Abstract:
An apparatus is disclosed in one embodiment of the invention as including an annular seal (e.g., an o-ring) and a backup ring to provide support to the annular seal. A gland is provided to accommodate the backup ring and the annular seal. The gland has a contact surface which is adapted to contact a corresponding contact surface of the backup ring upon inserting the backup ring into the gland. The diameters of the contact surfaces of the backup ring and gland are sized such that the contact surface of the backup ring radially interferes with the contact surface of the gland, thereby urging the backup ring out of the gland. A retention mechanism, such as interlocking grooves, protrusions, ridges, notches, slots, or the like may be provided in the backup ring and gland respectively to prevent the backup ring from completely exiting the gland.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to mechanical seals, and more particularly to self-energized backup rings for mechanical seals such as o-rings. 
     2. Description of the Related Art 
     Mechanical seals are used extensively to join systems or mechanical elements together to prevent leakage, contain pressure, or exclude contamination. O-rings are one of the most commonly used mechanical seals because of their simplicity and reliability. An o-ring is an elastomeric loop having a round (or rounded) cross-section that is designed to fit in a groove or gland in one or more sealing faces. The o-ring is compressed as the sealing faces are urged together, creating a seal at the interface. O-rings may be designed to have different diameters, cross-sectional areas, and cross-sectional shapes for different applications. Similarly, the glands or grooves they reside in may be designed to have different shapes and sizes. 
     In general, the pressure an o-ring is able to resist is directly related to the clearance gap between the sealing faces. The larger the gap, the less pressure the o-ring is able to resist without the aid of an external support. This is because the o-ring may begin to extrude into the clearance gap and cause damage to the o-ring as pressures are increased above a certain threshold. Various techniques may be used to reduce the o-ring&#39;s tendency to extrude, such as decreasing the clearance gap, selecting o-ring materials with an increased modulus of elasticity, or using backup rings to fill the clearance gap and thereby prevent the o-ring from extruding into the gap. Backup rings are a common choice for preventing extrusion and may be used in applications where pressures exceed 1500 psi. 
     When system pressure exceeds 1500 psi, there are generally two choices for producing an acceptable seal. The first and most costly choice is to maintain very tight machining tolerances on the mating components. The second more economical choice is to provide a backup ring to reduce o-ring extrusion into the clearance gap. This allows the mating components to be machined with normal tolerances. 
     While advantageous and effective, conventional backup rings may have various shortcomings. For example, some backup rings may be energized by the o-ring, meaning that compressing the o-ring also urges the backup ring into the clearance gap. While effective in some applications, such backup rings may not fill the clearance gap completely, be ineffective to fill larger gaps, or not function adequately at very high pressures. This may allow the o-ring to extrude into any remaining gap or be pinched between the backup ring and the sealing face. Furthermore, it may be difficult to retain current backup rings within the gland, especially in face seal applications. That is, prior to joining the mating surfaces, current backup rings may be easily dislodged from the gland, particularly in face seal applications. 
     In view of the foregoing, what is needed is an improved backup ring that improves many of the shortcomings of the prior art. Ideally, a backup ring would be self-energized rather than energized by the o-ring. Such a backup ring would also ideally bridge large gaps while still being effective at very high pressures. Further needed is a backup ring that is easily retained within the gland and may also help to retain the o-ring within the gland, particularly in face seal applications. Yet further needed is a backup ring that is effective to seal very high pressures with very little pressure exerted between the sealing faces. 
     SUMMARY OF THE INVENTION 
     The present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available backup rings for annular seals. Accordingly, the present invention has been developed to provide an improved backup ring for annular seals such as o-rings. The features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by practice of the invention as set forth hereinafter. 
