Abstract:
An essentially fully balanced plug valve is presented in which the flow control contour is interior to the moving member. The sealing edge of the moving member is at the exterior surface relative to the interior contour. This sealing edge is formed by use of matching angles on the interior of the moving member and the exterior of the stationary member. As a result, operation of the plug is fully balanced with the internal fluid pressure of the liquid therein. The sealing surface of the stationary member is positively retained therein to prevent blowout of the sealing surface. Should failure of the sealing surface occur, a secondary metal-to-metal seal will provide fluid containment albeit possibly at a reduced containment level.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
   This patent application is a continuation of co-pending U.S. patent application Ser. No. 10/702,420, filed Nov. 6, 2003 now U.S. Pat. No. 7,017,608, pending, the teachings and disclosure of which are hereby incorporated in their entireties by reference thereto. 

   FIELD OF THE INVENTION 
   The present invention relates generally to balanced plug valves, and more particularly to fully balanced plug valves having an internal seat contour governing flow rate modulation therethrough. 
   BACKGROUND OF THE INVENTION 
   Control systems and manual applications utilize various types of valves to turn fluid flows on and off, and also to modulate the rate of fluid flow through the valve. Fluid flow through a valve results from pressure differentials between upstream sources and downstream destinations. Fluid flow is a function of pressure differentials and conduit resistance. Control is generally achieved by varying the resistance to flow by varying the available flow area between zero and a maximum. A valve is the conventional method of varying area. 
   Sliding gate valves present one method of varying flow area. However, in such a valve, the differential pressure from the upstream side to the downstream side multiplied by the area of the obstruction separating each side results in a substantial number. This number represents a load on the guides supporting the gate. This load increases friction in a manner proportional to the area and pressure drop. With increased friction, the amount of force required to move the gate increases, thus requiring more powerful actuators. With greater actuator force requirements, costs escalate. Further, control system dead band becomes larger, which negatively affects system stability. 
   Plug type valves are an additional method of varying flow area. These valves reduce the flow area by forcing a plug into a hole. When the plug is lowered from the upstream side, typically the result is that the plug slams shut against a valve seat due to upstream pressure and inertia forces pushing the plug toward the hole. This slamming causes hammering which creates noise and valve damage. Forcing a plug into a hole from the downstream side can also reduce the flow area. In such a scenario, the obstruction pushes against a substantial opposing force, the force being proportional to hole size and pressure drop between the upstream and downstream sides. With increased opposing forces, the amount of force required to move the plug increases, thus requiring more powerful actuators. Again, with greater actuator force requirements, costs escalate. 
   In both the gate valve and plug valve instances, the difference in upstream and downstream pressures is the root of their shortcomings. To overcome these shortcomings, balancing of fluid forces is required. 
   One known arrangement utilizes two circular seats where the pressure forces cancel. These valves are relatively larger and more expensive than the standard gate and plug valves. Further, it is often difficult to ensure proper mechanical closure of both seats. 
   A second known arrangement utilizes one circular seat with a balancing chamber connected to the upstream pressure with a movable piston tied to a valve stem. These valves are complex, and again more expensive to manufacture. 
   As an alternative to the aforementioned larger and more costly balanced valves, it is known to create a balanced valve where the flow passes through a balanced plug that is typically in the shape of a cylinder. The cylindrical or other closed perimeter shaped plug that allows fluid to pass through is known as a balanced plug and is a key element in forming a balanced plug valve. The cylinder method successfully eliminates the friction and back pressure forces, thus forming a balanced valve. However, the known cylinder type balanced valves have their own shortcomings. These include the fact that they have poor capability for flow modulation or for tight shut-offs. 
   In view of the foregoing limitations and shortcomings of the above noted devices, as well as other disadvantages not specifically mentioned, a balanced plug valve with the ability to predictably modulate flow and also provide for tight shut-off of flow was developed by the assignee of the instant invention. This a balanced plug valve with a contour shaped wall is described and illustrated in U.S. Pat. No. 6,394,135, issued on May 28, 2002, the teachings and disclosure of which are incorporated herein in their entireties by reference thereto. The contour shaped wall of this balanced plug valve forms a gap with an edge of a balanced plug. Fluid is able to flow through an input port, through the balanced plug, through the gap, and out an output port. The shape of the contour and the relative position of the balanced plug to the contour shaped wall affect the modulation of the rate of the fluid flow through the gap, and thus, through the valve. Multiple possible variations of the dimensions of the contour shaped wall make possible a multitude of flow rate verses valve stroke relationships. Further, the use of a balanced valve decreases friction forces on the plug which allows for smaller, more efficient, and more economical valve actuators. 
