Patent Publication Number: US-2023151887-A1

Title: Non-contacting seal including an interference fit seal ring

Description:
BACKGROUND 
     Exemplary embodiments pertain to the art of seals and, in particular to a non-contact seals and seal assemblies that include an interference fit seal ring. 
     Non-contacting seals are typically used to seal a fluid in a shafted, rotating machine. Examples of such machines include compressors, pumps, blowers and other rotating machines. 
     In general, non-contacting seals operate by providing a seal between two rings. The two rings can rotate relative to each other. In general, one of the rings (seal ring) is axially movable and is urged by a compression spring or a bellows into face-to-face contact with the other ring, the mating ring, which is fixed against axial movement. Depending on the configuration, one of the seal or mating rings is mated to the rotating shaft/rotor of the rotating machine and rotates with it. The rotating ring can be mated to the rotor via a shaft sleeve. For example, in some instances of a bellow seal, the seal ring rotates but in other instances the mating ring rotates. 
     In operation, a layer of gas is developed between the two rings that forms a seal while allowing the rings to move relative to one another without contacting each other. The gas layer is formed from process or sealing gas injected into the non-contacting seal. 
     SUMMARY 
     Disclosed is a seal assembly for use with a rotating machine that includes a rotating shaft. The seal assembly includes a mating ring having a mating ring seal face and a seal ring defining an interior member having an axially extending annular surface and a radially extending seal ring seal face. The assembly also includes a first bellows that urges the seal ring toward the mating ring. In this embodiment, at least one of the mating and seal ring seal faces includes one or more grooves or surface features formed thereon that cause a gas to be drawn between the mating ring and the seal ring due to relative rotation between the seal ring and the mating ring and form a gas layer between the mating ring and the seal ring that urges the seal ring away from the mating ring. The assembly also includes an annular seal ring shell defining an exterior member having a foot portion defining an axially extending engagement surface, the axially extending engagement surface of the foot portion and the axially extending annular surface of the seal ring in direct interference fit along an interference diameter Ds between the axially extending engagement surface of the foot portion and the axially extending annular surface of the seal ring, the seal ring shell further including a radially extending shin portion connected to the foot portion and located radially outward of the foot portion, the foot portion at its engagement surface having an axial length greater than the axial length of the shin portion. 
     In any prior assembly, the grooves or surface features can draw the gas from an inner diameter of the seal ring toward an outer diameter of the seal ring. Alternatively, the grooves or surface features could draw the gas from an outer diameter of the seal ring toward an inner diameter of the seal ring. The exact direction will depend on the context in which the seal assembly is implemented and some assemblies could have 2 seals, one that draws gas in one direction and the other opposite or both in the same direction. 
     In any prior embodiment, the seal ring shell can further include an axially extending thigh portion connected to the shin portion and located radially outward of the shin portion, a hub extending radially outward from the connection of the shin portion with the thigh portion; and a back piece secured to the thigh portion. The first bellows can be secured to the back piece. 
     In any prior embodiment, the rotating machine is a pump, a compressor, a blower or a mixer. 
     In any prior embodiment, the engagement surface can be positioned so as to have a near-zero net moment about the center of gravity due to such engagement. 
     In any prior embodiment, the mating ring seal face can have a mating ring seal face width and the seal ring seal face can have a seal ring seal face width that is smaller than the a mating ring seal face width. 
     In any prior embodiment, the mating ring seal face width is 1.1 to 3 times larger than the seal ring seal face width. 
     In any prior embodiment, the assembly can include second bellows that urges the first bellows and the seal ring toward the mating ring. 
     Also disclosed is a dual pressurized non-contacting seal assembly for use with a rotating machine that includes a rotating shaft. The assembly includes a process side seal and an atmosphere side non-contacting seal. Either or both seals include some or all of the above combinations of elements in the prior assemblies. This assembly can further include housing surrounding the process side and atmosphere side non-contacting seals. This housing can include a gas inlet channel through which sealing gas can pass from outside the seal assembly into a region between the process side and gas atmosphere side non-contacting seals. 
     Additional technical features and benefits are realized through the techniques of the present invention. Embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed subject matter. For a better understanding, refer to the detailed description and to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The specifics of the exclusive rights described herein are particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the embodiments of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG.  1    is a cross-section of a non-contacting seal that includes an interference fit seal ring and a single bellows; 
         FIGS.  2   a - 2   d    show non-limiting examples of seal face surface texture patterns that can be provided on faces of the various rings in any embodiment of the seals or seal assemblies disclosed herein; 
         FIG.  3 A  is a cross-sectional view of a seal ring assembly of a non-contacting seal that includes a bellows; 
         FIG.  3 B  is a cross-sectional view of an alternative primary ring and an alternative primary ring shell embodying the features of the present invention; 
         FIG.  4    is an enlarged cross-sectional view of the seal ring and shell of the seal ring assembly of  FIG.  3   ; 
         FIG.  5    is a cross-sectional free-body diagram of the seal ring of  FIG.  4   , showing forces and pressure distribution under full operating temperature and external pressure applied by process/barrier gas; 
         FIG.  6    is cross-sectional free-body diagram of the seal ring of  FIG.  4   , showing contact forces and contact pressure distribution under full operating temperature and internal pressure applied by process/barrier fluid; 
         FIG.  7    is a cross-section of a non-contacting seal that includes an interference fit primary ring and two bellows; 
         FIG.  8    is a cross-section of dual non-contacting seal assembly according to one embodiment; 
         FIG.  9    is a cross-section of dual non-contacting seal assembly according to one embodiment; 
         FIG.  10    shows gas flow paths applicable to the embodiments of  FIGS.  8  and  9   ; 
         FIG.  11    is a cross sections of a non-contacting seal that includes a double bellow configuration on the process side including an interference fit and a single bellows configuration on the atmospheric side without interference fit; 
         FIG.  12    is a cross sections of a non-contacting seal that includes a double bellow configuration on the process side including an interference fit and a single bellows configuration on the atmospheric side with interference fit; 
         FIG.  13    is a cross-section of dual non-contacting seal assembly according to one embodiment; 
         FIG.  14    is a cross-section of an inward pumping dual non-contacting seal assembly according to one embodiment; 
         FIG.  15    is a cross-section of an inward pumping dual non-contacting seal assembly according to one embodiment; and 
         FIG.  16    is a cross-section of an inward pumping dual non-contacting seal assembly according to one embodiment. 
     
    
    
     The diagrams depicted herein are illustrative. There can be many variations to the diagram or the operations described therein without departing from the spirit of the invention. For instance, the actions can be performed in a differing order or actions can be added, deleted or modified. Also, the term “coupled” and variations thereof describes having a communications path between two elements and does not imply a direct connection between the elements with no intervening elements/connections between them. All of these variations are considered a part of the specification. 
