Abstract:
In accordance with the present invention, there is provided an axial drag control valve which includes an internal disk stack trim and an internal actuator. The fluid inlet and outlet of the valve are disclosed along a common axis, which is further shared with both the plug and the actuator. The plug and actuator move along this particular axis to control the fluid flow rate, pressure, or temperature of the system. The valve actuator may be powered by an operating fluid such as air supplied from an external source. A special, two-part packing with a lantern ring and leak-off port provides protection and safety for the actuator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable 
       STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates generally to control valves, and more particularly to an axial control valve product that provides high capacity and low noise performance characteristics. 
         [0005]    2. Description of the Related Art 
         [0006]    As is known in the control valve industry, three well known types of conventional fluid valves include rotary stem valves, sliding stem valves, and sleeve valves. Rotary stem valves generally comprise a rotary shaft or stem which is maintained within a valve body. The rotation of the shaft may be used to facilitate the alignment of a radial port of the shaft with a fluid port of the valve body to open a valve passage. Conversely, the rotation of the shaft may facilitate a misalignment of the ports to effectively close the valve passage. In operation, a typical rotary valve shaft or stem must rotate about 90° relative to the valve body between the fully open and closed positions. There exists in the prior art other types of rotary valve designs which utilize alternative geometries requiring a shaft rotation that is less than 90°, such as three way or angled ball valves. 
         [0007]    Rotary valves typically employ the use of seals, and often bearings, which are disposed between the rotary shaft and the valve body to prevent fluid from leaking from the valve body between the shaft and the valve body. In this regard, one of the primary drawbacks of rotary valves is that the significant movement of the shaft typically causes substantial wear to the seals and, if present, the bearings. Thus, the bearings and seals of a rotary valve must typically be replaced over time. Another drawback is that the seals, in order to function properly, also add friction between the valve body and the shaft. Substantial force is therefore typically necessary to overcome the seal friction and rotate the shaft. 
         [0008]    A sliding stem valve typically operates on a principle similar to a piston, and includes a valve plug on a stem that slides linearly within a valve body. The valve plug bears against a seat or closes a passage when moved to a closed position, and is spaced from the seat or clears the passage when moved to an open position. The valve stem and the valve plug must usually move relative to the valve body a significant distance between the fully open and closed positions. Like rotary stem valves, sliding stem valves typically employ seals, and often guides, between the stem and the valve body to prevent fluid from leaking from the valve body between the stem and the valve body. In this regard, one of the primary drawbacks of sliding stem valves is that the significant linear movement of the stem causes wear on the seals, thus often necessitating that the seals be replaced over time. Another drawback is that the seals also create friction that must be overcome in order to move the linear stem valve between its open and closed positions. 
         [0009]    Sleeve valves typically have a valve body defining an axial fluid flow passage. A stationary valve plug is usually fixed within the valve passage and carries or defines a valve seat positioned on an upstream end of the plug. A slideable valve sleeve is positioned in the valve passage and can be selectively moved between a fully closed position with a downstream end of the sleeve bearing against the valve seat, and a fully opened position with the downstream end of the sleeve being spaced a prescribed distance from the valve seat. Fluid can flow through the valve passage and the sleeve, around the valve plug, and an exit outlet of the valve. 
         [0010]    Sleeve valves as known in the prior art typically have a number of prescribed performance characteristics, such as fluid flow rate, fluid pressure, valve flow coefficient, as well as inherent, installed, and linear flow characteristics. Various flow characteristics of sleeve valves can typically be determined or controlled by a number of factors, including the size and shape or contour of the upstream end of the valve plug, the shape of the plug body beyond or downstream of the upstream end, and the passageway or orifice size and contour surrounding the valve plug. Other valve features can be designed and shaped to affect valve flow or performance characteristics as well, including contours of the valve sleeve outlet opening or the like. Along these lines, designing a particular valve plug shape is an often used means to achieve a desired valve performance or flow characteristic. However, as a result, a typical sleeve valve for a given system often has a unique, non-replaceable valve sleeve and plug. Thus, if a different valve flow characteristic is desired for a particular valve or system, or if a valve seat or plug is damaged within a valve or system, it is often necessary to remove and replace the entire valve assembly within the system. In this regard, to change the load characteristics or the valve plug, it has typically been necessary in the prior art to swap the entire sleeve valve with a newer replacement valve. 
         [0011]    The axial drag valve constructed in accordance with the present invention is adapted to overcome many of the deficiencies highlighted above in relation to known rotary, sliding stem, and sleeve valve designs. Various novel features of the present invention will be discussed in more detail below. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    In accordance with the present invention, there is provided multiple embodiments of an axial drag control valve which includes an internal disk stack trim and an internal actuator. The fluid inlet and outlet of the valve are disposed along a common axis, which is further shared with both the actuator and a plug of the valve. The plug and actuator move along this particular axis to control the fluid flow rate, pressure, or temperature of the system. In certain embodiments of the present invention, the valve actuator may be powered by an operating fluid from an external source, exemplary operating fluids including seven (7) bar air or eighty (80) bar air. A special, two-part packing with a lantern ring and leak-off port provides protection and safety for the actuator. 
         [0013]    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 
         [0014]    These, as well as other features of the present invention, will become more apparent upon reference to the drawings wherein: 
           [0015]      FIG. 1  is a cross-sectional view of an axial drag valve constructed in accordance with a first embodiment of the present invention as residing in its closed position; 
           [0016]      FIG. 2  is a cross-sectional view of the axial drag valve of the first embodiment as residing in its open position; 
           [0017]      FIG. 3  is a perspective view of the plug assembly of the axial drag valve of the first embodiment shown in  FIGS. 1 and 2 ; 
           [0018]      FIG. 3A  is a cross-sectional, perspective view of the plug assembly of the axial drag valve of the first embodiment shown in  FIGS. 1 and 2  taken along line  3 A- 3 A of  FIG. 3 ; 
           [0019]      FIG. 4  is a cross-sectional view of an axial drag valve constructed in accordance with a second embodiment of the present invention; 
           [0020]      FIG. 4A  is a cross-sectional view of a first potential variant of the axial drag valve of the second embodiment shown in  FIG. 4 ; 
           [0021]      FIG. 4B  is a cross-sectional view of a second potential variant of the axial drag valve of the second embodiment shown in  FIG. 4 ; 
           [0022]      FIG. 5  is a cross-sectional view of an axial drag valve constructed in accordance with a third embodiment of the present invention; and 
           [0023]      FIG. 6  is a cross-sectional view of an axial drag valve constructed in accordance with a fourth embodiment of the present invention. 
