Abstract:
In accordance with the present invention, there is provided a bi-directional shut-off trim for a valve which possesses the functional attributes of a pilot operated trim and a balanced trim through the integration of a spring loaded check valve into a pilot trim. In forward flow isolation, the bi-directional shut-off trim of the present invention acts as a normal pilot operated trim. In reverse flow, the check valve of the shut-off trim opens to balance the pressure on either side of the plug thereof.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent Application Ser. No. 61/353,589 entitled SHUT-OFF TRIM INCLUDING SPRING LOADED CHECK VALVE filed Jun. 10, 2010. 
    
    
     STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Technical Field of the Invention 
     The present invention relates generally to bi-directional valves for high pressure fluid flow and, more particularly, to a bi-directional shut-off trim for a valve which possesses the functional attributes of a pilot operated trim and a balanced trim through the integration of a spring loaded check valve into a pilot trim. In forward flow isolation, the bi-directional shut-off trim of the present invention acts as a normal pilot operated trim. In reverse flow, the check valve of the shut-off trim opens to balance the pressure on either side of the plug thereof. 
     2. Description of the Related Art 
     There is known in the prior art valve constructions which are adapted to provide pressure balance on opposite sides of a main valve assembly during both opening and closing movements of the main valve assembly with fluid flow in either direction through the valve. One such exemplary prior art bi-directional balanced valve is disclosed in U.S. Pat. No. 3,888,280 entitled BI-DIRECTIONAL PRESSURE BALANCED VALVE issued Jun. 10, 1975. 
     However, currently known valve constructions or designs providing a bi-directional pressure balanced function are often subject to early failure and malfunctioning when used under severe service conditions, e.g., under high temperature and high pressure operating conditions. More particularly, the failure or malfunctioning of currently known valve designs is often attributable to the rapid erosion of deterioration of their sealing areas, as well as other critical valve components. In this regard, the available seal materials usable in conjunction with currently known bi-directional pressure balanced valve designs are often not adequate for providing required shut-off characteristics, and further frequently make the valve susceptible to early failure when the such seal materials are subjected or exposed to the intended operational environment of the valve. 
     The present invention is intended to represent an improvement to existing bi-directional pressure balanced valve designs by providing a valve shut-off trim which combines a pilot operated trim and a balanced trim through the addition of a spring loaded check valve within the pilot trim. As indicated above, in forward flow isolation, the shut-off trim of the present invention acts as a normal pilot operated trim, while in reverse flow, the check valve thereof opens to balance the pressure on either side of the plug of the trim. Thus, the addition of the spring loaded check valve in the shut-off trim of the present invention causes the pilot operated trim to act as a balanced plug in the reverse flow direction. These, as well as other features and advantages of the present invention, will be described in more detail below. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a valve shut-off trim which includes a spring loaded check valve and is usable in applications requiring valves with bi-directional shut-off trim where the use of unbalanced trim designs is not feasible and the choice of seals is limited by temperature, and/or radiation, and/or chemistry of seal materials. The shut-off trim constructed in accordance with the present invention finds particular utility in applications requiring shut-off in a forward direction of Class V and shut-off in a reverse flow direction of Class IV, with forward flow being, for example, water at 440° F. and reverse flow being, for example, steam at 567° F. 
     In the present invention, to obtain Class IV shut-off in a reverse flow direction, carbon piston rings are integrated into the shut-off trim. By combining a pilot ported plug and a check valve (which allows flow in the reverse direction), the shut-off trim of the present invention allows isolation in forward and reverse directions. In the forward direction, the trim achieves leak-tight shut-off (pilot ported plug acts an unbalanced plug when in the closed position). In the reverse direction and during modulation, the shut-off trim acts as a balanced plug. Thus, when reverse pressure unseats the pilot plug, the trim acts a balanced plug as indicated above. The shut-off trim of the present invention preferably includes a spring for loading the pilot plug. 
     Due to its construction, which will be described with particularity below, the shut-off trim constructed in accordance with the present invention eliminates reliance on elastomeric balance seals for the forward flow direction, and allows for the use of, by way of example, carbon or metallic piston rings for the reverse direction shut-off requirements. Thus, the shut-off trim of the present invention eliminates the need for a lengthy seal qualification program and extends the qualified life of the equipment in the field with integrates the same. As a result, the shut-off trim constructed in accordance with the present invention has the capability of satisfying safety related isolation functions that have been imposed on control valves integrated or used in certain applications, such as those requiring the aforementioned Class V shut-off in a forward direction and a Class IV shut-off in a reverse direction. In many of these applications, the use of graphoil seals would not be suitable due to the number of open/close/small modulation cycles that are imposed by the application requirements. Additionally, elastomeric seals are generally unsuitable for obtaining Class V shut-off since this requirement often pushes such elastomeric seals to or beyond their documented usable limits, or undesirably shortens their qualified life due to, for example, the limited ability thereof to withstand radiation, as well as their susceptibility to hardening due to thermal aging. 
     The present invention is best understood in reference to the following detailed description when read in conjunction with accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These, as well as other features of the present invention, will become more apparent upon reference to the drawings wherein: 
         FIG. 1  is a side-elevational, partial cross-sectional view of a shut-off trim constructed in accordance with a first embodiment of the present invention; 
         FIG. 2  is a side-elevational, partial cross-sectional view of a shut-off trim constructed in accordance with a second embodiment of the present invention; 
         FIGS. 3A-3C  are side-elevational views illustrating a plug sleeve of the shut-off trim shown in  FIG. 2  in differing states of actuation; 
         FIG. 3D  is a cross-sectional view of the plug sleeve of the shut-off trim shown in FIGS.  2  and  3 A- 3 C; 
         FIGS. 4A-4C  are side-elevational views illustrating an auxiliary plug in differing states of actuation which may be used as an alternative to the plug sleeve shown in FIGS.  2  and  3 A- 3 D in a shut-off trim constructed in accordance with a third embodiment of the present invention; 
         FIG. 5  is a side-elevational, partial cross-sectional view of a shut-off trim constructed in accordance with a fourth embodiment of the present invention; and 
         FIGS. 6A-6B  are side-elevational views illustrating the check valve of the shut-off trim shown in  FIG. 5  in differing states of actuation. 
     
    
    
     Common reference numerals are used throughout the drawings and detailed description to indicate like elements. 
     DETAILED DESCRIPTION OF THE INVENTION 
     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,  FIG. 1  depicts a shut-off trim  10  constructed in accordance with a first embodiment of the present invention. It is contemplated that the trim  10  will be integrated into a valve construction wherein the valve includes a housing which defines an interior plug chamber  14 . The plug chamber  14  is partially defined by a generally cylindrical, tubular fluid energy dissipation device, such as the disc stack  16  shown in  FIG. 1 . The plug chamber  14  is further partially defined by a generally cylindrical, tubular plug sleeve  18  which is coaxially aligned with the disc stack  16 , one end of the plug sleeve  18  typically being engaged to a corresponding end of the disc stack  16 . 
