Abstract:
A fitting arrangement with an adapter for use in a fitting that uses a fitting body and nut of certain commonly used dimensions as described above, while retaining the gripping capability. The adapter is a ring that seals effectively against the body, while presenting a less shallow camming mouth for engagement by a ferrule. This combination of parts enables effective tube grip, fluid seal, and vibration protection.

Description:
[0001]    This application claims the benefit of the filing date of U.S. Provisional Application No. 60/481,593 filed Nov. 3, 2003, the entire disclosure of which is incorporated by reference. 
     
     TECHNICAL FIELD OF THE INVENTION 
       [0002]    The subject invention is generally directed to the art of fittings for pipe and tube. More particularly, the invention is directed to flareless fittings that include a fitting body with a shallow angle tapered surface and a tube gripping device, such as a ferrule or tube gripping ring. 
         [0003]    This application incorporates by reference the entire disclosure of International patent application no. PCT/US02/03430 filed on Feb. 6, 2002 for TUBE FITTING FOR STAINLESS STEEL TUBING. 
       BACKGROUND OF THE INVENTION 
       [0004]    Some known tube fittings employ parts that are at least partially standardized in dimension or configuration, thus being commonly used. For example, many fitting bodies have a shallow camming mouth or tapered surface, for example, twelve degrees (12°) or twenty degrees (20°), for engagement by a ferrule when the ferrule is forced against it by the nut. Many nuts have a forty-five degree (45°) angle on their drive face that contacts the ferrule to drive the ferrule against the camming mouth of the body. The gradual nature of the 12° camming angle on the body is conducive to embedding the ferrule into the tube surface to provide grip. This 12° angle is, however, not conducive to establishing a good seal between the ferrule and the body. Thus, the gripping and sealing functions are often at odds with each other in a fitting using such parts. The sealing function is often enhanced by adding an elastomeric seal element to the fitting. While fittings using elastomeric sealing elements generally seal effectively, they can have some drawbacks. For example, temperature limitations may be placed on the fitting because of the presence of the elastomeric (non-metallic) element. Incompatibilities may exist between the elastomeric seal element and certain system fluids. In addition, seal clipping or damage may occur during fitting make-up, or the seal element may fall out or be lost prior to fitting make-up. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention is directed to improving the sealing capability of a fitting that uses a fitting body and nut of certain commonly used dimensions as described above, while retaining the gripping capability. This is accomplished by providing a metal adaptor ring that seals effectively in a metal-to-metal manner against the body, while presenting a less shallow camming mouth for engagement by a ferrule. This combination of parts enables effective tube grip, fluid seal, and vibration protection. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    These and other aspects and advantages of the present invention will be apparent to those skilled in the art from the following description of the preferred embodiments in view of the accompanying drawings, in which: 
           [0007]      FIG. 1  is an embodiment of the invention for a single ferrule tube fitting including an adaptor ring; 
           [0008]      FIG. 2  is another embodiment similar to  FIG. 1  including an adaptor ring; 
           [0009]      FIG. 3  is another embodiment similar to  FIG. 1  including an adaptor ring; 
           [0010]      FIG. 4  is another embodiment similar to  FIG. 1  including an adaptor ring; 
           [0011]      FIG. 5  is another embodiment similar to  FIG. 1  including an adaptor ring; 
           [0012]      FIG. 6  is another embodiment similar to  FIG. 1  including an adaptor ring; 
           [0013]      FIGS. 7-9  are schematic illustrations of portions of adaptor rings that are other embodiments of the invention; 
           [0014]      FIG. 10  illustrates another adaptor ring used with a single ferrule tube fitting; 
           [0015]      FIG. 11  illustrates an adaptor ring used with a two ferrule tube fitting; and 
           [0016]      FIG. 12  illustrates a self-energizing effect of a tube fitting of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    In many tube fittings, the nose of a ferrule is cammed inward toward and into the tube by a shallow (for example, 12° or 20°) camming surface or tapered surface on the fitting body. This angle is suitable for effecting tube gripping by the ferrule but is not optimal for also effecting a seal on the body by the ferrule. On the other hand, a steeper (for example, 45°) camming angle, can be better to effect a seal by the ferrule but can be less effective at producing the needed grip. The present invention as described below with reference to exemplary (but not limiting) embodiments addresses this issue. 
