Patent Publication Number: US-2007120084-A1

Title: Fully independent, redundant fluid energized sealing solution with secondary containment

Description:
FIELD OF THE INVENTION  
      The present invention relates generally to seals and sealing, and more particularly to pressurized seals for sealing a reciprocating stem or shaft. The present invention finds particular utility in valves that regulate a process fluid where leakage of that process fluid is to be minimized.  
     BACKGROUND OF THE INVENTION  
      Flow regulating valves are devices that can be adjusted to restrict or increase the flow of a fluid through a conduit. Such valves are generally well known in the art and have many practical applications. For example, in the commercial natural gas production industry, flow-regulating valves are commonly used to vary the flow of natural gas through a network of gas collection pipes. The network of collection pipes will often connect and branch together tens to hundreds of natural gas ground wells in a localized geographic region. The individual wells will feed natural gas through the network of gas collection pipes to a common output location. Often, the desired natural gas output is less than the maximum production capacity of the several wells combined. Such demands can change due to cyclical seasonal trends and for other economic reasons. This creates a need for regulating and monitoring natural gas production from each well to control the supply.  
      To regulate the production output of each individual well, a branch collection pipe for each individual well typically includes a flow-regulating valve and a gas flow sensor arranged in fluid series. The gas flow sensor indicates the amount of natural gas that flows through the collection pipe. The regulating control valve provides a variable degree of opening that forms a restriction orifice in the collection pipe and thereby sets the natural gas flow rate in the collection pipe.  
      To adjust the restriction orifice within the collection pipe, the flow-regulating valve is typically a movable/positionable type of valve such as a linearly translatable valve. A valve of this design generally includes a valve body through which a flow passage is disposed. Other components include a plug member located within the flow passage and an elongated valve stem. The plug member is attached to the valve stem and the valve stem passes through a valve bonnet. Using the valve stem, the plug member can be linearly translated toward or away from a valve seat within the flow passage between a fully opened position and a fully closed position, and intermediate positions therebetween. The plug member blocks all flow when in the fully closed position and allows for maximum flow when in the fully opened position.  
      To linearly translate the plug member towards and away from the valve seat, the valve stem is connected to an actuator. The actuator is typically located adjacent the valve bonnet and imparts linear translation motion to the valve stem. Accordingly, the valve stem will have to move with respect to the valve housing that it passes into. To prevent the undesirable loss of process fluids passing through the valve, the intersection between the reciprocating valve stem and the valve bonnet into which the stem passes should be well sealed. This is especially true where the process fluid is flammable and capable of potentially producing an explosion (e.g., natural gas, gaseous fuel), is poisonous, or is environmentally harmful.  
      Several devices and sealing methods have been proposed for sealing a linearly moving valve stem in a pressurized seal arrangement as disclosed in, for example, U.S. Pat. Nos. 6,161,835 and 5,746,435 to Arbuckle, U.S. Pat. Nos. 5,772,216 and 5,607,165 to Bredemeyer, and U.S. Pub. Applns. 2004/0135112 and 2004/0134665 to Greeb, et al., each of which is incorporated herein in its entirety by this reference. Such pressurized dynamic sealing arrangements may be used in the process gas industry for valves and the like to promote sealing and ensure that the process gas does not leak or produce a hazardous external environment. These patents disclose that using a pressurized barrier fluid or sealant (e.g., grease) provides opposing axial fluid forces on two spaced apart seals. In these arrangements, the barrier fluid has a pressure that is typically greater than a pressure of the process fluid. As such, if leakage is to occur, most or all of the leakage would be the barrier fluid rather than the process fluid since the barrier fluid is at the higher pressure of the two. Indicating mechanisms, which are disclosed in the above-noted patents, effectively indicate and inform a user whether leakage of the barrier fluid is occurring.  
      Unfortunately, the concepts disclosed in the Arbuckle and Bredemeyer patents are complex and costly to implement, have complex plumbing arrangements, are not practical to structurally implement, and/or require numerous complex components for establishing a preload barrier. Further, the indicating mechanism or indicators disclosed in at least some of these patents may have accuracy problems, may not readily indicate the exact source of the problem, and/or may be difficult or impractical to employ in the field or across different applications. Finally, these prior art concepts disclosed in the Arbuckle and Bredemeyer patents are subject to potential premature failure and leakage since they do not provide fully independent redundant seals in the sealing arrangements as well as an auxiliary (i.e., secondary) containment chamber to impound a leaking barrier fluid.  
