Abstract:
A spring seat for self aligning a bias-open or bias-close spring is disposed within a tubular control element of a gas regulator and designed to reduce side loading of the spring, which can cause the spring to prematurely fail. The spring seat can comprise a spring seat adaptor and a seat ring. The spring seat adaptor is fixed inside of the tubular control element and the seat ring is movably mounted on the spring seat adaptor via a ball and socket type joint. The movable seat ring is engaged by the spring and adapted to be self-aligned through three-dimensional displacement relative to the spring seat adaptor via the ball and socket joint.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The priority benefit of U.S. Provisional Application No. 61/173,013, filed Apr. 27, 2009, is hereby claimed and the entire contents thereof are incorporated herein by reference. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure generally relates to a fluid control device and, more particularly, to a fluid control device including a positioning device and a positioning device for a fluid control device. 
     BACKGROUND 
     Fluid control devices include various categories of equipment including control valves and regulators. Such control devices are adapted to be coupled within a fluid process control system such as chemical treatment systems, natural gas delivery systems, etc., for controlling the flow of a fluid therethrough. Each control device defines a fluid flow-path and includes a control member for adjusting a dimension of the flow-path. For example,  FIG. 1  depicts a known regulator  10  including a valve body  12  and an actuator  14 . The valve body  12  defines a flow-path  16  and includes a throat  18 . In  FIG. 1 , the regulator  10  is configured in a flow-up configuration. The actuator  14  includes an upper actuator casing  20 , a lower actuator casing  22 , a diaphragm subassembly  30  including a diaphragm  32 , and a positioning device assembly  34 . 
     The positioning device assembly  34  includes a tubular control member  33 , a coil spring  35 , a central rod  36 , a first spring seat  38 , and a second spring seat  40 . The tubular control member  33  is disposed within the upper and lower actuator casings  20 ,  22  and is adapted for bi-directional displacement in response to changes in pressure across the diaphragm subassembly  30 . So configured, the tubular control member  33  controls the flow of fluid through the throat  18  of the valve body  12 . Additionally, as is depicted, the regulator  10  includes a seat ring  26  disposed in the throat  18  of the valve body  12 . When the outlet pressure of the valve body  12  is high, a sealing surface  28  of the positioning device assembly  34  may sealingly engage the seat ring  26  and close the throat  18 . Similarly, absent any pressure in the actuator  14  or upon the failure of the diaphragm  32 , the coil spring  35 , which is carried by the central rod  36 , and disposed within the tubular control member  33  biases the tubular control member  33  into an open position, which is illustrated in  FIG. 1 . 
     Still referring to  FIG. 1 , the coil spring  35  of the conventional regulator  10  is carried by the central rod  36  between the first spring seat  38  and the second spring seat  40 . The first spring seat  38  generally comprises a flat plate that is fixedly coupled to the central rod  36 . The second spring seat  40  includes a more complex structure that is fixedly coupled to an inner wall of the tubular control member  33 . Typically, the second spring seat  40  is threadably coupled to the inner wall of the tubular control member  33 . As depicted in  FIG. 2 , the second spring seat  40  comprises a one-piece member having a complex geometrical cross-section for seating and aligning the spring  35  in the tubular control member  33 . 
     Specifically, the second spring seat  40  of the regulator  10  depicted in  FIG. 2  includes a cross-sectional geometry that generally resembles a modified conical or triangular shape including a fixation portion  42 , a seating portion  44 , and a rod receiving portion  46 . The fixation portion  42  includes a plurality of external threads  48  that threadably connect the second spring seat  40  to the tubular control member  33 . The rod receiving portion  46  defines an aperture  50  for receiving the central rod  36  (as shown in  FIG. 1 ) such that the tubular control member  33  and second spring seat  40  can move relative to the central rod  36  during operation of the regulator  10 . 
     The seating portion  44  of the second spring seat  40  is disposed between the fixation portion  42  and the rod receiving portion  46  and is adapted to be engaged by an end of the spring  35 . Specifically, the seating portion  44  includes a generally horizontal seating surface  52  and an alignment surface  54 . As illustrated in  FIG. 1 , an end of the spring  35  seats against the seating surface  52  and an inner side of the spring  35  is disposed adjacent to and/or in contact with the alignment surface  54 . So configured, the seating portion  44  of the second spring seat  40  operates to support and align the spring  35  within the tubular control member  33 . 
