Patent Description:
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.

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 <NUM> Bar (<NUM>,<NUM> 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.

<CIT> discloses a coated capillary with remelted coating for front sided sealing.

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. An outer diameter of the inner tube endface does not exceed an inner diameter of the intermediate tube endface. An outer diameter of the intermediate tube endface does not exceed an inner diameter of the outer tube endface.

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.

The present teaching will now be described in more detail with reference to embodiments thereof as shown in the accompanying drawings. While the present teaching is described in conjunction with various embodiments and examples, it is not intended that the present teaching be limited to such embodiments. On the contrary, the present teaching encompasses various alternatives, modifications and equivalents, as will be appreciated by those of skill in the art. Those of ordinary skill having access to the teaching herein will recognize additional implementations, modifications and embodiments, as well as other fields of use, which are within the scope of the present disclosure.

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> shows a view of a capillary coupling <NUM> at a stator portion <NUM> of a rotary shear seal valve for a liquid chromatography system. The fluidic coupling <NUM> includes a compression nut <NUM> and additional components (not visible). A tube <NUM> defines a fluid channel that conducts a fluid from a chromatographic system component to one of the stator ports <NUM> or from the stator port <NUM> to 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 portion <NUM> and 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 ports <NUM>.

<FIG> shows a cross-sectional view of a conventional fitting <NUM> that can be used, for example, to couple two fluid channels <NUM> and <NUM>. For example, the fitting <NUM> can be used to couple the tube <NUM> of <FIG> to an internal fluid channel in the rotary shear seal valve. The tube <NUM> includes the first fluid channel <NUM> which is coupled to the second fluid channel <NUM> inside the coupling body <NUM>. <FIG> is an expanded view of a portion of <FIG> that shows the sealing interface. As illustrated, a two-part ferrule 30A and 30B engages an inner conical surface of the coupling body <NUM> and the outer surface of the tube <NUM>. In other variations, a single part ferrule may be used. The resulting fluidic seal can withstand a high fluid pressure (e.g., greater than <NUM> Bar (<NUM>,<NUM> psi)); however, an unswept volume <NUM> is formed in the unoccupied region of the bore that surrounds the tube <NUM> and is to the right of the contact zone <NUM> where the ferrule part 30B is in contact with the conical surface in the figure. The presence of the unswept volume <NUM> may result in sample carryover. For example, as the sample moves from the first fluid channel <NUM> into the second fluid channel <NUM>, some of the sample can diffuse into the unswept volume <NUM>. Subsequently, the sample present in the unswept volume <NUM> can diffuse back into the main fluid flow and into the second fluid channel <NUM>. If the fitting <NUM> is used with components of a liquid chromatography system, such as illustrated in <FIG>, the fluid sample that diffuses back into the fluid flow (i.e., the carryover) can adversely affect chromatographic measurements.

<FIG> is a cross-sectional view of a fluidic coupling <NUM> such as disclosed in U. Patent Publication No. <NUM>/<NUM>. <FIG> is an expanded cross-sectional view of the fluidic coupling <NUM> in the region of a coupling seal <NUM>. The fluidic coupling <NUM> includes the coupling seal <NUM>, a tube assembly, a compression screw <NUM> and a coupling body <NUM>. As the compression screw <NUM> is rotated so that it advances into the coupling body <NUM>, a surface on the compression screw <NUM> engages a back surface of a ferrule <NUM> this is secured to the tube assembly. Continued rotation of the compression screw <NUM> results in moving the combined ferrule <NUM> and tube assembly as one further into the receptacle until the coupling seal <NUM> comes into contact with an internal sealing surface <NUM> of the coupling body <NUM>. Further rotation results in axial compression of the coupling seal <NUM> such that coupling seal <NUM> deforms and flows into an unoccupied volume <NUM> of the coupling body <NUM>. This deformation and flow into the unoccupied volume <NUM> prevents compression of the capillary <NUM> or damage to the capillary <NUM>.

While providing a fluid tight seal for many applications, the fluidic coupling <NUM> requires that the coupling seal <NUM> have a diameter greater than the tube assembly and that the receptacle have sufficient dimensions to accommodate the deformation shape of the coupling seal <NUM> while under compression. Moreover, the coupling seal <NUM> is 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 seal <NUM> from 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.