     DETAILED DESCRIPTION 
     A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. 
     It has been discovered by the inventors hereof that where a non-contacting seal is operated in locations where a fluid is being sealed in a rotating machine at an elevated temperature, the sealed fluid can form a layer of deposits around the outer diameter of the seal ring. The formation of deposits in such a location can make the face of the seal ring less “flat.” This in turn can lead to high sealing gas consumption rate and, in some cases, an eventual loss of non-contacting operation due to loss of gas film thickness and stiffness. One case where such an effect can be exhibited in the case of a dual pressurized non-contacting seal that includes a process side seal and an atmosphere side seal. In particular, such effects can be seen on the process side seal. 
     Herein disclosed is a seal that includes a seal ring that is resistant to such loss of flatness (e.g., deformation) because it is interference fitted to an annular shell. 
     One of the seal rings or mating rings includes surface texture patterns so that it can draw gas between rings to cause a separation, or lift off between the rings to allow for non-contacting operation. While the specific illustrate surface texture patterns are grooves, this is not meant as limiting and any type of surface pattern could be sued so long as it supports the above described separation or lift off. As will be more fully understood based at least in part on the disclosure herein, such a seal can have hydraulically balanced seal faces with a single bellows. Further, as compared to existing technologies that used a non-interference seal ring, an expensive clean flow of fluid to the process side seal interface that was necessary to prevent or delay the formation of deposited material can be eliminated. 
     In some instances the seal disclosed herein can be a standalone seal. In other instances it can be used as part of a seal system such as a dual pressurized non-contacting seal that includes two seals. Regardless, the seals can be used in pumps, blowers, or other rotating machines. 
     Herein, the term shaft will generally be used to refer to a shaft of any rotating machine and the shaft may or may not include a sleeve thereon. In the case where a sleeve is provided, the term “shaft” shall include the combination of the shaft and the sleeve. 
     Aspects of the present invention are applicable in all types of seals but may be especially beneficial in seals operating in elevated temperature fluids. As an example, high temperature crude oil corrosiveness is becoming a major concern in refineries due to an increased use of sour crudes containing the above organic acids and Sulphur compounds. As such, some or all of the metallurgy of the seals may be corrosion resistant alloys such as Alloy-718 metallurgy, which is resistant to the corrosive attack even at high temperature. In addition, corrosion resistant alloys retains their inherent strength much better at high temperatures, e.g. 800° F. or higher. Such alloys, however, may have a different differential thermal expansion coefficient between an corrosion resistant shell and a commonly used seal ring material is much higher than that with low corrosion resistant alloys. Therefore, a much higher interference is required between them in order to keep the shell properly secured at elevated temperature operations. 
     Turning now to an overview of technologies that are more specifically relevant to aspects of the invention, a non-contacting separation seal is provided. 
       FIG.  1    shows a cross-section of a seal  1  according to one embodiment. The seal  1  is shown is a single seal configuration but it shall be understood that the seal  1  could be used in combination with another seal form a dual non-contacting seal assembly. 
     The seal  1  is a dry gas seal in one embodiment and, as such, operates by developing a layer of gas between a seal ring  14  and a mating ring  16  to due relative motion between the primary ring  14  and the mating ring  16 . In particular, the layer of sealing gas is formed between seal faces  15 ,  17  of the seal and mating rings  14 ,  16 , respectively, and keeps gas within a chamber  4  from escaping therefrom along a shaft  2 . The sealing gas layer is formed from process or gas injected into the process side of the non-contacting seal and may be sourced from the chamber  4 . 
     The seal  1  also includes a bellows  18  that urges the seal ring  14  towards the mating ring  16 . One of the faces  15 ,  17  of the seal ring or mating ring  14 ,  16  can comprise a surface feature textured area, such that the rotation of the rings relative to one another causes sealing gas to be pumped between the faces  15 ,  17  to generate a force which opposes that applied by hydraulic forces and the bellows  18 . Such sealing gas also keeps the faces  15 ,  17  from contacting one another. 
     The sealing gas layer, when formed, separates the seal faces  15 ,  17  from each other and opposes the hydraulic forces and force from the bellows  18 . Herein, at least one of the seal faces  15 ,  17  can include surface texture features formed therein. The surface texture features can be configured such that they draw gas in from an outer diameter of one of the faces towards it center/inner diameter. Such a configuration is applicable to situations where pressure at the outer diameter is greater than at the inner diameter. In the opposite case (e.g., where the pressure is higher at the inner diameter as shown, for example, in  FIGS.  8   / 9 ), the surface texture patterns an extend outwardly from the inner diameter to the outer diameter. 
       FIG.  2   a    shows an example of generic seal face  200  that can be a seal face of either a seal ring or a mating ring ( 14 ,  16 ). The surface texture patterns/grooves  202  in this face  200  are unidirectional and extend from an outer diameter OD towards an inner diameter ID. 
       FIG.  2   b    shows another example of a generic seal face  204  that can be a seal face of either a seal ring or a mating ring ( 14 ,  16 ). The surface texture patterns/grooves  206  in this face  204  are also unidirectional and extend from an inner diameter ID towards an outer diameter OD. 
       FIG.  2   c    shows another example of a generic seal face  208  that can be a seal face of either a seal ring or a mating ring ( 14 ,  16 ). The surface texture features/grooves  210  in this face  208  are bidirectional and extend from an outer diameter OD towards an inner diameter ID. 
       FIG.  2   d    shows another example of a generic seal face  220  that can be a seal face of either a seal ring or a mating ring ( 14 ,  16 ). The surface texture features  230  in this face  208  are bidirectional and extend from an inner diameter ID towards an outer diameter OD. 
     In any of these cases, as gas enters the surface texture features/grooves it is compressed as faces rotate relative one another to create the lift off force that causes the faces to separate. In any of the above examples, the surface texture patterns/grooves can have a depth from 2 to 14 microns (μm). 
     Referring again to  FIG.  1   , as shown the bellows  18  is connected to and rotates with the shaft  2 . The shaft  2  is centered and rotates about a longitudinal axis  20 . The seal ring  14  is connected to the bellows  18  and, as such, can move axially relative to the shaft  2  while rotating with it. The bellows  18  can be connected to the shaft  2  through a sleeve  23 . The seal  1  includes a housing  25  that can be attached to a body  27  of a rotating machine. The mating ring  16  is attached to housing  25  such that they maintain a fixed relationship to one another. As will be understood, as the shaft  2  moves axially along the longitudinal axis  20  during operation, so will the bellows  18  and the seal ring  14  while the mating ring  16  remains still. The skilled artisan will realize that the compression due to the bellows  18  and the lift off due to the compressed gas can be balanced to achieve a stable distance between the faces  15 ,  17  during operation. 