       
    
    
       [0024]    Common reference numerals are used throughout the drawings and detailed description to indicate like elements. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    Referring now to the drawings wherein the showings are for purposes of illustrating preferred embodiments of the present invention only, and not for purposes of limiting the same,  FIGS. 1 and 2  depict an axial drag valve  10  constructed in accordance with a first embodiment of the present invention. In  FIG. 1 , the valve  10  is depicted in a closed position, while in  FIG. 2 , the valve  10  is depicted in a fully open position. 
         [0026]    The valve  10  comprises a housing  12 . The housing  12  itself comprises an inlet section  14  which defines an inlet passage  16 . In addition to the inlet section  14 , the housing  12  includes an outlet section  18  which defines an outlet passage  20 . The inlet and outlet sections  14 ,  18  of the housing  12  are rigidly attached to each other. As seen in  FIGS. 1 and 2 , the attachment of the inlet and outlet sections  14 ,  18  to each other is facilitated by the use of fasteners  22 , such as bolts. However, those of ordinary skill in the art will recognize that a wide variety of different attachment methods may be used to effectuate the rigid attachment of the inlet and outlet sections  14 ,  18  to each other. However, in the valve  10 , it is contemplated that any attachment method used to facilitate the attachment of the inlet and outlet sections  14 ,  18  to each other will be adapted to allow for the periodic separation of the inlet section  14  from the outlet section  18  as may be needed to access the interior of the housing  12  to allow for maintenance on other parts and components of the valve  10  which will be described in more detail below. 
         [0027]    In the outlet section  18  of the housing  12 , the outlet passage  20  defines three separate regions. More particularly, the outlet passage  20  defines an enlarged inlet region  20   a  which is in direct fluid communication with the inlet passage  16 . The inlet region  20   a  transitions into an arcuate central region  20   b , which itself transitions into an enlarged, generally cylindrical outlet region  20   c . Those of ordinary skill in the art will recognize that the configuration of the outlet passage  20  as shown in  FIGS. 1 and 2  is exemplary only, and that alternative configurations for the outlet passage  20  are contemplated to be within the spirit and scope of the present invention. Indeed, certain exemplary alternative embodiments of the outlet passage  20  will be described below in relation to other embodiments of the valve  10 . 
         [0028]    Disposed within the interior of the housing  12  and rigidly attached thereto is a hub cap  24 . The hub cap  24  defines an annular shoulder  26  which is abutted against an interior portion of the outlet section  18  of the housing  12 . That portion of the hub cap  24  extending between the shoulder  26  and the inlet passage  16  resides within the inlet region  20   a  of the outlet passage  20 . In addition to defining the shoulder  26 , the hub cap  24  also defines a central bore  28  which extends axially therethrough. Additionally, formed in that end of the hub cap  24  facing the inlet passage  16  is an annular channel  30  which extends to a prescribed depth within the hub cap  24 . The bore  28  and channel  30  are sized and configured to accommodate respective portions of an internal actuator of the valve  10 , such as a plug assembly  32  (shown in  FIGS. 3 and 3A ) which will be described in more detail below. 
         [0029]    In the valve  10 , the end or face of the hub cap  24  facing the outlet region  20   c  of the outlet passage  20  is abutted against one end or rim of a cylindrical, tubular piston sleeve  33 . The opposite end and the outer surface of the piston sleeve  33  are abutted against an interior portion of the outlet section  18  of the housing  12 . The end of the hub cap  24  facing the outlet region  20   c , the inner surface of the piston sleeve  33 , and a portion of the interior of the outlet section  18  collectively define a generally cylindrical, internal piston chamber  34  of the valve  10 . The piston chamber  34  is placeable into fluid communication with an external regulating device such as a spool valve via first and second air passages  36 ,  38  which each fluidly communicate with the piston chamber  34 . The first air passage  36  includes a first segment  36   a  which extends through the outlet section  18 , and a second segment  36   b  which extends through the hub cap  24  in a generally L-shaped configuration. In this regard, one end of the second segment  36   b  fluidly communicates with the piston chamber  34 , with the opposite end thereof fluidly communicating with the first segment  36   a . The second air passage  38  extends exclusively through the outlet section  18  of the housing  12 . The first and second air passages  36 ,  38  are adapted to selectively supply air to, or exhaust air from, the piston chamber  34  in a manner which will be described in more detail below. 
         [0030]    As is also seen in  FIGS. 1 and 2 , the hub cap  24  may be provided with one or more annular grooves  40  within the exterior surface thereof. The groove(s)  40  may include a sealing element such as an O-ring disposed therein for purposes of defining a sealed engagement between the hub cap  24  and other parts of the valve  10 . For example, as seen in  FIGS. 1 and 2 , the O-rings within two of the grooves  40  are used to create seals between the outer surface of the hub cap  24  and the interior of the outlet section  18  of the housing  12 , with the O-ring within the remaining one of the grooves  40  being used to create a seal between the hub cap  24  and one end of the piston sleeve  33 . 
