Patent Publication Number: US-6220819-B1

Title: Centrifugal pump impeller

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a centrifugal pump impeller and particularly to an impeller that can prevent turbulence at the inlet of the pump for improving pumping efficiency and enables accurate positioning of the vane for the impeller. 
     2. Description of the Prior Art 
     In the design and fabrication of impeller for centrifugal pump, how to improve pumping efficiency of the vane and to make positioning of the vane simple in the assembly are some of the heavily focused issues. The surface smoothness at the inlet of the impeller may directly affect flow streamline in the passage and pumping efficiency. To avoid forming abrupt surface change at the impeller inlet is one of the key design consideration. As an impeller usually has at least six blades and each blade is formed in an irregular spiral shape, to accurately position the blades for assembling the vane is not easy. When the blades are not accurately-positioned, the pumping efficiency will be negatively impacted. 
     Furthermore conventional rear vane cover plate of the pump usually is made by pressing. The cover plate has relatively large size and may result in lower structural strength. It also tends to form corrugation (with rough surface). This phenomenon happens most often to an impeller (or pump) with smaller specific speed. Conventional technique uses increased vane cover plate thickness to enhance strength and employs high cost machining work to further improve cover plate precision. It increases cost and drags down fabrication efficiency. 
     Some improvement techniques have been announced to address these issues. U.S. Pat. No. 5,082,425 discloses a technique that forms a plurality of corrugation structure on the vane cover plate mating with the vane base to facilitate the blade positioning in the impeller. The corrugation structure needs elaborated design and high precision machining, and also needs accurate soldering work to put the blades in place. The design and fabrication are expensive. Moreover the vanes at the inlet side still cannot totally align with the front end of the hub and suction port. As a result, a not smooth surface will be formed for the vane around the hub and suction port at the inlet area. Flowing fluid easily produces turbulence at this area and greatly impact pumping efficiency. 
     German Pat. No. DE 44 46 193 C2 discloses another impeller structure that has a plurality of thin spiral vanes soldering to the front and rear vane cover plate by means of laser soldering operation. It may improve surface smoothness of the vane at the inlet and reduce turbulence. However laser soldering operation costs higher, and the blade positioning problem remains unresolved. 
     SUMMARY OF THE INVENTION 
     In view of aforesaid disadvantages, it is therefore an object of this invention to provide a centrifugal pump impeller that has smooth surface at the inlet for reducing turbulence and enhancing pumping efficiency. It has simpler structure and costs lower to produce. The vane may be accurately positioned easily. 
     The pump impeller according to this invention includes a hub, a rear cover plate engaged with the hub, a front cover plate having an inlet and a plurality of vanes. Each vane has a front blade engaged with the front cover plate, a rear blade engaged with the rear cover plate and a blade bridges the front and rear blades. The vanes are located between the front and rear cover plates to form a plurality of spiral pumping passages. The impeller has the following characteristics: 
     The front blade adjacent the inlet has an indent section which does not extends out of cover plate at the inlet circumference. During pumping operation, fluid may flow into the impeller through the inlet smoothly without producing resistant flow. 
     The rear blade adjacent the pump spindle has a curved front edge mating closely with the impeller rim for initial positioning use. It also helps to make the vane passage smooth at the inlet around the hub for preventing turbulence. The rear blade has a vane balance hole formed at a front end close to the curved edge mating with a balance hole formed in the rear cover plate. The rear blade further has a positioning hole formed at a rear end thereof. Through these features, the vane may be accurately and easily positioned between the front and rear cover plates. It costs lower and is easier to fabricate and assemble. 
     In one aspect of this invention, the curved front edge of the rear blade further has a radial cutting edge located at a side remote from the blade. During vane positioning, the cutting edge is extending radially along the spindle. The front tip of the curved front edge of a rear vane (which has a radial cutting angle) may be close to the radial cutting edge of a front vane for preventing turbulence. 
     In another aspect, the rear cover plate has an outer fold rim formed by pressing that may enhance structural strength with greater precision and avoid the formation of corrugation at the outer rim of the rear cover plate. 
     It still another aspect, there is a rear sealing ring engaged between the rear cover plate and the impeller. The rear sealing ring has a ring balance hole mating against the rear cover plate balance hole. The rear sealing ring further has teeth-shaped inner ring formed by pressing for engaging with the hub for enhancing the axial alignment and bonding accuracy of the rear sealing ring with he spindle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This invention, as well as its many advantages, may be further understood by the following detailed description drawings in which: 
     FIG. 1 is a perspective view of a centrifugal pump impeller of this invention. 
     FIG. 2 is a sectional view of the impeller shown in FIG.  1 . 
     FIG. 3 is a top view of the impeller shown in FIG.  1 . 
     FIG. 4 is a top view of a vane of this invention. 
     FIG. 5 is a perspective view of a vane shown in FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1,  2  and  3 , the impeller  1  according to this invention may be housed in a pump casing (also not shown in the figures) for pumping fluid. The impeller  1  includes a hub  10 , a rear cover plate  30 , a rear sealing ring  20 , a front cover plate  40  and a plurality of vanes  50 . At the front end of the front cover plate  40 , there is an inlet  41 . The rear cover plate  30 , rear sealing ring  20 , front cover plate  40  and the vanes  50  are preferably made by pressing, or by casting or CNC machining. After the components are made, they are bonded together by soldering or adhering to form the impeller. 
     The impeller has a shaft hole  11  which may be fixedly engaged with the spindle (not shown in the figures) by means of a key (also not shown) and may be driven to rotate by the spindle. 
     The rear cover plate  30  is engaged with the hub  10  and has a plurality of balance holes  31  formed therein at selected locations to balance the fluid pressure between the front and rear sides (i.e., left and right side in FIG.  2 ). At the outer rim of the rear cover plate  30 , an outer fold rim  32  is formed by pressing to avoid the corrugation taking place at the outer rim and to enhance structural strength and dimensional precision. The pressing takes two process steps. The first step pressing is to form the rear cover plate  32  without the outer fold rim  32 . The second step pressing is to form the outer fold rim  32 . By the same taken, the front cover rim  40  may also be formed with an outer fold rim, although it is not shown in FIG.  2 . 
     The rear sealing ring  20  is mounted on the hub  10  and behind the rear cover plate  30 . It may have a teeth shaped inner ring  21  (shown in FIG. 6) to facilitate engagement with the hub  10 . The rear sealing ring  20  may also have a plurality of ring balance holes  22  mating against the rear cover plate holes  31  to enable fluid to pass through. The rear sealing ring  20  also may be made by two step pressing (with the first step pressing to form the main body, and the second step pressing to form the teeth structure in the inner ring  21 ). It thus may get accurate dimension to make precise positioning with the hub  10 . The teeth structure in the inner ring  21  helps to make precise axial alignment of the rear sealing ring  20  with the spindle. It also helps to maintain radial vertical alignment of the vane outlet against the spindle. As a result, it helps to improve pumping efficiency. The vane is located between the front and rear cover plate  40  and  30  and forms a plurality of spiral fluid passages in the space between the cover plates  40  and  30 . Each vane has a front blade  51  engaged with the front cover plate  40 , a rear blade  52  engaged with the rear cover plate  30  and a blade  53  bridges the front and rear blades  51  and  52  to become a Z shape (or reverse Z shape) structure. 
     Referring to FIGS. 4 and 5, the rear blade  52  has a curved front edge  521  and a radial cutting edge  523 . The curved front edge  521  is generally mating the hub  10  surface and has a length to equally divide the hub  10  surface according to the number of the vane  50  (e.g., taking vane number for six, the length of the curved front edge  521  may cover the hub  10  surface at about sixty degree angle). Such a structure may be used for initial positioning and may make the impeller inlet have smooth plane around the hub  10  to prevent turbulence. At the curved front edge  521 , there is further a vane balance hole  524  mating against the balance hole  31  in the rear cover plate  30 . The rear blade  52  remote from the curved front edge  521  has a positioning hole  522 . By means of the curved front edge  521  and the vane balance hole  524 , the vane  52  may be positioned between the front and rear cover plate  40  and  30  accurately and easily. 
     For assembly the vane  50  and the rear cover plate  30 , the vane balance hole  524  shall be aligned with the balance hole  31  (or by means of a pin, which is not shown in the figure, running through the positioning hole  522  and the vane balance hole  524 ). Then both sides of the vane  50  may be accurately positioned for the vane  50  to engage with the rear cover plate  30 . The engagement work is simple and low cost. 
     The curved front edge  521  adjacent the blade front edge  531  of the blade  53  further has a radial cutting angle (unmarked). The radial cutting edge  523  is located at the curved front edge remote from the blade front edge  531 . When the vanes  50  are positioned between the front and rear cover plate  40  and  30 , the radial cutting angle of a rear vane may be closed to the cutting edge  523  of a front vane (as shown in FIG.  3 ). Such structure and arrangement may prevent interference and also make the vane inlet (i.e., the two ends of the blade front edge  531 ) have smooth plane around the spindle, and may prevent turbulence from happening. 
     Because of the presence of the vane balance hole  524 , positioning hole  522 , and the positioning features of the curved front edge  521  set forth above, the positioning and assembly of the vane  50  may be made easily with great accuracy. The component (such as the rear cover plate) structure becomes simpler. It thus may effectively overcome the problems existing in the conventional centrifugal pump impeller. 
     Furthermore, the front blade  51  adjacent the blade front edge  531  (or inlet  41 ) may have an indent section  511  which enables the front blade  51  not protruding out of the front cover plate  40  at the inlet  41 . The juncture of the blade front edge  531  and the front cover plate  40  thus may form a smooth plane which allows fluid to flow smoothly through the inlet  41  into the impeller when the impeller is rotating for pumping. Turbulence and flow resistance may be greatly reduced. FIG. 4 shows the location and size of the indent section  511 . It is preferably formed by two radial lines centered at the spindle and with an α angle of 10-30 degree. 
     In summary, the components of the impeller of this invention are simply shaped and designed. The forming of the vane balance hole  524 , positioning hole  522 , curved front edge  521  and radial cutting edge  523  make positioning and assembly of the vane  50  accurate and simple, and may greatly reduce turbulence. Fabrication is easy and low cost. The structure of indent section  511 , curved front edge  521  and radial cutting edge  523  make the engagement juncture between the blade front edge  531  and the front cover plate  40  and the hub  10  front end smooth and may prevent turbulence and enhance pumping efficiency. 
     It may thus been seen that the objects of the present invention set forth herein, as well as those made apparent from the foregoing description, are efficiently attained. While the preferred embodiment of the invention has been set forth for purpose of disclosure, modifications of the disclosed embodiment of the invention as well as other embodiments thereof may occur to those skill in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.