Patent Publication Number: US-10330110-B2

Title: Pump impeller

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a National Stage of International Application No. PCT/EP2010/065045 filed Oct. 7, 2010, and which claims the benefit of Swedish Patent Application No. 0901289-9 filed Oct. 8, 2009, the disclosures of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     This invention relates to a pump impeller, and in particular to a pump impeller whose design significantly reduces clogging of the impeller by rags or other fibrous material entrained in the fluid being pumped, and which impeller is adapted to actively clear such contaminants from the impeller. 
     BACKGROUND OF THE INVENTION 
     Impellers are used in many different applications, one of the most demanding of which is in submersible pumps used for pumping sewage or other liquids having a solid content comprising rags or other material contaminants. These rags have a tendency to wrap themselves around the impeller, degrading the performance and ultimately clogging the pump. The pump must then be shut down and retrieved for repair, resulting in significant down time. The main clogging issue results from the rags becoming wrapped around or doubled over on the leading edge of the impeller vane, which both reduces the pumping performance of the vane, and leads to increased rag retention by the impeller. 
     There are also other clogging issues when using impellers for pumping liquids having rag or other solid content. For example the interior volume defined by the impeller vane may develop areas of low fluid circulation or even stagnation, within which pockets solids may gather, posing a further risk of clogging. 
     It is therefore an object of the present invention to provided a pump impeller which reduces or eliminates the above problems. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention there is provided a pump impeller for use in combination with a wear plate, the impeller comprising a single impeller vane defining an interior space through which fluid is displaced, the impeller vane having a leading edge, a trailing edge and an upper rim for location, in use, adjacent the wear plate; and a shroud from which the vane projects; wherein the leading edge is profiled to actively displace solid material entering the impeller in a direction away from the wear plate. 
     In an embodiment of the invention the leading edge is substantially concave in profile. 
     In an embodiment of the invention the leading edge defines a tip at the upper rim and a root at the shroud, the leading edge curving inwardly from both the tip and the root. 
     In an embodiment of the invention the leading edge defines an acute angle with both the shroud and the upper rim. 
     In an embodiment of the invention the leading edge increases in thickness from the tip to the root. 
     In an embodiment of the invention the impeller vane comprises a sloping inner wall. 
     In an embodiment of the invention at least a portion of the inner wall slopes radially outward from the shroud towards the upper rim. 
     In an embodiment of the invention at least a portion of the inner wall slopes axially upward from the shroud towards the upper rim. 
     In an embodiment of the invention the pump impeller comprises a relief hole extending through the impeller vane from an underside thereof to the interior space defined by the impeller vane. 
     In an embodiment of the invention the relief hole is positioned to issue, in use, a jet of fluid into the interior space defined by the impeller such as to improve circulation within the interior space. 
     In an embodiment of the invention the pump impeller comprises a cavity formed in the impeller in order to achieve dynamic balance during use. 
     In an embodiment of the invention the relief hole extends from the cavity, through the impeller vane, to the interior space. 
     In an embodiment of the invention the pump impeller comprises an annular wavy profile on an underside of the shroud. 
     In an embodiment of the invention the trailing edge overhangs the shroud. 
     In an embodiment of the invention the trailing edge is tapered. 
     According to a second aspect of the invention there is provided a pump comprising an impeller according to the first aspect of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a perspective view of a pump impeller according to an embodiment of the present invention; 
         FIG. 2  illustrates a sectioned elevation of the impeller shown in  FIG. 1 ; 
         FIG. 3  illustrates a sectioned view of a leading edge of an impeller vane forming part of the impeller of  FIGS. 1 and 2 ; 
         FIG. 4  illustrates the radial profile of the leading edge of the impeller vane, at various heights through the impeller; and 
         FIG. 5  illustrates an enlarged view of the trailing edge of the impeller vane. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring now to the accompanying drawings there is illustrated a pump impeller, generally indicated as  10 , for use within a submersible pump (not shown) or the like and for pumping liquids, in particular liquids having a solid content such as rags or other material which is known to cause clogging of pumps. 
     The impeller  10  comprises an impeller vane  12  which projects upwardly from, and is preferably formed integrally with a circular shroud  14 . In the embodiment illustrates the entire impeller  10  is cast of metal, for example cast iron, although any other suitable material may be employed. The vane  12  comprises a leading edge  16  and a trailing edge  18  located radially outwardly from the leading edge  16 . The trailing edge  18  preferably overhangs the shroud  14 , the reasons for which are set out hereinafter. 
     The vane  12  further comprises an upper rim  20  which, in use, is located in close proximity to a wear plate  37  forming part of the pump, which arrangement is well known in the art of impeller based pumps. The wear plate  37  will normally have a central opening therein which forms the inlet through which fluid is drawn into the impeller  10 , and which is then discharged from the impeller  10  through the channel defined between the leading edge  16  and the trailing edge  18 . The wear plate  37  essentially forms a cover about the upper rim  20 , such that in use the vane  12  is encapsulated between the wear plate and the shroud  14 , thereby allowing the vane  12  to build up a pressure head in order to be capable of pumping liquids. For this reason the gap between the wear plate  37  and the upper rim  20  should be kept to a minimum. This does however present problems during operation, one of which is the issue of rags or other solids becoming trapped or lodged between the wear plate  37  and the upper rim  20 . 
