Abstract:
An impeller for a self-primer pump is structured for attachment to the terminal end of a drive shaft by means of a bolt that is configured to provide a low profile such that the eye of the impeller is rendered capable of processing larger solids that are entrained in fluid.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a non-provisional application claiming priority to provisional patent application Ser. No. 60/707,088 filed Aug. 10, 2005. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates to self-priming centrifugal pumps which are used to process fluids containing solids. Specifically, this invention relates to providing an impeller bolt that has a low profile to thereby accommodate processing of fluids with larger solids entrained in the fluid.  
         [0004]     2. Description of Related Art  
         [0005]     Self-priming centrifugal pumps are well-known and frequently used in industries where processing fluids with entrained solids is required. Self-primer pumps, also known as trash pumps, are characterized as having a casing which houses a suction chamber and a separation chamber divided by a wall or plenum. An impeller positioned in a volute section of the pump receives fluid from the suction chamber and delivers it by centrifugal action into the separation chamber where it is eventually expelled through an outlet.  
         [0006]     Self-primer pumps are further characterized in the industry by the size of solids that can be processed by the pump. Self-primer, or trash, pumps are often rated by the size of solids that can be processed by the pump. Thus, a pump with a given diameter size of, for example, three inches may be rated as capable of processing solids up to two and one half inches in diameter while four to ten inch pumps may be rated as able to process solids up to three inches in diameter. However, it has been shown that the size or diameter of solids that are reported to be processable by a pump are actually not able to be processed. This is due in large part to the structure of the impeller, and principally to the bolt configuration at the eye of the impeller.  
         [0007]     Prior art impellers in self-primer pumps are attached to the end of a drive shaft by means of a screw that is spaced from the impeller by a washer that is conically-shaped. Consequently, the head of the screw and the washer/spacer extend outwardly from the impeller and into the space between the vanes. As a result, larger sized solids can become trapped or lodged between the head of the screw and the wear plate that is positioned adjacent the impeller on the suction side of the pump. Solids lodged between the impeller and wear plate can cause the impeller to slow or stop in its rotation and/or can impede the flow of fluid through the pump, thereby leading to reduced pumping efficiency, or even pump failure.  
         [0008]     Thus, it would be advantageous to provide an impeller design in a self-primer pump that enables the processing of larger solids so that pump efficiencies and operation are not compromised.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     In accordance with the present invention, the impeller of a self-primer pump is structured for attachment to the terminal end of a drive shaft by means of a bolt that is configured to provide a low profile such that the eye of the impeller is rendered capable of processing larger solids that are entrained in fluid. The bolt is also configured to eliminate the additional washer/spacer of prior art impellers, thereby reducing the cost of the pump and its repair or maintenance.  
         [0010]     As previously noted, devices used in the prior art of centrifugal pumps to attach an impeller to the terminal end of a drive shaft typically comprise screws and washers that have a configuration which results in the screw and washer extending into the eye of the impeller. Such devices may be said to have a “high-profile” because they extend a distance into the eye of the impeller.  
         [0011]     The present invention comprises a bolt for attaching the impeller to the terminal end of the drive shaft which is configured with a low-profile; that is, the bolt does not extend appreciably above the surface of the impeller and into the eye of the impeller. As a result, the impeller arrangement of the present invention allows the pump to process large-sized solids (e.g., three inches in diameter or larger) without having the solids become lodged between the impeller bolt and the wear plate.  
