure 2, Figure 4 is a schematic side elevation view of the rotor cross-section in accordance with Figures 2 and 3, Figure 5 is a schematic perspective view from below of an open rotor having three blades, wherein the rotor is an example of a rotor for a drainage pump configured for medium pressure and medium volume. Figure 6 is a schematic view from below of the rotor in accordance with Figure 5, Figure 7 is a schematic side view of the rotor cross-section in accordance with Figures 5 and 6, Figure 8 is a schematic perspective view from below of an open rotor having four blades, where the rotor is an example of a rotor for a drainage pump configured for higher pressure and lower volume, Figure 9 is a schematic view from below of the rotor in accordance with Figure 8, and Figure 10 is a schematic side view of the rotor cross-section in accordance with Figures 8 and 9. Detailed Description of the Invention The present invention relates specifically to the field of submersible pumps specially configured for pumping liquids containing abrasive / solid material, such as water containing sand and gravel. These submersible pumps are particularly suitable for wastewater and drainage applications. The present invention relates specifically to an open rotor suitable for this type of pump and these applications. Initially, reference is made to Figure 1, which shows a schematic illustration of a hydraulic unit of a submersible pump, generally designated as 1. A general submersible pump will be described with reference to Figure 1, although Figure 1 actually shows a hydraulic unit of a drainage pump; the structural elements are the same for a sewage pump. Submersible pump 1 will be referred to hereafter as the pump.The hydraulic unit of pump 1 comprises an inlet 2, an outlet 3, and a volute 4 located between inlet 2 and outlet 3; that is, volute 4 is downstream of inlet 2 and upstream of outlet 3. Volute 4 is partially enclosed by a wear plate 5 that surrounds inlet 2. Volute 4 is also enclosed by an intermediate wall 6 that separates volute 4 from the drive unit (removed from Figure 1) of pump 1. Volute 4 is also referred to as the pump chamber, and the wear plate 5 is also referred to as the suction cover. In some applications, the outlet 3 of the hydraulic unit also serves as the outlet of pump 1, and in other applications, outlet 3 of the hydraulic unit is connected to a separate outlet of pump 1. The outlet of pump 1 is configured to be connected to an outlet conduit (not shown).Pump 1 further comprises an open rotor, generally designated as 7, the rotor 7 being located in the volute 4, i.e., the hydraulic unit of pump 1 comprises a rotor 7. The hydraulic unit of a drainage pump further comprises an inlet filter 8 having perforations or holes 9, the inlet filter 8 being configured to prevent larger objects from reaching the inlet 2 and the volute 4. Otherwise, these larger objects may become stuck or obstruct the rotor 7. The pump drive unit 1 comprises an electric motor housed in a liquid-tight pump casing and a drive shaft 10 extending from the electric motor through the intermediate wall 6 and into the volute 4. The rotor 7 is connected to the drive shaft 10 and is driven into rotation by it during operation of the pump 1, whereby the liquid is drawn in at the inlet 2 and pumped out through the outlet 3 by means of the rotating rotor 7 when the pump 1 is active. The pump casing, wear plate 5, rotor 7, and other essential components are preferably made of metal, such as aluminum and steel. The electric motor is powered by an electrical power cable extending from a power source, and the pump 1 comprises a liquid-tight conduit that receives the electrical power cable. According to preferred embodiments, pump 1, more precisely the electric motor, is functionally connected to a control unit, such as an intelligent drive comprising a variable frequency drive (VFD). Thus, pump 1 is configured to operate at a variable operating speed (rpm) by means of the control unit. According to preferred embodiments, the control unit is located inside the liquid-tight pump housing; that is, it is preferred that the control unit be integrated into pump 1. The control unit is configured to control the operating speed of pump 1. According to alternative embodiments, the control unit is an external control unit, or the control unit is separated into an external subunit and an internal subunit.The operating speed of pump 1 is more precisely the rpm of the electric motor and rotor 7 and corresponds / refers to an output frequency of the control unit. The components of pump 1 are usually cooled by the liquid / water surrounding it. Pump 1 is designed and configured to operate in a submerged position, meaning that during operation it is located completely below the liquid surface. However, it should be noted that during operation, submersible pump 1 does not need to be completely below the liquid surface; it can be partially or fully above the surface continuously or intermittently. In dry-installed applications, submersible pump 1 includes dedicated cooling systems. The present invention is based on a new and improved open rotor 7, which is configured for use in pumps 1 that pump abrasive media, for