GB2314598A - Assembly for coupling fluid-bearing conduits in respective structures - Google Patents

Abstract

The structures 114A, 114B have the respective conduits 152A, 152B sealingly connected by an intermediate seal insert 120 with respective part-spherical sealing surfaces surrounding end ports for a through passage 184 and pressed against respective ports of part-spherical or frustoconical form for the structure conduits. The coefficient of thermal expansion of the structure ports may mutually differ and/or with that for the insert. Biassing of the parts together can be by springs 154 acting on structures 112A, 122A.

Description

2314598 APPARATUS FOR COUPLING FLUID-BEARING CONDUITS The present

invention relates to apparatus for coupling a fluid stream in a first fluid-bearing conduit to a second fluid-bearing conduit.

Fluid coupling apparatus are known in the art for receiving a fluid stream in a first fluid-bearing conduit and coupling the received fluid stream to a second fluid-bearing conduit. In many cases, the fluid connection is obtained by manual alignment and coupling of separate components that comprise a fluid conduit pair, such as by alignment and compression of a sealing insert between opposing openings in the first and second conduits.

The sealing insert on conventional fluid coupling apparatus is typically a connector that employs a tapered ferrule having a conical frustrum exterior and a through hole. A fluid handling device in the form of a tubular device is inserted into the through hole and the tubular devicelferrule assembly is then inserted into a second fluid handling device having a receiving feature that is shaped as a complementary conical frustrum. The receiving feature is sometimes referred to as the ferrule seat. The tubular devicelferrule assembly is then forced into the ferrule seat via pressure applied by a fastener.

Such an approach has several disadvantages. To effect a reliable, fluidtight seal, the ferrule must be properly oriented to the ferrule seat, which occurs only if the central axes of the ferrule and ferrule seat are perfectly coincident. Also, both the ferrule and the ferrule seat must be fabricated to be perfectly 2 circular and the diameter of the through hole in the ferrule must be uniformly and adequately compressed to effect a seal between the surface of the through hole and the exterior surface of the column.

Further, the connector may be subject to extended periods in a variable temperature environment. For example, a conventional connector may be employed in a gas chromatographic analysis system. The connector and the devices to which it is connected are subject to wide temperature variations that range from minus 190 degrees C. to 450 degrees C. The connector andlor the devices will typically have mating surfaces that are composed of materials having dissimilar thermal coefficients of expansion. When used in such an environment, the mating surfaces will accordingly be subject to differing rates of expansion and contraction. As a result, the fluid connection fails and the connector is subject to leakage or failure. The effects of such failure in, for example, a gas chromatograph can include: fluid degradation via oxidation; degradation of analytes in the fluid stream as they react with the atmosphere; inaccurate measurement of fluid flow; and the influence of air upon the sensing devices that depend upon a reliable fluid connection.

One conventional approach to resolving the foregoing difficulties includes a practice of fabricating the ferrule from a compliant material. A large insertion force is then used to force the ferrule into the ferrule seat, thus causing the ferrule to conform both to the shape of the ferrule seat and to the exterior of the tubular device. The drawback to this approach is that a high pressure, and thus a high degree of mechanical stress, is induced in the ferrule by such insertion force. Further, a high temperature environment can cause a compliant material to creep or fracture, thereby creating a fluid leak.

Another approach is to utilize a spring-loaded ferrule (see, e.g., U.S. Patent 5,163,215) so as to compensate for thermally-induced mechanical creep. This approach has the potential to prevent failures that are due to creep-induced leaks. However, a conventional ferrule requires a high spring force to achieve an adequate seal, which necessitates the use of a large spring and various other parts to provide a relatively massive spring assembly. Such an assembly has 3 sufficient thermal mass that it exhibits a large heat capacity. The spring-loaded ferrule assembly then becomes an unwanted, localized thermal sink (known as a cold spot") when positioned in a variable temperature environment. An alternative spring material, such as quartz (see, e.g., U. S. Patent 4,991,883) is less subject to temperature- induced creep but can exhibit a relatively large thermal mass.

There remains a practical need for a simple, reliable, and inexpensive coupling means for receiving a fluid stream in a first fluid-bearing conduit and delivering the fluid stream into a second fluid-bearing conduit in a fluid flow system without incurring leaks or other failures. The coupling means would desirably be constructed of a material which is suited for exposure to wide ranges of temperature and exhibits a low coefficient of thermal expansion. Further, it would be desirable for the mating surfaces of the coupling means to exhibit a coefficient of thermal expansion that matches the coefficient of thermal expansion of the material(s) to which it mates (e.g., the materials that defines the first and second fluid-bearing conduits). Further, there is a need for coupling apparatus that does not utilize excessive force at the interface(s) (i.e., the mating or sealing surfaces) that are accomplished between the fluidbearing conduits and the connector.