         [0031]    As indicated above, the bore  28  and channel  30  of the hub cap  24  are sized and configured to accommodate respective portions of a plug assembly  32  of the valve  10 . As seen in  FIGS. 3 and 3A , the plug assembly  32  comprises an elongate piston rod  42  defining opposed ends. Attached to the piston rod  42  in relative close proximity to one of the opposed ends thereof is a circularly configured piston head  44 . The piston head  44  defines a peripheral side surface  46  having a continuous groove  48  disposed therein. Disposed within the groove  48  is a sealing member such as an O-ring  50 . Also attached to the piston rod  42  in relative close proximity to the remaining end thereof is a hollow balanced plug  52 . The plug  52  defines an end portion  52   a  which transitions into an annular, generally cylindrical sidewall portion  52   b . Disposed in and extending through the end portion  52   a  between the inner and outer surfaces thereof is at least one, and preferably a plurality of balance holes  54 , the use of which will be described in more detail below. Additionally, formed in the inner surface of the sidewall portion  52   b  is an anti-rotation groove  56 , the use of which will also be described in more detail below. As best seen in  FIG. 3A , the anti-rotation groove  56  extends to the distal rim defined by the sidewall portion  52   b , and terminates a prescribed distance inwardly from the inner surface of the end portion  52   a . The groove  56  also extends in generally parallel relation to the axis of the piston rod  42 . As also seen in  FIG. 3A , extending axially through a portion of the length of the piston rod  42  is an elongate probe bore  58 . The probe bore  58  has a generally circular cross-sectional configuration, and extends from that end of the piston rod  42  disposed closest to the piston head  44  to a prescribed depth within the piston rod  42 . The use of the probe bore  58  will also be described in more detail below. 
         [0032]    In the valve  10 , the piston rod  42  of the plug assembly  32  is advanced through and reciprocally moveable axially within the central bore  28  defined by the hub cap  24 . Additionally, the interface of the plug assembly  32  to the hub cap  24  is such that the piston head  44  resides and is reciprocally moveable within the piston chamber  34  collectively defined by the outlet section  18 , hub cap  24  and the piston sleeve  33 . More particularly, the piston head  44  is moveable along the axis defined by the piston sleeve  33  (which is coaxially aligned with the axis of the piston rod  42 ), with the O-ring  50  being slidably moveable along the inner surface of the piston sleeve  33 . 
         [0033]    The valve  10  further comprises a generally cylindrical, tubular flow control element  60  which is disposed within the inlet region  20   a  of the outlet passage  20 . As seen in  FIGS. 1  and  2 , one end or annular rim defined by flow control element  60  is abutted against that end or annular rim of the hub cap  24  which faces the inlet passage  16 . The opposite, remaining end or annular rim of the flow control element  60  is abutted against an annular sealing member  62  which is itself abutted against an interior surface portion defined by the inlet section  14  of the housing  12 . Thus, the sealing member  62  is effectively captured and compressed between the flow control element  60  and the inlet section  14  of the housing  12 , with the flow control element  60  itself being captured and compressed between the hub cap  24  and the sealing member  62 . The positioning of the hub cap  24 , flow control element  60  and sealing member  62  relative to each other is such that the axis of the bore  28 , the axis of the flow control element  60 , and the axis of the sealing member  62  are all coaxially aligned with each other, and hence the axis of the piston rod  42  which is advanced through and reciprocally moveable within the bore  28  as indicated above. The sealing member  62  defines an annular sealing surface  64  which is disposed slightly radially inward of the inner surface of the flow control element  60 . In the valve  10 , it is contemplated that the flow control element  60  may comprise a stack of annular discs that collectively define a series of substantially radially directed passageways extending between the inner and outer radial surfaces or edges of the discs. Each of the radially directed passageways has a plurality of turns formed therewithin in order to reduce the velocity of fluid that is flowing through the flow control element  60 . An exemplary flow control element  60  is disclosed in commonly owned U.S. Pat. No. 5,687,763, the disclosure of which is incorporated herein by reference. 
         [0034]    As previously explained,  FIG. 1  depicts the valve  10  in its closed position, with  FIG. 2  depicting the valve  10  in its fully open position. As also indicated above, the interface of the plug assembly  32  to the hub cap  34  is such that the piston head  44  resides and is reciprocally moveable within the piston chamber  34 . In the valve  10 , the plug  52  is likewise reciprocally moveable axially within the interior of the flow control element  60  in a manner effectively facilitating the opening or closure of the valve  10 . More particularly, when the valve  10  is in its closed position as shown in  FIG. 1 , a peripheral portion of the outer surface of the end portion  52   a  of the plug  52  is abutted and effectively sealed against the sealing surface  64  defined by the sealing member  62 . When the plug  52  is in this particular orientation, the sidewall portion  52   b  thereof is aligned with but substantially removed from within the complimentary shaped channel  30  within the hub cap  24 . At the same time, the piston head  44  is oriented within the piston chamber  34  so as to be disposed proximate the hub cap  24 , with only a small gap being defined between the piston head  44  and the end of the hub cap  24  facing the outlet region  20   c  of the outlet passage  20 , as shown in  FIG. 1 . Conversely, when the valve  10  is moved to the fully open position as shown in  FIG. 2 , the plug  52  is moved axially away from the sealing member  62 , with the sidewall portion  52   b  of the plug  52  being drawn into the complimentary channel  30  and the end portion  52   a  of the plug  52  being effectively separated from the sealing surface  64  defined by the sealing member  62 . At the same time, the piston head  44  is oriented within the piston chamber  34  so as to reside in close proximity to that end of the piston sleeve  33  opposite that abutted against the hub cap  24 . 