         [0018]      FIGS. 1-4  illustrate different tube fittings  400 ,  400   a ,  400   b , and  400   c  in accordance with the invention. The various fittings  400 - 400   c  include differing features and combinations of features. A tube fitting in accordance with the present invention can include one or more of these features in different combinations. 
         [0019]    Showing one representative embodiment,  FIG. 1  illustrates a tube fitting  400  in accordance with the invention, for use in coupling a tube  410  to a body  420 . The fitting  400  includes a driver or drive nut  440 , an adaptor ring  450 , and a ferrule  302 . The body  420  and the drive nut  440  may have some “standard” features or dimensions, that is, features or aspects that are commonly found on some fittings, as described below. 
         [0020]    The tube  410  as illustrated has a cylindrical side wall  412  centered on an axis  414 . The side wall  412  defines a fluid flow passage  416  in the tube  410 . The tube side wall  412  has a cylindrical outer surface  418  centered on the axis  414 . (As used herein, the term “tube” is intended to cover hollow cylindrical pipes of different and varying diameters, including those commonly known as tube, pipe, and conduit.) 
         [0021]    The body  420  has a cylindrical inner surface  422  centered on the axis. The surface  422  defines a bore or tube socket  424  in which the end of the tube  410  is received. The body  420  has an external thread convolution  426  for engagement with the nut  440 , as described below. The fitting  400  is adapted to seal between the body  420  and the tube  410 , and to secure them to each other so that the tube does not come out of the bore  424  in the body. 
         [0022]    The body  420  has an annular end surface or back face  428  that extends radially inward from the thread convolution  426 . The body  420  also has a frustoconical camming surface or tapered surface  430  that extends between the inner surface  422  and the end surface  428 . The camming surface  430  extends at an angle to the axis  414 . In one exemplary embodiment, as shown, the camming surface  430  extends at about a 12° angle to the axis  414 . The camming surface  430  is presented radially inward toward the axis  414  and axially in a direction toward the drive nut  440 . The camming surface  430  is located adjacent to the surface  422  and defines a camming mouth  432  of the body  420  that is located adjacent to the tube socket  424 . The body  420  has an edge  434  at the intersection of the camming surface  430  and the end surface  428 . 
         [0023]    The driver or nut  440  includes a first cylindrical surface or inner surface  442  centered on the axis  414 . The surface  442  defines a bore  444  through which the tube  410  extends. At a location radially outward and spaced axially from the inner surface  442 , the nut  440  has an internal thread convolution  446  for engagement with the external thread  426  on the body  420 . 
         [0024]    The nut  440  has a frustoconical drive surface or drive face  448  that extends radially and axially between the inner surface  442  and the internal thread  446 . The drive face  448  extends at an angle to the axis  414  and is presented radially toward the axis and axially toward the body  420 . In the embodiment shown in  FIG. 1 . the drive face  448  extends at about a 45° angle to the axis  414 . The nut drive angle may be other than 45°. 
         [0025]    The adaptor ring  450  and the ferrule  302  are located in the space between the drive face  448  of the nut  440  and the body  420 . The adaptor ring  450  can be, but need not be, made from the same material as the ferrule  302 . 
         [0026]    The adaptor ring  450  in the embodiment of  FIG. 1  has a radially outer portion  452  and a radially inner portion  454  that are joined by a neck portion  456 . The outer portion  452  of the adaptor ring  450  has a cylindrical outer surface  458  that extends parallel to the axis  414 . The outer portion  452  of the ring  450  has an annular back face  460  that extends radially inward from the back end of the outer surface  458 , in a direction normal to the outer surface and to the axis  414 . The back face  460  is presented axially in a direction toward the nut  440 . 
         [0027]    The outer portion  452  of the ring  450  also has an annular front face  462  that extends radially inward from the front end of the outer surface  458 , in a direction normal to the outer surface and to the axis  414 . The front face  462  is presented axially in a direction toward the end surface  428  of the body  420 . In the particular adaptor ring  450  that is shown in  FIG. 1 , the front face  462  has a greater radial extent than the back face  460 , for example, two times the radial extent of the back face. 