     During operation, the tubular control member  33  and the second spring seat  40  move relative to the central rod  36  in response to changes in pressure across the diaphragm assembly  30 . This movement causes the spring  35  to cyclically expand and compress with the movement of the tubular control member  33 . However, expansion and compression of the spring  35  can result in misalignment of the first spring seat  38  relative to the tubular control member  33 . This misalignment can be the result of imperfections present in the manufacturing of such springs. These imperfections can cause uneven perimeter loading of the spring  35 , which can cause the spring  35  to shift laterally and contact the inner wall of the tubular control member  33  and/or push the first spring seat  38  laterally into the inner wall of the tubular control member  33 . This phenomenon is generally referred to as side loading and it can cause the spring  35  and/or the first spring seat  38  to wear prematurely and/or fail. This problem is exacerbated when the spring  35  comprises a large, high rate spring that generates substantial loads. 
     SUMMARY 
     One aspect of the present disclosure provides a positioning device assembly for regulating the flow of a fluid through a fluid flow-path of a regulator. The positioning device assembly comprises a tubular control member, a central rod, a first spring seat, a second spring seat, and a spring. The central rod is disposed at least partly within the tubular control member and is adapted to be fixed to a casing of the regulator. The first spring seat is disposed within the tubular control member and is fixed relative to the central rod. The second spring seat is at least partly disposed within the tubular control member and defines an opening through which the central rod extends. The spring is disposed between the first and second spring seats, and adapted to bias the tubular control member into a predetermined position relative to the casing of the regulator. The second spring seat comprises a spring seat adaptor fixed relative to the control member and a seat ring engaging the spring and adapted for displacement relative to the spring seat adaptor to thereby self-align the spring within the tubular control member. 
     In some embodiments, the seat ring articulates relative to the spring seat adaptor. 
     In some embodiments, the second spring seat comprises a ball and socket type joint between the spring seat adaptor and the seat ring such that the seat ring can articulate relative to the spring seat adaptor. 
     In some embodiments, the spring seat adaptor comprises a partial spherical convex surface and the seat ring engages the partial spherical convex surface of the spring seat adaptor. 
     In some embodiments, the seat ring comprises partial spherical concave surface engaging the partial spherical convex surface of the spring seat adaptor. 
     In some embodiments, the assembly further comprises a nylon guide ring disposed between the first spring seat and an internal surface of the tubular control member, the nylon guide ring facilitating movement between the first spring seat and the tubular control member. 
     Another aspect of the present disclosure is directed to a positioning device assembly for regulating the flow of a fluid through a fluid flow-path of a regulator. The positioning device assembly comprises a tubular control member, a central rod, a first spring seat, a second spring seat, and a spring. The central rod is disposed at least partly within the tubular control member and adapted to be fixed to a casing of the regulator. The first spring seat is disposed within the tubular control member and fixed relative to the central rod. The second spring seat is at least partly disposed within the tubular control member, and defines a convex external surface and an opening through which the central rod extends. The spring is disposed between the first and second spring seats, and adapted to bias the tubular control member into a predetermined position relative to the casing of the regulator. The spring has a portion that is in engagement with the second spring seat, and which is movably disposed relative to the convex external surface to thereby self-align the spring within the tubular control element. 
     In some embodiments, the portion of the spring in engagement with the second spring seat articulates relative to the convex external surface. 
     In some embodiments, the second spring seat defines a ball and socket type joint that can articulate. 
     In some embodiments, the second spring seat comprises a spring seat adaptor fixed relative to the control member and carrying the convex external surface, and a seat ring disposed between the spring seat adaptor and the spring, the seat ring movably engaging the convex external surface thereby facilitating self-alignment the spring within the tubular control member. 
     In some embodiments, the spring seat adaptor of the second spring seat is threadably coupled to the tubular control member. 
     In some embodiments, the convex external surface of the spring seat adaptor comprises a partial spherical convex surface and the seat ring engages the partial spherical convex surface of the spring seat adaptor. 
     In some embodiments, the seat ring comprises partial spherical concave surface engaging the partial spherical convex surface of the spring seat adaptor. 
     In some embodiments, the assembly can further comprise a nylon guide ring disposed between the first spring seat and an internal surface of the tubular control member, the nylon guide ring facilitating movement between the first spring seat and the tubular control member. 
