Fluidic fitting with integral face seal

A fitting for a fluidic coupling includes a tube assembly that includes an inner tube, an intermediate tube formed of a polymeric material and disposed over at least a portion of a length of the inner tube, and an outer tube formed of a metal and disposed over the intermediate tube. The inner tube has an inner tube endface and a first fluid channel. The intermediate tube includes an extruded portion having a length and an intermediate tube endface. The outer tube has an outer tube endface and an outer surface. First and second radial crimps are formed on the outer surface at first and second distances from the outer tube endface and extend for first and second axial lengths, respectively. The inner and outer tube endfaces are co-planar and the intermediate tube endface is separated from the inner and outer tube endfaces by the length of the extruded portion.

FIELD OF THE INVENTION

The invention relates generally to fluidic couplings such as those used in chromatographic systems. More particularly, the invention relates to a fluidic fitting having an integral face seal.

BACKGROUND

Chemical analysis systems often include fluid channels that accommodate high pressures. For example, a liquid chromatography system, such as a system designed for ultra performance liquid chromatography (UPLC®), can operate at pressure that may exceed 18,000 psi. The fluid channels in such systems may include tubing that is coupled to other components or tubing using a conventional coupling such as a standard compression fitting.

The improved performance of UPLC systems includes substantial increases in separation power. Adverse chromatographic effects such as carryover and peak tailing can result from the use of conventional couplings used to achieve fluid-tight seals and are more readily observable in system measurements. In typical couplings, the seal is formed along the side of the capillary. For example, many couplings use an annular sealing element such as a ferrule that has a conical outer surface. To form a fluid-tight coupling, a capillary having the annular sealing element displaced away from the endface is inserted into a receptacle of a coupling body. The receptacle is defined by a cylindrical bore that transitions to a conical bore and then to a smaller diameter cylindrical bore. A fluid channel extends from the surface at the bottom of the smaller diameter cylindrical bore into the coupling body. The cone angle of the conical bore is greater than the cone angle of the annular sealing element resulting in a seal along the circumferential contact between the annular sealing element and the conical surface of the conical bore. Additional force applied by a compression screw after achieving initial contact between the annular sealing element and conical bore surface results in a contact seal between the annular sealing element and the outer surface of the capillary. If the endface of the capillary is not in contact with the bottom of the cylindrical bore, the region between the outer surface of the capillary and the side wall of the smaller cylindrical bore below the circumferential contact seal represents an unswept volume. During a chromatographic measurement, analytes can become trapped in the unswept volume and gradually diffuse into the fluid flow, thereby degrading the chromatographic measurement data. Moreover, corrosion may occur at the capillary interface, leading to further degradation of chromatographic measurements.

SUMMARY

In one aspect, the invention features a fitting for a fluidic coupling. The fitting includes an inner tube, an intermediate tube and an outer tube. The inner tube has an inner tube endface and a first fluid channel. The intermediate tube is formed of a polymeric material and is disposed over at least a portion of a length of the inner tube. The intermediate tube includes an extruded portion having a length and an intermediate tube endface. The outer tube is formed of a metal and is disposed over the intermediate tube. The outer tube has an outer tube endface and an outer surface, a first radial crimp on the outer surface at a first distance from the outer tube endface that extends for a first axial length, and a second radial crimp on the outer surface at a second distance from the outer tube endface that extends for a second axial length. The outer tube endface is co-planar with the inner tube endface. The intermediate tube endface is separated from the inner tube endface and the outer tube endface by the length of the extruded portion.

In another aspect, the invention features a method of forming a fitting for a fluidic coupling. The method operates on a tube assembly that includes an inner tube having an inner tube endface and a fluid channel, an intermediate tube formed of a polymeric material and disposed over at least a portion of a length of the inner tube and having an intermediate tube endface, and an outer tube formed of a metal and disposed over the intermediate tube. The outer tube has an outer tube endface and an outer surface. The inner tube endface, intermediate tube endface and outer tube endface re coplanar. The method includes forming a first radial crimp on the tube assembly over a first crimp length at a first distance from the outer tube endface to secure the inner tube, intermediate tube and outer tube to each other and to extrude a portion of the intermediate tube such that the intermediate tube endface is separated from the inner tube endface and the outer tube endface by an extrusion length. The method further includes forming a second radial crimp on the tube assembly over a second crimp length at a second distance from the outer tube endface.

