Abstract:
A short stroke flow control device or valve which is adapted to provide velocity control trim in a short stroke. The valve constructed in accordance with the present invention comprises multiple disk stacks or cages which are separated from each other by intervening spacers, and are placed axially in a valve gallery clamped between a seat ring and bonnet of the valve. The fluid passageways in the cages are throttled in a controlled manner by a plug which defines multiple throttling elements or plug lobes, the number of plug lobes defined by the plug preferably being equal to the number of cages included in the valve. The plug lobes of the plug control the flow of fluid through the disk stacks or cages in tandem. All of the throttling elements or plug lobes of the plug, with the possible exception of the plug lobe which contacts the seat ring for closure, is larger in diameter than the remainder of the plug and has at least one kidney bean shaped flow passage extending therethrough. The flow area of such flow passages in the plug lobes is designed to satisfy prescribed seat bore velocity criteria.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable 
       STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Technical Field of the Invention 
         [0004]    The present invention relates generally to flow control devices and, more particularly, to a uniquely configured control valve which is adapted to provide velocity control trim in a short stroke to accommodate space or design constraints. 
         [0005]    2. Description of the Related Art 
         [0006]    There is currently known in the prior art control valves which include stems and plugs that are linearly displaced during normal operation of the valve. Within these valves, which are often referred to as linear displacement valves, the plug is disposed and moveable within a disk stack or valve cage which defines a multiplicity of tortuous and/or non-tortuous fluid passageways. Certain linear displacement valves are configured for “over plug flow” wherein fluid flows radially inward into the interior of the valve cage from the exterior thereof, with the fluid undergoing a pressure drop as a result of the flow through the passageways of the valve cage. In this arrangement, the valve is opened by lifting the plug off a seat ring which thus allows the fluid to flow from the interior of the valve cage and out of the valve via the unblocked seat ring. Conversely, movement of the seating surface of the plug into sealed engagement with the complimentary seating surface of the seat ring facilitates a closed or shut-off condition for the valve. 
         [0007]    As an alternative to over plug flow, other linear displacement valves are configured for “under plug flow” wherein fluid flows axially upwardly into the interior of the valve cage from the exterior thereof, with the fluid undergoing a pressure drop as a result of the flow of the fluid radially outwardly through the fluid passageways of the valve cage. In this arrangement, the valve is opened by lifting the plug off of the aforementioned seat ring, which thus allows the fluid to flow into the interior of the valve cage and thereafter radially outwardly through the fluid passageways of the valve cage. Conversely, the movement of the seating surface of the plug into sealed engagement with the complimentary seating surface of the seat ring facilitates a closed or shut-off condition for the valve. 
         [0008]    Linear displacement control valves are often used to control flow and pressure in a process. However, in some applications and valve designs, there is a limitation in the maximum allowable stroke due to space or design constraints. Such design constraints may be attributable to, for example, the use of bellows seals to prevent leakage through the stem seal in valves used in conjunction with toxic or radioactive process fluid. Thus, there exists a need in the art for a linear displacement control valve which is capable of providing a velocity control trim in a short stroke. The present invention addresses this particular need by providing a short stroke control valve which provides the same velocity control capacity as a conventional normal stroke control valve. These, as well as other features and advantages of the present invention will be described in more detail below. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    In accordance with the present invention, there is provided a short stroke flow control device or valve which is adapted to provide velocity control trim in a short stroke. The valve constructed in accordance with the present invention comprises multiple disk stacks or cages which are separated from each other by intervening spacers, and are placed axially in a valve gallery clamped between a seat ring and bonnet of the valve. The fluid passageways in the cages are throttled in a controlled manner by a plug which defines multiple throttling elements or plug lobes, the number of plug lobes defined by the plug preferably being equal to the number of cages included in the valve. The plug lobes of the plug control the flow of fluid through the disk stacks or cages in tandem. All of the throttling elements or plug lobes of the plug, with the possible exception of the plug lobe which contacts the seat ring for closure, is larger in diameter than the remainder of the plug and has at least one kidney bean shaped flow passage extending therethrough. The flow area of such flow passages in the plug lobes is designed to satisfy prescribed seat bore velocity criteria. 
