Abstract:
An improved pump impeller using both spaced disc stack and radial vanes to establish pumping, the vanes separated to form a circumferential array of convergent spaces. The vanes may be of increasing thickness towards their outer ends to create the convergent spaces, or a cover plate may have a sloping inside surface to accomplish the space convergency.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/107,195 filed on Nov. 5, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention concerns pumps and more particularly impellers for non positive displacement pumps. 
     A particular type pump impeller which has long been known is comprised of a stack of spaced apart discs. This type of pump uses a boundary layer effect causing a boundary layer adhesion of the fluid to the disc faces to cause liquid to be pumped upon rotation of the impeller, creating pressure and flow at an outlet in an enclosing pump housing. 
     Another well known impeller configuration has a series of radially extending vanes, which accelerate the fluid by directly acting on the fluid with the faces of the vanes as the impeller rotates. 
     The spaced disc impellers have the advantage of largely eliminating the low pressure regions and cavitation characteristic of vane pumps. Disc impellers also are more efficient in pumping viscous fluids and can pump fluids having entrained abrasives with less impeller wear. 
     On the other hand, the induced flow rate per unit area of the discs is low, and reduced efficiency is encountered in this type of impeller at high flow rates. 
     Turbulence and cavitation can still occur as the fluid exits the outer perimeter of the disc and flows into the volute space in a confining housing. Further, there is a tendency for adhesion of the fluid to the outer perimeter of the discs to create turbulence and thereby reduce the efficiency of the pump. 
     It has been heretofore been proposed to combine a vaned and spaced disc impeller, see U.S. Pat. No. 4,255,081 issued on Mar. 10, 1981 for a “Centrifugal Pump”. 
     This combination is intended to provide most of the advantages of both types of impellers. 
     However, cavitation may still occur of the outer ends of the vanes and turbulence in the regions beyond the impeller perimeter. 
     It is the object of the present invention to provide an improved pump impeller of a hybrid vane-disc type in which the tendency for cavitation is greatly reduced and which operates more efficiently than prior designs. 
     SUMMARY OF THE INVENTION 
     The above recited object and others which will become apparent upon a reading of the following specification and claims are achieved by combining a multiple disc impeller with a series of radial vanes defining intervening flow spaces which are convergent in a direction towards the outer perimeter of the impeller. This convergency has been found to minimize the tendency to cavitate by eliminating regions of low pressure as the fluid flow exits those spaces. 
     The vanes terminate at a relatively steep angle to the outer circumference so that flow is directed substantially radially outward when emerging from the convergent intervening spaces to reduce the adhesion tendencies. 
     The convergency is created in one embodiment by an increasing vane thickness to a maximum at the outer ends, which shape causes a decreasing flow space cross sectional area to a minimum area at the impeller perimeter spaces. In another embodiment, a cover sidewall is tapered to create the convergency of the flow spaces. 
     The disc stack may extend into the vane area, or may be confined within an inner diameter of the impeller. 
     Another improvement is in the scalloping of the outer edge of the discs between the ends of the vanes, which scalloping also contributes to a smooth nonturbulent transitional flow from the impeller perimeter into the pump housing. 
     In one version, the impeller may also have only a single cover plate, to simplify and lower the cost of manufacturing the impeller. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a first embodiment of the hybrid impeller according to the present invention. 
     FIG. 2 is a perspective view of the impeller shown in FIG. 1 with one cover plate removed. 
     FIG. 3 is a perspective view of a second embodiment of the pump impeller according to the present invention. 
     FIG. 4 is a perspective view of a modified form of the second embodiment. 
     FIG. 5 is an end view of the embodiment of FIGS. 1 and 2, with the end plate removed. 
     FIG. 6 is an end view of another form of the impeller of FIG.  1 . 
     FIG. 7 is a view of the section  7 — 7  in FIG.  1 . 
     FIG. 8 is a view of the section  8 — 8  in FIG.  3 . 