DETAILED DESCRIPTION

Reference in the specification to “one embodiment” or “an embodiment” means that a particular, feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the teaching. References to a particular embodiment within the specification do not necessarily all refer to the same embodiment.

As used herein, a coupling body means a body that has a bore to receive a tube assembly and a fluid channel to receive a fluid from or provide a fluid to the tube assembly. For example, a coupling body can be a structure provided between the endfaces of two capillaries (or tube assemblies) to enable fluid to pass from one capillary to the other capillary. Alternatively, a system component can include a coupling body. By way of examples, an injector valve or a chromatography column for a liquid chromatography system may include a coupling body to couple fluid to or from a capillary or another component of the liquid chromatography system.

A tube assembly refers to at least one tube (e.g., capillary) and additional structure such as a sleeve or a second tube disposed either inside or outside the first tube. A retaining ring, as used herein, includes a ring or clip typically formed of metal and shaped similar to the letter “C,” although other shapes, including nominally square, rectangular and tapered cross sectional shapes, may be used. The shape allows the ring to be installed in a crimp or groove on a cylindrical part to limit or prevent axial movement of an axial loading device along the cylindrical part. The retainer ring can open slightly from its original diameter to enable the ring to slide over the full diameter of a tube until the ring moves into the crimp or groove where the ring returns (i.e., “relaxes”) to its original shape and diameter. The retaining ring is sometimes referred to as a circlip or a C-clip.

FIG. 1shows a view of a capillary coupling10at a stator portion12of a rotary shear seal valve for a liquid chromatography system. The fluidic coupling10includes a compression nut14and additional components (not visible). A tube16defines a fluid channel that conducts a fluid from a chromatographic system component to one of the stator ports18or from the stator port18to the chromatographic system component. By way of examples, the chromatographic system component can be an injection valve or a chromatography column. A second fluid channel is defined inside the stator portion12and interfaces with a rotor portion of the rotary shear seal valve to couple or decouple the second fluid channel with a third fluid channel in communication with one of the other stator ports18.

FIG. 2Ashows a cross-sectional view of a conventional fitting20that can be used, for example, to couple two fluid channels22and24. For example, the fitting20can be used to couple the tube16ofFIG. 1to an internal fluid channel in the rotary shear seal valve. The tube26includes the first fluid channel22which is coupled to the second fluid channel24inside the coupling body28.FIG. 2Bis an expanded view of a portion ofFIG. 2Athat shows the sealing interface. As illustrated, a two-part ferrule30A and30B engages an inner conical surface of the coupling body28and the outer surface of the tube26. In other variations, a single part ferrule may be used. The resulting fluidic seal can withstand a high fluid pressure (e.g., greater than 15,000 psi); however, an unswept volume32is formed in the unoccupied region of the bore that surrounds the tube26and is to the right of the contact zone34where the ferrule part30B is in contact with the conical surface in the figure. The presence of the unswept volume32may result in sample carryover. For example, as the sample moves from the first fluid channel22into the second fluid channel24, some of the sample can diffuse into the unswept volume32. Subsequently, the sample present in the unswept volume32can diffuse back into the main fluid flow and into the second fluid channel24. If the fitting20is used with components of a liquid chromatography system, such as illustrated inFIG. 1, the fluid sample that diffuses back into the fluid flow (i.e., the carryover) can adversely affect chromatographic measurements.

FIG. 3Ais a cross-sectional view of a fluidic coupling40such as disclosed in U.S. Patent Publication No. 2015/0369403, the disclosure of which is incorporated herein by reference.FIG. 3Bis an expanded cross-sectional view of the fluidic coupling40in the region of a coupling seal42. The fluidic coupling40includes the coupling seal42, a tube assembly, a compression screw44and a coupling body46. As the compression screw44is rotated so that it advances into the coupling body46, a surface on the compression screw44engages a back surface of a ferrule48this is secured to the tube assembly. Continued rotation of the compression screw44results in moving the combined ferrule48and tube assembly as one further into the receptacle until the coupling seal42comes into contact with an internal sealing surface50of the coupling body46. Further rotation results in axial compression of the coupling seal42such that coupling seal42deforms and flows into an unoccupied volume52of the coupling body46. This deformation and flow into the unoccupied volume52prevents compression of the capillary54or damage to the capillary54.

