Abstract:
In a centrifugal pump of the pitot tube type, a replaceable wear ring is positioned in the rotating assembly of the pump in that area of the rotating case which is most subject to erosion from the processing of abrasive fluids by the pitot tube pump. The replaceable wear ring can be easily and quickly replaced when eroded, thereby eliminating the need to replace the rotating case of the pump and eliminating the need for costly and time-consuming re-balancing of the pump.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a non-provisional application claiming priority to provisional patent application Ser. No. 60/658,399 filed Mar. 3, 2005. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates to centrifugal pumps of the pitot tube type, and relates specifically to providing means for less expensively and more conveniently repairing the rotating case of the pump when the rotating case is damaged as a result of processing abrasive fluids.  
         [0004]     2. Description of Related Art  
         [0005]     Pitot tube pumps are a type of centrifugal pump which generally comprise a pump casing that forms a housing for a rotating assembly that surrounds a stationary pitot tube. The rotating assembly further comprises a rotating case and a rotor cover that together serve to enclose the pitot tube. The rotating assembly spins at a very high rate and as fluid enters the spinning rotating assembly, it is directed to the interior circumferential wall of the rotating case. The stationary pitot tube has an opening, or inlet, which is positioned in very close proximity to the interior circumferential wall of the rotating case. Fluid moving at high velocity in the rotating case encounters the inlet of the pitot tube and is pumped to the outside of the pump through the pitot tube.  
         [0006]     Pitot tube pumps do not process fluids containing abrasive solids very well. A pitot tube pump has a relatively high velocity of fluid rotating in the pump at nearly the same velocity as the rotating case of the pump. As a result, some of the high velocity fluid enters the pitot tube inlet and some passes by the stationary pitot tube. If the fluid being processed contains abrasive solids, those solids will contact the surface of the pitot tube and will erode it away. The abrasive solids also have a tendency to deflect off the area of the pitot tube near the inlet and cause erosion of the interior wall of the rotating case in close proximity to the pitot tube inlet.  
         [0007]     Many attempts have been made to improve the abrasive-resistant qualities of the pitot tube and rotating case. For example, pitot tubes have been manufactured with hard metal or ceramic inserts at the tube inlet, as disclosed in U.S. Pat. No. 5,997,243. The pitot tube has also been manufactured with hard metal coatings and diamond coatings on the surface. The rotating case has also been manufactured with several different material coatings, such as with hard metal coatings, ceramic coatings and urethane coatings. All of these changes and coatings have worked to extend the life of the components, but ultimately they have failed.  
         [0008]     Early attempts to repair worn rotating cases have also failed. Repairing the worn out area of the rotating case by such means as welding has not been successful. The heat from welding tends to relieve the internal casting stresses in the component, and the sides of the rotating case move inward, thus compromising the register fit between the rotating case and the rotor cover. This fit is critical to the operation of the pump, and without it the pump will vibrate beyond acceptable limits.  
         [0009]     Attempts have also been made to coat the worn area of the rotating case with an abrasion-resistant coating, but the same adverse effects result because of the heat required in the coating process. Even machining a groove in the rotating case to fill it with urethane will relieve the internal stresses in the part and compromise the register fit.  
         [0010]     Coatings have been difficult to maintain on the rotating case because, in operation, the case expands and contracts. As the rotating assembly accelerates from zero revolutions per minute (RPM) to operating speed (as high as 6750 RPM) the outside diameter of the rotating case expands a few thousands of an inch from the centrifugal force acting on it. The rotating case also expands and contracts in the axial direction as the internal pressure in the rotating case chamber changes during operation of the pump. This constant expansion and contraction of these surfaces during pump operation tends to over-stress the hard coatings and breaks the mechanical bond between the coating and surface of the rotating case. The coating then begins to flake off of the interior wall of the rotating case, often damaging the pitot tube in the process.  
         [0011]     Thus, it would be advantageous in the art to provide a means for effecting repair of the interior of a rotating assembly of a centrifugal pump which is relatively easy, less costly and which allows the repair to be done on-site, thereby limiting the time that the pump must be taken off-line for repair.  
       BRIEF SUMMARY OF THE INVENTION  
       [0012]     In accordance with the present invention, the rotating assembly of a pitot tube pump is structured to receive a replaceable wear ring that is positioned in the rotating assembly where the component is most subject to wear due to pumping of abrasive fluids. When the original wear ring becomes worn or damaged, it is removed from the rotating assembly, such as by simply grinding off a few tack welds that secure it to the rotating assembly, and is then lifted out of a preformed groove cast in the rotating assembly that is sized to receive the wear ring. A new wear ring is then placed in the groove and is secured in place.  
         [0013]     While the notion of a wear ring seems simple, certain obstacles had to be addressed and overcome in providing the present invention, namely, how to insert a wear ring into a groove in the rotating assembly, make sure that is it fully seated in the bottom of the groove so it will not move during operation of the pump, keep it from rotating relative to the rotating assembly, retain it in the groove during operation, be able to remove it from the groove and then replace it with a new wear ring without affecting the balance of the rotating assembly.  