example, water or wastewater / sewage comprising sand and stones. Rotors 7 wear out quite rapidly in this type of installation due to the solid / abrasive matter in the pumped liquid and conventionally need to be replaced every 7 weeks under harsh conditions due to the accelerated decrease in pump 1 efficiency as the rotor 7 wears. Tests have been carried out, and the present invention will extend the replacement requirement by approximately 30-50%, compared to conventional rotors that do not have the inventive fins. Figures 2 to 10, which show different examples of inventive rotor 7, are now referenced. Figures 2-4 show a first example of the rotor, Figures 5-7 show a second example, and Figures 8-10 show a third example. The following description applies to all inventive rotors 7, regardless of the figure referenced, unless otherwise stated. The rotor 7 comprises a cover plate 11, a hub 12 located in the center, and at least two spirally extending blades 13 connected to the cover plate 11 and the hub 12. In Figures 2-4, the rotor 7 comprises two blades 13, in Figures 5-7, the rotor 7 comprises three blades 13, and in Figures 8-10, the rotor 7 comprises four blades 13. The blades 13 are located equidistantly around the hub 12. The vanes 13 extend, viewed from the hub 12, towards the periphery of the rotor 7, in a direction opposite to the direction of rotation of the rotor 7 during the normal operation (pumping of liquid) of pump 1. Therefore, viewed from below, i.e., figures 3, 6 and 9, the direction of rotation of the rotors 7 during normal operation is counterclockwise. Each blade 13 comprises a leading edge 14 adjacent to the hub 12 and a trailing edge 15 on the periphery of the rotor 7. The leading edge 14 of the rotor 7 is located upstream of the trailing edge 15, with two adjacent blades 13 defining a channel between them that extends from the leading edges 14 to the trailing edges 15. The leading edge 14 is located at the inlet 2 of the hydraulic unit, and the leading edge 14 spirals outward from the hub in the same direction as the blade 13. During operation, the leading edges 14 grip the fluid, the channels accelerate the fluid, and the fluid exits the rotor 7 at the trailing edges 15. The fluid is then guided by the volute 4 of the hydraulic unit to the outlet 3. Thus, the fluid is drawn into the rotor 7 and expelled from the rotor 7.The channels are also delimited by the rotor 7 cover plate 11 and the volute 4 wear plate 5. The rotor 7 diameter and the shape and configuration of the channels / vanes determine the pressure build-up in the liquid and the pumped flow. Each vane 13 also comprises a lower edge 16, wherein the lower edge 16 extends from the leading edge 14 to the trailing edge 15 and separates a suction side / surface 17 of the vane 13 from a pressure side / surface 18 of the vane 13. The lower edge 16 is configured to be oriented towards and located opposite the wear plate 5 of the pump 1. Therefore, the suction side 17 of a vane 13 is located opposite the pressure side 18 of an adjacent vane 13. The leading edge 14 and the trailing edge 15 also separate the suction side 17 from the pressure side 18. The leading edge 14 is preferably rounded. At least one vane 13 comprises a fin 19 on the lower edge 16 of the vane 13, wherein the fin 19 is connected to and projects from the suction side 17 of the vane 13. The fin 19 has a lower wear surface 20 configured to be oriented and positioned opposite the wear plate 4 of the pump 1. The lower wear surface 20 of the fin 19 is preferably flush with the lower edge 16 of the vane 13. It is essential that the fin 19 be located radially to the outside of an inner radius (r_interior) of the rotor 7 and extend in the circumferential direction to the trailing edge 15 on the suction side 17 of the blade 13 located at a maximum radius (r_max) of the rotor 7. Therefore, the invention is based on the idea that the beginning of the fin 19, i.e., the inner radius (r_interior), must be distanced from the inlet 2, i.e., distanced from the interface between the leading edge 14 of the blade 13 and the trailing edge 16 of the blade 13. The inner radius (r_interior) is equal to the greater of: the maximum radius (r_max) of rotor 7 multiplied by 0.6, and - an inlet radius (r_entrada) of the rotor 7 multiplied by 1.2, wherein the inlet radius (r entrada) is taken at the interface between the leading edge 14 of blade 13 and the trailing edge 16 of blade 13 on the suction side 17 of blade 3. In Figures 3, 6 and 9, the interface between the lower wear surface 20 of the fin 19 and the lower edge 16 of the vane 13 is shown by means of a broken line 21, and it is clear that the fins 19 begin at a distance from the leading edge 14. The technical function of the fin 19 is to increase the width of the gap between the lower edge 16 of the vane 13 and the wear plate 5, in order to decrease the crossflow of liquid and abrasive material from the pressure side 18 to the suction side 17 and thereby decrease the wear of the vane 13. However, an increased gap width will also increase the wetted area of the gap, which will lead to an increase in frictional forces. The wetted area of the gap is the area of the vane 13 portion that is facing forward and