      The invention provides sealing system that solves each of the aforementioned shortcomings. These and other advantages of the invention, as well as additional inventive features will be apparent from the description of the invention provided herein.  
     BRIEF SUMMARY OF THE INVENTION  
      In one aspect, the invention provides a stem sealing system for preventing leakage of a fluid in a valve housing having a movable stem. The stem sealing system comprises a first set of dynamic seals, a second set of dynamic seals, an auxiliary barrier fluid chamber, and a barrier fluid indicator. The first set of dynamic seals engage the stem. The second set of dynamic seals also engage the stem and are in spaced relation to the first set of dynamic seals. The auxiliary barrier fluid chamber surrounds the shaft and is interposed between the first and second sets of dynamic seals. The barrier fluid indicator has a load member in a primary barrier fluid chamber. A first face of the load member is exposed to a process fluid and a second face of the load member exposed to a barrier fluid contained between two seals in the first set of dynamic seals and inhibited from fluid communication with the auxiliary barrier fluid chamber by a dynamic seal in the first set of dynamic seals. The load member is adapted to pressurize the barrier fluid.  
      In another aspect, the invention provides a valve bonnet in a valve. The valve bonnet comprises a bore, a first set of dynamic seals, a second set of dynamic seals, and a barrier fluid indicator. The bore is adapted to receive an actuatable valve stem and forms an auxiliary barrier fluid chamber. The auxiliary barrier fluid chamber surrounds the actuatable valve stem. The first set of dynamic seals engages the actuatable valve stem and includes a first dynamic seal. The second set of dynamic seals engages the actuatable valve stem. The first and second sets of dynamic seals are in spaced relation to each other and on opposing sides of the auxiliary barrier fluid chamber. The spaced relation is greater than a maximum stroke length of the actuatable valve stem. The barrier fluid indicator has a load member in a primary barrier fluid chamber. A first face of the load member is exposed to a process fluid while a second face of the load member is exposed to a barrier fluid and inhibited from fluid communication with the auxiliary barrier fluid chamber by the first dynamic seal. The load member is adapted to pressurize the barrier fluid.  
      In yet another aspect, the invention provides a valve. The valve comprises a valve body, a first redundant sealing system, a second redundant sealing system, and a barrier fluid indicator. The valve body has a flow passage and a bore adapted to receive a translatable valve member. The translatable valve member is adapted to regulate a flow of a process fluid through the flow passage. The bore forms an auxiliary barrier fluid chamber. The first redundant sealing system is sealingly interposed between the valve body and the translatable valve member. The second redundant sealing system is sealingly interposed between the valve body and the translatable valve member. The second redundant sealing system is in spaced relation to the first redundant sealing system. The first and second redundant sealing systems are spaced apart at least a maximum stroke length of the translatable valve member. The auxiliary barrier fluid chamber is interposed between the first and second redundant sealing systems. The barrier fluid indicator has a load member in a primary barrier fluid chamber containing a pressurizable barrier fluid. A first face of the load member is exposed to the process fluid in the flow passage while a second face of the load member is exposed to the barrier fluid and in fluid communication with the bore and the translatable valve member. A lower dynamic seal in the first redundant sealing system inhibits fluid communication between the first face of the load member and the auxiliary barrier fluid chamber.  
      Other aspects, objectives 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 view of an operating environment in which the teachings of the present invention may be implemented;  
       FIG. 2  is a bonnet from the valve of  FIG. 1  illustrating an auxiliary barrier fluid chamber and fully independent redundant dynamic seals in accordance with the teachings of the invention; and  
       FIG. 3  is an enlarged view of a portion of  FIG. 2  highlighting one type of dynamic seal known as a cup seal. 
    
    
      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  
      Referring to  FIG. 1 , a valve  10  that includes redundant fluid energized dynamic seals and an auxiliary chamber for barrier fluid is illustrated. As will be more fully explained below, the fully independent redundant sealing of the invention advantageously provides a higher level of reliability. Additionally, the auxiliary chamber for barrier fluid reduces the potential for leaks and lessens the chance that barrier fluid will blend or commingle with process fluid.  
