Patent Publication Number: US-2018045213-A1

Title: Impeller for centrifugal pumps

Description:
TECHNICAL FIELD 
     The present invention relates to an impeller for centrifugal pumps, particularly of the type with one or more stages. 
     BACKGROUND ART 
     As is known, a centrifugal pumps has an impeller conventionally made of a pair of shaped disk bodies facing each other so as to form a gap within which a series of vanes that connect the two disks are arranged. 
     Centrally to each impeller there is a hub, or an equivalent coupling device, that allows to fasten the impeller to a transmission shaft that is turned by a motor means. 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     Although impellers of the known type are widely used, they have drawbacks; among these, perhaps the most important is linked to the generation of axial thrusts. 
     The impeller of a centrifugal pump is in fact subjected to different pressures that act on the two faces: a pressure lower than the atmospheric pressure generally acts on the inlet side, while a pressure substantially equal to the delivery pressure acts on the opposite face. This produces an axial thrust which can even be considerable, such as to create great losses in terms of efficiency and overloads that damage the bearings of the motor. 
     Those problems are emphasized in the case of multistage pumps. 
     In an attempt to solve the problems linked to the generation of axial thrusts, some manufacturers of multistage pumps key half of the impellers in the opposite direction with respect to the remaining ones. 
     However, such solution creates significant difficulties in making the internal passage channels. 
     The prior art also includes a impeller for centrifugal pumps disclosed in the Italian patent application no. VI2014A000271, to this same applicant. Such impeller effectively solves the problems described above, but requires the provision of disk elements having different diameters. 
     Solution to the Problem 
     The aim of the invention is to solve the problems described above, providing a impeller for centrifugal pumps that allows to reduce axial thrusts, at the same time ensuring maximum efficiency, and provides for the use of disk elements with the same diameter. 
     Within the scope of this aim, a particular object of the invention is to provide an impeller that allows to solve the problems linked to the traction that is usually generated on the transmission shaft. 
     Another object of the invention is to provide an impeller that allows to preserve the bearings of the motor. 
     Another object of the invention is to provide an impeller that can be manufactured with a small number of components and is therefore advantageous also from a purely economic standpoint. 
     This aim, these objects and others that will become better apparent hereinafter are achieved by an impeller for centrifugal pumps comprising a first disk element, functionally arranged toward the inlet, which is coaxial to and faces a second disk element, which is functionally arranged toward the delivery; said second disk element being connected rigidly to said first disk element by angularly spaced vanes and being centrally provided with a fastening means for fastening to a transmission shaft; said impeller being characterized in that it comprises openings formed in the substantially peripheral region of said second disk element, between pairs of adjacent vanes, substantially at the areas subjected to the greatest axial thrust. 
     The present invention also relates to a centrifugal pump comprising a substantially hollow body that accommodates at least one impeller that is fastened to a transmission shaft which can rotate about a rotation axis; said transmission shaft being rotated by a motor means; said impeller comprising a first disk element, functionally arranged toward the inlet, which is coaxial to and faces a second disk element, which is functionally arranged toward the delivery; said second disk element being connected rigidly to said first disk element by angularly spaced vanes and being centrally provided with a fastening means for fastening to a transmission shaft; said impeller being characterized in that it comprises openings formed in the substantially peripheral region of said second disk element, between pairs of adjacent vanes, substantially at the areas subjected to the greatest axial thrust. 
     Advantageous Effects of the Invention 
     The impeller according to the invention allows to considerably reduce the axial thrusts but at the same time ensure maximum efficiency and head. 
     In fact, by emptying the areas that are subjected to the highest pressure in the second disk element, i.e. by forming the openings, it is possible to reduce the forces that generate the axial thrust. 
     Also, head and efficiency are not reduced because the profile of these openings is fully included within the second disk element. 
