Abstract:
In accordance with the present invention, there is provided a fluid or liquid barrier packing system which is adapted to minimize VOC emissions, while also providing live-loading and continuous load monitoring functions. The components of the packing system (including the liquid barrier) are adapted to be installed in a traditional stuffing box of a valve utilizing a top entry method, and without the necessity of having to inject the liquid through any side ports of the valve. The packing system reduces leakage levels as required by low emission leakage specifications by creating a reverse osmosis effect, limiting the diffusivity of a gas through the packing elements of the system. Thus, the packing system of the present invention provides a simplified method to load and monitor a barrier in the stuffing box of the valve to slightly higher pressure than processed fluid pressure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to U.S. Provisional Patent Application Serial No. 61/644,269 entitled LOW DIFFUSIVITY BARRIER FLUID PACKING SYSTEM filed May 8, 2012. 
     
    
     STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates generally to valves and, more particularly, to a liquid barrier packing system adapted for integration into a valve and operative to satisfy very low fugitive emission leakage standards. 
         [0005]    2. Description of the Related Art 
         [0006]    In a typical valve construction, a valve stem may undergo a turning or sliding movement, or a combination of both movements, within its sleeve during the process of the valve moving between its open and closed configurations. In this regard, the sealing of the stem must be adequate to contend with such movement, while at the same time ensuring maintenance of fluid tightness against the pressure of the fluid flowing through the valve. A widely used type of stem sealing is a compression packing in which a gland or sleeve is used to apply a compressive force to a compression packing which surrounds a portion of the length of the stem. The resulting radial pressure of the packing onto the stem provides the desired seal so long as the radial pressure exceeds the pressure of fluid in the valve. 
         [0007]    In certain valve configurations, compression may be applied to the packing through the use of packing bolts which are each attached at one end to a valve bonnet of the valve, and at their other end to a spigot, a flange or other projection bearing on, integral with or attached to the gland or sleeve which bears onto the packing. In this particular arrangement, the tightening of the bolts increases the pressure on the packing, thus facilitating the application of radial pressure onto the stem. In other valve configurations, it is known to attach a spring between the nut used to tighten the bolt and a surface of the spigot or flange. Although coil springs may be used, a conventional practice is to use Belleville springs which are essentially formed as a series of dished washers. These Belleville springs provide a “live-loaded” packing which can automatically compensate for changes that may take place in the packing under operating conditions of the valve, such as high pressures and temperatures. Since the volume of the packing material may reduce under certain operating conditions, or the temperature increase of the bolts and their further elongation may result in a load loss, the spring pressure compensates for such reduction and maintains the required pressure, thus avoiding potential harmful effects to the sealing of the stem in an unsprung valve which could result from the reduction in the packing material volume. Alternatively, if the volume of the packing material increases (which can happen with certain packing materials), the radial pressure of the stem in an unsprung valve could increase too much, thus possibly causing sticking of the stem. The spring value, however, can accommodate the pressure increase by means of further compression of the springs. 
         [0008]    Recently, there has been an increasing level of demand in many oil and gas applications for the low level emission of Volatile Organic Compounds (VOC&#39;s). In this regard, in a typical oil and gas production and processing plant, control valves are generally considered to be the largest contributors to the loss of VOC&#39;s. This has resulted in the owners of many of these facilities developing strict fugitive emission specifications to minimize VOC leakage attributable to the valve stem packing, with allowable valve stem packing leakage rates being very low. Additionally, various laws enacted in Europe and other jurisdictions currently define the maximum concentration level of pollutants that can be detected in the air in an industrial setting, and proximate valves located therein. These laws and regulations are having the effect of forcing valve manufactures to adopt new designs for valve packing and sealing systems to comply with the same. 
         [0009]    However, the packing system included in many valve designs, including those which include a live-loaded packing as described above, is still often susceptible to varying levels leakage about the valve stem. Though some solutions have been developed which make use of a barrier fluid, these particular solutions do not provide a live loaded system to maintain the barrier fluid pressure at a level higher than that of the process pressure, thus diminishing the longevity of the packing integrity once in service conditions (see, e.g., U.S. Pat. No. 7,118,114). In one existing barrier fluid solution, grease is laterally injected into a valve bonnet. However, in this particular solution, the grease is typically lost after repeated valve cycling, with its efficacy as a fluid barrier thus only being somewhat temporary unless replenished on a frequent basis. As will be recognized, a loss of efficacy of the grease as a fluid barrier prior to replenishment may result in undesirable leakage. Further, the attempted replenishment of the grease while the valve is still pressurized can jeopardize the integrity of the valve packing, thus creating a potential hazard to operators if high pressure gas escapes the valve bonnet. In addition, the use of the aforementioned lateral injection technique gives rise to the potential for lateral grease escape during the operation of the valve, thus creating a possible leak source. Still further, the aforementioned solution, as currently known, lacks modalities for detecting when the grease level is falling to an ineffective level. Other solutions are relatively complex to manufacture, assemble and service. Further, the existing solutions typically ignore the role of a seal to shaft interface in friction and seal wear, and the resultant impact on leakage levels. 
