Patent Document

CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to provisional U.S. Patent Application No. 60/390,770, incorporated herein by reference in its entirety. 
     
    
     BACKGROUND  
       [0002]     The present disclosure relates to a system and method for supporting large vertically-oriented pumps. More particularly, this disclosure relates to a system and method for vertically supporting a pump and for relieving stress against pump shaft bearings during periods of non-use in a dynamic environment such as the deck of a ship.  
         [0003]     To transfer fluids between containers or from one container to a point of use, reciprocating or centrifugal-type mechanical pumps are often employed. Industrial centrifugal pumps consist of a vertically extending column having an intake, and one or more stages of impellers mounted about a shaft at the lower end of the column. The impellers are driven by the shaft, which extends coaxially upward through the column to a drive motor mounted on top of a discharge head, which is mounted on top of the vertical column. During operation, the pump intake is located at the bottom of the pump and is submerged into the pumped liquid or is fed pressurized liquid from one or more feeder pumps. Rotation of the impellers causes the liquid to be drawn into the pump intake delivered to an outlet conduit in fluid communication with another container, conduit, or point of use.  
         [0004]     Depending on the particular application, these types of pumps may be of substantial size with typical column lengths of about 15 to about 20 feet (about 4.5 to about 6 meters) or more, and column diameters ranging up to about 3 feet (about 1 meter) or more. The pump is thus made up of several major components, each of which may weigh several hundred pounds, wherein the total weight of the pump can be in excess of about 10,000 to about 15,000 pounds (about 4,500 to about 6,800 kilograms) or more.  
         [0005]     As described above, such pumps are generally mounted on a fixed base such that there is little or no movement of the support base while the pump is operating. However, occasionally pumps are mounted on bases that are subject to motion (both during operation and during periods of non-operation of the pump). For example, when the pump is mounted on the deck of a ship, where the ship cants from side to side or comes down hard over the top of a wave. Such motion can impart significant accelerations against the pump and its components—potentially having a G-force of up to about 1.8 G when added to the normal force of gravity. These forces can cause brinneling of the bearings, which significantly reduces bearing life.  
         [0006]     In addition, pumps are not currently adequately supported to withstand side-to-side motion or canting of the pump support either during use or periods of non-use.  
       BRIEF SUMMARY  
       [0007]     These and other problems and deficiencies of the prior art are overcome by providing a pump shaft support and method in which an upward force is exerted against the pump shaft during said periods of non-use of the pump thereby off-loading bearings normally supportive of the shaft. In another embodiment, a vertically oriented pressure pot having a cap secured thereto at an upper end thereof has suspended therefrom a pump housing, and a lateral support fixed to a lower end of the pressure pot interacts with an extension of the pump housing to prevent the pump housing from swinging laterally within the pressure pot.  
         [0008]     The above described and other features are exemplified by the following figures and detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     These and other features will be described below with reference to the following figures, in which:  
         [0010]      FIG. 1  shows a cross-sectional view of a pump;  
         [0011]      FIG. 2  shows a detail of a pump shaft locking mechanism in an engaged position according to one embodiment;  
         [0012]      FIG. 3  shows the pump shaft locking mechanism of  FIG. 2  in a disengaged position;  
         [0013]      FIG. 4  shows a detail of a pump shaft locking mechanism according to a second embodiment; and  
         [0014]      FIG. 5  shows a partially exploded view of a lateral support. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     Referring now to  FIG. 1 , a pump  100  includes a suction pot  110  primarily supported by support ring  112  and support arms  114 . Attached to the top of suction pot  110  is a cap  116  from which a pump housing  118  is suspended. Mounted for rotation within pump housing  118  is pump shaft  120 , which carries at least one set of vanes  122 , which pump the fluid by centripetal force in a known manner. Fluid enters suction pot  110  through intake  124  under pressure from feeder pumps (not shown). The fluid enters pump housing  118  by inlet  126  at about the bottom  128  of suction pot  110 , which then passes through one or more sets of the vanes  122 , wherein each set of vanes constitutes a stage. At the top of the pumping chambers is an exhaust conduit  130 , which passes the fluid to an exhaust outlet (not shown). In this manner, fluid enters from the bottom  128  of the suction pot  110  and is discharged at an upper portion of the suction pot  110  via the exhaust conduit  130 . Shaft  120  is driven by electric motor  132  to facilitate movement of the sets of vanes  122  during operation. A vibration sensor  134  is coupled to the suction pot  110  for detecting abnormal vibrations that could indicate a bearing failure or other malfunction.  