<FIG>, <FIG> and <FIG> show a perspective view, a side cross-section view and an endface view, respectively, of a portion of an embodiment of a fitting <NUM> for a fluidic coupling. The fitting <NUM> includes a tube assembly having an inner tube <NUM>, an intermediate tube <NUM> and an outer tube <NUM>. The inner tube <NUM> includes 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 tube <NUM> is a capillary made of fused silica. In other embodiments, the inner tube <NUM> may be a different type of glass tube or a metal tube such as a titanium tube or a stainless steel tube. The intermediate tube <NUM> is formed of a polymeric material such as a thermoplastic polymer (e.g., a polyether ether ketone (PEEK)). The outer tube <NUM> is 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 tube <NUM> has an inner diameter that is slightly larger than the outer diameter D<NUM> of the inner tube <NUM> to permit the intermediate tube <NUM> to slide over an end of the inner tube <NUM>. The outer tube <NUM> has an inner diameter slightly larger than the outer diameter D<NUM> of the intermediate tube <NUM> to allow the intermediate tube <NUM> (and inner tube <NUM>) to be inserted into the outer tube <NUM>. A positive clearance is provided between the inner tube <NUM> and the intermediate tube <NUM>, and between the intermediate tube <NUM> and the outer tube <NUM>. For example, the clearance may be less than <NUM> (<NUM> in. ) or may be <NUM> (<NUM> in) or more. The intermediate tube <NUM> has a length L<NUM> and the outer tube <NUM> has a length L<NUM>. As illustrated, the length L<NUM> of the intermediate tube <NUM> exceeds the length L<NUM> of the outer tube <NUM>; however, in other embodiments the lengths L<NUM> and L<NUM> are the same or the length L<NUM> of the outer tube <NUM> may exceed the length L<NUM> of the intermediate tube <NUM>.

Prior to applying a radial crimping process that yields the illustrated tube assembly, the three tubes <NUM>, <NUM> and <NUM> are arranged with respect to each other so that their endfaces <NUM>, <NUM> and <NUM>, respectively, are co-planar. Preferably, the endfaces <NUM>, <NUM> and <NUM> are perpendicular to the tube axes <NUM> and polished with the endfaces <NUM>, <NUM> and <NUM> free of scratches and other surface defects. The fitting <NUM> is then created by forming on the outer surface of the outer tube <NUM> a first radial crimp <NUM> of crimp depth Δ<NUM> and crimp length LC1, and subsequently forming a second radial crimp <NUM> having a crimp depth Δ<NUM> and a crimp length LC2. As illustrated, the crimp depths Δ<NUM> and Δ<NUM> are equal and the crimp lengths LC1 and LC2 are equal although this is not a requirement. Although shown in <FIG> as a near step-like change in diameter of the outer surface of the outer tube <NUM>, in other embodiments the cross-sectional shape of the crimps <NUM> and <NUM> may include a more gradual slope for the diameter transition at the left and right crimp edges. In addition, the "bottom" of the crimps <NUM> and <NUM> may not be as flat as shown in the figure.

Dashed circles <NUM> and <NUM> in <FIG> indicate the post-crimp reduced diameters D<NUM>' and D<NUM>', respectively, of the intermediate tube <NUM> and outer tube <NUM> in the region of the first radial crimp <NUM>, i.e., at a length L<NUM> from the outer tube endface <NUM>. The first radial crimp <NUM> acts to secure, or "capture," the inner tube <NUM> with respect to the intermediate and outer tubes <NUM> and <NUM>. In addition, the first radial crimp <NUM> creates a desired strain of the intermediate tube <NUM> such that the polymeric material flows parallel to the tube assembly axis <NUM> between the more rigid inner and outer tubes <NUM> and <NUM>. As a result of the extrusion of the polymeric material, the intermediate tube endface <NUM> is separated from the inner and outer tube endfaces <NUM> and <NUM> by an extrusion length Δ<NUM>. A predetermined extrusion length Δ<NUM> for the polymeric material is achieved by controlling certain parameters, including the crimp depth Δ<NUM> and crimp length LC1 of the first radial crimp <NUM> and the distance L<NUM> of the first radial crimp <NUM> from the inner and outer tube endfaces <NUM> and <NUM>. In some embodiments, the extrusion length is less than <NUM> (<NUM> in.

After forming the first radial crimp <NUM>, the second radial crimp <NUM> is formed at a distance L<NUM> from the outer tube endface <NUM>. The second radial crimp <NUM> enables a retaining ring <NUM> (e.g., a C-clip) to be installed. <FIG> shows a cross-sectional view through the installed retaining ring <NUM>. Circle <NUM> indicates the outer surface of the outer tube <NUM> at the outer tube diameter D<NUM>. The retaining ring <NUM> has an inner diameter D<NUM> that is equal to or greater than the crimp diameter D<NUM>'on the outer tube <NUM> at the second radial crimp <NUM> and an outer diameter D<NUM> that is greater than the outer tube diameter D<NUM>. Thus the retaining ring <NUM> can be installed at the second crimp <NUM> and is free to move axially along the length LC2 of the crimp <NUM>.