         [0028]    The adaptor ring  450  has a camming surface  464  that is presented radially inward toward the axis  414  and also is presented axially toward the back of the fitting, in a direction toward the drive face  448  of the nut  440 . The camming surface  464  extends at an angle to the axis  414 , which, in the embodiment illustrated in  FIG. 1 , is an angle of about 45°. 
         [0029]    The inner portion  454  of the adaptor ring  450  has a cylindrical inner surface  466  that extends parallel to the axis  414 . The inner surface  466  defines a bore  468  in which the tube  410  is slidably received. The inner surface  466  overlies and is spaced apart from the outer surface  418  of the tube  410 , before the fitting  400  is made up. The adaptor ring  450  has an edge  470  at the intersection of the inner surface  466  and the camming surface  464 . 
         [0030]    The inner portion  454  of the ring  450  has an annular front face  472  that extends radially outward from the inner surface  466 , in a direction normal to the inner surface and to the axis  414 . The front face  472  is presented axially in a direction toward the camming mouth  432  of the body  420 . The front face  472  of the inner portion  454  of the ring is farther forward in the fitting  400 , that is, is located closer to the body  420  and farther from the nut  440 , than is the front face  462  of the outer portion  452  of the ring. A chamfer breaks the edge defined by surface  462  and surface  472 . 
         [0031]    The inner portion of the adaptor ring  450  also has an engagement surface  474  that extends between and interconnects the front face  472  of the inner portion  454  of the ring, and the front face  462  of the outer portion  452  of the ring. The engagement surface  474  may be a single concave or planar surface, or may be a series of concave or planar surfaces, or a combination of various types of surfaces. The engagement surface  474  spans the neck portion  456  of the adaptor ring  450 , extending between the front face  472  of the inner portion  454  and the front face  462  of the outer portion  452 . The engagement surface  474  is presented toward the body  420  and, specifically, toward the edge  434  on the body. On the opposite side of the adaptor ring  450 , the camming surface  464  of the adaptor ring  450  spans the neck portion  456  of the adaptor ring, extending between the inner surface  466  and the back face  460  of the outer portion  452 . 
         [0032]    The dimensions of the adaptor ring  450  are selected so that its radially inner portion  454  can move into the camming mouth  432  of the body  420 , while the radially outer portion  452  can not. Specifically, movement of the adaptor ring  450  in a direction axially toward the camming mouth  430  of the body  420  is blocked, as described below, by engagement of the adaptor ring engagement surface  474  (or the front face  462 ) with the body  420 . 
         [0033]    When the fitting  400  is made up, the nut  440  is tightened on the body  420 , and moves axially toward the body (in a direction to the left as viewed in  FIG. 1 ). The 45° drive face  448  of the nut engages the back wall  324  of the ferrule  302 . The ferrule  302  is driven forward until it engages the adaptor ring  450 . The nose  310  of the ferrule  302  engages the 45° back face  464  of the adaptor ring  450 . 
         [0034]    The adaptor ring  450  is moved forward by the ferrule  302  until it engages the body  420 . The engagement surface  474  of the adaptor ring  450  engages the edge  434  on the body  420  to act as a stop for the adaptor ring. This engagement blocks any further substantial movement of the adaptor ring  450  toward the body  420 , and may be sensed by sensing torque on the nut  400  to determine sufficient pull up. The adaptor ring  450  is captured between the ferrule  302  and the body  420 , and the ferrule is captured between the adaptor ring and the nut  440 . 
         [0035]    The inner portion  454  of the adaptor ring  450  is located in the camming mouth  432  of the body  420 , radially inward of the camming surface  430  but not in engagement with the camming surface. Alternatively, the adaptor ring  450  can engage the camming surface  430 . The outer portion  452  of the adaptor ring  450  is located radially outward of the camming surface  430  of the body  420 , and axially between the end face  428  of the body and the drive face  448  of the nut  440 . 
         [0036]    As the nut  440  is tightened further, the ferrule  302  is compressed and plastically deformed, and is driven into gripping and sealing engagement with the adaptor ring  450  and the tube  410 . The ferrule  302  may hinge and/or collet, and may be hardened to make it more suitable for use with the relatively steep 45° camming angle of the adaptor ring  450 . 