   While this balanced plug valve presents significant advantages to the art and provides fully balanced operation on a two-way valve with an external contour, operation with an internal contour, such as shown in  FIG. 6  of the Erickson et al. &#39;135 patent, is not quite balanced. That is, when the valve is closed, fluid pressure acts on one end of the plug, while the internal edge of the plug that sealing engages the contoured edge is isolated from this fluid pressure. As a result, there is a pressure differential across the plug, resulting in unbalanced forces. 
   Therefore, there exists a need in the art for a fully balanced plug valve that includes an internal seat flow control contour that governs the flow modulation through the valve, and that provides for tight shut-off of flow. 
   BRIEF SUMMARY OF THE INVENTION 
   In view of the above, the present invention provides a new and improved balanced plug valve. More particularly, the present invention provides a new and improved balanced plug valve. More particularly, the present invention provides a new and improved balanced plug valve having an internal contour, the shape of which controls the modulated flow rate through the improved plug valve. Still more particularly, the present invention is directed to an improved balanced plug valve having a reduced cost and enhanced performance over previous valves by including a new plug/seat configuration. 
   The internal contour of the present invention provides a far more streamlined flow path allowing higher flow ratings and reduced manufacturing cost. Further, increased control and predictability of flow rates may be achieved through the present invention. 
   In another aspect of the present invention, the balanced plug valve of the present invention provides a metal displacement method of seat ring retention eliminates or substantially reduces the possibility of seat blow out. This is accomplished in one embodiment of the present invention with positive containment method that also may have applicability to unbalanced valves. 
   In a further aspect of the present invention, flow through the contoured flow restriction paths are available at velocity levels that could incite plug vibration due to varying combinations of a number of flow forces in prior designs. This aspect is achieved in accordance with an aspect of the present invention by narrowing the flow path for better guiding, and adding alternate flow paths. Such alternative flow paths include, in one embodiment of the present invention, the addition of radial flow through one or more holes or gaps in the flow throttling area of the internal contour. 
   In addition to fully balanced operation, the sealing end configuration of the balanced plug provides for ANSI 4 or bubble tight sealing during normal operation. Further, this configuration provides an ANSI 3 metal-to-metal seal in the event of O-ring failure of the valve seat. This end configuration also provides a metal stop to prevent O-ring over compression during normal operation, thereby enhancing seal life. 
   While it is common to use continuous sliding seals for pistons having the continuous seals installed in grooves, the rigidity of the elastic cross-section prevents effective use of outside diameter contact due to the high friction from the compression of the cross-section. In such arrangements, radial stretch is required to control the sliding friction. However, the stretch factor varies greatly with temperature, especially with non-elastomers such as PTFE (Teflon®). In accordance with an aspect of the present invention, PTFE tubing is cut to the proper length and installed with the ends butted together against each other in the groove. The squeeze of the tubing is used for proper sealing and sliding forces. This allows ease of installation, and removes the requirement of specific sealed diameters for specific sized valves. Further, sensitivity to temperature variation is significantly reduced. 