     In the arrangement of  FIG.  1    it is contemplated that the surface texture pattern or grooves will extend from the inner diameter towards the outer diameter of one of the faces  15 ,  17 . Also, in the arrangement of  FIG.  1   , the body  27  can be part of, for example, a mixer, a fan, a turbine and the like. As shown, the seal  1  includes a single bellows  18  but as discussed below, this is not meant as limiting but may be beneficial in that in some prior systems, the seal required two bellows to hydraulically balance the seal faces to allow for reverse pressure capability. Having only a single bellows will reduce complexity. 
     As discussed above, in prior systems a non-contacting seal is operated in locations where a fluid is being sealed in a rotating machine at an elevated temperature, the sealed fluid can form a layer of deposits around the outer diameter of the seal ring  14 . The formation of deposits in such a location can make the face of the seal ring less “flat.” 
     To avoid such distortion the seal ring  14  can be held by a seal ring assembly  60  embodying the present invention. With reference to  FIGS.  3   a ,  3   b   , and  4 , the seal ring assembly  60  includes a shell  62 , the seal ring  14  and bellows  18 . A rotating shaft  2 , centered about a longitudinal axis  20 , extends through the seal ring assembly  60 . It should be noted that the term axial and axially as used in describing the embodiments mean longitudinally along the axis  20  of the shaft  2 . The terms radial and radially as used in describing the embodiments mean in a plane generally perpendicular to the axis  20  of the shaft  2  toward and away from the axis. 
     The seal ring  14  defines an axially extending annular outer surface  53  and a radially extending seal face  15 . The annular outer surface  53  is a section of the outer surface of the seal ring  14  adapted for engagement with the shell  62 , to be discussed further below. It should be noted that the annular outer surface  53  is not necessarily a radially outermost surface, as evidenced by the annular surface adjacent to the seal face  15  located more radially outward. The seal face  15  of the seal ring  14  is adapted for engagement with a corresponding seal face of a mating ring. Possible materials for construction of the seal ring  14  include carbon, impregnated carbon, tungsten carbide (WC), silicon carbide (SiC), silicon/carbon graphite composite, and bronze. 
     The shell  62  is made up of two pieces, a front-piece  22  and a back-piece  24 , which are welded together at their junction  26 . Possible materials for construction of the primary ring shell pieces  22  and  24  include Alloy 718, Alloy 625, Alloy 620, Alloy 20, Alloy C-276, Alloy 42, AM 350, and stainless steel. Preferably the material for construction of primary ring shell pieces  22  and  24  is a corrosion resistant alloy. The bellows  18  is welded to the back-piece shell  24  at their junction  28 . The bellows  18  can be of single or multi-ply construction. Possible materials for construction of the bellows  18  include Alloy 718, Alloy X-750, Alloy C-276, AM350, Alloy 20, and stainless steel. Preferably the material for construction of the bellows  18  is a high strength corrosion resistant alloy. 
     Hereinafter, such seals will be referred to as the high temperature and corrosive application seal or “HTC” seal for short. 
     The above described two-piece shell arrangement utilizes a geometrical shape that may be quite intricate but can be machined into the front-piece  22 . Such a configuration can achieve seal face stability over the operating temperature and pressure ranges having minimum amount of face coning or distortion in either direction, which is commonly known as “OD” or “ID high.” Such enhanced face stability, in turn, results in reduced leakage and longer seal life. The enhanced, two-piece design can be used to attach a seal face to most traditional seal designs (i.e., pusher) with the similar performance benefits or other adaptive hardware. 
     The front-piece shell  22  is shown to have an engaging foot portion  30  into which the seal ring  14  is interference-fitted. The engaging foot portion  30  defines an axially extending engagement surface  32  for interference-fit engagement with outer surface  53  of the seal ring  14 . The foot portion  30  has an inner foot portion  34 , a middle foot portion  36 , and an outer foot portion  38 . The contact region of the engagement surface  32  at the back of the engaging foot portion is the heel  40  and its front part is the toe  42 . Between the inner foot portion  34  and an upper shell region or thigh portion  44 , there is a recess  46 , whereas the annular region joining the thigh portion  44  and the foot portion  30  is the shin portion  48 . The shin portion  48  extends radially from the foot portion  30 . A front shell piece  22  with the hub portion  50  can be included as shown in  FIG.  3   b    but is omitted is shown by line  51 . in  FIG.  3   . The shin portion  48  has an axial length Ls that allows the shin portion to flex upon the seal ring  14  interference-fitted into the front piece shell  22 . The inner foot portion  34  at its engagement surface, near the heal  40 , has an axial length Lh. The foot portion  30  at its engagement surface  32  has an axial length Lf. The axial length Lf of tie foot portion  30  at its engagement surface is preferably greater than the axial length Ls of the shin portion. This increased contact region between the foot portion  30  and the seal ring  14 , as compared to prior art seal designs, allows the pressure at the interface to be less concentrated at one particular point. 
     Furthermore, two possible primary ring nose configurations are shown in  FIGS.  3   a  and  3   b   , one having a blunt nose  54  as shown in  FIG.  3   a    and the other having a step nose  56  as shown in  FIG.  3   b   . The blunt-nose  54  configuration is typically used with the hard seal ring materials e.g. silicon and tungsten carbides, whereas the step-nose  56  configuration is typically used with the softer materials like carbon. Also,  FIGS.  3   a  and  3   b    show two possible configurations of the back-piece shell  24 . In the conventional configuration as shown in  FIG.  3   a   , this back-piece shell  24  inside diameter (ID) is extended low at  58  towards the inside diameter of seal ring  14 . In the second configuration as shown in  FIG.  3   b   , the back-piece shell  24  is truncated at  60  to have a higher ID. 
     To control the contract pressure distribution caused by the interference fit between the foot portion and the seal ring mating surface, preferably, the ratio (Lh/Lf) of inner foot portion length Lh at its engagement surface to foot portion length Lf at its engagement surface is greater than 0.5. More preferably, the ratio (Lh/Lf) of inner foot portion length Lh at its engagement surface to foot portion length Lf at its engagement surface is between 0.500 and 1.000. It is important to distribute this contact pressure about the body center of rotation to achieve a near zero net moment on the seal ring. This is necessary to maintain face flatness as the application pressure and temperature change. Traditional shell designs, having an inner foot portion length to foot portion length at their engagement surfaces ratio closer to zero (0), do not have an evenly distributed contact pressure and exhibit difficulty controlling face flatness. 