         [0010]    In the short stroke control valve of the present invention, the disk stacks or cages each feature labyrinth grooves and seals to reduce the leakage flow pass the plug and to reduce the effects of multiple clearance flows. Additionally, depending on the need for low end throttling, the number of labyrinth grooves within each of the cages may be different between stages. Further, the Cv in each of the disk stacks or cages may be varied to result in an overall custom characteristic curve for the valve. Further, any resistance in flow from upstream sections of the fluid system including the valve of the present invention may be mitigated by varying the number of stages (i.e., cages and plug lobes) at the same lift of the plug. In this regards, the number of cages or disk stacks and the number of plug lobes (which are preferably equal as indicated above) included in the valve may be varied based on the specific application. Still further, the plug may also be configured to be balance or unbalanced. 
         [0011]    The present invention is best understood by reference to the following detailed description when read in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    These, as well as other features of the present invention, will become more apparent upon reference to the drawings wherein: 
           [0013]      FIG. 1  is a cross-sectional view of a short stroke control valve constructed in accordance with the present invention, illustrating the plug thereof in a closed position; and 
           [0014]      FIG. 2  is a cross-sectional view of the short stroke valve constructed in accordance with the present invention, but illustrating the plug thereof in an open position. 
       
    
    
       [0015]    Common reference numerals are used throughout the drawings and detailed description to indicate like elements. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Referring now to the drawings wherein the showings are for purposes of illustrating a preferred embodiment of the present invention only, and not for purposes of limiting the same,  FIGS. 1 and 2  are cross-sectional views of a short stroke control valve  10  constructed in accordance with the present invention. As will be described in more detail below, the valve  10  is shown in  FIG. 1  in a closed or shut-off position, and is shown in  FIG. 2  in an open position which allows for the flow of a fluid therethrough. 
         [0017]    The valve  10  comprises a valve body  12  which defines an inflow passage  14  and an outflow passage  16 . The inflow and outflow passages  14 ,  16  each fluidly communicate with an interior chamber or valve gallery  18  defined by the body  12 . In addition to the body  12 , the valve  10  includes a bonnet  20  which is attached to the body  12  and partially encloses the gallery  18 . As seen in  FIGS. 1 and 2 , the attachment of the bonnet  20  to the body  12  is preferably facilitated through the use of mechanical fasteners  22  comprising a nut and bolt combination, though other attachment methods are contemplated to be within the spirit and scope of the present invention. The bonnet  20  defines a bore  24  which extends axially therethrough, the use of which will be described in more detail below. 
         [0018]    Disposed within the gallery  18  of the body  12  is an annular seat ring  26 . The seat ring  26  defines a circularly configured inflow opening  28 , one end of which is circumvented by a tapered seating surface  30 . The seat ring  26  is oriented within the body  12 , and in particular the gallery  18  thereof, such that the inflow opening  28  effectively defines a fluid path between the inflow passage  14  and the gallery  18 . In addition to the inflow opening  28 , the seat ring  26  defines annular top and bottom grooves  32 ,  34  which are disposed in respective ones of the top and bottom surfaces of a radially extending flange portion of the seat ring  26  in opposed relation to each other, as viewed from the perspective shown in  FIGS. 1 and 2 . Disposed within each of the top and bottom grooves  32 ,  34  is a sealing member such as an O-ring or gasket, the use of which will also be described in more detail below. 