   Other features and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention. In the drawings: 
       FIG. 1  is a cross sectional illustration of a normally open fully balanced globe valve constructed in accordance with the teachings of the present invention, shown in its open position; 
       FIG. 2  is a cross sectional illustration of a normally open fully balanced globe valve constructed in accordance with the teachings of the present invention, shown in its closed position; 
       FIG. 3  is a cross sectional illustration of a normally closed fully balanced globe valve constructed in accordance with the teachings of the present invention, shown in its closed position; 
       FIG. 4  is a cross sectional illustration of a normally closed fully balanced globe valve constructed in accordance with the teachings of the present invention, shown in its open position; 
       FIG. 5  is a cross sectional illustration of a fully balanced three-way globe valve constructed in accordance with the teachings of the present invention, shown in its up position; 
       FIG. 6  is a cross sectional illustration of a fully balanced three-way globe valve constructed in accordance with the teachings of the present invention, shown in its down position; 
       FIG. 7  is an isometric illustration of an embodiment of a balanced plug constructed in accordance with the teachings of the present invention; 
       FIG. 8  is a partial sectional view of the balanced plug of  FIG. 7 ; 
       FIG. 9  is an exploded detail view of a sealing edge of the balanced plug of  FIG. 7 ; 
       FIG. 10  is a sectional view of an embodiment of a contoured seat for use in a fully balanced globe valve constructed in accordance with the teachings of the present invention; 
       FIG. 11  is a expanded detail sectional view of a seal retaining portion of the contour seat of  FIG. 10 ; 
       FIG. 12  is an expanded detail sectional view of the seal retainer portion of the contour seat of  FIG. 10  shown with a seal member retained therein; 
       FIG. 13  is a cross-sectional view of an embodiment of a two-way fully balanced globe valve shown in its open position; 
       FIG. 14  is a cross-sectional view of an embodiment of a two-way fully balanced globe valve shown in its closed position; 
       FIG. 15  is a partial cross-sectional view of an alternate embodiment of a sealing arrangement for the fully balanced globe valve of the present invention; and 
       FIG. 16  is a partial sectional view of a v-shaped contour seat for use in an embodiment of the present invention. 
   

   While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims. 
   DETAILED DESCRIPTION OF THE INVENTION 
   Turning now to the drawings, there is illustrated in  FIG. 1  a partial cross-sectional view of a normally open fully balanced globe valve  20  constructed in accordance with the teachings of the present invention. This valve  20  includes a valve body  22  having an inlet coupling  24  and an outlet coupling  26 . Regulation of the flow of fluid from the inlet  24  to the outlet  26  is accomplished through the cooperation of the balanced plug  28  and the contoured seat  30  as will be described more fully below. In this embodiment of the present invention, the contoured seat  30  is held in position within the valve body  22  by bonnet  32  that is fixably attached to the valve body  22 . The relative positioning of the balanced plug  28  in relation to the contoured seat  30  is accomplished by moving valve stem  34  linearly into or out of the valve body  22  slidably through packing  36 . While not illustrated in this  FIG. 1 , the linear movement of valve stem  34  is typically accomplished through the provision of an actuator. 
   The balanced plug  28  is generally cylindrical in shape, but can be of other closed perimeter shapes as well. Valve stem  34  is mounted to the plug  28  at a center hub  38 . This balanced plug  28  is prevented from moving in directions other than generally along the vertical axis of  FIG. 1  by a guide  40  extending from the valve body  22 . The guide  40  may be integral with the valve body  22 . A sliding seal O-ring  42  is positioned within a groove  44  of guide  40 , sealing the balanced plug  28  at a perimeter wall  46  to block fluid passage between the exterior of the perimeter wall  46  of the balanced plug  28  and the guide  40 . A close off O-ring seal  48  is positioned within a groove  50  of the contoured seat  30  to block fluid passage between the exterior of the perimeter wall  46  of the balanced plug  28  and the contoured seat  30  when the balanced plug  24  is in a closed position as illustrated in  FIG. 2 . 
   An alternate embodiment of a normally closed fully balanced globe valve  20 ′ is illustrated in its normally closed position in partial cutaway illustration of  FIG. 3 . As may be seen from an examination of this figure, the valve stem  34  now linearly slides through packing  36  which is secured within bonnet  32 . This valve stem  34  also traverses the contoured seat  30  before coupling to the balanced plug  28 . In this normally closed embodiment  20 ′, a valve stem travel stop  52  is removably positioned through valve body  22  by nut  54 . As may be seen from the partial cross-sectional illustration of  FIG. 4 , this valve stem travel stop  52  is utilized to prevent over travel of valve stem  34  which could result in disengagement of the fully balanced plug  28  with the guides  40 . 
   A further alternate embodiment of a fully balanced globe valve constructed in accordance with the teachings of the present invention is illustrated in partial cross-sectional view in  FIG. 5 . Specifically, this embodiment is a three-way fully balanced globe valve  20 ″ shown in an up location in  FIG. 5  and in a down location in  FIG. 6 . It should be noted that such a three-way valve is often used as a mixing valve when the flow is in the direction of flow arrows  56 , and as a diverting valve when the flow is in the direction of arrows  58 . 