While providing a fluid tight seal for many applications, the fluidic coupling40requires that the coupling seal42have a diameter greater than the tube assembly and that the receptacle have sufficient dimensions to accommodate the deformation shape of the coupling seal42while under compression. Moreover, the coupling seal42is a separate component that must be attached to the end of the tube assembly before creating the seal. Care is required to avoid separating the coupling seal42from the tube assembly and to prevent loss of the coupling assembly during handling due to its small size.

In brief overview, the invention relates to a fitting for a fluidic coupling. The fitting includes a tube assembly that includes an inner tube, an intermediate tube formed of a polymeric material and an outer metal tube. The intermediate tube is made from a polymeric material and includes an extruded portion formed during a crimping process. The extruded portion extends away from the end of the tube assembly. During installation of the fitting, the extruded portion of the polymeric tube is deformed against a sealing surface of a coupling body or other device, resulting in a liquid tight face seal between fluid channels defined by the inner tube and the coupling body.

Advantageously, the fitting does not require a ferrule or a separate seal component to establish the fluidic seal. Moreover, the receptacle of the coupling body is not required to have a conical or other specialized port configuration as long as the tube assembly can pass into the coupling body such that the extruded portion of the intermediate tube is compressed against a suitable sealing surface. As the seal is integral with the tube assembly, problems associated with handling small sealing components are avoided. Moreover, the face seal achieved with the fitting substantially reduces or eliminates unswept volume at the fluidic coupling.

FIGS. 4A, 4B and 4Cshow a perspective view, a side cross-section view and an endface view, respectively, of a portion of an embodiment of a fitting60for a fluidic coupling. The fitting60includes a tube assembly having an inner tube62, an intermediate tube64and an outer tube66. The inner tube62includes a fluid channel to be coupled to another fluid channel. Not shown is a compression screw that is used to establish a face seal between an end of the fluid channel an end of another fluid channel. In preferred embodiments, the inner tube62is a capillary made of fused silica. In other embodiments, the inner tube62may be a different type of glass tube or a metal tube such as a titanium tube or a stainless steel tube. The intermediate tube64is formed of a polymeric material such as a thermoplastic polymer (e.g., a polyether ether ketone (PEEK)). The outer tube66is preferably a stainless steel tube although metals which are more rigid that the polymeric material and which have suitable material properties (e.g., ductility) may be used. The intermediate tube64has an inner diameter that is slightly larger than the outer diameter D1of the inner tube62to permit the intermediate tube64to slide over an end of the inner tube62. The outer tube66has an inner diameter slightly larger than the outer diameter D2of the intermediate tube64to allow the intermediate tube64(and inner tube62) to be inserted into the outer tube66. A positive clearance is provided between the inner tube62and the intermediate tube64, and between the intermediate tube64and the outer tube66. For example, the clearance may be less than 2.5 μm (0.0001 in.) or may be 75 μm (0.003 in) or more. The intermediate tube64has a length L1and the outer tube66has a length L2. As illustrated, the length L1of the intermediate tube64exceeds the length L2of the outer tube66; however, in other embodiments the lengths L1and L2are the same or the length L2of the outer tube66may exceed the length L1of the intermediate tube64.

Prior to applying a radial crimping process that yields the illustrated tube assembly, the three tubes60,62and64are arranged with respect to each other so that their endfaces68,70and72, respectively, are co-planar. Preferably, the endfaces68,70and72are perpendicular to the tube axes82and polished with the endfaces68,70and72free of scratches and other surface defects. The fitting60is then created by forming on the outer surface of the outer tube66a first radial crimp74of crimp depth Δ1and crimp length LC1, and subsequently forming a second radial crimp76having a crimp depth Δ2and a crimp length LC2. As illustrated, the crimp depths Δ1and Δ2are equal and the crimp lengths LC1and LC2are equal although this is not a requirement. Although shown inFIG. 4Bas a near step-like change in diameter of the outer surface of the outer tube66, in other embodiments the cross-sectional shape of the crimps74and76may include a more gradual slope for the diameter transition at the left and right crimp edges. In addition, the “bottom” of the crimps74and76may not be as flat as shown in the figure.

