Abstract:
An impeller assembly includes an impeller ( 10 ), the impeller ( 10 ) having a pair of plate means ( 12, 14 ) adapted for individual connection to a drive shaft for rotation by the drive shaft about an axis and vane means ( 15 ) disposed intermediate the pair of plate means ( 12, 14 ) and adapted for rotation with the pair of plate means ( 12, 14 ). The impeller assembly further includes means for applying force parallel to the axis of the impeller ( 10 ) to the impeller ( 10 ) so as to clamp the pair of plate means ( 12, 14 ) and intermediate vane means ( 15 ) together.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to impeller assemblies that are commonly used in pumps for liquids. In particular, this invention relates to the assembly of impeller components.  
         BACKGROUND OF THE INVENTION  
         [0002]    Impeller assemblies typically include an impeller housing which is mounted on or operably connected with a central drive shaft. Attached to the shaft, within the housing, is an impeller. The impeller typically includes upper and lower cover plates and, in applications where the impeller is manufactured from pressed metal components, a vane plate located between the respective cover plates. Alternatively, the vanes of the impeller may be formed integrally with one or both cover plates. Fluid to be pumped is introduced into the impeller housing at one side thereof. The shaft rotates so as to rotate the impeller assembly thereby creating regions of high and low fluid pressure within the impeller housing and impelling fluid through the assembly.  
           [0003]    Depending on the application of the pump, a pump can be a single-stage model i.e. having one impeller assembly, or a multi-stage model i.e. having a number of impeller assemblies in series on the same shaft passing through each of the impeller housings.  
           [0004]    Typically, the lower cover plate of the impeller assembly incudes a central boss, formed integrally with the cover plate. The central boss defines an aperture and receives the drive shaft of the impeller assembly. The boss is typically keyed to the drive shaft so that the drive shaft directly drives the lower cover plate. The vane plate and upper cover plate have central apertures, considerably larger than the drive shaft and are located over the boss of the lower plate. The vane plate and upper cover plate are fastened to the lower cover plate e.g by welding at the vanes, gluing, or riveting. As such, the load of the entire impeller is carried by the lower cover plate as it is rotated by the drive shaft.  
           [0005]    This distribution of load can lead to several problems when the impeller is in operation, particularly during acceleration/deceleration which may be experienced during start up or engine braking or may be due to the introduction of a foreign object into the pump housing. Because the lower cover plate only is being driven, the inertial loads of the entire impeller are transmitted to the drive feature of the lower cover plate. This plate must be accordingly stronger to resist these loads, which typically leads to a heavier, more expensive, drive feature requirement.  
           [0006]    In the case of a laminated, pressed metal impeller, the lower plate is typically manufactured from thicker gauge material to compensate for the extra loading. In a diecast impeller, extra thickness is added locally around the drive.  
           [0007]    Manufacture of an impeller assembly in this manner is time consuming and labour intensive, requiring, in the case of welding, numerous spot welds between the lower cover plate and the vane plate, and between the vane plate and the upper cover plate. The plates must be securely fixed together so as to prevent slippage and fluid flow between the plates.  
           [0008]    In the case of plastic impellers, welding can introduce variation in the axial length of the impeller assembly. With too much welding, this length is reduced, leading to a reduction in the impeller flow output. With insufficient welding, the impeller axial length will be increased, potentially leading to overloading of the drive motor.  
           [0009]    Mechanical fastening, in the form of riveting can lead to failure due to fretting and is also known to lead to corrosion problems, as materials are more prone to stress induced corrosion after riveting.  
           [0010]    Permanent fastening of the impeller components also prevents easy dismantling and replacement of individual components in the assembly if they become worn or faulty.  
           [0011]    The above disadvantages are of course amplified when the pump is a multi-stage model. In particular, variation in the axial length of individual assemblies is multiplied, leading to fitment problems on mating seal components, in addition to the performance variation described previously.  
