Abstract:
A control valve positioner mounting system is configured to include a control valve, a control valve positioner, an attachment lever translating movement of the control valve to the control valve positioner, and a control valve attachment system for attaching the control valve to the attachment lever using a spring loaded attachment affixed to the control valve and applying spring force to the attachment lever.

Description:
FIELD OF THE INVENTION  
       [0001]    This application relates to a mounting kit for attaching a control valve positioner to a control valve stem, in particular to a system for attaching the control valve positioner to the control stem using a closed spring force circuit that applies the spring force to the attachment arm. 
       BACKGROUND  
       [0002]    A control valve is typically used to control the flow of liquids, gas and steam in a variety of industrial applications including chemical, petrochemical, bio-tech, food and beverage, pharmaceutical, general industrial, and research applications. Control valves may be configured in a variety of different ways to provide precision control for the wide variety of applications. Typical control valve designs range from ¼ to 2 inch flow channels; handle pressures from vacuum to 60,000 PSI; handle temperatures from cryogenic to 1500° F., and control the flow of a wide selection of materials. Although typical control valves are described above, custom control valves can be configured from most any application. 
         [0003]    Typical control valves are driven by a pneumatic actuator, referred to herein as a control valve actuator. The control valve actuators control the volume of liquid and/or gas flowing through the control valve based on a control signal received at the actuator. Accordingly, control valves may be controlled to provide greater or lesser flow volumes based on a current demand, based on a desired flow volume, etc. 
         [0004]    In operation, control valves may experience a difference between a set flow volume, representing a desired flow volume and the actual flow volume allowed by the control valve. The deviations may be corrected for using control valve positioners. 
         [0005]    Control valve positioners are used to avoid the influence of forces such as friction and/or differential pressures that can affect the valve position. These forces typically are created from different pressures in the valve itself. 
         [0006]    A control valve positioner relates the input signal indicating a measured flow volume to the valve position representing the desired flow volume, and will provide a signal to the control valve actuator to correct for deviations in the two values. The control valve positioner is usually fitted to a yoke or pillars of the actuator, and it is linked to a spindle of the actuator by a feedback arm in order to monitor the valve position. The control valve positioner measures the actual stroke of the valve and compares it with a set point received from an external device. Depending on the actual stroke and the signal the positioner creates a pneumatic signal to the control valve actuator. Typically, the actual stroke is measured with a lever with a rotating connection to the positioner. Thus, the linear movement of the valve stem is translated to a rotating movement in the positioner. 
         [0007]    Typical mounting kits use a spring, either internal or external, to maintain the lever on the control valve stem. However, these springs can induce forces into the valve stem system. Further, erosion of materials in the connection point caused by the constant movement of the valve stem can cause drifting in the position values measured by the control valve positioner. 
         [0008]    Accordingly, there remains a need for a control valve positioner mounting that does not introduce additional forces to the valve stem system. There further remains a need for such a mounting that compensates for erosion of materials caused by the constant movement of the valve stem. 
       SUMMARY OF THE INVENTION  
       [0009]    The invention provides a system and method for attaching a control valve positioner to a control valve stem, in particular to a system for attaching the control valve positioner to the control stem using a closed spring force circuit that applies the spring force to an attachment arm. The closed spring three circuit applied to spring force to minimize or negate transference of spring force to the control valve stem. 
         [0010]    According to one exemplary embodiment, a control valve positioner mounting system is configured to include a control valve, a control valve positioner, an attachment lever translating movement of the control valve to the control valve positioner, and a control valve attachment system for attaching the control valve to the attachment lever using a spring loaded attachment affixed to the control valve and applying spring force to the attachment lever. 
         [0011]    The spring loaded attachment may include a pair of bushings positioned on opposing sides of the attachment lever, where the spring force is applied to the attachment lever by one of the pair of bushings is biased in the direction of the bushing on the opposing side. Further, the spring force may be applied in a closed force circuit by anchoring a spring applying the spring force such that the spring force the applied to the attachment lever. 
         [0012]    According to another variation, the attachment lever includes a pair of parallel bars and the pair of bushings are mounted to a bushing support bar positioned between the parallel bars. The bushing support bar may be slidably mounted between the parallel bars such that the bushing support bar can slide along the length of the attachment lever, where each bushing of the pair of bushings includes a sloping face on a face proximate to the opposing bushing such that the spring force applied to the parallel bars is consistent independent of wear on the pair of bushings. 
         [0013]    According to another variation, the material forming the pair of bushings is electrically neutral to avoid sparking. One such material may be Teflon. 
         [0014]    According to one exemplary embodiment, a control valve positioner mounting system is configured to include a control valve, a control valve positioner, an attachment lever including a pair of parallel bar arms translating movement of the control valve to the control valve positioner, and a control valve attachment system for attaching the control valve to the attachment lever using a spring loaded attachment affixed to the control valve and applying spring force to the parallel bar arms of the attachment lever wherein the force applied to a first parallel bar arm is the same as the force applied to a second parallel bar arm. 
