Patent Publication Number: US-2022228675-A1

Title: Valve packing having independently loaded packing rings

Description:
FIELD OF THE DISCLOSURE 
     This disclosure relates generally to valve packing and, more particularly, to valve packings having independently loaded packing rings. 
     BACKGROUND 
     Industrial process plants (e.g., refineries, chemical plants, petrochemical plants, pharmaceutical plants, etc.) include process control loops to control temperatures, the flow of fluids, etc. Industrial control systems typically include control loops to automatically adjust the values of process variables to equal a desired set-point. Some industrial control systems include control valves to manipulate a flowing fluid, such as gas, steam, water, or chemical compounds to compensate for load disturbances and maintain the regulated process variables as close as possible to the desired set points. Control valves typically include at least one packing to maintain a seal around a stem or shaft to prevent leakage of process fluid into the environment. 
     SUMMARY 
     An example packing assembly for a fluid valve includes a first packing ring and a first follower to be disposed at least partially within a bore of a bonnet of the fluid valve to apply a first load to the first packing ring. The example apparatus further includes a second packing ring sized to fit within a bore of the first follower, and a second follower to be disposed at least partially within the bore of the first follower to apply a second load to the second packing ring within the bore of the first follower. 
     An example apparatus to seal a valve includes a first packing ring disposed in a valve bonnet and coupled to a first surface of a first spring disposed in the valve bonnet, and a first follower coupled to a second surface of the first spring, the second surface of the first spring opposite of the first surface of the first spring, the first follower coupled to a flange of the valve bonnet. The example apparatus also includes a second packing ring disposed on a surface of the first follower, the surface of the first follower spaced apart from the first spring, the second packing ring coupled to a first surface of a second spring. The example apparatus further includes a second follower coupled to a second surface of the second spring, the second surface of the second spring opposite of the first surface of the second spring, the second follower coupled to at least one of the first follower and the flange. 
     An example apparatus to seal a valve includes a first packing ring disposed in a valve bonnet to prevent first leakage from the valve in response to a first load. The example apparatus further includes a second packing ring disposed in the valve bonnet to prevent second leakage from the valve in response to a second load, the second packing ring having a different diameter from the first packing ring, and the first load substantially independent from the second load. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of an example control valve in accordance with the teachings of this disclosure. 
         FIG. 2  illustrates a cross-sectional view of an example prior packing for a control valve. 
         FIG. 3  illustrates a cross-sectional view of an example packing in accordance with the teachings of this disclosure. 
         FIG. 4  illustrates a cross-sectional view of an alternative example packing in accordance with the teachings of this disclosure. 
     
    
    
     The figures are not to scale. Instead, the thickness of the layers or regions may be enlarged in the drawings. Although the figures show layers and regions with clean lines and boundaries, some or all of these lines and/or boundaries may be idealized. In reality, the boundaries and/or lines may be unobservable, blended, and/or irregular. In general, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts. As used herein, unless otherwise stated, the term “above” describes the relationship of two parts relative to Earth. A first part is above a second part, if the second part has at least one part between Earth and the first part. Likewise, as used herein, a first part is “below” a second part when the first part is closer to the Earth than the second part. As noted above, a first part can be above or below a second part with one or more of: other parts therebetween, without other parts therebetween, with the first and second parts touching, or without the first and second parts being in direct contact with one another. As used in this patent, stating that any part (e.g., a layer, film, area, region, or plate) is in any way on (e.g., positioned on, located on, disposed on, or formed on, etc.) another part, indicates that the referenced part is either in contact with the other part, or that the referenced part is above the other part with one or more intermediate part(s) located therebetween. As used herein, connection references (e.g., attached, coupled, connected, and joined) may include intermediate members between the elements referenced by the connection reference and/or relative movement between those elements unless otherwise indicated. As such, connection references do not necessarily infer that two elements are directly connected and/or in fixed relation to each other. As used herein, stating that any part is in “contact” with another part is defined to mean that there is no intermediate part between the two parts. 