         [0014]     The most difficult obstacle to overcome was how to replace the wear ring without affecting the balance of the rotating assembly of the pump. The rotating assembly (i.e., the rotating case and rotor cover) weighs about 150 pounds and is dynamically balanced to 0.15 inch ounces at 1000 rpm. This is a very accurate balance and is very expensive to achieve. This level of balance is required to maintain the vibration levels within acceptable limits for the life of the pump. In a pitot tube pump, balance and vibration are directly related. The better the rotating assembly is balanced, the lower the vibration level will be which results in a longer bearing life for the pump. This level of balance is very difficult to achieve by someone outside of the factory and is often never achieved in the field. Special tooling and structuring is required to achieve these levels.  
         [0015]     Conventionally, to effect the rebalancing of a rotating assembly, the pump must first be removed from its place of operation and taken to a repair station. Removing the pump from its installation involves disconnecting the piping, seal flush lines and couplings, and unbolting the pump from its base plate. Removal of the pump in this manner requires the pump to be re-aligned to the drive train when it is re-installed. Removal and re-installation of the pump can take from several hours to several days depending on the complexity of the pump operating system. The pump then has to be completely disassembled and a new rotating assembly installed on the shaft. The rotating assembly has to then be re-balanced. Then the pump can be rebuilt and re-installed on its base plate and re-aligned to the drive train.  
         [0016]     The present invention avoids the conventional need for removing the pump from its base, thereby compromising the balance of the pump. With the present invention, the front or suction side of the pump casing can be opened while it remains on its base plate, and the wear ring can be replaced with relatively simple ease. Consequently, with the present invention, only the suction and discharge piping and the front of the pump need to be disassembled and then reassembled. The ease and simplicity of replacing the worn wear ring results in significant labor savings and reduces the amount of down-time of the pump.  
         [0017]     Erosion in the rotating assembly (e.g., rotating case) happens in an uneven way, which causes the rotating assembly to become unbalanced. From the first instant that the pump is put into operation the balance of the rotating assembly is being degraded. The ability to simply replace a wear ring and keep the pump within the balance specification for a longer period of its life results in longer pump operation with lower maintenance costs. These and other advantages of the present invention will become more apparent with the following detailed description of the invention.  
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0018]     In the drawings, which currently illustrate the best mode for carrying out the invention:  
         [0019]      FIG. 1  is an isometric view, in cross section, of a prior art centrifugal pump of the pitot tube type;  
         [0020]      FIG. 2  is an isometric view, in partial cross section, of the rotating assembly of the prior pump shown in  FIG. 1 , with the pitot tube assembly removed;  
         [0021]      FIG. 3  is an isometric view, in partial breakaway, of a rotating assembly of a pitot tube pump with the pitot tube assembly in position within the rotating assembly;  
         [0022]      FIG. 4  is a partial cross section view in elevation of the rotating case and rotor cover, with the pitot tube assembly removed;  
         [0023]      FIG. 5  is a partial cross section view in elevation of a rotor formed in accordance with the present invention;  
         [0024]      FIG. 6  is a perspective view of a wear ring of the present invention;  
         [0025]      FIG. 7  is an isometric view, in partial cut-away, of a rotating assembly of a pitot tube pump configured in accordance with the present invention and illustrating the wear ring in position within the rotating assembly; and  
         [0026]      FIG. 8  is an enlarged view of the rotating assembly configured in accordance with the present invention and illustrating the securement of the wear ring in position within the rotating assembly.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]      FIG. 1  illustrates a conventional centrifugal pump  10  of the pitot tube type. The pump  10  generally comprises a pump casing  12  that forms a housing for a rotating assembly  14  and a pitot tube  16 . The rotating assembly  14  further comprises a rotating case  18  and a rotor cover  20 , the combination of which provide an interior space  22  within which the pitot tube  16  is positioned. The rotating assembly  14  is rotated by a drive shaft  24  connected to a motor (not shown). While the rotating assembly  14  of the pump  10  rotates during operation of the pump, the pitot tube  16  is stationary.  
         [0028]      FIG. 2  further illustrates just the rotating assembly  14  and drive shaft  24  of a centrifugal pump of the pitot tube type, with the pitot tube removed. It may be seen more clearly that the rotor cover  20  is removably secured to the rotating case  18  by means of a plurality of fasteners  25 , such as bolts. Further, the rotor cover  20  is formed with an opening  26  through which the pitot tube (not shown) extends when the pump is fully assembled. It can also be seen in  FIG. 2  that the rotating case  18  is somewhat bowl-shaped in that the rotating case  18  has an axially-extending peripheral wall  28 .  
         [0029]     As best illustrated in  FIGS. 1 and 3 , the pitot tube  16  is formed with an inlet  30  through which high velocity fluid enters as the rotating assembly  14  rotates. The inlet  30  of the pitot tube  16  is positioned in close proximity to the peripheral wall  28  of the rotating case  18  for this purpose. When the high velocity fluid strikes the inlet  30  of the pitot tube  16 , some of the fluid will enter the inlet  30 , but some of the fluid is deflected by the pitot tube  16  and is thrown against the peripheral wall  28  of the rotating case  18 .  