         [0037]    The nose  310  of the ferrule engages the 45° camming surface  464  on the adaptor ring, rather than the 12° camming surface  430  on the body  420 . Thus, the nose  310  of the ferrule  302  is cammed radially inward toward and into the tube  410  by a 45° camming surface, rather than by a 12° camming surface. 
         [0038]    A seal is established between the engagement surface  474  of the adaptor ring  450  and the edge  434  of the body  420 . This seal prevents fluid from the tube  410  from passing radially outward of the adaptor ring  450 . This seal is not a sliding seal, that is, is not of the type established when a ferrule cams and slides against a camming surface of a fitting body. In contrast, the adaptor ring  450  is positively stopped from movement relative to the body  420 , and the engagement surface  474  thus seals in a fixed manner against the edge  434  of the body. The adaptor ring  450  does not have to establish a seal against the tube  410 . 
         [0039]    Another seal is established between the nose  310  of the ferrule  302  and the camming surface  464  of the adaptor ring  450 . A third seal is established between the nose  310  of the ferrule  302  and the tube  410 . These seals together provide the desired sealing function of the fitting  400 , preventing fluid from passing radially inward of the adaptor ring. At the same time, the nose  310  of the ferrule  302  is driven into the material of the tube  310  to form a generally radial shoulder  476 , blocking removal of the tube from the bore  424  in the body  420  and thus providing the desired gripping function of the fitting  400 . The underside of the adaptor ring can be configured to allow space for the chip of tubing that is curled up by the ferrule nose. Thus, with the use of the adaptor ring  450 , the fitting  400  can give up the increased grip benefit of the 12° camming surface, because excellent grip is provided from the ferrule  302 , that is cammed into the tube by the 45° camming surface of the adaptor ring. 
         [0040]      FIG. 2  illustrates a tube fitting  400   a  that is similar to the tube fitting  400  but which uses a different adaptor ring. The fitting  400   a , for use in coupling the tube  410  to the body  420 , includes the same drive nut  440  and the same ferrule  302 . The fitting  400   a  also includes an adaptor ring  450   a  which is slightly different from the adaptor ring  450  shown in  FIG. 1 . Specifically, in the adaptor ring  450   a , the radially inner portion  454   a  is different than the radially inner portion  454  in the adaptor ring  450 . Also, the engagement surface  474   a  in the adaptor ring  450   a  is different than the engagement surface  474  in the adaptor ring  400 . 
         [0041]    The radially inner portion  454   a  of the adaptor ring  450   a  has a convex configuration including a convex outer surface  478  presented toward the camming surface  430  of the body  420 . The convex outer surface  478  merges into a concave engagement surface  474   a  that merges into the front face  462   a  of the radially outer portion  452   a  of the adaptor ring  450   a . The resulting configuration of the adaptor ring  450   a  includes a “bullnose” shaped inner portion  454   a  that still fits into the camming mouth  432  of the body  420 , but that also projects radially outward sufficiently to engage the camming surface  430  of the body when the fitting  400   a  is made up. 
         [0042]    When the drive nut  440  pushes the ferrule  302  into the adaptor ring  450   a , the adaptor ring is pushed into engagement with the body  420 , as shown in  FIG. 2 . The outer surface  478  of the inner portion  454   a  of the adaptor ring is wedged into tight engagement with the camming surface  430  of the body  420 . The radially extending front face  462   a  of the outer portion  452   a  of the adaptor ring  450  preferably engages the end face  428  of the body to provide a stop. The concave engagement surface  474   a  of the adaptor ring  450   a  may or may not engage the edge  434  of the body  420 . 
         [0043]    In the embodiment of  FIG. 2 , the adaptor ring  450   a  is interposed between the ferrule  302  and the body  420 , so that the nose  310  of the ferrule engages the 45° camming surface  464   a  on the adaptor ring, rather than the 12° camming surface  430  on the body  420 . A seal is established between the convex outer surface  478  on the radially inner portion  454   a  of the adaptor ring  450   a  and the camming surface  430  of the body  420 . Another seal is established between the nose  310  of the ferrule  302  and the camming surface  464   a  of the adaptor ring  450   a . A third seal is established between the nose  310  of the ferrule  302  and the tube  410 . These seals together provide the desired sealing function of the fitting  400   a . At the same time, the nose  310  of the ferrule  302  is driven into the material of the tube  310  to form a generally radial shoulder  476 , blocking removal of the tube from the body  420  and thus providing the desired gripping function of the fitting  400   a.    