      As illustrated in  FIG. 1 , the valve  10  comprises an actuator  12 , a valve body  14 , a translatable member  16 , and a valve bonnet  18 . While the valve  10  may be a linearly translatable valve, a rotary valve, or other movable/positionable valves as known in the art, the well head valve depicted in  FIG. 1  is a linearly translatable type of valve and shall be used to describe the invention. Prior to describing the invention in detail, the operation of the valve shall be explained to aid in the understanding of the invention.  
      The actuator  12 , which can be electrical in nature, generally includes such components as a gear box  20 , an actuator stem  22 , a spring housing  24 , a spring  26 , and a support structure  28 . The gear box  20  is coupled to, and provides translational movement to, the actuator stem  22 . The actuator stem  22  passes into the spring housing  24  that is confining and guiding the spring  26 . In one embodiment, the spring  26  includes thereon a support structure  28  that permits a reversal of the spring activation force. Each of these components is generally reside within an actuator housing  30 . Depending on the particular use of the valve  10 , and the various different types of actuators well known in the art, the actuator  12  can include a plethora of various other components and features.  
      The valve body  14  defines a flow passage  32  that extends between and through mounting flanges  34 ,  36  on, in the illustrated embodiment, opposing ends  38 ,  40  of the valve body  14 . Even so, other flow passages having different configurations may be used. The mounting flanges  34 ,  36  are adapted to couple and/or mount the valve  10  to a collection pipe (not shown) that is configured to transport, for example, a process fluid such as, for example, natural gas, gaseous fluid, and the like.  
      Still referring to  FIG. 1 , the translatable valve member  16  includes an elongate valve stem  42  and a plug  44 . The valve stem  42  generally extends through the valve bonnet  18  and the valve body  14 . The valve stem  42  is coupled at one end to the plug  44  and at another end to the actuator stem  22 . As such, the valve and actuator stems  42 ,  22  can transmit the selective positioning force from the actuator  12  to the plug  44 .  
      The plug  44  is situated in and guided by a metering cage  46  in the valve body  14 . The metering cage  46  radially restrains and guides movement of the plug  44 . The plug  44  and the metering cage  46  are situated along the flow passage  32  to provide and/or form a restriction orifice that regulates flow of the process fluid through the flow passage  32  in the valve body  14 . Courtesy of the actuator  12 , the plug  44  is linearly translatable toward and away from a valve seat  48  in and on the valve body  14 . As such, the plug  44  can be manipulated between fully closed and fully open positions, as well as intermediate positions therebetween. The plug  44  blocks all flow when in the fully closed position and allows for maximum flow when in the fully open position.  
      To provide for installation of the translatable valve member  16 , the valve body  14  and valve bonnet  18  may be composed of multiple pieces and/or components. In such cases, one or more static seals  47  can be situated between the valve body  14  and valve bonnet  18 . Also, since the valve bonnet is generally interposed and/or “sandwiched” between the actuator  12  and the valve body  14 , one or more static seals  47  can be placed between the valve bonnet  18  and the actuator  12  as well. In one embodiment, the valve body  14  and the valve bonnet  18  can be integrally formed together. The valve bonnet  18  generally provides a leak proof closure for the valve body  14 . In other words, the valve bonnet  18  acts like a “hood” for the valve body  14 .  
      Now that an operating environment has been described, the invention as implemented in the valve bonnet  18  shall now be described. Referring to  FIGS. 1 and 2 , the valve bonnet  18  comprises a valve bonnet body  50 , a bore  52  or passage forming an auxiliary (or secondary) barrier fluid chamber  54  or reservoir, a first set of dynamic seals  56 , a second set of dynamic seals  58 , and a barrier fluid indicator  60 .  
      The bore  52  generally extends entirely through the valve bonnet body  50 . Further, the bore  52  is dimensioned and configured to permit the valve stem  42  of the translatable member  16  to be translatably and/or rotatably received therein. The bore  52  includes notches  62  dispersed along a bore length that are adapted to receive and accommodate a dynamic (i.e., a fluid energized) seal such as, for example, a cup seal, a wiper seal, and the like. The notches  62  can also receive snap rings, washers, spacers, and the like, to position and/or secure the dynamic seals as well known in the art.  