         [0030]     When the fluid being processed by the pump contains solids, thereby rendering the fluid abrasive, the fluid that is deflected by the inlet  30  of the pitot tube  16  eventually causes an area of erosion in the peripheral wall  28  of the rotating case  18 , as depicted by the trough  34  illustrated in  FIG. 4 . The trough  34  or area of erosion of the rotating case  18  is principally confined to that area of the peripheral wall  28  that is directly adjacent the inlet  30  of the pitot tube  16 . As noted previously, various attempts have been made to improve the abrasion-resistant character of the rotating case  18  in the area of typical erosion, but without success.  
         [0031]      FIGS. 5-8  illustrate the solution provided by the present invention. In  FIG. 5 , it can be seen that a groove  40  is formed in the peripheral wall  28  of the rotating case  18  in that portion of the peripheral wall  28  adjacent the position of the pitot tube inlet and, consequently, that portion of the wall  28  that would be conventionally eroded by fluid deflected away from the inlet of the pitot tube. The groove  40  is formed in the circumference of the peripheral wall  28  during the casting process and is sized is axial width and radial depth to accommodate a removable wear ring  42 , as shown in  FIG. 6 . Notably, while the groove  40  is shown formed in the rotating case  18 , it may be suitable to form the groove  40  in the wall of the rotor cover  20  if the rotating assembly  14  is so configured.  
         [0032]     The wear ring  42  of the present invention is generally formed as a band sized in axial width  44 , length  46  and radial depth  48  to fit snugly within the groove  40  formed in the rotating case  18 , as shown in  FIG. 7 . While the wear ring  42  is illustrated here as comprising a flattened band, the profile in cross section, as taken through the radial depth  48  of the wear ring  42 , may be other than flat (e.g., triangular shaped) to conform to a selected similar shape of groove  40  formed in the rotating case  18 . The radial depth  48  of the wear ring  42  is preferably equal to the radial depth of the groove  40 ; however, the radial depth  48  of the wear ring  42  may be slightly greater or slightly less than the radial depth of the groove  40 . It is only important that the radial depth  48  of the wear ring  42  be sized such that the pitot tube does not impact the wear ring  42  at any time during operation of the pump.  
         [0033]     The wear ring  42 , which is most suitably formed of a hard metal, ceramic or alloy material, is formed in a manner that allows the circumference of the wear ring  42  to be slightly flexible or able to expand and contract in an amount sufficient to allow positioning of the wear ring  42  within the groove  40 , and to allow removal of the wear ring  42  from the groove when replacement is required. As shown in  FIG. 6 , the contractibility and expandability of the wear ring  42  may be provided by forming the wear ring  42  with two free ends  50 ,  52  that enable one end  50 ,  52  of the wear ring  42  to be positioned in overlapping juxtaposition to the other end  50 ,  52  so that the circumference of the wear ring  42  can be contracted an amount sufficient to fit the wear ring  42  into the groove  40  formed in the rotating case  18 .  
         [0034]     Once positioned in the groove, as shown in  FIGS. 7 and 8 , the wear ring  42  may then expand, or spring back, to its original position with the two free ends  50 ,  52  positioned adjacent each other as shown in  FIGS. 6 and 8 . The wear ring  42  may be structured or configured in other suitable ways to enable the wear ring  42  to be positioned in the groove  40  of the rotating case  18 , including a configuration where the wear ring  42  is continuous (i.e., without free ends). As shown in  FIG. 8 , once the wear ring  42  is positioned in the groove  40 , the two free ends  50 ,  52  may be secured in position by any appropriate means, such as tack welds  54 .  
         [0035]     When the wear ring  42  becomes eroded or otherwise damaged, the worn wear ring  42  may be conveniently and quickly removed from the groove  40  in the rotating case  18  and replaced with a new wear ring  42 . For example, to remove the damaged wear ring  42  from the rotating case  18 , the groove  40  may be structured with a small notch  56 , as shown in  FIG. 8 . To replace the wear ring  42 , the tack welds  54  are broken to release the free ends  50 ,  52  of the wear ring  42 . An object, such as the blade of a screwdriver or pocket knife, is positioned in the notch  56  and one of the free ends  50  of the wear ring  42  is thereby lifted from the groove  40 . The raised free end  50  can then be used to pull the worn wear ring  42  from the groove. A new wear ring  42  may then be positioned in the groove  42 , making sure to position the free ends  50 ,  52  near the notch  56 , and may be tack welded  54  into place.  
         [0036]     It may be appreciated from  FIG. 1 , that effecting a replacement of the worn wear ring  42  involves simply removing the front or suction casing  60  portion of the pump casing  12 , removing the rotor cover  20  from the rotating case  18  and removing the pitot tube  16  from the rotating assembly  14 . Removal of those components of the pump  10  does not affect the balance of the pump, and does not require moving any other portion of the pump which would compromise its installation. Therefore, it can be appreciated that the wear ring of the present invention provides a significantly improved means for effecting repair of the rotating assembly caused by erosion or other damage. The wear ring of the present invention may be adapted for use in other types of pumps and, consequently, reference herein to specific details of the invention are by way of example and not by way of limitation.