Abstract:
Fluid control valves having an adjustable valve stem and piston assembly are described herein. An example fluid control valve includes a piston to control a flow of fluid through a valve body, a bonnet having a threaded bore and a housing to be removably disposed within and threadably coupled to the bonnet. The housing includes a first portion to be disposed in the bonnet, a roller assembly to be pivotally mounted to the first portion, the roller assembly to engage the piston to control a position of the piston. The housing including a second portion with a threaded outer surface to couple to the threaded bore of the bonnet. A valve stem is to move through the housing to control the movement of the roller assembly and the piston.

Description:
FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to fluid valves and, more particularly, to a fluid control valve having an adjustable valve stem and piston assembly. 
     BACKGROUND 
     Process control systems often employ fluid control valves to control a flow of fluid. In some low-flow sanitary fluid valves, a valve stem moves within a bonnet that houses a roller assembly. In operation, an actuator moves the valve stem through the bonnet, which causes the roller assembly to move a plate attached to a piston that moves a fluid control member (e.g., a membrane or diaphragm) relative to an orifice or valve seat to control fluid flow. 
     In such low-flow applications, the movements of the piston are relatively small and, thus, such valves must be calibrated accurately to tightly control the relationship between the movement of the valve stem and the movement of the piston. In many such known valves, this calibration is performed at the time of manufacture (e.g., in a factory setting) by holding the valve stem, the plate and the piston at fixed positions relative to the bonnet (e.g., such that the valve is in a closed position) and then affixing the piston to the plate (e.g., gluing with adhesive). As a result, any recalibration to these known valves typically requires disassembly and/or rebuilding of the valves (e.g., in a manufacturing environment). 
     SUMMARY 
     An example fluid control valve includes a piston to control flow of fluid through a valve body, a bonnet having a threaded bore and a housing to be removably disposed within and threadably coupled to the bonnet. The housing includes a first portion to be disposed in the bonnet, a roller assembly to be pivotally mounted to the first portion, the roller assembly to engage the piston to control a position of the piston. The housing including a second portion with a threaded outer surface to couple to the threaded bore of the bonnet. A valve stem is to move through the housing to control the movement of the roller assembly and the piston. 
     In another example, a fluid control valve includes a bonnet and a housing. A valve stem moves through the housing to control a piston. The housing couples to the bonnet and can be adjusted to calibrate the valve. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a known fluid control valve. 
         FIG. 2  illustrates an example fluid control valve described herein. 
         FIG. 3  illustrates the housing and the valve stem of the example valve of  FIG. 2 . 
         FIG. 4  is a detailed view of the housing of the example valve of  FIG. 2 . 
         FIG. 5  is a detailed view of the piston of the example valve of  FIG. 2 . 
         FIGS. 6A and 6B  illustrate example valve stems having different flow profiles. 
     
    
    
     DETAILED DESCRIPTION 
     In general, the example fluid control valve described herein provides self-alignment of its internal components during manufacture of the valve, the ability to perform field adjustments to calibrate the valve and the ability to select different fluid flow characteristics. More specifically, the example valve includes a unitary piece that functions as a housing through which the valve stem moves and a mount for a roller assembly that moves a piston within the valve. The housing has a threaded outer surface that couples to a threaded bore in the bonnet. The threaded coupling between the housing and the bonnet ensures that the valve stem remains aligned with the roller assembly and also enables the housing to be field-adjusted to calibrate the valve (e.g. by rotating the housing relative to the bonnet). The example valve also provides an externally accessible screw that can be used to more precisely calibrate the valve. In addition, the housing contains a pin that stops the movement of the valve stem at a predetermined position (e.g., such that the valve is closed), thereby ensuring that the movement of the valve stem from a closed position always starts at the same point. This permits the use of valve stems having different shapes and flow profiles, such as an equal percentage profile. 
     Before discussing an example fluid control valve in detail, a brief description of a known fluid control valve  100  is provided in connection with  FIG. 1 . The known fluid valve  100  includes a bonnet yoke  102  that defines a cavity  104  into which a valve body (not shown) is placed. Openings  106  and  108  in the bonnet yoke  102  receive bolts (not shown) to fix the valve body in the cavity  104 . A bonnet  110  couples the bonnet yoke  102  to an actuator (not shown) and includes an opening  112  to slidably receive a valve stem  114 , which operatively couples the actuator to a flow control member (not shown) disposed within the valve body. The fluid valve  100  also includes a roller assembly  116  disposed within a cavity  117  of the bonnet  110 . The roller assembly  116  includes first and second arms  118   a  and  118   b , first and second upper rollers  120   a  and  120   b , first and second lower rollers  122   a  and  122   b  and first and second pivots  124   a  and  124   b.    