      In the illustrated embodiment of  FIG. 2 , the first set of dynamic seals  56  includes a top dynamic seal  64 , a middle dynamic seal  66 , and a lower dynamic seal  68 . Each of the seals  64 ,  66 ,  68 , is an annular seal that encircles and/or surrounds the valve stem  42 . The seals  64 ,  66 ,  68 , as shown in  FIG. 2 , are interposed between the valve bonnet body  50  and the valve stem  42  and are arranged in fluidic series. As illustrated in  FIG. 3 , the seals in the illustrated embodiment (e.g.,  66 ,  68 ) form a “cup” that is adapted to catch a pressurized fluid. The legs of the cup are biased outwardly away from each other and against the valve bonnet body  50  and the valve stem  42  to inhibit and/or prevent the pressurized fluid from passing the seal. As depicted in  FIG. 2 , the open end of the cup in the top and middle dynamic seals  64 ,  66  faces toward the auxiliary barrier fluid chamber  54  and away from the actuator  12 . In contrast, the open end of the cup in the lower dynamic seal  68  is directed away from the auxiliary barrier fluid chamber  54  and toward the actuator  12 . Such an arrangement of dynamic seals provides an exemplary level of redundancy and gives the valve bonnet  18  and/or the valve  10  high reliability.  
      Again, in the illustrated embodiment, the second set of dynamic seals  58  includes an upper dynamic seal  70  and a bottom dynamic seal  72 . Again, each of the dynamic seals  70 ,  72  is an annular seal that encircles and/or surrounds all or a portion of the valve stem  42 . The seals  70 ,  72 , as shown in  FIG. 2 , are interposed between the valve bonnet body  50  and the valve stem  42  and are arranged in fluidic series. The seals  70 ,  72  form a “cup” that is adapted to catch a pressurized fluid. Like above, the legs of the cup seals are biased outwardly and away from each other and inhibit and/or prevent the pressurized fluid from passing the seal. As depicted in  FIG. 2 , the open end of the cup in the upper dynamic seal  70  is directed toward the auxiliary barrier fluid chamber  54  and away from the plug  44 . In contrast, the open end of the cup in the bottom dynamic seal  72  is directed away from the auxiliary barrier fluid chamber  54  and toward the plug  44 . In one embodiment, the upper and bottom dynamic seals  70 ,  72  can be combined such that they form a single bidirectional seal. Again, such dynamic seals provide an exemplary level of redundancy and give the valve bonnet  18  and/or the valve  10  higher reliability.  
      As depicted in  FIG. 2 , the first and second sets of dynamic seals  56 ,  58 , are in spaced relation to each other and generally disposed on opposing sides of the auxiliary barrier fluid chamber  54 . In a preferred embodiment, the first and second sets of dynamic seals  56 ,  58 , and in particular the lower seal  68  and the upper seal  70 , are most proximate the auxiliary barrier fluid chamber  54  and spaced apart a distance equal to or greater than a maximum stroke length of the valve stem  42 . Such an arrangement inhibits and/or prevents wear to the valve stem  42 , the bore  52 , and/or the sets of dynamic seals  56 ,  58 . Additionally, the spacing of the independent dynamic seals  64 ,  66 ,  68 ,  70 ,  72  prevents the failure of one seal from causing the failure of one or more of the other seals.  
      While the first set of dynamic seals  56  is illustrated as including three dynamic seals  64 ,  66 ,  68  and the second set of dynamic seals  58  is illustrated as having two dynamic seals  70 ,  72 , additional dynamic seals can be included to provide even more redundancy.  
      In the illustrated embodiment, the auxiliary barrier fluid chamber  54  is formed by providing a portion of the bore  52  with a greater diameter. As such, the auxiliary barrier fluid chamber  54  is adapted to receive a barrier fluid upon the failure of lower dynamic seal  68 . During normal operation, and when the lower dynamic seal  68  is intact, the auxiliary barrier fluid chamber  54  is preferably predominantly free of barrier fluid. A small amount of the barrier fluid may seep around the lower dynamic seal  68  and into the auxiliary barrier fluid chamber  54  during typical operation without catastrophic and/or harmful effect. The auxiliary barrier fluid chamber  54  is most suited and provided to capture an excessive and/or large amount of the barrier fluid should the lower dynamic seal  68  suffer a total and/or substantial failure.  