         [0035]    As will be recognized by those of ordinary skill in the art, the plug assembly  32 , and in particular the plug  52  thereof, is effectively moved between closed and fully open positions relative to the sealing member  62  as a result of the reciprocal axial movement of the piston rod  42  of the plug assembly  32  relative to the hub cap  24 . Such reciprocal axial movement of the piston rod  42 , and hence the plug  52 , is facilitated by the selective application of air pressure to either side of the piston head  44  within the piston chamber  34 . More particularly, to facilitate the movement of the plug  52  to the closed position shown in  FIG. 1 , pressurized air is input into the piston chamber  34  via the second air passage  38 , such pressurized air acting against the piston head  44  in a manner effectively forcing it toward the hub cap  24 , the movement of the piston head  44  toward the hub cap  24  being discontinued as a result of the abutment of the plug  52  against the sealing surface  64  of the sealing member  62 . As will be recognized, when the second air passage  38  is pressurized as occurs to facilitate the actuation of the plug  52  to the closed position, the first air passage  36  acts as an exhaust port so that air captured in the piston chamber  34  between the piston head  44  and the hub cap  24  does not impede the movement of the piston head  44  toward the hub cap  24 . 
         [0036]    Conversely, to facilitate the movement of the plug  52  to the fully open position shown in  FIG. 2 , the first air passage  36  is pressurized so as to facilitate the input of air into the piston chamber  34  in a manner acting against the piston head  44  as results in its movement away from the hub cap  24  toward the outlet region  20   c  of the outlet passage  20 . Such movement of the piston head  44  effectively draws the plug  52  away from the sealing member  62  and into its nested orientation within the hub cap  24  as shown in  FIG. 2 . As will be recognized, when the first air passage  36  is pressurized to facilitate the movement of the plug  52  toward the fully open position, the second air passage  38  effectively functions as an exhaust port so that any air trapped between the piston head  44  and the outlet section  18  of the housing  12  does not impede the movement of the piston head  44  away from the hub cap  24 . Within the piston chamber  34 , pressurized air is prevented from migrating between the peripheral edge of the piston head  44  and the inner surface of the piston sleeve  33  by the sliding, sealed engagement effectuated by the above-described O-ring  50 . 
         [0037]    In the valve configuration shown in  FIGS. 1 and 2 , fluid normally enters the valve  10  via the inlet passage  16  in the direction designated by the arrow A in  FIG. 1 . When the plug  52  is in the closed position, the fluid within the inlet passage  16  is effectively prevented from entering the outlet passage  20 . When the plug  52  is moved from the closed position shown in  FIG. 1  toward the fully open position shown in  FIG. 2 , the fluid is able to flow through the sealing member  62  and thereafter radially outwardly through the flow control element  60  and into the outlet passage  20 . Since the fluid must flow through the flow control element  60  to reach the outlet passage  20 , the energy of the fluid is effectively reduced due to the above-described functional attributes of the flow control element  60 . 
         [0038]    The opening of the valve  10  may be effectuated without necessarily actuating the plug  52  to the fully open position shown in  FIG. 2 . In this regard, in the valve  10 , the axial movement of the plug  52  away from the sealing member  62  may be regulated or controlled depending on the desired level of fluid energy dissipation. Along these lines, as will be recognized, the greater the amount of axial movement of the plug  52  away from the sealing member  62 , the greater the number of energy dissipating flow passageways of the flow control element  60  that will be exposed to the incoming fluid flow via the inlet passage  16 . In this regard, maximum energy dissipation of the inlet fluid is achieved when the plug  52  is moved to the fully open position shown in  FIG. 2 . 
         [0039]    In order to monitor and thus tightly regulate or control the position of the plug  52  relative to the sealing member  62 , the valve  10  is provided with a position feedback device  66  which is oriented between the piston chamber  34  and the outlet region  20   c  of the outlet passage  20 , and is accommodated within a complimentary internal recess defined by the outlet section  18  of the housing  12 . The feedback device  66  includes an elongate, generally cylindrical probe portion  68  which is coaxially aligned with and slideably advanced into the probe bore  58  of the piston rod  42 . The probe bore  58  and probe portion  68  of the feedback device  66  have complimentary configurations, with the advancement of the probe portion  68  into the probe bore  58  being operative to allow the feedback device  66  to effectively monitor the relative position of the piston rod  42 , and hence the plug  52 . As is apparent from  FIGS. 1 and 2 , the piston rod  42  is moveable relative to the probe portion  68  which remains stationary, with at least some segment of the probe portion  68  always remaining within the interior of the probe bore  58  throughout the movement of the plug  52  between the closed and fully open extremes. 
         [0040]    In the valve  10 , the feedback device  66  is effectively sealed within its complimentary recess defined by the outlet section  18  by a sealing cap  70  which is rigidly attached to the outlet section  18 . The sealing cap  70  defines a continuous groove which accommodates a sealing member such as an O-ring  72 . The abutment of the O-ring  72  against the outlet section  18  as occurs when the sealing cap  70  is rigidly attached to the outlet section  18  effectively prevents fluid flowing through the outlet passage  20  from reaching and possibly affecting the performance of the feedback device  66 . A hard wired connection to the feedback device  66  to facilitate the electrical connection thereof to an external control device may be obtained via a probe outlet passage  74  which extends through the outlet section  18  of the housing  12  and into communication with the internal recess accommodating the feedback device  66 . The detachment of the sealing cap  70  from the outlet section  20  provides access to the feedback device  66  as may be needed for the periodic maintenance thereof. 
         [0041]    As the plug  52  moves between the fully open and closed positions during operation of the valve  10 , it is desirable to effectively prevent any rotation of the plug  52  relative to the hub cap  24 . Such anti-rotation is accomplished in the valve  10  by the inclusion of an anti-rotation member  76  which is partially embedded within the hub cap  24 , and protrudes into the channel  30  defined thereby. As is most apparent from  FIG. 2 , the exposed portion of the anti-rotation member  76  has a configuration which is complimentary to the anti-rotation groove  56  included in the inner surface of the sidewall portion  52   b  of the plug  52 . When the plug  52  is in any position other than its closed position, at least a portion of the anti-rotation member  76  is slidably received into the complimentary anti-rotation groove  56 , thus effectively preventing any rotation of the plug  52  relative to the hub cap  24 . 
