Abstract:
A pneumatic valve actuator for moving the valve stem of a control valve comprises an upper casing and a lower casing each having flanges, a diaphragm plate operatively coupled to the valve stem, a spring arranged to bias the diaphragm plate in a first direction, a diaphragm movable in conjunction movement of the diaphragm plate, an air inlet defined in the casing and arranged for attachment to an air supply source to bias the diaphragm plate in a second direction, and a ring disposed between the upper flange and the lower flange and positioned to engage the outer portion of the diaphragm. The ring includes a protrusion positioned to engage a surface of the outer portion of the diaphragm.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to valve actuators such as pneumatic valve actuators used on process control valves. More specifically, the present invention relates to a device and method for retaining the diaphragm within a pneumatic valve actuator. 
     BACKGROUND 
     It is generally known that process plants, such as refineries, chemical plants or pulp and paper plants, consist of numerous process control loops connected together to produce various consumer products. Each of these process control loops is designed to keep some important process variable such as pressure, flow, level, or temperature, within a required operating range to ensure the quality of the end product. Each of these loops receives and internally creates load disturbances that affect the process variable and control of the process control loops within the plant. To reduce the effect of these load disturbances, the process variables are detected by sensors or transmitters and communicated to a process controller. The process controller processes this information and provides changes or modifications to the process loop to get the process variable back to where it should be after the load disturbance occurs. The modifications typically occur by changing flow through some type of final control element such as a control valve. The control valve manipulates a flowing fluid, such as gas, steam, water, or a chemical compound, to compensate for the load disturbance and maintain the regulated process variable as close as possible to the desired control or set point. 
     It is generally understood that various control valve configurations may be specifically applicable for certain applications. For example, when a quick-opening valve with a narrow control range is suitable, a rotary control valve, such as a butterfly valve, may be used. Alternatively, when precise control over a large control range is required, a sliding stem control valve may be used. In any configuration, such control valves are generally coupled to a control device such as an actuator, which controls the exact opening amount of the control valve in response to a control signal. Thus, when designing a process, the process engineer must consider many design requirements and design constraints. For example, the design engineer must determine the style of valve used, the size of the valve, the type of actuator, etc. 
     In some systems, especially in pneumatically controlled fluid process systems, the actuator for any given fluid process control device may include a diaphragm actuator. Typical diaphragm actuators comprise a housing containing a spring-biased diaphragm assembly. The diaphragm assembly is operatively coupled to a flow control element via a valve stem or other actuator rod, in order to control the opening amount of the fluid process control device. 
     One known diaphragm assembly comprises a diaphragm and one or more diaphragm plates. The diaphragm comprises a flexible disk-shaped member constructed of a fluid-tight fabric, polymer, or other suitable material. The plates are disposed adjacent to the diaphragm and are adapted to be engaged by one or more springs disposed within the housing. Additionally, the plates provide a rigid mechanical connection to the stem. The springs serve to bias the diaphragm assembly into a predetermined position such that the actuator may bias the control device into an open or closed configuration. 
     In each of these known diaphragm assemblies, it is also necessary to secure the outer portion of the diaphragm to the outer portion of the actuator housing. Preferably, the outer portion of the diaphragm is secured in a manner that minimizes the chances of diaphragm failure, and in a manner that simplifies assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an exemplary control valve having a pneumatic actuator and assembled in accordance with the teachings of the present invention. 
         FIG. 2  is a cross-sectional view of the control valve of  FIG. 1  and illustrating a diaphragm and retention ring assembly assembled in accordance with a disclosed example of the present invention. 
         FIG. 3  is an enlarged fragmentary cross-sectional view taken through the right hand side of the pneumatic actuator shown in  FIG. 2  and illustrating aspects of the retention ring. 
         FIG. 4  is a further and large fragmentary cross-sectional view similar to  FIG. 3 . 
         FIG. 5  is a perspective view of an exemplary retention ring. 
         FIG. 6  is an enlarged fragmentary exploded view illustrating a portion of the retention ring, the diaphragm, and an insert. 
         FIG. 7  is an enlarged fragmentary exploded view illustrating a portion of a retention ring assembled in accordance with another disclosed example of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Although the following text sets forth a detailed description of an exemplary embodiment of the invention, it should be understood that the legal scope of the invention is defined by the words of the claims set forth at the end of this patent. The detailed description is to be construed as exemplary only and does not describe every possible embodiment of the invention since describing every possible embodiment would be impractical, if not impossible. Based upon reading this disclosure, those of skill in the act may be able to implement one or more alternative embodiments, using either current technology or technology developed after the filing date of this patent. Such additional indictments would still fall within the scope of the claims defining the invention. 