         [0019]    In addition to the seat ring  26 , disposed within the gallery  18  are three (3) flow control elements, and more particularly a first (lower) disk stack or cage  36 , a second (middle) disk stack or cage  38 , and a third (upper) disk stack or cage  40 . The first, second and third cages  36 ,  38 ,  40  each preferably have an annular configuration, and define a multiplicity of tortuous and/or non-tortuous fluid energy dissipating flow passageways extending radially therethrough (i.e., between the inner and outer circumferential surfaces thereof). In the valve  10 , the first cage  36  is separated from the seat ring  26  by an intervening annular first spacer  42 . More particularly, the bottom surface of the first cage  36 , when viewed from the perspective shown in  FIGS. 1 and 2 , is abutted against the top surface of the first spacer  42 , with the opposed bottom surface of the first spacer  42  being abutted against the top surface of the radially extending flange portion of the seat ring  26 . 
         [0020]    Similar to first cage  36  being separated from the seat ring  26  by the first spacer  42 , the second cage  38  is separated from the first cage  36  by an intervening annular second spacer  44 . In this regard, when viewed from the perspective shown in  FIGS. 1 and 2 , the bottom surface of the second cage  38  is abutted against the top surface of the second spacer  44 , with the bottom surface of the second spacer  44  being abutted against the top surface of the first cage  36 . In a similar fashion, the third cage  40  is separated from the second cage  38  by an intervening annular third spacer  46 . More particularly, when viewed from the perspective shown in  FIGS. 1 and 2  the bottom surface of the third cage  40  is abutted against the top surface of the third spacer  46 , with the bottom surface of the third spacer  46  being abutted against the top surface of the second cage  38 . 
         [0021]    In addition to the first, second and third spacers  42 ,  44 ,  46  described above, the valve  10  includes an annular fourth spacer  48  which extends between the bonnet  20  and the first cage  36 . More particularly, when viewed from the perspective shown in  FIGS. 1 and 2 , the top surface of the fourth spacer  48  is abutted against the bonnet  20 , with the opposed bottom surface of the fourth spacer  48  being abutted against the top surface of the third cage  40 . Disposed within the top surface of the fourth spacer  48  which is opposite the bottom surface abutted against the third cage  40  is an annular groove  50  which accommodates a sealing member such as an O-ring or gasket. 
         [0022]    As further seen in  FIGS. 1 and 2 , partially captured between the second spacer  44  and the first cage  36  is an annular first seal  52 . Similarly, partially captured between the third spacer  46  and the second cage  38  is an annular second seal  54 , while partially captured between the fourth spacer  48  and the third cage  40  is an annular third seal  56 . In the valve  10 , the second and third spacers  44 ,  46  are preferably identically configured to each other, and thus are of equal size. However, the first spacer  42  is of substantially reduced height in comparison to the second and third spacers  44 ,  46 , with the fourth spacer  48  having an increased height in comparison to the second and third spacers  44 ,  46 . 
         [0023]    As is further seen in  FIGS. 1 and 2 , formed in the entirety of the inner circumferential surface of the first spacer  42  are a plurality of labyrinth grooves  58 . Thus, the labyrinth grooves  58  within the first spacer  42  extend from the top surface of the radially extending flange portion of the seat ring  26  to the first cage  36 . Labyrinth grooves  58  are also formed in portions of the inner circumferential surfaces of the second and third spacers  44 ,  46 . More particularly, labyrinth grooves  58  are formed in an upper portion of the inner circumferential surface of the second spacer  44 , the labyrinth grooves  58  of the second spacer  44  thus extending to the top surface thereof and hence to the second cage  38 . Similarly, labyrinth grooves  58  are formed in the upper portion of the inner circumferential surface of the third spacer  46 , the labyrinth grooves  58  of the third spacer  46  thus extending to the top surface thereof and hence to the third cage  40 . The labyrinth grooves  58  of the first, second and third spacers  42 ,  44 ,  46  are used to create labyrinth seals within the valve  10 , as will be discussed in more detail below. 