         [0042]    As indicated above, the plug  52  integrated into the valve  10  is “balanced” as a result of the inclusion of the balance holes  54  within the end portion  52   a  thereof. As a result of the inclusion of the balance holes  54  therein, when the plug  52  is in its closed position, high pressure fluid flowing through the inlet passage  16  in the direction of the arrow A is able to pass through the balance holes  54  and into the interior chamber  78  collectively defined by the inner surfaces of the end and sidewall portions  52   a ,  52   b  of the plug  52 , the outer surface of the piston rod  42 , and a portion of the hub cap  24 . The placement of the plug  52  into a balanced condition as a result of the inclusion of the balance holes  54  therein gives rise to greater ease in the movement of the plug  52  between the fully open and closed positions. Despite fluid flowing into the interior chamber  78  when the plug  52  is in the closed position, such fluid is still effectively prevented from flowing through the flow control element  60  and hence into the outlet passage  20 . 
         [0043]    As will be recognized by those of ordinary skill in the art, the proper operation of the valve  10  could be compromised if fluid flowing into the interior chamber  78  when the plug  52  is in the closed position is able to migrate between the outer surface of the piston rod  42  and that surface of the hub cap  24  defining the bore  28  into the piston chamber  34 . To prevent the flow of fluid from the interior chamber  78  into the piston chamber  34 , a live load packing is preferably interposed between the piston rod  42  and the hub cap  24 . As seen in  FIGS. 1 and 2 , the live load packing comprises annular first and second packing elements  80 ,  82  which reside within the central bore  28  in spaced relation to each other. Captured between the first and second packing elements  80 ,  82  is an annular lantern ring  84 . The piston rod  42  is slidably advanced through the first and second packing elements  80 ,  82  and the lantern ring  84 . The first and second packing elements  80 ,  82  and the lantern ring  84 , as well as ancillary packing elements disposed adjacent respective ones of the first and second packing elements  80 ,  82 , are all maintained in a compressive state by an annular packing bushing  86  which is rigidly attached to the hub cap  24  and partially resides within the interior chamber  78 . The piston rod  42  is also slidably advanced axially through the packing bushing  86 . 
         [0044]    The sealing arrangement provided by the first and second packing elements  80 ,  82  and intermediate lantern ring  84  is effective in preventing any fluid migration from the interior chamber  78  to the piston chamber  34 . However, in the event that such seal degrades over time as a result of the axial movement of the piston rod  42 , any fluid reaching the lantern ring  84  from the interior chamber  78  may be effectively bled off by a leak off passage  88  of the valve  10 . As seen in  FIGS. 1 and 2 , the leak off passage  88  includes a first segment  88   a  which extends through the outlet section  18 , and a second segment  88   b  which extends through the hub cap  24 . In this regard, one end of the second segment  88   b  fluidly communicates with that portion of the bore  28  adjacent the lantern ring  84 , with the opposite end thereof fluidly communicating with the first segment  88   a.    
         [0045]    Referring now to  FIG. 4 , there is shown an axial drag valve  100  constructed in accordance with a second embodiment of the present invention. The axial drag valve  100  is substantially similar in structure and function to the axial drag valve  10  described above. Accordingly, only the distinctions between the valves  10 ,  100  will be highlighted below. 
         [0046]    The primary distinction between the valve  100  and the above-described valve  10  lies in the configuration of the housing  112  of the valve  100  in comparison to the housing  12  of the valve  10 . More particularly, the housing  112  of the valve  100  comprises an inlet section  114  and an outlet section  118  which are rigidly attached to each other. As seen in  FIG. 4 , the attachment of the inlet and outlet sections  114 ,  118  to each other is facilitated by the use of fasteners  122 , such as bolts. In the valve  100 , it is contemplated that any attachment method used to facilitate the attachment of the inlet and outlet sections  114 ,  118  to each other will be adapted to allow for the periodic separation of the inlet section  114  from the outlet section  118  as may be needed to access the interior of the housing  112  to allow for maintenance on other parts and components of the valve  100 . 
         [0047]    In the valve  100 , the inlet section  114  defines an inlet passage  116 . Additionally, the inlet and outlet sections  114 ,  118  collectively define an outlet passage  120 . In this regard, an inlet region  120   a  of the outlet passage  120  is defined by the inlet section  114 . The inlet region  120   a  transitions into a central region  120   b , which itself transitions into an enlarged outlet region  120   c . The central and outlet regions  120   b ,  120   c  are each defined by the outlet section  118  of the housing  112 . As further seen in  FIG. 4 , the outlet region  120   c  is formed to have a prescribed diameter D, which in many applications may be approximately twelve (12) inches. 
         [0048]    A further distinction between the valves  10 ,  100  lies in the configuration of the sealing cap  170  of the valve  100  in comparison to the sealing cap  70  of the valve  10 . In this regard, due to the alternative configuration of the outlet passage  120  in comparison to the outlet passage  20 , the sealing cap  170  is formed to have a more cone-like configuration in comparison to the sealing cap  70  of the valve  10 . The cone-like configuration of the sealing cap  170  in the valve  100  promotes a smoother transition for fluid flowing from the central region  120   b  of the outlet passage  120  into the outlet region  120   c  thereof. 
         [0049]    Referring now to  FIG. 4A , there is shown an axial drag valve  100   a  which comprises a first potential variant of the valve  100  described above in relation to  FIG. 4 . More particularly, the sole distinction between the valves  100 ,  100   a  lies in the outlet region  120   c  of the outlet passage  120  in the valve  100   a  being defined by an outlet flange  190   a  which is rigidly attached to that end of the outlet section  118  opposite the end which is rigidly attached to the inlet section  114 . The attachment of the outlet flange  190   a  to the outlet section  118  in the valve  100   a  is preferably facilitated by the use of fasteners  192   a  such as bolts. However, those of ordinary skill in the art will recognize that a wide variety of different attachment methods may be used to effectuate the rigid attachment of the outlet flange  190   a  to the outlet section  118 . However, in the valve  100   a , it is contemplated that any attachment method used to facilitate the attachment of the outlet flange  190   a  to the outlet section  118  will be adapted to allow for the optional detachment of the outlet flange  190   a  from the outlet section  118  for potential replacement with an alternatively configured outlet flange. In the outlet flange  190   a  shown in  FIG. 4A , the outlet region  120   c  of the outlet passage  120  defined thereby is of a diameter D which in certain applications may be approximately twelve (12) inches. 