         [0016]     In certain applications, pump  100  may be subjected to relatively large accelerations that have the potential of putting undue stress on shaft support bearings  136  (three sets shown). To relieve the stress against the shaft support bearings  136 , a shaft support system  150  is employed during periods of non-use of pump  100 .  
         [0017]      FIGS. 2 and 3  illustrate one embodiment of the shaft support system  150  during pump operation and when the pump is not in use, respectively. In the shaft support system  150 , it is noted that shaft  120  extends upwardly through an opening  138  (in the cap  116  of suction pot  110  as shown in  FIG. 1 ). A threaded upper end  152  of the shaft  120  includes a washer  154  secured against a shoulder  156  of the threaded upper end  152  by at least one or more nuts  158 . Configured about shaft  120  is a cylinder shaped opening  160  (shown generally by arrow  160 ), which extends between end plates  162  and  164 . Each one of the end plates  162 ,  164  includes an opening through its center through which the pump shaft  120  extends. Disposed between the shaft  120  and within the cylinder shaped opening  160  is an annular piston  166 . Annular piston  166  includes a first stem  168  extending up through the opening formed in end plate  164  and a second stem  170  extending down through the opening formed in end plate  162 . The annular piston  166  is preferably sealed against an inner wall of the cylinder  160 , and an inner wall of the openings formed in end plates  162 ,  164 . End plate  162  is further sealed to cap  116  ( FIG. 1 ) of the suction pot  110 , and end plate  164  is further sealed to cap  172 , which covers the threaded upper end  152  of the pump shaft  120 .  
         [0018]     End plate  162  further includes an inlet  174  in fluid communication with a pressure space  176  formed between the annular piston  166  and end plate  164 . In addition, end plate  162  includes inlet  178  that is in fluid communication with a pressure space  180  formed between piston  166  and end plate  162 . A compression spring  182  is disposed in pressure space  180  for biasing the annular piston  166  towards end plate  162 .  
         [0019]     As shown in  FIG. 3 , during periods of non-use of pump  100 , pressurized fluid, e.g., nitrogen, is supplied to inlet  174 , causing the fluid pressure within pressure space  176  to increase. Inlet  178  is connected to a low-pressure source, such as atmospheric pressure. When the pressure differential between pressure spaces  176  and  180  overcomes the forces exerted by compression spring  182 , the annular piston  166  moves in an upward direction causing rim  184  of the first stem  168  to move and contact washer  154 . Pressure within pressure space  176  may be regulated to a predetermined amount of pressure using a control system  204 , thereby applying a predetermined amount of force against washer  154 . Sufficient force is thereby exerted against washer  154  to off-load bearings  136  (see  FIG. 1 ) from the weight of shaft  120  and vanes  122  carried thereon, thereby protecting bearings  136  from brinneling due to overloading such as may be caused by movement of the support system  150 , for example.  
         [0020]     The control system  204  as shown generally includes a gas source  206  in fluid communication with a pressure regulator  208  and an actuatable valve  210  such as a solenoid valve. Circuitry means are provided for actuating the valve and controlling the pressure. In this manner, the control system  204  can be used to engage and disengage the shaft support system  150  during use and on-use of the pump  100 .  
         [0021]     An optional vent  212  is preferably disposed in fluid communication with a space defined between the second stem  170  and wall of the end plate  162  as shown. The vent prevents fluid from being mixed with the actuating gas  206  of the shaft support system  150 . Mixture of the actuating gas and the fluid being pumped is prevented even in the event of seal failure.  
