Abstract:
A self-adjusting liner assembly for installation within a centrifugal pump of the type having an impeller and a pump casing having a suction inlet is provided, comprising a liner having a sealing end, the sealing end having at least one substantially planar outer most surface for contacting an outer surface of the impeller; and a resilient member disposed in the liner, said resilient member providing a force so that the at least one outer most surface remains in substantially continuous contact with the outer surface of the impeller.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to centrifugal pumps in general and more specifically to a self-adjusting liner assembly for centrifugal pumps for substantially reducing recirculation damage to the impeller. 
       BACKGROUND OF THE INVENTION 
       [0002]    Centrifugal pumps are commonly used to move mixtures of solids and liquids through piping. The mixture enters the pump impeller along or near the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute (casing) which surrounds the impeller from where it exits into the downstream piping. 
         [0003]    Most centrifugal pumps which handle mineral slurries, for example, oil sand slurries, run into problems with respect to solid particles of the slurry becoming trapped between the rotating impeller and the surrounding volute during operation, thereby causing wear and abrasion of both the impeller and the volute. This results in downtimes for repair and ultimately reduces the life of the pump and its hydraulic efficiency. The problem tends to be more serious on the suction side of the impeller, where the high pressure liquid inside the discharge portion of the volute tends to flow towards the low pressure zone in the suction portion of the pump. This is commonly referred to as suction-side recirculation, which results in a loss of pump hydraulic performance and efficiency. 
         [0004]    In particular, increase in suction-side recirculation may directly contribute to loss of efficiency. Since efficiency is a ratio of output work against input power, and since output work (flow and head) is less with the same amount of input power, efficiency is lower. Furthermore, as wear increases, the gap between the impeller and the volute becomes larger if unaddressed and a higher rate of flow can pass through the gap, speeding the deterioration process. Thus, the pump life span will be reduced. 
         [0005]    Many centrifugal slurry pumps are now equipped with an annular suction liner (also referred to as an annular wear ring), which is located between the suction side of the impeller and the volute to decrease the wear due to recirculation. However, these suction liners still create a gap where solids can cause abrasion damage. Furthermore, the entire operation (e.g., pumps) must be stopped in order to replace the suction liner when it has become sufficiently worn. Also, it is somewhat unpredictable as to when the suction liner will need to be replaced, which may result in unexpected pump failures. 
         [0006]    In an attempt to at least partially remedy some of the problems encountered above, CA 2,214,415 and U.S. Pat. No. 5,921,748 teach a wear ring which is axially adjustable by means of one or more adjustment screws. The adjustment screws are located outside of the pump and, thus, the wear ring (suction liner) can be adjusted while the pump is in operation. However, one will still have to rely on human intervention to adjust the wear ring according to a schedule or a particular criterion. Furthermore, in between these adjustments, wear will occur, allowing a continuing increase in recirculation. 
         [0007]    U.S. Pat. No. 7,189,054 teaches a wear ring which is axially self-adjusting by means of balanced flush water pressures. However, in this design, physical contact between the wear ring and the impeller is expressly avoided. When pressurized water is applied to the water inlet end of the seal, the seal will move to a self-compensating balance between the pump casing and the impeller of the pump. Therefore, the seal cannot be independently adjusted. 
         [0008]    It would be desirable to have a suction liner assembly which would automatically adjust according to the wear thereon so that a proper seal between the suction side of the impeller and the volute can always be maintained, resulting in substantially reduced suction-side recirculation for longer periods of time. While the design in U.S. Pat. No. 7,189,054 has this feature, the driving force to create the adjustment is limited by the use of balanced hydraulic forces to locate the adjustable component. If, as seems likely, solid material were to accumulate in the gaps on either side of the adjustable component, the hydraulic force required to advance towards the impeller may not be sufficient to overcome the friction due to solids accumulation; the adjustment mechanism seems vulnerable to loss of function. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention relates to centrifugal pumps in general and more specifically to a self-adjusting liner assembly for a centrifugal pump. 