     The impeller vane  12  includes an inner wall  22  and an outer wall  24 , the inner wall  22  having a sloping profile such as to define a path through the impeller  10  which extends helically downward from the upper rim  20  to the shroud  14 . Referring in particular to  FIG. 2  it can be seen that providing this helical path through the impeller  10  from the inlet to the outlet requires significant portions of infill directly above the shroud  14 . This eliminates dead space within the impeller  10  which can give rise to clogging, in particular where solids such as rags or the like are being pumped with the fluid, for example in the case of sewage. This is achieved by sloping the inner wall  22  radially inwardly from the upper rim  20 , in particular in the region adjacent the leading edge  16 , with the slope of the inner wall  22  reducing towards the trailing edge  18 , such that the inner wall  22  in the region of the trailing edge  18  is substantially vertical. Thus the thickness of the vane  12  increases in the axial direction from the upper rim  20  downward towards the shroud  14 , and again this increase in thickness is more pronounced in the region of the leading edge  16 . In this way, as the leading edge extends down from the upper rim  20  to the shroud  14  it opens out into the flow of fluid through the impeller  10 . 
     Referring now in particular to  FIGS. 3 and 4 , it can be seen that the leading edge  16 , in particular when viewed in profile, is substantially concave in shape. The leading edge  16  extends rearwardly into the vane  12  from a root  26  at the shroud  14 , before curving back outwardly towards a tip  28  at the upper rim  20 . Thus the leading edge  16  can be said to curve inwardly, with respect to the vane  12 , at both the root  26  and at the tip  28 . Referring to  FIG. 3  it can be seen that this results in the leading edge  16  defining an acute angle β h  with the upper surface of the shroud  14  at the root  26  and an acute angle β t  with the upper rim  20  at the tip  28 . The leading edge  16  preferably has a smooth radius of curvature r between the root  26  and the tip  28 , in order to prevent snagging of rags or other solids. 
     This concave profiling of the leading edge  16  has the effect, in use, of causing any rags or other solids which wrap themselves around the leading edge  16  to be forced downwardly away from the upper rim  20  and associated wear plate  37  between which such rags may otherwise become trapped, eventually leading to clogging of the impeller  10 . As the rags move down along the trailing edge  18  towards the shroud  14  they are moving in to an area of a greater radial flow of fluid out of the impeller  10 , and thus become re-entrained in the fluid flow and leave the leading edge  16  free of clogging. In addition, as the leading edge increases in thickness from the tip  28  to the root  26 , as a rag is drawn along the leading edge  16  towards the root  26  it will be opened out to become less doubled over around the leading edge  16 . This will reduce the adherence of the rag to the leading edge  16 , allowing it to peel off the leading edge  16  and exit the impeller  10  in the flow of fluid. This increase in thickness can be clearly seen from  FIG. 4 , showing the radial profile of the leading edge  16  at various heights through the impeller  10 . 
     The use of the profiled leading edge  16  not only ensures that rags or other solids do not accumulate on the leading edge  16 , which would reduce the performance of the impeller  10 , but also ensure that such rags do not become trapped between the upper rim  20  and the wear plate  37 , which increases friction between the impeller  10  and the ware plate, thus reducing the performance of the associated pump (not shown), and also increase wear on the wear plate, leading to greater losses in the pump. The profile of the leading edge  16  ensures that rags which initially enter the impeller  10  and adhere to the leading edge  16  are immediately pushed down along the leading edge  16  in order to prevent such rags from lodging between the upper rim  20  and the wear plate  37 . Then as the thickness of the leading edge  16  increases from the tip  28  to the root  26  the rags will be released from around the leading edge  16 . 
     In order to further improve the anti-clogging functionality of the impeller  10 , a relief hole  30  is provided in the impeller vane  12 , and extends from a balancing cavity  32  which is open to the underside of the impeller  10 , through to the interior space defined within the vane  12 . The balancing cavity  32  is provided in order to reduce the mass of the impeller  10  on the heavier side thereof, in order to achieve dynamic balance of the impeller  10  during use. This is necessary due to the significant infill used to achieve the sloping helical path through the impeller  10 . 
     In use, the underside of the impeller  10 , in which the balancing cavity  32  is formed, is at a greater pressure than the interior space defined within the vane  12 . This pressure differential results, in use, in a jet of fluid issuing from the relief hole  30  into the space defined within vane  12 . This jet of fluid helps to increase the circulation of fluid within the vane  12  in order to further reduce the possibility of clogging. The relief hole  32  may be positioned and/or dimensioned such as to direct the jet of fluid towards a particular region of the space defined by the vane  12  in order to target areas in which clogging is more likely to occur. 
     The relief hole  30  also facilitates a reduction in the pressure difference between the high and low pressure sides of the impeller  10 , thus reducing pressure and therefore wear on the bearings etc, and so increasing the performance and/or longevity of the pump (not shown) of which the impeller  10  is a part. On this point it can be seen from  FIG. 2  that the impeller  10  comprises a central bore  34  into which, in use, the main shaft of the pump (not shown) is located and terminates, allowing the impeller  10  to be bolted thereto. The shroud  14  is also provided an annular wavy profile  36  of known form, which protect the mechanical seals within the pump during operation. 
     Finally, referring to  FIG. 5 , the trailing edge  18  is shown in detail. As mentioned above, it is preferable that the trailing edge  18  overhangs the shroud  14 , which allows the shroud  14  to be relatively smaller in diameter for a given diameter of vane  12 . As a result of the smaller diameter of the shroud  14 , the impeller  10  will have lower power consumption for a given pumping capacity. The trailing edge  18  is also preferably tapered in order to reduce turbulence and losses. 
     The impeller  10  of the present invention therefore provides improved anti-clogging performance through the use of a specially profiled leading edge  16 , in addition to the relief hole  30 , which together actively reduce clogging when pumping fluids having a solid content, in particular in the form of rags.