Abstract:
A process control valve includes a valve stem, a valve plug. The valve stem and the valve plug are attached to one another by an arrangement that includes a locking pin that passes through substantially aligned bores in the valve stem and the valve plug. The locking pin is positively retained mechanically and prevented from extending outside of the bores in the valve stem and the valve plug.

Description:
RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Application Serial No. 60/410,496, filed Sep. 13, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to valves and more particularly to on/off valves, throttling valves and control valves.  
         DESCRIPTION OF THE RELATED ART  
         [0003]    Throttling valves, on/off valves and control valves are used in a wide number of process control system applications to control some parameter of a process fluid. While the process control system uses such a valve to ultimately control the pressure, level, pH or other desired parameter of a fluid, the valve basically controls the rate of fluid flow.  
           [0004]    Typically, an on/off valve, throttling valve, or control valve includes a fluid inlet passage coupled through an orifice to a fluid outlet passage and a closure member disposed in the orifice, which controls the amount of fluid flow therethrough. The closure member may include a valve plug having a surface which seats against a seat ring disposed at the orifice. During operation, the control system moves the valve plug towards and away from a surface of the seat ring to provide a desired fluid flow through the orifice and, therefore, the valve.  
           [0005]    It is desirable to positively retain valve trim components within a valve body of a control valve to minimize the chance of loose pieces traveling downstream and causing damage to other process equipment such as, for example, compressors, pumps, or turboexpanders. For example, in some control valves, the valve plug may be threadably secured to a valve stem, and prevented from rotating with respect to the valve stem by a locking pin that may be disposed within a bore passing through both the valve plug and the valve stem. The locking pin may be press fit into the bore, or alternatively, a bolt may be used in place of the locking pin that may be threadably received within the bore passing through the valve plug and the valve stem.  
           [0006]    In order to prevent the locking pin or locking bolt from exiting the bore, by selecting the appropriate pin material, stem material, and hole size, a tightly fitting pin , such as a groove pin, may be used, to reliably stay in place without positive mechanical restraint. However, the locking pin must be drilled out for removal during valve maintenance. In addition, some valves are configured such that a cage trim, disposed between the valve seat and the valve bonnet, serves to prevent the locking pin or locking bolt from exiting the bore during valve operation. However, if the valve is disassembled by separating the valve bonnet from the valve body, the locking pin or locking bolt may be accessed and removed if desired.  
           [0007]    In addition, for some applications, it may not be desirable to utilize a valve cage. For example, if the fluid being controlled is likely to clog the valve cage (such as, for example, a gritty or sticky process fluid), a different configuration for retaining the locking pin or locking bolt without the use of a cage trim, may be desirable.  
         SUMMARY OF THE DISCLOSURE  
         [0008]    A valve trim assembly is provided for a process control valve having a valve body and a bonnet. The valve trim assembly includes a valve plug adapted to move to one of a plurality of operational positions with respect to the valve body. The valve plug includes a plug bore, and a movable valve stem is attached to the valve plug. The movable valve stem includes a stem bore therein that is adapted to substantially align with the plug bore. A locking member is disposed in the stem bore and the plug bore and a retaining member may be attached to the bonnet. The retaining member substantially surrounds the locking member at all operational positions of the valve plug. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The advantages of the present invention will be apparent upon reading the following description in conjunction with the drawings, in which:  
         [0010]    [0010]FIG. 1 is a cross-sectional view of a control valve including a mechanically retained locking pin in accordance with the teachings of the present invention; and  
         [0011]    [0011]FIG. 2 is an enlarged detail view of a portion of the control valve of FIG. 1. 
     
    
     DETAILED DESCRIPTION  
       [0012]    With reference initially to FIG. 1, a process control valve  20  includes a valve body  22  that includes an outlet passage  24 , an inlet passage  26 , an orifice  27  disposed between the outlet passage  24  and the inlet passage  26 , and a bonnet  28 . (In an alternate example, the inlet passage  26  and the outlet passage  24  may be reversed, such that the fluid inlet passage becomes the fluid outlet passage, and the fluid outlet passage becomes the fluid inlet passage, thereby changing an upward flow valve to a downward flow valve.) An actuator housing  30  is attached to the bonnet  28 .  
         [0013]    A valve trim assembly, generally indicated at  31 , includes a valve stem  32  and a valve plug  34  that may be secured to a lower end  36  of the valve stem  32 , as oriented in FIG. 1. The valve stem  32  may extend through the actuator housing  30 , the bonnet  28 , and partially into the valve body  22 .  
         [0014]    The valve plug  34  may be sized and shaped to sealingly engage a valve seat ring  38  disposed within the orifice  27  in the valve body  22  when the process control valve  20  is in a closed configuration. The valve stem  32  may be moved vertically in a known manner with respect to the bonnet  28 , the actuator housing  30 , and the valve body  22 . For example, a diaphragm  40  within the actuator housing  30  may be used to facilitate vertical movement of the valve stem  32 . The diaphragm  40  may be secured to the valve stem  32  using nuts  41  and upper and lower diaphragm washers  43  and  45 , respectively. The actuator housing may be secured to the bonnet  28  using cap screws  47 .  
         [0015]    The valve plug  34  may be threadably connected to the lower end  36  of the valve stem  32 , as best seen in FIG. 2. A locking member such as a locking pin  42  may be disposed in a stem bore  44  in the valve stem  32  that is aligned with a corresponding plug bore  46  in the valve plug  34 . The locking pin  42  may be sized such that a first end  48  and a second end  50  of the locking pin  42  are both disposed within the plug bore  46 .  