         [0015]    Other features of the invention, besides those discussed above, will be apparent to those of ordinary skill in the art from the description of the preferred embodiments which follows. In the description, reference is made to the accompanying drawings, which form a part hereof, and which illustrate examples of the invention. Such examples are illustrative, but for the scope of the invention, reference is made to the claims which follow the description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0016]      FIG. 1  is an exploded view of a sliding stem control valve assembly, according to an exemplary embodiment; 
           [0017]      FIG. 2  is a cut away diagram illustrating a mounting kit for mounting an attachment lever to an actuator stem of the control valve actuator, shown in  FIG. 1 , according to an exemplary embodiment; 
           [0018]      FIG. 3  is a first perspective of the mounting kit of  FIG. 3 , shown in situ, according to an exemplary embodiment; and 
           [0019]      FIG. 4  is a second perspective of the mounting kit of  FIG. 4 , shown in situ, according to an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    Referring to  FIG. 1 , a control valve assembly  100  including a control valve  110  and a control valve actuator  150  is shown, according to an exemplary embodiment. Although a specific control valve  110  and a specific control valve actuator  150  are illustrated as an exemplary valve assembly  100 , the specific type and configuration of control valve  110  and control valve actuator  150  can vary. 
         [0021]    The control valve  110  may be one that is commercially distributed by Badger Meter, Inc., the assignee of the present invention. An example is the Model 9000 valve, a globe style valve with bolted bonnet and post guided innervalve designed for modulating control of liquids and vapors in medium duty industrial applications such as chemical plants, pulp paper and textile mills, refineries and other industries. 
         [0022]    Control valve  110  includes a housing  112  having an inlet port  114 , an outlet port  116  and a flow channel  118  for transporting a liquid and/or gas between inlet port  114  and outlet port  116 . Control valve  110  further includes a metering valve  120  positioned in the flow channel  118  to control the flow volume passing between the inlet port  114  and the outlet port  116 . 
         [0023]    The metering valve  120  may be implemented as a sliding stem type control valve, a rotary valve, a butterfly valve, etc. The metering valve  120  is controlled via manipulation of a control valve stem  122  connected by mechanical coupling to the metering valve  120 . For example, wherein control valve  110  is a sliding stem type valve, movement of the control valve stem  122  towards and away from the flow channel  118  may be utilized to control the flow volume. 
         [0024]    Control valve actuator  150  is a device configured to accurately locate the metering valve  120  in a position dictated by a control signal by manipulation of the control valve stem  122 . The control valve actuator  150  may be implemented as a pneumatic or electric actuator although the present application will describe the control valve actuator with reference to a pneumatic actuator. The actuator  150  accepts a signal from a control system (not shown) and, in response, moves the valve  110  to a fully-open or fully-closed position, or a more open or a more closed position (depending on whether ‘on/off’ or ‘continuous’ control action is used). Control valve actuators  150  may be piston actuators, diaphragm actuators, reverse acting actuators, direct acting actuators, etc., although actuator  150  is shown and described herein as a diaphragm actuator. 
         [0025]    Actuator  150  includes a housing  152  holding a diaphragm  154  coupled to an actuator stem  156  and configured to maintain the actuator stem  156  in a neutral position by a return spring  158  in an unloaded position. In operation, diaphragm actuators have compressed air or a fluid applied to diaphragm  154  to displace the actuator stem  156  from the neutral position and loading the return spring  158 . The compressed air is typically applied to a single side of the diaphragm  154 . Return spring  158  may be configured as one of a direct acting (spring-to-retract) or reverse acting (spring-to-extend) spring. The diaphragm and the actuator stem  156  may be connected to the control valve stem  122  such that the control valve stem  122  is held in a default position such as open, closed, neutral, etc. when the diaphragm  154  is in the unloaded position. 
         [0026]    Many forces act on the control valve stem  122  and control valve  120 , including for example spring forces from the spring  158 , fluid forces, and frictional forces. It is understood that valves and their associated forces are well known in the art and that the above description is merely representative of many different types of forces. These forces may cause a deviation between a set value of the control valve  120  and an actual position of the valve and/or a deviation between a set value of the flow volume and an actual flow volume. 
         [0027]    Accordingly, control valve assembly  100  further includes a positioner  160  to correct for the deviations between a set position and an actual position of the control valve  120 . Referring now to  FIGS. 4 and 5 , it will be noted that the positioner  160  includes a sliding assembly  162 . The sliding assembly  162  is configured to determine the relative position of the actuator stem  156 . In turn, the position of the control valve  120  is determined and if the control valve  120  is not positioned appropriately, a corresponding correction signal can be generated by the positioner  160 . The correction signal is then used to adjust the pressure differential in the actuator  150  to position the control valve  120  as desired. 