   As may be seen from these  FIGS. 5 and 6 , the three-way fully balanced globe valve of the present invention includes a diverter/mixing coupling  60  coupled to the valve body  22 . A valve seat  62  is attached at the interior end of the coupling  60  to provide sealing engagement with the balanced plug  28  in its down location as illustrated in  FIG. 6 . In the up location ( FIG. 5 ) the sealing engagement is provided between the contoured seat  30  and the opposite sealing edge of the balanced plug  28 . It should be noted that in addition to these two exclusive positions of  FIGS. 5 and 6 , some applications may adjustably position the balanced plug  28  between these two extreme locations to control the relative flows into or out of couplings  64 ,  66 . As will be discussed more fully below, the shape of the contours of the contoured seat  30  and the seat  62  may also aid in controlling the relative flow through the valve. 
   Having now described various embodiments of a fully balanced valve constructed in accordance with the teachings of the present invention, attention is now directed to  FIG. 7  wherein an embodiment of a balanced plug for use in such valves is illustrated. As may be seen from this isometric illustration, the balanced plug  28  includes the central hub  38  which is adapted to receive the valve stem therethrough. Supporting the center hub  38  are multiple spokes  70  extending to the perimeter wall  46  of the plug  28 . The edges  72 ,  74  of the balanced plug  28  are specifically profiled to ensure fully balanced operation of the valve as will be discussed more fully below. 
   As may be seen from the cross-sectional illustration of  FIG. 8 , the support spokes  70  are preferably shorter than the perimeter wall  46  of the balanced plug. In this way, a portion  76  of perimeter wall  46  may accommodate the contoured seat without interference from the supporting spokes  70 . Also preferably, the width of the spokes  70  is also such to allow edge  74  of the balanced plug  28  to extend beyond the spokes  70 . 
   The details of sealing edge  72  may be better observed with reference to the expanded partial sectional view of  FIG. 9 . Specifically, this sealing edge  72  defines a seal contact point  78  that is adapted to form a sealing contact with the sealing O-ring  48  ( FIG. 1 ). A pressure equalizing contact wall  80  is defined next to the sealing contact point  78  to ensure pressure equalization across the perimeter wall  46  when the valve is in a sealing engagement with the contoured seat of the fully-balanced globe valve as will be discussed more fully below. This pressure equalizing wall  80  is unique to the balanced plug of the present invention and enables the fully balanced operation described herein. This end  72  also includes a sealing step  82  that terminates in shoulder  84 . This shoulder  84  also serves to allow pressure equalization across the perimeter wall  46  of the balanced plug  28 , and provides the backup function of a secondary seal in the event failure of the primary sealing O-ring, as will be discussed more fully below. 
   An embodiment of the contoured seat  30  is illustrated in cross-sectional view in  FIG. 10 . As may be seen from this cross-sectional illustration, the contoured seat is generally cylindrical in shape to mate with the balanced plug  28  discussed above. To allow this contoured seat to be used in various types of valve configurations such as those discussed above with regard to  FIGS. 1–6 , the contoured seat  30  preferably defines an internal cavity  86  through the center thereof. This central cavity  86  communicates with the threaded mounting hole  88  in the bonnet mounting portion  90  of the seat  30 . As may be recalled from the discussion of  FIGS. 1 and 3  above, this mounting hole  88  of bonnet mounting portion  90  may be used to either simply secure the seat  30  to the bonnet  32  for normally open type valves, or may receive the packing  36  to accommodate the slidable translation of valve stem  34  therethrough in the case of normally closed valve embodiments. 
   The contoured seat  30  may include a flow regulating contoured wall portion  92  having a profile that acts in relation to the balanced plug to regulate the flow of fluid therethrough. As may be better seen in the expanded partial sectional view of  FIG. 11 , the contoured surface  92  preferably terminates in a secondary sealing surface  94 . The O-ring groove  50  is formed therebelow such that this secondary sealing surface  94  also serves the dual purpose of retaining the O-ring seal therein. This retention of the O-ring is further facilitated by the provisions of the wrap wall portion  96 . Specifically, and with reference to  FIG. 12 , once the O-ring  48  has been placed within the groove  50  of the contoured seat  30 , the wrap wall portion  96  is rolled to wrap around the O-ring  48 . In this way, the O-ring seal  48  is inhibited from being blown out by the fluid pressure through the valve as could often occur with other valves which are dependent upon O-ring tension for retention. 
   Having now described various embodiments of fully balanced globe valves and an embodiment of the balanced plug and contoured seat of the present invention, attention is now directed to  FIGS. 13 and 14  wherein the balanced operation of a valve of the present invention will be described in relation to a further alternate embodiment. 