         [0010]    In one aspect of the present invention, a self-adjusting liner assembly for installation within a centrifugal pump of the type having an impeller and a pump casing having a suction inlet is provided, comprising:
       a liner having a sealing end, the sealing end having at least one substantially planar outer most surface for contacting an outer surface of the impeller; and   a resilient member disposed in the liner, said resilient member providing a force so that the at least one outer most surface remains in substantially continuous contact with the outer surface of the impeller.       
 
         [0013]    In one embodiment, the at least one outer most surface comprises a wear ring. In another embodiment, the liner includes a recessed portion for housing the resilient member and the wear ring. The wear ring may vary in diameter relative to the liner and, in one embodiment, may have an outer diameter essentially the same as the outer diameter of the liner itself. 
         [0014]    In one embodiment, the resilient member is a spring such as a wave spring. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Referring to the drawings wherein like reference numerals indicate similar parts throughout the several views, several aspects of the present invention are illustrated by way of example, and not by way of limitation, in detail in the figures, wherein: 
           [0016]      FIG. 1  is a cross-sectional view of the interior of a conventional single stage centrifugal pump. 
           [0017]      FIG. 2  is a cross-sectional view of the interior of a single stage centrifugal pump having an embodiment of a self-adjusting liner assembly of the present invention. 
           [0018]      FIG. 3  is a cross-sectional view of an embodiment of a self-adjusting liner assembly of the present invention prior to wear of the liner. 
           [0019]      FIG. 4  is an isometric exploded view of the embodiment of the self-adjusting liner assembly of  FIG. 3 . 
           [0020]      FIG. 5  is an isometric exploded view of the embodiment of the insert as shown in  FIG. 3 . 
           [0021]      FIG. 6  is a cross-sectional view of another embodiment of a self-adjusting liner assembly of the present invention prior to wear of the liner which includes a lubricating and cooling system. 
           [0022]      FIG. 7  shows a sealing arrangement for a wear ring of the present invention. 
           [0023]      FIG. 8  shows an embodiment of the sealing face of an impeller useful in the present invention. 
           [0024]      FIG. 9  is an isometric exploded view of another embodiment of a self-adjusting liner assembly of the present invention. 
           [0025]      FIG. 10   a  is a cross-sectional view of a portion of the self-adjusting liner assembly of  FIG. 9  where the spring is fully contracted. 
           [0026]      FIG. 10   b  is a cross-sectional view of a portion of the self-adjusting liner assembly of  FIG. 9  where the spring is fully expanded. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0027]    The detailed description set forth below in connection with the appended drawing is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details. 
         [0028]      FIG. 1  is a cross-sectional view of a prior art conventional single stage centrifugal pump  10 . Centrifugal pump  10  comprises a stationary casing (volute)  20  having a suction inlet  22  which is the point of entry of the slurry. Housed within the stationary casing  20  is an impeller  14  and a shaft  12  for rotating the impeller  14 . Typically, the shaft is coupled to a motive power such as an electric motor (not shown). Impeller  14  has a gland side shroud  31  and a suction side shroud  32 . The impeller vanes  24  are located in between the gland side shroud  31  and the suction side shroud  32 , and serve to accelerate the fluid towards the high-pressure region  28 . 
         [0029]    The slurry to be pumped enters the pump via suction inlet  22  (see arrows  13 ) and is forced at high pressure through the rotating impeller  14  into the high pressure region  28  inside the pump casing  20  from where it is discharged via a discharge pipe (not shown). However, some of the slurry will tend to flow from the high pressure region  28  back into the low pressure region  30  in the suction inlet  22 . Therefore, the suction surface  18  of impeller  14  typically wears more quickly than the gland surface  16  due to the recirculation of the incoming slurry (see arrows  11 ). Thus, a suction liner  26  is provided, which liner can be made from a variety of materials such as chrome white iron, elastomers and the like, as is known in the industry. The suction liner  26  takes up some of the clearance at the suction side  18  of the impeller  14  to reduce suction side  18  recirculation and the possibility of abrasive solids being trapped between the rotating impeller  14  and the casing  20  and suction liner  26 . 