     The dimensions (e.g. lengths and thicknesses) of all these aforesaid regions described in the previous paragraphs, including the seal ring dimensions, are treated as parameters for the optimization process and are iteratively designed to get optimal performance characteristics. These control parameters allow for precise adjustment to control the interference contact pressure, the contact stress, and face stability for a variety of primary ring geometries and materials over a wide range of operating temperatures and pressures or a specific set of temperatures and pressures. The optimized design is thermally insensitive and has an axially constant contact stress distribution in the interference-fit region. The control parameters: inner foot portion  34 , outer foot portion  38 , shin portion  48 , hub portion  50  and thigh portion  44 , can be adjusted in thickness and length to accommodate varying seal ring geometries and materials. Seal geometries that tend to be more asymmetrical about the cross-sectional center of gravity/rotation, would require more asymmetry in the lengths and thicknesses of these control parameters. The relative location of the front-piece shell with respect to the seal ring is also a design control parameter to further manage face coning or distortion due to relaxation of the interference-fit caused by changes in temperature. 
     In one embodiment, the front-piece shell  22  is joined to the back-piece shell  24  after the initial interference-fitting of the front piece shell  22  with the seal ring  14 . This process eliminates bending stresses and moments in the area of the hinge that are present in the traditional one-piece arrangements. 
     In the embodiment of  FIGS.  3  and  4    (as well as others that include a seal ring assembly  60 ), the nominal interference diameter DS, which is also called the sealing diameter, is designed to be very close to the Mean Effective Diameter EDZ of the bellows as shown in  FIG.  3   . The Effective Diameter or “ED” of a bellows is a fictitious diameter up to which the applied pressure effectively penetrates to exert a closing force on the seal. This is akin to the “balance diameter” of a pusher-type seal. The Mean Effective Diameter is a theoretical effective diameter at zero differential pressure applied on the primary ring  14 , which is taken to be the arithmetic mean of the bellows core outside and inside diameters. The seal face  15  of the seal ring  14  is designed so that the Mean Effective Diameter position gives rise to an initial balance at zero differential pressure in which the Mean Effective Diameter EDZ passes through the seal face  15  as shown in  FIG.  3   . 
     The seal ring  14  can be asymmetrical and balanced. The illustrated seal ring  14  is considered asymmetrical because the two sides of the seal ring  14  located axially from its center of gravity CG are not symmetrical. The illustrated seal ring  14  is considered balanced because the Mean Effective Diameter EDZ of the bellows  18  passes through the seal face  15  at zero differential pressure. 
     When external pressure differential is applied, the bellows effective diameter shifts downward to a lower value EDOD, as shown in  FIGS.  3  and  5   . Again, the seal face has been so designed that the above ED shift increases the balance ratio to an adequate level, which is based on the prior experience with conventional non-contacting seals, so that leakage is minimized 
     In more detail,  FIG.  5    shows the external pressure acting on the seal ring  14 . As seen, while the full external pressure acts on the overhung portion of the seal ring  14  outside the engaging foot portion  30  of the shell  62 , on the face  15 , however, the pressure decreases to a zero differential level at the ID. Although the face pressure profile is shown to be linear, in actuality, it could be curved inward or outward, depending on the effects of the seal face surface texturing features (or grooves). 
     The net axial force (including force from lift off created by the surface texture features acting on the seal ring  14  tends to cause axial slippage compress the bellows. between the seal ring  14  and the shell  62  at the contact region and push the seal ring  14  towards the back-piece shell  24 . 
     Similarly, when the internal differential pressure is applied, the bellows effective diameter shift upward from EDZ to EDID, as shown in  FIGS.  3  and  6   . Similar to the external pressure situation, the seal face design ensures that the new balance ratio at the internal pressure meets the design requirement. 
     By locating the inference diameter DS very close to the effective diameter EDZ of the bellows at zero differential pressure, the net axial force in the axial direction is minimized under internal pressure and external pressure as provided above. Preferably, the interference diameter DS is within plus and minus 10% (+10% and −10%) of the effective diameter EDZ of the bellows at zero differential pressure. More preferably, the interference diameter DS is within +6% and −6% of the effective diameter EDZ of the bellows at zero pressure. It is important to minimize the hydraulic forces acting in an axial direction to move the seal ring relative to the shell. As these forces increase, the amount of contact force provided by the interference fit must be increased to prevent movement. 
     As discussed above, while the interference fit diameter does not change, the effective diameter does vary with system pressure. Depending on the application, it may be desirable to bias the interference diameter toward either extreme of the effective diameter shift range. 
     To assemble the seal ring assembly  60  as shown in  FIG.  3   , the seal ring  14  is first interference-fitted into the front-piece shell  22  that is then welded to the back-piece shell  24  and the bellows  18 . The shape of the front-piece shell  22  has been optimized in such a way that the extent of the contact region between its engaging foot portion  30  and the seal ring  14  is almost 100%, extending from its heel  40  to the toe  42 . In contrast, a conventionally interference-fitted primary-ring assembly will have a relatively concentrated contact near the heel  40 , extending over about 20% of the corresponding foot portion length. 
     In the above discussion, a single bellows  18  has been utilized. In one embodiment, multiple bellows may be utilized. For example, with reference to  FIG.  7   , in an alternative embodiment, a seal  700  is provided that includes generally the same elements as the seal  1  of  FIG.  1    but has a second bellows  718 . The second bellows  718 , as shown, is connected between the sleeve  23  and the first bellows  18 . In particular, a ring  702  or other carrier can be provided between the first and second bellows  18 ,  718 . The ring  702  is moveable relative to the shaft  2  in one embodiment. 
     The above described embodiments have been illustrated as being related to a single seal system. In such systems, the sealed gas typically serves as gas that is being drawn between the rings. In other embodiments, a seal system having two or more seals is provided. One or more of the seals are HTC seals as disclosed herein and shown, for example, in  FIGS.  1  and  7   . 
     In one embodiment there is provided a dual, non-contacting seal system/assembly for a rotating machine configured to inhibit the emission of process fluid between a housing and a rotating shaft. The seal system can include a process side non-contacting seal, an atmosphere side non-contacting seal and a separation gas supply subsystem that provides a separation gas to an area between the seals. The process side seal can be an HTC seal and the atmosphere side seal can be any type of non-contacting seal including an HTC seal. In such a system, the process side non-contacting seal can include a mating ring having a process side mating ring seal face and a seal ring defining an interior member having an axially extending annular surface and a radially extending process side seal ring face. One or more bellows are provided that urge the first seal ring toward a mating ring. One or both of the seal rings and mating rings can include surface texture features that cause lift-off between the faces of the rings due to relative rotation between them. The process side seal ring is interference fit to an annular seal ring shell as described above. The seal assembly includes a housing surrounding the process side and atmosphere side non-contacting seals and including a gas inlet channel through which gas can pass from outside the seal assembly into a region between the process side and atmosphere side non-contacting seals. This gas is drawn, in normal operation as more fully described below, outwardly from the shaft through the process side and atmosphere side non-contacting seals and directed in to a process chamber and to atmosphere, respectively. 