         [0028]    Referring now to  FIG. 2 , a cut away diagram illustrating a mounting kit  300  for mounting an attachment lever  310  to an actuator stem  156  of the control valve actuator  150 , shown in  FIG. 1 .  FIGS. 3 and 4  show the mounting kit  300  in situ and using different perspective views for illustrative purposes. The mounting kit  300  affixes the positioner  160  to the actuator stem  156  to allow the positioner to adjust the position of the actuator stem  156  and correspondingly, adjust the control valve  120  to adjust the flow volume through the control valve  110 . 
         [0029]    Mounting kit  300  includes a pair of bushings  320 , including an inner bushing  330  and an outer bushing  340 , and a compression spring  350  configured to bias together the two bushings of the pair of bushings  320  as described in detail below. The pair of bushings  320  are configured such that the inner bushing  330  includes a central aperture  332  configured to be slidably mounted over the actuator stem  156  such that the actuator stem  156  is enclosed within the inner bushing  330 . The length of the inner bushing  330  is configured such that the pair of bushings  320  can slide easily along the actuator stem  156 . According to exemplary embodiment, the cross-section of the central aperture  332  is such that the actuator stem  156  can slide easily within the inner bushing  330  to create a sliding area such that any forces that are transferable between actuator stem  156  and the pair of bushings  320  are minimized. 
         [0030]    Inner bushing  330  further includes a spring anchor  334  positioned at a first end of the inner bushing  330 , and an attachment lever interface  336  positioned at a second, opposite end of the inner bushing  330 . Spring anchor  334  is configured to provide a seat against which a first end of the spring  350  presses. In operation, the spring  350 , seated on spring anchor  334 , biases the outer bushing  340  away from the first end of the inner bushing  330  and spring anchor  334  towards the second, opposite end of the inner bushing  330  and the attachment lever interface  336 . The spring anchor  334  is configured such that spring force generated by the spring  350  are transferred between the spring anchor  334  and outer bushing  340 , and such that spring forces transferred to the actuator stem  156  are minimized or eliminated. 
         [0031]    Outer bushing  340  also includes an aperture  342  that is greater in diameter than the width of the actuator stem  156  and the inner bushing  330  such that outer bushing  340  is slidably mounted over both of actuator stem  156  and the inner bushing  330 . Similar to inner bushing  330 , the cross-section of the central aperture  312  is such that the actuator stem  156  and inner bushing  330  can slide easily within central aperture  342  of the outer bushing  340 . 
         [0032]    Outer bushing  340  further includes a spring anchor  344  positioned at a first end of the outer bushing  340 , and an attachment lever interface  346  positioned at a second, opposite end of the outer bushing  340 . Spring anchor  344  is configured receive a second end of the spring  350  opposite the end proximate the spring anchor  334 . In operation, the spring  350 , pressing against spring anchor  344 , biases the attachment lever interface  346  of outer bushing  340  towards the attachment lever interface  336  of inner busing  330 . 
         [0033]    Attachment lever interfaces  336  and  346  and configured to seat against attachment lever  310 . Attachment lever interfaces  336  and  346  are pressed together and see attachment lever  310  by the spring force is generated by spring  350  to attach the attachment lever  310  to actuator stem  156 . 
         [0034]    Attachment lever interfaces  336  and  346  include corresponding abrasion areas  338  and  348 , respectively. During normal operation, movement of the actuator stem  156  and the mounting kit  300  will cause wearing in the pair of bushings  320 , represented by the abrasion areas  338  and  348 . Advantageously, attachment lever interfaces  336  and  346  include sloping faces configured to mate with the attachment lever  310  such that the compression spring forces generated by spring  350  will provide consistent attachment to attachment lever  310  during operation of the pair of bushings  320 . In operation, the abrasion, represented by abrasion areas  338  and  348 , is consistent both over and under the axis of the actuator stem  156  such that the position of the attachment lever  310  remains consistent even with increasing abrasion. 
         [0035]    According to exemplary embodiment, the pair of bushings  320  may be formed from a material having a low coefficient of friction. One exemplary material providing the low coefficient of friction is Teflon although one of ordinary skill in the art would appreciate a variety of materials that are suitable. Advantageously, Teflon facilitates sliding of the pair of bushings along actuator stein  156  and further between inner bushing  330  and outer bushing  340 . Additionally, Teflon is electrically neutral to avoid sparking caused by movement between the pair of bushings  320  and attachment arm  310 . 
         [0036]    Particular configuration of bushings and attachment lever  310  can be vary and still provide advantages described herein. For example attachment lever  310  is shown as a pair of parallel bars, but alternative configurations may include a single bar attachment lever. In such a configuration, the type of bushings used in the pair of bushings  320  may be modified to properly seat against the single bar attachment arm  310  without negating the advantages described herein. 
         [0037]    This has been a description of the preferred embodiments, but it will be apparent to those of ordinary skill in the art that variations may be made in the details of these specific embodiments without departing from the scope and spirit of the present invention, and that such variations are intended to be encompassed by the following claims.