     In operation, an actuator moves the valve stem  114  toward the roller assembly  116  to rotate the upper rollers  120   a  and  120   b , which causes the first and second arms  118   a  and  118   b  to rotate about the first and second pivots  124   a  and  124   b . This rotation of the arms  118   a  and  118   b  causes the lower rollers  122   a  and  122   b  to rotate and move plate  125  and a piston  126  toward the valve body (i.e., downward in the orientation of  FIG. 1 ) to cause a flow control member to restrict the flow of fluid through valve body. When the valve stem  114  is moved far enough, the piston  126  moves the flow control member to a closed position to prevent any fluid flow through the valve body. An actuator moves the valve stem  114  away from the roller assembly  116  to rotate the upper rollers  120   a  and  120   b  in the opposite direction, which causes the first and second arms  118   a  and  118   b  to rotate about the first and second pivots  124   a  and  124   b . This rotation of the arms  118   a  and  118   b  causes the lower rollers  122   a  and  122   b  to rotate and move the plate  125  and the piston  126  away from the valve body (i.e., upward in the orientation of  FIG. 1 ) to cause the flow control member to increase the flow of fluid through the valve body. 
     In low-flow applications, the amount of fluid that flows through the valve body is relatively small. As such, the movements of the piston  126  and the flow control member are also small. Typically, there is a fixed relationship between the movement of the valve stem  114  and the movement of the piston  126 , and the fluid valve  100  must be calibrated accurately to ensure that this relationship remains in effect. This calibration is typically performed at the time of manufacture by holding the valve stem  114 , the plate  125  and the piston  126  in fixed positions such that the valve  100  is in a closed position. The piston  126  is then affixed to the plate  125  (e.g. glued with adhesive). If there is an error during manufacture or if the relationship between the movement of the valve stem  114  and the movement of the piston  126  changes after manufacture, the fluid valve  100  can only be re-calibrated by disassembly and replacement of parts. Also, to ensure the proper operation of the fluid valve  100 , the valve stem  114  must be centered relative to the roller assembly  116 . This alignment is performed at the time of manufacture and cannot be easily changed thereafter. 
       FIG. 2  illustrates an example fluid control valve  200  described herein. The example fluid valve  200  includes a bonnet yoke  202  that defines a cavity  204  into which a valve body (not shown) is placed. Openings  206  and  208  in the bonnet yoke  202  receive bolts (not shown) to fix the valve body in the cavity  204 . A bonnet  210  couples the valve body to an actuator (not shown) and includes a threaded bore  212 . A housing  214  disposed within a cavity  215  of the bonnet  210  has a first portion  216 , on which a roller assembly  218  is mounted, and an elongated second portion  220 , which has a threaded outer surface  221  that couples to the threaded bore  212 . The first portion  216  of the housing  214  and the second portion  220  of the housing  214  are depicted as being part of a unitary piece. However, if desired, the housing  214  may be composed of multiple pieces. A valve stem  222  moves through the second portion  220  of the housing  214  to operatively couple an actuator (not shown) to a flow control member (not shown) disposed within the valve body. The second portion  220  of the housing  214  has a teflon sleeve  223  that provides a self-lubricating bearing surface for the valve stem  222  as it moves within the sleeve  223  through the housing  214 . The roller assembly  218  includes first and second arms  224   a  and  224   b , first and second upper rollers  226   a  and  226   b , first and second lower rollers  228   a  and  228   b  and first and second pivots  230   a  and  230   b . O-ring seals  231   a ,  231   b ,  231   c ,  231   d ,  231   e  and  231   f  are provided to prevent leakage of process fluid. 