This need is especially apparent in coupling one or more fluid streams in an apparatus for performing high-resolution chromatography.

The present invention is directed to fluid coupling means that will find useful application in a variety of fluid handling systems that benefit from the delivery or connection of a discrete or continuous flow of a fluid stream. Such fluid handling systems are especially employed in a wide variety of analytical applications, such as sample extraction, purification, and analysis; clinical assay and analysis; industrial processing; and reagent dispensing. Further examples of instruments that are particularly benefited by an application of the present invention include instruments for performing gas, liquid, or supercritical 4 fluid chromatography. In particular, the preferred embodiment is especially suited for connecting inlet and outlet tubing in a cryogenic sample focusing apparatus in a gas chromatograph.

Preferred embodiments of the present invention will find particularly advantageous use in establishing fluid coupling between fluid handling conduits in a sample analysis system such as a gas chromatograph.

The present invention seeks to provide novel coupling means for coupling a first fluid-bearing conduit to a second fluid-bearing conduit, thereby providing substantially leak-free fluid communication between the first and second fluid-bearing conduits.

According to one aspect of the present invention, there is provided apparatus for coupling first and second fluid bearing conduits, comprising:

a first fluid-bearing structure including said first fluid-bearing conduit and a first port surface in fluid communication with said first fluid-bearing conduit; a second fluid-bearing structure including said second fluid-bearing conduit and a second port surface in fluid communication with said second fluid-bearing conduit; a seal insert comprising upper and lower portions each respectively including first and second sealing surfaces and a central fluid-bearing bore extending therebetween, said seal insert being locatable between said first and second fluid-bearing structures, and said first and second sealing surfaces being of a configuration complementary to said first and second port surfaces so as to establish a fluid-tight seal when superimposed; means for locating said seal insert between said first and second fluidbearing surfaces and for aligning said first and second sealing surfaces with said first and second port surfaces; and biasing means for urging said first and second port surfaces respectively onto said first and second sealing surfaces.

The first and second fluid-bearing conduits are preferably provided in respective first and second fluid-handling structures. The contemplated coupling means constructed according to the present invention may also be advantageously employed for easily and releasible fluid coupling of the first fluidbearing conduit in fluid-tight communication to the second fluid-bearing conduit.

In a first preferred embodiment of the present invention, the first fluidbearing conduit is located in a first fluid handling structure and communicates with a first port. The second fluid-bearing conduit is located in a second fluid handling structure and communicates with a second port. The first and second ports define respective first and second port surfaces at the exterior of the first and second fluid- handling structure. The first and second port surfaces engage respective first and second sealing surfaces on a seal insert that may be interposed between the first and second fluid conduits. A central bore defining a fluid-bearing passageway extends between the first and second sealing surfaces so as to allow fluid communication to be established between the first and second fluid-bearing conduits when the first and second fluid handling structures are compressed upon the seal insert.

The seal insert preferably includes first and second hemispherical portions each of which is circular when viewed in transverse cross section such that when the port surfaces are urged onto the seal insert by the biasing means, the mating surfaces of the seal insert will 6 engage the port surfaces in a substantially circular line contact.

The seal insert preferably includes at least three external features: a first sealing surface operable for effecting a fluid-tight seal between the first fluid-bearing conduit and the central fluid-bearing bore within the seal insert, a second sealing surface operable for effecting a fluidtight seal between the fluid-bearing bore and the second fluidbearing conduit, and a cylindrical collar operable for aligning the seal insert between first and second fluid-bearing structures.

A preferred embodiment of the fluid coupling means includes a seal insert formed of material that exhibits a coefficient of thermal expansion that matches or is effectively similar to that of the material that forms the port surfaces in the fluid bearing conduits, thus avoiding the problems associated wfth dissimilar coefficients of thermal expansion.

The preferred embodiment of the fluid coupling means includes a seal insert formed of deformable material.

The compression force is preferably provided by a biasing means having moderate biasing force to prevent undue deformation of the insert andlor damage to the first and second fluid handling structures.

Preferably, the seal insert is simple and inexpensive to construct and therefore is disposable. The seal insert is easily aligned with, and urged against, the first and second port surfaces. In particular, the port surfaces are shaped to accommodate the hemispherical shape of the upper or lower hemispherical portions so as to define a large included angle. Accordingly, a biasing means having moderate biasing force may be used to maintain a fluid-tight seal between each of the first and second sealing surfaces and the respective port surfaces.