     With reference now to  FIGS.  8 - 10   , an assembly  800  including a process side non-contacting seal  801  and an atmosphere side non-contacting seal  802  is illustrated. It shall be understood that the exact configuration shown is not required and for generality the terms first and second seals can replace process and atmosphere herein in any configuration. The assembly include a housing  804  that surrounds portions of the first and second dry gas seals  801 ,  802 . The housing  804  can be attached to a body  27  of any type or rotating machine that includes as rotating shaft  2  having a shaft axis  20 . For example, the body  27  can be a pump body. The housing  804  surrounds portions of the first and second dry gas process and atmosphere side non-contacting seals  801 ,  802  and defines a gas inlet channel  840  through which gas can pass from outside the seal assembly into a region  842  (gas chamber) between the second seals  801 ,  802 . The manner in which the gas travels from the inlet channel  840 , into the gas chamber  842  and though the first and second seals  801 ,  802  is discussed in more detail below. 
     In the illustrated embodiment, the first and second seals are process and atmospheric sided seals. Thus, as shown, both the process side and atmosphere side seals have two rings, one of which rotates with the shaft  2 . To that end, a sleeve  823  is provided that is configured and arranged so that it carries or otherwise supports a rotating ring for each seal. The sleeve  823  is connected to and rotates with the shaft  2  It shall be understood that while the sleeve is shown as a single piece that couples rotating rings of the process side and atmosphere side non-contacting seals  801 ,  802  to the shaft  2 , the sleeve  823  could be formed of multiple pieces. 
     The process side non-contacting seal  801  can be a seal as shown in either  FIG.  1    or  FIG.  7    or variations thereof. In more detail, the process side non-contacting seal  801  includes a seal ring  14  and a mating ring  16  configured as above. Due to relative motion between the seal ring  14  and the mating ring  16  a layer of gas is developed between them. In particular, the layer of gas is formed between seal faces  15 ,  17  of the seal and mating rings  14 ,  16 , respectively, and keeps gas within a chamber  4  from escaping therefrom along a shaft  2 . The gas layer is formed from process or sealing gas injected into the non-contacting seal and may be sourced from the chamber  4 . 
     The process side seal  801  can include one or more bellows. As shown, the seal  801  includes bellows  18  that urges the seal ring  14  towards the mating ring  16 . Of course, additional bellows could be used to urge the rings together. For example, the process side seal  801  can include a second bellows  718  arranged relative to the first bellows  18  in a manner that is the same or similar to that shown in  FIG.  7   . 
     One of the faces  15 ,  17  of the seal ring or mating ring  14 ,  16  can comprise a grooved or textures area, such that the rotation of the rings relative to one another causes seal gas to be pumped between the faces  15 ,  17  to generate a force which opposes that applied by the bellows  18 . Such gas also keeps the faces  15 ,  17  from contacting one another. 
     The gas layer, when formed, separates the seals faces  15 ,  17  from each other and opposes the bellows  18 . Herein, at least one of the seal faces  15 ,  17  can include grooves or other surface features formed therein. The grooves can be configured such that they draw gas in from an inner diameter of one of the face towards it outer diameter. Such a configuration is applicable to situations where pressure at the inner diameter is greater than at the outer diameter. Examples of such grooves are shown in  FIGS.  2   b   / 2   d.  As discussed above, In any of these cases, as gas enters the grooves is compressed as one face rotates to create the lift off force that causes the faces to separate. 
     Referring again to  FIG.  8   , as shown the bellows  18  is connected to and rotates with the shaft  2 . The shaft  2  is centered and rotates about a longitudinal axis  20 . The seal ring  14  is connected to the bellows  18  and, as such, can rotate with and move axially relative to the shaft  2 . The bellows  18  can be connected to the shaft  2  through a sleeve  823 . As shown, an optional attachment element  824  connects the bellows  18  to the sleeve  823  but this could be omitted and the bellows  18  could be connected directly to the sleeve  823 . 
     The assembly includes a housing  804  that can be attached to a body  27  of a rotating machine. The mating ring  16  is attached to housing  804  such that they maintain a fixed relationship to one another. As will be understood, as the shaft  2  moves axially along the longitudinal axis  20  during operation, so will the bellows  18  while the mating ring  16  remains still. The skilled artisan will realize that the compression due to the bellows  18  and the lift off due to the compressed gas can be balanced to achieve a stable distance between the faces  15 ,  17  during operation. 
     As discussed above, in prior systems a non-contacting seal is operated in locations where a fluid is being sealed in a rotating machine at an elevated temperature, the sealed fluid can form a layer deposits around the outer diameter of the seal ring. The formation of deposits in such a location can make the face of the seal ring less “flat.” 
     To avoid such distortion the seal ring  14  can be held by a seal ring assembly  60  embodying the present invention and that was discussed above with respect to  FIGS.  3 - 6    above. All of the disclosure in the above is, thus, applicable to the seal ring assembly  60  shown in  FIG.  8   . 
     Similar to the process side seal  801 , the atmosphere side seal  802  includes an atmosphere side seal ring  860  and an atmosphere side mating ring  862 . The atmosphere side seal ring  860  is coupled to the shaft  2  and rotates with it. As shown, the atmosphere side seal ring  860  is connected in a conventional manner that does not include the particular seal ring assembly  60  of the process side seal  802 . The skilled artisan will realize that the atmosphere side seal  802  could be so configured. Such a configuration is shown in  FIG.  8   . The assemblies in  FIGS.  8  and  9    work in a similar manner and both have the sealing gas flow paths described in relation to  FIG.  10    below. 
     Similar to the process side seal one of the faces  861 ,  863  of the seal ring or mating rings  860 ,  862  of the atmosphere side seal  802  can comprise a grooved or textured area, such that the rotation of the rings relative to one another causes seal gas to be pumped between the faces thereof to generate a force which opposes that applied to the seal ring  860  by a biasing device. Such gas also keeps the faces of the atmosphere side seal from contacting one another. As shown in  FIG.  9   , the biasing device is a bellows  890 . In alternative embodiments, the biasing device can be a spring or an equivalent thereof. The seal ring assembly  860  is connected to and biased by biasing member  890  which is coupled to the sleeve  823 . 
     In operation, the rotating shaft  2  can be operably coupled to a pump impeller or other device (not shown) disposed in a process cavity  880  of a rotating machine. Process fluid present in the process cavity  880  can be sealed from the environment by a seal assembly  800 . While seal assembly  800  is depicted and described with two seals  801 ,  802 , a greater or fewer number of seals are contemplated. Additionally, in some embodiments, a shroud, bushing, labyrinth, or clearance seal can extend over a radial opening formed between the rotating shaft  2  and the housing  804 , thereby further inhibiting the free flow of process fluid from the process cavity  880  to the environment. 