     Unless specifically stated otherwise, descriptors such as “first,” “second,” “third,” etc. are used herein without imputing or otherwise indicating any meaning of priority, physical order, arrangement in a list, and/or ordering in any way, but are merely used as labels and/or arbitrary names to distinguish elements for ease of understanding the disclosed examples. In some examples, the descriptor “first” may be used to refer to an element in the detailed description, while the same element may be referred to in a claim with a different descriptor such as “second” or “third.” In such instances, it should be understood that such descriptors are used merely for identifying those elements distinctly that might, for example, otherwise share a same name. As used herein, “approximately” and “about” refer to dimensions that may not be exact due to manufacturing tolerances and/or other real world imperfections. 
     DETAILED DESCRIPTION 
     Industrial process plants (e.g., refineries, chemical plants, petrochemical plants, pharmaceutical plants, etc.) include process control loops to control temperatures, the flow of fluids, etc. In some examples, industrial control systems include control valves to manipulate a flowing fluid, such as gas, steam, water, or chemical compounds to compensate for load disturbances and maintain the regulated process variables as close as possible to desired set points. Control valves typically include packings to help maintain a seal within the valve to reduce leakage of the flowing fluid during operation. Minimizing the leakage via the packing helps to maintain environmental safety regulations and reduce loss of product for the industrial process plant. 
     Environmental standards for control valves continue to urge or require the improvement of packing designs in control valves to further reduce leakage. However, there are challenges related to designing packing systems. For example, increasing the stress (load) on the packing can generally reduce leakage. However, increasing the stress can also cause an increase in friction and wear of the packing, which results in an overall reduction in the operational life of the packing. Adding packing rings in the control valve, such as a duplex packing, can be effective in reducing leakage. However, the effectiveness of such packings is limited by the response of the packing rings to an applied load. In the case of multiple packing rings (e.g., duplex packings), an increase in stress does not result in a uniform increase in radial load throughout the packing. Instead, the radial load is typically highest in a single area of the packing. Therefore, simply adding packing rings in a control valve provides diminishing returns for reducing leakage. 
     Examples disclosed herein include a packing that has two or more packing rings that are independently loaded. In examples disclosed herein, two or more packing followers are nested inside each other and are loaded independently through the use of different springs and packing fasteners. In examples disclosed herein, a first packing ring and a first spring are inserted into a bonnet of a control valve followed by a first follower. In examples disclosed herein, the first follower is tightened until flush with the bonnet flange. In examples disclosed herein, a second packing ring and a second spring are inserted into the bonnet after the first follower. In examples disclosed herein, a second follower is inserted into the bonnet and fastened to either to the first follower or the bonnet flange. 
     In examples disclosed herein, the first follower applies a load to the first spring and the first packing ring. In examples disclosed herein, the load applied by the second follower is applied to the second spring and the second packing ring and supported by the first follower so that the load on the first packing ring does not increase upon installation of the second follower. In examples disclosed herein, the first spring and the second spring provide live loading to the first packing ring and the second packing ring, respectively. 
     In examples disclosed herein, the load applied to the first packing ring and the second packing ring are selected so that total load is balanced between the two packing rings, rather than one packing ring carrying a much higher load than the other as would be the case if they were not loaded independently. Examples disclosed herein result in a longer life for the packing system along with better sealing capability in the control valve. 
     “Including” and “comprising” (and all forms and tenses thereof) are used herein to be open ended terms. Thus, whenever a claim employs any form of “include” or “comprise” (e.g., comprises, includes, comprising, including, having, etc.) as a preamble or within a claim recitation of any kind, it is to be understood that additional elements, terms, etc. may be present without falling outside the scope of the corresponding claim or recitation. As used herein, when the phrase “at least” is used as the transition term in, for example, a preamble of a claim, it is open-ended in the same manner as the term “comprising” and “including” are open ended. The term “and/or” when used, for example, in a form such as A, B, and/or C refers to any combination or subset of A, B, C such as (1) A alone, (2) B alone, (3) C alone, (4) A with B, (5) A with C, (6) B with C, and (7) A with B and with C. As used herein in the context of describing structures, components, items, objects and/or things, the phrase “at least one of A and B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. Similarly, as used herein in the context of describing structures, components, items, objects and/or things, the phrase “at least one of A or B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. As used herein in the context of describing the performance or execution of processes, instructions, actions, activities and/or steps, the phrase “at least one of A and B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. Similarly, as used herein in the context of describing the performance or execution of processes, instructions, actions, activities and/or steps, the phrase “at least one of A or B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. 