     Consistent with the foregoing and in accordance with the invention as embodied and broadly described herein, an apparatus is disclosed in one embodiment of the invention as including an annular seal (e.g., an o-ring) and a backup ring to provide support to the annular seal. A gland is provided to accommodate the backup ring and the annular seal. The gland has a contact surface that is adapted to contact a corresponding contact surface of the backup ring upon inserting the backup ring into the gland. The diameters of the contact surfaces of the backup ring and the gland are sized such that they radially interfere with one another, thereby urging the backup ring out of the gland. A retention mechanism, such as interlocking grooves, protrusions, ridges, notches, slots, or the like may be incorporated into the backup ring and the gland respectively to prevent the backup ring from completely exiting the gland. 
     In selected embodiments, the contact surfaces of the backup ring and gland respectively are along their outside diameters. In other embodiments, the contact surfaces of the backup ring and gland are along their inside diameters. In certain embodiments, the backup ring and gland together create a dovetail-shaped recess to retain the annular seal within the gland. In certain embodiments, the backup ring is fabricated from at least one of a metal, a metal alloy, a plastic, a polymer, and hardened rubber. In selected embodiments, the annular seal is one of a face seal and a tapered seal. 
     In another aspect of the invention, a method in accordance with the invention may include providing a backup ring to provide support to an annular seal. The backup ring may be inserted into a gland. The diameter of the backup ring may be sized to radially interfere with the gland, thereby urging the backup ring out of the gland. The backup ring may nevertheless be retained at least partially within the gland. 
     In another aspect of the invention, an apparatus in accordance with the invention may include a backup ring to provide support to an annular seal. A gland is provided to accommodate the backup ring and the annular seal. The diameters of the backup ring and gland are sized to generate hoop stress in the backup ring upon inserting the backup ring into the gland. This hoop stress urges the backup ring out of the gland. A retention mechanism is provided to prevent the backup ring from completely exiting the gland. 
     The present invention provides a novel backup ring for mechanical seals. The features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by practice of the invention as set forth hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through use of the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view of one embodiment of a backup ring in accordance with the invention, incorporated into a face seal; 
         FIG. 2  is an enlarged cross-sectional view of the backup ring and face seal of  FIG. 1 ; 
         FIG. 3  is an enlarged cross-sectional view of the backup ring and face seal of  FIG. 1  when the clearance gap is very small; 
         FIG. 4  is an enlarged cross-sectional view of the backup ring and face seal of  FIG. 1  when the clearance gap is relatively large; 
         FIG. 5  is an enlarged cross-sectional view of one embodiment of a face seal utilizing dual backup rings; 
         FIG. 6  is an enlarged cross-sectional view of another embodiment of a backup ring in a face seal; 
         FIG. 7  is an enlarged cross-sectional view of another embodiment of a face seal utilizing dual backup rings; 
         FIG. 8  is a cross-sectional view of another embodiment of a backup ring incorporated into a tapered seal; and 
         FIG. 9  is an enlarged cross-sectional view of the backup ring and tapered seal of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It will be readily understood that the components of the present invention, as generally described and illustrated in the Figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of apparatus and methods in accordance with the present invention, as represented in the Figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of certain examples of presently contemplated embodiments in accordance with the invention. The presently described embodiments will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. 
     Referring to  FIG. 1 , one embodiment of a face seal  10  incorporating a self-energized backup ring  12  in accordance with the invention is illustrated. As shown, the face seal  10  may include an annular seal  14 , such as an o-ring  14 , residing in a gland  16  formed in one of two faces  18   a ,  18   b , or mating surfaces  18   a ,  18   b . The self-energized backup ring  12  may also reside in the gland  16  and may provide support to the annular seal  14  to prevent extrusion thereof into any clearance gap that may exist between the mating surfaces  18   a ,  18   b . Ideally, the backup ring  12  will fill the clearance gap as much as possible to prevent the extrusion. 
     The annular seal  14  may be fabricated from any suitable material including natural rubbers, synthetic rubbers, or other natural, synthetic, or semi-synthetic elastomers. The choice of material may ultimately depend on criteria such as temperature, sealing pressure, lubrication requirements, or the like associated with the application. The annular seal  14  may have any number of profiles, including circular, square, x-shaped, or other profiles known to those of skill in the art. Similarly, the self-energized backup ring  12  may be fabricated from any material having suitable hardness and resiliency to support the annular seal  14 , such as various metals, metal alloys, plastics, hardened rubbers, polymers, or the like. 