     As shown the process side bellows  18  and the biasing member  890  are both connected to and rotate with the shaft  2 . The shaft  2  is centered and rotates about a longitudinal axis  20 . The seal ring  14  is connected to the bellows  18  and, as such, can rotate with and move axially relative to the shaft  2 . The bellows  18  can be connected to the shaft  2  through the sleeve  823 . As shown, an optional attachment element  824  connects the bellows  18  to the sleeve  823  but this could be omitted and the bellows  18  could be connected directly to the sleeve  823 . 
     Similarly, seal ring assembly  860  is connected to the biasing member  890  and, as such, can rotate with and move axially relative to the shaft  2 . The biasing member  890  can be connected to the shaft  2  through the sleeve  823 . As shown, an optional attachment element  825  connects the bellows  18  to the sleeve  823  but this could be omitted and the bellows  18  could be connected directly to the sleeve  823 . 
     A fluidic path can be defined between the rotating rings (e.g., seal rings  14 ,  860 ) and the stationary rings (e.g., mating rings  16 ,  862 ) through which a sealing gas can flow (as depicted in  FIG.  10    by a series of arrows). The sealing gas can be any appropriately dense gas, such as carbon dioxide (CO2), nitrogen (N2), air, steam, or other gases. The sealing gas can be introduced into the fluidic path via a sealing gas inlet  840 . Thereafter, the sealing gas can flow through a conduit into the gas chamber  842 , where it can be divided into a process side seal gas flow and an atmosphere side seal gas flow. The process side seal gas flow can flow between the seal ring and mating ring  14 ,  16  of the first seal  801  and into the process chamber  880 . The atmosphere side seal gas flow can flow between the seal ring and mating ring  860 ,  862  of the atmosphere side seal  802  and be released to the environment. In both the process side and atmosphere side gas flows the gas flows radially outward from the shaft  2  between the seal faces. 
       FIG.  9    shows another embodiment that is similar to that shown in  FIG.  8   . In this embodiment, the process side seal  801  includes two bellows,  18  and  718  The configuration of these two bellows is the same or similar to that shown in  FIG.  7    above. In this embodiment, the assembly include a housing  804  that surrounds portions of the first and second dry gas seals  801 ,  802 . The housing  804  can be attached to a body  27  of any type or rotating machine that includes as rotating shaft  2  having a shaft axis  20 . For example, the body  27  can be a pump body. The housing  804  surrounds portions of the first and second (process and atmosphere side) non-contacting seals  801 ,  802  and defines a gas inlet channel  840  through which gas can pass from outside the seal assembly into a region  842  (gas chamber) between the second seals  801 ,  802 . The manner in which the gas travels from the inlet channel  840 , into the gas chamber  842  and though the first and second seals  801 ,  802  is discussed in more detail below. 
     In the illustrated embodiment, the first and second seals are process and atmospheric sided seals. Thus, as shown, both the process side and atmosphere side seals have two rings, one of which rotates with the shaft  2 . To that end, a sleeve  823  is provided that is configured and arranged so that it carries or otherwise supports a rotating ring for each seal. The sleeve  823  is connected to and rotates with the shaft  2  It shall be understood that while the sleeve is shown as a single piece that couples rotating rings of the process side and atmosphere side non-contacting seals  801 ,  802  to the shaft  2 , the sleeve  823  could be formed of multiple pieces. 
     The seal ring  14  can be held by a seal ring assembly  60  embodying the present invention and that was discussed above with respect to  FIGS.  3 - 6    above. All of the disclosure in the above is, thus, applicable to the seal ring assembly  60  shown in  FIG.  8     
     In more detail, the process side non-contacting seal  801  includes a seal ring  14  and a mating ring  16  configured as above. The seal ring  14  can be held by a seal ring assembly  60  embodying the present invention and that was discussed above with respect to  FIGS.  3 - 6    above. All of the disclosure in the above is, thus, applicable to the seal ring assembly  60  shown in  FIG.  8     
     Due to relative motion between the seal ring  14  and the mating ring  16  a layer of gas is developed between them. In particular, the layer of gas is formed between seal faces  15 ,  17  of the seal and mating rings  14 ,  16 , respectively, and keeps gas within a chamber  4  from escaping therefrom along a shaft  2 . The gas layer is formed from process or sealing gas injected into the non-contacting seal and may be sourced from the chamber  4 . 
     The process side seal  801  show includes two bellows  18 ,  718  that urge the seal ring  14  towards the mating ring  16 . One of the faces  15 ,  17  of the seal ring or mating ring  14 ,  16  can comprise a grooved or textured area, such that the rotation of the rings relative to one another causes seal gas to be pumped between the faces  15 ,  17  to generate a force which opposes that applied by the bellows  18 . Such gas also keeps the faces  15 ,  17  from contacting one another. 
     The gas layer, when formed, separates the seals faces  15 ,  17  from each other and opposes the bellows  18 . Herein, at least one of the seal faces  15 ,  17  can include grooves or other surface features formed therein. The grooves can be configured such that they draw gas in from an inner diameter of one of the face towards it center/inner diameter. Examples of such grooves are shown in  FIGS.  2   b   / 2   d.  As discussed above, in any of these cases, as gas enters the grooves is compressed as one face rotates to create the lift off force that causes the faces to separate. 
     Referring again to  FIG.  11   , as shown the bellows  18 ,  718  are connected to and rotates with the shaft  2 . The shaft  2  is centered and rotates about a longitudinal axis  20 . The seal ring  14  is connected to the bellows  18 ,  718  and, as such, can rotate with and move axially relative to the shaft  2 . The bellows  18  can be connected to the shaft  2  through a sleeve  823 . 
     As shown, an optional attachment element  824  connects the bellows  18  to the sleeve  823  but this could be omitted and the bellows  18  could be connected directly to the sleeve  823 . 
     The assembly includes a housing  804  that can be attached to a body  27  of a rotating machine. The mating ring  16  is attached to housing  804  such that they maintain a fixed relationship to one another. As will be understood, as the shaft  2  moves axially along the longitudinal axis  20  during operation, so will the bellows  18  while the mating ring  16  remains still. The skilled artisan will realize that the compression due to the bellows  18 ,  718  and the lift off due to the compressed gas can be balanced to achieve a stable distance between the faces  15 ,  17  during operation. 