     The impeller according to the present invention allows to solve the problems linked to the traction that is usually generated on the transmission shaft of centrifugal pumps with one or more stages. This allows, for example, to avoid damage to the bearings of the motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further characteristics and advantages will become better apparent from the description of preferred but not exclusive embodiments of a impeller according to the invention, illustrated by way of nonlimiting example in the accompanying drawings, wherein: 
         FIG. 1  is a front view of an impeller according to the invention; 
         FIG. 2  is a rear view of an impeller according to the invention; 
         FIG. 3  is a sectional side view of the impeller according to the invention; 
         FIG. 4  is a front view of an impeller according to a further embodiment of the invention; 
         FIG. 5  is a rear view of the impeller of  FIG. 4 ; 
         FIG. 6  is a sectional side view of the impeller of  FIGS. 4 and 5 ; 
         FIG. 7  is a front view of an impeller according to a further embodiment of the invention; 
         FIG. 8  is a rear view of the impeller of  FIG. 7 ; 
         FIG. 9  is a sectional side view of the impeller of  FIGS. 7 and 8 ; 
         FIG. 10  is a front view of an impeller according to a further embodiment of the invention; 
         FIG. 11  is a rear view of the impeller of  FIG. 10 ; 
         FIG. 12  is a sectional side view of the impeller of  FIGS. 10 and 11 ; 
         FIG. 13  is a front view of an impeller according to a further embodiment of the invention; 
         FIG. 14  is a rear view of the impeller of  FIG. 13 ; 
         FIG. 15  is a sectional side view of the impeller of  FIGS. 13 and 14 ; 
         FIG. 16  is a front view of an impeller according to a further embodiment of the invention; 
         FIG. 17  is a rear view of the impeller of  FIG. 16 ; 
         FIG. 18  is a sectional side view of the impeller of  FIGS. 16 and 17 . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
       FIGS. 1 to 3  illustrate an impeller for a centrifugal pumps, globally designated by the reference numeral  1 , according to the invention. 
     The example illustrated herein relates to the case in which the impeller  1  is used in a multistage centrifugal pump; however, it is evident to the person skilled in the art that the impeller according to the present invention can also be fitted on pumps of another type. 
     The multistage centrifugal pump, which is per se known and is not shown in the figures, is constituted by a substantially hollow body that accommodates a set of impellers provided according to the present invention, which are coaxially fastened to a transmission shaft that is turned by a motor means. 
     The impeller  1  includes a first disk element  2 , which is functionally arranged towards the inlet, and a second disk element  3 , which is functionally arranged towards the delivery. 
     The diameter of the second disk element  3  is substantially equal to, or slightly smaller than, the diameter of the first disk element  2 . 
     The two disk elements  2  and  3  are coaxial to a rotation axis  1000  and face each other so as to form a substantially cylindrical interspace. 
     Vanes  4  are arranged within the interspace and rigidly connect the first disk element  2  to the second disk element  3 . 
     The vanes  4 , which are angularly distributed around the rotation axis  1000 , extend from the center toward the peripheral region of the two disk elements  2  and  3 , without protruding outward, following an adapted profile. 
     In the illustrated solution, for example, the vanes  4  are curved so as to form ducts that diverge and are arranged radially. 
     Advantageously, the second disk element  3  is fastened to a transmission shaft by means of a fastening means. The transmission shaft, which is not shown in the figures, rotates about the rotation axis  1000 . 
     The fastening means comprises a hub  5 , which can be associated mechanically with the transmission shaft, provided at the center of the second disk element  3 . 
     A through hole  6  is centrally provided on the first disk element  2 , opposite to the hub  5 ; the through hole  6  has a diameter that is larger than that of the transmission shaft. 
     The through hole  6  is connected to a collar  7  that protrudes from the first disk element  2 . 
     In practice, when the impeller  1  is mounted on the transmission shaft, the collar  7  surrounds the shaft, forming an annular opening that constitutes the intake of the impeller. 
     According to the present invention, the impeller  1  includes a series of openings formed in the substantially peripheral region of the second disk element  3 , between pairs of adjacent vanes  4 , in which it is possible to identify the areas of the disk that are subject to the greatest axial thrust. 
     The radially peripheral side of each opening extends for a distance that is shorter than that of the peripheral edge of the second disk element  3 , with respect to the rotation axis  1000 . 
     In other words, the openings are completely included within the profile of the second disk element  3 . 