           [0012]    It is therefore an object of the invention to provide an impeller assembly that at least in part alleviates one or more of the above disadvantages.  
         SUMMARY OF THE INVENTION  
         [0013]    The invention accordingly provides an impeller assembly including:  
           [0014]    an impeller, the impeller including:  
           [0015]    a pair of plate means adapted for individual connection to a drive shaft for rotation by the drive shaft about an axis; and  
           [0016]    vane means disposed intermediate the pair of plate means and adapted for rotation with said pair of plate means;  
           [0017]    wherein the impeller assembly further includes means for applying force parallel to the axis of the impeller to the impeller so as to clamp the pair of plate means and intermediate vane means together.  
           [0018]    Advantageously, the pair of plate means define upper and lower cover plates of the impeller. Each of the upper and lower cover plates and the vane means preferably include a central aperture adapted to receive the drive shaft. The respective central apertures are preferably keyed to the shaft such that each impeller component is separately driven by the drive shaft. The central apertures, and a corresponding portion of the exterior surface of the drive shaft, may be formed with pair of opposed flats, or may be octagonal or hexagonal, for example.  
           [0019]    Advantageously, the vane means define fluid flow paths and are located intermediate the upper and lower cover plates. One or both of the pair of plate means may incorporate the vane means. Preferably, the vane means are formed integrally with the lower cover plate. Alternatively, the vane means may be a separate vane plate which is disposed between the upper and lower cover plates.  
           [0020]    Preferably, the drive shaft includes a portion larger in diameter than the keyed portion of the shaft thereby defining a step. When the impeller is assembled, the lower cover plate advantageously sits adjacent and is pressed against the step of the shaft.  
           [0021]    The impeller assembly preferably further includes a generally cylindrical spacer means. One end of the spacer means if preferably received within a central portion of the upper cover plate. The end of the spacer not received by the upper cover plate serves as a support for either the lower cover plate of the next impeller in series in multi-stage model pumps, or for the tightening nut, depending on the location of the impeller within the pump.  
           [0022]    In one embodiment of the invention, the means for applying force to the impeller is preferably a combination of the stepped shaft, a tightening nut, and one or both of the pair of plate means.  
           [0023]    In this embodiment, the outside annular portion of the upper cover plate surrounding the central aperture, is tapered downwardly and outwardly from the central aperture. When force is applied to the upper cover plate by the tightening nut, the tapered portion is forced downwardly and caused to deform outwardly against the adjacent lower cover plate or vane means.  
           [0024]    The outside annular portion of the lower cover plate surrounding the central aperture may also be tapered, in this case, upwardly and outwardly from the central aperture. When force is applied to the lower cover plate by the tightening nut, the tapered portion of the lower cover plate is forced upwardly and caused to deform outwardly against the adjacent upper cover plate or vane means.  
           [0025]    Deformation of either or both of the upper and lower cover plates assists in maintaining pressure and therefore a seal between the impeller components.  
           [0026]    One end of the drive shaft preferably includes a screw thread or similar corresponding to a screw thread on the tightening nut. The tightening nut is fitted to the drive shaft and as it is tightened, respective spacers and impeller plates in the impeller assembly are clamped against the stepped portion at the opposite end of the drive shaft.  
           [0027]    The invention also extends to a pump for liquids, the pump including an impeller housing having an inlet port and an outlet port, and at least one impeller assembly, according to an embodiment of the invention, located between the inlet port and the outlet port and operable to impel liquid from the inlet port to the outlet port.  