         [0050]    Referring now to  FIG. 4B , there is shown an axial drag valve  100   b  which comprises a second potential variant of the valve  100  described above in relation to  FIG. 4 . More particularly, the sole distinction between the valves  100 ,  100   b  lies in the outlet region  120   c  of the outlet passage  120  in the valve  100   a  being defined by an outlet flange  190   b  which is rigidly attached to that end of the outlet section  118  opposite the end which is rigidly attached to the inlet section  114 . The attachment of the outlet flange  190   b  to the outlet section  118  in the valve  100   a  is preferably facilitated by the use of fasteners  192   b  such as bolts. However, those of ordinary skill in the art will recognize that a wide variety of different attachment methods may be used to effectuate the rigid attachment of the outlet flange  190   b  to the outlet section  118 . However, in the valve  100   a , it is contemplated that any attachment method used to facilitate the attachment of the outlet flange  190   b  to the outlet section  118  will be adapted to allow for the optional detachment of the outlet flange  190   b  from the outlet section  118  for potential replacement with an alternatively configured outlet flange. In the outlet flange  190   b  shown in  FIG. 4A , the outlet region  120   c  of the outlet passage  120  defined thereby is effectively reduced to a diameter D which in certain applications may be approximately six (6) inches. Those of ordinary skill in the art will recognize that the outlet flange  190   b  may be optionally replaced with the outlet flange  190   a  described above in relation to  FIG. 4A . 
         [0051]    Referring now to  FIG. 5 , there is shown an axial drag valve  200  constructed in accordance with a third embodiment of the present invention. The axial drag valve  200  is substantially similar in structure and function to the axial drag valve  100  described above. Accordingly, only the distinctions between the valves  100 ,  200  will be highlighted below. 
         [0052]    The primary distinction between the valve  200  and the above-described valve  100  lies in the configuration of the housing  212  of the valve  200  in comparison to the housing  112  of the valve  100 . More particularly, the housing  212  of the valve  200  comprises an inlet section  214 , and intermediate section  215 , and an outlet section  218  which are rigidly attached to each other. As seen in  FIG. 5 , the attachment of the inlet and intermediate sections  214 ,  215  to each other is facilitated by the use of fasteners  222 , such as bolts. In the valve  200 , it is contemplated that any attachment method used to facilitate the attachment of the inlet and intermediate sections  214 ,  215  to each other will be adapted to allow for the periodic separation of the inlet section  214  from the intermediate section  215  as may be needed to access the interior of the housing  212  to allow for maintenance on other parts and components of the valve  200 . As is apparent from  FIG. 5 , it is contemplated that the outlet section  218  will be rigidly attached to the intermediate section  215  through the use of an attachment means other than the above-described fasteners  222 . 
         [0053]    In the valve  200 , the inlet section  214  defines an inlet passage  216 . Additionally, the inlet, intermediate and outlet sections  214 ,  215 ,  218  collectively define an outlet passage  220 . In this regard, an inlet region  220   a  of the outlet passage  220  is defined by the inlet section  214 . The inlet region  220   a  transitions into a central region  220   b  of the outlet passage  220  which is defined by the intermediate section  215 . The central region  220   b  itself transitions into an outlet region  220   c  of the outlet passage  220  which is defined by the outlet section  218  of the housing  212 . As further seen in  FIG. 5 , the outlet region  220   c  of the outlet passage  220  is effectively reduced to a diameter D which in many applications may be approximately six (6) inches. 
         [0054]    Referring now to  FIG. 6 , there is shown an axial drag valve  300  constructed in accordance with a fourth embodiment of the present invention. The valve  300  comprises a housing  312 . The housing  312  itself comprises an inlet section  314  and an outlet section  318  which are rigidly attached to each other. The attachment of the inlet and outlet sections  314 ,  318  to each other is facilitated through the use of fasteners  322 , such as bolts. However, those of ordinary skill in the art will recognize that a wide variety of different attachment methods may be used to effectuate the rigid attachment of the inlet and outlet sections  314 ,  318  to each other. However, in the valve  300 , it is contemplated that any attachment method used to facilitate the attachment of the inlet and outlet sections  314 ,  318  to each other will be adapted to allow for the periodic separation of the inlet section  314  from the outlet section  318  as may be needed to access the interior of the housing  312  to allow for maintenance on other parts and components of the valve  300  which will be described in more detail below. 
         [0055]    The inlet section  314  of the housing  312  defines an inlet passage  316 . Additionally, the inlet and outlet sections  314 ,  318 , when rigidly attached to each other, collectively define an outlet passage  320 . The outlet passage  320  includes a first region  320   a  which is defined by the inlet section  314 , and a second region  320   b  which is defined by the outlet section  318 . As seen in  FIG. 6 , the second region  320   b  of the outlet passage  320  is configured to be effectively reduced to a diameter D which in many applications may be approximately six (6) inches. Those of ordinary skill in the art will recognize that the configuration of the outlet passage  320  as shown in  FIG. 6  is exemplary only, and that alternative configurations for the outlet passage  320  are contemplated to be with the spirit and scope of the present invention. 
         [0056]    Disposed within the interior of the housing  312  and rigidly attached thereto is a plug sleeve  333 . The plug sleeve  333  defines an end portion  333   a  which transitions into an annular, generally cylindrical side wall portion  333   b . Abutted against the distal end or rim defined by the sidewall portion  333   b  is an annular guide bushing  324 . Whereas the plug sleeve  333  resides within both the first and second regions  320   a ,  320   b  of the outlet passage  320  (though extending predominantly within the second region  320   b ), the guide bushing  324  resides exclusively in the first region  320   a  of the outlet passage  320 . 