         [0010]    The present invention addresses the problem of packing leakage as it relates to VOC&#39;s by providing a low diffusivity barrier fluid or liquid packing system which is configured to be accommodated by a traditional valve stuffing box, and is further adapted to minimize VOC emissions, while also providing live-loading and continuous load monitoring functions. These, as well as other features and attributes of the present invention will be discussed in more detail below. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    In accordance with the present invention, there is provided a fluid or liquid barrier packing system which is adapted to minimize VOC emissions, while also providing live-loading and continuous load monitoring functions. The components of the packing system (including the liquid barrier) are adapted to be installed in a traditional stuffing box of a valve utilizing a top entry method, and without the necessity of having to inject the liquid through any lateral side port(s) within the bonnet of the valve. In this regard, the packing system of the present invention has a simplified construction and does not rely upon the use of external components, thus eliminating many of the complexities of prior art approaches, as well as the need for any external pumps to inject the fluid or liquid into the valve at high pressures. Further, the packing system of the present invention reduces leakage levels as required by low emission leakage standards and specifications by creating a reverse osmosis effect, limiting the diffusivity of a gas through the packing elements of the system. Thus, the packing system of the present invention provides a simplified method to load and monitor a barrier in the stuffing box of the valve to slightly higher pressure than processed fluid pressure. 
         [0012]    As indicated above, the packing system of the present invention is provided with, among other things, live-loading and a continuous load monitoring system. The packing system also makes use of a valve stem having a hard coated and super-finish stem coating, and is specifically configured to reduce wear, friction on valve seals, and to further keep the packing under continuous load to satisfy very low fugitive emission leakage standards. The hard coated and super-finish stem coating of the valve stem used in conjunction with the packing system of the present invention is instrumental in reducing wear and friction of the seals. These features minimize packing leakage and barrier fluid loss resulting in significant leakage reduction, while at the same time increasing the longevity of the packing system once in service. In one embodiment of the present invention, spring live loading is installed into the stuffing box of the valve via a top entry method, thus reducing the number of components and facilitating ease of assembly. 
         [0013]    The present invention is best understood in reference to the following detailed description when read in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    These, as well as other features of the present invention, will become more apparent upon reference to the drawings wherein: 
           [0015]      FIG. 1  is a partial cross-sectional view of a valve including a fluid packing system constructed in accordance with a first embodiment the present invention; 
           [0016]      FIG. 2  is a partial cross-sectional view of the valve shown in  FIG. 1  but depicting the fluid packing system of the first embodiment in a partially assembled state; 
           [0017]      FIG. 3  is a partial cross-sectional view of a valve including a fluid packing system constructed in accordance with a second embodiment the present invention; and 
           [0018]      FIG. 4  is a partial cross-sectional view of the valve shown in  FIG. 3  but depicting the fluid packing system of the second embodiment in a partially assembled state. 
           [0019]    Common reference numerals are used throughout the drawings and detailed description to indicate like elements. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    Referring now to the drawings wherein the showings are for purposes of illustrating preferred embodiments of the present invention only, and not for purposes of limiting the same,  FIGS. 1 and 2  partially depict an exemplary valve  100  which includes a low fugitive emission, fluid or liquid barrier packing system  101  constructed in accordance with a first embodiment of the present invention. The exemplary valve  100  having the packing system  101  integrated therein possesses certain structural features. More particularly, the valve  100  includes a body, which itself comprises a valve bonnet  4 . Extending axially through the valve bonnet  4  is a central passageway  12 . As seen in  FIGS. 1 and 2 , the passageway  12  extending through the valve bonnet  4  is not of uniform inner diameter. Rather, the passageway  12  is divided into an upper section which is of the first inner diameter, and a lower section which is of a second inner diameter exceeding that of the upper section. As a result, the upper and lower sections of the passageway  12  are separated from each other by an annular shoulder. Advanced through the passageway  12  is elongate valve stem  1  of the valve  100 , the reciprocal or rotary movement of which opens and closes the valve  100  in a conventional manner. 
         [0021]    The valve stem  1  of the valve  100  is preferably provided with a hard coated and super-finish stem coating for reasons which will be discussed in more detail below. Additionally, as further seen in  FIGS. 1 and 2 , the diameter of the valve stem  1  is less than that of the upper section of the central passageway  12 , such that an annular gap is normally defined between the valve stem  1  and that inner surface portion of the valve bonnet  4  defining the upper section of the central passageway  12 . 
