Abstract:
A seal arrangement for an impeller assembly, the impeller assembly including an impeller housing ( 34 ) adapted to receive a drive shaft. An impeller ( 10 ) is located within the impeller housing ( 34 ) and is adapted for connection to the drive shaft for rotation by the drive shaft about an axis. The seal arrangement includes an annular seal ( 24 ) located axially between the impeller housing ( 34 ) and the impeller ( 10 ) to provide a substantially fluid tight seal between the impeller housing ( 34 ) and the impeller ( 10 ).

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to housings for impeller assemblies that are commonly used in pumps for liquids. In particular, this invention relates to an improved sealing arrangement for use in an impeller assembly.  
         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 a vane plate located between the respective 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 pumping fluid passing through the impeller 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 impellers in series on the same shaft passing through each of the impeller housings.  
           [0004]    In order to maintain the desired pressure levels within the impeller assembly, the fluid flow path through each of the impeller assemblies within the pump must be sealed. One conventional means of sealing the impeller housing against the drive shaft is to provide a caged annular seal, located radially between the impeller housing and the drive shaft. The seal ring is contained within a radial cavity and is provided with room to float radially to compensate for radial movement of the impeller relative to the impeller housing.  
           [0005]    This type of seal has proven to be effective but suffers a number of disadvantages. Firstly, the floating seal is not free to float axially, meaning that any axial movement of the impeller relative to the impeller housing cannot be compensated for. Secondly, the seal is located within a groove formed in the impeller housing. Installation, as well as removal and replacement of the seal, is an intricate operation given the “hidden” location of the seal. Further, in order to provide an adequate seal, the sealing ring and drive shaft must be manufactured with very small tolerances in internal diameter so that it closely receives the drive shaft of the impeller assembly.  
           [0006]    The above disadvantages are of course amplified when the pump is a multi-stage model.  
           [0007]    It is therefore an object of the invention to provide a sealing arrangement for an impeller assembly that at least in part alleviates one or more of the above disadvantages.  
         SUMMARY OF THE INVENTION  
         [0008]    The invention accordingly provides a seal arrangement for an impeller assembly, the impeller assembly including:  
           [0009]    an impeller housing adapted to receive a drive shaft; and  
           [0010]    an impeller located within the impeller housing and adapted for connection to the drive shaft for rotation by the drive shaft about an axis;  
           [0011]    wherein the seal arrangement includes an annular seal located axially between the impeller housing and the impeller to provide a substantially fluid tight seal between the impeller housing and the impeller.  
           [0012]    Advantageously, the annular seal includes two opposed substantially flat faces and a circumferential edge face. When the impeller assembly is assembled, one flat face of the seal contacts an int rior face of the impeller housing. The opposite flat face of the seal faces a first surface of the impeller.  
           [0013]    The impeller is preferably made up of lower and upper cover plates, which are operably connected to form the impeller. Advantageously, vanes defining fluid flow paths are located intermediate the upper and lower cover plates and may be formed integrally with the lower cover plate. The lower cover plate preferably includes an integral central upstanding boss through which the drive shaft passes. More preferably, the boss is keyed onto the drive shaft.  
           [0014]    Advantageously, the outer surface of the upper cover plate of the impeller includes a raised annular lip. Alternatively, the raised lip may be provided on the surface of the seal facing the impeller.  
           [0015]    The annular seal is placed over the central boss such that one flat face of the seal sits against the raised lip of the impeller. Alternatively, when the seal includes the raised annular lip, the raised annular lip sits against the upper cover plate. The annular lip serves to provide a small gap between the surface of the impeller and the seal such that, in use of the impeller, fluid under pressure enters into the gap. The action of the low fluid pressure in the impeller eye and the high fluid pressure in the gap between the seal and the impeller serves to force the seal away from the impeller and against the interior face of the impeller housing, thereby substantially sealing the impeller assembly.  
           [0016]    The annular seal is preferably a floating seal moveable in the axial direction to compensate for axial displacement of the impeller relative to the impeller housing, allowing the assembly to be more tolerant of production variability. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The invention will now be described by way of example, with reference to the accompanying drawings, in which:  
         [0018]    [0018]FIG. 1 is an isometric exploded view of an impeller assembly according to an embodiment of the invention;  
         [0019]    [0019]FIG. 2 is a plan view of the face of the impeller with the floating neck ring fitted;  
         [0020]    [0020]FIG. 3 is a side cross-sectional view of the impeller assembly of FIG. 1 when assembled, taken along the line A-A; and  
         [0021]    [0021]FIG. 4 is a side cross-sectional view of part of an assembled multi-stage model- 2  impeller assemblies are illustrated. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    Referring to the drawings, FIG. 1 illustrates the primary components of a typical impeller assembly. The impeller assembly illustrated includes an impeller  10  having upper and lower cover plates  12 ,  14 . Lower cover plate  14  includes integral vanes  16  formed on the interior face of the lower cover plate such that they are intermediate the lower and upper cover plates. Vanes  16  may be constructed in any conventional manner, and may be formed as a separate intermediate vane plate. The vanes  16  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  16  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 pump fluid through the impeller assembly.  