Advantages of the preferred embodiments include the capability for effecting a reliable fluid seal at a low spring force without the need for substantial adjustment or tightening of the coupling means. The coupling means (and particularly the biasing means) therefore exhibit less thermal mass than found in fluid coupling 7 devices constructed according to the prior art.

The coupling means may be employed to achieve substantially fluid-tight coupling of a fluid stream subject to a highly-variable temperature environment. Alignment, assembly, or disassembly of the coupling means with respect to the first or second structures may be performed easily and without damage to the first or second fluid-bearing conduits. The coupling means avoids many of the failure modes that otherwise would occur due to the effects of assembly or disassembly, or due to the extreme temperature variations, to which the coupling means may be subjected.

Embodiments will now be described, by way of example only, with reference to the accompanying drawings, of which:

Figure 1 is a side view of a preferred seal insert; Figures 2 and 2A are plan and side sectional views of the seal insert in Figure 1; Figures 3A and 313 are exploded, side sectional views of a preferred embodiment of fluid coupling means; and Figure 4 is a side sectional view of another embodiment of fluid coupling means which has been enlarged for clarity.

For the purposes of this description, "fluid-bearing" shall refer to the characteristic or capability of a means for conducting fluid between at least two points; "fluid-tight" shall refer to the characteristic or capability of a means for establishing a fluid connection that is substantially leak-free with respect to the intended operation of such means.

Accordingly, Figures 1, 2, 2A, 3A, and 313 illustrate preferred fluid coupling means which include a seal insert 120 contemplated for use in a seal assembly 110 for coupling a first fluidbearing conduit 134 in the form of a tubular or capillary conduit within a first fluid-bearing 8 structure 112 to a second fluid-bearing conduit 136 in the form of a tubular or capillary conduit within a second fluid-bearing structure 122. The seal insert 120 preferably includes a first sealing surface 190, a second sealing surface 192, and a central ly-d isposed bore 184 therebetween. A neck portion 180 is useful for grasping, receiving, aligning, or retaining the seal insert 120 between the first and second structures 112, 122.

The bore 184 communicates between the center of a hemispherical upper portion defined by the first sealing surface 190 and the center of a hemispherical lower portion defined by the second sealing surface 192. The bore 184 has an internal bore diameter substantially equal to, or slightly larger than, the exit diameter of the first and second fluidbearing conduits 134, 136 such that inward compression of first and second port surfaces 142, 144 on the first and second sealing surfaces 190, 192 respectively, will effect a fluid-tight seal therebetween.

As illustrated by alternative seal assembly 11 OA, the first and second port surfaces 142A, 144A may alternatively be defined by frustoconical or conical sealing surfaces.

Preferably, a biasing action provided by suitable biasing means effects a biasing force for receiving, aligning, or retaining the seal insert 120 between the first and second structures 112, 122. The biasing force accomplishes two sealing functions at once: Firstly, the first sealing surface 190 conforms with the first port surface 142, thus causing a fluid-tight seal between the seal insert 120 and the first conduit 134, and the second sealing surface 192 conforms with the second port surface 144 thus causing a fluid-tight seal between the seal insert 120 and the second conduit 136.

Accordingly, when seal insert 120 is located within the seal assembly 110 such that the first sealing surface 190 meets the first port surface 202, a circular segment of the upper portion of the seal insert 120 engages the port surface 142. This engagement will result in a circular line contact between the first sealing surface 190 and the first port surface 142. Similarly, when seal insert 120 is located within the seal assembly 110 such that the second sealing surface 192 meets the second port surface 144, a circular segment of the lower portion of the 9 seal insert 120 engages the second port surface 144, and a circular line contact between the second sealing surface 192 and the second port surface 144 is established.

Only a low to moderate biasing force need be applied to compress the first and second structures 112, 122 on the seal insert 120 such any expansion or contraction of the seal insert 120 and the first or second structures 112, 122 during ambient temperature fluctuations will not impair the sealing engagement of the seal insert 120 with the first and second port surfaces. In contrast to prior art ferrules and ferrule seats, which are typically of frustoconical andlor cylindrical shapes, the upper and lower portions of the seal insert 120 are preferably hemispherical so as to ensure complete but reversible line contact between the seal insert 120 and the port surfaces 142, 144 (or 142A, 144A) using such biasing forces. It will be appreciated that in order to achieve the circular line contact desired between the seal insert 120 and the port surfaces 142, 144 (or 142A, 144A), the port surfaces are preferably formed to define a large included angle that is sufficiently complementary to the radii of the upper and lower portions of the seal insert 120.

The engagement or disengagement of the fluid-tight seal between seal insert 120 and port surfaces 142, 144 is enhanced by the ease with which the upper and lower portions of the seal insert 120 can interface with the port surfaces 142, 144, particularly when the central axis of the seal assembly 110 (which typically is coaxial with the central axis of the seal insert 120) is not completely aligned with the central axis of the first and second port surfaces 142, 144.

The provision of substantial line contact sealing between the seal insert 120 and the first and second port surfaces 142, 144 obviates the necessity, often seen in the prior art, for machining such parts to extremely close tolerances in an attempt to achieve mated, gas-tight engagement between relatively large contact surfaces.

The fluid-tight coupling is maintained even when the illustrated apparatus is subject to mishandling, temperature extremes, etc. because the biasing action will maintain the seal insert 120 in contact with the first and second structures 112, 122 while accommodating the expansion and contraction of the seal insert 12 0 and the port surfaces 142, 144. The illustrated seal assemblies 110, 11 OA thus provide an effective means for establishing substantially leak-free fluid communication between the fluid-bearing conduits 134, 136.

The seal insert 120 will provide a reliable fluid-tight seal even when subjected to wide temperature variations in the ambient environment or during conditions of low compression (sealing) force, angular misalignment, andlor variations in the included angle of the first or second port surfaces 142, 144.

Accordingly, the port surfaces in the first and second structures 112, 122 can be composed of material(s) having a coefficient(s) of thermal expansion that differ from one another, or differ from the coefficient of thermal expansion exhibited by the material that forms the sealing surfaces 190, 192 in the seal insert 120. For example, the port surface 142 in the first structure 112 may be fabricated from stainless steel and the port surface 144 in the second structure may be fabricated from fused quartz 122.

As shown in Figure 4, another preferred embodiment of seal assembly 11 OC may be located within separable support portions 11 4A, 11 4B to define fluid-bearing cavities 152A, 152B. Biasing means in the form of compression springs 154 are slidably disposed within the interior surface of inner walls 124. Flanges 160 form annularly extending shoulders 164. The springs 154 and seal insert 120 are retained in the seal assembly 11 OC by means of flanges 160 which also act as a mechanical stop. Accordingly, the springs 154 urge the first and second structures 112, 122 onto the seal insert 120. The seal assembly 11 OC is assembled by coaxially aligning the support portions 11 4A, 1 14B such that springs 154 impinge upon first structure 11 2A and second stnucture 122A so as to suitably align the seal insert 120 and provide a fluid-tight seal between first and second structures 11 2A, 122A. The bore 184 then allows fluid communication between the cavities 152A, 152B. The illustrated configuration of the seal assembly 1 10C is then made secure by suitable retaining means such as threaded fasteners or deformable snap mounts (not shown).

11 Whereas the biasing means is illustrated in the form of one or more springs 154, it will be recognized that other biasing means can be employed, such as: one or more flexural members; helical coils; corrugated leaves; resilient cylinders, pads, or toroids; etc. Use of biasing means formed of quartz or similar material has particular advantage when the contemplated seal assembly is to be used in very high temperature environments where metallic springs might yield or fail.

Further, certain components of the seal assembly 110 are contemplated as being fabricated from ductile materials. For example, the seal insert 120 is preferably made of a ductile material that exhibits at least some capacity for deformation at a minimum or, more preferably, some elasticity. The term "ductile" as used herein refers to a material which, under compression, deforms to the extent necessary to achieve a fluid seal. Suitable materials for use in forming the seal insert 120 include polyamide, polyimides and various other polymeric materials which need not considered to be elastic but are deformable as that term is used above.

It is also preferred that certain components of the seal assembly 110, such as the seal insert 120, be formed of inexpensive (hence disposable), inert, thermally-stabie materials, such as graphite or an organic polymer; exemplary inert polymers are polyimides, aramid polymers, acetate resins, and poly(tetrafluoroethylene) such as available from the DuPont Company (Wilmington, Del.) under the trade names Vespel, Keviar, Delrin, and Teflon, respectively; and poly(chlorotrifluoroethylene), such as available from the 3M Company (Newark, N.J.) under the trade name Kel-F.

Means for retaining alignment of the seal assembly 110 may differ than as shown. For example, differing types of retention devices such as threaded, socketed, or friction-fitting retaining device(s) of differing construction may be employed. Preferably, the attachment should be made reversible or releasable 12 so as to allow the seal assembly 110 to be removed and disassembled for servicing or replacement of the insert 120 when necessary.