Reference is made to <FIG> which is a perspective view of a portion of the fitting <NUM> of <FIG> with a compression screw <NUM> installed and to <FIG> which is a cutaway perspective view of the fitting of <FIG>. The compression screw <NUM> has a counterbore that includes a cylindrical hole <NUM> terminating at a bottom surface. The hole <NUM> has a diameter that is greater than the outer diameter D<NUM> of the retaining ring <NUM> when the retaining ring <NUM> is positioned in the second radial crimp <NUM> in a relaxed state. The counterbore also includes a through-hole that extends from the bottom surface of the hole <NUM> to the opposite end of the compression screw <NUM>. The through-hole has a diameter that is greater than the outer tube diameter D<NUM> and less than the outer diameter of the retaining ring <NUM> in its relaxed state. Thus the compression screw <NUM> can be inserted over the tube assembly so that the tube assembly passes through the through-hole; however, once the retaining ring <NUM> is installed at the second crimp <NUM>, the compression screw <NUM> can be moved axially from right to left in the figure until the bottom surface at the hole <NUM> engages the retaining ring <NUM>. Further axial movement of the compression screw <NUM> along the tube assembly is prevented once the compression screw <NUM> pushes the retaining ring <NUM> up against the left side of the second crimp <NUM>.

The engagement of the compression screw <NUM> with the retaining ring <NUM> is relied upon during the installation of the fitting into a coupling body <NUM> to achieve a face seal as shown in <FIG>. The illustrated coupling body <NUM> includes a counterbore having a hole with a bottom surface <NUM> and a through-hole extending from the bottom surface <NUM> that defines a fluid channel <NUM> to conduct the fluid received from the tube assembly. The hole has a diameter greater than the outer tube diameter D<NUM> to enable the tube assembly to be inserted into the coupling body <NUM>. To seal the two fluid channels, the compression screw <NUM> engages a threaded bore of the coupling body <NUM> and is rotated until the bottom surface at the hole <NUM> in the compression screw <NUM> comes into contact with the retaining ring <NUM> as described above. Further rotation of the compression screw <NUM> moves the retaining ring <NUM> to the left until the retaining ring <NUM> comes into contact with the left edge of the second radial crimp <NUM>. Subsequent rotation seats the retaining ring <NUM> fully into the counterbore of the compression screw <NUM> then drives the fitting forward to form a face seal as the intermediate tube endface <NUM> (see <FIG>) comes into contact with the bottom surface of the coupling body <NUM>. At this time there is increased resistance to rotation of the compression screw <NUM>. A small additional rotation of the compression screw <NUM> results in compression of the extruded portion of the polymeric material to provide a fluidic face seal at the intermediate tube endface <NUM> and the bottom surface <NUM> inside the coupling body <NUM>.

Claim 1:
A fitting (<NUM>) for a fluidic coupling, comprising:
a tube assembly comprising:
an inner tube (<NUM>) having an inner tube endface (<NUM>) and a first fluid channel;
an intermediate tube (<NUM>) formed of a polymeric material and disposed over at least a portion of a length of the inner tube (<NUM>), the intermediate tube (<NUM>) including an extruded portion having a length and an intermediate tube endface (<NUM>); and
an outer tube (<NUM>) formed of a metal and disposed over the intermediate tube (<NUM>), the outer tube (<NUM>) having an outer tube endface (<NUM>) and an outer surface, a first radial crimp (<NUM>) on the outer surface at a first distance from the outer tube endface (<NUM>) and extending for a first axial length, and a second radial crimp (<NUM>) on the outer surface at a second distance from the outer tube endface (<NUM>) and extending for a second axial length, the outer tube endface (<NUM>) being co-planar with the inner tube endface (<NUM>), the intermediate tube endface (<NUM>) being separated from the inner tube endface (<NUM>) and the outer tube endface (<NUM>) by the length of the extruded portion, wherein an outer diameter of the inner tube endface (<NUM>) does not exceed an inner diameter of the intermediate tube endface (<NUM>) and wherein an outer diameter of the intermediate tube endface (<NUM>) does not exceed an inner diameter of the outer tube endface (<NUM>).