         [0022]    The packing system  101  integrated into valve  100  resides within both the upper and lower sections of the passageway  12 , with portions of the packing system  101  surrounding and exerting radial pressure against the valve stem  1 . When viewed from the perspective shown in  FIG. 1 , the packing system  101  comprises an annular, upper packing  13  which circumvents the valve stem  1  and has a generally U-shaped cross-sectional configuration. The upper packing  13  is preferably fabricated from a material which is adapted to maintain a fluid tight seal against the outer surface of the valve stem  1  even upon the sliding movement of the valve stem  1  relative to the upper packing  13 . In addition to the upper packing  13 , the packing system  101  includes a lower packing  6  which is identically configured to, and may be fabricated from the same material as, the upper packing  13 . As such, the lower packing  6  also circumvents the valve stem  1  and is operative to maintain a fluid tight seal against the outer surface of the valve stem  1  despite any sliding movement of the valve stem  1  relative thereto. 
         [0023]    As further seen in  FIG. 1 , the upper and lower packings  13 ,  6  each reside within the upper section of the central passageway  12 , and are disposed in spaced relation to each other such that annular channels defined by the upper and lower packings  13 ,  6  as a result of the U-shaped cross-sectional configurations thereof face each other. The upper and lower packings  13 ,  6  are also effectively compressed between the outer surface of the valve stem  1  and that interior surface of the valve bonnet  4  defining the upper section of the passageway  12  such that the upper and lower packings  13 ,  6  are each disposed in slidable, sealed engagement with the valve bonnet  4 , in addition to being in slidable, sealed engagement with the valve stem  1 . 
         [0024]    The packing system  101  further comprises a fluid or liquid barrier  14  which is captured between the upper and lower packings  13 ,  6 . More particularly, as seen in  FIG. 1 , the barrier  14  is disposed or filled into that portion of the annular gap between the valve stem  1  and valve bonnet  4  which is bounded by the upper and lower packings  13 ,  6 . The migration of the barrier  14  beyond the upper and lower packings  13 ,  6  is prevented by the above-described fluid tight engagement between such upper and lower packings  13 ,  6  and each of the valve stem  1  and valve bonnet  4 . In an exemplary embodiment of the present invention, the barrier  14  is a viscous liquid such as grease which is formulated to provide certain fluid sealing characteristics within a prescribed range of operating temperatures for a prescribed type of process fluid flowing through the valve  100 . 
         [0025]    The packing system  101  further comprises an annular load sensor or load cell  15  which is positioned upon and directly abuts the upper packing  13 . As such, the load cell  15  also resides within the upper section of the passageway  12  within the annular gap defined between the valve stem  1  and the valve bonnet  4 . The load cell  15  is effectively captured between the upper packing  13  and a packing follower  16  which is also included in the packing system  101 . As seen in and as viewed from the perspective shown in  FIG. 1 , the packing follower  16  includes an annular upper section which is of a first outer diameter, and a tubular lower section which protrudes from the upper section and is of a second outer diameter less than that of the first outer diameter of the upper section. As a result, the upper and lower sections of the packing follower  16  are separated by an annular shoulder. The lower section is also of the length L shown in  FIG. 1 . The packing follower  16  further defines a central bore which extends axially therethrough, and an ancillary passage  17 . The valve stem  1  is slidably advanced through the central bore of the packing follower  16 . Additionally, one end of the passage  17  terminates at the outer, peripheral surface of the upper section of the packing follower  16 , with the opposite end terminating at the distal end or rim of the lower section thereof. The passage  17  is used to accommodate an electrical signal transfer wire  18  which extends from the load cell  15 , through the packing follower  16 , and hence to the exterior of the valve  100  as shown in  FIG. 1 . As will be recognized, the lower section of the packing follower  16  is dimensioned so that the same is capable of being slidably advanced into the upper section of the passageway  12  into the annular gap defined between the valve stem  1  and the valve bonnet  4 . It is contemplated that the lower section of the packing follower  16  will normally be advanced into the upper section of the passageway  12  to a depth whereat the shoulder defined between the upper and lower sections of the packing follower  16  will be abutted against or disposed in close proximity to the top, distal end of the valve bonnet  4  as viewed from the perspective shown in  FIG. 1  (and as also shown in  FIG. 3  related to the second embodiment of the present invention). 