     As used herein, singular references (e.g., “a”, “an”, “first”, “second”, etc.) do not exclude a plurality. The term “a” or “an” entity, as used herein, refers to one or more of that entity. The terms “a” (or “an”), “one or more”, and “at least one” can be used interchangeably herein. Furthermore, although individually listed, a plurality of means, elements or method actions may be implemented by, e.g., a single unit or processor. Additionally, although individual features may be included in different examples or claims, these may possibly be combined, and the inclusion in different examples or claims does not imply that a combination of features is not feasible and/or advantageous. 
       FIG. 1  is an illustration of an example control valve  100  in accordance with the teachings of this disclosure. The example control valve  100  includes an example valve body  102 , an example valve actuator  104 , an example valve controller  106 , and an example packing system  108 . In the illustrated example of  FIG. 1 , the valve body  102  includes the flow control member for the control valve  100 . In the illustrated example, the flow control member is a plug that is adjusted to allow a fluid to flow through the valve body  102  or to stop a fluid from flowing through the valve body  102 . However, in other examples, the control valve  100  may include any other flow control member such as a globe, a ball, a butterfly, etc. 
     The example packing system  108  of  FIG. 1  maintains a seal within the control valve  100  to reduce leakage of the process fluid in the valve body  102  during operation. In the illustrated example, the packing system  108  provides a seal around the stem of the valve actuator  104 . In some examples, the packing system  108  surrounds the outer surface of the stem to prevent any leakage of the fluid from the valve body  102 . An example packing system that may be included in the control valve  100  is described in further detail below in connection with  FIG. 3 . 
     In the illustrated example of  FIG. 1 , the control valve  100  illustrates an example of a control valve that may be used in accordance with the teachings of this disclosure. However, other valve types may additionally and/or alternatively be used in accordance with the teachings of this disclosure. For example, other control valves such as gate valves, butterfly valves, ball valves, etc. may include packing systems in accordance with the teachings of this disclosure. 
       FIG. 2  illustrates a cross-sectional view of an example known packing system  200  for a control valve. The known packing system  200  of  FIG. 2  includes a stem  202 , a bonnet  204 , a packing assembly  206 , a follower  208 , springs  210 A,  210 B, studs  212 A,  212 B, nuts  214 A,  214 B, and a packing washer  216 . 
     In  FIG. 2 , the insertion of the stem  202  though the bonnet  204  provides a potential path for fluid to leak from the valve body between the surfaces of the stem  202  and the bonnet  204 . The packing assembly  206  is engaged between the stem  202  and an internal bore of the bonnet  204  to provide a seal against fluid leakage. In  FIG. 2 , the packing assembly  206  expands in response to a load, and the expansion of the packing assembly  206  between the stem  202  and the internal bore of the bonnet  204  provides the seal to reduce fluid leaking from the bonnet  204 . In the illustrated example, the packing assembly  206  includes multiple packing rings. In some examples, the packing assembly  206  can include one packing ring, three packing rings, five packing rings, etc. The packing assembly  206  can include packing ring(s) that include graphite material, polytetrafluoroethylene (PFTE) material, etc. 
     The packing washer  216  is coupled between the packing assembly  206  and the follower  208 . The follower  208  is coupled to the packing washer  216  to apply a load to the packing assembly  206  to expand the material of the packing assembly  206  between the stem  202  and the internal bore of the bonnet  204 . The follower  208  compresses the packing assembly  206  along a longitudinal axis of the packing assembly  206  to cause the radial expansion of the material of the packing assembly  206 . In  FIG. 2 , the springs  210 A,  210 B provide the dynamic load to the follower  208 . The stiffness of the springs  210 A,  210 B determines the amount of load applied to the follower  208 . The springs  210 A,  210 B are coupled to the follower  208  to evenly distribute the load across the follower  208 . In  FIG. 2 , the studs  212 A,  212 B and the nuts  214 A,  214 B generate the load applied by the springs  210 A,  210 B. The studs  212 A,  212 B and the nuts  214 A,  214 B compress the springs  210 A,  210 B to generate the load applied to the follower  208  and the packing assembly  206 . Specifically, the tightening torque applied to the nuts  214 A,  214 B determines the load generated by the springs  210 A,  210 B. For example, an increase in the tightening torque applied to the nuts  214 A,  214 B increases the compression of the springs  210 A,  210 B, which increases the load applied to the follower  208 . The tightening torque applied to the nuts  214 A,  214 B can be adjusted to increase or decrease the load applied to the packing assembly  206  depending on the sealing needs for the valve. 