         [0024]    As is apparent from  FIGS. 1 and 2 , when the first, second and third cages  36 ,  38 ,  40  and the first, second, third and fourth spacers  42 ,  44 ,  46 ,  48  are stacked upon the seat ring  26  in the aforementioned manner, the outer circumferential surfaces of these particular components are substantially aligned with each other. Also in substantial alignment with each other are the inner circumferential surfaces of the stacked first, second and third cages  36 ,  38 ,  40  and first, second, third and fourth spacers  42 ,  44 ,  46 ,  28 . Importantly, the first, second and third seals  52 ,  54 ,  56  are oriented such that the inner circumferential surfaces thereof are also substantially aligned with the inner circumferential surfaces of the stacked, first, second and third cages  36 ,  38 ,  40 , and first, second, third and fourth spacers  42 ,  44 ,  46 ,  48 . However, the inner circumferential surface of the seat ring  26  which defines the inflow opening  28  thereof is oriented radially inward relative to the aligned inner circumferential surfaces of the first, second and third cages  36 ,  38 ,  40  and first, second, third and fourth spacers  42 ,  44 ,  46 ,  48 . 
         [0025]    In addition to the foregoing, in the valve  10 , the stack seat ring  26 , first, second and third cages  36 ,  38 ,  40 , the first, second, third and fourth spacers  42 ,  44 ,  46 ,  48 , and the first, second and third seals  52 ,  54 ,  56  are effectively compressed in an axial direction when viewed from the perspective shown in  FIGS. 1 and 2  between the bonnet  20  and the body  12 . As a result, the gasket disposed within the bottom groove  34  of the seat ring  26  is effectively compressed between the radially extending flange portion thereof and the body  12  thereby creating a fluid-tight seal therebetween. Additionally, the gasket disposed within the top grooves  32  of the seat ring  26  is effectively compressed between the radially extending flange portion thereof and the bottom surface of the first spacer  42  thereby creating a fluid-tight seal therebetween. Similarly, the gasket disposed within the groove  50  of the fourth spacer  48  is compressed between the bonnet  20  and the fourth spacer  48  thereby creating a fluid-tight seal therebetween. 
         [0026]    The valve  10  constructed in accordance with the present invention further comprises an elongate, generally cylindrical plug  60 . Integrally connected to and protruding axially from one end of the plug  60  is an elongate, generally cylindrical stem  62 . As seen in  FIGS. 1 and 2 , the plug  60  resides predominantly within the gallery  18  and, more particularly, within an elongate bore  64  collectively defined by the aligned inner circumferential surfaces of the first, second and third cages  36 ,  38 ,  40 , and the first, second, third and fourth spacers  42 ,  44 ,  46 ,  48 . The stem  62  protruding from the plug  60  is advanced through the bore  24  defined by the bonnet  20 . Though not shown in  FIGS. 1 and 2 , it is contemplated that the portion of the stem  62  protruding from the bonnet  20  may be mechanically coupled to an actuator which is operative to selectively move the stem in either an upward or downward direction relative to the body  12  and bonnet  21  when viewed from the perspective shown in  FIGS. 1 and 2 . In this respect, the bore  24  and stem  62  are sized relative to each other such that the stem  62  is slidably moveable within the bore  24  in a reciprocal fashion. As will be recognized by those of ordinary skill in the art, the selective movement of the stem  62  in an upward or downward direction in turn facilitates the concurrent movement of the plug  60  in an upward or downward direction relative to the body  12  and bonnet  20 , and hence the stacked seat ring  26 , first, second and third cages  36 ,  38 ,  40 , and first, second, third and fourth spacers  42 ,  44 ,  46 ,  48 . In this respect, as will be described in more detail below, the plug  60  is selectively moveable by the stem  62  between the above-described closed or shut-off position shown in  FIG. 1 , and the open position shown in  FIG. 2 . 
         [0027]    The plug  60  of the valve  10  comprises three identically configured, generally cylindrical plug lobes and, more particularly, a first (bottom) plug lobe  66 , a second (middle) plug lobe  68 , and a third (top) plug lobe  70 . The first and third plug lobes  66 ,  70  are separated from the second plug lobe  68  by a spaced pair of continuous channels  72 , each of the channels  72  having a generally U-shaped cross-sectional configuration. In the valve  10 , the outer diameters of the first, second and third plug lobes  66 ,  68 ,  70  are equal to each other, and slightly less than the diameter of the bore  64 , thus allowing the plug  60  to be reciprocally movable therein between the closed and open positions. 