         [0026]    The packing system  101  further comprises an annular lower spacer  7  which directly abuts the lower packing  6 . As such, the spacer  7  also resides within the upper section of the passageway  12  within the annular gap defined between the valve stem  1  and the valve bonnet  4 . The spacer  7  is effectively captured between the lower packing  6  and a tubular loading piston  8  which is also included in the packing system  101 . As seen in and as viewed from the perspective shown in  FIG. 1 , the loading piston  8  includes a tubular upper section which is of a first outer diameter, and an annular lower section which is of a second outer diameter exceeding that of the first outer diameter of the upper section. As a result, the upper and lower sections of the loading piston  8  are separated by an annular shoulder. The loading piston  8  further defines a central bore which extends axially therethrough, and slidably accommodates the valve stem  1 . Disposed in the peripheral outer surface of the lower section of the loading piston  8  is a continuous groove or channel which accommodates an annular bushing  9 . The bushing  9  is sized and configured to be disposed in continuous, sliding contact with that interior surface of the valve bonnet  4  defining the lower section of the passageway  12 . As seen in  FIG. 1 , the upper section of the loading piston  8  is dimensioned so that the same is capable of being slidably advanced into the upper section of the passageway  12  into the annular gap defined between the valve stem  1  and the valve bonnet  4 . However, the size and configuration of the lower section of the loading piston  8  makes it incapable of being advanced into the upper section of the passageway  12 , the lower section of the loading piston  8  thus being confined to the lower section of the passageway  12 . 
         [0027]    The packing system  101  further comprises an annular spring retainer  11  which circumvents the valve stem  1  and is constrained to a prescribed location within the lower section of the passageway  12 . As further seen in  FIG. 1 , positioned and extending between the lower section of the loading piston  8  and the spring retainer  11  is at least one, and preferably a series of internal springs  10 . When viewed from the perspective shown in  FIG. 1 , the spring(s)  10 , are operative to normally bias the loading piston upwardly toward the top, distal end of the valve bonnet  4 . In the packing system  101 , the lower spacer  7 , loading piston  8 , spring(s)  10  and spring retainer  11  collectively define a live-loading sub-assembly  111  of the packing system  101  which is operative to maintain a prescribed level of compressive pressure on the upper and lower packings  13 ,  6  and the barrier  14  disposed therebetween. 
         [0028]    Those of ordinary skill in the art will recognize that from the perspective shown in  FIG. 1 , the structural features of the valve  100  to the right side of the valve stem  1  (though not being fully shown) are essentially a mirror image of those shown to the left of the valve stem  1 , the exception being that the packing follower  16  includes only the single ancillary passage  17  formed therein and extending therethrough. Additionally, in  FIG. 1 , the packing follower  16 , the load cell  15  and the upper packing  13  are further shown in phantom to the right side of the valve stem  1  in non-final states of assembly prior to the advancement thereof to their preferred locations or orientations within the upper section of the central passageway  12 . As previously explained, it is contemplated that in the valve  100  including the fully assembled packing system  101 , the upper packing  13 , the load cell  15  positioned thereon, and the lower section of the packing follower  16  will each reside within the upper section of the passageway  16  in the annular gap defined between the valve stem  1  and valve bonnet  4 , with the shoulder defined between the upper and lower sections of the packing follower  16  abutting or being disposed in close proximity to the top, distal end of the valve bonnet  4 . 
         [0029]    During the operation of the valve  100  including the packing system  101 , the combination of the upper and lower packings  13 ,  6  and the barrier  14  therebetween provides an effective, fluid-tight seal which prevents fluid migrating upwardly through the lower section of the passageway  12  from further migrating through the upper section of the passageway  12  and escaping the valve  100  via the top, distal end of the valve bonnet  4 . Despite the reciprocal upward and downward or rotary movement of the valve stem  1  during the operation of the valve  100 , the upper and lower packings  13 ,  6  and barrier  14  therebetween are essentially maintained in the orientation shown in  FIG. 1 , though the upper and lower packings  13 ,  6  are capable of some measure of slidable movement along that interior surface of the valve bonnet  4  defining the upper section of the passageway  12 . Providing the valve stem  1  with the hard coated and super-finish stem coating reduces friction and thus premature wear of the upper and lower packings  13 ,  6  despite repeated cycles of the slidable movement of the valve stem  1  relative thereto. 