         [0057]    The valve  300  further comprises a generally cylindrical, tubular flow control element  360  which also resides within the first region  320   a  of the outlet passage  320 . As seen in  FIG. 6 , one end or annular rim defined by the flow control element  360  is abutted against the annular guide bushing  324 . The opposite, remaining end or annular rim of the flow control element  360  is abutted against an annular sealing member  362  which is itself abutted against an interior surface portion defined by the inlet section  314  of the housing  312 . Thus, the sealing member  362  is effectively captured and compressed between the flow control element  360  and the inlet section  314  of the housing  312 , with the flow control element  360  itself being captured and compressed between the guide bushing  324  and the sealing member  362 . The positioning of the plug sleeve  333 , guide bushing  324 , flow control element  360  and sealing member  362  relative to each other is such that the axes thereof are coaxially aligned with each other. The sealing member  362  defines an annular sealing surface  364  which is disposed slightly radially inward of the inner surface of the flow control element  360 . In the valve  300 , it is contemplated that the flow control element  360  may comprise a stack of annular discs having the structural and functional attributes described above in relation to the flow control element  60  of the valve  10 . As further seen in  FIG. 6 , captured between a portion of the guide bushing  324  and a portion of the rim of the flow control element  360  abutted against the guide bushing  324  is an annular seal  325 , the use of which will be discussed in more detail below. 
         [0058]    The valve  300  further comprises a plug  352  which is reciprocally moveable axially relative the plug sleeve  333  between a closed position as shown in  FIG. 6  and a fully open position. The plug  352  has a generally cylindrical configuration, and defines a first portion  352   a  which is of a first diameter, and a second portion  352   b  which is of a second diameter exceeding the first diameter of the first portion  352   a . As a result, a continuous, annular shoulder  354  is defined between the outer surfaces of the first and second portions  352   a ,  352   b . Disposed within the peripheral side surface defined by the second portion  352   b  is a spaced pair of continuous grooves  356 . Each of the grooves  356  is adapted to accommodate a sealing element (not shown) such as an O-ring. Extending axially through a portion of the plug  352  is an elongate probe bore  358  which has a generally circular cross-sectional configuration. The probe bore  358  extends from the end or face of the plug  352  defined by the second portion  352   b  thereof and terminates approximately midway within the first portion  352   a , as shown in  FIG. 6 . The use of the probe bore  358  will be described in more detail below. 
         [0059]    As previously explained,  FIG. 6  depicts the valve  300  in its closed position. The interface of the plug  352  to the plug sleeve  333  is such that the plug  352  is reciprocally moveable within the interior of the piston sleeve  333 , as well as the interior of the flow control element  360 , in a manner effectively facilitating the opening or closure of the valve  300 . More particularly, when the valve  300  is in its closed position as shown in  FIG. 6 , a peripheral portion of the outer surface of the first portion  352   a  of the plug  352  is abutted and effectively sealed against the sealing surface  364  defined by the sealing member  362 . At the same time, the second portion  352   b  is oriented within the plug sleeve  333  such that the shoulder  354  is substantially aligned with the distal end or annular rim defined by the sidewall portion  333   b  of the plug sleeve  333 . Conversely, when the valve  300  is moved to its fully opened position, the plug  352  is moved axially away from the sealing member  362 , with the plug  352  being drawn into the interior of the plug sleeve  333  to an orientation wherein only a small portion, if any, of the plug  352  protrudes into the interior of the flow control element  360 . 
         [0060]    As will be recognized by those of ordinary skill in the art, the plug  352  is effectively moved between closed and fully open positions relative to the sealing member  362  as a result of the reciprocal axial movement of the plug  352  relative to the plug sleeve  333  and flow control element  360 . Such reciprocal axial movement of the plug  352  is facilitated by the selective application of air pressure to the end or face of the plug  352  defined by the enlarged second portion  352   b  thereof. More particularly, to facilitate the movement of the plug  352  to the closed position shown in  FIG. 6 , an operating fluid such as pressurized air is input into the interior of the plug sleeve  333  via an air passage  338 . The air passage  338  includes a first segment  338   a  which extends through the outlet section  318  of the housing  312 , and a second segment  338   b  which extends through the plug sleeve  333 . More particularly, one end of the second segment  338   b  fluidly communicates with the first segment  338   a , with the opposed, remaining end of the second segment  338   b  extending to the inner surface of the sidewall portion  333   b  of the plug sleeve  333 , thus fluidly communicating with the hollow interior of the plug sleeve  333 . Such pressurized air or other operating fluid acts against the plug  352  in a manner effectively forcing it toward the sealing member  362 . In this regard, the axial movement of the plug  352  is discontinued as a result of the abutment of the plug  352  against the sealing surface  364  of the sealing member  362 . 
         [0061]    Conversely, to facilitate the movement of the plug  352  to the fully open position, the air passage  338  is converted to an exhaust port. In this regard, high pressure fluid entering the inlet passage  316  in the direction designated by the arrow A in  FIG. 6  acts against the plug  352 , and in particular the distal end or face defined by the first portion  352   a  thereof, in a manner effectively forcing the plug  352  toward the end portion  333   a  of the plug sleeve  333 . Since the air passage  338  effectively functions as an exhaust port, any air or other operating fluid trapped between the plug  352  and the end portion  333   a  of the plug sleeve  333  does not impede the movement of the plug  352  away from the sealing member  362 . As such movement occurs, high pressure fluid entering the valve  300  via the inlet passage  316  in the direction of the arrow A is effectively prevented from migrating beyond the guide bushing  324  by the sliding seal created between the seal  325  and the outer surface of the first portion  352   a  of the plug  352 . To the extent that any high pressure fluid migrates between the seal  325  and the plug  352 , such fluid is still effectively prevented from migrating between the peripheral edge of the second portion  352   b  and the inner surface of the sidewall portion  333   b  of the plug sleeve  333  by the sliding, sealed engagement effectuated by the O-rings disposed within the grooves  356  within the second portion  352   b  of the plug  352 . 