     Another aspect of the present disclosure is directed to a regulator comprising a valve body, an actuator casing, a tubular control element, a central rod, a first spring seat, a second spring seat, and a spring. The valve body defines a flow-path for a fluid. The actuator casing is coupled to the valve body. The tubular control member is at least partly disposed within the actuator casing and adapted for displacement relative to the valve body for regulating a flow of the fluid through the flow-path. The central rod is disposed at least partly within the tubular control member and fixed to the actuator casing. The first spring seat is disposed within the tubular control member and fixed relative to the central rod. The second spring seat is at least partly disposed within the tubular control member and defining an opening through which the central rod extends. The spring is disposed between the first and second spring seats, and biases the tubular control member into a predetermined position relative to the actuator casing. The second spring seat comprises a spring seat adaptor fixed relative to the tubular control member and a seat ring engaging the spring and adapted for displacement relative to the spring seat adaptor to thereby self-align the spring within the tubular control member. 
     In some embodiments, the seat ring articulates relative to the spring seat adaptor. 
     In some embodiments, the second spring seat comprises a ball and socket type joint between the spring seat adaptor and the seat ring such that the seat ring can articulate relative to the spring seat adaptor. 
     In some embodiments, the spring seat adaptor comprises a partial spherical convex surface and the seat ring engages the partial spherical convex surface of the spring seat adaptor. 
     In some embodiments, the seat ring comprises partial spherical concave surface engaging the partial spherical convex surface of the spring seat adaptor. 
     In some embodiments, the assembly further comprises a nylon guide ring disposed between the first spring seat and an internal surface of the tubular control member, the nylon guide ring facilitating movement between the first spring seat and the tubular control member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional side view of a conventional regulator; 
         FIG. 2  is a detailed partial cross-sectional view of a spring seat of the conventional regulator of  FIG. 1 ; 
         FIG. 3  is a cross-sectional side view of a regulator constructed in accordance with the present disclosure; and 
         FIG. 4  is a detailed partial cross-sectional view of a spring seat of the regulator of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 3 , one embodiment of a control device constructed in accordance with the principles of the present disclosure includes a pressure regulator  100 . The pressure regulator  100  generally includes a valve body  102  and an actuator  106 . The valve body  102  defines a flow-path  108  extending between an inlet  110  and an outlet  112 , as well as into the actuator  106 , as will be discussed. The actuator  106  includes a control assembly  114  that is moveable between an open position, as is shown in  FIG. 3 , and a closed position (not shown), wherein the control assembly  114  engages a seat ring  104  disposed within a throat  116  of the valve body  102 . Movement of the control assembly  114  occurs in response to fluctuations in the pressure of the fluid at the inlet  110  and outlet  112 . Accordingly, the position of the control assembly  114  relative to the seat ring  104  affects a flow capacity of the pressure regulator  100 . 
     The actuator  106 , as stated above, includes the control assembly  114  and additionally, an upper actuator casing  122 , a lower actuator casing  124 , and a cage  126 . The upper and lower actuator casings  122 ,  124  are secured together by at least one threaded fastener  119  and corresponding nut  121 . The upper actuator casing  122  defines a central opening  123 , at least one first control inlet  125 , and a travel chamber  127 . The travel chamber  127  contains a travel indicator  131 , which indicates the position of the control assembly  114  within the actuator  106 . The lower actuator casing  124  defines at least one second control inlet  129 . The control opening  123  receives a cap plate  117 , which is secured to the upper actuator casing  122  by at least one threaded fastener  113 . 
     In cooperation, the upper and lower actuator casings  122 ,  124  define a cavity  135  in communication with an actuator opening  115  in the valve body  102 . As identified in  FIG. 3 , the cage  126  of the actuator  106  has a first end  126   a  extending into the cavity  135  and a second end  126   b  defining the seat ring  104 . 
     Still referring to  FIG. 3 , the control assembly  114  includes a diaphragm subassembly  133  and a positioning device assembly  138 . The positioning device assembly  138  includes a tubular control member  130 , a mounting subassembly  132 , a central rod  186 , a first spring seat  188 , a second spring seat  190 , and a coil spring  193 . 
     The tubular control member  130  has a generally cylindrical inner surface  143  and a generally cylindrical outer surface  147 . The inner surface  143  defines a central bore through the tubular control member  130 . Additionally, the tubular control member  130  includes an upper end  130   a  and a lower end  130   b . The upper end  130   a  is disposed within the cavity  135  of the actuator  106  and the lower end  130   b  is disposed within the cage  126 . The upper end  130   a  of the tubular control member  130  is open and includes a circumferential flange  140  formed on the outer surface  147 . Additionally, the upper portion  130   a  of the tubular control member  130  includes a threaded portion  141  on the inner surface  143 . The lower end  130   b  of the tubular control member  130  is open and accommodates the mounting subassembly  132 . 