     Referring to  FIG. 2 , prior to joining the mating surfaces  18   a ,  18   b  together, a top surface  20  of the annular seal  14  may reside at a position above the mating surface  18   b . Upon bringing the mating surfaces  18   a ,  18   b  together, the annular seal  14  may be compressed to generate a seal at the interface. The size of the annular seal  14  and the distance it protrudes from the mating surface  18   b  prior to being compressed are design criteria known to those of skill in the art. 
     A self-energized backup ring  12  in accordance with the invention may reside within the gland  16  and be urged in a generally upward direction  22  out of the gland  16 . This may be accomplished by providing a backup ring  12  with an outside diameter that is slightly larger than the outside diameter of the gland  16 . This will create radial interference between the two contact surfaces  24 ,  26 . This radial interference, in combination with the angled orientation of the contact surfaces  24 ,  26  (characterized by an angle  28 ) will generate force urging the backup ring  12  in the direction  22  relative to the mating surface  18   b . The size of the angle  28  and the amount of radial interference between the contact surfaces  24 ,  26  may be adjusted to vary the force urging the backup ring  12  in the direction  22 . For example, a larger angle  28  may tend to generate greater force in the direction  22 . In selected embodiments, the contact surfaces  24 ,  26  may be machined, polished, or lubricated to reduce friction between the contact surfaces  24 ,  26 , thereby increasing the backup ring&#39;s propensity to move in the direction  22 . 
     Due to the radial interference between the backup ring  12  and the gland  16 , the backup ring  12  may tend to exit the gland  16  altogether absent some device or mechanism to prevent the exit. Thus, in selected embodiments, a retention mechanism may be provided to retain the backup ring  12  within the gland  16 . In selected embodiments, this retention mechanism may include a surface feature  30 , such as a ridge, protrusion, ledge, groove, or the like, incorporated into the gland  16 . This surface feature  30  may engage a corresponding surface feature  32 , such as a ridge, protrusion, ledge, groove, or the like, incorporated into the backup ring  12 . 
     The surface feature  30  of the gland  16  may be designed (e.g., sized, shaped, etc.) to allow the backup ring  12  to be installed into (e.g., snapped into) the surface feature  30 , while preventing the backup ring  12  from completely exiting the gland  16 . Thus, in selected embodiments, the surface feature  30  may include a chamfer or rounded surface to allow the backup ring  12  to be installed into the gland  16 . The surface features  30 ,  32  may allow downward movement of the backup ring  12  relative to the mating surface  18   b  until the backup ring  12  nears or contacts the bottom of the gland  16 . Similarly, the surface features  30 ,  32  may allow upward movement of the backup ring  12  relative to the mating surface  18   b  until the surface features  30 ,  32  come into contact. A top surface  34  of the backup ring  12  may protrude a certain distance  35  from the mating surface  18   b  when the surface features  30 ,  32  are in contact. 
     The cross-section of the gland  16  and backup ring  12  may be formed in various different shapes to provide different features. For example, the gland  16  and backup ring  12 , as illustrated in  FIG. 2 , may be shaped to form a dovetail-shaped recess that is helpful to retain the annular seal  14  within the gland  16 . The resilient annular seal  14  may be inserted into the gland  16  by simply pushing the seal  14  into the dovetail-shaped recess. 
     Referring to  FIG. 3 , upon bringing the mating surfaces  18   a ,  18   b  together, the backup ring  12  may be urged into the gland  16 . This will generate space between the surface features  30 ,  32  and the backup ring  12  will automatically fill any clearance gap  36  that may exist between the mating surfaces  18   a ,  18   b  without requiring assistance from the annular seal  14 . Similarly, the annular seal  14  may be compressed to provide a seal between the mating surface  18   a  and the gland  16 . 