oriented toward the wear plate 5. With the start of the fin 19 spaced away from the leading edge 14, the gap width, i.e., the width of the fin 19, can be increased with a larger rotor diameter 7 without increasing the wetted area of the gap, and by increasing the gap width with a larger rotor diameter 7, the rotor 7 will be more wear-resistant. Preferably all the rotor blades 13 are provided with fins 19 of the same dimensions to have a balanced rotor 7. According to various modalities, the width (W) of the lower wear surface 20 of the fin 19, taken along the diameter of the rotor 7, increases from zero at the inner radius (r_inner) to a maximum width (W_max) at the trailing edge 15 on the suction side 17 of the blade 13. The blade 13 of the rotor 7 has a height (H) at the maximum width (W_max) of the fin 19, and the height (H) is measured along a line extending perpendicular to an imaginary line coinciding with the lower edge 16 of the blade 13, and is measured between the imaginary line and the imaginary interface between the suction side 17 of the blade 13 and the lower surface 22 of the cover plate 11. The height of the blade can vary depending on the distance from the central axis of the rotor 7. According to preferred embodiments, the ratio between the maximum width (W_max) of the lower wear surface 20 of the fin 19 and the height (H) of the vane 13 is equal to or greater than 0.4 and equal to or less than 0.6, when the height (H) is greater than 50 mm. This is for, for example, rotors 7 configured for drainage pumps. According to other preferred embodiments, the ratio between the maximum width (W max) of the lower wear surface 20 of the fin 19 and the height (H) of the vane 13 is equal to or greater than 0.5 and equal to or less than 0.8, when the height (H) is equal to or less than 50 mm. This is for, for example, rotors 7 configured for wastewater pumps. The maximum width (W_max) of the lower wear surface 20 of the fin 19 is measured parallel to the lower wear surface 20, and is measured from the imaginary interface between the suction side 17 of the vane 13 and the upper surface 23 of the fin 19. The upper side 23 of the fin 19 faces the lower wear surface 20 of the fin 19. According to various embodiments, the thickness (T) of the fin 19 is equal to or greater than 2.5 mm and equal to or less than 7 mm, preferably equal to or greater than 3 mm and equal to or less than 6 mm. A fin 19 that is too thin will be subject to deformation, and a fin 19 that is too thick will have a negative effect on the effective flow area of the rotor channel 7 and the weight of the rotor 7, and therefore on the efficiency of pump 1. According to the preferred embodiments, the thickness (T) of fin 19 is maximum at the maximum width (W_max) of the lower wear surface 20 of fin 19, at the maximum radius (r_max) of the rotor 7. It is also preferred that the thickness (T) of fin 19 increases in the circumferential direction along fin 19. Therefore, fin 19 is thickest at its outermost portion, i.e., in the area where fin 19 is subjected to greater wear and forces. Another way to define the thickness (T) of the fin is in relation to the height (H) of the blade 13. Consequently, the ratio between a thickness (T) of the fin 19 and the height (H) of the blade 13, taken at the maximum width (W_max) of the lower wear surface 20 of the fin 19, is equal to or greater than 0.05 and equal to or less than 0.3. For all rotors 7 the angle (a) between the lower wear surface 20 of the fin 19 and a central axis of the rotor 7 is obtuse, i.e., greater than 45 degrees. The distance between the lower wear surface 20 of the fin 19 and the wear plate 5 is equal to or greater than 0.1 mm and equal to or less than 0.5 mm, preferably equal to or greater than 0.15 mm and preferably equal to or less than 0.4 mm. Feasible modifications of the invention The invention is not limited solely to the embodiments described above and shown in the figures, which are primarily for illustrative and exemplary purposes. This patent application is intended to cover all adjustments and variations of the preferred embodiments described herein. Therefore, the present invention is defined by the text of the appended claims, and the equipment may be modified in all manner of ways within the scope of the appended claims. cu nenn / cznz / E / YiAi It should also be noted that all information regarding terms such as above, below, superior, inferior, etc., must be interpreted / read with the equipment oriented according to the figures, and the figures oriented so that the references can be read correctly. Therefore, such terms only indicate mutual relationships in the modalities shown, relationships that may change if the inventive equipment is provided with a different structure / design. It should also be noted that, although it is not explicitly stated that the characteristics of one specific modality can be combined with characteristics of another modality, the combination should be considered obvious, if the combination is possible. It is noted that with regard to this date, the best method known to the applicant to put the aforementioned invention into practice is the one that is clear from the present description of the invention.