         [0030]    However, during use of the pump  10 , both the suction liner  26  and the impeller  14  wears and the space between the suction liner  26  and the impeller  14  increases, leading to increased recirculation and eventually the pump  10  needs to be shut down so that both the suction liner  26  and the impeller  14  can be replaced. It would be desirable to avoid the number of shut downs of the pump  10  which are necessary for replacing the suction liner  26  and/or impeller  14 . One way to accomplish this would be to provide a self-adjusting suction liner assembly which would adjust during operation to continuously ensure that the space between the suction liner and the suction side of impeller is eliminated or kept at a minimum. 
         [0031]      FIG. 2  shows one embodiment of a pump  110  which has been fitted with a self-adjusting suction liner assembly  180  of the present invention. In this embodiment, self-adjusting suction liner assembly  180  comprises suction liner  126  having an insert  142 , which insert  142  can be seen more clearly in  FIG. 5 , and in the cross-sectional of self-adjusting suction liner assembly  180  in  FIG. 3 . As can be seen in  FIG. 2 , the substantially planar outer most surface  160  of inset  142 , which comprises wear ring  154 , lies essentially flush with impeller  114  and therefore prevents recirculation by blocking the flow of slurry (see arrows  115 ). 
         [0032]      FIG. 4  is an isometric exploded view of the embodiment of the self-adjusting liner assembly  180  in  FIG. 3 . With reference now to  FIGS. 3 and 4 , annular liner  126  has a recess  144  which houses insert  142 . Insert  142  comprises annular gasket  146 , an annular bottom cartridge plate  148 , annular wave spring  150 , annular top cartridge plate  152  and annular wear ring  154 . Wear ring  154  may be made from any wear resistant material known in the industry such as urethane, elastomers, tungsten carbide, chrome white iron and the like, or a combination thereof. Choice of material will be driven by the need to reduce friction and abrasive wear. It is understood than any resilient, compressible member such as a coil/compression spring or the like could be used, however, wave springs are more desirable as they generally reduce the spring height by as much as 50% while still exerting the same force and deflection as ordinary coil/compression springs. Each of annular gasket  146 , annular bottom cartridge plate  148 , annular top cartridge plate  152  and annular wear ring  154  further comprise a number of notches  162  around their respective peripheries, which, when the insert  142  is assembled, line up and slide over anti-rotation keys  164  located in the recess  144  of annular liner  126  to ensure that insert  142  does not rotate during operation of the slurry pump. 
         [0033]    In use, initially, the wave spring  150  is essentially fully compressed and forces the outer surface  160  of wear ring  154  to be essentially flush against the suction side of impeller  114 , as shown in  FIG. 2 . As wear ring  154  wears, however, the wave spring  150  continuously expands to provide a constant force on the wear ring  154 , which allows the outer surface  160  to be continuously flush against the impeller. Thus, recirculation is continuously reduced, resulting in longer wear life for the pump parts. It is understood that the choice of annular spring, i.e., resilience member, will determine the forces desirable for the wear ring  154  on the suction side of impeller  114 . Generally, excessive spring force is to be avoided, as this may result in excessive wear of the wear ring  154  and overheating due to excessive friction. Thus, generally, a relatively weak spring is desirable. 