     In operation, an actuator moves the valve stem  222  toward the roller assembly  218  to rotate the upper rollers  226   a  and  226   b , which causes the first and second arms  224   a  and  224   b  to rotate about first and second pivots  230   a  and  230   b . This rotation of the arms  224   a  and  224   b  causes the lower rollers  228   a  and  228   b  to rotate and move along a surface  229  and move a piston  232  toward the valve body (i.e., downward in the orientation of  FIG. 2 ) to cause a flow control member to restrict the flow of fluid through the valve body. When the valve stem  222  is moved far enough, the piston  232  moves the flow control member to a closed position to prevent fluid flow through the valve body. An actuator moves the valve stem  222  away from the roller assembly  218  to rotate the upper rollers  226   a  and  226   b  in the opposite direction, which causes the first and second arms  224   a  and  224   b  to rotate about first and second pivots  230   a  and  230   b . This rotation of the arms  224   a  and  224   b  causes the lower rollers  228   a  and  228   b  to rotate and move the piston  232  away from the valve body to cause the flow control member to increase the flow of fluid through the valve body. 
     The housing  214  mounts the roller assembly  218  and also receives the valve stem  222  so that the valve stem  222  and the roller assembly  218  are properly aligned along an axis  234 . Furthermore, because the housing  214  couples to the bonnet  210  through threaded surfaces, the position of the housing  214  can easily be adjusted for calibration (e.g., by rotating the housing  214  relative to the bonnet  210 ). A relatively finer threading on the threaded surfaces may be provided to enable more precise calibration. In addition, the housing  214  contains a pin  236  that stops the movement of the valve stem  222  at a predetermined position (e.g., a closed position). The piston  232  includes a spring  238  to reduce vibrations and ensure proper functioning of the piston  232 . Also, an externally accessible screw  240  can be used to adjust the position of the piston  232  for more precise calibration. 
     The valve  200  can be calibrated by adjusting the housing  214  and/or by adjusting the piston  232 . Coarse calibrations can be made by rotating the housing  214  relative to the bonnet  210 . Rotating the housing  214  clockwise causes the housing  214  and the mounted roller assembly  218  to move closer to the piston  232 . Conversely, rotating the housing  214  counter-clockwise causes the housing  214  and the roller assembly  218  to move away from the piston  232 . Moving the housing  214  and the roller assembly  218  in either direction changes the position at which the valve stem  222  causes the valve  200  to be in a closed position. 
     Similarly, fine calibrations can be made by adjusting the position of the piston  232  relative to the bonnet  210 . Specifically, moving (e.g., by turning) the externally accessible screw  240  further into the valve  200  causes the piston  232  to move away from the bonnet  210 . Conversely, moving the screw  240  further out of the valve  200  causes the piston  232  to move toward the bonnet  210 . Moving the piston  232  in either direction changes the position at which the valve stem  222  causes the valve  200  to be in a closed position. 
       FIGS. 3 and 4  illustrate a detailed view of the housing  214  of the example valve  200  of  FIG. 2 . The first portion of the housing  216  is generally cylindrically shaped, which allows the housing  214  to rotate within the bonnet  210 . The upper rollers  226   a  and  226   b  and the lower rollers  228   a  and  228   b  are mounted on the first portion  216  of the housing  214 . Openings  300   a ,  300   b ,  300   c  and a fourth opening (not shown) are used to mount the pivots  230   a  and  230   b . Openings  400   a  and  400   b  are used to mount the pin  236 . A bolt head  302  integrated to the housing  214  may be used to rotate the housing  214  to perform a calibration. 
       FIG. 5  is a detailed view of the piston  232  of the example valve  200  of  FIG. 2 . The piston  232  includes protrusion or lip  500  that guides the screw  240  and prevents the piston  232  from rotating. The screw  240  is tapered such that its diameter increases further from the lip  500 . Moving the screw  240  toward the lip  500  causes the piston  232  to move further from the bonnet  210 . Moving the screw  240  away from the lip  500  causes the piston  232  to move closer to the bonnet. 
     The surface  229  in the example shown has a linear taper along which the roller assembly  218  moves. However, a different shape could be used to provide the valve assembly with a different flow profile. 
     Alternatively or additionally, a differently shaped valve stem may be used to provide a different flow profile.  FIGS. 6A and 6B  illustrate example valve stems having different flow profiles.  FIG. 6A  depicts a valve stem  600  having a linear profile. A tip  602  of the valve stem  600  is shaped to ensure a linear profile.  FIG. 6B  depicts a valve stem  604  having an equal percentage profile. A tip  606  of the valve stem  604  is shaped to ensure an equal percentage profile. 
     Although certain example methods and apparatus have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus, and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.