         [0030]    In addition, despite increases or decreases in the volume of the barrier  14  and/or changes in the dimensional characteristics of the upper and lower packings  13 ,  6  resulting from changes in the operating condition of the valve (e.g., pressures and/or temperature changes), the fluid pressure of the barrier  14  is maintained above the process pressure of the fluid flowing through the valve  100  as a result of the live-loading thereof attributable to the above-described live-loading sub-assembly  111  comprising the lower spacer  7 , loading piston  8 , spring(s)  10  and spring retainer  11 . As is apparent from  FIG. 1 , this live-loading sub-assembly  111 , and in particular the loading piston  8  thereof, is capable of a range of movement roughly equal to that defined by the dimension H 1  shown in  FIG. 1 . In the embodiment of  FIG. 2 , the loading piston  8  is depicted at the upward limit of its range of movement toward the top, distal end of the valve bonnet  4 , such upward movement being limited by the abutment of the shoulder defined between the upper and lower sections of the loading piston  8  against the shoulder defined between the upper and lower sections of the central passageway  12 . When the loading piston  8  is at its upward movement limit, the same is separated from the spring retainer  11  by a gap which accommodates the spring  10  and is of the height L 1  shown in  FIG. 2 . Further, the load cell  15 , which is captured between the upper packing  13  and packing follower  16  as described above, is operative to facilitate continuous load monitoring of the load applied to the seal collectively defined by the upper and lower packings  13 ,  6  and intervening barrier  14 , thus providing an additional modality to monitor the integrity of such seal through verification of the fluid pressure of the barrier  14  exceeding the process pressure of the fluid pressure flowing through the valve  100 . 
         [0031]    In the valve  100 , it is contemplated that the upper and lower packings  13 ,  6  of the packing system  101  may be fabricated from different materials rather than from the same material, may have the same or differing geometries. Over time, due to gas diffusivity into the upper and lower packings  13 ,  6 , gas may further solubilize into the barrier  14 . In the event this happens, the formation of the upper and lower packings  13 ,  6  from materials which impart the same tightness capacity may cause gas to escape from the upper packing  13  and migrate out of the valve  100 , rather than escaping from the lower packing  6  which would normally result in the gas cause instead being directed back into the interior of the valve  100 . In this regard, fabricating the lower packing  6  from a material imparting slightly less tightness in comparison to the upper packing  13  may be used to facilitate a back re-diffusion of barrier solubilized gas back into the interior of the valve  100 . 
         [0032]      FIG. 2  depicts the valve  100 , and in particular the packing system  101  thereof as shown in  FIG. 1 , in a partially assembled state. More particularly, as shown in  FIG. 2 , with the live-loading sub-assembly of the packing system  101  being fully assembled, the lower spacer  7  being positioned upon the upper section of the loading piston  8 , and the lower packing  6  being positioned upon the lower spacer  7 , a liquid barrier filling device  3  is used to facilitate the introduction of the barrier  14  into the packing system  101 . As seen in and as viewed from the perspective shown in  FIG. 2 , the filling device  3  is similarly configured to the packing follower  16 , and includes an annular upper section which is of a first outer diameter, and a tubular lower section which protrudes from the upper section and is of a second outer diameter less than that of the first outer diameter of the upper section. As a result, the upper and lower sections of the filling device  3  are separated by an annular shoulder. The filling device  3  further defines a central bore which extends axially therethrough, and an ancillary passage  19 . The valve stem  1  is slidably advanced through the central bore of the filling device  3 . Additionally, one end of the passage  19  terminates at the outer, peripheral surface of the upper section of the filling device  3 , with the opposite end terminating at the distal end or rim of the lower section thereof. Disposed within the inner surface of the upper section of the filling device  3  which partially defines the central bore thereof is a continuous groove or channel which accommodates an O-ring  2 . Similarly, disposed within the outer surface of the tubular lower section of the filling device  3  is a continuous groove or channel which accommodates an O-ring  5 . 
         [0033]    As further seen in  FIG. 2 , the lower section of the filling device  3  is dimensioned so that the same is capable of being slidably advanced into the upper section of the passageway  12  into the annular gap defined between the valve stem  1  and the valve bonnet  4 . When the filling device  3  is used to facilitate the introduction of the barrier  14  into the packing system  101 , it is contemplated that the lower section of the filling device  3  will initially be advanced into the upper section of the passageway  12  to a depth whereat the shoulder defined between the upper and lower sections of the filling device  3  will be abutted against or disposed in close proximity to the top, distal end of the valve bonnet  4  as viewed from the perspective shown in  FIG. 2 . Upon such advancement, the O-ring  2  effectively creates a seal between the filling device  3  and the valve stem  1 , with the O-ring  5  effectively creating a seal between the filling device  3  and the valve bonnet  4 . Thereafter, the passage  19  of the filling device  3  is used to channel the barrier  14  from the exterior of the valve  100  to and above the lower packing  6 . 