     Although the known packing system  200  of  FIG. 2  provides a seal against the fluids of a valve, the performance of the known packing system  200  may not provide a sufficiently tight seal between the stem  202  and the bonnet  204 . The known packing system  200  includes only one load that is applied to the packing assembly  206 . In some applications, the packing assembly  206  does not prevent all leakage from the valve. For example, some fluid may leak between the packing assembly  206  and the stem  202  as well as between the packing assembly  206  and the bonnet  204 . In  FIG. 2 , to create a tighter seal, the load applied to the packing assembly  206  must be increased. However, increasing the load on the packing assembly  206  also increases the friction and wear on the packing assembly  206 , which decreases the lifespan of the packing assembly  206 . In some examples where the packing assembly  206  includes multiple packing rings, increasing the load on the packing assembly  206  does not distribute the load evenly throughout the packing rings. In such examples, increasing the load on the packing assembly  206  increases the friction and wear unevenly between the packing rings of the packing assembly  206 , which decreases the lifespan of the packing assembly  206 . In  FIG. 2 , the known packing system  200  includes design constraints by only including one follower (e.g., the follower  208 ) and packing assembly (e.g., the packing assembly  206 ) to distribute load in the known packing system  200 . The known packing system  200  requires a tradeoff between increasing the load on the packing assembly  206  (and, thus, friction) for a tighter seal and more frequent replacement of the packing assembly  206 , or decreasing the load to improve the lifespan of the packing assembly  206  but increase the leakage through the packing assembly  206 . 
       FIG. 3  illustrates a cross-sectional view of an example packing system  300  in accordance with the teachings of this disclosure. In some examples, the packing system  300  may be implemented as the packing system  108  of  FIG. 1 . The example packing system  300  includes an example stem  302 , an example bonnet  304 , an example first packing ring  306 , an example first spring  308 , an example outer follower  310 , an example second packing ring  312 , an example second spring  314 , an example inner follower  316 , an example static seal  318 , example studs  320 A,  320 B, and example nuts  322 A,  322 B. 
     The first packing ring  306  is disposed in a bore  324  within the bonnet  304 . The first packing ring  306  is coupled to a first surface  326  (e.g., an outer surface) of the stem  302  and the bore  324  of the bonnet  304  to provide a seal against fluid leakage. In the illustrated example of  FIG. 3 , the first packing ring  306  expands in response to a load applied thereto, and the expansion of the first packing ring  306  between the stem  302  and the bore  324  of the bonnet  304  provides a seal to reduce fluid leaking from the valve body. In some examples, the first packing ring  306  can include graphite material, PFTE material, etc. In some examples, the first packing ring  306  can be a packing assembly that includes multiple packing rings. For example, the first packing ring  306  can include one packing ring, three packing rings, five packing rings, etc. 
     The first spring  308  is disposed in the bore  324  of the bonnet  304  and coupled to a second surface  328  (e.g., top surface or upper surface) of the first packing ring  306 . In some examples, the first spring  308  may include one or more wave springs, Belleville springs, etc. In the illustrated example, the outer follower  310  is disposed partially in the bore  324  of the bonnet  304  and coupled to a third surface  330  (e.g., top surface or upper surface) of the first spring  308 . The outer follower  310  is disposed partially outside of the bore  324  of the bonnet  304  and coupled to an outside surface  332  of the bonnet  304  (e.g., a flange of the bonnet  304 ). In some examples, the outer follower  310  is coupled to the bonnet  304  via the studs  320 A,  320 B and the nuts  322 A,  322 B. 