           [0028]    Preferably, the pump includes a plurality of impeller assemblies arranged in series between the inlet port and outlet port. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]    The invention will now be described by way of example, with reference to the accompanying drawings, in which:  
         [0030]    [0030]FIG. 1 is an isometric exploded view of an impeller assembly according to a first embodiment of the invention;  
         [0031]    [0031]FIG. 2 is an isometric view of the impeller assembly of FIG. 1 when constructed;  
         [0032]    [0032]FIG. 3 is a partial side cross-sectional view of a multistage pump incorporating the impeller assembly of FIG. 1;  
         [0033]    [0033]FIG. 4 is an isometric exploded view of an impeller assembly according to a second embodiment of the invention;  
         [0034]    [0034]FIG. 5 is an isometric view of the impeller assembly of FIG. 4 when assembled;  
         [0035]    [0035]FIG. 6 is a side cross-sectional view of the impeller assembly of FIG. 5;  
         [0036]    [0036]FIG. 7 is a side cross-sectional view of an impeller assembly according to a second embodiment of the invention; and  
         [0037]    [0037]FIG. 8 is an isometric exploded view of the impeller assembly of FIG. 7. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]    Referring to the drawings, FIG. 1 illustrates the primary components of an impeller assembly according to a first embodiment of the invention. The impeller assembly illustrated includes an impeller  10  having upper and lower cover plates  12 ,  14  and vane plate  15 . In the context of this specification, the terms “upper” and “lower” do not indicate a particular orientation of the components or the assembly, or a particular relative position, but are employed as is commonly the practice in this art for distinguishing purposes or perhaps to indicate a likely arrangement in use.  
         [0039]    Vane plate  15  may be constructed in any conventional manner. The vanes of vane plate  15  may be formed integrally on the interior face of the lower cover plate such that they are intermediate the lower and upper cover plates. The vanes extend between the upper and lower plates so as to form passageways for fluid from the centre of the impeller to the outer edge of the impeller. The vanes are typically involute and serve to create regions of high and low pressure within the impeller assembly, as it is rotated at high speed, so as to impel fluid through the assembly.  
         [0040]    Vane plate  15  is typically of pressed metal construction, however in this design it may instead be manufactured from a relatively soft polymeric material so as to improve sealing between the impeller components.  
         [0041]    As shown in FIG. 3, the impeller  10  is received within impeller housing  34 . Housing  34  includes central aperture, or ‘eye’,  35  through which a rotatable drive shaft  28  passes. Housing  34 ′ illustrated in FIG. 3 serves to separate different areas of pressure within the pump housing and between individual impellers in series in multi-stage model pumps.  
         [0042]    The arrows in FIG. 3 indicate the direction of fluid flow through the impeller. The impeller assembly includes various seals such as  23  which ensure that the pump housing the impeller assemblies is substantially fluid tight.  
         [0043]    [0043]FIG. 3 illustrates the general orientation of the impeller components relative to each other in a multi-stack model pump. It will be appreciated that the scale of the components shown in FIG. 3 has been exaggerated in the axial direction for clarity. As illustrated, in this embodiment, lower cover plate  14  is a flat annular plate, and vane plate  15  is shaped to define a number of vanes as described above. Each of the lower cover plate  14 , vane plate  15 , and upper cover plate  12 , includes a central portion  21  which defines a central aperture  22 . The central portion  21  of upper cover plate is recessed or well-shaped so that it can receive the end of spacer  16 , as described below, while the outside portion  25  of upper cover plate overlies the vanes of vane plate  15 . The central portions  21  of plates  12 ,  14 ,  15  are adapted to lie in face-to-face contact when the impeller is assembled, with the vane plate sandwiched between the other two. Each of the plates is the same diameter.  
         [0044]    A collar spacer  16  is provided and serves the dual purpose of spacing adjacent impeller assemblies in series in multi-stage pumps, and as a means for nut  32  to act on, as described below. Spacer  16  is generally cylindrical and has an upper end  18  and lower end  17 . Lower end  17  is received within the central portion  21  of upper cover plate  12 . Drive shaft  28  extends coaxially through the hollow interior  13  of collar spacer  16 .  