     Referring now to the drawings,  FIGS. 1 and 2  show a control valve  20  of the type commonly employed in process control systems. The control valve  20  includes a valve body  22 , a valve inlet  24 , a valve outlet  26 , and a flow passage  28  that extends between the inlet  24  and the outlet  26 . The flow passage  28  includes an inlet passage  30 , an outlet passage  32 , and a control passage  34 . 
     As shown in  FIG. 2 , the control valve  20  includes a moveable control component  36  which, in the disclosed example, takes the form of a valve plug  38 . The valve plug  38  is connected to a valve stem  40 , and the valve plug  38  and the valve stem  40  are sized and positioned such that the valve plug is disposed in the control passage  34 . The control component  36  may take the form of, by way of example rather than limitation, a valve sleeve, a valve disc, or any other type of control component commonly employed in the field of control valves. Further, the valve stem  40  may be a sliding stem, a rotary stem, or any other form of moveable or shiftable valve stem. The control valve  20  also includes a bonnet  42  having a packing box  44  having a packing nut  46 , a yoke  48 , an actuator  50  connected to the yoke  48 , and may include a valve positioner  52 . The illustrated actuator  50  is a pneumatic actuator, which may be suitably connected to the valve positioner  52  or to any other mechanism for controlling the actuator. The actuator  50  includes a diaphragm casing  54  having an upper portion  56  and a lower portion  58 , which are joined together along a circumferential joint  60 . 
     Referring still to  FIG. 2 , the actuator  50  also includes an internal diaphragm plate  62  that is suitably connected to an output shaft  64 , and the output shaft  64  in turn is connected to the valve stem  40  using a suitable coupling  66 . A suitable biasing assembly  68  is disposed within the actuator  50 . In the illustrated example, the biasing assembly  68  bears against a top portion of the diaphragm plate  62 , and also bears against an inside or bottom surface of the top portion  56  of the diaphragm casing  54 . In the disclosed example, the biasing assembly is a plurality of springs. The actuator also includes a flexible diaphragm  70 , which bears against a central portion  72  of the diaphragm plate  62 . The diaphragm includes an outer portion  74 , which is sized to extend radially outward so as to be disposed at the joint  60  between the upper portion  56  and the lower portion  58  of the diaphragm casing  54 . As shown in  FIG. 2  (and explained in greater detail below), a retention ring  76  assembled in accordance with the teachings of a disclosed example of the present invention is disposed within the diaphragm casing  54  along the joint  60 . In response to operation of the positioner  52 , the pressure changes within the diaphragm casing  54 , which in turn moves the diaphragm  70  and the diaphragm plate  62  up and down within the diaphragm casing  54 . This up and down movement changes the position of the control component  36  in order to control the flow of a process fluid through the control valve  20 . 
     Referring now to  FIGS. 3 and 4 , the upper portion  56  and the lower portion  58  of the diaphragm casing  54  are shown in greater detail, as are the outer portion  74  of the diaphragm  70  and the retention ring  76 . The upper portion  56  and the lower portion  58  of the diaphragm casing  54  each include an outer flange  78  and  80 , respectively, and the outer flanges  78  and  80  are connected together by a plurality of attachment bolts  82  to form the joint  60 . The diaphragm plate  62  ( FIG. 3 ) includes an upwardly extending portion  84  having a surface  84   a . The diaphragm  70  includes a convolution  85 , such that a portion of the diaphragm  70  rolls against the surface  84   a  as the diaphragm plate  62  moves up and down. As outlined above, the outer portion  74  of the diaphragm  70  extends between the outer flange  78  and the outer flange  80 . Preferably, the diaphragm  70  includes a plurality of attachment holes  86  (which are shown more clearly in  FIG. 6 ) which are sized to receive a corresponding one of the attachment bolts  82  and which may be positioned to register with a selected one of a plurality of attachment holes  88  in the outer flange  78  and attachment holes  90  in the outer flange  80 . The retention ring  76  is sized for placement between the outer flange  78  and the outer flange  80 , and the retention ring  76  also includes a plurality of attachment holes  91  which register with the attachment holes  86  and  88 , as well as with the attachment holes  86  on the outer portion  74  of the diaphragm  70 . Accordingly, the flanges  78 ,  80 , the outer portion  74  of the diaphragm  70 , the retention ring  76 , and the attachment bolts  82  together form the joint  60 . 
