Abstract:
The disclosure pertains to a tubing and ferrule assembly for use in joining a clad tubing to a fitting. The ferrule is bound to the clad tubing, which includes a partial jacket of stainless steel, such that the inert core protrudes from, and has a common outer diameter with, the jacket. The ferrule is bound to the jacket slightly more distant than necessary for the inert core to contact a fitting. When the ferrule is retained in place, the inert core is compressed and provides a true zero dead volume connection between the clad tubing and the fitting. The relationship of the ferrule, the clad tubing, and the fitting limits the position of the clad tubing and therefore precludes damaging of the associated valve or component.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 62/303,757 entitled “Zero dead volume fitting assembly” filed on Mar. 4, 2016 in the United States Patent and Trademark Office and which is incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable. 
       FIELD 
       [0003]    This disclosure pertains to fittings for use in systems designed for chemical analysis where zero dead volume is required. 
       BACKGROUND 
       [0004]    It is necessary in analytical systems to have fittings that create leak-tight seals. In such analytical systems, it is also desirous to have fittings which are inert relative to the sample components, which provide a flow path without inducing turbulence or mixing, and which adds minimal volume to the system. 
         [0005]    Fitting designs which best address the aspect of added volume allow the tube ends which pass through such fittings to butt directly to each other or have bores which match the tubing bore, leaving no dead or unswept volume. Such fittings are called zero dead volume fittings. In analytical testing apparati dead volume is to be avoided as it reduces efficiencies of the test equipment, including gas columns. 
         [0006]    One of the most common&#39;types of such zero dead volume fittings is a compression fitting. A zero dead volume compression fitting consists of a fitting having a female fitting detail, tubing, a ferrule loosely riding on the tubing, and a male nut, also riding on the tubing. In operation the tubing is placed into the fining until the tubing end passes through the inner bore of the fitting, and seats correctly at the bottom of the fitting detail, the ferrule is then slid along the tubing until, it engages the mating walls of the fitting, and the nut is threadedly engaged so as to be retained in place and to deform the ferrule against the mating wall of the fitting detail, causing the ferrule to apply pressure to the tubing and force such tubing against the bottom of the fitting detail. 
         [0007]    Basic problems with such system are inherent in the type and number of parts, namely the fitting, the ferrule, the tubing and nut. The fitting and ferrule need be sufficiently sized so that the ferrule can be deformed against the fitting to provide a seal, which often provides some volume at the interface of these components. The ferrule in these systems necessarily must be deformable to provide a seal, but the force necessary to do so may be exceeded and thus overdrive the tubing into the fitting and interfere with operation of the associated valve. This problem is acerbated in a multi-ported valve having a plurality of fitting bodies associated with it and the overtightening into one or more of the detail associated with a port. Moreover, these systems must sustain the associated high pressures, must not deform the associated fitting, and must not have any extraneous volume creating an undesirable mixing chamber. 
       SUMMARY 
       [0008]    The present disclosure provides a high pressure tubing system including a tubing and a ferrule for use with a zero dead volume fitting as an ultra-high performance capillary tube connector. The zero dead volume fitting has a zero dead volume fitting detail sized to receive a clad tubing, a zero dead volume fitting detail pilot terminating at a zero dead volume fitting detail pilot bottom, and a zero dead volume fitting detail ferrule seat. The clad tubing has an inert polymer core and a stainless steel jacket, a core length, a jacketed core outer diameter, an unjacketed core outer diameter, a core first end, a core first end segment, a core second end, a core second end segment, a core intermediate segment and a core lumen therethrough. The inert polymer core is composed of a single monolithic piece and has a common diameter throughout The core length extends from the core first end to the core second end. The core first end has a flat core first face at the core first end. The core intermediate segment is intermediate the core first end segment and the core second end segment. The stainless steel jacket has a jacket length, a jacket outer diameter, a jacket inner diameter, a jacket thickness and a jacket first end. The core length is greater than the jacket length. The stainless steel jacket is positioned about the core intermediate segment. The jacket thickness is half the difference between the jacket outer diameter and the jacket inner diameter. The jacket inner diameter is equivalent to the jacketed core outer diameter and the jacket outer diameter is equivalent to the unjacketed core outer diameter. The stainless steel jacket is positioned about the core intermediate segment. The ferrule initially is slidably positioned about the clad tubing to the stainless steel jacket, and has a first end and a ferrule second end and has a wedge-shaped face sized to contact the zero dead volume fitting detail ferrule seat proximate the ferrule first end at a point of contact. The ferrule is ultimately retained in position around the clad tubing such that the ferrule first end is at a tubing pilot length from the core first end of the inert polymer core. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    So that the manner in which the described features, advantages and objects of the disclosure, as well as others which will become apparent, are attained and can be understood in detail, more particular description of the disclosure briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the drawings, which drawings form a part of this specification. It is to be noted, however, that the appended drawings illustrate only a typical preferred embodiment of the disclosure and are therefore not to be considered limiting of its scope as the disclosure may admit to other equally effective embodiments. 
           [0010]    In the drawings: 
           [0011]      FIG. 1  is a cross sectional view of the assembly in connection with a fitting prior to insertion, 
           [0012]      FIG. 2  is a cross sectional view of the assembly in connection with a fitting at initial insertion. 
           [0013]      FIG. 3  is a cross sectional view of the assembly in connection with a fitting at thin point of contact of the ferrule and retaining member with the fitting. 
           [0014]      FIG. 4  is a cross sectional view of the first end of the clad tubing. 
           [0015]      FIG. 5  is an isometric view of the first end of the clad tubing. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    The zero dead volume fitting assembly is provided in the present disclosure. Referring to  FIG. 1 , the high pressure tubing system  100 , a capillary tubing connector system, includes a ferrule  116  and a clad tubing  108 , to be used in connection with a retaining member  124 , which may be a nut or other threaded body. The high pressure capillary tubing connector system  100  provides a zero dead volume connection particularly beneficial for chromatography. The high pressure capillary tubing connector system  100  provides a zero dead volume connection to a zero dead volume fitting  102  which has a zero dead volume fitting detail  104 , and which includes a zero dead volume fitting detail pilot  106  sized to receive the clad tubing  108 . The zero dead volume fitting detail pilot  106  terminates at a zero dead volume fitting detail pilot bottom  110 . The zero dead volume fitting detail  104  also has a zero dead volume fitting detail ferrule seat  112  and a zero dead volume fitting retention section  114 , such as female threads, therein, 
         [0017]    Referring to  FIG. 1 , the present disclosure provides the stainless steel jacket  136  about the inert polymer core  134 , which stainless steel jacket  136  prevents deformation of the inert polymer core  134  in response to high pressure, but which terminates short of the polymer end, resulting in a jacketed core intermediate segment  152 , a core first end segment  146 , and a core second end segment  148 . The stainless steel jacket  136 , which is positioned about substantially all of the inert polymer core  134 , ensures that the core first end segment  146  and the core second end segment  148  extend beyond the stainless steel jacket  136  so as to provide a compressible sealing surface composed solely of the inert polymer core  134 . 
         [0018]    To accommodate higher pressures and to provide a surface for the ferrule  116  to bite into, the clad tubing  108  includes an inert polymer core  134  and a stainless steel jacket  136 , which is positioned about substantially all of the inert polymer core  134  and is clad thereabout. The inert polymer core  134  is adapted to convey a sample of liquid or gas, potentially at a high pressure, without contaminating the sample, by construction from an inert material. The inert polymer core  134  is also selected from an inert material which can be compressed to provide a seal against a mating flat surface. The mating flat surface may be composed of steel. The inert polymer core  134  may be of a flexible inert materials PEEK (Poly Ether Ether Ketone), PTFE (PolyTetraFluoroEthylene), ETFE (ethylene-tetrafluoroethylene), FEP (Flouridated Ethylene-Propylene), PFA (Perfluoroalkoxyethylene), and nylon. Such an inert polymer core  134 , while providing an inert surface for transportation of a sample, is known to be unable to sustain the pressure associated with such chromatographic uses. 
         [0019]    Referring to  FIG. 1 , the high pressure capillary tubing connector system  100  includes a ferrule  116 , which encircles, and may be ultimately fixed in position about, the clad tubing  108 . The ferrule  116  has a ferrule first end  120 , sometimes referred to as a nose, and a ferrule second end  122 , sometimes referred to as a heel, and has a ferrule wedge-shaped conical section  168  proximate the ferrule first end  120 . The clad tubing  108  has a tubing pilot length  142  greater than the zero dead volume fitting detail pilot length  374 . The tubing pilot length  142  is more than the sum of the zero dead volume fitting detail pilot length  374  illustrated in  FIG. 1  and the core first end segment length  468  illustrated in  FIG. 4 . Thus, the tubing pilot length  142  is slightly greater than a zero dead volume fitting detail pilot length  374  of the zero dead volume fitting detail  104 , and generally becomes closer to the, zero dead volume fitting detail pilot length  374  when the core first end segment  146  is compressed by the driving force of the ferrule  116  to provide a seal at the core first end flat face  156  against the zero dead volume fitting pilot bottom  110 . 
         [0020]    Referring to  FIGS. 1, 4 and 5 , the inert polymer core  134  has a core length  138 , a jacketed core outer diameter  440 , an unjacketed core outer diameter  442 , a core first end  144 , a core first end segment  146 , a core second end  150 , a core second end segment  148 , a core intermediate segment  152 , and a core lumen  154  therethrough. The core length  138  extends from the core first end  144  to the core second end  150 . The core lumen  154  has a fixed, constant, small core lumen diameter  155  throughout, which may be less than 0.03 inches. This fixed and constant core lumen diameter  155 , together with the core first end flat face  156  at the core first end  144  ensures a fixed cross sectional area throughout and therefore avoids any potential “mixing chamber” within the fitting. 
         [0021]    Referring to  FIGS. 1 and 4 , the stainless steel jacket  136  has a jacket length  158 , a jacket outer diameter  460  and a jacket inner diameter  462 , a jacket thickness  464 , and a jacket first end  466 . The core length  138  is greater than the jacket length  158 , resulting in the core first end segment  146  and the core second end segment  148  extending beyond the stainless steel jacket  136 . The stainless steel jacket  136  is therefore positioned about the core intermediate segment  152 . The stainless steel jacket  136  may have a thickness half the difference between the jacket outer diameter  460  and the jacket inner diameter  462 . 
         [0022]    Referring to  FIGS. 1 and 4 , because the stainless steel jacket  136  surrounds the inert polymer core  134  and is positioned about the core intermediate segment  152 , the jacket inner diameter  462  is equivalent to the jacketed core outer diameter  440 . Because the jacket length  158  is less than the core length  138 , the inert polymer core  134  extends sufficiently beyond the stainless steel jacket  136 , to provide a core first end segment  146  at the core first end  144  and the core second end segment  148  at the core second  150 . The core intermediate segment  152  is intermediate the core first end segment  146  and the core second end segment  148 . Additionally, the jacket outer diameter  460  is equivalent to the unjacketed core outer diameter  442 . This tight encirclement of the inert polymer core  134  by the stainless steel jacket  136  permits the use of a chemically inert tubing in contact with the fluid flowing therethough and permits the pressure in the inert polymer core  134  to exceed the capabilities of the inert polymer core  134 . The potential for the inert polymer core  134  to fail under pressure is eliminated by the encirclement of the core first end segment  146  within the zero dead volume fitting detail pilot  106  and the jacketing of the inert polymer core  134  by the stainless steel jacket  136 , which resist any high pressure deformation or failure. 
         [0023]    Referring to  FIGS. 1, 4 and 5 , the fixed and constant core lumen diameter  155  of the core lumen  154  and the core first end flat face  156 , together provide a primary seal surface across the end of the clad tubing  108 . Unlike the prior art, which may provide a hardened ring about the perimeter of the tubing, the provision of the core first end fiat face  156  at the core first end  144  under compression precludes the creation of a mixing chamber intermediate the end of the core lumen  154  and the zero dead volume fitting detail bottom  110 . In operation, this provides the primary seal upon compression of the core first end segment  146 . This compression is provided by force applied from a ferrule  116  maintained in the zero dead volume fitting  102  at a fixed and beneficial location which precludes unnecessary force being applied to the zero dead volume fitting detail bottom  110  and thus overtightening. 
         [0024]    Referring to  FIG. 1 , the ferrule  116  is fixed or bound to the clad tubing  108  by cutting into the stainless steel jacket  136  with the ferrule first end  120 , with the ferrule first end  120  is positioned at a tubing pilot length  142 . By fixing the ferrule  116  to the clad tubing  108  at this point, the extent of compression of the core first end segment  146  is fixed and the force applied to the core first end flat face  156  of the clad tubing  108  is limited so as to neverapply such force as to damage the associated valve. 
         [0025]    Referring to  FIG. 2 , the assembled ferrule  116  and retention member  124  may alternatively initially be loosely positioned on the clad tubing  108 . This initially freely-moving assembly may be desirable to address any potential tolerance issues of the specific zero dead volume fitting  102 . As can be appreciated, a zero dead volume fitting detail pilot length  374  may vary from zero dead volume fitting  102  to zero dead volume fitting  102 . Thus, it may be desirable to cause the ferrule  116  to become fixed to the clad tubing  108  in connection with a particular zero dead volume fitting  102 . The clad tubing  108  is positioned into the zero dead volume fitting detail  104  of the zero dead volume fitting  102 , and particularly into the zero dead volume fitting detail pilot  106 , until the core first end  144  contacts the zero dead volume fitting detail pilot bottom  110  at the core first end flat face  156 . 
         [0026]    Referring to  FIGS. 1 and 3 , the loose ferrule  116  is driven into the zero dead volume fitting detail  104  and maintained in position by the retention member  124 , which engages the retention section  114  of the zero dead volume fitting  102 . The zero dead volume fitting detail  104  includes a zero dead volume fitting detail pilot  106  sized to receive and fit about the clad tubing  108  at its core first end  144  and particularly to receive the core first end segment  146 , thus constraining the inert polymer core  134  against deformation from internal pressures. Some portion of the stainless steel jacket  136  preferably also is received in the zero dead volume fitting detail pilot  106 . The sferrule wedge-shaped conical section  168  of the ferrule  116  contacts the zero dead volume fitting detail ferrule seat  112  at the point of contact  370 . Any coupling means may be used in addition to the threaded assembly for the retaining member  124  and the retention section  114 , such as a cam and groove connector, an express coupling, a Guillemin symmetrical clutch coupling, a Mulconroy IX fitting, or any other fitting, particularly those adapted to high pressure situations. The retaining member  124  may have wings, such as associated with a wingnut, or may have an outer surface which presents an irregular or non-circular surface, such as a hex head, or a head providing a keyed surface, such as an extending body, about which a mating collar can fit and provide leverage for rotation. 
         [0027]    Referring to  FIGS. 1 and 3 , further tightening of the retention member  124  first causes the retention member  124  to proceed further into the zero dead volume fitting  102  and to apply force against the ferrule  116 , causing it to be slightly deformed and, because of the narrowing of the zero dead volume fitting detail ferrule seat  112 , to cause the, ferrule  116 , at the ferrule first end  120 , to be constricted about its circumference and to bite into the clad tubing  108 . Once the ferrule  116  bites into the clad tubing  108 , the ferrule  116  is bound to, or made up with, the clad tubing  108 . The ferrule  116  having bitten into the stainless steel jacket  136  of the clad tubing  108 , the ferrule first end  120  is fixed a tubing pilot length  142  from the zero dead volume fitting detail pilot bottom  110 , as illustrated in  FIGS. 1 and 3 . Thereafter the ferrule  116  and the clad tubing  108  are not readily separated or the position of the ferrule  116  on the clad tubing  108  to be altered, as described in connection with  FIG. 1 . 
         [0028]    Referring to  FIGS. 1 and 3 , beneficially, once the ferrule  116  has bitten into the clad tubing  108 , in the event they are removed from the zero dead volume fitting  102 , the two can be replaced in the zero dead volume fitting  102  and lightly tightened into position, such as by fingertightening or by use of a small tool. Now, the retaining member  124  can only be tightened into the zero dead volume fitting retention section  114  until the ferrule  116  contacts the zero dead volume detail fitting seat  112 , after which further tightening provides no advance of the ferrule  116  moreover, the ferrule  116  acts as stop to prevent unnecessary force being applied to the zero dead volume fitting detail bottom  110 . 
         [0029]    With the ferrule  116  bound to the clad tubing  108  tightening of the retention member  124  causes the clad tubing  108  to be driven forward toward the zero dead volume fitting detail pilot bottom  110  and to compress the core first end segment  146  against the zero dead volume fitting detail pilot bottom  110  until the ferrule wedge-shaped conical section  168  of the ferrule  116  contacts the zero dead volume fitting detail ferrule seat  112  at the point of contact  370  and can be driven no further forward. Thus, tightening the retaining member  124  in the zero dead volume fitting  102  at the zero dead volume fitting retention section  114  applies sufficient force for the core first end segment  146  to be compressed against the zero dead volume fitting detail pilot bottom  110  and for the core first end flat face  156  of the core first end  144  to contact so as to provide a sufficient primary seal. Additionally, this provides sufficient force for the ferrule  116  to be pressed tightly against the zero dead volume fitting detail ferrule seat  112  to provide a secondary seal and prevent unnecessary force being applied primary seal. 
         [0030]    Referring to  FIGS. 1, 4 and 5 , unlike the prior art, because the clad tubing  108  provides a core lumen  154  of fixed, constant, small core lumen diameter  155 , no mixing chamber is created within the zero dead volume fitting detail  104 . Moreover, because the ferrule  116  has bitten into the clad tubing  108 , and because the clad tubing  108  provides compressible core first end segment the force which may thereafter be applied by the core first end flat face  156  at the core first end  144  against the zero dead volume fitting detail pilot bottom  110  is limited and made insufficient to distort any chromatographic component with which the zero dead volume fitting  102  is associated, particular a valve. That distortion was known to cause separation of the rotor and stator in a valve, causing undesirable leakage and loss of pressurization. Moreover, the ferrule  116 , which cannot be fingertightened beyond the point of contact  370 , serves as a stop to prevent distortion or destruction of associated component, often a valve. Where such as stop is not provided, overdriving of tubing is known to distort or permanently damage the associated fitting, resulting in at least degraded data. 
         [0031]    Referring again to  FIGS. 1 and 3 , as the ferrule wedge-shaped conical section  168  of the ferrule  116  contacts the zero dead fitting  102  at a point of contact  370  a secondary seal is provided. Because the force to tighten the ferrule  116  and to bite into the clad tubing  108  may be greater than necessary to maintain contact with the zero dead volume  102 , and thus provide a seal, the retaining member  124  may be loosened while maintaining contact with the point of contact  370 . As can be appreciated, the retaining member  124  may require only minimal force to sufficient engage the zero dead volume fitting  102 , such as by fingertightening. This may be particularly beneficial in chromatography uses, where the zero dead volume fitting  102  may be one of several ports associated with a single, small valve, each of which would have a clad tubing emanating therefrom about the valve&#39;s central axis. 
         [0032]    It will be understood that while a preferred embodiment of the disclosure has been shown and described, the disclosure is not limited thereto. Many modifications may be ad e and will become apparent to those skilled in the art.