      The barrier fluid indicator  60  includes a load member, illustrated as a piston  74 , disposed in a primary barrier fluid chamber  76  or reservoir. The piston  74  has a first face  78  and a second face  80 . The first face  78  is exposed to, and in fluid communication with, a process fluid such as, for example, the process fluid that flows or resides in the flow passage  32  ( FIG. 1 ) of the valve body  14 . In the illustrated embodiment, the first face  78  is exposed to the process fluid via a process fluid channel  82  that passes through the valve bonnet body  50 .  
      The second face  80  of the piston  74  is exposed to a barrier fluid and is, via barrier fluid channel  84 , in fluid communication with a portion of the valve stem  42 . The barrier fluid channel  84  preferably terminates between the middle and lower dynamic seals  66 ,  68 . As such, the barrier fluid within the primary barrier fluid chamber  76  is pressurized and able to adequately lubricate the translating valve stem  42 . As shown in  FIGS. 1 and 2 , in the illustrated embodiment, the valve stem  42  moves along a first axis  100  and the piston  74  (i.e., load member) moves along a second axis  102 . Notably, the two axes  100 ,  102  are approximately perpendicular, which is meant to include exactly perpendicular, to each other. In addition, to guard against leakage of the barrier fluid, the barrier fluid indicator  60  can include one or more static and/or dynamic indicator seals  86 .  
      Since the barrier fluid in the primary barrier fluid chamber  76  is typically at a pressure that is higher than a pressure of the process fluid flowing through or residing in the flow passage  32  in the valve body  14  ( FIG. 1 ), the piston  74  is biased against the valve bonnet body  50  toward the valve stem  42  as shown in  FIG. 2 . If the pressure of the barrier fluid drops, the pressure of the process fluid will eventually begin to exceed the pressure of the barrier fluid. This causes the piston  74  of the indicator  60  to move away from the valve stem  42 . In this manner, the barrier fluid indicator  60  is capable of visually notifying a user of the well head  10  about the status of the barrier fluid. The status of the barrier fluid can, by inference, reveal that there is a problem with the integrity of one or more of the seals  64 ,  66 ,  68 ,  70 ,  72 , that the auxiliary barrier fluid chamber  54  has been called upon, that the process fluid pressure has dangerously increased, and the like. To make the barrier fluid indicator  60  easy to see and read, a portion of the indicator can be visible through, or protruding from, a sidewall  88  of the valve bonnet  18 .  
      In the illustrated embodiment, a failure of the lower dynamic seal  68  causes the barrier fluid from the primary barrier fluid  76  to spill and/or creep into the auxiliary barrier fluid chamber  60 . A failure of the middle dynamic seal  66  immediately enlists the top dynamic seal  64  to contain the barrier fluid. For the barrier fluid to get to the flow passage  32  and commingle with the process fluid, the auxiliary barrier fluid chamber  54  would have to fill and each of the upper and bottom dynamic seals  70 ,  72  would have to fail. Therefore, the valve bonnet  18 , with its first and second sets of dynamic seals  56 ,  58  arranged in fluidic series and its auxiliary barrier fluid chamber  54 , provides an exemplary level of redundancy. The seals  64 ,  66 ,  68 ,  70 ,  72  and/or the auxiliary barrier fluid chamber  54  redundantly ensure that the barrier fluid and the process fluid remain isolated from each other and do not end up mixing together. In other words, the process fluid is protected from contamination by the barrier fluid.  
      As shown in  FIG. 2 , in one embodiment the valve bonnet  18  includes a vent  90 . The vent  90  is in fluid communication with the bore  52  via a vent channel  92  passing through the valve bonnet body  50 . In a preferred embodiment, the vent channel  92  terminates between the top and middle dynamic seals  64 ,  66 . In one embodiment, the vent  90  has an outlet  94  formed in the sidewall  88  of the valve bonnet  18 .  
      The vent  90  can be used for a number of purposes depending upon the particular application of the valve  10 . The vent  90  can be connected to some form of instrumentation such as, for example, a barrier fluid sensor (not shown). In such cases, the sensor is adapted to detect leakage of the barrier fluid, a change in barrier fluid pressure, and the like. This additional feature provides a safeguard in the event that the barrier fluid indicator  60  has malfunctioned, the barrier fluid indicator is not visible, that one or more channels  82 ,  84  are plugged, and the like.  
      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 entirely 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) is 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.