     The second packing ring  312  is disposed in a bore  334  of the outer follower  310  and coupled to a fourth surface  336  (e.g., top surface or upper surface) of the outer follower  310 . The second packing ring  312  is sized to closely fit within the bore  334  of the outer follower  310 . In the illustrated example, the second packing ring  312  has a different (e.g., smaller) diameter than the first packing ring  306  to fit within the bore  334  of the outer follower  310 . The second packing ring  312  is coupled to the first surface  326  of the stem  302  and an internal surface  338  of the bore  334  of the outer follower  310  to provide a seal against fluid leakage from the first packing ring  306 . In the illustrated example of  FIG. 3 , the second packing ring  312  expands in response to a load applied thereto, and the expansion of the second packing ring  312  between the stem  302  and the internal surface  338  of the bore  334  of the outer follower  310  provides a seal to reduce fluid leaking from between the first packing ring  306  and the stem  302 . In some examples, the second packing ring  312  can include graphite material, PFTE material, etc. In some examples, the second packing ring  312  can be a packing assembly that includes multiple packing rings. For example, the second packing ring  312  can include one packing ring, three packing rings, five packing rings, etc. 
     The example second spring  314  is disposed in the bore  334  of the outer follower  310  and coupled to a fifth surface  340  (e.g., top surface or upper surface) of the second packing ring  312 . Thus, the second spring  314  is disposed between the second packing ring  312  and the inner follower  316 . In some examples, the second spring  314  may include one or more wave springs, Belleville springs, etc. In the illustrated example, the inner follower  316  is disposed partially within the bore  324  of the bonnet  304  and coupled to a sixth surface  342  (e.g., top surface or upper surface) of the second spring  314 . The inner follower  316  is sized to fit within the bore  334  of the outer follower  310 . The inner follower  316  is disposed partially outside of the bore  324  of the bonnet  304  and coupled to an outside surface of the bonnet  304 . In the illustrated example, the inner follower  316  is coupled to the fourth surface  336  of the outer follower  310  outside of the bonnet  304 . In some examples, the inner follower  316  may be coupled to a flange of the bonnet  304 . In some examples, the inner follower  316  is coupled to the fourth surface  336  of the outer follower  310  or to the flange of the bonnet  304  via the studs  320 A,  320 B and the nuts  322 A,  322 B. 
     The static seal  318  is coupled to an outer surface  344  of the outer follower  310  and an inner surface  346  of the bonnet  304 . The static seal  318  prevents or reduces any leakage from between the first packing ring  306  and the bonnet  304 . In some examples, the first packing ring  306  may not completely prevent fluid leakage between the first packing ring  306  and bonnet  304 . Thus, the static seal  318  provides an additional seal between the outer follower  310  and the bonnet  304  to seal against any fluid that has leaked past the first packing ring  306 . In some examples, the static seal  318  includes an O-ring. However, other static seals may additionally and/or alternatively be used. 
     In the illustrated example of  FIG. 3 , the studs  320 A,  320 B and the nuts  322 A,  322 B generate the loads for the outer follower  310  and the inner follower  316 . The studs  320 A,  320 B and the nuts  322 A,  322 B apply a load to the outer follower  310  and the inner follower  316 . The outer follower  310  and the inner follower  316  compress the first spring  308  and the second spring  314  to transmit the loads to the first packing ring  306  and the second packing ring  312 , respectively. In the illustrated example, the first spring  308  is disposed between the first packing ring  306  and the outer follower  310 . The outer follower  310  applies a load to the first packing ring  306  via the first spring  308 . In the illustrated example, the load from the compression of the first spring  308  radially displaces (e.g., expands) the materials of the first packing ring  306  to create a seal to prevent leakage. 
     In the illustrated example, the second spring  314  is disposed between the second packing ring  312  and the inner follower  316 . The inner follower  316  applies a load to the second packing ring  312  via the second spring  314 . In the illustrated example, the load from the compression of the second spring  314  radially displaces (e.g., expands) the materials of the second packing ring  312  to create an additional seal in the valve to prevent leakage. In some examples, the first packing ring  306  may not completely prevent leakage from the valve between the first packing ring  306  and the stem  302  (e.g., creates a leakage path between the first packing ring  306  and the stem  302 ). The second packing ring  312  creates an additional seal between the second packing ring  312  and the stem  302  to seal against a portion of fluid leakage that passed the first packing ring  306 . 