         [0016]    As is generally understood in the art, movement of the diaphragm  40  causes movement of the valve plug  34  to one of a plurality of operational positions with respect to the valve body  22 . Accordingly, by controlling the pressure present in the upper and/or lower chambers of the actuator housing  30 , the position of the valve plug  34  may be controlled. As shown in FIG. 1, the process control valve  20  may include a preload spring  49  and an adjusting screw  51  for adjusting the amount of force provided by the preload spring  49 . It will be appreciated that other types of actuators in addition to the diaphragm actuator illustrated in FIG. 1 may be used without departing from the present invention.  
         [0017]    In order to provide proper sealing, packing  52  may be provided between the valve stem  32  and the bonnet  28 . The bonnet  28  may be secured to the valve body  22  by a hammer nut  54  threadably secured to the valve body  22 . The packing  52  may be secured in place by a packing retainer  56  that may be threadably attached to the bonnet  28  and that may be further secured in place by a lock nut  58 . The lock nut  58  may be configured as described in commonly assigned and co-pending U.S. Provisional Patent Application Serial No. 60/410,620 entitled, “Retainer Lock Nut for Fluid Pressure Control Device”.  
         [0018]    The packing retainer  56  includes a lower portion  60  that extends downwardly, as oriented in FIGS. 1 and 2. The lower portion  60  may be cylindrically-shaped, and serves as a retaining member that surrounds the locking pin  42  during operation of the process control valve  20 . Specifically, while the valve is in operation, both the first end  48  and the second  50  of the locking pin  42  are prevented from extending beyond the surface of the valve plug  34  by the presence of the lower portion  60  of the packing retainer  56 . The location of the locking pin  42  may be selected such that the valve seat ring  38  does not allow the valve plug  34  to travel downward sufficiently to expose the locking pin  42  below the lower portion  60  of the packing retainer  56 . Thus, over its entire range of travel, between a first or upper travel limit, and a second or lower travel limit, the valve plug  34  will always remain in a position such that the first end  48  and the second end  50  of the locking pin  42  will be constrained by the lower portion  60  of the packing retainer  56 .  
         [0019]    During valve maintenance, it may be highly desirable to access the locking pin  42  (for example, in order to replace or refinish the valve plug  34 ) without disassembling the actuator housing  30  or disturbing the position of the adjusting screw  51 . Accordingly, the process control valve  20  may be designed with sufficient stem travel to allow the locking pin  42  to be exposed and not covered by the lower portion  60  of the packing retainer  56  when the process control valve  20  is disassembled by removing the hammer nut  54  from the valve body  22 . The amount of actuator travel may be controlled by the distance between the lower diaphragm washer  45  and the cap screws  47 . The hammer nut  54  has sufficient thread engagement with the valve body  22  to provide a safe, easy way to control the stem position during valve disassembly without disturbing the position of the adjusting screw  51 .  
         [0020]    By positively retaining the locking pin  42  by mechanical means, the locking pin material, stem material, and the amount of mechanical interference between the locking pin  42  and the bores  44  and  46  in the valve stem  32  and the valve plug  34 , respectively, may be such that the locking pin may be easily removed with a hammer and a punch during valve maintenance procedures. For example, the locking pin material may be UNS S17400 and the stem material may be UNS S20910. Additionally, the amount of mechanical interference in the illustrated embodiment may be defined by a {fraction (5/32)} inch (0.397 cm) Type E groove pin, per American Society of Mechanical Engineers (ASME) Standard B18.8.2, with corresponding bore diameters  44  and  46  each in a range of from approximately 0.158 inches (0.401 cm) to approximately 0.160 inches (0.406 cm). This condition is sometimes referred to as a “loose” pin connection, and avoids situations in which the locking pin must be drilled out for removal, as may be required if an interference fit is used in the absence of such mechanical restraint.  
         [0021]    Since the packing retainer  56  is threaded to the bonnet  28 , the packing retainer  56  will not remain stuck inside the valve body  22  when the bonnet  28  is removed. The alignment and retention of the plug  34  onto the valve stem  32  may be achieved without the need for a cage, which may be advantageous, especially in certain applications, such as, for example, where the process fluid is gritty or sticky and therefore a cage can cause the valve to become clogged or the valve plug  34  to bind.  
         [0022]    As configured in accordance with the present disclosure, the disassembly of the process control valve  20  does not require disassembly of the packing  52 . Accordingly, the level of packing stress or preload may be preserved, ensuring that packing sealing performance is consistent with pre-maintenance operation. This configuration simplifies valve maintenance for assemblies that simply have worn or damaged trim and do not require packing adjustment or packing replacement. In addition, by not having to remove the packing or the valve stem, packing damage may be avoided and therefore the need for packing replacement due to damage during valve maintenance may also be avoided. The configuration also has an advantage of avoiding the need to disassemble the actuator housing  30  during valve maintenance, thus maintaining proper spring adjustment.  
         [0023]    The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art. For example, the invention is applicable to many types of valves in addition to on/off valves, throttling valves, and control valves, and is also applicable to valves that include a different type of locking member, such as a locking bolt instead of a locking pin for securing the valve stem to the valve plug.  
         [0024]    Thus, while the present invention has been described with reference to specific examples, which are intended to be illustrative only and not to be limiting of the invention, it will be apparent to those of ordinary skill in the art that changes, additions or deletions may be made to the disclosed embodiments without departing from the spirit and scope of the invention.