   When the valve of the present invention is operated in a manner to allow fluid flow therethrough, the balanced plug  28  is positioned relative to the contoured seat  30  such that a flow gap  100  is formed between the contoured wall  92  of seat  30  and wall  80  of the plug  28 . The flow of fluid through this flow gap  100  may be adjusted by vertically adjusting the relative position of the plug  28  to the seat  30 . Various flow profiles may be defined for such vertical positioning by changing the contour  92  of the seat  30  to provide the desired flow characteristics. While operating in this mode, the plug  28  is essentially fully balanced. That is, the fluid pressure P 2  of the source fluid acting on surface  74  of the plug  28  tending to push the plug  28  in a downward direction of  FIG. 13  is balanced by the fluid pressure P 2  acting on surface  80 , which tends to push the plug  28  in an upward direction of  FIG. 13 . Because these pressure forces are balanced across the plug  28 , no additional force to counteract a fluid pressure imbalance is required from the actuator to reposition the stem  34  as desired. This greatly enhances the ability to precisely control the fluid flow through the valve, and presents a significant advantage over unbalanced valves described above. 
   When the flow of fluid through the valve is desired to be stopped, the plug  28  is positioned such that sealing point  78  comes in sealing engagement with O-ring seal  48 . In this way, no fluid is able to flow through flow gap  100  to the valve outlet. However, it is important to note that surface  180  is still exposed to the fluid pressure P 2  of the fluid source while the valve is in this closed position. In this way, the plug  28  is still balanced, and will not require any additional power from the actuator to overcome a fluid imbalance that exists with prior valves. That is, because the fluid pressure P 2  is still able to act on surface  80  of plug  28 , this fluid pressure balances the fluid pressure that continuously acts on surface  74 . Without such a gap, the fluid pressure P 2  acting on surface  74  would tend to hold the valve in its closed position, and would require additional force to be applied from the actuator to overcome the fluid pressure differential across the plug  28 . In prior valves, this often resulted in an overshoot once the valve was opened and the fluid pressure was again balanced across the plug. Such an overshoot made precise flow control difficult. However, such pressure imbalance while in the closed position is eliminated with the design of the present invention. 
   An additional advantage is provided by the design of the sealing end  72  of the balanced plug  28  of the present invention. Specifically, if the sealing O-ring  48  were to be lost from groove  50 , surface  80  of the plug  28  would be forced into contact with surface  94  of the contoured seat  30  to provide a backup seal in the event of this type of failure. While the original seal between point  78  and O-ring  48  is of an ANSI IV or bubble tight nature, the contact of surfaces of  80  and  94  will still provide a type ANSI III seal. 
   As may be seen from the alternate embodiment of the sealing end  72  of the balanced plug  28  illustrated in  FIG. 15 , the actual configuration of this operative end of the balanced plug may differ significantly in its various embodiments. In the embodiment of  FIG. 15 , the sealing end portion  72  includes the sealing contact point  78  in the form of a finger protrusion that contacts the O-ring seal  48 . A shoulder land  102  and a pressure equalization surface  104  are provided to allow the pressure balancing across the plug  28  as discussed above. Additionally, the configuration of the embodiment of  FIG. 15  also provides additional functionality. That is, in one embodiment the shoulder land  102  is provided at a relative location such that the shoulder land  102  may contact surface  94  of the contoured seat  30  to prevent O-ring over compression and extend its life. While surfaces  102  and  94  are in contact, the pressure equalization surface  104  is still able to be acted upon by the fluid source pressure to maintain a pressure balance across the plug  28 . Further, surfaces  102  and  94  provide a metal-to-metal seal, or a type ANSI III seal that acts as a redundant or backup seal in the case of loss of O-ring seal  48 . 
   A further alternate embodiment of a fully balanced valve constructed in accordance with the teachings of the present invention is illustrated in  FIG. 16 . As may be seen from this figure, the valve seat  62 ′ has a contoured surface  110  that is used, relative to the position of the plug  28 , to regulate the flow of fluid therethrough. In this specific embodiment, the contour is constructed in the form of v-shaped opening. The angle of the contour may be set as desired to achieve a desired flow rate profile as the plug  28  is moved into and out of contact with seat  62 ′. 
   All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
   The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
   Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.