         [0045]    In one embodiment of the invention, the lower end  17  of spacer  16 , may be formed as a broadly flared or frustoconical portion  19 . The flared or frustoconical portion  19  extends radially from the lower end  17  to an annular end face  20 , as best illustrated in FIG. 3. In this embodiment, the flared or frustoconical portion  19  acts as a diaphragm, eliminating freeplay between individual components. When a force is applied to the upper end  18  of the collar spacer  16 , the frustoconical portion  19  is forced downwardly and is caused to deform outwardly against the facing surface of the upper cover plate, generating an opposing axial load. This loading assists in maintaining the pressure applied to the impeller components thereby maintaining them in a substantially fluid tight relationship and also acts as a brake on the locking nut  32 , preventing accidental disengagement.  
         [0046]    As described above, shaft  28  is keyed to receive the impeller plates. This keyed region is indicated at “A” in FIG. 3. One end  29  of the shaft  28  is not keyed and has a larger diameter than portion “A” so as to create an annular step  30 . Lower cover plate  14  of the impeller assembly sits against step  30  when the impeller plates are located on the drive shaft  28 . The opposite end  31  of the shaft  28  is provided with a screw thread or similar to receive nut  32 .  
         [0047]    To assemble the impeller assembly, the lower cover plate  14 , vane plate  15 , and upper cover plate  12 , are placed on the shaft  28  in sequence, such that lower cover plate  14  sits against step  30 . Spacer  16  is then placed on the shaft such that lower end  17  is received by upper cover plate  12 . If the pump is a multi-stage model, successive impeller assemblies are mounted on the shaft, such that a spacer  16  is always placed on the shaft last. Nut  32  is then tightened onto the shaft against the upper end  18  of the exposed spacer  16  thereby pressing spacer  16  and subsequent spacers against step  30 . As a result, the impeller plates are tightly pressed together thereby forming an assembly of impellers. When it is necessary to remove or replace one or more of the impeller plates, the nut  32  is removed and the impeller plates removed and replaced as required.  
         [0048]    An impeller assembly according to a second embodiment of the invention is illustrated in FIGS.  4  to  6 . In these Figures, the same reference numerals (with  100  added) are used to indicate features similar to those of the first embodiment.  
         [0049]    Referring to FIG. 4, the impeller assembly  110  includes an impeller having upper and lower cover plates  112 ,  114 . Vanes  115  are formed integrally with the lower cover plate  114  during casting or moulding. Vanes  115  are formed on the surface of lower cover plate  114  facing upper cover plate  112  such that the vanes are disposed intermediate the pair of cover plates  112 ,  114 . The vanes  115  form passageways for fluid from the centre of the impeller to the outer edge of the impeller as described above. The impeller assembly  110  is received within an impeller housing substantially the same as the impeller housing  34  illustrated in FIG. 3.  
         [0050]    As shown in FIGS. 4 and 6, lower cover plate  114  is a substantially flat annular plate with vanes  115  formed on one surface thereof. The lower cover plate  114  includes a central portion  121  which defines a central aperture  122 . Central aperture  122  receives a rotatable drive shaft (not shown). In this embodiment, the central aperture  122  is a hexagonal shape. The exterior surface of central drive shaft is preferably also a hexagonal shape such that the lower cover plate is keyed to the drive shaft for rotation thereby.  
         [0051]    Upper cover plate  112  also includes a central aperture  122 . The interior walls  43  of the central aperture  122  define a hexagon which corresponds to the exterior surface of the drive shaft as for the lower cover plate  114 . Spaced radially from the central aperture is an annular flange  44  extending coaxially with the drive shaft. The annular region  45  between the annular flange  44  and the central aperture  122  is spanned by a plurality of support members  46  which connect the annular flange  44  to the central aperture  122 . The annular region  45  is left substantially open to allow fluid flow into the impeller assembly  110 . The support members  46 , are preferably formed as additional impeller blades, thereby increasing the efficiency of the impeller.  
         [0052]    As best illustrated in FIG. 6, upper cover plate  112  is not a flat annular plate. Instead, the outside portion  125  of the upper cover plate  112  is slightly tapered downwardly and outwardly from the central aperture  122 . The upper cover plate  112  is thereby pre-loaded as will be described below. The central apertures  122  are adapted to lie in face-to-face contact when the impeller is assembled on the drive shaft.  