     Referring to  FIG. 4 , when the clearance gap  36  increases, the backup ring  12  may automatically fill the clearance gap  36  up until the surface feature  32  of the backup ring  12  contacts the surface feature  30  of the gland  16 . Thus, the backup ring  12  and the gland  16  may be designed to fill a maximum clearance gap  36 . Because the backup ring  12  is self-energized, the backup ring  12  may firmly contact the mating surface  18   a  regardless of the force exerted on the backup ring  12  by the annular seal  14 . When pressure exerts a force in a direction  38  against the annular seal  14 , the backup ring  12  will provide backup support to the seal  14  to prevent or reduce extrusion into the clearance gap  36 . 
     A design similar to the backup ring  12  illustrated in  FIGS. 1 through 4  has been shown to maintain pressure integrity in the presence of very high pressures (e.g., 8-15K psi) even where the clearance gap  36  is relatively large (e.g., 20 mils or more). For example, using a design similar to the illustrated embodiment, an o-ring  14  and backup ring  12  was shown to maintain an effective seal up to a pressure of 14.5K psi with a clearance gap of approximately 20 mils, at which point the seal began to leak. This seal  14  and backup ring  12  re-sealed after the pressure was lowered to 13K psi. Furthermore, the mating surfaces  18   a ,  18   b  were brought together using a threaded connection that was tightened by hand, showing that the seal  14  and backup ring  12  may maintain pressure integrity with only minimal force exerted between the mating surfaces  18   a ,  18   b.    
     Referring to  FIG. 5 , in other embodiments of the invention, a backup ring  12  in accordance with the invention may be installed on an inside diameter of the gland  16  either in place of or in addition to the backup ring  12  illustrated in  FIG. 4 . For example, dual backup rings  12   a ,  12   b  may be installed on the inside and outside diameters of the gland  16  to provide support to an annular seal  14  in either direction. Such a design may be useful where high pressures alternate from one side of the seal  14  to the other. 
     In embodiments where a backup ring  12   b  is installed on the inside diameter of the gland  16 , the inside diameter of the backup ring  12   b  may be sized to be slightly smaller than the inside diameter of the gland  16  to create radial interference between the two contact surfaces. This radial interference in combination with the angled orientation of the contact surfaces may urge the backup ring  12   b  out of the gland  16  toward the mating surface  18   a , like the previous examples. 
     Referring to  FIGS. 6 and 7 , in selected embodiments, a backup ring  12  and gland  16  in accordance with the invention may be designed to have various different shapes and configurations. For example, a backup ring  12  and gland  16  may be designed such that together they form a substantially rectangular recess to accommodate the annular seal  14 .  FIG. 6  shows an embodiment using a single backup ring  12 .  FIG. 7  shows an embodiment using dual backup rings  12   a ,  12   b.    
     Referring to  FIG. 8 , in another embodiment, a self-energized backup ring  12  may be incorporated into a tapered seal  60  and may operate in a similar manner to the backup seal  12  of  FIG. 1 . More specifically, an annular seal  14  may provide a seal between the tapered conical members  62 ,  64 . To self-energize the backup ring  12 , an outside diameter  66  of the backup ring  12  may be sized to radially interfere with an outside diameter of the gland  16 . This radial interference will create hoop stress in the ring  12  that will urge the backup ring  12  out of the gland  16  and against the inside diameter of the tapered conical member  64 . 
     Referring to  FIG. 9 , when a clearance gap  36  exists between the mating surfaces  18   a ,  18   b , the radial interference between the backup ring  12  and the gland  16  will cause the backup ring  12  to fill the clearance gap  36 . This will provide support to the annular seal  14  and prevent extrusion into the clearance gap  36  when pressure pushes from a direction  70 . Like the embodiment illustrated in  FIG. 1 , a retention mechanism may be provided to retain the backup ring  12  within the gland  16 . This retention mechanism may include a surface feature  30  (e.g., a ridge, protrusion, ledge, groove, or the like) incorporated into the gland  16  and adapted to engage a corresponding surface feature  32  incorporated into the backup ring  12 . 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.