         [0034]    After a prescribed amount of the barrier  14  has been introduced into the upper section of the passageway  12 , the filling device  3  is completely retracted and withdrawn from within the passageway  12 , and removed from the valve  100 . Such retraction and removal of the filling device  3  is followed by the advancement of the upper packing  13  into the upper section of the passageway  12  to assume the orientation shown in phantom in  FIG. 1 . Subsequent to the load cell  15  being positioned upon the upper packing  13  while still in its position shown in phantom in  FIG. 1 , the packing follower  16  is then advanced over the valve stem  1  and used to effectively push the upper packing  13  and load cell  15  downwardly into the passageway  12  to the general orientations also shown in  FIG. 1  wherein the upper packing  13  also comes into contact with the barrier  14  previously filled into the passageway  12 . Those of ordinary skill in the art will recognize that the use of the filling device  3  is exemplary, and that the assembly of the packing system  101  within the valve  100  may potentially be accomplished through the use of alternative assembly techniques which do not entail the use of the filling device  3 . 
         [0035]    Referring now to  FIGS. 3 and 4 , there is partially depicted an exemplary valve  200  which includes a low fugitive emission, fluid or liquid barrier packing system  201  constructed in accordance with a second embodiment of the present invention. The exemplary valve  200  having the packing system  201  integrated therein possesses certain structural features. More particularly, the valve  200  includes a body, which itself comprises a valve bonnet  20 . Extending axially through the valve bonnet  20  is a central passageway  22 . As seen in  FIGS. 3 and 4 , the passageway  22  extending through the valve bonnet  20  is not of uniform inner diameter. Rather, the passageway  22  is divided into an upper section which is of the first inner diameter, and a lower section which is of a second inner diameter which is less than that of the upper section. As a result, the upper and lower sections of the passageway  22  are separated from each other by an annular shoulder. Advanced through the passageway  22  is elongate valve stem  23  of the valve  200 , the reciprocal or rotary movement of which opens and closes the valve  200  in a conventional manner. 
         [0036]    The valve stem  23  of the valve  200  is preferably provided with a hard coated and super-finish stem coating for reasons which will be discussed in more detail below. Additionally, as further seen in  FIGS. 3 and 4 , the diameter of the valve stem  23  is less than that of the upper section of the central passageway  22 , such that an annular gap is normally defined between the valve stem  23  and that inner surface portion of the valve bonnet  20  defining the upper section of the central passageway  22 . 
         [0037]    The packing system  201  integrated into valve  200  resides solely within the upper section of the passageway  22 , with portions of the packing system  201  surrounding and exerting radial pressure against the valve stem  23 . When viewed from the perspective shown in  FIG. 3 , the packing system  201  comprises an annular, upper packing  24  which circumvents the valve stem  23  and has a generally U-shaped cross-sectional configuration. The upper packing  24  is preferably fabricated from a material which is adapted to maintain a fluid tight seal against the outer surface of the valve stem  23  even upon the sliding movement of the valve stem  23  relative to the upper packing  24 . In addition to the upper packing  24 , the packing system  201  includes a lower packing  25  which is identically configured to, and may be fabricated from the same material as, the upper packing  24 . As such, the lower packing  25  also circumvents the valve stem  23  and is operative to maintain a fluid tight seal against the outer surface of the valve stem  23  despite any sliding movement of the valve stem  23  relative thereto. 
         [0038]    As further seen in  FIG. 3 , the upper and lower packings  24 ,  25  each reside within the upper section of the central passageway  22 , and are disposed in spaced relation to each other such that annular channels defined by the upper and lower packings  24 ,  25  as a result of the U-shaped cross-sectional configurations thereof face each other. The upper and lower packings  24 ,  25  are also effectively compressed between the outer surface of the valve stem  23  and that interior surface of the valve bonnet  20  defining the upper section of the passageway  22  such that the upper and lower packings  24 ,  25  are each disposed in slidable, sealed engagement with the valve bonnet  20 , in addition to being in slidable, sealed engagement with the valve stem  23 . 
         [0039]    The packing system  201  further comprises a fluid or liquid barrier  26  which is captured between the upper and lower packings  24 ,  25 . More particularly, as seen in  FIG. 3 , the barrier  26  is disposed or filled into that portion of the annular gap between the valve stem  23  and valve bonnet  20  which is bounded by the upper and lower packings  24 ,  25 . The migration of the barrier  26  beyond the upper and lower packings  24 ,  25  is prevented by the above-described fluid tight engagement between such upper and lower packings  24 ,  25  and each of the valve stem  23  and valve bonnet  20 . In an exemplary embodiment of the present invention, the barrier  26  is a viscous liquid such as grease which is formulated to provide certain fluid sealing characteristics within a prescribed range of operating temperatures for a prescribed type of process fluid flowing through the valve  200 . 