         [0053]    In multi-stage model pumps, subsequent impeller assemblies are located on the drive shaft in series. These multiple impeller assemblies are separated by a collar spacer (not shown). The collar spacer is generally cylindrical tube. The collar spacer is located on the drive shaft between adjacent upper and lower cover plates in series and serves the dual purpose of spacing adjacent impeller assemblies in series in multi-stage pumps, and as a means for a nut ( 32  as shown in FIG. 3) to be tightened against. As described in relation to the first embodiment, (see FIG. 3) one end  29  of the drive shaft  28  has larger diameter than the keyed portion “A” of the shaft so as to create an annular step  30 . Lower cover plate  114  of the impeller assembly sits against the step  30  when the impeller plates are located on the drive shaft  28 . The opposite end of the shaft  28  is provided with a screw thread or similar to receive nut  32 . The collar spacer may be formed integrally with one or both of the cover plates of the impeller assembly.  
         [0054]    The tapered outside portion  125  of the upper cover plate  112  acts as a diaphragm in the same manner as the flared or frustoconical portion  19  of the first embodiment of the invention. When a force is applied to the upper annular face  47  of the central portion  121 , (either by the spacer or nut  32  depending on where the impeller assembly is located in the stack), the tapered portion  125  is forced downwardly and is caused to deform outwardly against the vanes  115  on the lower cover plate  114 . This loading assists in maintaining the pressure applied between the impeller components and eliminates freeplay between individual components.  
         [0055]    In a third embodiment of the invention, illustrated in FIGS. 7 and 8, vane plate  215  is formed as a separate component, as in the first embodiment, and includes central portion  221  which defines a central aperture  222 . In this embodiment, the outside portion  225  of the lower cover plate  214  is slightly tapered upwardly and outwardly from the central aperture  222 .  
         [0056]    As in previous embodiments, upper and lower cover plates  212 ,  214  also include central portions  221  and central apertures  222 , and each of the upper and lower cover plates are the same diameter.  
         [0057]    As best illustrated in FIG. 7, the outside portion  225  of the lower cover plate  214  is tapered upwardly and outwardly towards vane plate  215 . The lower cover plate  214  is thereby pre-loaded, in addition to the upper cover plate  212  which is pre-loaded as described in relation to the second embodiment of the invention above.  
         [0058]    When a force is applied to the lower annular face  247  of the central portion  221  of the lower cover plate  215 , the tapered portion  225  is forced upwardly and is caused to deform outwardly against the vane plate  215 .  
         [0059]    Loading the impeller assembly from both sides using the upper and lower cover plates  212 ,  214 , further increases the pressure applied between the components of the impeller assembly and substantially eliminates freeplay between individual components.  
         [0060]    The impeller assembly  110 ,  210  of the second and third embodiments is assembled in a similar manner to the impeller assembly  10  of the first embodiment of the invention. Lower cover plate, vane plate and upper cover plate are placed on the drive shaft in sequence, such that lower cover plate sits against step  30 . The spacer is then placed on the shaft and, if the pump is a multi-stage model, successive impeller assemblies and spacers are mounted on the shaft. Nut  32  is then tightened onto the shaft against the upper face of the upper cover plate, or against a spacer. The impeller plates are tightly pressed together as the nut  32  is tightened and the tapered portion of the upper cover plate and/or lower cover plate is forced to deform, thereby forming an assembly of impellers.  
         [0061]    It will be appreciated that the impeller assembly of the invention is easy and relatively quick to assemble, and disassemble when required. Because each of the impeller components is individually keyed to the drive shaft, mechanical fastening of individual components to each other is no longer required and the product is made inherently more reliable. Additionally, the load of the entire impeller assembly is not borne by one plate and thus the drive feature of the impeller is under less stress, while at the same time, the impeller components are clamped together in a substantially fluid tight relationship.  
         [0062]    It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.