     Referring to  FIGS. 5 and 6 , the retention ring  76  includes an inner portion  92  and an outer portion  94 , with the attachment holes  91  preferably formed generally adjacent the outer portion  94 . The retention ring  76  also includes a protrusion  96 . Preferably, the protrusion  96  is formed generally adjacent the inner portion  92  of the retention ring  76 . In the disclosed example, the protrusion  96  is formed at an innermost end  92   a  of the retention ring  76  when viewing the retention ring  76  in cross-section as shown in  FIGS. 3 ,  4  and  6 . The retention ring  76  includes an upper surface  98  and a lower surface  100 . Accordingly, when the retention ring  76  is positioned as shown in the disclosed example as illustrated in  FIGS. 3 and 4 , the upper surface  98  is positioned adjacent a lower surface  102  of the outer portion  74  of the diaphragm  70 . The lower surface  100  is positioned adjacent in upper surface  104  of the outer flange  80 . Consequently, in the disclosed example, the outer portion  74  of the diaphragm  70  is positioned between the upper surface  98  of the retention ring  76  and the lower surface of the outer flange  78 . When positioned as shown, the protrusion  96  extends upwardly from the upper surface  98  of the retention ring so as to engage and compress an adjacent portion  106  of the diaphragm  70  from below. It will be appreciated that the retention ring may also be positioned above the outer portion  74  of the diaphragm  70  such that the protrusion  96  extends downwardly into an upwardly facing surface of the diaphragm  70 , thus engaging the retention diaphragm  70  from above. 
     Referring now to  FIGS. 3 ,  4  and  6 , the protrusion  96  is shown in cross-section. In accordance with the disclosed example, the cross-section of the protrusion  96  is curved or generally semicircular. Other shapes for the cross-section may prove suitable. In accordance with the disclosed example, the protrusion  96  is integrally formed with the balance of the retention ring  76  out of a single piece of material. Consequently, in the example shown, the protrusion  96  is formed by a thickened lip  104 . Alternatively, the protrusion  96  may be formed from a separate and distinct component, such as a separate ring that is glued, welded, bonded or otherwise suitably secured to the balance of retention ring  76 . Further, although the protrusion  96  is shown adjacent the inner portion  92 , the protrusion also may be formed in a central portion  95  of the retention ring  76 , or adjacent the outer portion  94 . 
     As best shown in  FIGS. 4 and 6 , the hole  86  preferably is sized to receive an insert  108 . In the example shown, the hole  86  is larger than the hole  91 . The insert has an outer diameter D 1  sized to match a diameter D 2  of the hole  86 , and has an inner bore  110  sized to receive the attachment bolt  82 . In accordance with the disclosed example, the insert  108  spreads out loads experienced at an interface between the diaphragm  70  and the bolts  82 , and avoids stress risers in the diaphragm  70 . 
     As shown in  FIG. 7 , an alternative embodiment for the retention ring is shown and is referred to by the reference numeral  176 . As shown in  FIG. 7 , the retention ring  176  includes a thickened portion  178 . As shown, the thickened portion  178  is disposed adjacent an inner end  180  of the retention ring  176 , such that the inner end  180  is thicker than an outer end  182 . Alternatively, the thickened portion  178  may be spaced at the inner end  180  or slightly away from the inner end  180 . As shown, the retention ring  176  may have a slightly wedge-shaped cross-section in which an inner end  180  is thicker than the outer end  182 . 
     The control valve  20  incorporating any one of the above-described retention rings  76 ,  176  may be assembled from a conventional valve as follows. After sizing the outer flanges  78  and  80 , including the location of the attachment holes  88  and  90 , the diaphragm  70  may be chosen from conventional materials and may be sized based on conventional sizing principles. The diaphragm,  70  will be provided with the attachment holes  91 , which are sized and located to register with the attachment holes  88  and  90  and to receive the bolts  82 . The holes  86  preferably will be sized to receive the inserts  108 . 
     The retention ring  76  is provided with the annular ring-shaped protrusion sized to fit between the upper flange and the lower flange, and the diaphragm is positioned between the upper flange and the lower flange, and positioning the protrusion such that the bears against an adjacent surface of an outer portion of the diaphragm. The flanges are then secured together. 
     Preferably, the annular ring-shaped protrusion may be formed on a ring sized to fit between the upper flange and the lower flange and is provided with attachment holes through an outer portion of the ring, with each attachment hole sized to receive a fastener. The ring is aligned or positioned such that the attachment holes are aligned with holes in the upper and lower flanges, and spacers or inserts are inserted in the attachment holes between the flanges. The ring-shaped protrusion may be formed adjacent an inner portion of the ring, an outer portion of the ring, or adjacent a central portion of the ring. The protrusion may have a curved cross-section, and may be formed by providing a thickened portion adjacent an inner portion of the ring or adjacent any other suitable portion of the ring. The ring-shaped protrusion may be formed by shaping a selected one of the upper flange or the lower flange to have an angled cross-section, such that an inner portion of the selected flange has a first thickness and an outer portion of the selected flange has a second thickness less than the first thickness. 
     Numerous modifications and alternative embodiments of the invention will be apparent to those skilled in the art in view of the forgoing description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the present disclosure may be varied without departing from the spirit of the invention, and the exclusive use of all modifications which are within the scope of the claims is reserved.