     The mounting subassembly  132  includes a mounting member  142 , a disk retainer  144 , a disk holder  146 , and a sealing disk  148 . In the disclosed form, the mounting member  142  includes a generally cylindrical body threaded into the open lower end  130   b  of the tubular control member  130  and defining a through-bore  150 . The through-bore  150  is generally axially aligned with the tubular control member  130 . The disk retainer  144  includes a generally cylindrical body fixed to the mounting member  142  with a pair of fasteners  152 . In the form illustrated, the fasteners  152  include threaded fasteners. Similar to the mounting member  142 , the disk retainer  144  defines a through-bore  154 . The through-bore  154  of the disk retainer  144  has a diameter substantially identical to a diameter of the through-bore  150  in the mounting member  142  and is axially aligned therewith. 
     As depicted, the disk retainer  144  secures the disk holder  146  and the sealing disk  148  to the mounting member  142  of the retainer assembly  132 . The disk holder  146  includes a generally ring-shaped plate constructed of a rigid material such as steel. The sealing disk  148  includes a generally ring-shaped disk made of a resilient material and fixed to the disk holder  146 . In one form, the sealing disk  148  is fixed to the disk holder  146  with an adhesive. In accordance with the disclosed form, the configuration of the disk retainer  144  limits radial deformation of the sealing disk  148  when the control assembly  114  is in a closed position and compressing the sealing disk  148  against the seat ring  104 . 
     Referring now to the upper portion of the regulator  100  depicted in  FIG. 3 , the diaphragm subassembly  133  includes a diaphragm  134 , an upper diaphragm plate  136   a  and a lower diaphragm plate  136   b . The upper and lower diaphragm plates  136   a ,  136   b  are clamped onto the circumferential flange  140  of the tubular control member  130 . The diaphragm plates  136   a ,  136   b  are secured together via fasteners  156 , thereby fixing the tubular control member  130  and the diaphragm plates  136   a ,  136   b  together. Additionally, the diaphragm plates  136   a ,  136   b  sandwich a radially inward portion of the diaphragm  134 . A radially outward portion of the diaphragm  134  is fixed between the upper and lower actuator casings  122 ,  124 . 
     The central rod  186 , the first and second spring seats  188 ,  190 , and the spring  193  of the positioning device assembly  138  are generally disposed within the tubular control member  130  to bias the tubular control member  130  into the open position depicted in  FIG. 3 . 
     The central rod  186  includes a first threaded end  186   a  and a second threaded end  186   b . The first threaded end  186   a  extends through the cap plate  117  and a pair of external nuts  194  are threaded onto the first threaded end  186   a  to limit axial displacement of the central rod  186  in the downward direction relative to the orientation of the regulator  100  depicted in  FIG. 3 . The central rod  186  further includes a shoulder  196  disposed opposite the cap plate  117  from the external nuts  194  to limit axial displacement of the central rod  186  in the upward direction relative to the orientation of the regulator  100  depicted in  FIG. 3 . Accordingly, the first threaded end  186   a  of the central rod  186  is effectively fixed against axial displacement relative to the cap plate  117 , actuator  106 , and valve body  102 , while the second threaded end  186   b  extends into the actuator  106 . 
     The second threaded end  186   b  of the central rod  186  extends into the tubular control member  130  and is disposed adjacent the second end  130   b  of the tubular control member  130  for supporting the first spring seat  188 . More specifically, the first spring seat  188  includes a generally flat plate that defines a central opening  188   a  and a plurality of apertures  188   b . The plurality of apertures  188   b  are in fluid communication with the flow path  108  through the valve body  102  via the through-bores  150 ,  154  in the mounting subassembly  132  to facilitate operation of the regulator  100  in a known manner. 
     The central opening  188   a  receives the second end  186   b  of the central rod  186  at a location adjacent a shoulder  187  formed on the central rod  186 . A retention nut  198  is threaded onto the second threaded end  186   b  of the central rod  186  and forces the first spring seat  188  against the shoulder  187  such that the first spring seat  188  is fixed relative to the central rod  186 . As such, the first spring seat  188  is slidably disposed relative to the tubular control member  130 , as will be discussed in more detail below. As illustrated, the first spring seat  188  supports a lower portion  193   b  of the spring  193  within the tubular control member  130 , thereby positioning an upper portion  193   a  of the spring  193  in engagement with the second spring seat  190 . 