         [0028]    Formed within each of the first, second and plug lobes  66 ,  68 ,  70  is at least one flow passage  74 . As is apparent from  FIGS. 1 and 2 , the flow passages  74  are generally linearly aligned with each other, and are radially offset from the aligned axes of the first, second and third plug lobes  66 ,  68 ,  70 , though extending in generally parallel relation thereto. More particularly, the flow passage  74  disposed in the first plug lobe  66  extends between the bottom surface of the first plug lobe  66  and that channel  72  separating the same from the second plug lobe  68 . The flow passage  74  disposed within the second plug lobe  68  extends between the channels  72 , with the flow passage  74  disposed within the first plug lobe  70  extending between the top surface of the third plug lobe  70  and the channel  72  separating the same from the second plug lobe  68 . Though not apparent from  FIGS. 1 and 2 , each of the channels  72  is preferably formed so as to have a kidney bean shaped cross-sectional configuration. 
         [0029]    In addition to the first, second and third plug lobes  66 ,  68 ,  70 , the plug  60  includes a cylindrically configured plug body  76  which protrudes axially from the top surface of the third plug lobe  70  when viewed from the perspective shown in  FIGS. 1 and 2 . In this regard, the stem  62  is connected to and extends axially from the plug body  76 . As also apparent from  FIGS. 1 and 2 , the outer diameter of the plug body  76  is less than the outer diameters of the first, second and third plug lobes  66 ,  68 ,  70 . The plug  60  also includes a sealing protrusion  78  which is formed on and extends axially from the bottom surface of the first plug lobe  66  when viewed from the perspective shown in  FIGS. 1 and 2 . The sealing protrusion  78  defines a tapered, peripheral sealing surface  80  which is sized and configured to be complimentary to and to engage the sealing surface  30  defined by the seat ring  26  when the plug  60  is moved to its closed position. 
         [0030]    As indicated above, the valve  10 , and in particular the plug  60  thereof, is shown in its closed or shut-off position in  FIG. 1 . When the plug  60  is in the closed position, the seating surface  80  defined by the seating protrusion  78  of the plug  60  is firmly seated and sealed against the complimentary seating surface  30  defined by the seat ring  26 . As a result, fluid flowing through the inflow passage  14  of the body  12  in the direction designated by the flow direction arrow in  FIG. 1 , though also flowing into the inflow opening  28  of the seat ring  26 , is effectively blocked from flowing into the bore  64  (and hence the gallery  18 ) by the plug  60 . When the plug  60  is in its closed position, a portion of the plug body  76  resides within a complimentary opening  82  defined by the bonnet  20 , such opening  82  being coaxially aligned with the bore  64  collectively defined by the aligned inner circumferential surfaces of the first, second and third cages  36 ,  38 ,  40 , and the first, second, third and fourth spacers  42 ,  44 ,  46 ,  48 . 
         [0031]    The movement of the plug  60  to its open position is facilitated by the upward movement of the stem  62  in any amount which is sufficient to cause the bottom surface of the first plug lobe  66  to be elevated above the bottom surface of the first cage  36  when viewed from the perspective shown in  FIGS. 1 and 2 . As will be recognized, such upward movement of the plug  60  facilitates the separation of the sealing surfaces  30 ,  80  from each other, thus allowing fluid to enter the bore  64 . In  FIG. 2 , the plug  60  of the valve  10  is shown in its fully open position, i.e., the maximum extent of its upward movement when viewed from the perspective shown in  FIGS. 1 and 2 . 
         [0032]    When the plug  60  is moved to its open position as shown, for example, in  FIG. 2 , fluid is able to flow from the inflow passage  14 , through the inflow opening  28 , through the interior of the first spacer  42 , and thereafter into the interior of the first cage  36 . Thus, fluid initially fills that portion of the bore  24  collectively defined by the inner circumferential surfaces of the first spacer  42  and first cage  36 . Fluid entering the interior of the first cage  36  is able to flow radially outwardly through the tortuous and/or non-tortuous flow passageways defined thereby in the manner shown by the flow directional arrows included in  FIG. 2 . After exiting the fluid flow passageways of the first cage  36  at the outer circumferential surface thereof, the fluid is able to flow into the outflow passage  16  defined by the body  12 . 