         [0044]      FIG. 3  illustrates a tube fitting  400   b  that is similar to the fittings  400  and  400   a , but including a different adaptor ring. The fitting  400   b , for use in coupling the tube  410  to the body  420 , includes the same drive nut  440  and the same ferrule  302  (with a shortened back wall  324 ). The fitting  400   b  also includes an adaptor ring  450   b  which is different from the adaptor ring  450  shown in  FIG. 1  and from the adaptor ring  450   a  shown in  FIG. 2 . 
         [0045]    The adaptor ring  450   b  has an outer portion  452   b  that is longer axially than the outer portion of either of the rings  450  and  450   a . The outer portion  452   b  of the adaptor ring  450   b  includes a nose portion  480  that projects forward (in a direction toward the body  420 ), overlying the inner portion  454   b  of the ring and extending past the surface  474   b . The outer portion  452   b  also includes a tail portion  482  that projects backward (in a direction toward the nut  440 ), overlying a significantly greater part of the ferrule  302  (in the illustrated embodiment, over most of the ferrule) than does the outer portion  452  of the adaptor ring  450  ( FIG. 1 ). 
         [0046]    When the fitting  400   b  is made up, as shown in  FIG. 3 , the nose portion  480  of the adaptor ring engages the end face  428  of the body  420  to act as a stop for movement of the adaptor ring. This engagement limits further movement of the adaptor ring  450   b  in a direction toward the body  420  and provides a seal between the adaptor ring and the body. The nose  310  of the ferrule  302  engages the camming surface  464   b  of the adaptor ring  450   b  to provide a seal, and is cammed into the tube  410 , as described above, to grip and to provide an additional seal. 
         [0047]    When the fitting  400   b  is made up, the tail portion  482  engages the drive face  448  of the nut  440  to as a stop to limit movement of the nut  440  in a direction toward the body  420 . This can provide torque sensing to ensure sufficient pull up of the fitting  400   b.    
         [0048]      FIG. 4  illustrates a tube fitting  400   c  that is similar to the fittings  400 ,  400   a  and  400   b , and including a different adaptor ring and ferrule. The fitting  400   c , for use in coupling the tube  410  to the body  420 , includes the same drive nut  440 . The fitting  400   c  also includes an adaptor ring  450   c  which is different from the adaptor rings  450 ,  450   a , and  450   b . The fitting  400   c  also includes a ferrule  302   c  which is different from the ferrule  302 . 
         [0049]    The back wall  324   c  of the ferrule  302   c  extends radially outward farther than the back wall  324  of the ferrule  302  ( FIG. 1 ). A stop surface  480  on the back wall  324   c  of the ferrule  302   c  is presented toward the body  420 . 
         [0050]    The outer portion  452   c  of the adaptor ring  450   c  includes a tail portion  482   c  that projects backward (in a direction toward the nut  440 ), overlying a significantly greater part of the ferrule  302  than does the outer portion  452  of the adaptor ring  450  ( FIG. 1 ). The tail portion  482   c  of the adaptor ring  450   c  includes a stop surface  486  that is presented toward the nut  440  and the back wall  324   c  of the ferrule  302   c.    
         [0051]    The inner portion  454   c  of the adaptor ring  450   c  is elongated axially in a forward direction, compared to the inner portion  454  of the adaptor ring  450  ( FIG. 1 ). The inner portion  454   c  of the adaptor ring  450   c , like the bullnose on the adaptor ring  454   a  ( FIG. 2 ), moves into the camming mouth  432  of the body  420  and engages the camming surface  430  of the body. The inner portion  454   c  of the adaptor ring  450   c  seals against the tapered surface  430  of the body  420 . The concave engagement surface  474   c  of the adaptor ring  450   c , and the radially extending front face  462   c  of the outer portion  452   c  of the ring, may or may not engage the edge  434  of the body  420  and/or the end face  428  of the body. 