     Similar to the process side seal  801 , the atmosphere side seal  802  includes an atmosphere side seal ring  860  and an atmosphere side mating ring  862 . The atmosphere side seal ring  860  is coupled to the shaft  2  and rotates with it. As shown, the atmosphere side seal ring  860  is connected in a conventional manner that does not include the particular seal ring assembly  60  of the process side seal  802 . The skilled artisan will realize that the atmosphere side seal  802  could be so configured which a seal ring assembly  60  as is shown in  FIG.  12   . 
     Similar to the process side seal one of the faces  861 ,  863  of the seal ring or mating rings  860 ,  862  of the atmosphere side seal  802  can comprise a grooved or textured area, such that the rotation of the rings relative to one another causes seal gas to be pumped between the faces thereof to generate a force which opposes that applied to the seal ring  860  by a biasing device. Such gas also keeps the faces of the atmosphere side seal from contacting one another. As shown in both  FIGS.  11  and  12   , the biasing device is a bellows  890 . In alternative embodiments, the biasing device can be a spring or an equivalent thereof. The seal ring assembly  860  is connected to and biased by biasing member  890  which is coupled to the sleeve  823 . 
     In operation, the rotating shaft  2  can be operably coupled to a pump impeller or other device (not shown) disposed in a process cavity  880  of a rotating machine. Process fluid present in the process cavity  880  can be sealed from the environment by a seal assembly  800 . While seal assembly  800  is depicted and described with two seals  801 ,  802 , a greater or fewer number of seals are contemplated. Additionally, in some embodiments, a shroud, bushing, labyrinth, or clearance seal can extend over a radial opening formed between the rotating shaft  2  and the housing  804 , thereby further inhibiting the free flow of process fluid from the process cavity  880  to the environment. 
     As shown the process side bellows  18  and the biasing member  890  are both connected to and rotate with the shaft  2 . The shaft  2  is centered and rotates about a longitudinal axis  20 . The seal ring  14  is connected to the bellows  18  and, as such, can rotate with and move axially relative to the shaft  2 . The bellows  18  can be connected to the shaft  2  through the sleeve  823 . As shown, an optional attachment element  824  connects the bellows  18  to the sleeve  823  but this could be omitted and the bellows  18  could be connected directly to the sleeve  823 . 
     Similarly, seal ring assembly  860  is connected to the biasing member  890  and, as such, can rotate with and move axially relative to the shaft  2 . The biasing member  890  can be connected to the shaft  2  through the sleeve  823 . As shown, an optional attachment element  825  connects the bellows  18  to the sleeve  823  but this could be omitted and the bellows  18  could be connected directly to the sleeve  823 . 
     As shown in  FIG.  13   , alternative paths can be envisioned where at least in the atmosphere side seal the sealing gas flows between seal faces of the rings of the atmosphere side seal  1100  in a direction that is radially inward toward the shaft  2 . In  FIG.  11   , the process side seal  801  is the same or similar to that shown in  FIGS.  8  and  9   . In this embodiment, the atmosphere side seal  1100  includes a rotating mating ring  902  that is coupled to a sleeve  904 . The sleeve  904 , in the manner of the sleeve  823  above, rotates with the shaft and thus, so does the mating ring  902 . The mating ring  902  includes a rotating face  903 . 
     The atmosphere side seal  1100  also includes a seal ring  904  that is moveably coupled to the housing  1104 . The housing  1104  is connected to the body  27  of the rotating machine and as shown is formed at two parts but could be formed as a single element or multiple elements. The seal ring  904  is moveably connected to the housing  1104  by a biasing member  1125  that in this case is illustrated as a spring. The seal ring  904  includes a stationary face  905 . The interaction of the spring to the sealing gas film formed between faces  903 ,  905  is similar to that described above. 
     Herein, at least one of the seal faces  903 ,  905  can include grooves or surface texture features formed therein. The features can be configured such that they draw gas in from an outer diameter of one of the face towards it center/inner diameter. Such a configuration is applicable to situations where pressure at the outer diameter is greater than at the inner diameter. Examples of such grooves are shown in  FIG.  2   a   . As discussed above, In any of these cases, as gas enters the feature is compressed as one face rotates to create the lift off force that causes the faces to separate and to compress the biasing member  1125 . Arrow A illustrates the direction for gas flow through the second seal  1100 . 
     The housing  1104  surrounds portions of the process side and atmosphere side non-contacting seals  801 ,  1100  and defines a gas inlet channel  1140  through which gas can pass from outside the seal assembly into a region  1142  (gas chamber) between the process side and atmosphere side non-contacting seals  801 ,  1100 . Similar to the above, a fluidic path can be defined between the rotating rings (e.g., rings  14 ,  902 ) and the stationary rings (e.g., rings  16 ,  904 ) through which a sealing gas can flow. The sealing gas can be any appropriately dense gas, such as carbon dioxide (CO2), nitrogen (N2), air, steam, or other gases. The sealing gas can be introduced into the fluidic path via the gas inlet channel  1140 . Thereafter, the sealing gas can flow through a conduit into the gas chamber  1142 , where it can be divided into a process side sealing gas flow and an atmosphere side sealing gas flow. The process side sealing gas flow can flow through the process side seal  801  and into the process cavity  880 . The atmosphere side sealing gas flows between the rings  902 ,  904  of the atmosphere side seal  802  in direction A and is then released to the environment. 
     It is contemplated that the configurations shown above could be “reversed” so that the seals of, for example,  FIGS.  8 - 12    are inward pumping rather than outward pumping. That is, and as shown in  FIGS.  14 - 16    below, the seal assembly can be configured such that it “pumps” the sealing gas through the process and atmosphere side seals towards the shaft as opposed to away from it as illustrated in  FIG.  10   , for example. 
     With reference now to  FIGS.  12 - 14   , an assembly  800  including a process side non-contacting seal  801  and an atmosphere side non-contacting seal  802  is illustrated. In all of these seals, the seal rings of both the process side non-contacting seal  801  and an atmosphere side non-contacting seal  802  are coupled to the housing  804 . In all cases, the seal ring of the primary is connected by one or more bellows to the housing  804 . In this manner, the seal ring can be urged toward the mating rings. The mating rings on the atmosphere side non-contacting seal are connect to and rotate with the shaft  2  via a sleeve  1400 . The sleeve  1400  can support both mating rings  16 ,  862  and can be fixedly attached to the shaft  2  in known manners. It shall be understood that while the sleeve  1400  is shown as a single piece that couples rotating rings of the process side and atmosphere side non-contacting seals  801 ,  802  to the shaft  2 , the sleeve  1400  could be formed of multiple pieces. 
     It shall be understood that the exact configuration shown is not required and for generality the terms first and second seals can replace process and atmosphere herein in any configuration. 