     In addition to the plug chamber  14 , the housing  12  of the valve into which the trim  10  is integrated also defines an inflow passage  20  and an outflow passage  22  which each fluidly communicate with the plug chamber  14 . The inflow and outflow passages  20 ,  22  are more easily seen in those embodiments of the shut-off trim depicted in  FIGS. 2 and 5 . In the valve including the trim  10 , fluid traveling through the inflow passage  20  flows radially inwardly through the disc stack  16  and into the plug chamber  14 . When the trim  10  is in an open condition or state as will be described in more detail below, fluid entering the plug chamber  14  is able to flow into the outflow passage  22 , and thereafter exit the valve including the trim  10 . Typically, the interface between the outflow passage  22  and the plug chamber  14  is defined by an annular seat ring  24 . 
     The trim  10  constructed in accordance with the first embodiment of the present invention comprises a main pilot plug  28  which, from the perspective shown in  FIG. 1 , defines a top surface  30 , a bottom surface  32 , a side surface  34 , and a beveled sealing surface  36  which extends between the bottom and side surfaces  32 ,  34 . The pilot plug  28  is not solid, but rather has a bore  38  extending axially therethrough. As is also apparent from  FIG. 1 , the bore  38  is not of uniform diameter. Rather, the bore  38  defines four (4) different segments or sections, each of which is of a differing diameter. More particularly, the diameters of the bore sections defined by the bore  38  progressively decrease from the top surface  30  to the bottom surface  32 , with the lowermost bore section extending to the bottom surface  32  thus being of the smallest diameter of the four bore sections. The uppermost and upper middle bore sections are separated from each other by an annular shoulder  40 . Similarly, the upper middle and lower middle bore sections are separated by an annular shoulder  42 , with the lower middle and lowermost bore sections being separated by an annular shoulder  44 . Disposed within the shoulder  40  is a plurality of elongate grooves or channels  46 , the use of which will be described in more detail below. Additionally, disposed in the side surface  34  of that portion of the pilot plug  28  which defines the uppermost bore section is a plurality of sealing rings  48  which circumvent the pilot plug  28  and are used for reasons which will also be described in more detail below. 
     When the trim  10  is in a closed position within the exemplary valve including the same, the sealing surface  36  defined by the pilot plug  28  is firmly seated and sealed against the seat ring  24 . The trim  10  assumes an open position when, from the perspective shown in  FIG. 1 , the pilot plug  28  is caused to move upwardly as results in the sealing surface  36  thereof effectively being separated from the seat ring  24 . Such separation allows fluid within the plug chamber  14  to flow between the sealing surface  36  and seat ring  24  into the outflow passage  22 . 
     In addition to the pilot plug  28 , the trim  10  includes check valve assembly comprising an auxiliary plug  50  which resides within the bore  38  of the pilot plug  28 . Like the pilot plug  28 , the auxiliary plug  50 , when viewed from the perspective shown in  FIG. 1 , defines a top surface  52 , a bottom surface  54 , a side surface  56 , and a beveled sealing surface  58  which extends between the bottom and side surfaces  54 ,  56 . As is apparent from  FIG. 1 , the side surface  56  of the auxiliary plug  50  is not of uniform outer diameter. Rather, the side surface  56  defines four (4) side surface sections or segments which may be of differing outer diameter. Along these lines, it is contemplated that the outer diameter of the lowermost segment of the side surface  56  to which the sealing surface  58  extends will be of the greatest diameter in the auxiliary plug  50 . In the auxiliary plug  50 , the lowermost and lower middle segments of the side surface  56  are separated by an annular shoulder  60 . 
     In the trim  10 , the auxiliary plug  50  is operatively coupled to a collar  62  of the check valve assembly which is attached to the bottom end of the stem  64  of the valve including the trim  10 . When viewed from the perspective shown in  FIG. 1 , the collar  62  defines a top surface  66 , a bottom surface  68 , and a side surface  70 . The side surface  70  is also not of uniform outer diameter, but rather includes two (2) side surface sections or segments which are of differing outer diameter. In this regard, that segment of the side surface  70  extending to the top surface  66  exceeds the outer diameter of that segment of the side surface  70  extending to the bottom surface  68 . These upper and lower segments of the side surface  70  are separated by an annular shoulder  72 . 
     In the trim  10 , the auxiliary plug  50  is moveably attached to the collar  62  via the receipt of a portion of the auxiliary plug  50  into a complimentary interior cavity  74  defined by the collar  62 . As seen in  FIG. 1 , that portion of the auxiliary plug  50  defining the uppermost segment of the side surface  56  thereof is captured and maintained within the interior cavity  74 , as is at least a portion of the auxiliary plug  50  which defines the upper middle segment of the side surface  56  thereof. The cooperative engagement between the auxiliary plug  50  and the collar  62  allows for the reciprocal movement of the auxiliary plug  50  relative to the collar  62  in a manner either decreasing or increasing the distance separating the shoulder  60  of the auxiliary plug  50  from the bottom surface  68  of the collar  62 . In this regard, the check valve assembly of the trim  10  preferably includes a biasing spring  76  which extends between the shoulder  60  and the bottom surface  68 . The biasing spring  76  normally biases the auxiliary plug  50  away from the collar  62 , i.e., maximizes the distance separating the shoulder  60  of the auxiliary plug  50  from the bottom surface  68  of the collar  62 . As will be recognized, the movement of the auxiliary plug  50  away from the collar  62  attributable to the action of the biasing spring  76  is eventually limited by the abutment of that portion of the auxiliary plug  50  defining the uppermost segment of the side surface  56  against an inner surface portion of the collar  62  which partially defines the interior cavity  74  thereof. 
     As indicated above, the pilot plug  28  of the trim  10  is moveable between a closed position wherein the sealing surface  36  thereof is sealed against the seat ring  24 , and an open position wherein the sealing surface  36  of the pilot plug  28  is separated from the seat ring  24 , thus allowing fluid to flow therebetween into the outflow passage  22 . The movement of the pilot plug  28  between its closed and open positions is facilitated by the upward and downward movement or actuation of the stem  64 , and more particularly, the collar  62  attached to one end thereof. As will be recognized, the reciprocal movement of the stem  64  and collar  62  as is needed to facilitate the movement of the pilot plug  28  between its closed and open positions is facilitated by an actuator which is operatively coupled to that end of the stem  64  opposite that having the collar  62  attached thereto. The downward movement of the stem  64  when viewed from the perspective shown in  FIG. 1  causes the shoulder  72  defined by the collar  62  to act against the shoulder  40  of the pilot plug  28  in a manner which forces the sealing surface  36  of the pilot plug  28  against the seat ring  24  and maintains the sealed engagement therebetween. 