         [0040]    The packing system  201  further comprises an annular load sensor or load cell  27  which is positioned upon and directly abuts the upper packing  24 . As such, the load cell  27  also resides within the upper section of the passageway  22  within the annular gap defined between the valve stem  23  and the valve bonnet  20 . The load cell  27  is effectively captured between the upper packing  24  and a packing follower  28  which is also included in the packing system  201 . As seen in and as viewed from the perspective shown in  FIG. 3 , the packing follower  28  includes an annular upper section which is of a first outer diameter, and a tubular lower section which protrudes from the upper section and is of a second outer diameter less than that of the first outer diameter of the upper section. As a result, the upper and lower sections of the packing follower  28  are separated by an annular shoulder. The lower section of the packing follower is also of the length L. The packing follower  28  further defines a central bore which extends axially therethrough, and an ancillary passage  29 . The valve stem  23  is slidably advanced through the central bore of the packing follower  28 . Additionally, one end of the passage  29  terminates at the outer, peripheral surface of the upper section of the packing follower  28 , with the opposite end terminating at the distal end or rim of the lower section thereof. The passage  29  is used to accommodate an electrical signal transfer wire  30  which extends from the load cell  27 , through the packing follower  28 , and hence to the exterior of the valve  200  as shown in  FIG. 3 . As will be recognized, the lower section of the packing follower  28  is dimensioned so that the same is capable of being slidably advanced into the upper section of the passageway  22  into the annular gap defined between the valve stem  23  and the valve bonnet  20 . It is contemplated that the lower section of the packing follower  28  will normally be advanced into the upper section of the passageway  22  to a depth whereat the shoulder defined between the upper and lower sections of the packing follower  28  will be abutted against or disposed in close proximity to the top, distal end of the valve bonnet  20  as shown in  FIG. 3 . 
         [0041]    The packing system  201  further comprises an annular upper spacer  31  which directly abuts the lower packing  25 . As such, the upper spacer  31  also resides within the upper section of the passageway  22  within the annular gap defined between the valve stem  23  and the valve bonnet  20 . Also included in the packing system  201  is an annular lower spacer  32  which directly abuts the shoulder defined between the upper and lower sections of the passageway  22 . As such, the lower spacer  32  also resides within the upper section of the passageway  22  within the annular gap defined between the valve stem  23  and the valve bonnet  20 . As further seen in  FIG. 1 , positioned and extending between the upper and lower spacers  31 ,  32  is at least one, and preferably a series of internal springs  33 . When viewed from the perspective shown in  FIG. 1 , the spring(s)  33 , are operative to normally bias the upper spacer  31  upwardly toward the top, distal end of the valve bonnet  20 . In the packing system  201 , the upper and lower spacers  31 ,  32  and spring(s)  33  collectively define a live-loading sub-assembly  211  of the packing system  201  which is operative to maintain a prescribed level of compressive pressure on the upper and lower packings  24 ,  25  and the barrier  26  disposed therebetween. 
         [0042]    Those of ordinary skill in the art will recognize that from the perspective shown in  FIG. 3 , the structural features of the valve  200  to the left side of the valve stem  23  (though not being shown) are essentially a mirror image of those shown to the right of the valve stem  23 , the exception being that the packing follower  28  includes only the single ancillary passage  29  formed therein and extending therethrough. During the operation of the valve  200  including the packing system  201 , the combination of the upper and lower packings  24 ,  25  and the barrier  26  therebetween provides an effective, fluid-tight seal which prevents fluid migrating upwardly through the lower section of the passageway  22  from further migrating through the upper section of the passageway  22  and escaping the valve  200  via the top, distal end of the valve bonnet  20 . Despite the reciprocal upward and downward or rotary movement of the valve stem  23  during the operation of the valve  200 , the upper and lower packings  24 ,  25  and barrier  26  therebetween are essentially maintained in the orientation shown in  FIG. 3 , though the upper and lower packings  24 ,  25  are capable of some measure of slidable movement along that interior surface of the valve bonnet  20  defining the upper section of the passageway  22 . Providing the valve stem  23  with the hard coated and super-finish stem coating reduces friction and thus premature wear of the upper and lower packings  24 ,  25  despite repeated cycles of the slidable movement of the valve stem  23  relative thereto. 
         [0043]    In addition, despite increases or decreases in the volume of the barrier  26  and/or changes in the dimensional characteristics of the upper and lower packings  24 ,  25  resulting from changes in the operating condition of the valve (e.g., pressures and/or temperature changes), the fluid pressure of the barrier  26  is maintained above the process pressure of the fluid flowing through the valve  200  as a result of the live-loading thereof attributable to the above-described live-loading sub-assembly  211  comprising the upper and lower spacers  31 ,  32 , and spring(s)  33 . As is apparent from  FIGS. 3 and 4 , this live-loading sub-assembly  211  is capable of a prescribed range of movement. In  FIG. 4 , the upper spacer  31  is depicted at the upward limit of its range of movement toward the top, distal end of the valve bonnet  20 . In this instance, the upper and lower spacers  31 ,  32  are separated from each other by a gap which accommodates the spring(s)  33  and is of the height L 1  shown in  FIG. 4 . Further, the load cell  27 , which is captured between the upper packing  24  and packing follower  28  as described above, is operative to facilitate continuous load monitoring of the load applied to the seal collectively defined by the upper and lower packings  24 ,  25  and intervening barrier  26 , thus providing an additional modality to monitor the integrity of such seal through verification of the fluid pressure of the barrier  26  exceeding the process pressure of the fluid pressure flowing through the valve  200 . Additionally, in the valve  200 , it is contemplated that the upper and lower packings  24 ,  25  of the packing system  201  may be fabricated from different materials to provide the same functional characteristics as described above in relation to the upper and lower packings  13 ,  6  of the packing system  101 . 