         [0033]    As is also shown in  FIG. 2 , in addition to the fluid flowing radially outwardly through the flow passageways of the first cage  36 , a portion of the fluid also flows upwardly through the flow passage  74  defined by the first plug lobe  66 . Upon exiting such flow passage  74 , the fluid enters the channel  72  separating the first plug lobe  66  from the second plug lobe  68 . When the plug  60  is in an open position, at least a portion of the channel  72  between the first and second plug lobes  66 ,  68  is radially aligned with the second cage  38 , and in particular the inner circumferential surface thereof. In this regard, fluid flowing into the channel  72  between the first and second plug lobes  66 ,  68  flows radially outwardly through the tortuous and/or non-tortuous flow passageways defined by the second cage  38  in the manner shown by the flow directional arrows included in  FIG. 2 , the fluid exiting such flow passageways at the outer circumferential surface of the second cage  38  also flowing into the outflow passage  16 . 
         [0034]    In addition to the fluid flowing radially outwardly through the flow passageways of the second cage  38 , a portion of the fluid also flows upwardly through the flow passage  74  defined by the second plug lobe  68 . Upon exiting such flow passage  74 , the fluid enters the channel  72  separating the second plug lobe  68  from the third plug lobe  70 . When the plug  60  is in an open position, at least a portion of the channel  72  between the second and third plug lobes  68 ,  70  is radially aligned with the third cage  40 , and in particular the inner circumferential surface thereof. In this regard, fluid flowing into the channel  72  between the second and third plug lobes  68 ,  70  flows radially outwardly through the tortuous and/or non-tortuous flow passageways defined by the third cage  40  in the manner shown by the flow directional arrows included in  FIG. 2 , the fluid exiting such flow passageways at the outer circumferential surface of the third cage  40  also flowing into the outflow passage  16 . 
         [0035]    As is further seen in  FIG. 2 , a portion of the fluid which flows into the channel  72  separating the second and third plug lobes  68 ,  70  from each other is also able to flow upwardly through the flow passage  74  of the third plug lobe  70 . As is apparent from  FIG. 2 , fluid exiting the flow passage  74  of the third plug lobe  70  enters a portion of the bore  64  defined by a portion of the inner circumferential surface of the fourth spacer  48 . Such flow through the flow passage  74  of the third plug lobe  70  makes the plug  60  “balanced” within the valve  10 . However, those of ordinary skill in the art will recognize that the plug  60  of the valve  10  may alternatively be “unbalanced” by not including the flow passage  74  within the third plug lobe  70 . 
         [0036]    As the plug  60  is moved from its closed position shown in  FIG. 1  to its fully open position shown in  FIG. 2 , the plug body  76  of the plug  60  is increasingly retracted into the opening  82  defined by the bonnet  20 . Conversely, when the plug  62  is moved from its fully open position back to its closed position, the plug body  76  is partially advanced out of the opening  82 . Despite the reciprocal movement of the plug body  76  into and out of the opening  82 , any fluid entering the bore  64  above the thirds plug lobe  70  when viewed from the perspective shown in  FIGS. 1 and 2  (irrespective of whether the plug  60  is balanced or unbalanced) is prevented from flowing between the plug body  76  and the bonnet  20  by an annular seal  84  which is captured therebetween. As will be recognized by those of ordinary skill in the art, as the plug  60  moves between its closed and open positions, the plug body  76  is slidably moveable along an inner circumferential surface of the seal  84  in a reciprocal fashion. To the extent that any fluid is able to migrate between the plug body  76  and the seal  84 , such fluid is prevented from escaping to the ambient environment by an annular packing  86  interposed between the outer surface of the stem  62  and that surface of the bonnet  20  defining the bore  24  extending therethrough. As will also be recognized by those of ordinary skill in the art, as the plug  60  moves between its closed and open positions, the stem  62  is also slidably moveable along the inner circumferential surface of the packing  86  in a reciprocal fashion. 