     When the pilot plug  28  is in its closed position, the biasing force exerted against the auxiliary plug  50  by the biasing spring  76  causes the sealing surface  58  of the auxiliary plug  50  to firmly engage and establish sealed contact with a portion of the pilot plug  28  at the inner periphery of the shoulder  44  thereof, as shown in  FIG. 1 . As is further shown in  FIG. 1 , in the check valve assembly integrated into the trim  10 , a biasing spring  78  extends between the shoulder  42  of the pilot plug  28  and the shoulder  72  of the collar  62 . From the perspective shown in  FIG. 1 , when the stem  64  is actuated to facilitate the movement of the pilot plug  28  to the closed position, the downward biasing force exerted against the pilot plug  28  by the biasing spring  78  assists in maintaining the sealed engagement between the sealing surface  36  of the pilot plug  28  and the seat ring  24  even if the shoulder  72  of the collar  62  ceases to apply force directly to the shoulder  40  of the pilot plug  28 . 
     When the trim  10  is in a state or condition wherein the sealing surface  36  of the pilot plug  28  is sealed against the seat ring  24  and the sealing surface  58  of the auxiliary plug  50  is sealed against the pilot plug  28 , the pressure level P 1  in the inflow passage  20  will typically exceeds the pressure level P 2  in the outflow passage  22 . The pressure level P 1  also exists in the plug chamber  14 . In this regard, when viewed from the perspective shown in  FIG. 1 , the plug chamber  14  is at the pressure level P 1  both above and below the level of a plug plate  80  which is attached to the top surface  30  of the pilot plug  28  through the use of, for example, fasteners such as bolts  82 . The plug plate  80 , which is used for reasons described in more detail below, includes at least one flow opening  84  which extends between the opposed top and bottom surfaces thereof. 
     In the valve including the trim  10 , that portion of the plug chamber  14  located above the plug plate  80  reaches the pressure level P 1  as a result of anticipated leakage which occurs between the inner surface of the plug sleeve  18  and the sealing rings  48  disposed in the side surface  34  of the pilot plug  28 . In this regard, the sealing rings  48  facilitate the pressurization of that portion of the plug chamber  14  located above the plug plate  80  in a regulated, metered manner. As is also seen in  FIG. 1 , the side surface  34  of the pilot plug  28  is not of uniform outer diameter, but rather defines an annular shoulder  84  which is disposed in relative close proximity to the sealing surface  36 . Advantageously, the fluid pressure at the pressure level P 1  within that portion of the plug chamber  14  below the plug plate  80  and in between the side surface  34  and the inner surfaces of the disc stack  16  and plug sleeve  18  is able to act against the shoulder  84  in a manner supplementing or increasing the force of the sealed engagement between the sealing surface  36  and seat ring  24 . Such sealed engagement is further supplemented by the pressure level P 1  within that portion of the plug chamber  14  disposed below the plug plate  80  acting against the shoulders  40 ,  42 ,  44  of the pilot plug  28 . In this regard, fluid migrating between the pilot plug  28  and plug sleeve  18  into that portion of the plug chamber  14  disposed above the plug plate  80  is able to flow into the uppermost section of the bore  38  via the at least one flow opening  84  of the plug plate  80 . Even if the shoulder  72  of the collar  62  is firmly seated against the shoulder  40  of the pilot plug  28 , fluid is also able to flow into the upper middle and lower middle sections of the bore  38  via the channels  46  in the shoulder  40 , at least portions of which extend radially beyond that segment of the side surface  70  of the collar  62  of greater diameter extending to the top surface  66  thereof. Such flow results in the upper middle and lower middle sections of the bore  38  reaching the fluid pressure level P 1  along with the uppermost section of the bore  38 . Advantageously, the pressure level P 1  in the lower middle section of the bore  38  also acts against the shoulder  60  of the auxiliary plug  50  which supplements or enhances the sealed engagement between the sealing surface  58  of the auxiliary plug  50  and the pilot plug  28 . 
     In the valve including the trim  10 , the movement of the pilot plug  28  from its closed position to an open position is facilitated by the upward movement of the stem  64 , and hence the collar  62 , when viewed from the perspective shown in  FIG. 1 , such upward movement being facilitated by the actuator cooperatively engaged to the stem  64 . The upward movement of the stem  64  initially causes the collar  62  to act against that portion of the auxiliary plug  50  residing within the interior cavity  74  as effectively removes the sealing surface  58  from its sealed engagement to the pilot plug  28 . The movement of the auxiliary plug  50  out of sealed engagement with the pilot plug  28  creates a balanced pressure condition between the plug chamber  14  and the outflow passage  22 . In this regard, the removal of the auxiliary plug  50  from its sealed engagement to the pilot plug  28  allows for open flow between the plug chamber  14  (including that portion disposed above the plug plate  80 ) and the outflow passage  22  via the bore  38  and flow passage  84  of the plug plate  80 . 
     The continued upward movement of the collar  62  after the auxiliary plug  50  is unseated from the pilot plug  28  results in the top surface  66  of the collar  62  acting against the bottom surface of the plug plate  80 . By virtue of the attachment of the plug plate  80  to the pilot plug  28 , the continued upward movement of the collar  62  after the same engages the plug plate  80  results in the sealing surface  36  of the pilot plug  28  being lifted off of and thus separated from the seat ring  24 , thereby causing the trim  10  to assume an open position. 
     In the trim  10  constructed in accordance with the present invention, it is contemplated that in a further mode of operation, a balanced pressure condition between the plug chamber  14  and outflow passage  22  may be achieved if the pilot plug  28  is in its closed position, but the pressure level P 2  in the outflow passage  22  exceeds the pressure level P 1  in the inflow passage  20  and plug chamber  14 . In this instance, it is contemplated that the pressure level P 2  will act against the bottom surface  54  of the auxiliary plug  50  in a manner facilitating the compression of the biasing spring  76  and removal of the sealing surface  58  from its sealed engagement to the pilot plug  28 . The upward movement of the auxiliary plug  50  by virtue of the compression of the biasing spring  76  is accommodated by the clearance between that portion of the auxiliary plug  50  residing within the interior cavity  74  and those surfaces of the collar  62  defining the interior cavity  74 . Once the auxiliary plug  50  is unseated from the pilot plug  28 , fluid is able to flow into the lower middle and upper middle sections of the bore  38 , and thereafter into the uppermost section of the bore  38  via the channels  46  disposed in the shoulder  40 . Fluid flowing into the uppermost section of the bore  38  is in turn able to flow into that portion of the plug chamber  14  disposed above the plug plate  80  via the flow opening  84  within the plug plate  80 . The equalization of the pressure level in the plug chamber  14  with the pressure level in the outflow passage  22  results in the sealing surface  58  of the auxiliary plug  50  being returned to sealed engagement to the pilot plug  28  by operation of the biasing spring  76 . Similarly, the sealed engagement between the sealing surface  36  of the pilot plug  28  and the seat ring  24  is maintained by the biasing spring  78 . 