         [0062]    In the valve configuration shown in  FIG. 6 , when the plug  352  is in the closed position, the fluid within the inlet passage  316  is effectively prevented from entering the outlet passage  320 . When the plug  352  is moved from the closed position shown in  FIG. 6  toward the fully open position, the fluid is able to flow through the sealing member  362  and thereafter radially outwardly through the flow control element  360  and into the outlet passage  320 . Since the fluid must flow through the flow control element  360  to reach the outlet passage  320 , the energy of the fluid is effectively reduced due to the above-described functional attributes of the flow control element  360 . 
         [0063]    The opening of the valve  300  may be effectuated without necessarily actuating the plug  352  to the fully opened position. In this regard, in the valve  300 , the axial movement of the plug  352  away from the sealing member  362  may be regulated or controlled depending on the desired level of fluid energy dissipation. Along these lines, as will be recognized, the greater the amount of axial movement of the plug  352  away from the sealing member  362 , the greater the number of energy dissipating flow passageways of the flow control element  360  that will be exposed to the incoming fluid flow via the inlet passage  316 . In this regard, maximum energy dissipation of the inlet fluid is achieved when the plug  352  is moved to the fully opened position. The degree to which the plug  352  is moved away from the closed position may be controlled by regulating the manner in which air is exhausted from between the plug  352  and the plug sleeve  333  via the air passage  338 . 
         [0064]    In order to monitor and thus regulate or control the position of the plug  352  relative to the sealing member  362 , the valve  300  is provided with a position feedback device  366  which is accommodated within a complimentary recess defined by the end portion  333   a  of the plug sleeve  333 . The feedback device  366  includes an elongate, generally cylindrical probe portion  368  which is coaxially aligned with and slidably advanced into the probe bore  358  of the plug  352 . The probe bore  358  and probe portion  366  have complimentary configurations, with the advancement of the probe portion  368  into the probe bore  358  being operative to allow the feedback device  366  to effectively monitor the relative position of the plug  352 . The plug  352  is moveable relative to the probe portion  368  which remains stationary, with at least some segment of the probe portion  368  always remaining within the interior of the probe bore  358  throughout the movement of the plug  352  between the closed and fully open extremes. 
         [0065]    In the valve  300 , the feedback device  366  is effectively sealed within its complimentary recess defined by the plug sleeve  333  by a sealing cap  370  which is rigidly attached to the end portion  333   a  of the plug sleeve  333 . The sealing cap  370  defines a continuous groove  372  which accommodates a sealing member such as an O-ring. The abutment of the O-ring against the plug sleeve  333  effectively prevents fluid flowing through the outlet passage  320  from reaching and possibly affecting the performance of the feedback device  366 . A hard wired connection to the feedback device  366  to facilitate the electrical connection thereof to an external control device may be obtained via a probe outlet passage  374  which extends through the outlet section  318  of the housing  312 , through the end portion  333   a  of the plug sleeve  333 , and through the sealing cap  370 , as shown in  FIG. 6 . The detachment of the sealing cap  370  from the plug sleeve  333  provides access to the feedback device  366  as may be needed for the periodic maintenance thereof. 
         [0066]    As indicated above, as the plug  352  moves between the closed and fully open positions during operation of the valve  300 , high pressure fluid entering the valve  300  via the inlet passage  316  in the direction of the arrow A is effectively prevented from migrating beyond the guide bushing  324  by the sliding seal created between the seal  325  and the outer surface of the first portion  352   a  of the plug  352 . To the extent that any high pressure fluid migrates between the seal  325  and the plug  352 , such fluid is still effectively prevented from entering into any open area defined between the plug  352  and the end portion  333   a  of the piston sleeve  333  by the O-rings disposed within the grooves  356 . 
         [0067]    As is further seen in  FIG. 6 , the inlet section  314  of the housing  312  preferably includes a fluid passage  326  formed therein and communicating with the inlet passage  316 . The fluid passage  326  allows for the effective monitoring of the inlet pressure of the high pressure fluid entering the valve  300  via the inlet passage  316 . Similarly, the outlet section  318  of the housing  312  preferably includes a fluid passage  328  which is formed therein and fluidly communicates with the outlet passage  320 . Similar to the functionality of the fluid passage  326 , the fluid passage  328  allows for the monitoring of the fluid pressure of the fluid flowing through the outlet passage  320  and out of the valve  300 . Further, the sidewall portion  333   b  of the plug sleeve  333  is preferably formed to include a fluid passage  330 , one end of which fluidly communicates with the outlet passage  320 . The fluid passage  330  is used to communicate the pressure of the fluid flowing into the outlet passage  320  into a space or region which is defined between the shoulder  354  and the guide bushing  324  when the plug  352  is actuated out of its closed position. 
         [0068]    The valve  10  discussed above and constructed in accordance with the present invention may be packless or sealess to atmosphere, thus avoiding potential risks related to outside leaks. Leak susceptibility is also reduced as a result of the feedback device  66  being internally located within the valve  10 , thus facilitating the full closure of all the internal movements of the valve  10 . The valve  10  also provides the additional benefit of optimizing the process pressure ratio factor which refers to the situation in which the valve  10  is fully open to allow for the maximum flow rate at a minimum pressure drop as required by most new processes for energy saving to maximize differential pressure across the valve  10  when the valve  10  is going to close. In this regard, the valve  10  can reach the highest value of [ΔP min. at max. flow/ΔP max. when going to close], thereby resulting in the aforementioned energy savings. Further benefits include keeping the center of gravity within the pipeline center to provide additional safety when the valve  10  is used in a seismically active environment, and optimizing the flow control element  60  by adding the inherent outlet area expansion, which is particularly important for large mass-flow and high pressure drop or compressible fluids such as gas or vapor. 
         [0069]    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.