         [0052]    When the fitting  400   c  is made up, the stop surface  486  on the tail portion  482   c  of the adaptor ring  450   c  engages the stop surface  480  on the back wall  324   c  of the ferrule  302   c . At the same time, the front face  462   c  of the adaptor ring  450   c  engages the end surface  428  of the body  420 . As a result, the outer portion  452   c  of the adaptor ring  450   c  and the back wall  324   c  of the ferrule  302 , together, act as a stop to limit movement of the nut  440  in a direction toward the body  420 . This can provide torque sensing to ensure sufficient pull up of the fitting  400   c.    
         [0053]      FIG. 5  illustrates a tube fitting  400   d  for use in coupling a tube  410  to a fitting body  420 . The fitting body  420  has a 12° camming surface  430  that defines a camming mouth  432 . The fitting  400   d  includes a drive nut  440 . The fitting  400   d  also includes an adaptor ring  450   d  and a ferrule  302   d.    
         [0054]    The adaptor ring  450   d  has an extended nose  490  that fits into the camming mouth  432 . The nose  490  has a sharp edge  492  that digs into the camming surface  430 , upon make-up, to provide a seal between the adaptor ring  450   d  and the fitting body  420 . The ferrule  302   d  has a relatively small nose  496  that fits under the relatively small 45° camming mouth  494  of the adaptor ring  450   d . The ferrule  302   d  seals against the 45° back end or camming mouth  494  of the adaptor ring  450   d  and grips on the tube  410 . 
         [0055]    The fitting  400   d  does not have a positive stop built into it. Instead, the fitting  400   d  is designed to be pulled up a given number of turns of the nut, thereby ensuring sufficient pull up of the fitting. 
         [0056]      FIG. 6  illustrates a tube fitting  400   e  for use in coupling a tube  410  to a fitting body  420 . The fitting  400   e  includes a drive nut  440 . The fitting  400   e  also includes one of three different adaptor rings  500 ,  502 , and  504  that are illustrated, and one of three different ferrules  510 ,  512  and  514  that are illustrated. As a result, there are nine possible combinations of the illustrated parts. 
         [0057]    The one adaptor ring  500  has a long and slender nose  520  that fits into the camming mouth  432 . The nose  520  has a sharp edge  522  that digs into the camming surface to provide a seal between the adaptor ring  500  and the fitting body  420 . Because the nose  520  is long and slender, it produces less tendency to swell out the fitting body  420  when the fitting  400   d  is made-up. 
         [0058]    The adaptor ring  504 , in contrast, has a shorter and thicker nose  524  that seals between the adaptor ring and the fitting body  420 . Because the nose  524  of the adaptor ring  504  is shorter and thicker in cross-section, it has a greater resistance to axial compression under load. The qualities of the intermediate adaptor ring  502  illustrated fall between the qualities of the rings  500  and  504 . The three nose designs are illustrated to show that the length and thickness of the nose are variables and that the designer can select between them or can select a nose with a different length and thickness. 
         [0059]    The fitting  400   e  has a positive stop built into it. This can provide torque sensing to ensure sufficient pull up of the fitting. Specifically, the nut  440  is designed to bottom out on the adaptor ring  500 - 504 . The three different ferrules  510 - 514  that are illustrated in  FIG. 6  have different lengths and heights and thus allow for differing amounts of nut travel before the nut  440  bottoms out on the back of the adaptor ring  500 - 504 . The three ferrule designs  510 - 514  are illustrated to show that the size of the ferrule is a variable and that the designer can select between them or can select a ferrule with different dimensions. The choice of adaptor ring is dependent on which one effectively makes a seal against the camming mouth without swelling the body while resisting axial compression under load. The choice of ferrule is based on to what extent it is desired to have the ferrule grip into the tube by the time the nut stops against the back side of the adaptor ring. 
         [0060]    As noted above, the ferrule grips the tube to prevent the tube from coming out of the tube socket in the fitting body. Under high pressure, a significant amount of strain can be present in the tube, evidenced as an axially outwardly directed force on the tube and on any component that is attached to or gripping the tube. Sufficient strain on the tube, if transmitted to the adaptor ring, can break or reduce the seal between the adaptor ring and the body. It is preferable to prevent this from occurring. 