         [0012]     The low-profile impeller bolt is generally formed with a unitarily formed shaft and head that eliminates the separate washer or spacer of prior art bolts. The head of the bolt of the present invention is substantially flattened in profile, thereby limiting the distance that the bolt extends into the eye of the impeller. As a result, larger solids that may be processed by the pump do not become lodged between the impeller and the wear plate of the pump. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0013]     In the drawings, which illustrate what is currently considered to be the best mode for carrying out the invention:  
         [0014]      FIG. 1  is an exploded view of a prior art impeller and drive shaft illustrating conventional means for attachment of the impeller to the drive shaft;  
         [0015]      FIG. 2  is a view in cross section of a portion of a centrifugal pump of the prior art illustrating the positioning of the impeller to the pump inlet;  
         [0016]      FIG. 3  is an exploded view of an impeller illustrating the low-profile impeller bolt of the present invention; and  
         [0017]      FIG. 4  is a view in cross section of a portion of a centrifugal pump illustrating the low-profile impeller bolt of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     A typical impeller arrangement of the prior art is shown in  FIGS. 1 and 2  as a comparative illustration of the problem solved by the present invention. In  FIG. 1 , which illustrates an exploded view of an impeller  10 , drive shaft  12  and means  14  for attaching the impeller  10  to the drive shaft  12 , the means  14  for attachment comprises a standard socket head cap screw  18  and a washer  20 . As seen in  FIGS. 1 and 2 , the screw  18  fits through the washer  20  and through the central opening  22  in the impeller  10  to threadingly engage the terminal end  24  of the drive shaft  12 .  
         [0019]     The washer  20  typically used in prior art impeller attachment is conically-shaped. As best illustrated in  FIG. 2 , when the washer  20  is secured in place by the screw  18 , the washer  20  is positioned against the surface of the base or shroud  26  of the impeller  10 . The washer  20  consequently provides a spacer  28  between the screw  18  and the shroud  26  of the impeller  10 . So configured, the screw  18  and washer  20  of the prior art impeller  10  extend considerably away from the shroud  26  and into the eye  29  of the impeller  10 . Larger sized solids  30  may then become trapped or lodged between the means for securing the impeller  14  and the wear plate  32 , which is positioned adjacent the impeller  10 , as depicted in  FIG. 2 .  
         [0020]     In the impeller  40  of the present invention, shown in  FIGS. 3 and 4 , the means for securing the impeller  40  to the drive shaft  12  comprises a unitarily formed bolt  42  comprising a shaft portion  44  and a combined head and washer portion  46  having a low, or considerably flattened profile. The impeller  40  is formed with a central opening  48  through the back shroud  50  of the impeller  40  through which the shaft  44  of the bolt  42  is positioned to threadingly engage the terminal end  24  of the drive shaft  12 .  
         [0021]     As best seen in  FIG. 4 , the bolt  42  of the present invention presents a low-profile such that the head  46  of the bolt  42  does not extend appreciably above the surface of the impeller and into the eye  29  of the impeller  40 . The distance that the bolt  42  of the present invention may extend above the surface of the impeller  40  may range from about one sixteenth of an inch to about one half inch. Consequently, the low-profile of the bolt  42  enables larger size solids  30  to enter into the eye  29  of the impeller  40  without becoming trapped or lodged between the impeller  40  and the wear plate  32 . This results in improved pump operation.  
         [0022]     In the embodiment of the impeller  40  shown in  FIG. 4 , the impeller  40  may be formed with a recessed land  52  surrounding the central opening  48  which is sized in diameter to accommodate the head  46  of the bolt  42  within the recessed land  52 . The head  46  of the bolt  42  is thereby recessed into the surface of the shroud  50  lessening even more the potential impedance of the bolt  42  on solids  30  passing through the eye of the impeller  40 . In such an embodiment, the bolt  42  may extend into the eye of the impeller  40  about, for example, one eighth of an inch. Alternatively, however, the impeller  50  may be formed without a recess such that the rear surface  56  of the head  46  of the bolt  42  is flush with the surface of the shroud  50 , while still maintaining a low-profile.  
         [0023]     The bolt  42  of the present invention may be structured with any suitable means for securing the bolt  42  in position against the impeller  40  as described, but is illustrated in  FIGS. 3 and 4  as having a tool-receiving socket  54  for enabling securing and tightening of the bolt  42  to the drive shaft  12 .  
         [0024]     The low-profile impeller bolt of the present invention may be configured in a variety of ways to provide a low profile relative to the eye of the impeller. For example, the distance that the head of the bolt extends above the back shroud of the impeller may vary. Additionally, the circumferential shape or geometry of the head of the bolt may vary widely, especially if the head of the bolt is configured to be flush with the surface of the back shroud. Thus, reference herein to particular details or configurations of the low-profile impeller bolt of the present invention are by way of example, and not by way of limitation.