         [0034]      FIG. 6  describes an additional embodiment, where a fluid for lubrication and cooling is provided via multiple nozzles  290 , which are fitted closely to holes formed in the wear ring  254 . The fluid is forced through the wear ring by the aforementioned close fit, and enters a small groove (not shown) created on the surface of the wear ring  254  for the purpose of distributing the fluid along the full circumference of the wear ring. This groove may be extended, in a spiral or radial fashion, to the outer diameter of the wear ring  254 , so that the cooling and lubricating fluid would tend to travel in that direction and carry contaminants away from the continuous sealing surface between the groove  291  and the inner diameter of the wear ring  254 . The flow and pressure of the cooling and lubricating fluid would be monitored and controlled external to the pump, so it would be possible to find the minimum pressure required to overcome the spring pressure and create a thin film of fluid between the wear ring  254  and the impeller sealing surface  18 , which is likely to greatly reduce the wear rate of these two surfaces. 
         [0035]      FIG. 7  describes the sealing arrangement  170  of the wear ring  154  in the groove  144  created in the suction liner  126 , the purpose of which is twofold. First, the seal must prevent flow from travelling from the high pressure region  28  to the low pressure region  30 , along a path underneath the wear ring  154  and through the wave spring  150 . Second, the seal must be located so that the fluid pressure at the outer diameter of the wear ring  154  has equal access to both the sealing face and the underside of the wear ring  154 . This will prevent a net pressure imbalance on these two surfaces of the wear ring, which could result in a significant force that would overwhelm the wave spring. The seal should be located at the inner diameter of the wear ring, and should allow for axial travel of the wear ring in the groove  144 , while maintaining a seal. An o-ring, lip seal or similar arrangement may be appropriate. 
         [0036]      FIG. 8  describes a possible embodiment of the sealing face of the impeller  14 , which may be lined with a material  200  other than chrome white iron, such as tungsten carbide, polyurethane, or any other material with desirable properties. Either the same or different materials as those used in the wear ring  154  may be employed here. The sealing face of the impeller  14  may be flush with the impeller surface  18 , or it may be recessed (as shown in  FIG. 8 ), so as to create a circuitous path for any leakage across the sealing face. 
         [0037]      FIG. 9  is an isometric exploded view of another embodiment of a self-adjusting liner assembly  280  of the present invention. In this embodiment, annular liner  326  has a recess  344  which houses insert  342 . Recess  344  comprises a number of holes  266  for receiving anti-rotation pins  368 , to prevent rotation of the insert  342  during operation of the slurry pump. Insert  342  comprises an annular bottom steel plate  348 , and annular top steel plate  352  and an annular spring  350  positioned therebetween. Both the annular bottom steel plate  348  and the annular top steel plate  352  further comprise a comparable number of holes  266  as the recess  344  of the annular line  326  to also receive anti-rotation pins  368  to prevent rotation of the insert  342  during operation of the pump. 
         [0038]    Insert  342  further comprises O-ring  368  for providing the proper sealing arrangement for assembly  380 . Annular liner  326  comprises a groove  357  for receiving O-ring  368 . In this embodiment, wear ring  354  comprises a recess  355  for receiving steel plate  369 . Generally, the wear ring is made of rubber, polyurethane, and the like. The embedded steel ring  369  provides structure to the wear ring  354 , which wear ring can be made of more flexible, non-metallic materials. Furthermore, the embedded steel ring  369  may comprise threaded holes (not shown) to receive screws for attaching the wear ring  354  and steel ring  369  to the annular top steel plate  352 . The annular bottom steel plate  348  contains threaded holes to receive screws for attaching the insert  342  to the annular liner  326 . The assembly  380  is installed in the pump in the same manner as a regular annular liner with no self-adjusting insert  342  would be. 
         [0039]      FIGS. 10   a  and  10   b  are partial cross-sectional views of the embodiment of the self-adjusting liner assembly  380  shown in  FIG. 9 .  FIG. 10   a  shows the annular spring  350  of insert  342  in its full contracted state and  FIG. 10   b  shows the annular spring  350  of insert  342  in its fully expanded state. 
         [0040]    From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope consistent with the claims, wherein reference to an element in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.