     FIG. 9 is an end view with a cover plate removed of the impeller shown in FIG.  3 . 
     FIG. 10 is a sectional view of the impeller of FIG.  10 . 
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims. 
     Referring to FIG. 1, a first embodiment of the hybrid pump impeller  10  is shown, which includes a series of spaced apart annular discs  12  in the inner region adjacent a hub  14  adapted to be fixed on a driving shaft (not shown). A pair of cover pieces  16 A,  16 B overlie each side of the impeller  10 , cover piece  16 A having an opening  18 A aligned with openings  18 B of the discs  12 . The inner areas of the cover pieces  16 A,  16 B also act as a boundary layer discs  12  to establish a radial fluid flow upon rotation of the impeller  10  when fluid is supplied into the area within the diameter  18  defined by discs  14  and cover piece  16 A. 
     Surrounding the outer perimeter of the discs  14  is a circumferential array of curved vanes  20 , extending in a primarily radial direction to intersect the outer perimeter at a steep angle rather than to be curved into tangentially. 
     Each of the vanes  20  is tapered so as to be of increasing thickness, measured in a circumferential direction, along its length in a radially outward direction (see FIG.  7 ). The inversely tapered shape of the vanes  20  creates convergent flow spaces  22  receiving the fluid flow created by rotation of the discs  14 . 
     The radially extending concave surfaces  24  of the vanes  20  creates a pumping action due to the reaction of the fluid against the surfaces in the well known manner. 
     It has been found that the convergent space vane pumping action combined with the multiple disc pumping action produces a highly efficient high capacity pumping action having the advantages of both types of pump. 
     The convergency of the spaces has been found to minimize any tendencies for cavitation which otherwise would be present. 
     The vanes  20  extend at a steep angle to the outer perimeter, so that the spaces direct the fluid flow primarily radially outward when the fluid exits the spaces, efficiently directing the flow out into the volute space in the pump housing (not shown). 
     The impeller  10  can advantageously be molded from a suitable plastic material to reduce cost, weight and increase corrosion resistance. A suitable type of plastic is polyphenlene sulfide. 
     In this embodiment the multidisc and vane impeller stages are in series, with the vanes  20  arranged around the outer perimeter of the discs  14 . 
     It is also possible to extend the pumping discs radially outwardly into the vane area. 
     This is incorporated in the second embodiment shown in FIGS. 3,  8  and  9 . In this impeller  24 , the annular discs  26  extend radially out from the inner diameter  28  to the outside perimeter of the impeller  24 , as do cover discs  30 ,  32 . The cover disc  32  has a hub  34  for attachment to a driving shaft (not shown), while cover disc  30  has an inner opening  35  aligned with the inner diameter  28  of the annular discs  26 , fluid entering the opening  38  created by the annular shape of discs  26  and cover  30 . 
     A series of aligned arrays of vane  40  extend through the spaces between each of the discs  26  and covers  30 ,  32 . The curved shape vanes  40  extend radially to the outer perimeter of the impeller  24 . 
     The vanes  40  are tapered to increase in width towards their outer ends, creating intervening  42  spaces  42  which are of decreasing cross-sectional area along the radial direction to achieve the advantages described above. 
     Both vane and boundary layer pumping action occurs through the spaces  42 . 
     A further improvement is shown in FIG. 4, where a series of scallops  44  are formed in the outermost perimeter of the covers  30 A,  32 A, and discs  26 A aligned with opening  42  and in between the outer ends of the vanes  40 . This has been found to reduce adhesion of the fluid and to aid in causing the pumped fluid to more readily escape the perimeter of the impeller  24 A. 
     FIGS. 6 and 11 show another form of the impeller of FIG. 1, in which untapered vanes  20 A are provided. In this configuration, the spaces  22  are converged by a sloping side wall  52  defined the inside surface of the cover  50 . 
     Accordingly, an improved pump impeller is provided for obtaining a high efficiency pumping action and with the other advantages described.