     The check valve assembly integrated into the trim  10  comprises the auxiliary plug  50 , collar  62  and biasing springs  76 ,  78 . Importantly, the functional attributes provided to the trim  10  by the check valve assembly allow the trim to achieve a Class V shut-off when subjected to an operational condition wherein the pressure level P 1  within the inflow passage  20  and plug chamber  14  exceeds the pressure level P 2  in the outflow passage  22 . The unique structural and functional attributes of the trim  10  also allow the same to achieve a Class IV shut-off when subjected to an operational condition wherein the pressure level P 2  in the outflow passage  22  rises to the level which exceeds that of the pressure level P 1  in the inflow passage  20  and plug chamber  14 . 
     Referring now to FIGS.  2  and  3 A- 3 C, there is shown a shut-off trim  100  constructed in accordance with a second embodiment of the present invention. The trim  100  comprises a main pilot plug  128  which, from the perspective shown in  FIG. 2 , defines a top surface  130 , a bottom surface  132 , a side surface  134 , and a sealing surface  136  which extends between the bottom and side surfaces  132 ,  134 . The pilot plug  128  is not solid, but rather has a bore  138  extending axially therethrough. The bore  138  is not of uniform diameter. Rather, the bore  138  defines four (4) different segments or sections, each of which is of a differing diameter. More particularly, the bore  138  includes an uppermost section, an upper middle section, and a lower middle section which are of a progressively decreasing diameter. The bore  138  also defines a lowermost section which is of the greatest diameter, exceeding that of the uppermost section thereof. The uppermost and upper middle sections of the bore  138  are separated by a shoulder  140 . Similarly, the upper middle and lower middle sections of the bore  138  are separated by an annular shoulder  142 . Additionally, disposed in the side surface  134  of that portion of the pilot plug  128  which defines the uppermost bore section is a plurality of sealing rings  148  which circumvent the pilot plug  128  and are used for reasons which will also be described in more detail below. 
     When the trim  100  is in a closed position within the exemplary valve including the same, the sealing surface  136  defined by the pilot plug  128  is firmly seated and sealed against the seat ring  24 . The trim  100  assumes an open position when, from the perspective shown in  FIG. 2 , the pilot plug  128  is caused to move upwardly as results in the sealing surface  136  thereof effectively being separated from the seat ring  24 . Such separation allows fluid from within the plug chamber  14  to flow between the sealing surface  136  and seat ring  24  into outflow passage  22 . 
     In addition to the pilot plug  128 , the trim  100  includes a check valve assembly comprising a fastener  186  which is secured to that end of the stem  64  opposite the end portion cooperatively engaged to the actuator. As best seen in  FIGS. 3A-3C , the fastener  186  comprises a cylindrically configured shank portion, an enlarged head portion which is formed on one end of the shank portion, and an externally threaded attachment portion which is threadably advanced into a complimentary, internally threaded aperture disposed within the end surface of the stem  64 . As is also apparent from  FIGS. 3A-3C , the end portion of the stem  64  defining the end surface having the internally threaded aperture formed therein is enlarged relative to the remainder of the stem  64 . The end surface of the stem  64  which includes the internally threaded aperture therein also includes an annular groove or channel  188  which is formed therein and effectively circumvents the internally threaded aperture. The use of the channel  188  will be described in more detail below. The advancement of the attachment portion of the fastener  186  into the complimentary, internally threaded aperture of the stem  64  is continued until such time as the shank portion of the fastener  186  abuts the end surface of the stem  64 . 
     In addition to the fastener  186 , the check valve assembly comprises a generally cylindrical, tubular plug sleeve  190  which is cooperatively engaged to both the fastener  186  and stem  64 , and is reciprocally movable relative thereto in a manner which will be described in more detail below. An enlarged, cross-sectional view of the plug sleeve  190  standing alone is shown in  FIG. 3D . The plug sleeve  190  includes a bore  192  which extends axially therethrough. The bore  192  is also not of uniform diameter. Rather, the bore defines two (2) different segments or sections, each of which is of differing diameter. More particularly, when viewed from the perspective shown in  FIGS. 3A-3D , the bore  192  defines upper and lower sections which are separated from each other by an annular wall portion  194  of the plug sleeve  190  which is integrally connected to a main body portion  196  thereof, and protrudes from the inner surface of the main body portion  196  radially inwardly into the bore  192 . The wall portion  194  defines opposed, generally annular first and second shoulders  198 ,  199 , the first shoulder  198  being directed toward the upper section of the bore  192 , and the second shoulder  199  being directed toward the lower section of the bore  192  which is of a reduced diameter in comparison to the upper section thereof. 
     In the check valve assembly of the trim  100 , the cooperative engagement of the plug sleeve  190  to the fastener  186  and stem  64  is facilitated by advancing the end portion of the main body portion  196  disposed furthest from the wall portion  194  into the channel  188  of the stem  64 . In this regard, the channel  188  has a configuration which is complimentary to that of the end portion of the main body portion  196  which is advanced thereinto. At the same time, the enlarged head portion of the fastener  186  is received into and reciprocally moveable within the reduced diameter lower section of the bore  192 . The shank portion of the fastener  186  resides within the increased diameter upper section of the bore  192 . The check valve assembly of the trim  100  further includes a biasing spring  178  which also resides within the upper section of the bore  192  of the plug sleeve  190 , and extends between the first shoulder  198  and the end surface of the stem  64 . The biasing spring  178  normally biases the plug sleeve  190  away from the stem  64 , i.e., maximizes the distance separating the wall portion  194  from the end surface of the stem  64 . In the check valve assembly, the movement of the plug sleeve  190  away from the stem  64  attributable to the action of the biasing spring  178  is eventually limited by the abutment of the second shoulder  199  defined by the wall portion  194  against the enlarged head portion of the fastener  186 . Conversely, the movement of the plug sleeve  190  toward the stem  64  is limited by the eventual abutment or bottoming out of the main body  196  of the plug sleeve  190  against the bottom, innermost surface of the channel  188 . 
     As indicated above, the pilot plug  128  of the trim  100  is movable between a closed position wherein the sealing surface  136  is sealed against the seat ring  24 , and an open position wherein the sealing surface  136  is separated from the seat ring  24 , thus allowing fluid to flow therebetween into the outflow passage  22 . The movement of the pilot plug  128  between its closed and open positions is facilitated by the upward and downward movement or actuation of the stem  64 . The reciprocal movement of the stem  64  as is needed to facilitate the movement of the pilot plug  128  between its closed and open positions is facilitated by an actuator which is operatively coupled to that end of the stem  64  opposite that having the fastener  184  attached thereto. The downward movement of the stem  64  when viewed from the perspective shown in  FIG. 2  causes a peripheral portion of the end surface thereof having the internally threaded aperture and channel  188  formed therein to act against the shoulder  140  of the pilot plug  128  in a manner which forces the sealing surface  136  of the pilot plug  128  against the seat ring  24  and maintains the sealed engagement therebetween. 