     The assembly includes a housing  804  that surrounds portions of the first and second dry gas seals  801 ,  802 . The housing  804  can be attached to a body  27  of any type or rotating machine that includes as rotating shaft  2  having a shaft axis  20  either directly or with an intermediate ring  1402  as shown. For example, the body  27  can be a pump body. 
     The housing  804  surrounds portions of the first and second dry gas process and atmosphere side non-contacting seals  801 ,  802  and defines a gas inlet channel  840  through which gas can pass from outside the seal assembly into a region  842  (gas chamber) between the second seals  801 ,  802 . The manner in which the gas travels from the inlet channel  840 , into the gas chamber  842  and though the first and second seals  801 ,  802  is generally opposite to that as described above. That is, in the embodiments in  FIGS.  12 - 14    the gas flows through the first and second seals  801 ,  802  from an outer diameter of the seals (and rings that form them) towards the shaft  2  (e.g., towards the inner diameter of the seals and rings that form them). 
     In the illustrated embodiment, the first and second seals are process and atmospheric sided seals. Thus, as shown, both the process side and atmosphere side seals have two rings, one of which rotates with the shaft  2 . It shall be understood that while the sleeve is shown as a single piece that couples rotating rings of the process side and atmosphere side non-contacting seals  801 ,  802  to the shaft  2 , the sleeve  823  could be formed of multiple pieces. 
     The process side non-contacting seal  801  includes a seal ring  14  and a mating ring  16  configured as above. Due to relative motion between the seal ring  14  and the mating ring  16  a layer of gas is developed between them. In particular, the layer of gas is formed between seal faces  15 ,  17  of the seal and mating rings  14 ,  16 , respectively, and keeps gas within a chamber  4  from escaping therefrom along a shaft  2 . The gas layer is formed from process or sealing gas injected into the non-contacting seal and may be sourced from the chamber  4 . 
     The process side seal  801  can include one or more bellows. As shown, the seal  801  includes bellows  18  that urges the seal ring  14  towards the mating ring  16 . Of course, additional bellows could be used to urge the rings together. For example, the process side seal  801  can include a second bellows  718  ( FIG.  16   ) arranged relative to the first bellows  18  in a manner that is the same or similar to that shown in  FIG.  7   . The bellows  18 / 718  can be attached to the housing  804 /ring  1402  by an optional connection element  842   
     One of the faces  15 ,  17  of the seal ring or mating ring  14 ,  16  can comprise a grooved or textures area, such that the rotation of the rings relative to one another causes seal gas to be pumped between the faces  15 ,  17  to generate a force which opposes that applied by the bellows  18 . Such gas also keeps the faces  15 ,  17  from contacting one another. 
     The gas layer, when formed, separates the seals faces  15 ,  17  from each other and opposes the bellows  18 . Herein, at least one of the seal faces  15 ,  17  can include grooves or other surface features formed therein. The grooves can be configured such that they draw gas in from an outer diameter of one of the face towards it center/inner diameter. Examples of such grooves are shown in  FIGS.  2   a   / 2   c.  Thus, the direction of gas flow through the seals as in the direction A shown in both  FIGS.  13 - 16   . In any of these cases, as gas enters the grooves/surface features it is compressed as one face rotates to create the lift off force that causes the faces to separate. 
     In all of  FIGS.  14 - 16   , as shown the bellows  18 / 718  are connected housing  804  and do not rotate with shaft. 
     The shaft  2  is centered and rotates about a longitudinal axis  20 . The seal ring  14  is connected to the bellows  18  and, as such, can move axially relative to the shaft  2 . As shown, an optional attachment element  824  connects the bellows  18 / 718  to the housing  804 / 1402  but this could be omitted in certain cases. 
     The mating ring  16  is attached shaft as described above. As will be understood, as the shaft  2  moves axially along the longitudinal axis  20  during operation, mating ring  16 . Thus, the mating ring  16  moves with but not relative to the shaft  2 . The skilled artisan will realize that the compression due to the bellows  18  and the lift off due to the compressed gas can be balanced to achieve a stable distance between the faces  15 ,  17  during operation. 
     In  FIG.  14 - 16   , the seal ring  14  can be held by a seal ring assembly  60  embodying the present invention and that was discussed above with respect to  FIGS.  3 - 6    above. All of the disclosure in the above is, thus, applicable to the seal ring assemblies  60  shown in any of  FIGS.  14 - 16   . 
     Similar to the process side seal  801 , the atmosphere side seal  802  includes an atmosphere side seal ring  860  and an atmosphere side mating ring  862 . The atmosphere side seal ring  860  is coupled to the body  804  and does not rotates with the shaft. As shown, the atmosphere side seal ring  860  is connected with a seal ring assembly  60  as described above. However, this is not required and, as shown in  FIG.  15   , the seal ring  860  of the process side seal  802  can be connected in the conventional manner 
     Similar to the process side seal one of the faces  861 ,  863  of the seal ring or mating rings  860 ,  862  of the atmosphere side seal  802  can comprise a grooved or textured area, such that the rotation of the rings relative to one another causes seal gas to be pumped between the faces thereof to generate a force which opposes that applied to the seal ring  860  by a biasing device. Such gas also keeps the faces of the atmosphere side seal from contacting one another. As shown in  FIGS.  14 - 16   , the biasing device is a bellows  890 . In alternative embodiments, the biasing device can be a spring or an equivalent thereof. The seal ring assembly  60  is connected to and biased by biasing member  890  which is coupled to the housing  804 . 
     In operation, the rotating shaft  2  can be operably coupled to a pump impeller or other device (not shown) disposed in a process cavity  880  of a rotating machine. Process fluid present in the process cavity  880  can be sealed from the environment by a seal assembly  800 . While seal assembly  800  is depicted and described with two seals  801 ,  802 , a greater or fewer number of seals are contemplated. Additionally, in some embodiments, a shroud, bushing, labyrinth, or clearance seal can extend over a radial opening formed between the rotating shaft  2  and the housing  804 , thereby further inhibiting the free flow of process fluid from the process cavity  880  to the environment. 
     Various embodiments of the invention have been described herein with reference to the related drawings. Alternative embodiments of the invention can be devised without departing from the scope of this invention. Various connections and positional relationships (e.g., over, below, adjacent, etc.) are set forth between elements in the following description and in the drawings. These connections and/or positional relationships, unless specified otherwise, can be direct or indirect, and the present invention is not intended to be limiting in this respect. Accordingly, a coupling of entities can refer to either a direct or an indirect coupling, and a positional relationship between entities can be a direct or indirect positional relationship. Thus, any coupling or connection herein may later be called direct in the claims below even if not specifically recited in that manner above. Moreover, the various tasks and process steps described herein can be incorporated into a more comprehensive procedure or process having additional steps or functionality not described in detail herein. 
     The term “about” is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof. 
     While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims.