Abstract:
A tubing connection provides a unique nut assembly that does not loosen or leak when exposed to the initial heat/cool cycles of a chemistry setup. The nut assembly includes a outer housing portion, and a concentric inner locking ferrule. A cavity defined between the inner and outer portion houses a stainless steel spring secured therein by a snap-engaged spring retainer. As the outer nut is rotated on the threads of the fitting, it drives the spring retainer toward the ferrule, thereby compressing the spring and causing it to maintain the engagement of the tubing end on the connector fitting.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of the priority date of Provisional Application Ser. No. 60/695,560, filed Jun. 29, 2005. 
     
    
     FEDERALLY SPONSORED RESEARCH  
       [0002]     Not applicable.  
       SEQUENCE LISTING, ETC ON CD  
       [0003]     Not applicable.  
       BACKGROUND OF THE INVENTION  
       [0004]     1. Field of the Invention  
         [0005]     This invention relates to tubing connectors for chemical use and, more particularly, to tubing connectors fabricated of relatively soft polymer materials such as Teflon.  
         [0006]     2. Description of Related Art  
         [0007]     In chemistry laboratories, chemical processing installations, and other users of chemistry equipment, a ubiquitous component in chemical processing layouts is the common tubing connector. Most processing is conducted in a liquid-based processing scheme and whether for solvents and solutions, feedstock or waste flow, washes or etches, the instruments, pumps, reaction vessels, tanks, and valves are interconnected using inert tubing and tubing connectors. One standard arrangement for tubing connector typically has a flexible tubing with an end that is expanded elastically outwardly in diameter, in order to slidably engage the tapered end of a connector nipple. A nut is secured about the fitting and about the tubing, and is threaded onto the nipple. In installations where corrosive or poisonous fluids are used, it is commonplace to employ fittings and tubing of the most chemically inert materials, such as Teflon, fused quartz, and the like  
         [0008]     Conventional Teflon nuts and conventional Teflon tubing tend to loosen from the rigid tubing fitting during heat/cool cycles. This tendency may be attributed to the expanded Teflon tubing relaxing or changing its flared shape in relation to the fitting on which it is placed, or creeping away from any squeezing action, a phenomenon common to Teflon and some other materials, whether through plastic flow, thermal expansion hysteresis, or the like. As this “change of shape” occurs, the nut may loosen and may typically requires additional tightening to provide the correct gripping force of the tubing on the fitting.  
         [0009]     The main problem with the above arrangement is that at the very least the connection system becomes loose and can weep chemistry as the nut is spontaneously loosened by multiple initial hot/cold cycles. This creates an undesirable situation in which a potentially dangerous chemistry must be continually cleaned up in the area of the connection system. At the worst, if the style of the nut does not provide a locking ferrule such as that found in the latest series of FlareLok II by Entegris, the connection system can become a danger to personnel working in close proximity. The Teflon tubing changes shape or rather extrudes with heat/cool cycles, allowing it to slip out of the expanded elastic engagement with the fitting, and can become free from the fitting and nut. When this occurs, dangerous heated chemistry can be sprayed in any direction in the immediate area. Needless to say, this is not a safe event and there have been documented cases where personnel nearby required emergency medical treatment when tubing became separated from the flared tube fitting.  
         [0010]     It should be noted that the nuts that are used in this environment have to be made of materials that are compatible with the various chemistries that will be in use. This fact is well-known, and it implies that there are not too many alternatives to choose from that will be acceptable to the end user. There is an opportunity to rectify the failings of the prior art flared tubing connection, and it is found in the design of the nut that is used with the flared tubing and fitting.  
       BRIEF SUMMARY OF THE INVENTION  
       [0011]     The present invention generally comprises a tubing connection that overcomes the drawbacks of the prior art as described above. In particular, the invention provides a unique nut assembly designed for tubing connections that does not loosen or leak when exposed to the heat/cool cycles of a chemistry setup.  
         [0012]     The nut of the present invention provides an internal spring that stores energy to be released as needed to compensate for the changing shape of the tubing and the typical loosening of the nut. The internal spring is designed to be able to provide a pre-load force in the range of 10-79 pounds when the spring is compressed by approximately 0.100 inch. When the expanded Teflon tubing alters its shape around the tubing fitting, the spring loaded nut is able to release a percentage of its stored energy to compensate and maintain a constant force on the Teflon tubing. The result is that the tubing is continually gripped tightly, despite any flow or extrusion effect. The Teflon tube cannot change shape and extrude backwards through the nut, which would otherwise result in an un-restrained tubing end.  
         [0013]     One advantageous aspect of the design is that the spring is disposed internally to the working parts, and it is never exposed to any of the potentially damaging chemicals that may be passing through the connection. This is accomplished by placing the spring in a cavity that is defined by sliding O-ring seals between moving parts.  
         [0014]     The nut assembly generally comprises a main outer body portion, and a concentric inner body portion or locking ferrule. A cavity is defined between the inner and outer portions, and a stainless steel spring is secured in the cavity by a spring retainer. As the outer nut portion is rotated on the threads of the fitting, the outer nut will drive the spring retainer toward the ferrule, thereby compressing the outer end of the spring. The inner end of the spring impinges on the locking ferrule, causing it to maintain the engagement of the flared tubing end on the connector fitting, despite subtle changes in shape that may accompany heat/cool cycling of the fitting assembly.  
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0015]      FIG. 1  is a partial cross-sectional view of the spring-loaded nut assembly for male tubing fittings of the present invention.  
         [0016]      FIG. 2  is an assembly view of the spring-loaded nut assembly as shown in  FIG. 1 .  
         [0017]      FIG. 3  is a cross-sectional view of the spring-loaded nut assembly for a standard type of female tubing connector.  
         [0018]      FIG. 4  is an assembly view of the spring-loaded nut assembly as shown in  FIG. 3 .  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     The present invention generally comprises a unique connector assembly having a fitting that receives a flared tubing end and secures it with a compression nut. It is intended for use in harsh chemical environments, where the presence of corrosive liquids and the potential for contamination of process chemistry necessitates the use of Teflon components. In the following description it is presumed that components are made of Teflon or an equivalent polymer material that is inert with respect to a wide range of harsh chemicals and solvents.  
         [0020]     More particularly, as shown in  FIGS. 1 and 2 , one embodiment of the invention is designed to operate with a typical pressurized fluid (liquid or gas) connector assembly  11  having a male connector fitting  12 . The fitting  12  includes a body  13 , and nipple  14  extending therefrom, with external threads  16  and a tapered end  17 . The end  18  of resilient tubing  19  is dimensioned to expand and slidably engage the nipple  14 ; this arrangement being similar to that known in the prior art.  
         [0021]     One embodiment of the invention provides a nut assembly  21  for engaging the threads  16  and securing the tubing end  18  on the nipple  14 . The nut assembly includes an outer cylindrical housing  22  having an internal bore  23 , and a threaded opening  24  joining the inner end of the bore  23 . The bore  23  includes a retaining groove  46  formed therein adjacent to the distal end of the housing  22 . Threads  16  and  24  are complementary and mutually engaging, and opening  24  and bore  23  are concentric with tubing end  18 . The exterior surface of the nut may be provided with any surface configuration (polyhedron or the like) that is engageable for turning the nut to thread and unthread from the fitting  11 .  
         [0022]     A locking ferrule  31  is dimensioned to be received concentrically and freely within the bore  23 . At the proximal end, the ferrule  31  is provided with an annular shoulder  32  extending radially outwardly, with an O-ring seal  33  supported in the peripheral surface thereof. The O-ring  33  is dimensioned to establish a sliding seal with the bore  23 . The outer cylindrical surface of the ferrule  31  and the bore  23  define an annular space  34 . A reduced diameter neck  36  extends from the distal end of the ferrule, and is provided with an O-ring seal  37 . The ferrule  31  is provided with an internal axial bore having a broader proximal end portion  38  and a narrower distal portion  39  joined by an annular step  41 . Note that the diameter of proximal portion  38  is sufficient to establish a close tolerance fit with the tubing end  18  engaged on the nipple  14 , and the diameter of the distal portion  39  is sufficient to receive the tubing  19  in a sliding fit. Moreover, the diameter of the portion  39  is less than the diameter of the nipple  14 , so that the step  41  is driven by proximal motion of the ferrule  31  to clamp the flared portion of the tubing against the tapered end  16  of the nipple and establish a very good sealing relationship.  
         [0023]     Within the annular space  34  a helical coil spring  42  (stainless steel or the like) is secured about the ferrule  31 , with the proximal end of the spring  42  impinging on the shoulder  32 . A spring retaining ring  43  has an outer flange  44  extending from a proximal portion thereof. The inner bore of the ring  43  forms a complementary fit to the neck  36 , and establishes a sliding seal with O-ring  37 . Flange  44  is dimensioned to engage retaining groove  46  formed in the inner bore  23  adjacent to the distal end of the bore  23 . Thus the components of the nut assembly  21  may be joined by placing the ferrule  31  within the bore  23 , then placing the spring  42  in the annular space  34 , then inserting and snapping the retaining ring  43  into groove  46 . Note that the O-ring seals  33  and  37  enclose the space  34  and protect the spring  42  from the corrosion and contamination that might otherwise occur.  
         [0024]     In a typical installation procedure, the tubing end  18  is passed through the nut assembly  21  and pushed onto the tapered end  17  of nipple  14 . The nut assembly  21  is then threaded onto the threads  16  of nipple  14 , thereby translating proximally and concentrically about the flared tubing conjunction. The nut assembly advances proximally until the step  41  moves proximate to the flared end  17 , and the tubing wall clamped therebetween prevents further proximal movement of the ferrule  31 . Continued threaded advancement of the nut in the proximal direction will then cause the spring retainer ring  43  to move proximally against the spring  42 , compressing the spring and resiliently loading the ferrule in the proximal direction, whereby the annular step  41  is resiliently biased to maintain engagement with the tapered end  17 .  
         [0025]     In a typical real-world example, the spring  42  may have sufficient stiffness to exert a compressive force of approximately 35 pounds (in the range of 10-79 pounds) after undergoing a compression of about 0.1 inch. Given the 1-20 threads used in standard fittings, this spring loading may be achieved in approximately 2 full turns of the nut assembly  21  after the ferrule  31  reaches the limit of proximal travel.  
         [0026]     The pre-loading condition of the ferrule on the tubing conjunction assures that the step  41  maintains firm contact with the flared portion of the tubing and sustains the clamping engagement of the expanded portion. Even though the assembly may undergo movement and yielding during the thermal cycles of the connector assembly, the pre-loading condition maintains the seal and stops the leaks that would otherwise occur, e.g., with Teflon tubing. The Teflon tube cannot change shape and extrude backwards through the nut, which would otherwise result in an un-restrained tubing end.  
         [0027]     With regard to  FIGS. 3 and 4 , a further embodiment of the invention is adapted for use with another typical tubing connector assembly  111  having a cylindrical stem  112  extending outwardly with a female receptacle  113  formed coaxially in the outer end of the stem  112 . The stem is provided with external threads  116 . The receptacle  113  includes a flared outer end  117  and an inner stepped shoulder  118  that is formed as a truncated coaxial cone. and an axial flow passage  119  extending therethrough. The assembly  111  further includes a tubular insert  151  that is adapted to be introduced into the end of the tubing  152  that is intended to be secured in the assembly  111 . The insert  151  includes a flared distal end  153  in an arrow shape, and a proximal flange portion  154 . A flow passage  155  extends axially through the insert  151 , and is provided with a beveled counterbore  156  at the proximal end thereof. The insert  151  is forcefully inserted into the end of the tubing to elastically deform the tubing about the flared end  153 . The flange  154  projects radially outwardly a distance approximately equal to the thickness of the tubing, so that the flange and tubing form a generally contiguous profile that is dimensioned to be received in the receptacle  113  in close tolerance fit. These components are generally known to be used in industry-standard tubing connector designs.  
         [0028]     Another embodiment of the invention provides a nut assembly  121  for engaging the threads  116  and securing the tubing end  152  to the nipple  112 . The nut assembly  121  includes an outer cylindrical housing  122  having an internal bore  123 , and a threaded opening  124  joining the inner end of the bore  123 . The bore  123  includes a retaining groove  146  formed therein adjacent to the distal end of the housing  122 . Threads  116  and  124  are complementary and mutually engaging, and opening  124  and bore  123  are concentric with tubing end  152 . The exterior surface of the nut may be provided with any surface configuration (polyhedron or the like) that is engageable for turning the nut to thread and unthread from the stem  112 .  
         [0029]     A locking ferrule  131  is dimensioned to be received concentrically and freely within the bore  123 . At the proximal end, the ferrule  131  is provided with an annular shoulder  132  extending radially outwardly, with an O-ring seal  133  supported in the peripheral surface thereof. The O-ring  133  is dimensioned to establish a sliding seal with the bore  123 . The outer cylindrical surface of the ferrule  131  and the bore  123  define an annular space  134 . A reduced diameter neck  136  extends from the distal end of the ferrule, and is provided with an O-ring seal  137 . The ferrule  131  is provided with an internal axial bore  138  having a broader proximal beveled counterbore  139 . An annular shoulder  141  projects proximally at the conjunction of the bore and counterbore, and is dimensioned and oriented to impinge on the tubing end  152  at the portion thereof that is expanded by the insert  151 , in a manner that is analogous to the function of the annular step  41  of the previous embodiment. The shoulder  141  interacts with the flared surface of the insert  151  to clamp the tubing tightly therebetween and form a sealing relationship, as shown in  FIG. 3 .  
         [0030]     Within the annular space  134  a helical coil spring  142  (stainless steel or the like) is secured about the ferrule  131 , with the proximal end of the spring  142  impinging on the shoulder  132 . A spring retaining ring  143  has an outer flange  144  extending from a proximal portion thereof. The inner bore of the ring  143  forms a complementary fit to the neck  136 , and establishes a sliding seal with O-ring  137 . Flange  144  is dimensioned to engage retaining groove  146  formed in the inner bore  123  adjacent to the distal end of the bore  123 . Thus the components of the nut assembly  121  may be joined by placing the ferrule  131  within the bore  123 , then placing the spring  142  in the annular space  134 , then inserting and snapping the retaining ring  143  into groove  146 . Note that the O-ring seals  133  and  137  enclose the space  134  and protect the spring  142  from the corrosion and contamination that might otherwise occur.  
         [0031]     In a typical installation procedure, the tubing end  152  is passed through the nut assembly  121 , and the insert  151  is installed in the tubing end. The nut assembly  121  is then threaded onto the threads  116  of stem  112 , The nut assembly advances proximally until the shoulder  141  moves proximate to the flared end of the insert, and the tubing wall clamped therebetween prevents further proximal movement of the ferrule  131 . Continued threaded advancement of the nut in the proximal direction will then cause the spring retainer ring  143  to move proximally against the spring  142 , compressing the spring and resiliently loading the ferrule in the proximal direction, whereby the annular shoulder  141  is resiliently biased to maintain engagement with the tubing at the flared end of the insert  151 . The resilient force directed proximally by the spring  142  also forces the expanded tubing about the insert to impinge on the complementarily formed sidewall of receptacle  113  and form a sealing relationship therewith as well. It should be noted that the beveled counterbore  156  is dimensioned to engage the truncated conical shoulder  118 , so that the insert  151  is self-centering in the receptacle  113 .  
         [0032]     A broad view of the two embodiments reveals that the essential aspect of the invention is the implementation of a locking ferrule to establish a sealing relationship between a tubing end and a tubing connector, a spring to resiliently bias the locking ferrule to impinge on the tubing connector and maintain the sealing relationship, and a nut housing to enclose the spring, thread onto the fitting, and drive a spring retainer ring to compress the spring and resiliently bias the locking ferrule in the sealing direction. There are other standard tubing connection arrangements known in the prior art, and perhaps many other ways to arrange structures and components to carry out the essential invention. It is anticipated that the accompanying claims will cover all such variations.  
         [0033]     The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and many modifications and variations are possible in light of the above teaching without deviating from the spirit and the scope of the invention. The embodiment described is selected to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as suited to the particular purpose contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.