     When the pilot plug  128  is in its closed position, the biasing force exerted against the plug sleeve  190  by the biasing spring  178  causes an annular sealing surface  197  defined by the main body portion  196  of the plug sleeve  190  to firmly engage and establish sealed contact with a portion of the pilot plug  128  at the inner periphery of the shoulder  142  thereof in the manner shown in  FIG. 3A . Further, when the trim  100  is in a state or condition wherein the sealing surface  136  of the pilot plug  128  is sealed against the seat ring  24  and the sealing surface  197  of the plug sleeve  190  is sealed against the pilot plug  128 , the pressure level P 1  in the inflow passage  20  will typically exceed the pressure level P 2  in the outflow passage  22 . The pressure level P 1  also exists in the plug chamber  14 . In this regard, when viewed from the perspective shown in  FIG. 2 , the plug chamber  14  is at the pressure level P 1  both above and below the level of a plug plate  180  which is attached to the top surface  130  of the pilot plug  128  through the use of, for example, fasteners such as bolts  182 . The plug plate  180  includes flow openings  184  which are disposed therein and extend between the opposed top and bottom surfaces thereof. 
     In the valve including the trim  100 , that portion of the plug chamber  14  located above the top surface  130  of the pilot plug  128  reaches the pressure level P 1  as the result of anticipated leakage which occurs between the inner surface of the plug sleeve  18  and the sealing rings  148  disposed in the side surface  134  of the pilot plug  128 . In this regard, the sealing rings  148  facilitate the pressurization of that portion of the plug chamber  14  located above the pilot plug  128  in a regulated, metered manner. As seen in  FIG. 2 , the side surface  134  of the pilot plug  128  is not of uniform outer diameter, but rather defines an annular shoulder  184  which is disposed in relative close proximity to the sealing surface  136 . Advantageously, fluid pressure at the pressure level P 1  within that portion of the plug chamber  14  below the top surface  130  and in between the side surface  134  and the inner surfaces of the disc stack  16  and plug sleeve  18  is able to act against the shoulder  184  in a manner supplementing or increasing the force of the sealed engagement between the sealing surface  136  and seat ring  24 . Such sealed engagement is further supplemented by the pressure level P 1  within that portion of the plug chamber  14  disposed above the pilot plug  128  acting against the top surface  130  thereof. The pressure level P 1  also acts against the shoulders  140 ,  142  within the bore  138  of the pilot plug  128 , thus further supplementing the force of the sealed engagement to be between the sealing surface  136  and the seat ring  24 . In this regard, fluid migrating between the pilot plug  128  and plug sleeve  18  into that portion of the plug chamber  14  disposed above the pilot plug  128  is able to flow into the uppermost and upper middle sections of the bore  138  to act against the shoulders  140 ,  142  via the flow openings  184  of the plug plate  180  and one or more additional flow openings  185  which are disposed in the peripheral portion of the enlarged end portion of the stem  64  having the internally threaded aperture and the channel  188  formed therein. Even if the end surface of the stem  64  is firmly seated against the shoulder  140  of the pilot plug  128 , fluid is able to flow into the upper middle section of the bore  138  via the flow openings  185 . Such flow results in the uppermost and upper middle sections of the bore  138  reaching the fluid pressure level P 1 . 
     Moreover, in the valve including the trim  100 , the movement of the pilot plug  128  from its closed position to its open position is facilitated by the upward movement of the stem  64 , such upward movement being facilitated by the actuator cooperatively engaged to the stem  64 . The upward movement of the stem  64  initially causes the head portion of the fastener  186  to act against the shoulder  199  defined by the wall portion  194  of the plug sleeve  190  in a manner which effectively removes the sealing surface  197  of the plug sleeve  190  from its sealed engagement to the pilot plug  128 . The movement of the plug sleeve  190  out of sealed engagement with the pilot plug  128  creates a balanced pressure condition between the plug chamber  14  and outflow passage  22 . In this regard, the removal of the plug sleeve  190  from its sealed engagement to the pilot plug  128  allows for open flow between the plug chamber  14  and the outflow passage  22  via the bore  138 , the flow passages  184  of the plug plate  180 , and the flow passages  185  within the enlarged end portion of the stem  64 . 
     The continued upward movement of the stem  64  after the plug sleeve  190  is unseated from the pilot plug  128  results in the enlarged end portion of the stem  64  acting against the bottom surface of the plug plate  180 . By virtue of the attachment of the plug plate  180  to the pilot plug  128 , the continued upward movement of the stem  64  after the same engages the plug plate  180  results in the sealing surface  136  of the pilot plug  128  being lifted off of and thus separated from the seat ring  24 , thereby causing the trim  100  to assume an open position. 
     In the trim  100 , it is contemplated that in a further mode of operation, a balanced pressure condition between the plug chamber  14  and the outflow passage  22  may be achieved if the pilot plug  128  is in its closed position, but the pressure level P 2  in the outflow passage  22  exceeds the pressure level P 1  in the inflow passage  20  and plug chamber  14 . In this instance, it is contemplated that the pressure level P 2  will act against an annular end surface  195  of the plug sleeve  190  which is defined by the main body portion  196  thereof. In this regard, the sealing surface  197  extends to the outer peripheral edge of the end surface  195 . More particularly, the pressure level P 2  reaches the end surface  195  via the lowermost and lower middle sections of the bore  138 , and acts against the end surface  195  in a manner facilitating the compression of the biasing spring  178  and removal of the sealing surface  197  from its sealed engagement to the pilot plug  128 . The upward movement of the plug sleeve  190  by virtue of the compression of the biasing spring  178  is accommodated by the clearance between that end surface of the main body portion  196  opposite the end surface  195  and the bottom of the channel  188 . Once the plug sleeve  190  is unseated from the pilot plug  128 , fluid is able to flow from the outflow passage  22  into that portion of the plug chamber  14  above the pilot plug  128  via the bore  138  and the flow passages  185 ,  184 . The equalization of the pressure level in the plug chamber  14  with the pressure level in the outflow passage  22  results in the sealing surface  197  of the plug sleeve  190  being returned to sealed engagement to the pilot plug  128  by operation of the biasing spring  178 . The check valve assembly integrated to the trim  100  provides the same functional characteristics of the trim  10  described above. 
     Referring now to  FIGS. 4A-4C , there is shown in different states of actuation a check valve assembly  200  which may be integrated into a shut-off trim constructed in accordance with a third embodiment of the present invention, the check valve assembly  200  shown in  FIGS. 4A-4C  being used as an alternative to the check valve assembly shown in  FIGS. 3A-3D . In this regard, the check valve assembly  200  is used in conjunction with the same pilot plug  128  possessing the same structural and functional attributes as described above in relation to the trim  100 . The check valve assembly  200  is also used in conjunction with the aforementioned plug plate  180  which is attached to the pilot plug  128  in the same manner described above in relation to the trim  100 . 