     In the illustrated example, the load applied by the inner follower  316  is transmitted to the second spring  314  and the second packing ring  312  and is supported by the outer follower  310  so that the load on the first packing ring  306  is not significantly increased upon installation of the inner follower  316 . The two different followers (e.g., the outer follower  310  and the inner follower  316 ) allow for the first packing ring  306  and the second packing ring  312  to be independently loaded from one another (e.g., have two different loads). 
     In some examples, the tightening torque applied to the nuts  322 A,  322 B determines the different values/amounts of the loads applied by the first spring  308  and the second spring  314 . For example, an increase in the torque applied to the nuts  322 A,  322 B increases the compression force applied by the outer follower  310  and the inner follower  316  to the first spring  308  and the second spring  314 , respectively, which increases the different loads applied the first packing ring  306  and the second packing ring  312 , respectively. In some examples, the tightening torque applied to the nuts  322 A,  322 B can be adjusted to increase or decrease the different loads applied to the first packing ring  306  and the second packing ring  312  depending on the sealing needs for the valve. 
     In some examples, the selection of the loads on first packing ring  306  and the second packing ring  312  is such that, rather than one packing ring (or packing assembly) carrying a much higher load than the other packing ring (or packing assembly) as would be the case if they were not loaded independently, the overall load is balanced between the first packing ring  306  and the second packing ring  312 . In some examples, the balance of loads between the first packing ring  306  and the second packing ring  312  results in a longer life for both the first packing ring  306  and the second packing ring  312  while still increasing the load to improve the sealing capability. In some examples, the packing system  300  of  FIG. 3  can include additional packing rings (e.g., more than 2). In some examples, the packing system  300  of  FIG. 3  can include additional packing assemblies (e.g., more than 2). In such examples, the packing system  300  also includes additional followers (e.g., one for each additional packing ring or packing assembly) to control the load applied to the packing rings or packing assemblies. In some examples, increasing the number of packing rings or packing assemblies may further improve the sealing capability of the packing system  300 . 
       FIG. 4  illustrates a cross-sectional view of an alternative example packing system  400  in accordance with the teachings of this disclosure. In some examples, the packing system  400  may be implemented as the packing system  108  of  FIG. 1 . The packing system  400  includes the stem  302 , the bonnet  304 , the first packing ring  306 , the first spring  308 , an outer follower  410 , the second packing ring  312 , the second spring  314 , an inner follower  416 , and the static seal  318 . The packing system  400  further includes studs  420 A,  420 B,  420 C,  420 D and nuts  422 A,  422 B,  422 C,  422 D. 
     In the illustrated example, the packing system  400  includes two different sets of fasteners (e.g., one set for the outer follower  410  and a different set for the inner follower  416 ). In such examples, the first set of fasteners (the studs  420 A,  420 B and the nuts  422 A,  422 B) apply a first load on the outer follower  410 , and a second set of fasteners (the studs  420 C,  420 D and the nuts  422 C,  422 D) apply a second load on the inner follower  416 . In some examples, the outer follower  410  is coupled to the flange of the bonnet  304  using the studs  420 A,  420 B and the nuts  422 A,  422 B to generate the first load, and the inner follower  416  is coupled to the fourth surface  336  of the outer follower  410  using the studs  420 C,  420 D and the nuts  422 C,  422 D to generate the second load. 
     From the foregoing, it will be appreciated that example methods, apparatus and articles of manufacture have been disclosed that improve a valve packing by using independently loaded packing rings. The example methods, apparatus and articles of manufacture use multiple packing rings that are loaded independently to balance the total load between the packing rings instead of one packing ring carrying a significantly higher load. The example methods, apparatus and articles of manufacture improve the sealing capability in a valve by increasing the load applied to the packing system, which creates a tighter seal. The example methods, apparatus and articles of manufacture also increase the life for the packing system by load balancing between multiple packing rings. 
     Example methods, apparatus, systems, and articles of manufacture for valve packings having independently loaded packing rings are disclosed herein. Further examples and combinations thereof include the following: 
     Example 1 includes a packing assembly for a fluid valve, the packing assembly comprising a first packing ring, a first follower to be disposed at least partially within a bore of a bonnet of the fluid valve to apply a first load to the first packing ring, a second packing ring sized to fit within a bore of the first follower, and a second follower to be disposed at least partially within the bore of the first follower to apply a second load to the second packing ring within the bore of the first follower. 
     Example 2 includes the packing assembly of example 1, further including a first spring to be disposed within the bore of the bonnet of the fluid valve between the first packing ring and the first follower. 
     Example 3 includes the packing assembly of example 2, further including a second spring sized to fit within the bore of the first follower between the second packing ring and the second follower. 
     Example 4 includes the packing assembly of example 3, wherein the first follower applies the first load via the first spring and the second follower applies the second load via the second spring. 
     Example 5 includes the packing assembly of example 1, wherein the first follower is to be disposed at least partially outside of the bore of the bonnet of the fluid valve and to be coupled to an outside surface of the bonnet. 
     Example 6 includes the packing assembly of example 1, wherein the second follower is to be disposed at least partially outside of the bore of the bonnet of the fluid valve and to be coupled to at least one of an outside surface of the bonnet or a surface of the first follower that is disposed at least partially outside of the bore of the bonnet. 
     Example 7 includes an apparatus to seal a valve, the apparatus comprising a first packing ring disposed in a valve bonnet and coupled to a first surface of a first spring disposed in the valve bonnet, a first follower coupled to a second surface of the first spring, the second surface of the first spring opposite of the first surface of the first spring, the first follower coupled to a flange of the valve bonnet, a second packing ring disposed on a surface of the first follower, the surface of the first follower spaced apart from the first spring, the second packing ring coupled to a first surface of a second spring, and a second follower coupled to a second surface of the second spring, the second surface of the second spring opposite of the first surface of the second spring, the second follower coupled to at least one of the first follower and the flange. 
     Example 8 includes the apparatus of example 7, wherein the first follower is coupled to the flange via first bolts, and wherein the second follower is coupled to the at least one of the first follower or the flange of the valve bonnet via second bolts. 
     Example 9 includes the apparatus of example 8, wherein the first bolts apply a first load on the first follower and the second bolts apply a second load on the second follower. 
     Example 10 includes the apparatus of example 9, wherein the first bolts apply the first load via the first spring and the second bolts apply the second load via the second spring. 
     Example 11 includes the apparatus of example 10, wherein the first load on the first packing ring is applied substantially independent from the second load on the second packing ring. 
     Example 12 includes the apparatus of example 7, wherein the first packing ring is to allow a leakage including a portion of fluid in the valve, the first packing ring to cause a first leakage path and a second leakage path for the leakage. 
     Example 13 includes the apparatus of example 12, wherein the second packing ring is to prevent fluid leaking from the first leakage path. 
     Example 14 includes the apparatus of example 12, further including a static seal coupled to an outer surface of the first follower and an inner surface of the valve bonnet to prevent fluid leaking from the second leakage path. 
     Example 15 includes the apparatus of example 14, wherein the static seal includes an O-ring. 
     Example 16 includes the apparatus of example 7, wherein the first spring and the second spring include at least one of a wave spring or a Belleville spring. 
     Example 17 includes an apparatus to seal a valve, the apparatus comprising a first packing ring disposed in a valve bonnet to prevent first leakage from the valve in response to a first load, and a second packing ring disposed in the valve bonnet to prevent second leakage from the valve in response to a second load, the second packing ring having a different diameter from the first packing ring, and the first load substantially independent from the second load. 
     Example 18 includes the apparatus of example 17, wherein the first load prevents the first leakage from the valve through the first packing ring and the second load prevents the second leakage from the valve through the second packing ring, the first load having a different value than the second load. 
     Example 19 includes the apparatus of example 18, wherein the first load displaces materials of the first packing ring to create a seal in the valve to prevent the first leakage. 
     Example 20 includes the apparatus of example 18, wherein the second load displaces materials of the second packing ring to create a seal in the valve to prevent the second leakage, the second leakage including a portion of the first leakage from the first packing ring. 
     Although certain example methods, apparatus and articles of manufacture have been disclosed herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the claims of this patent. 
     The following claims are hereby incorporated into this Detailed Description by this reference, with each claim standing on its own as a separate embodiment of the present disclosure.