         [0023]    The three plates of the impeller assembly may connected in any conventional manner. The plates may be fastened e.g. by welding at the vanes or by gluing. There are many variations of the design of an impeller and the present invention is directed to use with an impeller having at least one cover plate, such as cover plate  12  having a substantially planar outer surface  21 .  
         [0024]    The impeller  10  is received within impeller housing  34 . Housing  34  includes central aperture  35  through which a rotatable drive shaft (not shown) passes. Housing  34 ′ illustrated in FIG. 1 serves to house the next impeller assembly in series in multi-stage model pumps.  
         [0025]    Impeller  10  includes a central boss  18  which is integrally formed with lower cover plate  14 . The boss  18  is keyed to the rotatable drive shaft. For this purpose, the inside surface of boss  18  includes a pair of opposed flats  17 , 19  which correspond to flats on the exterior surface of the drive shaft. The impeller  10  and housing  34  are secured onto the drive shaft using a nut or locking ring (not shown).  
         [0026]    Upper cover plate  12  has a central aperture  13  through which the boss  18  and drive shaft extend. At the edge of the central aperture  13  is an annular flange  22 . When the impeller is assembled, annular flange  22  is spaced radially from the boss  18  and extends coaxially therewith. The exterior circumference of flange  22  is sized to match the inside circumference of floating seal  24 , as described below.  
         [0027]    Spaced radially from the annular flange  22 , and formed integrally with the upper cover plate  12 , is a raised annular lip  20 . Lip  20  may be formed separately and attached to the surface  21 . As will be described below, the purpose of lip  20  is to raise the seal  24  from the surface  21  of the impeller  10 , when the impeller  10  is assembled.  
         [0028]    Seal  24  is a flat circular ring, having two opposed planar surfaces  26 ,  28  and interior and exterior edge faces  30 ,  32 . The seal  24  may include one or more small through-holes (not shown) formed in the planar surfaces  26 ,  28  of the seal  24 , in order to improve lubrication on the surface  28  of the seal. The seal  24  may additionally or alternatively also be formed with a radial slit or break (not shown) in the seal  24 . Forming the seal with a radial slit or break enables the inner diameter of the seal  24  to adapt to the outer diameter of the boss  18 .  
         [0029]    When the impeller  10  is assembled, surface  26  of the seal  24  sits against raised lip  20 , the lip  20  creating a small gap between the surface  21  of the impeller and the face  26  of the seal  24 . The raised lip  20  is not as wide as the seal  24  leaving part of the surface  26  of the seal  24  raised from the face of the impeller  10 .  
         [0030]    The impeller  10  and seal  24  are located within impeller housing  34  such that face  28  of the seal  24  faces the interior face  33  of the impeller housing  34 .  
         [0031]    Referring to FIG. 4, where arrows illustrate the direction of fluid flow in use, fluid is pumped through the impeller assembly from the centre of the impeller, via the vanes  16  to the edge  15  of the impeller  10 . Fluid from the edge of the impeller can flow either in the direction of the next impeller housing  34  in series/the outlet of the pump or can flow behind the impeller  10  toward the seal  24 . Fluid which flows in the direction of the seal  24  enters into the gap between the seal  24  and the impeller surface  21  thereby forcing the seal  24  against the interior  33  of the impeller housing  34 . A substantially fluid tight seal is formed between the face  28  of seal  24  and the interior  33  of housing  34 . Fluid flowing in this direction is therefore prevented from exiting the impeller housing  34  and is forced to exit the impeller housing via subsequent impeller housing or pump outlet. (not shown).  
         [0032]    It will be appreciated that it is the action of the high pressure fluid acting against the seal  24  which forces the seal  24  against the interior  33  of the impeller housing and creates the seal.  
         [0033]    The present invention therefore provides an effective fluid tight seal for an impeller assembly. The seal is free to float axially thereby compensating for axial movement of the impeller relative to the impeller housing. The seal is easy to position and, if necessary, can be removed and replaced by simply opening the impeller housing. Having an easily and readily accessible seal is particularly advantageous in multi-stage models which include a number of impeller assemblies.  
         [0034]    It will be understood that the invention disclosed and defined herein 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.