     The check valve assembly  200  integrated to the trim constructed in accordance with the third embodiment of the present invention comprises an auxiliary plug  286  which is secured to that end of the stem  64  opposite the end portion cooperatively engaged to the actuator. The auxiliary plug  286  comprises a cylindrically configured main body portion  287  having an elongate stem portion  289  protruding therefrom. Disposed within and extending through the stem portion  289  is an elongate slot  291 . Additionally, disposed in the main body portion  287  is an annular channel  293  of a prescribed depth, the channel  293  circumventing the base of the stem portion  289 . The auxiliary plug  286  further defines an annular plan flange portion  295  which circumvents the channel  293 , and thus also circumvents the base of the stem portion  289 . 
     In the check valve assembly  200 , the stem portion  289  of the auxiliary plug  286  is slideably advanced into a complimentary aperture disposed within the end surface of the enlarged end portion of the stem  64 . Subsequent to the advancement of the stem portion  289  into the complimentary aperture within the stem  64 , a pin  297  is advanced through the stem  64  and through the slot  291  disposed within the stem portion  289 . As seen in  FIGS. 4A-4C , the advancement of the pin  297  through the slot  291  allows for the reciprocal movement of the auxiliary plug  286  toward and away from the stem  64 , but maintains the auxiliary plug  286  in attachment to the stem  64 . 
     As is apparent from  FIGS. 4A-4C  and as indicated above, the end portion of the stem  64  defining the end surface having the aperture formed therein is enlarged relative to the remainder of the stem  64 . The end surface of the stem  64  which includes such aperture for receiving the stem portion  289  also includes an annular groove or channel  288  which is formed therein and circumvents the aforementioned aperture. The use of the channel  288  will be described in more detail below. 
     In the check valve assembly  200 , the cooperative engagement of the auxiliary plug  286  to the stem  64  is facilitated the advancing the stem portion  289  into the complimentary aperture in the end surface defined by the enlarged end portion of the stem  64 , and securing the auxiliary plug  286  to the stem  64  through the use of the pin  297  advanced through the slot  291  within the stem portion  289 . At the same time, the flange portion  295  of the auxiliary plug  286  is slidably advanced into the channel  288  which has a configuration complimentary to that of the flange portion  295 . As is also apparent from  FIGS. 4A-4C , the check valve assembly  200  further includes a biasing spring  278  which is disposed within the channel  293 , and extends between the main body portion  287  of the auxiliary plug  286  and a portion of the end surface of the enlarged end portion of the stem  64  which circumvents the aperture therein for accommodating the stem portion  289 . The biasing spring  278  normally biases the auxiliary plug  286  away from the stem  64 . In the check valve assembly  200 , the movement of the auxiliary plug  286  away from the stem  64  attributable to the action of the biasing spring  278  is eventually limited by the abutment of the pin  297  against that end of the slot  291  disposed closest to the distal end of the stem portion  289 . Conversely, the movement of the auxiliary plug  286  toward the stem  64  is limited by the abutment of the pin  297  against the opposite end slot  291  and/or the abutment or bottoming out of the flange portion  295  of the auxiliary plug  286  against the bottom of the channel  288  within the enlarged end portion of the stem  264 . 
     The pilot plug  128  of the trim including the check valve assembly  200  is movable between a closed position wherein the sealing surface  136  is sealed against the seat ring  24 , and an open position wherein the sealing surface  136  is separated from the seat ring  24 , thus allowing fluid to flow therebetween into the outflow passage  22 . The movement of the pilot plug  128  between its closed and open positions is facilitated by the upward and downward movement or actuation of the stem  64 . As in the prior embodiments discussed above, the reciprocal movement of the stem  64  as is needed to facilitate the movement of the pilot plug  128  between its closed and open positions is facilitated by an actuator which is operatively coupled to that end of the stem  64  opposite that having the auxiliary plug  286  attached thereto. The downward movement of the stem  64  when viewed from the perspective shown in  FIGS. 4A-4C  causes a peripheral portion of the end surface thereof having the aperture and channel  288  formed therein to act against the shoulder  140  of the pilot plug  128  in a manner which forces the sealing surface  136  of the pilot plug  128  against the seat ring  24  and maintains the sealed engagement therebetween. 
     When the pilot plug  128  is in its closed position, the biasing force exerted against the auxiliary plug  286  by the biasing spring  278  causes an annular sealing surface  299  defined by the main body portion  287  of the auxiliary plug  286  to firmly engage and establish sealed contact with a portion of the pilot plug  128  at the inner periphery of the shoulder  142  thereof in the manner shown in  FIG. 4A . Further, when the trim including the check valve assembly  200  is in a state or condition wherein the sealing surface  136  of the pilot plug  128  is sealed against the seat ring  24  and the sealing surface  299  of the auxiliary plug  286  is sealed against the pilot plug  128 , the pressure level P 1  in the inflow passage  20  will typically exceed the pressure level P 2  in the outflow passage  22 . The pressure level P 1  also exists in the plug chamber  14 . In this regard, when viewed from the perspective shown in  FIGS. 4A-4C , the plug chamber  14  is at the pressure level P 1  both above and below the level of a plug plate  180  which is attached to the top surface  130  of the pilot plug  128  through the use of the bolts  182 . As indicated above, the plug plate  180  includes flow openings  184  which are disposed therein and extend between the opposed top and bottom surfaces thereof. 
     In the valve including the trim having the check valve assembly  200 , that portion of the plug chamber  14  located above the top surface  130  of the pilot plug  128  reaches the pressure level P 1  as the result of anticipated leakage which occurs between the inner surface of the plug sleeve  18  and the sealing rings  148  disposed in the side surface  134  of the pilot plug  128 . In this regard, the sealing rings  148  facilitate the pressurization of that portion of the plug chamber  14  located above the pilot plug  128  in a regulated, metered manner. As indicated above, the side surface  134  of the pilot plug  128  is not of uniform outer diameter, but rather defines an annular shoulder  184  which is disposed in relative close proximity to the sealing surface  136 . Advantageously, fluid pressure at the pressure level P 1  within that portion of the plug chamber  14  below the top surface  130  and in between the side surface  134  and the inner surfaces of the disc stack  16  and plug sleeve  18  is able to act against the shoulder  184  in a manner supplementing or increasing the force of the sealed engagement between the sealing surface  136  and seat ring  24 . Such sealed engagement is further supplemented by the pressure level P 1  within that portion of the plug chamber  14  disposed above the pilot plug  128  acting against the top surface  130  thereof. The pressure level P 1  also acts against the shoulders  140 ,  142  within the bore  138  of the pilot plug  128 , thus further supplementing the force of the sealed engagement to be between the sealing surface  136  and the seat ring  24 . In this regard, fluid migrating between the pilot plug  128  and plug sleeve  18  into that portion of the plug chamber  14  disposed above the pilot plug  128  is able to flow into the uppermost and upper middle sections of the bore  138  to act against the shoulders  140 ,  142  via the flow openings  184  of the plug plate  180  and one or more additional flow openings  285  which are disposed in the peripheral portion of the enlarged end portion of the stem  64  having the aperture and the channel  288  formed therein. Even if a portion of the end surface of the stem  64  is firmly seated against the shoulder  140  of the pilot plug  128 , fluid is able to flow into the upper middle section of the bore  138  via the flow openings  285 . Such flow results in the uppermost and upper middle sections of the bore  138  reaching the fluid pressure level P 1 . 