         [0061]    As illustrated schematically in  FIG. 7 , the nose  530  of the adaptor ring  532 , that is, the portion that is located radially inward of the camming surface  534 , can have a rounded tip  536 . This helps to avoid transmission of tube strain under high pressure to the adaptor ring. 
         [0062]    In a second manner, the nose of the adaptor ring, that is, the portion radially inward of the camming surface, can be ramped or chamfered radially outward, away from the outer surface of the tube, as illustrated schematically in  FIG. 8 . The adaptor ring  540  shown in  FIG. 8  is illustrated as having an inner ramp surface or chamfer  542  that tapers radially outward as measured in a direction from the back of the ring toward the tip of the ring. 
         [0063]    Third, the nose of the adaptor ring can be both rounded and ramped, as illustrated schematically by the adaptor ring  544  shown in  FIG. 9 . 
         [0064]    In these manners, or in another manner, with an adaptor ring so configured, then under high pressure the tube can freely move and strain outward. As other examples, an elliptical end portion can be provided, or the nose portion can be broken off by broaching, for example, to provide the desired non-sharp configuration for the nose portion or end portion of the adaptor ring. Combinations of tapers and curved surfaces are also possible. The features of the adaptor rings shown in  FIGS. 7-9  and as described herein can equally apply to all the adaptor rings illustrated. During pull up, if the inside forward portion of the adaptor ring comes in contact with the tube, it touches with a negative rake angle with respect to the tube surface, that is, an acute angle between the tube surface and the surface of the inside forward portion of the adaptor ring. 
         [0065]      FIGS. 10 and 11  show two further embodiments of the invention.  FIG. 10  illustrates a tube fitting  590  including a fitting body  592  having a tube socket  594  receiving an end portion of a tube  596 , a ferrule  598 , and an adaptor ring  600 . The adaptor ring  600  is illustrated as having a taper and rounded tip  602 . 
         [0066]      FIG. 11  illustrates a two ferrule tube fitting  560  including a fitting body  562  having a tube socket  564  receiving an end portion  566  of a tube  568 . A driver  570  in the form of a nut is coupled to the fitting body  562  to drive a back ferrule  572 , a front ferrule  574 , and an adaptor ring  576 . The adaptor ring  576  has a nose portion  578  that seals against a relatively shallow, twelve degree to twenty degree tapered surface  582  on the fitting body  562 . The adaptor ring  576  has a back face  584  that forms a relatively less shallow camming surface, in the range of from about 30 degrees to about 45 degrees that is engaged by the nose portion of the front ferrule  574 . The back ferrule  572  is captured between the front ferrule  574  and the nut  570 . Upon make up (not shown) of the fitting  560  both the front ferrule  574  and the back ferrule  572  grip and seal on the tube  568 . In this embodiment, as well as in the embodiment of  FIG. 10 , sufficient pull up of the fitting can be ensured by torque sensing or in another manner, such as by ensuring sufficient axial stroke of the nut as determined by number of turns of the nut. 
         [0067]      FIG. 12  illustrates a self-energizing effect under high pressure of an adaptor ring in accordance with the invention. The ring illustrated is the adaptor ring  450   c  that is discussed above with reference to  FIG. 4 . Under very high pressure, the tube  410  may begin to pull out of the tube socket in the fitting body  420 . As this occurs, the ferrule  302   c  bites deeper into the material of the tube  410  to resist tube pullout and seal better. Fluid under pressure flows into the annular cavity that is located radially outward of the tube  410  and radially inward of the adaptor ring  450   c . The fluid pressure acts to force the adaptor ring  450   c  away from the tube  410 . The nose portion  454   c  of the adaptor ring  450   c  is pressed more tightly against the camming surface  430  of the fitting body  420 . The adaptor ring  450   c  is also pressed more tightly against the ferrule  302   c . As a result, the sealing capability of the adaptor ring  450   c  is increased because of the increased pressure in the tube  410 . 
         [0068]    From the above description of the invention, those skilled in the art will perceive improvements, changes, and modifications in the invention. Such improvements, changes, and modifications within the skill of the art are intended to be included within the scope of the appended claims.