Dashed circles78and80inFIG. 4Cindicate the post-crimp reduced diameters D2′ and D3′, respectively, of the intermediate tube64and outer tube66in the region of the first radial crimp74, i.e., at a length L3from the outer tube endface72. The first radial crimp74acts to secure, or “capture,” the inner tube62with respect to the intermediate and outer tubes64and66. In addition, the first radial crimp74creates a desired strain of the intermediate tube64such that the polymeric material flows parallel to the tube assembly axis82between the more rigid inner and outer tubes62and66. As a result of the extrusion of the polymeric material, the intermediate tube endface70is separated from the inner and outer tube endfaces68and72by an extrusion length Δ3. A predetermined extrusion length Δ3for the polymeric material is achieved by controlling certain parameters, including the crimp depth Δ1and crimp length LC1of the first radial crimp74and the distance L3of the first radial crimp74from the inner and outer tube endfaces68and72. In some embodiments, the extrusion length is less than 0.50 mm (0.02 in.).

After forming the first radial crimp74, the second radial crimp76is formed at a distance L4from the outer tube endface72. The second radial crimp76enables a retaining ring83(e.g., a C-clip) to be installed.FIG. 5shows a cross-sectional view through the installed retaining ring83. Circle84indicates the outer surface of the outer tube66at the outer tube diameter D3. The retaining ring83has an inner diameter D4that is equal to or greater than the crimp diameter D3′ on the outer tube66at the second radial crimp76and an outer diameter D5that is greater than the outer tube diameter D3. Thus the retaining ring83can be installed at the second crimp76and is free to move axially along the length LC2of the crimp76.

Reference is made toFIG. 6Awhich is a perspective view of a portion of the fitting60ofFIG. 4Awith a compression screw86installed and toFIG. 6Bwhich is a cutaway perspective view of the fitting ofFIG. 6A. The compression screw86has a counterbore that includes a cylindrical hole85terminating at a bottom surface. The hole85has a diameter that is greater than the outer diameter D5of the retaining ring83when the retaining ring83is positioned in the second radial crimp76in a relaxed state. The counterbore also includes a through-hole that extends from the bottom surface of the hole85to the opposite end of the compression screw86. The through-hole has a diameter that is greater than the outer tube diameter D3and less than the outer diameter of the retaining ring83in its relaxed state. Thus the compression screw86can be inserted over the tube assembly so that the tube assembly passes through the through-hole; however, once the retaining ring83is installed at the second crimp76, the compression screw86can be moved axially from right to left in the figure until the bottom surface at the hole85engages the retaining ring83. Further axial movement of the compression screw86along the tube assembly is prevented once the compression screw86pushes the retaining ring83up against the left side of the second crimp76.

The engagement of the compression screw86with the retaining ring83is relied upon during the installation of the fitting into a coupling body87to achieve a face seal as shown inFIG. 7. The illustrated coupling body87includes a counterbore having a hole with a bottom surface88and a through-hole extending from the bottom surface88that defines a fluid channel90to conduct the fluid received from the tube assembly. The hole has a diameter greater than the outer tube diameter D3to enable the tube assembly to be inserted into the coupling body87. To seal the two fluid channels, the compression screw86engages a threaded bore of the coupling body87and is rotated until the bottom surface at the hole85in the compression screw86comes into contact with the retaining ring83as described above. Further rotation of the compression screw86moves the retaining ring83to the left until the retaining ring83comes into contact with the left edge of the second radial crimp76. Subsequent rotation seats the retaining ring83fully into the counterbore of the compression screw86then drives the fitting forward to form a face seal as the intermediate tube endface70(seeFIG. 6B) comes into contact with the bottom surface of the coupling body87. At this time there is increased resistance to rotation of the compression screw86. A small additional rotation of the compression screw86results in compression of the extruded portion of the polymeric material to provide a fluidic face seal at the intermediate tube endface70and the bottom surface88inside the coupling body87.

While the invention has been shown and described with reference to specific preferred embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention as defined by the following claims. For example, some embodiments described above include a compression screw to advance a tube assembly into a coupling body to achieve an axial compression of the intermediate tube. It will be recognized that other means of achieving compression of the intermediate tube against a sealing surface may be used. In addition, the seating and positioning of the retaining ring can be established prior to threading the compression screw into the coupling body.