         [0044]      FIG. 4  depicts the valve  200 , and in particular the packing system  201  thereof as shown in  FIG. 3 , in a partially assembled state. More particularly, as shown in  FIG. 4 , with the live-loading sub-assembly of the packing system  201  being fully assembled, and the lower packing  25  being positioned upon the upper spacer  31 , a liquid barrier filling device  34  is used to facilitate the introduction of the barrier  26  into the packing system  201 . As seen in and as viewed from the perspective shown in  FIG. 4 , the filling device  34  is similarly configured to the packing follower  28 , and includes an annular upper section which is of a first outer diameter, and a tubular lower section which protrudes from the upper section and is of a second outer diameter less than that of the first outer diameter of the upper section. As a result, the upper and lower sections of the filling device  34  are separated by an annular shoulder. The filling device  34  further defines a central bore which extends axially therethrough, and an ancillary passage  35 . The valve stem  23  is slidably advanced through the central bore of the filling device  34 . Additionally, one end of the passage  35  terminates at the outer, peripheral surface of the upper section of the filling device  34 , with the opposite end terminating at the distal end or rim of the lower section thereof. Disposed within the inner surface of the upper section of the filling device  34  which partially defines the central bore thereof is a continuous groove or channel which accommodates an O-ring  36 . Similarly, disposed within the outer surface of the tubular lower section of the filling device  34  is a continuous groove or channel which accommodates an O-ring  37 . 
         [0045]    As further seen in  FIG. 4 , the lower section of the filling device  34  is dimensioned so that the same is capable of being slidably advanced into the upper section of the passageway  22  into the annular gap defined between the valve stem  23  and the valve bonnet  20 . When the filling device  34  is used to facilitate the introduction of the barrier  26  into the packing system  201 , it is contemplated that the lower section of the filling device  34  will initially be advanced into the upper section of the passageway  22  to a depth whereat the shoulder defined between the upper and lower sections of the filling device  34  will be abutted against or disposed in close proximity to the top, distal end of the valve bonnet  20  as viewed from the perspective shown in  FIG. 4 . Upon such advancement, the O-ring  36  effectively creates a seal between the filling device  34  and the valve stem  23 , with the O-ring  37  effectively creating a seal between the filling device  34  and the valve bonnet  20 . Thereafter, the passage  35  of the filling device  34  is used to channel the barrier  26  from the exterior of the valve  200  to and above the lower packing  25 . 
         [0046]    After a prescribed amount of the barrier  26  has been introduced into the upper section of the passageway  22 , the filling device  34  is completely retracted and withdrawn from within the passageway  22 , and removed from the valve  200 . Such retraction and removal of the filling device  34  is followed by the advancement of the upper packing  24  into the upper section of the passageway  22 . Subsequent to the load cell  27  being positioned upon the upper packing  24 , the packing follower  28  is advanced over the valve stem  23  and used to effectively push the upper packing  24  and load cell  27  downwardly into the passageway  22  to the general orientations shown in  FIG. 3  wherein the upper packing  24  also comes into contact with the barrier  26  previously filled into the passageway  22 . Typically, the live loading sub-assembly  211  is concurrently compressed in a manner wherein the gap between the upper and lower spacers  31 ,  32  is reduced to the height L 2  shown in  FIG. 3  from the height L 1  shown in  FIG. 4 . Those of ordinary skill in the art will recognize that the use of the filling device  34  is exemplary, and that the assembly of the packing system  201  within the valve  200  may potentially be accomplished through the use of alternative assembly techniques which do not entail the use of the filling device  34 . 
         [0047]    This disclosure provides exemplary embodiments of the present invention. The scope of the present invention is not limited by these exemplary embodiments. Numerous variations, whether explicitly provided for by the specification or implied by the specification, such as variations in structure, dimension, type of material and manufacturing process may be implemented by one of skill in the art in view of this disclosure. For example, it is contemplated that the packing systems  101 ,  201  may each be used in conjunction with valves which have structural and functional features differing from those described above in relation to the valves  100 ,  200 .