         [0037]    In the valve  10 , it is contemplated that the number of cages (e.g., the first, second and third cages  36 ,  38 ,  40 ) and the number of plug lobes (e.g., the first, second and third plug lobes  66 ,  68 ,  70 ) will always be equal, and define the number of “stages” included in the valve  10 . Thus, in the exemplary configuration shown in  FIGS. 1 and 2 , the valve  10  includes three (3) stages attributable to the inclusion of the first, second and third cages  36 ,  38 ,  40  and the first, second and third plug lobes  66 ,  68 ,  70  of the plug  60 . However, those of ordinary skill in the art will recognize that the valve  10  may be constructed so as to include greater or fewer than three stages without departing from the spirit and scope of the present invention, it being contemplated that the number of stages included in the valve  10  will be no less than two, but potentially three or more. Irrespective of the number of stages included in the valve  10 , the first, second and third seals  52 ,  54 ,  56  and the labyrinth grooves  58  described above work in concert with each other to effectively reduce leakage flow as the plug  60  moves between its closed and open positions. In this regard, the first, second and third seals  52 ,  54 ,  56  and labyrinth grooves  58  described above reduce leakage flow past the interfaces between the plug  60  and flow control assembly comprising the stacked seat ring  26 , first, second and third cages  36 ,  38 ,  40 , and first, second, third and fourth spacers  42 ,  44 ,  46 ,  48  as the plug  60  moves between its closed and open positions. 
         [0038]    In addition to the foregoing, based on the aforementioned description of fluid flow through the valve  10 , such valve  10  is configured for under plug flow. However, those of ordinary skill in the art will recognize that valve  10  may also be configured for over plug flow without departing from the spirit and scope of the present invention. In an over plug flow condition, the outflow passage  16  would become the inflow passage, with fluid flowing therethrough toward the flow control assembly comprising the stacked seat ring  26 , first, second and third cages  36 ,  38 ,  40 , and first, second, third and fourth spacers  42 ,  44 ,  46 ,  48 . Once reaching this stacked flow control assembly, the fluid would flow radially inwardly through the tortuous and/or non-tortuous flow passageways defined by the first, second and third cages  36 ,  38 ,  40 . If the plug  60  is in its closed position as shown in  FIG. 1 , the fluid would be prevented or blocked from entering the bore  64  by respective ones of the first, second and third plug lobes  66 ,  68 ,  70  of the plug  60 . 
         [0039]    However, when the plug  60  is moved to its open position as shown in  FIG. 2 , fluid would be able to flow from the flow passageways of the third cage  40  into the channel  72  between the third and second plug lobes  70 ,  68 , from the flow passageways of the second cage  38  into the channel  72  between the second and first plug lobes  68 ,  66 , and from the flow passageways of the first cage  36  into that portion of the bore  64  collectively defined by the first cage  36  and first spacer  42 . Fluid entering the channel  72  between the third and second plug lobe  70 ,  68  would also flow downwardly into that portion of the bore  64  collectively defined by the first cage  36  and first spacer  42  via the flow passages  74  disposed in the first and second plug lobe  66 ,  68  and the channel  72  therebetween. Similarly, fluid entering the channel  72  between the first and second plug lobes  66 ,  68  would also flow into that portion of the bore  64  collectively defined by the first cage  36  and first spacer  42  via the flow passage  74  disposed within the first plug lobe  66 . As will be recognized, fluid flowing into that portion of the bore  64  collectively defined by the first cage  36  and first spacer  42  would thereafter flow downwardly through the inflow opening  28  of the seat ring  26 , and thereafter through the outflow passage which would be defined by the inflow passage  14  if the valve  10  were used in an over plug flow configuration. 
         [0040]    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.