     In the embodiment shown in  FIGS. 1 to 3 , the openings are constituted by shaped slots  8  provided in the peripheral region of the second disk element  3 , between pairs of adjacent vanes  4 . 
     Each contoured slot  8  has an arc-like profile  9 , at the radially peripheral side; the arc-like profile  9  has a convexity facing the rotation axis  1000 . 
     The arc-like profile  9  is connected with an opposite contoured profile  10 , which, in the example shown in  FIGS. 1 to 3 , has a curved portion, with the convexity facing the rotation axis  1000 . 
       FIGS. 4 to 6  show an impeller, generally designated by the reference numeral  101 , which is similar to the impeller  1  but is provided with contoured profiles  110  with the convexity facing the outside of the second disk element  3 . 
     According to the embodiment shown in  FIGS. 7 to 9 , in which the impeller according to the invention is generally designated by the reference numeral  201 , the arc-like profiles  9  and the contoured profiles  10 , or likewise the contoured profiles  110 , of the contoured slots  8  are joined by one or more radially extended tabs  211  that have the function of stiffening the structure. 
     According to the embodiment illustrated in  FIGS. 10 to 12 , in which the impeller according to the invention is designated by the reference numeral  301 , the openings are constituted by through holes  308  provided in the substantially peripheral region of the second disk element  3 , between pairs of adjacent vanes  4 . 
     In the example shown in  FIGS. 10 to 12 , the centers of the through holes  308  are arranged substantially along an arc of a circumference that is centered on the rotation axis  1000 ; however, it is evident to the person skilled in the art that the through holes might be arranged in other equivalent manners. 
     For example,  FIGS. 13 to 15  show a impeller, designated by the reference numeral  401 , which is similar to the impeller  301  but has through holes  408  that are formed substantially along multiple arcs which are concentric and centered with respect to the rotation axis  1000 . 
       FIGS. 16 to 18  show an impeller, according to the invention, generally designated by the reference numeral  501 , which includes through holes  508  provided in the second disk element  3 , between pairs of adjacent vanes  4 , and arranged substantially along arcs of a circumference the center of which is arranged outside the disk. 
     In the embodiments shown in  FIGS. 4 to 18 , the elements that correspond to the elements that have already been described with reference to the embodiment shown in  FIGS. 1 to 3  have been designated by the same reference numerals. 
     The impeller according to the invention may be manufactured by means of various techniques, by using metallic materials such as, for example, steel, stainless steel, die-cast steel, cast iron, brass, and the like, or other materials provided with the necessary technological characteristics, such as for example some techno-polymers. 
     Also, it should be noted that the details of construction of the contoured slots  8  and/or of the through holes  308 ,  408  or  508  can in any case vary in a substantially equivalent manner in the shape, dimensions, proportions and arrangements, without however abandoning the scope of the inventive concept. 
     As regards the operation of the impeller according to the invention, experimental tests and careful analysis of the results have allowed to observe that the openings provided in the second disk element  3  entail a higher fluid-dynamics efficiency and a good head for an equal reduction of axial thrusts. 
     In practice it has been found that the impeller for centrifugal pumps, according to the invention, fully achieves the intended aim, since it allows to reduce considerably the axial thrusts but at the same time ensure maximum efficiency and head. 
     In fact, by emptying the areas that are subjected to the highest pressure in the second disk element, i.e., by forming the openings, it is possible to reduce the forces that generate the axial thrust. 
     Also, head and efficiency are not reduced because the profile of these openings is fully included within the second disk element. 
     The impeller according to the present invention therefore allows to solve the problems linked to the traction that is usually generated on the transmission shaft of centrifugal pumps with one or more stages. This allows, for example, to avoid damage to the bearings of the motor. 
     The impeller for centrifugal pumps, and the centrifugal pump thus conceived are susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept; all the details may furthermore be replaced with other technically equivalent elements. 
     In practice, the materials used, so long as they are compatible with the specific use, as well as the contingent shapes and dimensions, may be any according to the requirements of the state of the art. 
     This application claims the priority of Italian Patent Application No. VI2015A000081, filed on Mar. 20, 2015, the subject matter of which is incorporated herein by reference.