The insert 120 can be of any size that permits sufficient flow of the fluid to accomplish the desired fluid coupling for a particular application. In one prototype embodiment, the first and second sealing surfaces 190, 192 each were constructed to define a 4mm radius ball and the diameter of the bore 184 was 4mm. Biasing means that provide the biasing force can be of various spring materials that withstand the expected operating temperature range. In the prototype embodiment, Inconel-x-750 was used to withstand an upper temperature extreme of approximately 40WC.

Preferably, the seal insert 120 is constructed of ductile material such that biasing means need not exert substantial compression force to cause adequate fluid-tight coupling of the first and second conduits. Such a design choice is advantageous in that the springs 154 and the remaining alignment, assembly, or mounting hardware (not shown) need not be designed to accommodate large biasing force. Accordingly, these components can occupy a smaller volume and have lower mass, thus reducing the thermal capacity problem exhibited by the designs in the prior art. In an alternative embodiment, a minimally deformable (i.e., hard) material may be employed if the sealing surfaces are of sufficient quality and the alignment of the first and second structures 112, 122 are held to close tolerances. However, the biasing force of the biasing means would have to be increased.

The small included angles on the port surfaces 142, 144 are designed to allow an adequate seal to be made between the seal insert 120 and the first and second structures 112, 122 with use of less compression force. Assembly and disassembly of the seal assembly is then reliable and easy. Nonetheless, should the seal insert 120 become jammed in one of the port surfaces (i.e., nearly or completely inseparable), the seal insert 120 may be easily grasped and removed, then discarded. A new seal insert 120 may be easily and inexpensively employed to re-establish a fluid-tight connection.

As described in the foregoing, the seal assembly 110 13 is preferred for the delivery of fluid stream in one or more fluid- bearing conduits in a sample analysis system. However, the contemplated seal assembly 110 will find application for the delivery of a fluid stream to or from differing or additional components that may be present in other fluid handling systems. For example, the contemplated delivery of a fluid stream is not limited to only the illustrated fluid handling structures. It will be appreciated that the seal assembly 110 may be fitted to other components such as tubular fittings, piping, tubing, needles, canulas, drains, nipples, and other such fluid-handling apparatus or devices. While such systems are not shown in the Figures, they are contemplated.

The disclosures in United States patent application no. 08/673,609, from which this application claims priority, and in the abstract ace omp anying this application are incorporated herein by reference.

14

Claims (11)

1 Apparatus for coupling first and second fluid-bearing conduits, comprising: a first fluid-bearing structure including said first fluidbearing conduit and a first port surface in fluid communication with said first fluid-bearing conduit; a second fluid-bearing structure including said second fluid-bearing conduit and a second port surface in fluid communication with said second fluid-bearing conduit; a seal insert comprising upper and lower portions each respectively including first and second sealing surfaces and a central fluid-bearing bore extending therebetween, said seal insert being locatable between said first and second fluid-bearing structures, and said first and second sealing surfaces being of a configuration complementary to said first and second port surfaces so as to establish a fluid-tight seal when superimposed; means for locating said seal insert between said first and second fluidbearing surfaces and for aligning said first and second sealing surfaces with said first and second port surfaces; and biasing means for urging said first and second port surfaces respectively onto said first and second sealing surfaces.

2. Apparatus according to claim 1, wherein the seal insert comprises a portion including therein at least a selected one of said first and second sealing surfaces, and a respective one of the first and second port surfaces is shaped such that the selected one of said first and second sealing surfaces engages the respective one of said first and second port surfaces in a substantially circular line contact.

3. Apparatus according to claim 1 or 2, wherein the or each respective one of the first and second port surfaces is substantially frustoconical.

4. Apparatus according to claim 1 or 2, wherein the or each selected one of said first and second sealing surfaces is substantially hemispherical.

5. Apparatus according to claim 1 or 2, wherein said first and second sealing surfaces are hemispherical and the respective first and second port surfaces are frustoconica).

6. Apparatus according to any preceding claim, wherein the biasing means comprises a spring.

7. Apparatus according to any preceding claim, wherein at least one of the first and second sealing surfaces comprise a ductile material.

8. Apparatus according to any preceding claim, wherein at least one of the first and second port surfaces comprise a ductile material.

9. Apparatus according to any preceding claim, wherein at least one of said first and second port surfaces comprises fused quartz.

10. Apparatus according to any preceding claim, wherein at least one of said first and second sealing surfaces is substantially formed of first material having a first coefficient of thermal expansion, and a respective one of said first and second port surfaces is substantially formed of a second material having a second coefficient of thermal expansion, and wherein said first and second coefficients of thermal expansion are dissimilar.

11. Apparatus for coupling first and second fluid-bearing conduits substantially as described herein with reference to the accompanying drawings.