     The second spring seat  190  of the disclosed embodiment includes two separate and distinct components comprising a spring seat adaptor  200  and a seat ring  202 . The spring seat adaptor  200  is fixed to the tubular control member  130  and supports the seat ring  202 . The seat ring  202  is disposed in engagement with the spring seat adaptor  200  and movable relative thereto to self-align the seat ring  202 , which in turn self-aligns the spring  193  and the first spring seat  188  within the tubular control member  130  during assembly and operation of the regulator  100 . 
     For example, with reference to  FIG. 4 , one embodiment of the second spring seat  190  including the spring seat adaptor  200  and the seat ring  202 , which is a separate and distinct component from the spring seat adaptor  200 , is depicted in more detail. 
     The spring seat adaptor  200  includes a cross-sectional geometry that generally resembles a modified conical or triangular shape including a fixation portion  204 , a seating portion  206 , and a rod receiving portion  208 . The fixation portion  204  is generally cylindrical and includes a plurality of external threads  210  that threadably connect the spring seat adaptor  200  to the plurality of threads  141  on the inner surface  143  of the tubular control member  130 , as depicted in  FIG. 3 . The rod receiving portion  208  is also generally cylindrical and includes an end wall  208   a  defining an aperture  212  for receiving the central rod  186 , as depicted in  FIG. 3 , such that the tubular control member  130  and second spring seat  190  can move relative to the central rod  186  during operation of the regulator  100 . 
     The seating portion  206  of the second spring seat  200  is disposed between the fixation portion  204  and the rod receiving portion  208  and is adapted to be engaged by and movably support the seat ring  202 , and therefore, the upper portion  193   a  of the spring  193  that engages the seat ring  202 . Specifically, the seating portion  206  includes a wall extending at an angle between the fixation portion  204  and the rod receiving portion  208 , and which defines an external surface  214  for being seated against by the seat ring  202 . 
     The disclosed embodiment of the seat ring  202 , as depicted, includes a generally L-shaped cross-section defining a seating surface  216 , an alignment surface  218 , and an internal surface  220 . The internal surface  220  of the seat ring  202  engages the external surface  214  of the spring seat adaptor  200  and is adapted for displacement relative thereto, as will be discussed. In the disclosed embodiment, the seating and alignment surfaces  216 ,  218  are disposed at approximately ninety-degrees relative to each other. As illustrated in  FIG. 3 , the upper portion  193   a  of the spring  193  seats against the seating surface  216  of the seat ring  202  and an inner portion  193   c  of the spring  193  is disposed adjacent to and/or in contact with the alignment surface  218 . So configured, the seat ring  202  of the second spring seat  190  operates to support and align the upper portion  193   a  of the spring  193  within the tubular control member  130 , while the first spring seat  188  supports the lower portion  193   b  of the spring  193 . So configured, the spring  193  is compressed between the first spring seat  188  and the seating surface  216  of the seat ring  202  of the second spring seat  190 . 
     As mentioned, the seat ring  202  of the second spring seat  190  is movable relative the spring seat adaptor  200 . Specifically, in the disclosed embodiment, the external surface  214  of the spring seat adaptor  200  includes a convex partial spherical surface and the internal surface  220  of the seat ring  202  includes a concave partial spherical surface. In one embodiment, the external surface  214  and internal surface  220  can have the same radius of curvature. As such, the external surface  214  and the internal surface  220  define a ball-and-socket type joint  222  between the spring seat adaptor  200  and the seat ring  202  that allows the seat ring  202  to articulate, pivot, rotate, and otherwise freely move relative to the spring seat adaptor  200 . 
     So configured, the second spring seat  190  of the disclosed regulator  100  advantageously provides a self-aligning function to the seat ring  202 , coil spring  193 , and first spring seat  188  by enabling the seat ring  202  and the coil spring  193  to move relative to the external surface  214  of the spring seat  190 . For example, during operation, the tubular control member  130  and the second spring seat  190  move up and down relative to the central rod  186  in response to changes in pressure across the diaphragm assembly  133  in the actuator  106 . This movement causes the spring  193  to cyclically expand and compress as the tubular control member  130  moves toward and away from the valve seat  104  of the cage  126 . If the coil spring  193  has imperfections, the coil spring  193  and/or the first spring seat  188  can undergo side loading due to uneven perimeter loading of the spring  193 . 