Claims
1. An open rotor for a submersible pump configured for pumping liquid containing abrasive material, wherein the rotor comprises a cover plate, a hub located in the center, and at least two spirally extending blades connected to the cover plate and the hub, each blade comprising a leading edge adjacent to the hub and a trailing edge at the periphery of the rotor and a lower edge, wherein the lower edge extends from the leading edge to the trailing edge and separates a suction side of the blade from a pressure side of the blade, and wherein the lower edge is configured to be oriented and located opposite a wear plate of the submersible pump, at least one blade comprises a fin on the lower edge, wherein the fin is connected to the suction side of the at least one blade and projects from the suction side of the at least one blade,characterized in that the fin is located radially to the outside of an inner radius of the rotor and extends in the circumferential direction to the trailing edge on the suction side of the vane located at a maximum radius of the rotor, the fin having a lower wear surface configured to be oriented and located opposite the wear plate of the submersible pump, the inner radius being equal to the greater of: - the maximum radius of the rotor multiplied by 0.6, and - an inlet radius of the rotor multiplied by 1.2, the inlet radius being taken at the interface between the leading edge of the vane and the lower edge of the vane on the suction side of the vane.
2. Open rotor according to claim 1, characterized in that the lower wear surface of the fin is flush with the lower edge of the blade.
3. Open rotor according to any of claims 1 or 2, characterized in that a width of the lower wear surface of the fin, taken along the diameter of the rotor, increases from zero at the inner radius to a maximum width at the trailing edge on the suction side of the blade.
4. Open rotor according to claim 3, characterized in that the rotor blade has a height at the maximum width of the fin.
5. Open rotor according to claim 4, characterized in that the height is measured along a line extending perpendicular to an imaginary line coinciding with the lower edge of the blade, and is measured between the imaginary line and the imaginary interface between the suction side of the blade and the lower surface of the cover plate.
6. Open rotor according to any of claims 4 or 5, characterized in that the ratio between the maximum width of the lower wear surface of the fin and the height of the blade is equal to or greater than 0.4 and equal to or less than 0.6, when the height is greater than 50 mm.
7. Open rotor according to any of claims 4 to 6, characterized in that the ratio between the maximum width of the lower wear surface of the fin and the height of the blade is equal to or greater than 0.5 and equal to or less than 0.8, when the height is equal to or less than 50 mm.
8. Open rotor according to any of claims 3 to 7, characterized in that the maximum width of the lower wear surface of the fin is measured parallel to the lower wear surface cu nenn / eznz / E / YiAi, and is measured from the imaginary interface between the suction side of the vane and the upper surface of the fin.
9. Open rotor according to any of the preceding claims, characterized in that a fin thickness is equal to or greater than 2.5 mm and equal to or less than 7 mm, preferably equal to or greater than 3 mm and equal to or less than 6 mm.
10. Open rotor according to claim 9, characterized in that the fin thickness is maximum at the maximum width of the lower wear surface of the fin, at the maximum radius of the rotor.
11. Open rotor according to any of claims 9 or 10, characterized in that the fin thickness increases in the circumferential direction along the fin.
12. Open rotor according to claim 4, characterized in that the ratio between a fin thickness and the blade height, taken at the maximum width of the lower wear surface of the fin, is equal to or greater than 0.05 and equal to or less than 0.
3.
13. Open rotor according to any of the preceding claims, characterized in that cm nenn / eznz / E / YiAi 30 the angle between the lower wear surface of the fin and a central axis of the rotor is obtuse.
14. Submersible pump configured for pumping liquid comprising abrasive material, wherein the submersible pump comprises a hydraulic unit having an inlet, an outlet, and a volute located between the inlet and the outlet, the volute being partially delimited by a wear plate enclosing the inlet, characterized in that it comprises an open rotor in accordance with any of claim 113.
15. Submersible pump according to claim 14, characterized in that the distance between a lower wear surface of the fin and the wear plate is equal to or greater than 0.1 mm and equal to or less than 0.5 mm, preferably equal to or greater than 0.15 mm and preferably equal to or less than 0.4 mm.