     Moreover, in the valve including the trim having the check valve assembly  200 , the movement of the pilot plug  128  from its closed position to its open position is facilitated by the upward movement of the stem  64 , such upward movement being facilitated by the actuator cooperatively engaged to the stem  64 . The upward movement of the stem  64  initially causes the pin  297  to act against the stem portion  289  of the auxiliary plug  286  in a manner which effectively removes the sealing surface  299  of the auxiliary plug  286  from its sealed engagement to the pilot plug  128 . The movement of the auxiliary plug  286  out of sealed engagement with the pilot plug  128  creates a balanced pressure condition between the plug chamber  14  and outflow passage  22 . In this regard, the removal of the auxiliary plug  286  from its sealed engagement to the pilot plug  128  allows for open flow between the plug chamber  14  and the outflow passage  22  via the bore  138 , the flow passages  184  of the plug plate  180 , and the flow passages  285  within the enlarged end portion of the stem  64 . 
     The continued upward movement of the stem  64  after the auxiliary plug  286  is unseated from the pilot plug  128  results in the enlarged end portion of the stem  64  acting against the bottom surface of the plug plate  180 . By virtue of the attachment of the plug plate  180  to the pilot plug  128 , the continued upward movement of the stem  64  after the same engages the plug plate  180  results in the sealing surface  136  of the pilot plug  128  being lifted off of and thus separated from the seat ring  24 , thereby causing the trim including the check valve assembly  200  to assume an open position. 
     In the trim of the third embodiment including the check valve assembly  200 , it is contemplated that in a further mode of operation, a balanced pressure condition between the plug chamber  14  and the outflow passage  22  may be achieved if the pilot plug  128  is in its closed position, but the pressure level P 2  in the outflow passage  22  exceeds the pressure level P 1  in the inflow passage  20  and plug chamber  14 . In this instance, it is contemplated that the pressure level P 2  will act against a circular end surface  283  of the auxiliary plug  286  which is defined by the main body portion  287  thereof. In this regard, the sealing surface  299  extends to the outer peripheral edge of the end surface  283 . More particularly, the pressure level P 2  reaches the end surface  283  via the lowermost and lower middle sections of the bore  138 , and acts against the end surface  283  in a manner facilitating the compression of the biasing spring  278  and removal of the sealing surface  299  from its sealed engagement to the pilot plug  128 . The upward movement of the auxiliary plug  286  by virtue of the compression of the biasing spring  278  is accommodated by the clearance between the flange portion  295  and the bottom of the channel  288 . Once the auxiliary plug  286  is unseated from the pilot plug  128 , fluid is able to flow from the outflow passage  22  into that portion of the plug chamber  14  above the pilot plug  128  via the bore  138  and the flow passages  285 ,  184 . The equalization of the pressure level in the plug chamber  14  with the pressure level in the outflow passage  22  results in the sealing surface  299  of the auxiliary plug  286  being returned to sealed engagement to the pilot plug  128  by operation of the biasing spring  278 . The check valve assembly  200  provides the same functional characteristics of the trim  10  described above. 
     Referring now to FIGS.  5  and  6 A- 6 B, there is shown a shut-off trim  300  constructed in accordance with a fourth embodiment of the present invention. The trim  300  comprises a pilot plug  328  which, from the perspective shown in  FIG. 5 , defines a top surface  330 , a bottom surface  332 , a side surface  334 , and a sealing surface  336  which extends between the bottom and side surfaces  332 ,  334 . The pilot plug  328  is not solid, but rather has a bore  338  extending axially therethrough. The bore  338  is not of uniform diameter. Rather, the bore  338  defines three (3) different segments or sections, each of which is of a differing diameter. More particularly, the bore  338  includes an upper section and a middle section which is of a reduced diameter in comparison to the upper section. The bore  338  also defines a lower section which is of the greatest diameter, exceeding that of the upper section thereof. The upper and middle sections of the bore  338  are separated by a shoulder  340 . Disposed in the side surface  334  of that portion of the pilot plug  328  which defines the upper bore section is a plurality of sealing rings  348  which circumvent the pilot plug  328  and are used for reasons which will also be described in more detail below. 
     When the trim  300  is in a closed position within the exemplary valve including the same, the sealing surface  336  defined by the pilot plug  328  is firmly seated and sealed against the seat ring  24 . The trim  300  assumes an open position when, from the perspective shown in  FIG. 2 , the pilot plug  328  is caused to move upwardly as results in the sealing surface  336  thereof effectively being separated from the seat ring  24 . Such separation allows fluid from within the plug chamber  14  to flow between the sealing surface  336  and seat ring  24  into outflow passage  22 . 
     The pilot plug  328  included in the trim  300  further includes a check valve assembly  301  which is shown with particularity in  FIGS. 6A and 6B . More particularly, the check valve assembly  301  comprises a flow passage  303  which extends from the top surface  330  of the pilot plug  328  to and into fluid communication with the lower section of the bore  338  thereof in the manner best shown in  FIG. 5 . The flow passage  303  is not of uniform inner diameter. Rather, when viewed from the perspective shown in  FIG. 5 , the flow passage  303  includes an upper section and a lower section which are separated from each other by an annular shoulder  305 , the diameter of the upper section exceeding that of the lower section. Disposed within the upper section of the flow passage  303  is a check ball  307 . The diameter of the check ball  307  presents the same from entering into the lower section of the flow passage  303 . The check ball  307  is maintained within the upper section of the flow passage  303  by an annular cap  309  which is partially advanced into the upper section of the flow passage  303 , and extends in substantially flush relation to the top surface  330  of the pilot plug  328 . At least a portion of that surface of the pilot plug  328  defining the upper section of the flow passage  303  is internally threaded, with the outer surface of the cap  309  being externally threaded so as to provide for the threadable engagement of the cap  309  to the plug  328 . 
     The check valve assembly  301  further comprises a biasing spring  311  which is disposed within the upper section of the flow passage  303 . One end of the biasing spring  311  is abutted against or engaged to the check ball  307 , with the opposite end of the biasing spring  311  being abutted against that end surface of the cap  309  which is opposite the end surface extended in substantially flush relation to the top surface  330  of the pilot plug  328 . As seen in  FIG. 6A , the biasing spring  311  normally biases the check ball  307  against the inner peripheral edge of the shoulder  305 , thus causing the check ball  307  to define a blockage or seal between the upper and lower sections of the flow passage  303 . By virtue of its annular configuration, the cap  309  defines a flow opening which extends axially therethrough and facilitates the fluid communication between the flow passage  303  and that portion of the plug chamber  14  disposed above the pilot plug  328  when viewed from the perspective shown in  FIG. 5 . 