     The movable seat ring  202  of the second spring seat  190  and the movable upper portion  193   a  of the spring  193 , however, advantageously counteract such perimeter loading by pivoting, articulating, rotating, and otherwise self-adjusting their positions relative to the spring seat adaptor  200  according to the varying perimeter forces generated by the spring  193 . As such, side loading of the spring  193  and first spring seat  188  can be reduced, which in turn can reduce wear and increase the useful life of the spring  193  and the first spring seat  188 . 
     Another advantage of the disclosed design is that it provides for easier assembly over conventional designs. Specifically, to assemble the positioning device assembly  138  disclosed herein, a technician can first attach the first spring seat  188  to the second end  186   b  of the central rod  186  and position the rod  186  into the tubular control member  130 . The spring  193  can then be dropped into the tubular control member  130  and positioned about the rod  186 . The seat ring  202  can then be positioned on the spring  193  such that the alignment surface  218  fits into and the seating surface  216  engages the upper portion  193   a  of the spring  193 . Finally, the technician can then place the aperture  212  in the rod receiving portion  208  of the spring seat adaptor  200  onto the first end  186   a  of the central rod  186 , which will cause the external surface  214  of the seating portion  206  to engage the internal surface  220  of the seat ring  202 . 
     So positioned, the threads  210  on the fixation portion  204  of the spring seat adaptor  200  can then be tightened into the threads  141  on the inner surface  143  of the tubular control member  130 . While tightening the spring seat adaptor  200  into the tubular control member  130 , the spring seat adaptor  200  is rotated relative to the spring  193  and seat ring  202 . In conventional designs, the torque applied to the spring seat would transfer directly to the spring, thereby frustrating the alignment of the spring and making tightening of the spring seat difficult, especially when the spring required pre-loading. With the design disclosed herein, however, the amount of torque transferred to the spring  193  from tightening the spring seat adaptor  200  into the tubular control member  130  is reduced because the seat ring  202  directly engages the spring  193  and the spring seat adaptor  200  is specifically designed to be able to rotate relative to the seat ring  202  while generating minimal friction. Accordingly, the assembly process of the disclosed positioning device assembly  138  is much easier than conventional positioning device assemblies. 
     Furthermore, in addition to the advantages discussed thus far, the spring compression design could be utilized to accomplish various spring set points in the field. For example, in the field, the cap plate  117  could easily be removed from the upper actuator casing  122 , the spring seat adaptor  200  could then be removed from the tubular control member  130 , and the seat ring  202  could be replaced with a different seat ring  202  having a different thickness dimension, for example, for pre-loading the spring  193  a different amount. Moreover, the spring  193  itself could be removed and replaced with a different spring having a different spring force. Further still, the compression of the spring  193  can be adjusted by adjusting the axial position of the second spring seat  190  relative to the tubular control element  130 , which can easily be done by partly unthreading or further threading the spring seat adaptor  202  therein. 
     While the external surface  214  of the spring seat adaptor  200  disclosed herein has been described as being convex partial spherical, and the internal surface  220  of the seat ring  202  has been described as being concave partial spherical with a radius of curvature equal to a radius of curvature of the external surface  214 , alternative embodiments could be configured differently. For example, in one alternative embodiment the external surface  214  and internal surface  220  could be convex and concave, respectively, but not necessarily partial spherical. 
     In another embodiment, the radius of curvatures of the external and internal surfaces  214 ,  220  could be different. For example, the radius of curvature of the external surface  214  on the spring seat adaptor  200  could be greater than the radius of curvature of the internal surface  220  of the seat ring  202 . So configured, the seat ring  202  could also pivot relative to the spring seat adaptor  200  without creating any friction, but rather, the external surface  214  could advantageously act as a fulcrum, for example. 
     In another embodiment, the external surface  214  of the spring seat adaptor  200  could be convex, but the internal surface  220  of the seat ring  202  may include a circular edge such that only a line contact between the seat ring  202  and the spring seat adaptor  200  exists. In still another embodiment, the external surface of the spring seat adaptor  200  could be concave or even flat. 
     In yet another embodiment, the second spring seat  190  could include an anti-friction component disposed between the seat ring  202  and the spring seat adaptor  200  to reduce friction and facilitate movement of the seat ring  202 . The anti-friction component could include a nylon ring, for example, or a layer of graphite, a layer of lubricant, a layer of Teflon, etc. 
     While the foregoing has described various embodiments, features, and components of a regulator and a positioning device assembly for such a regulator, the invention is not intended to be limited to the specifics described, but rather is intended to be defined by what a person having ordinary skill in the art would understand is the contribution to the art.