         [0022]     Among the advantages of the shaft support system  150  shown in  FIG. 2  is that support of the shaft  120  can be automatically operated and engaged when the pump  100  is shut down. In addition, support of the shaft  120  can be disengaged on demand when the pump  100  is started or activated. An interlocking mechanism comprising a pressure switch in operative communication with pressure space  176  is preferably used to prevent operation of pump  100  when support of the shaft  120  is engaged, thereby preventing damage to the various components of the support system  150  and pump  100 . In addition, by using pneumatic pressure in compression space  176 , the annular piston  166  automatically compensates for thermal variances resulting from the materials used for the shaft  120  and the pump housing  118 . For example, the shaft  120  is preferably fabricated from stainless steel. In contrast, the pump housing  118  is preferably fabricated from aluminum. When pump  100  is used for pumping cryogenic fluids, the stainless steel shaft  120  and the aluminum pump housing  118  will react differently due to their differing thermal coefficients of expansion. The support system  150  advantageously maintains a relatively constant lifting force against the threaded upper end  152  of the pump shaft  120  during the period of non-use. For example, after pumping cryogenic fluid such as liquefied hydrogen, liquefied nitrogen, liquefied natural gas, or other cryogenic fluids having a temperature of between 0° K. to 125° K. or more the pump components will be significantly chilled. The shaft support system  150  as described herein can be engaged, if desired, at these temperatures and remain engaged after the pump warms up during the period of non-use.  
         [0023]      FIG. 4  shows a second embodiment of shaft support system  150  that provides a simpler design than the embodiment of  FIGS. 2 and 3 . In this embodiment, the shaft support system  150  is manually operated. Shaft  120  extends upward through hole opening  138  in cap  116  of suction pot  110 . A support  186  supports platform  188 , which includes an opening through which the threaded upper end  152  of the pump shaft  120  passes therethrough. During periods of non-use of pump  100 , a nut  158  is threaded over upper end  152  of shaft  120  to a predetermined torque, thereby relieving bearings  136  of excess stress generated during movement of the support structure for pump  100 . When the pump is to be used, nut  158  is removed completely and cap  172  is placed over the upper end of the shaft  120 .  
         [0024]     Referring again to  FIG. 1 , it is noted that the primary support for suction pot  110  is by support ring  112  and support arms  114 . The pump housing  118  is suspended entirely from cap  116  of suction pot  110 . Thus, when subjected to lateral forces such as canting of a ship or other structure on which pump  100  is disposed, tremendous stresses occur against suction pot  110  and pump housing  118  due to induced lateral movement thereof. To reduce or eliminate such lateral movement, a lateral support  190  is provided at a lower end of suction pot  110 . As shown more clearly in  FIG. 5 , the lateral support  190  of the pump  100  comprises a holder  192  extending through and welded to the bottom  112  of suction pot  110 . Holder  192  includes a recess  194  into which a post  196  depends. Post  196  is fixedly coupled to a lower end of the pump located distal to vanes  122 . The post  196  ( FIG. 1 ) and recess  194  cooperate to prevent relative lateral movement therebetween. A thermal block  200  is preferably disposed at a lower end of holder  194 , which extends into a cup  198 . Cup  198  is secured to a rigid support surface  202  external to the pump  100 , which may comprise the bottom of the chamber (not shown) housing the pump  100  or another support surface available. Thus, cup  198  and thermal block  200  cooperate to prevent lateral movement of the suction pot  110 .  
         [0025]     This configuration is particularly advantageous for pumping cryogenic fluids such as liquefied hydrogen, nitrogen, natural gas or other such low temperature liquids in the range of 0° K. to 125° K. or more. As previously discussed, shaft  120  and suction pot  110  are preferably formed of stainless steel (e.g., 316 stainless steel) whereas pump housing  118  is preferably formed of aluminum. Since aluminum has a greater thermal expansion coefficient than stainless steel, it is expected that the lower end of pump housing  118  will move with respect to the bottom  128  of the- suction pot  110 . Furthermore, as temperatures change it is expected that the bottom  128  of the suction pot  110  will move with respect to surface  202 . The recess  194  and cup  198  preferably have a sufficient depth to permit relative motion between the post  196 , the holder  192 , and cup  198  to allow thermal expansion yet at the same time prohibit substantial lateral movement. Thermal block  202  is preferably formed of a high strength structural material that has thermal insulative properties to prevent heat from surface  202  and cup  198  from being conducted through to the interior of suction pot  110  by holder  192 . If pump  100  is not intended to be used for cryogenic fluids, thermal block  200  may not be required or may be incorporated into holder  192  as a single element depending on the thermal properties of the fluid.  
         [0026]     While the disclosure has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. Terms such as first and second as used herein are not intended to imply an order of importance or location, but merely to distinguish between one element and another of like kind. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.

Technology Category: 2