     The pilot plug  328  of the trim  300  is movable between a closed position wherein the sealing surface  336  is sealed against the seat ring  24 , and an open position wherein the sealing surface  336  is separated from the seat ring  24 , thus allowing fluid to flow therebetween into the outflow passage  22 . The movement of the pilot plug  328  between its closed and open positions is facilitated by the upward and downward movement or actuation of the stem  64 . As in the prior embodiments discussed above, the reciprocal movement of the stem  64  as is needed to facilitate the movement of the pilot plug  328  between its closed and open positions is facilitated by an actuator which is operatively coupled thereto. The downward movement of the stem  64  when viewed from the perspective shown in  FIG. 5  causes a peripheral portion of the end surface thereof to act against the shoulder  340  of the pilot plug  328  in a manner which forces the sealing surface  336  of the pilot plug  328  against the seat ring  24  and maintains the sealed engagement therebetween. 
     When the pilot plug  328  is in its closed position, the biasing force exerted against the check ball  307  by the biasing spring  311  causes the check ball  307  to be firmly seated and sealed against the shoulder  305 , thus effectively blocking fluid communication between the outflow passage  22  and plug chamber  14  as would otherwise be provided by the flow passage  303 . Further, when the trim  300  is in a state or condition wherein the sealing surface  336  of the pilot plug  328  is sealed against the seat ring  24  and the check ball  307  is sealed against the shoulder  305 , the pressure level P 1  in the inflow passage  20  will typically exceed the pressure level P 2  in the outflow passage  22 . The pressure level P 1  also exists in the plug chamber  14 . In this regard, when viewed from the perspective shown in  FIG. 5 , the plug chamber  14  is at the pressure level P 1  both above and below the level of a plug plate  380  which is attached to the top surface  330  of the pilot plug  328  through the use the bolts  382 . The plug plate  380  includes flow openings  384  which are disposed therein and extend between the opposed top and bottom surfaces thereof. 
     In the valve including the trim  300 , that portion of the plug chamber  14  located above the top surface  330  of the pilot plug  328  reaches the pressure level P 1  as the result of anticipated leakage which occurs between the inner surface of the plug sleeve  18  and the sealing rings  348  disposed in the side surface  334  of the pilot plug  328 . In this regard, the sealing rings  348  facilitate the pressurization of that portion of the plug chamber  14  located above the pilot plug  328  in a regulated, metered manner. The side surface  334  of the pilot plug  328  is not of uniform outer diameter, but rather defines an annular shoulder  384  which is disposed in relative close proximity to the sealing surface  336 . Advantageously, fluid pressure at the pressure level P 1  within that portion of the plug chamber  14  below the top surface  330  and in between the side surface  334  and the inner surfaces of the disc stack  16  and plug sleeve  18  is able to act against the shoulder  384  in a manner supplementing or increasing the force of the sealed engagement between the sealing surface  336  and seat ring  24 . Such sealed engagement is further supplemented by the pressure level P 1  within that portion of the plug chamber  14  disposed above the pilot plug  328  acting against the top surface  330  thereof. The pressure level P 1  also acts against the shoulder  340  within the bore  338  of the pilot plug  328 , thus further supplementing the force of the sealed engagement to be between the sealing surface  336  and the seat ring  24 . In this regard, fluid migrating between the pilot plug  128  and plug sleeve  18  into that portion of the plug chamber  14  disposed above the pilot plug  328  is able to flow into the upper section of the bore  338  to act against the shoulders  140  via the flow openings  384  of the plug plate  380 . Such flow results in the upper section of the bore  338  reaching the fluid pressure level P 1 . Fluid at the pressure level P 1  also flows from the plug chamber  14  into the upper section of the flow passage  303  via the flow opening defined by the cap  309 . Such fluid at the pressure level P 1  acts against the check ball  307  in a manner supplementing the biasing force exerted thereagainst by the biasing spring  311 , thus enhancing the sealed engagement of the check ball  307  against the shoulder  305 . 
     Moreover, in the valve including the trim  300  having the check valve assembly  301 , the movement of the pilot plug  328  from its closed position to its open position is facilitated by the upward movement of the stem  64 , such upward movement being facilitated by the actuator cooperatively engaged to the stem  64 . When the pilot plug  328  is in its closed position, a sealing surface defined by the enlarged end portion of the stem  64  engages and is sealed against the inner peripheral rim defined by the shoulder  340  of the pilot plug  328 , thus effectively creating a blockage or barrier between the upper and middle sections of the bore  338 . The upward movement of the stem  64  initially causes the sealing surface of the stem  64  to be removed from its sealed engagement to the pilot plug  328 , thus creating a balanced pressure condition between the plug chamber  14  and outflow passage  22 . In this regard, the removal of the sealing surface defined by the enlarged end portion of the stem  64  from its sealed engagement to the pilot plug  328  allows for open flow between the plug chamber  14  and the outflow passage  22  via the bore  338  and flow passages  384  of the plug plate  380 . 
     The continued upward movement of the stem  64  after the sealing surface thereof is unseated from the pilot plug  328  results in the enlarged end portion of the stem  64  acting against the bottom surface of the plug plate  380 . By virtue of the attachment of the plug plate  380  to the pilot plug  328 , the continued upward movement of the stem  64  after the same engages the plug plate  380  results in the sealing surface  336  of the pilot plug  328  being lifted off of and thus separated from the seat ring  24 , thereby causing the trim  300  to assume an open position. 
     In the trim  300  including the check valve assembly  301 , it is contemplated that in a further mode of operation, a balanced pressure condition between the plug chamber  14  and the outflow passage  22  may be achieved if the pilot plug  328  is in its closed position, but the pressure level P 2  in the outflow passage  22  exceeds the pressure level P 1  in the inflow passage  20  and plug chamber  14 . In this instance, it is contemplated that the pressure level P 2  will act against the check ball  307  in a manner overcoming the biasing force exerted thereagainst by the biasing spring  311 , thus effectively forcing the check ball  307  toward the cap  309  and out of its sealed engagement to the shoulder  305 . As will be recognized, since the diameter of the check ball  307  is less than that of the upper section of the flow passage  303 , the movement of the check ball  307  out of sealed engagement to the shoulder  305  effectively unblocks the flow passage  303 , thus allowing open fluid communication between the outflow passage  22  and that portion of the plug chamber  14  disposed above the pilot plug  328 . As will be recognized, the pressure level P 2  reaches the check ball  307  via the lower section of the bore  338  and the lower section of the flow passage  303 . As indicated above, once the check ball  307  is unseated from the shoulder  305 , fluid is able to flow from out outflow passage  22  into that portion of the plug chamber  14  above the pilot plug  328  via the lower section of the bore  338  and flow passage  303 . The equalization of the pressure level in the plug chamber  14  with the pressure level in the outflow passage  22  results in the check ball  307  of the check valve assembly  301  being returned to sealed engagement to the shoulder  305  by operation of the biasing spring  311 . The trim  300  including the check valve assembly  301  provides the same functional characteristics of the trim  10  described above. 
     This disclosure provides exemplary embodiments of the present invention only. 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.